CA1195683A - Systems, apparatus and methods for measuring while drilling - Google Patents

Abstract

Abstract of the Disclosure Improved systems, apparatus and methods for measuring downhole parameters in a well being drilled in the earth with apparatus comprising a drill string, a mud pump for circulating drilling fluid, and flow restriction means located near the bottom of the string so as to cause a pressure drop between the restriction means and the borehole annulus that surrounds the drill string. In accordance with one aspect of the invention, the improvements involve downhole pulser means for generating negative mud pressure pulses which are utilized to transmit information concerning downhole parameters to above ground equipment. The improved downhole pulser means utilizes valve means to bypass the restriction means in a manner that results in the efficient generation of effective pulses with minimum expenditure of electric energy.
In accordance with another aspect of the invention, improved structure is provided for housing the pulser means and for accommodating associated downhole apparatus. In accordance with another aspect of the invention, improved methods are provided for extracting negative mud pressure pulse signals from interfering signals resulting from mud pressure variations due to the mud pump means. In accordance with a further aspect of the invention, improved direct current downhole power supplies are provided.

Description

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This a divisional Application of copending Canadian Application Serial No. 426,572, filed April 22, 1983.
This invention generally pertains to logging while drilling apparatus, systems and methods and more particularly pertains to systems, apparatus, and methods utilizing mud pulsations for telemetry to transmit signals representing one or more downhole parameters to the earth's surface.
Many efforts have been made to develop successful logging while drilling systems, as suggested by the following examples: Karcher, United States Patent No. 2~096,279 proposes a system utilizing electrical conductors inside the drill pipe. Heilhecker, United States Patent No. 3,825,078 proposes a system utilizing extendable loops of wire inside the drill pipe. Silverman, United States Patent No. 2,354,887 proposes a system utilizing inductive coupling of a coil or coils with the drill pipe near the drill bit with measurement of the induced electrical potential at the earth's surface. Arps, United States Patent No. 2,787,759 and Claycomb, United States Patent No. 3,488,629 propose systems in which pulsed restrictions to the drilling mud flow produce pressure pulse signals at the earth's surface. Other related United States Patents are Nos. 3,186,222, 3,315,224, 3,408,561, 3,732,728, 3,737,845, 3,949,354 and ~001,774.
Each of the abovementioned proposals has had some drawback of suff-icicnt consequence to prevent its commercial acceptance. ~or example, the incon-velliellce and time involved for the large number of connections and disconnections oE electrical connectors is a significant drawback in systems such as proposed by Karcher. Though an induced electric potential system such as proposed by Silverman may be considered operable for a short distance, the signal to noise ratio of such a system prohibits its use as a practical matter in deep wells.

:`' )` ) ~ cn modern jet bit drilling became commonplace and very large mud volu;nes and high mud prcssures were employed, the systems as proposcd by Arps, proved to be unreliable and subject to rapid deterioration. The introduction of a controlled restriction into the verf powerful mud stream, of necessity, required large and po~erful apparatus and operation was unsatisfactory because of rapid we~r and very high energy requirements.
The environmcnt is very hostile at the bottom of a well during dril-ling. Drill bit ~nd drill collar vibrations may be in the order of 50 g. The tempcrature is frequently as much as 400F. The bottom hole pressure can be more th~n 15,000 psi. The drilling fluid flowing through the drill collars and drill bit is highly abrasive. With present driliing equipment including im-proved drill bits, thc continued drillin~ time with a particular bit can be in the order of 100 - 300 hours and sometimes longer before it becomes necessary to change the drill bit. Accordingly, a downhole formation condition sensing and signal transmitting unit mounted near the drill bit must be capable of operating unattendcd for long periods of time without adjustment and with a con-tinuing sourcc of electrical power. Also, the signal communication apparatus must be capable of transmitting a continuing usable signal or signals to the eartll's sur~ce aftcr each additional joint of drill pipe is conventionally added to the drilling string as the drilled borehole is increased in depth.
In gencral, systems using mud pulsations for telemetry are considered the most pr~ctical since the drilling operation is least disturbed. To date, ho~cver, thc rcli~l)ility th~t h~s bcen achieved l~ith such systems is not satis-factory. Tl~c prcvious methods such as thosc of ~rps and Claycomb~ utili~e tlle inser~ion of a controllcd restriction into the mud flow circ~it. Ho-~evcr, when the rnud floli surp~sscs 600 gpm and pwnp pressures pass 3000 psi, controlling tllis l~rge cncrgy ~y varying a restriction to produce telemctry signals is complicated and rec~uires powerful downhole machinery.
A general objective of the present invention is to pro-vide a successful logging while drilling system of the -type uti-lizing mud pulsations for telemetry to transmit signals repre-senting one or more downhole parameters to the earth's surface.
According to a first broad aspect, the present inven~
tion provides a measurement while drilling apparatus for use in a borehole down through which drilling fluid is forced to fl.ow in a circulation system and having a restriction in said system causing a high fluid pressure zone and a low fluid pressure zone, said apparatus comprising a valve interposed between said zones, said valve being moveable to open a passage for flow of drilling fluid from said high pressure zone to said low pressure zone and to close said passage, means for detecting the magnitude of a downhole parameter and for producing electrical signals repre-senting said magnitude, an electromagnetic solenoidal means comp-rising a source of electrical energy and responsive to said e]ec-trical signals for generating an electromagnetic force for cont-rolling the opening of said passage, and a means inclependent of electrical energy for causing the closure of said passage where-~y l:he openings and the closures of said passage are effective in generating pressure variations in the drilling fluid, said p.ressure variations represen-ting the magnitude of said parameter and a means at the earth's surface to detect said pressure var-iations to provide a measure of said magnitude.
According to a second broad aspect, the present inven-tion provides a method of making measurements in a borehole in _ ,~ _ ~9~

which drilling fl.uid is forced to flow in a circulation system having a restriction in the system causing a high fluid pressure zone and a low fluid pressure zone, and including a valve inter-posed between said zones, said valve being moveable to open a passage for flow of drilling fluid from said high pressure zone to said low pressure zone and to close said passageway, including a source of electrical energy, comprising the steps of:
determining the magnitude of one or more selected para-meters in the borehole and generating electrical signals represen-ting said magnitude, applying electrical energy in response to said elec-trical signals to open said valve, closing said valve in absence of the application of electrical energy, the openings and closings of said valve serv--ing to create pressure pulses in said drilling fluid; and detecting said pressure pulses at the earth's surface to provide a measure of said magnitude.
According to a third broad aspect, the present invention provides a measurement while drilling apparatus for use in a orehole down through which drilling fluid is forced to flow in a circulation system and having a restriction in said system cau-slng a high Eluid pressure zone and a low fluid pressure zone, said apparatus comprising a valve interposed between said zones, said valve being moveable in a first direction to open a passage ~or flow of drilling fluid from said high pressure zone to said low pressure zone, and moveable in a second direction to close said passage, means for detecting the magnitude oE a downhole parameter and for producing an electrical signal representing said magnitude, an actuating means for moving said valve in said two directions, said actuating means comprising:
a source of electrical energy, a first, electromagnetic solenoidal means deriving elec~-rical energy from said source and responsive to said electrical signal for developing an electromagnetic force in said first direction, a second means independent of said electrical energy lor developing a second force in said firs-t direction, and a third means for developing a third force in said second direction whereby the motion of said valve in said two directions is effective to cause pressure variations in the dril-ling fluid, said pressure variations representing the magnitude of said parameter, and a means at the earth's surface to detect sa.id pressure variations to provide a measure of said magnitude.
The invention, as well as that of copending Application Serial No. 401,576 will now be described in greater detail wlth reference to -the accompanying drawings, in which:
~() Figure 1 is a schematic illustration of a conventional rotary dr.illing rig showing apparatus of the presen-t invention incorporated thereini Figure 2A is a schematic illustration of a negative mud pressure pulse generator with its valve in the open position;
Figure 2B is a schematic illustration of the negative mud pressure pulse generator of Figure 2A, with its valve in the closed position;

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Figure 3A is a schematic illustration of a physlcal embodiment o~ the negative mud pressure pulse genera-tor of Figures 2A and 2B, together with instrumentation and sensor sections in place in a drill string near the drill bit;

-4b-5~33 Figure 3B is a d-rawing of the negative T.lud pressure pulse generator of Figures 2A and 2B taken in proportional dimensions Erom an engineering assembly drawing used in actual manufacture of the device;
Figure 3C is a schematic diagram of a radioactivity type sensor and associated instrumen~ation;
Figure 3D is a schematic diagram of a temperature type sensor and associated instrumentation;
Figure 3E is a schematic diagram o:E ~ypical instrumentation for con-5~
trolling actuation of the valve of the negative mud pressure pulse generator;
Figure 3F is a schematic illustration of one type of self-eontained do~nhole power source that may be utili~ed;
Figure 3G is a schematic illus~ration of another type of self-eontained dot~nhole po~:er source that may be utilized;
Figure 4 is a schematic illustra~ion sho~ing typical aboveground equipment in accordance with a preferred embodiment of the invention, wherein the do~-~hole parameter being sensed is radioactivity;
~ igure 5 is a graphic illustration, in idealized form, showing cer-tain wave fo~ns and pulses and time relationships to aid in explana ion of the signal extractor portion 102 of ~igure 4;
Figure 6 is a schematic bloek diagram sho~ing component 105 of thesignal extractor 102 of Figure 4 in further detail;
Figure 7 is a schematie block diagr~n showing componen~ 107 of the signal extractor 102 of ~i~1re 4 in further de~ail;
Figure 8 is a schematie bloc~ diagram showing another form of above-ground equipment that may be utilized;
Figure 9 is a schematie bloc~ diagra~ showlng still another form of aboveground e~uipment that may be utilized;
~0 Fi~ure lO is a sehematie block diagr~m showing an alternate timing ~ulse generator that m~y be utilized;
~ igure ll is a sehematic bloe~ diagram sllo~ing still another form of ~boveground equipment that may be utilized.
Before proceeding t~ith deseriptioll of preferred embodiments of tlle invention, it is believed that understanding ~ill be enhanced by diseussion of some basie faetors.
In a lO,000' length of 4 1/2" drill pipe, the mud volume ;ns;de the pipe is of the order of 5,000 gallons. Ass~ning tha~ the bulk elastic modulus for compressed drilling mud is 400,000, thcn discharging .5 gallons of fluid will cause a prcs~ure drop of 40 psi, (if we consider the 5,000 gallons as be-ing in a simple ~an~)O It can be assumed, ~herefore, that discharging mud near the bottom of such drill pipe at the rate of 0.125 gallons/sec. will cause a si~al of 10 psi/sec. at the surface. l~e shall refer to the rate of change of pressure as the dt inde~ and in this case the dp inde~ is equal to 10 Three important e~peri~ents were performed;
1. ~leasurcments were made in a test well at 1,800' and moderate dif-ferential pressurcs of 1,000 psi across a valve at the bottom.

2. ~teasurements were made in an oil field drilling well at 8,000' and low differential pressures of 400 psi.

3. ~leasurements were made in a second oil field drilling well at 5,000' and high diffcrential pressures ~l,G00 psi~.
All three series of experiments irdicated that the ~ inde~ of the pressure pulse receivcd at the surfa~e when the valve is suddenly opened was subst~ntially higher tl-an calculated. The reasons for this are:
. (a) highly compressed drilling mud may have an elastic modulus somewhat higher than 400,000;
tb) thcre is somc wave guide action by the drill pipe that causes the signal to travel much more favorably th~n it would in ~ larse t~n~ of the same volume; and ~c) the suddcn o~ening of a valvc at the bottom of the well causes a hi~her ~ indc~ th~n in the case of t]lC large tan~ because of the elasticity of the mud column abovc it.
In a typical 15,000 foot drill string (~ith the bottom end closed off), if a mar~cr werc pl~ccd at the top of ~l~c mud column, this mar~er would dIop some 110 fe~t ~hcn 3,000 psi mud pump pressure is applied (3,000 psi is a rather typical mud pump pressure in deep ~ells). One can, thereforc, consider the mud column as being continually compressed by some 100 feet and acting as a long spring in ~ihich a large amoun~ of potential energy is stored. When a valve at the bottom of the drill pipe is suddenly opened, this potcntial energy is re-leased, causing a large nega~ive mud pressure pulse; such mud pressurè pulse being subst~ntially larger than would be the case if the mud l~ere incompres-sible.
In the e~periments conducted at 5,000' in a drilling well, a small passageway ~.056 in.2 area) between the inside of the drill collar and the an-nulus, was opened and shut in accordance s~ith a controlled sequence. The pres-sure across the valve ~as 1,600 psi and the discharge was calculated to be appro~imately .25 gallons/sec. The volume of mud inside the drill pipe was appro~imately 2,500 gallons and assuming an elastic modulus for the mud of

4~0~00', the pressure drop was calculated to be 40 psi/sec. ~again using the ass~ption that mud col~lmn was a simple tan~). In the tests the pressure drop at the surace ~as measured to be over 100 psi/sec. or considerably more than would be e~pected rom the simple tank calculation. The follo~ing conclusion was reached: With high pressures existing across the drill bit ~1,000 psi or more), large sh~rp si~nals can be developed at the surface by opening and clos-in~ a very sm~ll bypass valve at the sub-surface near the drill bit. Valves h~vin~ an opening of .05 in. can produce lar~e signals from ~ 5,000' depth and the re~uction in sign~l m~gnitude from depths bet~een 2,5~0' and 5,000' have been found to be vcry small; thus, indicating that the signal attenuation is S;il~l 1 .
Thc systcm of the present invcntion has a n~lmber of important advan-t~gcs: The r~pid discharge a~ a rate of as little as 0.125 g~llonsjsec will generate a "sharp" pulse~ that is a pulse con~ainin~ a high rate of change of pressure, i.e., a high dP index (e.g. 40). Furthermore, the rapid opening of the bypass valve hill also mini~i7e wear for the follo~ing reasons: l~en the bypass valve is closed, there obviously is no wear on ~he val~e seat. I~en the valve is open (and the valve are~ is large co~p~red to a res.riction or restric-tions follo~ing it), the valve will be exposed to low velocity fluid and, con-sequently, the l~ear t~ill be mostly in the following res~riction or restrictions which can be made e~pendable and of very non-errodable material such as boron earbide. I~ear occurs in the bypass valve only ~hen it is in the process of opening or closing, i.e., is "crac~ed" and the velocity through the valve seat is then very high. The ~alve operation should, therefore, be as fast as pos-sible for openin~ and closing and there is no limit to the desirable speed.
The r~te of disch~T~e through the val~e should also be fast but there is an upper limit be~ond ~hich faster discharge does not benefit. The reason for this is the limit .o high frequency transmission through the mud. Fre~uencies higher than about 100 H~ are strongly attenuated and are of little value in building up a fast pu1se at the surface. To determine the maximum useEul rate of discharge, it was necessary to set up experiments on a full seale using real drilling oil wells an~ long lengths of conventional drill pipe. The e~periment-al arrangemCIl~s comprised a special large valve follol~ed by an adjustable ori-ice.
Ch:ln~ing the ori~ice size can determine the flow rate in gallons per seeo~ld. It ~as determined that flo~s l~rger than about .3 gallons per second produced little improvement in the signal. In comparing the si~nals flom a dcpth of 5,012 fee~, three different orifice sizes l~ere tested, .509" diameter, .427" diame~er and .26S" di~eter. It was determined that the o26S~ dianeter or;fice generated a siO~nal a~ the surface nearly as intense as the one gener~ted by thc .509" diametcr orifice.
Refcrring no.~ to Figure 1, there is schematically illustrated a typic~l drilling rig 10 including a mud circulating pump 12 connected to a dis-charge pipe 14, a standpipe 16~ a high pressure flexible rotary hose 18, a s~ el 20 and a drilling string 22, comprising the usual drill pipe and drill coli~rs, and a jet t)pe bit 26. A short distance above the bit 26, and mounted within drill collar 24, is a negative mud pressure pulse generator 2~ and a sensing and instrumentation unit 30.
The negativc Mud pressure pulse generator 2S is of a spec al desig...
It generates a series of progr~ù~ed pulses and, each pulse consists of a short momentary reduction in mud pressure. In one embodiment, this is accomplished by means including a valve that mom.entarily opens a passageway betl~een the in-side and the outsidc of the drill collar 24, i.e., the valve controls a passage-~ay bet-;een thc insidc of the drill collar 24 and the annulus 29 formed by the outside o~ the drill collar and the well bore.
Abovcgrol~ld equipment, generally designated as 32, is connected to a pressurc tr~sducer 100, ~hich in turn is connected to standpipe 16. Alter-nativcly, the transduccr 100 could be connected into the stationary pol~tion of sl~;vel 20, if dcsired.
Fi~urcs 2A and 2B sho~ the negative mud pressure pulse generator 28 in di;lgramatic form to f~cilitate e~plallation of its function and manner of o~eration. The ncgative mud pressure pulse generator comprises a valve inlet ch~mber 42, a valvc outlct cllamber 44, and a compcnsator chamber 72. The valve inlct chambcr 4' is hydraulically connected via an inlct passaOe~ay 3~ to the inside of the drill collar 24. The valve inlet cham~cr 42 is also hydraulically coi;nected via ~ p~ssa~e~ay 4S to the valvc outlet ch~,lber 4~. Hydraulic flol.
through passa~el~a~ 4S is controlled by the cooperation of a valve 36 with its lo seat 37. The v~lve outlet chamber 44 is hydraulically connec-ted via an outlet pass~ge~ay 51 ~o the annulus 29. Interposed in the outlet passageway 51 are first and second compensator orifices 52, 5~. The chamber 40 between the ori-fices 52, 53 is hydr~ulically connected via a c~nduit 74 to the compensator chambe~ 72. The inl~t chamber 42 communic tes ~ h compensator chamber 72 via a cylinder 49, which receives a cornpensating~ piston 50 that is connected to the valve 36 by means of a shaft 46. The valve 36 is also connected, by means of a shaft 47 ~see Fi~urcs 3A and 3B) to an actuator device 54.
The function and operation of the negative mud pressure pulse genera-tor 2~ will not~ be e~plained. Figure 2B shows the valve 36 of the negative mud pressure pulse gener~tor 28 in the "closed" condition. In this figure, the striated part indic~tes "high" pressure and the blank part indicates "lol~"
pressure. ~Pressure magnitudes~ such as "high", "low" and "intermediate" are relative pressures, i.e., the difference between the pressure at a given loca-tion and the annulus pressure which is here considered to be zero; the actual or real pressure l~ould be equal to these magnitudes plus tlle hydrostatic h~ad, which may be 10,000 psi or higher.) The effective ~rea of the valve 36 is made some~hat larger than the efective area of the piston 50 on the shaft side and, consequently~ when the valve 3G is closed or ne~rly closed, the force on the shaft 46 is in the direc-tion sholm by the 3rro~ in Figure 2B alld may be equ~l to abo~lt 1,000 X ta - a') where a is the effective area o the valve 36 and a' is tho effective area of the compensatin~ piston S0 on the shaft side.
Fi~ure 2A sllo~;s the val~e 36 in the "op~n" condition, i.e., permit~ing mud rlo~ from v~lve inlet chamber ~2 to valve outlet chamber 44 and ~ia outlet p~ssa,~ewny 51 to the arlllulus 79. ~he first ~nd second compens~tor ~rifices 5 an~ 53 cach plOVi~C a predetermined restriction to thc mud flol. and eacll causcs .

a prcssure drop. Consequcntly, thc pressurc insidc the chambcr 72 can be made to have any valuc bct:;een the maxim~n pressure inside chamber 44 and the minimum value at thc e~it of outlct passageway 51 ~'}liCh corresponds to the pressure in-sidc the ~nnulus 29.
As is pointcd out abo~e, in Figure 2A, as in Figure 2B, the striated par~ indicates "high" pressure and the blan~ part at the exit of outlet passa~e-way 51 is "lo~;" pressure. During the valve "open" flow condition, the n~ud encounters t-~o restrictions to flow: orifice 52 and orifice 53, as a conse-~uence of l~hich, the pressure in the chamber 40 is intermediate bet~een the "high" prcssurc indicated by the striated section and the "lo~Y" pressure at the exit of outlet passage~ay 51. This "intermediate" pressure is indicated by the stippled area in Figure 2A. ~his l'intermediate" pressure is originated in the cll~.,ber 40 bct\;cen orifices 52 and 53 and communicates via conduit 74 to the compensator cha;..bcr 72. The pressure in this compensator cham.ber 72 can, con-sequently, be adjusted to an~ reasonable ~alue between the "high" pressure in valve outlct chambcr ~ and the "low" pressure at the e~it of outlet passa~e~iay sl. Thc proportionino of the si~es of the orifices 52 and 53, therefore, con-trols thc ~rcssurc in compensator chamber 72 and, consequently~ the forcc on co~pcns3tor ~is~on 50. If the orifice S; were the same si~e as orifice 52J then thc pressurc in cll~mbcr 40 ~and compensator chamber 72) l~ould be about mid~i~y bc~ecn that o~ valvc outlet chamber 4~ and tlle annulus 29. ~s thc si7e of orificc 5~ is madc lar~cr th~l that of orificc $2, the pressure in com~cns~tor ch~m~cr 72 will ~e relatively decreased, ~nd as the size of orifice 53 is m~de smaller th~ll th~t of orificc 52, the pressure in compensator c]lambcr 72 will be relatively incrc~sc~. For exalllple, if orificc 53 is madc small comparcd to orificc 52, thc prcssurc in comp211s~tor chambcr 72 IYill bc hi~h and, thcrefore, thc forcc on tllc llcad of pis~on 50 ~ill bc hi~h and tcnd to closc the v~lve 36~

~35~3 On the othcr h~nd~ if orifice 53 is largc compared to orifice 52, the pressurc in chamber 72 will be low, thus, tending tc ~llow the valve ~6 to remain open.
It is seen, thcrefore, that the force on the head o~ piston S0 can be adjusted bct~ieen widc limits, thus providing a means for adjusting the action of the valve 36.
It is importan~ ~o note that ~he force ~ending to close the valve 3~
in Figure 2B, and the force tending to open thc valve 36 in Figure 2A, are de-ter~ined by first and second independent parameters, i.e., khe force tending to close the valve is dcrived from the effecti~e area differences of the valve 36 and the rod side of compensa~oT piston 50; whereas the force tending to open the valve is derived from the relative sizes of ~he oriices 52 and 53. By suitably adjustin~ these parameters, the valve 36 can be madc ~o open or close by the application of a small external mechanical force.
It is also important to note that the valve 36 has a "bi-stable" ac-tion, i.e., thc valve is "flipped" or "toggled" from the "open" to the "closed"
position or vicc vcrsa. In other words, thc first said independent parameter is chosen so that ~ en the valve is within the regioil of nearly closed to fully closed, a predominant force of predete~nined magnitude in the valve "close"
dircc~ion is applicd and main~ained; and the second said independent parameter is clloscn so tha~ ~hcn the valve is ~ hin the region of nearly opcn to fully opcn, a prcdomin.~lt forcc of predetermincd ma~nitude in the valvc "open" direc-tion is ~pplicd .Ind maint~ined.
Yllus, it is ~py~rent that thc neg~ti~c mud prcssurc pulse generator 2S of thc prcscnt illVClltiOIl utili~es existing energy derived from thc mud pres-surc in such a nlal)nCr SO as to grcatly reducc the ~mount of extcrnal cncrgy Te-quircd to opcratc thc valve ~6 zn~, in addition, to impar~ to thc v~lvc 36 a "bi-sta~le" or "to~lc" action~

Furthc. discussion of the negative mud pressure pulse generator 23 will be facilit~ted by reference to Figures 3A and 3B which will now be de-scribed. Figure 3A illustrates in schematic form a physic~l embodi~ent of the nega~ive mud pressure pulse generator 28 and associated do~nhole e~uipmen~ as it would be installed in the drilling apparatus of Figure 1. The reference numerals that are applied in Figures 1~ 2A ~na 2B refer to cor-esponding parts ~hen applied to Figure 3A. In Figure 3A a sub 5S which is ty~ically 6 3/4 O.D. and 3 long supports an inner housing 56 by means of a~ns or perforaLed or slotted support melnbers ~not sho m). The inner housing 56 contains the negat~e mud pressure pulse generator 28 and carries at its lo~er end porLion instru~entation sections 62 66 and sensor section 64. The mud from inside the drill collar 24 p~cses around the housing 56 in the direction of the 2rro-~s.
A filter 60 prevents mud solids from entering the housing. The valve ~6 is sho:-n to be opcrated by an actuating device S~ en the valve 36 is open as shc:;n in FiD~ure 2A so:~c ml1d is bypassed into the ~nnulus 29. ~he bel1t arro-s shc.l t1~e dircction of this b~assed mud. The pressure that forces the mud into the annulus 29 is the pressure across the je s of bit 26. llhen valve 36 is closed the b~pass to the ~lnullls 29 is closed.
~lC flo~tin~ piston 76 separates cham~er 72 from an oil filled chamber 7~. Actuating dcvicc 51 is mou1lted ~ithin an oil fillecl ch~ll;lber S0. An equal-i7;.n~ paSS;l~C\~'ay ~2 con1lccts ch~lber 78 ~ith chalnber S0. Tluls in coopera-tioa witll flo:lting piston 76 all~ passageway 74 thc challlbcrs 72 7S and S0 are m~int~.ined at essentially the same pressure as the chamber 40. Passage~ay S2 is p3rti~11y sl~ol.~ in dashed lines in Fi~ure 3A and is not sho!~n in Figure 3B
since it is locatcd in a different plane from the cross seetion sho~
Nur.eral 6S rc1resents a s~ndard drill coll~r and numcral 69 a bo~-bo~ sub. Secticn 6G is 2 3/S in diameter and fits into a standard 15 6 3/4 - 14 _ O.D. - 3 1/4" I.D. drill collar. The unit 30 is provided with special central-i~er ar~s 70 which fit snugly into box-bo~ sub 69. The centralizer arms 70 are dcsigned to centrali7e the unit 30 while allowing free passage of mud.
Figure 3B bears the corresponding reference numerals of Fi~lres 2A, 2B ~nd ~A ~nd sho~s thc negative mud pressure p~lse genera.or 2S in sufficien-propor~ion and dctail to illustrate to one skilled in the ~rt its actual con-struc;ion. It may be noted that in Figure 3B the actuating device 54 comprises a pair of electrical solenoids arranged in opposiLion. The winding 55 of the upper solenoid is disposed to e.~ert a force in the upward direction on its arma-ture 57, while the windina 59 of the lower solenoid is disposed to exert a force in the do~ ard direction on its anDature 61. The armatures 57, 61 are loosely coupled to a mechanical linXage 63 that is fi~ed to the shaft 47 so that a "i~ ~er" effcct is achieved; i.e., when a solenoid winding is energized, its armature moves a short distance before picking up tlle load of shaft ~l7 wiLh a h~Der li~e impact. This "hammer" action has a hcneficial effect upon the opening and closing opcrations of the valve ~6. Suitable solenoids for this application ~ e the Si7e 6EC, medium stro~e, conical face, type manufactured by Ledex, Inc., of Dayton, Ohio.
Revertill~ now to discussion of ~he negative mud pressure pulse gen-erator 2~, there ~rc several further factors and features that should be con-s idcl cd .
~ he orificcs 52, 53 are made to have smaller opening areas than that of the p~ss3~e~ lS, so that the velocity of mud flolY over tlle sealin~ surfaccs of v;llve 3G ~an~ ;ts seat ~7 is si~nificalltly rcduccd sYben comparcd to tbc velo-city of mud flow throu~l~ the orificcs 52, 53; tllus, conccntrating ~c~r on the orificcs 52~ 5~, which are madc of ~ear resiskant material ~such as boron car-bi~e~ ~nd l~llicll are also madc rcadily replaceablc in the "field'i, as inclicated in Figure 3B. These small non-erodable orifices 52~ 53 ma~e the negative mud pressure pulse generator 28 completely "fail safe", i.e., no matter ~hat happens to the operation of valvc ~6 (such as being stuc~ in the open position) the amount of mud tllat is allot~ed to flol~ through the orifices 52, 53 ~ould have no significant ad~erse effects on the drilling. A furtller advantage of ma~ing the orifices 52, 53 readil~ replaceable in the "field" is that they can be charged to best suit var~ino weights and viscosities of mud.
Because thc negative mud pressu~e pulse genera.or 28 is exposed to severe vibration forccs, the design must provide for stability of the valve 36 in bo~h its open or closed posi~ion. The requisike stability is provided by the "hydraulic deten~" or "bi-stable" action of the valve 36 ~hich was previous-ly herein described.
The vertical acceleration encountered in drilling is more severe in thc up~.ard than in the do~mtYard direction. When the teeth of drill bit 26 en-co~ln.er a hard roc~, the drill bit and drill collars 24 are ~orced upwards, i.e.
accc .r~tcdin theu~ ard direction9 bu~ once the drill bit is raised up~ard and O~'L or contact with thc rocX, there is little force other than the acceleration due to gravity that forces the drill bi~ and drill collars dot.~nwardly. Conse-quently, the accelcration upl~ard cc~n be se~eral hundred g's but the acceleration down~rd is only of tl)e or~er of lg. The valve 36, therefore, must be designed so th;lt when in tl~c closed position, high upwards acceleration tends ~o keep it closcd, i.c., ma'.:es it seat better, and higll dosrnwald acceleration (assumed ~o bo sm~ll) tcnds to opcn the valve. This h~s been accomplished in the design, as c~n bc scen fl~or,l ~igures 3A and 3B.
I dctcrl~inc~, by conducting v~rious tests and e~pcrimcnts~ that a forcc of appro.~ima~cl~ pounds would be re~uircd to actuate til valve 36 ~hcn tl)c ~irst and SCCOlld indcpelldcnt par~mcters hercinbcfore described had bcen 6l~3 chosen to providc appropriate "hydraulic detent" or "bi-stable" action to acllicve adcquatc st~bility for thc val~c 36. ~ith good engineering safe*y factors added, thc re~uired orce bec~ne 70 - 100 pounds. The application of force of this m~ni~u~}c over the required distance of valve travel, with elec-tro.~agnetic drive solcnoids of reasonable si~e, would require about 350 watts of electric power; i.c., nearly 1/2 horsepower. IYith such a large power require-ment it would ~ppe~r at firs~ glance that the energy needed for the number of actuations of thc val~e 36 that would be nece~sary for successful operation ~iould be f~r be~ond the capacity of any available self-contained downhole power sou~ce. This ~pparcn~ energy problem is overcome, ho~ever, ~hen ît is consider-ed th~t the negative mud pressure pulse generator 2S of the present inven~ion proviaes a very r~pid action for the valve 36; i.e., the valve 36 can be made to open ~or to closc) ~ith the application of the required 350 watts for only about 20 milliseconds. The amoun~ of energy required to open ~or close) the vai~e is, thcrcfore, looo 60 . 60 ~ ' l~att hours l`here are a~ailablc modcrn high density batteries of reasonable si-e and capable of being includcd in tile space pro~ided l~ithin the drill collar 24 and ~ihich c~n e~sily providc 2,0~0 ~tt hours of energy. Therefore (even l~ithout recllarging, as is dcscribcd l~ter hcrcin) a re~sonable bat~ery can pl~o~ide enougl~ energy to opcr~tc tl~e valvc 36 a~out one million tiloes. Assulling that thc valve is ope-rated oncc ever)~ foul scconds, a sin,,le b~ttcry charge is ablc to operatc the valve continuouslv for o~er onc montl~. It is an i~portan~ requircmcnt in log-ging t~hile drillinn tllat the do~.~holc ~ppar~tus be capable of opcratioll un-attcl~cd (i.c., withou~ battcry recll~rgc) for at le~st the length of timc bctween "round trips", i.c., thc timc th~t a single bit can drill witho-lt re plnccnlcnt, thc bcst bits l;~st onl; ~lolt 100 - 300 hours and, thcrefore, the _ l7 _ 30 day figure above is more than adequ~te.
The pr~ctical design of the negative mud pressure pulse gener~t~r 28 is a comple~ matter. In my e~perience, althou~h careful calculations ~iere made using much of modern hydrodynamic theory, in the inal stages, many of .he para-meters had to be detcrmined by empirical methods. An important reason for this is bec~use the "viscosity" of drilling mud is thixotropic and the dynamic be-havior i5 quite diffcrent from tha~ of liquids having classical or so called Ne~toni~n viscosity. Drilling mu~ "t~eight" (grams per ec) and "viscosity" vary over ~id2 rang~es and consideration must be given to the fact tha- "weight" usu-ally varies ovcr a much smaller range than "viscosity". Drilling mud usually eontains not only colloidal particles in suspension but also larger grains of sand and other particles.
An e.~perimen.~l set up ~as designed to determine the minimum si~e ofthe discharge orificc (which controls the rate of fluid diseharge into the an-nulus). In this set up, a large "servo" valve (l" diameter) l~as follol~ed by smaller replaceable orifices. In 8,000' and 5,000' well depth experiments care-ful me~surements ~cre made of the magnitude of tlle negative mud pressure pulse at the surfaee as n fullction of the size of the discharge orifice. As this si7e was successively redllced, the magnitude of the pulse at the surface seemed al-most in~epell(!ellt of the si7e of the orifice until the surprisingly small .05 in. orifice ar6~ s reached, at ~ihich tin;e a slight reduction in pulse magni-tude ~as observed. This phenomenon ~as quite une~pected, but s~s late-r under-stood ~fter eareul consideration of the el~stic propcrties of the mud column alld the stored potential energy therein ~s l~as hereillabove e~plained. This discov,2ry produeed the re~liz~tioll tl~at a small negative mud pressure pulse generator could produee useul sigulals at thc surface. Caleulations ~crc thcre-af,er m:lde an(l it l~as determilled that the "servo" principle for the valve actu-ation ~as not necessary and the "SCIVO" valve approacll was abandoned. The di-rect, very fast acting~ ne~ative mud pressure pulse generator of this invention as thereupon designcd and has proved to be successful.
In a nenative mud pressure pulse generator 28 of practical design the follo~ing dimcnsions ~ay be considered as typical; orifice ~27 0.500" in diam-eter; orifice 53, 0.306" in diameLer, strol;e of valve 36, 0.125"; diameter oE
piston 50, 0.3S~"; diameter of valve 36 at its seating surfâce, 0.430"; angle of se~t 37 relative to axis of valve movement, 60; diameter of opening at seat 37 or passa~el~ay 4S, 0.375"; diameter of ~al~e shaft 46, 47, 0.1S7".
In Figure ~ there is schematically illustrated a special type of battery that is well adapted to powering the do~nhole equipment of the presen~
invent iOIl .
Deep oil ~ells frequently have high bottom hole temperatures 300--400F and many electric batteries cannot operate at this temperature. l~tere is ho::ever, an e~ceptioil; the modern .~nolten salt bat,eries. They opera,e ~ell at hi~h tcml~eratllrcs of 100 - 500C or even higher but will not opera,e properly at lower telilperatures principally because the electrolyte solidifies znd ceases to cond~ct electrically. A lithi-lm aluminum iron sulphide molten salt battery is manufactured by the Eagle Pitcher Co., Joplin ~lissouriO Other manufacturers also m~nuf~cture hin~h ~nergy molten salt batteries th~ are especiall~ intended for electric vehicle use. These batteries are very well ad~ted for higll tem-per;tture oper;ltion.
~ s illustmted in ~igure 3F, I provide ~n arrangement th~t ~
"stnrt ul~" the ~tter~ before it is immersed into tlle hot envirollnmellt of the oil l~ell ~nd ~ill m~int;~ it eh~rged t~hell in use. In Figure 3F, referenee nu~er~l 155 desigll~tes the battery pro~er; reEerenee lluineral 156 desigll~tes lle~tinn elerlents th~t ~re arr~nged to provide a sm~ll amount of he~tin~ to tlle _ 19 -battery 155; and refcrence numeral 157 desivnates a j~c~et containing the~al insulation, as for eYample, a ma,erial ~no~n as "Super Insulation" mznufactured by the Union Carbide Co., Ne:Y York, N.Y. or "~lultifoil" , manufactured by The Thermo Electron Co., l~althem, ~lass. Initially an e~ternal voltage ~not shown) is applied to the terminal 15S ~wnile the instrument is at the surface and be-fore i~mersion into the lell). This voltage activates the heating elements lS6 and the battery elcctrolyte melts. Furthermore, the battery 155 is charved by the voltage applied at 15~ before the ins.rument is immersed in the oil well.
l~en the battery lS~ is in its nor~al operating ~emperature range, the circuit to the heating element 156 is opened by the thermos~atic swiLch 159, which clos-es during periods lihen additional heat to the battery 155 is re~uired. ~Yhen lo~ging IYhile drilling, the vibration of the tool lYill cause the device 160 to generate a eh~rging current. The device 160 is described in United Sta,es Pat-ent 3,970,S77, Russell, et al. Instead of the Russell, et al, device, a small mud f1Ot~ pol~ered turbine and electric genera~or could be used to maintain tlle battery char~ecl, since on1y about l ~att of continuous charging power is re-quired.
In ~igure 3G there is schematically shown another special type of battcry that m~y be used to polier the dol~nhole equipment of the present inven-tion. Tllis b~t~ery preferably uses cells of the Lithium Sulphur t}~e, such as are m~nuf~ctured b)~ Power Conversion Ine., of ~It. Ve1l)on, Nel~ Yor~. It may also us.~ LeClanehe type cells or Lead Acid type eells. All sueh eells, if exposed to higll temperatures (sucll as those normally eneountered in deep earth boreholes) oukl develop Illgll interllal pressure~ so th~t the cells lYould tend to e~plode.
In one aspeet of the present invention, there is provided an arrangement (il-lustr3ted by l`igure ~G) by wllich this problem is overcome. In ~igure ~G, a plur3lit~ of individu~l cells 161 such as one of the above ment;oned t~pes are Tradem3r~
.

connected in series bet~een a ground te~minal 162 and a positive tenninal 163.
Each eell preferably is provided ~ conventional pressure release cap or vent 16~. In accordance with the invention, ~he cells lGl are plaeed in a eontainer or reservoir 165 \~hich is cap~ble of ~ithstanding pressures exeeeding those that eould be developed hy the electrolyte of the cells 161. IYithin the reservoir 165 there is plaeed a liquid 166 having the same or similar pressure-temperature charaeteristics as .]le electrolyte, i.e., the liquid 166 will produee ~apor pressure (t~hen e~posed to eleva~ed temperatures) that is substantially equal to the vapor pressure of the electrolyte in the cells 161. In the simple case of the LeCl,mche type or Le~d Aeid type cell, the liquid 166 can be water since the eontainer 165 is hel~etie and pressure resistantj the liquid 166 (in this ex-ample, water) ~lill ncver boil - no matter ho~ high the temperature. It ~
simply build up vayor pressure in the space above the liquid 166 high e~lough to be ar. equili~rium ~iti) ~he v,,por pressure generated by the hot liquid 166.
The same principle can be used when the cells are of the Lithium Sulyi.ur t~-ye, the liquid 166 could be Sulphur Dioxide. The Sulpllur Dio~ide vapor generated by the cells 161 ~ill all~ays be in pressure equilibrium l~ith the eon;ainer 165 because the Sulphur Dio~ide liquid in this au~illiaI~ eontaill-er 165 will al~ays generate pressures equal to those generated by the eells 161.
!0 Sulphur ~io~ide and ~ater> given as examples above, are often ~msatis-factory ~a~ becallse Sulphur Dio.~ide is highly corrosive and bee~-lse l~ater is an electric condllctor ~nd ean shor~ out the batteries. An altel~lative substanee is diel~lorodifluolometllane, popularly ealled Freon and manufactured by E.I.
CuPont an(l Co., l~'ill;lin~toll, Dela~are. ~1any ~ypes of ~reons have bcen develoyed with ~lmost an ulllil~ited number of thermod~namie properties, i.e., pressure-temI)erat~lre rel~tions. Other substane~s c:~n readily be found, 5~1Ch as h~dro-earboll vapors, propalle or butalle or mi~tures of vapors and gases. S~lIiCC it '' ~1 J ~56~

to s~ty th;tt I enclose tle battery cells 161 in a container 165 and place in this container a smtll qu~n~it~ of a substance having similar pressure-tempera-ture relations to that of the eleetrolyte in the battery cells 161. In Figures 3F tnd 3G I show only a small nwnber of cells eonnected in series. In actuali-ty> ~ larger nu~ber is norm211y e~ployed. In the manufactured instrument of Fi~re 3G I employ 17 Pol~er Conversion Co. Lithium Sulphur cells.
Another i~ortant feature of the present invention is that the length of ti~e the val~e 36 is m~intained open has no relation to the ~ount of energ~ required. The only energy required is that e~pended to actuate the va ~e 36 to tlle open position. The impor ance of this feature is fully appreciated rom the follolling consideration:
It has been deter~ined by experiment that in ordeT to provide a strong si~l froi~ a depth of 10 000 to 20 000 the valve must remain open for about 1/2 to one second and any electromechanieal (solenoid or other) deviee oper~tting for thi~ lcngth of ti~ would not only require large a~ounts of energv but would overhe~t alld under well eonditiens probably burn up rrem its self generated he~t.
As is herein~ove pointed out two typical sensors are diselosed as ox~mples of the t~l)es that ean be emplo~ed in the operation of the pr~sent in-vention. Figure 3C illustrttes a natural ~amm~ ra)~ sensor and its associated eircuitr)~ which in this e.~mple is of the anaiog t)l e. Figure 3D il]ustrates a telnper;ttlre sensor whicll in this e~almple is of the digital t~e. Either one of these sensors e~n be eolmeeted to the input terminal of the instr~tmentation illustr~te~ by Figure 3~ wi)icll tYill be hereinafter deseri~ed.
l~ith reference to ~i~lre 3C a geiger eounter 16S is provided with the eonvention~l higll voltage supply +~l~. The geiger eounter 16S ~ener;ttes pulses and is connectel through a eapacitor 169 to am~lifier 171 ~hich generates ~ J ~ ~ ~5~

pulses at its output that correspond to those of the geiger counter 168. A
scale of 1024 circuit 172 generates one output pulse for each 1024 geiger eounter pulses and its output is sho~n as pulses having a sep~ration tl. The higher the g~mma ray intensity~ ~he higher ~ill be the frequency of the pulses at .he output of the scale of 102~ circuit 172 and the sm~ller ~ill be the ti~e tl.
Figure 3n illustrates the case of thc ~emperature sensor. The tem-perature is sensed by a Lhermistor 173, i.e., a serniconductor that varies in rcsistancc with temperature (it is provided with a suitable po1~er supply, not sho~ nd it is assumed that the output of the thermistor 173 is a DC voltage proportioned to temperature. The amplifier 174 amplifies tnis DC voltage and impresses it on an analog-to-digital convertor 175 which in turn generates a series of binary bytes, one after the other, each representati~e of a number pro-portional to the sensed temperature. The outputs of the power amplifiers lS5, 186 a.e utili ed to control ener~i7ation of the windings of the "bac1~-to-bacl"
coupled solenoids (hercinabove described) to actua~e the valve 36. I~he~ inding 55 is energi~ed the solcnoid a~nature 57 (see Figure 3B) is mo~ed up~ardly, pushin~ up~ardly on shaft 47 to aetuate valve 36 to the "open" position. l`~len win~ing 59 is enernized, the solenoid armature 61 is moved do~ ardly, pulling do~-~n~rd on the sh~ft ~7 to actuate the valve 36 to the "close" position.
In tile sensors utili_ed in the present in~ention, the magnitude o~ tl~e do-~ilhole para~eter is represented by electric pulses. The sequence of the puls-es reyresents a code (binary or other) and this sequence represents tl-e magni-tude o~ the p~r~meter. Figure ~E illustrates ho:~ each single pulse Or this eo~le is processed to operate the valve 36. In Fi~ure 3E, numeral 177 represents one suell pulse ~ihich is narrol~ in time; being only a fet~ microseconds long.
Tllis pulse 177 is lmplessed UyOII the circuitry contained in bloc~ 17S. This block 178 contains a so called i'one shot" univibrntor and suitable inverting rectif~ing circuits well ~no-~n ;n the electronics ~rt and provides (in response to the single input pulse~ tlio output pulses separ~ted in time by ~1 (the first pulse is nor~ally time coincident with the input pulse and the second appears later by an amount of time equal to tl) as sho~-n by pulses 179 and lS0. ~hese electric pulses 179, lS0 are now impressed, respectively, upon the eircuitry contained in bloc~s 1~1, 18~ ese ~I~O eircuits are identical and are so ealled pulse lengthening circuits, also l~ell ~nown in the electronics art. Each input pulse is lengthened to provide output pulses 183 and lS4. These pulses are respectively applied to the- "Darlington" power amplifiers 185 and lS6 (as manufac,ured by Lambd~ ~)fa. CO. of ~lelville, New-York, and sold under the type P~ID16~100).
In the pr;lctical desi~l of the electronic logic and power circui,ly of ~igure 3E that I use in this preferred embodiment, I have chosen as eonstanLs tl - 500 milliseconds and t2 = 20 milliseconds. In operation, l~hen a single pulse 177 is i~l-resse~ on lead 167, the Darlington lS5 is turn~d on for 20 milli-seconds and then tullled of~. Then 500 milliseconds later the Darlington lS6 is turn~d on for 20 mil~iseconds and then turned off. Thus, the valve 36 is opened for 500 milliseconcls without requiring any energy during this period. Energy is require~ only durin~g tlle short 20 millisecond periods that are required to aetu ate the valve 36 ~o tl~e "open" or to the "close" position. The f.ig-lres a~iven above ~re for illustrative purposes only. Suffice it to say that by ma~ g the aetion of the v~lve 36: ~a) very fast and tb) bi-stable; very lligll pressures and volumes of mud ean be valved ~ithout the neeessi~y of emplo~ing large amo-lnts of enervy and as lleroinabove described, rel~tivcly small ener~y battcries can operate tl~e v~l~e abollt one million times.
In a t~l~ical emhodin~ent of this appar~tus, the weight of the entire valve mechanism 36 of ~igures 2A or 3A, including the solenoid armature 54, shaft 46 and piston S0 is apl~ro~imately 9 ounces. Tll~ valve 36 has been clesigned to operate at a diffcrential pressure of 1,600 psi and proportioned ~o operate at optim~un performance, including the consequence that the force required to open and shut the val~e ~6 must e~ceed the force due to vertical acceleration of all the appar~tus ncar the bit 26.
Assuming a vibration figure of 60 g and the weight o~ 9 ounces, maxi-mum vertical force on valve 36 due to the vib}aLion of the tool ~6 will be about 34 pounds. To be certain that the valve ~6 will not open accident~lly, the force l~eeping the ~alve closed in Figure 2B and the force ~eeping the valve open in Figure 2A mus. both exceed about ~4 po~mds. By suitable choice of the first and second indcpendent parameters hereinabove described, a "balancedl' con-dition is achieved. By "balanced" is meant that the force required to open the val~J~- 36 is equal to the force required to close it.
Above groLmd equipment utili7ed ~ith the present inventio?l, particular-ly as to metllods ~nd apparatus for eliminating intelrerring effects that are pr~sent in the output of pressure transducer 100, can tal~e various forn~.s, as will nol~ be describcd.
Figure 4 sholis t~pical above ground equipinent in accordance ~ith a preferred embodi~r.ent of the invention, ~lerein the do~-nhole parameter being sensed is the radio~cti-it~ of formations traversed by the bore while drilling i~ in progress. Tlle corresponding portion of the loggillg equipment l~hich is bclo~ thc ear~h' s surface has been previousl)~ described and shol~n in Figures 2A, 2B, ancl 3A-G.
Referrin~ nol~ to Figure ~, pressure transduccr lO0 conneeted to the st~lndpire 16 converts the vari~tion of n~ud pressurc within the standpipe into a v~r~in~ electrical volt~e. This voltage represents a mi~ture of t~o co1nponent 3L3L~S6~3 signals: the useful, lnformation carrying signal and the interferring signal.
The information c~rrying signal is a succession of short, negative mud prcssure pulscs produced by thc sudden opcning and closing of the val~e 36. The inter-ferring si~nal is in the form of relatively slot~ and periodic pressure varia-tions which are genera.ed by the stro~es of the mud pump 12. These mud pump signals tend ~o mas~ or obscure the infonmation one desires to obtain by utili7-ing the short ncgativc mud pressure pulses.
One of ~hc objectives of this invention is to recover> froin the "con-taminated" signal produced by the transducer, a "clean" sign~l which gives the desired information. This is accomplished by means of a signal e~ractor 102 which is applied to thc outpu~ terminal 101 of the pressure transducer 100. The signal extractor climinates the interferring effects and produces across its outpu$ terminal 10S a succession of pulses from ~hich the information regarding the dc..~hole par~metcr can be readily obtained.
Thc signal e~tractor 10~ is controlled in a predetermined m~nner by a succession of timing pulses obtained from a pulse genera~or 111 and applied to thc control tcrminals 11:, 114. The pulse generator 111 is mechanicallv driven by the mud pump 12 to produce an appropri~te number of timing pulses per revolu-tion of thc pump. A chain drive transmission assembly 11~ is provided fol~ this purpose.
Thc "cle~n" information carryin~ signal ob.ained from the e~tr~ctor ~ in tllc for~ of pulses derivcd from the actuation of valve 36 of gener~tor 28. Thc rolcv~nt information is provided by thc tirne intervals separating the pulscs. A timc-to-~lnpli~Ludc convertor 115 connccted to the sigllal e~tractor output tcrmin~l 10S convcrts those pulses dcrivcd from the actu~tion of ~he v~lvc 36 of gellcrntot 2S into sign~ls h~ving magnitudes repres~ntin~ thc in~cr-vals thcrcbctliccn. Thc convcrtor 115 is a ~iell ~no~.n electronic devicc ~nd c~n - `) `
~ 5~

be made up of componcnts manufactured by the Burr-Brot~n company of Tuscon, Arizona, U.S.A. For f-1rther detailed descrip~ion of time-to-amplitude conver-tors see: ~1. Bertolaccini and S. Cova, "Logic Desien of High Precision Ti~e to Pulse Hei~,ht Convertors", Nuclear Instruments and ~lethods 121 (1974), pp.
54ï - 566, ~orth Hollalld Publishing Co., The signals derived from the convertor llS are in t~lrn applied to the inpu; terminal 109 of a reciprocation circuit llS. The reciprocation circuit llS (as, for exa~lple, man~tfact~red by Analog Devices, Inc. of ~or.;ood, ~lass.) preduccs output volt~ges ~vhich are the reciprocals of the input voltates. ~tus, ;f a voltage of magnitude ~1 is applied to reciprocation circuit 118, an output voltage having magnitude l/M is obtained. These signals having magnitu~es lJ-i are in turn recorded on the chart of a recorder 120. The record chart ol record-er 120 is moved in cor.elation ~ith changing depth of the sensor unit 30 by a deptll sensing device 121. The depth sensing device may be. for e~a~ple. a modi-fication or adaptation of equipment such as mar~eted by The Geolegrap]l ~leaeavis Compan~ of O~lallomt Cit~, O~laho~a, U.S..~.
In order to shol~ more eleariy the operating eatures of the signal extractor 102, we ~ill analyze the behavior of the various signals ~hich are involved. They are she~m schematically in a simplified and idealized form as ~0 tlley v~r~ ith time in Figure 5. Let F(t) = S(t) + N~t) (1) ~here Stt) is tl~e usefnl information carr~ing signal formed by the negative m~ld prcssurc pulscs Pl, P2, and P3 ~ligned along the time a~is t. rSee Fî~lre 5 (a~is .~)] The tin~es of arrival of tllese pulses, which correspond to the tinles of aetuation of ~he valYe ~6 of generator 2S, are tl, t2 and t3, respectivel~.
~e ti~e intervals ~hich separate these pulses are ~1 = t2 ~ t1, A2 = t3 ~ t29 A~ - t4 - t~, etc. are indicative of the intensit~ of the ra~iation meas~lred.
If these ti~e interva]s are larrre, ~he intensity is rela~ivel~ t.~ea~ and con-1~956E}3 versely, i~ ~hcy are small, the intcnsity is rel~ti~ely strong. The interfering signal produccd by thc mud pump 12 is represented in Figure S (axis .~) by a periodic but not necess~rily sinusodal func~ion N(t) having a period T. The length of the period is relatcd to ~he speed of ro~a~ion of the pump.
To f~cilit~tc e.~plana~ion, ~he relative scales in Figur~ 5 have been distorted. In ~ctu~l pr~ctice, tllere may be S0 ~o 80 oscillations of N(.) bet~ecn the ~i~e of arrival of Pl and P2. Thus~ ~1 and 12 may Yary from 50T to 80T. Ho~;ever7 in Figure S (axis A) only a few oscillations of ~(-) between Pl ar.d P2 have been shol~n. Furthermore, in actual practice the negative mud pres-sure pulses Pl, P2, P~ do not have clean rectangular forms as in Pigure 5(a~is A). ~lorcovcr, the actual pulses are much s-maller than those ~hich have bcen shol.n in Figure 5 (a~is A). In actual experience, the magnitude of Pl, P2 or P3 is about 0.1 to 0.01 of the ma~imum amplitude of the pulsations N(t).
Axes A - E in Figure 5 are positioned one belo~ the other so that one can compare the si~nals in their time relaLionsnips one to another. Using ~hese figures, ~ie can row enumcrate the inst~lmental s~eps ~nich are involved ill the opcra~ion of ~he sign~l e~tractor 102. These are as follows:
St~p I
l~ displace thc input F(t) by an amount T, to obtain '0 Ftt - T) = Stt - T) ~ N(t - T) (2) t~llcre Stt - T) ~ld \'(- - T) are~ respcctively, the displ~ced uscful signal and ~isplacc~ illtcr~crin~ signal. Botll s;gnals are shol~n in Figure S ~axis B). ~le si~nal S~t - T) is rcprcscnted by pulses p1ta), p2(a) and P3t~j which ha~e been obtaine~l by displacin~ b) ~n amount T the corresponding pulses Pl, P2 and P3 in Figurc 5 t~is A). Tllc signal N(t - T) in Figure 5 ~axis B) is shown ~o be in ex~ct s~nchronism l~ith N(t) in Figurc 5 (a~is A). This is duc ~o thc pcriodicity of thc si~nal. Thus,

5~ ) N~. - T) - ~(t) (~) Step 2 l~e subtrac~ the displaced input function F(e - T) from ~he original input unction F(t) to obtain ~I(t) = ~(t) - F~t - T) ~4) Takin~ into account (1), (2) and (3), we obtain ~ I(t) = S(t) - S(t - T) (5) Thus> the interfering si~nal has been elimina~ed and does no~ appe2T in ~l(t).
This can also be seen fro~ inspection of Figure 5 (axes A and B).
As sho-.~ in Figure 5 ~axis C), ~ ) consists of impulses which occur in pairs. Each p~ir contains a negative and a positive pulse separated one from another by a time interval T. Thus, ~e observe a pair consisting of pl(b) and pl(b) which is follo~ed by a succe~ding p~ir consis~ing of P2(b) and P2~b) , thcn by another pair consisting of p3(c) and p3(c) and so on.
Step 3 l~e displacc ~1(;) by a time T so as to obtain ~I(t - T). Thus, the entire sec~uence of pulses in Fi~re 5 taxis C~ is shifted along the timc a~is by T so as to appc3r as shown in Pigure 5 ~a~is D). The arrangement of pulses as in p3irs has been prcservcd in Figure 5 (a~is D). However, each pair such as ~0 Pl( ) and Pl( ) is displ~ccd with respect to the pair Pl( ) and pl(b) [sho~rn in l'igure S (a.~is C)] b)~ r. Similarly, thc p~ir P2(C) and P~( ) is displ~ced with rospcct to thc pair P2(b) and P2(b) by T9 and so on.
Stcp 4 l~'c co;np~rc el~c displaccd pulses in ~igure 5 (a~is D) with those in Figurc 5 (a~is C). h'c note that SOIIIC of thcse in ~igurc 5 (a~is D) are in ~ime coincidencc witl~ some of the pulscs in Figure 5 (a~is C). The instances ~t icl~ coincidcncc occurs arc rccordcd in ~igurc 5 ~a~is E) as pulscs Pl( ), _ 29 -~ ) ?

P2(d) L~nd p3(d) Thus, Pl(d) coincides with Pl(~) and Pl(C) P2(d) coincides with P2(b) and P2~C) P3( ) eoincides with P3~ ) and P3( ) The times at ~hich the pulses pl(d), p2(d) and p3~d) occur ar~ tl + T, t2 + T
and t3 ~ T-The pulses Pl( ), P~( ) and p3(d) correspond to the pulses Pl, P2 andP3 shol~n in Figure 5 (a~is A). Consequently, the pulses in Figure ~ (a~is E' also represent this useful function l~hich now is S(t - T) since it has only been displaeed by T. It is evident tha~ the pulses in Figure 5 (axis E) provide the inform3tion IYhich ~Ye are seeking to obtain. The ~ime interval between Pl(d) and P2( ) is Al, ~nd the ti~,e intel~al bet~èen P2~d) and p3~d) is ~2~ ete.. The quL~tities ~ 2J ete. are indieative of the radiation m~asured by the gamma Tar deteetor.
The above steps ~ill now be considered as they relate to the perfor-manee of the siL~nal e~,raetor 102 and more p~rticularly to that of its t~/o eom-ponent parts design~ted in FiLL~ure 4 as 105 and 107 and SIlO~v~ schematically in Figures 6 and 7, respecti~ely.
The COmpOnellt 105 receives at its input terminal 101 (~Yhieh is the s~me as th~t of the sign~l e~traetor 102 of Figure 4) the sign~l F(t). As sho~Yn in Figllre 6, tltis sigll~l is trans'nitted through an amplifier 130 to the input terlllin;ll 131 of a del~y networ~ 132. ~le dela~ net~Yor~ delays F(t) by T, thus, produeing at its output terminal 13~ the signal Ftt - T). This signal is a sum of t~o eomponellt si~lals S(t - T~ and ~(t - T) whicll are sho\~n in Figure 5 ~a~is B)-The signal F~t - T~ is applied to one inpu~ terminal 13~1 of a sub-tractor 1~5. The other input terminal 136 of the subtr~ctor receives directly the sign~l F(t), which is transmitted from terminal 101 by means of cond~lctor 1~7. Thus, at the outpu~ termin~l 106 of the sub.r2c~0r 1~5 we ob~ain ~he dif-fcrcncc signal ~I(t) = F(t~ - F(t ~ T). This is shos~ in Figure 5 (axis C).
The delay ne~s:or~ 132 is provided ~ith control terminal 113 ~hich receives a sign~sl con~rolling the delzy T. It is importan~ tha~ the length of thc dcl~y T bc the same as the period of mud pressure oscillations produced by the mud pu~p I~.
The amount of the delay T is controlled by the timing impulses derived from pulse gcncr~tor 111 sho:in also in Fi~lre 4 and applied via conductor 110 to the control tcrmina1 113. It is noted that the delay T is the s~me as the period of oscillation of mud prcssure produced in the successive strokes of the mud pump 12. Conse~uently, the frequency of these timing pulses must be controlled by the rot~tion o~ the pulnp.
Assumc that thc pump produces Nl stro~es per second. Thus, T = l/Nl.
~le pulse gencrator 111 produces timing pulses at a reiatively higll rate ~12~
which is a multiplc of ~'1 ~nus, ~2 = ~Nl~ where X is a cons,ant s~hich has been choscn to bc 512. Thus, if the stro~es of the pump are one per second this l.ould re~uirc the si~nal ~encrator to produce 512 pulses per second. It is app~rent th~st the rate of pulsation of the mud pu~p 12 varies with time and, accordingly, N2 l~ill vsry so as to insure that t1le delay produced by delay networ~ 13~ will alt~ay5 bc c~usl to onc pcriod oE the mud prcssure oscillatiolls produced by the ml!CI p~ltllp 12.
~le dclay ncts~or~ s.hic1l is controlledJ as described abovc, may be s r~cticon ~lodcl S.~D-1O~ I DUa1 Ana10g DC1aY L;TIC as tnar~ctcd by Rcticon Corpor~-tiOtl, Ss~nny~lc, Californi~, U.S.A.
c instrllmclltal s~eps hcre~eforc dcscribed are thc s~eps 1 and 2 per-~ormed b- thc co~pollcnt lOS of thc si~nal e~troc~or 102. I~c hs~e tr~nsformcd the input signal F(t) [representcd by i~s components in Figure 5 (axis A)] into an output signal ~l~t) which appears as a succession of pairs of pulses and is shown in Figurc 5 (a~is C). We will now proceed to describe further instrumental steps ~hich are requircd in order to accomplish the desired objectives. These are performcd by the component 107 of the signal extractor 102.
We refer now to Figure 7. The signal M~t) is now applied through conduc~or 140 to a delay net:.orX 141. This delay network is iden~ical to that designated as 1~2 in Figure 6. I~ receives, at its control term~lnal 114, the s~me control sign~1 which was applied to the control terminal 113 of the delay networ~ 105. Consequently, the amount of delay produced by dela~ networ~ 141 is T and the signal appearing at the output of 141 i5 ~ T) as shown in Figure 5 (axis D). This output signal is transmi~ted througll an amplifier 143 to one input terminal 145 of an AND gate 146. AL the same time, the und~layed sign~l ~l~t) is applied through .he conductor 147 and ampli~ier 148 to the o~her inpu~
tcr~inal 1~9 o~ the A~D gate 146. These two inpu~ signals ~I(t) and ~l~t - T) w]lich are applied to the .~'D gate 146 are shol~ in Figure 5 (3~es A ~nd D), respectively. lYe ha~c previously observed that some impulses sho~m in Fig~ure 5 ta~is C) occur in coincidence with impulses in Figure 5 ta.~is D). Those impulses that OCCUl` in coincidcnce appear in tlle output of the AND gate 146. They are designa,ed in Fi~urc 5 (a~is E) as Pl(d), P2(d) and p3(d) These coincidellt pulses arc thc Olltpll. of pulses o the component 107, and consequently of the signal c~tractor 102~
It is thus apl)arcnt that by means of the component 107, ~e have per-ormcd the insLrunlclltal stcps ~ ~nd 4. lYc h~ve transfol~led thc sign~l ~I(t) sho~m in ~i~urc 5 (a~is C) into the signal S(t - T3 shown in ~igure ~ ~a~is E).
The l~ttcr providcs tlle q~lalltities ~ 2~ ~3~ etc., ~hich reprcsent the infoT-mation it was dcsircd to obtain. It sllould bc recallcd that thc si~n~l S(t - T) ) is rcpresented by a succession of pulses as shown in Fi~ure 5 (~xis E~ ese pulses are tr~nsmitted to the time-to amplitude convertor 115 to produce at the output of the time-to-a~plitude conbertor llS signnls of various magnitude such as ~ 2~ ~3~ etc., that represent time in~ervals between the arriv21 of pulses.
These signals are in turn fed to and transformed by the reci?roca~ion circuit llS of Figure 4 in~o other reciprocal si~nals ha~ing magni.udes 1/~1, 1/~2, 1/~3s respecti~el}. ~lese ~eciprocal signals arcrecorded by recorder 120 of Figure 4O It is a~parcnt that the quantities 1/~ 2 and 1~3 represent the in.cnsity of radioactiYit~ of formations sensed by the sensor unit 30 at ~arious depths in the borehole.
We have described above an instrt~ental means for performing logical steps 1 ading from the function F(t) to a function S(t - T). These steps have been performed by representing these ft~ctions in ~t analog (non~digiLal) form.
Alterna,ively, if desired, the entir~ process can be digitali_ed, as sho~
diagral~atically by Figure S. In Figure 8, the o~tput of tlle pressure transducer 100 is fed to an analog~-to-digital convertor 103, the ou~put of whicl1 is fed to a digital computer 104. The oper~tions indicated in Figure 8 are performed by the eler.tents designated 122, 123, 124, 125 and 126 in the digital comp~lter 104.
Timino signals fro~ a pulse generator 111 or 140 are introduced ~o the digital coml)uter 104 in order to control the delays in accord,tl1ce with tlle p~lmp speed~
Tlle oper~tiolls in(licatcd in the dotted rectal1gle of Figure S are perfo~ned mnthematically in a sequcnce which may be flow charted. The out~ut of the com-~uter 104 is fed to a digital-to-analog con~ertor 127, the output of ~hich is fe~l to tl~e recorder 1~0.
In Fioure 9, there is shown a~ arla.,ge~ent similar in so~ respects to that of Figure 4, ~ut lihereill the data to be obLaincd and recorded is the te~-- ~er~tur^ at the location of sensor ttnit ~0 of Fi~urc 1. In Figurc 9, these data,

6~
as prcscntcd to the signal extractor 102 are in digital form ~see Figure ~D).
The signal extractor 102 of Figure 9 is idcntic~l ~o that of Figure 4, but the timc to-amplitude convcrtor 115 and ~he reciprocation circuit 118 of Figure 4 are replaced by a digital-to-analog convertor 141. The olutput signals of an appropriate pulse gencrator will be applied to the con.rol ter~inal 110 of the signal e~tractor 102.
It is not always convenient to provide a mechanic~l connection to the mud pump 12, as shol~ by the chain drive transmission assembly 112 in Fi~lre 4, and an altcrnate means for generating the pulses required for the signal e~trac-tor may be desirablc. Figure 10 illustrates such an alternate means. In a typic~1 e~mple, the signal extractor 102 of Figure 4 is provided at its ter-minal 110 l~ith pulses at a rate of 512 pulses per full pump stro~e. It mus, be clearly understood that ,his rate DlUS~ be rigorously synchronized ~ith the ~Impstro~es. All the "~imcs" sho~n as T, tl, t2, etc. in Fi~ure 5 are not so-callcd "real time", but arc dircctly related to the speed of the mud pump 12 and ri~orously, T, tl, t2, etc. should be expressed, not in seconds or minutes of "time" but in "gallons of mud". ~len it said tha~ at ~erminal 110 of Figure 4, thcre arc 512 pulses per mud pump stro~e, it is meant that at terminal 110 therearc prcsent voltaoc pulses having a frequency equal to the 512tll harmonic of the pump stro~c frcqucncy. Fi~ure 10 sho~s how this can be accomplished without mecll~nical connectioll to thc p--mp shaft.
In ~igurc 10, component 145 is a VC0 or "voltage controlled oscillator"
~hich at its outl)llt 110 produces electric pulses the frequency of ~rhich is con-trollcd by thc DC vol.a~e applied at its input terminal 10~. Compon^nt 150 is a binary dividcr or sc~lcr tllat di~idcs the frequency of the pulses impressed on its input termin~l llG an~ gcner~tcs OUtpllt pulses at its output te~minal 117 havin~ a frcquellcy cqual to l/512th of frcquenc~; of the inpu~ pulses. Componcnt - ~ ) ~5~i~3 119 is a phase comr,~rator that comp2res t~Yo inputs (one from scaler output ter-min~l 117 and one fIom the output terminal 130 of pressure tTansducer 100), and provides at its outpu~ terminal 12S ~ voltage which is zero volts DC wllen the two inputs 117 and 150 are e~actly equal in phase; and pro~,ides a posiLive voltage when the input at 117 leads the input at 130 in phase; and a negative DC volta~e when the input ~t 117 iags ~he input at 1~0 in phase. A baLtery 129 is provided to properly bi~s the VC0 14~. The circuit 151, just describ~d, is ~no-~n as ; "phase locked loop". The opera~ion is best e~plained by an e~mple: Assume that the pump pulse fre~uency (pump stro~e frequency) is 1 Hæ and the VCO is generat-ing 512 H~. The output of the scaler 150 3~ill then generate e~actly 1 H7. The 1 Hz rom the scaler 150 and ~he 1 H7 from the pressure transduce~ 100 ~ill then be e~actly match~d in frequency and phase and the output Or the comparator at termin~l 12S will be zero volts, and the VC0 145, when properly biased by batterv 129, will gener~;e e~ctly 512 pulses per stro~e.
Ass~le now th~t the mud pwnp 12 ~peeds up. The requency at t~rminal 130 will than be sor.~ewhat greater than 1 H - i.e., 1 ~ ,3 The comparator 119 wil} then provide .~1 output at terminal 128 whicll will no longer be ~ero volts DC, but for e~mple, ~ ~2V, this sm~ oltage increment will be applied to tlle VC0 1~5 at terminal 10~ and increase its frequency ur,til the no)ninal 512 pulses per second is increased to a value f such th.at f/512 = 1 + ~1 Thus, the frc~lency at termin~l 110 will al~Yays accur.ltely follol~ the re~uenc~ of the mud pur.lp 12 and ~ill always be its 51~h multiple.
Two arranzer!ents or obtaining timing pulses for the signal extractor 10~ h~-e been heleinabo~:e described ~pulse generator 111 of ~i~ure 4 and the "pl~,se loc~ed lool)" circuit 151 of Figure 10). A third arranoement that may be used for o~tainino such timing pulses is illustrated by Figure ll and is base~
on "auto-correl~,tion". In Figure 11, the input terminal 15~ c, a correlator 152 - ~ ) ) is supplied by the output of the pressure transducer 100, and receives the func-tion ~t) ~hich contains the periodic signal N(t~ and the function S~t) ~hich mzy be considered a random function. The output of the pressure transducer 100 is also applied to the input teTminal 101 of the signal extractor 102. The eor-relator 152 is ~dap~ed to produce across its output terminals the autocorrela~io~
functio~ of F(t) whicll is ~fftT) = [S~;) + ~(t)] [S(~ ~ T) + N~ + T)] ~6) IYhere the bar in the above expression indicates ~veraging over an approRriate period of time. The funct~on ~ff (T) can be e~pressed as 10 ~f~T) ~SS(~) + ~nn~) (7) where (T) = S~t)S~L t T) (S) and ~nn(~ L)~ ~t ~ 1) (9) Tl~e function ~55~l) reaches zero at so~e value of T = To and be~ond ~O, we have ~f(T) = ~n;,(l) (10) Since ~nnl~) is ~eriodic, the function ~ff(~) is also periodic and it h~s the period ~. This fullctioll, which is obtailled in the output of tl~e correlator 152 is ill tUltl applie~ to a pulse multiplier 15~ ich prodi~ces ~ succe~sion of' timin~ pulses simil~r to those pro~luced by the pulse generato~ 111 in Figure 4 Mld ~hieh are apl~lied to input termin~l 110 of the signal e~tractor 102. The pulse multi~lier 15~ mllltip1ies the freque~cy of the input pulses by a ph~se loc:;ed loop system similar to that of Fi~ure 10 or by an~ other eonventional me;u~s~ The rem~ inS elements in Figure 11 ~re the same as those in ~ ure 4, e~cert, of course, tll~t the pulse ~ener~tor 111 ~nd i~s chain drive tr~ns~ission - 36 _ ~sscmbly 11 ~re elimin~ted.
There are co~ne~ciall~ available instrumental means based on auto-correlation for recovcring a periodic signal from a mixture of a periodic and a rando~ signal (see, for example, Statistical Theory of Communications~ by Y.lY.
Lee, John l~'iley, Ne~ Yor~ .Y., 1960, pp. 2SS - 290). ~le correllator 152 of Figure 11 may be ~lodel ~721.~ manufactured by He~lett P~ckard Coinpany of Palo Alto, Califorllia. The correllator 152 could also be on~ of the t-.~pes described in the follo~;in~ references: A.E. Hastillgs and J.E. ~eade "A Device or Comput-ing Correla~ion Functions", Reviel~ of Scientific Instruments, Vol. 23, 19i2, pp. 347 - 349; and F.E. Broo~s, Jr. arld H.l~l. Smith, '1A Computer for Correlation Functions", Re~ie~ of Scielltific Instruments, Vol. 23, 1952, pp. 121 - 126.
I\~lile I h~e sho:~m my invention in several forms, it will be obvious to those s~illed in the art that it is not so limited, bu~ i5 susceptible of ~arious changes ~ld modifications without departing from the spirit thereof.
I have disclosed herein, as e~amples, sensors for only ts~o dos~-n}sole par3;"eters, it is, ho-;e~er, to be understood that sensors for various other do~
hole parameters could be used as s~ell. It is also to be understood that sensors for a plurality of do~nhole par~netels may be used at the same time, in s;hich ease, conventional techniques would be e~ployed (such as time sllaring, multiple~-in~, or the li~e~ to halldle the data representillg the pluralit~ of p~r~neters.
I~nsen deviated or inclined wells are drillecl, a tur~ e or "mud motor"
such ~s a D~ladrill, manufactured by Slnith Industrics, Inc~, Houston, Te~as) is fre~uelltly em~)loye~l. In such case, the drill string 31 o Figure 1, is not ~otatcd by the rotary t~sble ~t tlle surfaee. The rot~ting actio~l to tum thc bit 26 is derived from SUCll a mud motor~ s~hich usu~lly is locatcd i~nedi~tcly abo~e the bit 26 in the drill string com~rising elements, 22, 24, 2~, 30, oE Fi~ure 1.
~'lsen suc!l ~ mud motor is e~plo~ed, ~ large pressure ~ro~ occurs across it ~5~3 (since thc mud motor derives its power from the mud flo:~). This large pressure drop can be utilizcd to supply the pressure difference bet~een the inside of the drill string and thc annulus and, in such case, a "jet" type bit need not be employed.
The prcscncc of the pressure drop across the mud mo~or merely enhances the operation of my invcntion so long as the negative mud prcssure pulse genera-tor is locatcd above thc ~lud motor.
The term "flo~ restriction means", for purposes herein, applies ~o either a jet type bit, or a mud motor, or both. The term "high pressure zone"
applies to the d~illing fluid pressure on the upstream side of the "flow restric-tion means" and ~he term "low pressure zone" applies to the drilling fluid pres-sure on the dol~stream side of the "flow restriction means".
It is recogni-ed that, in some instances> a plurality of mud pumps are employed on a single drilling rig and these pumps are not necessarily opera~ed in synchronis~.
In an c~ple Oc three pumps~ the periodic pressure curve of Figuro 5A
would, in the ~r ctical case, no~ be a simple pcriodic func~ion as shown by N~t~
but would be the surn of three componcnts, each component being periodic and hav-ing its o~m distinct period.
By thc employcmerlt of three delay systems, as sho~n in Figure 6, each s~chronizcd with its own pump, each pcriodîc component of ~he interfering mud pulsc prcssurc si~nal can l-e scparatcly nullified. Suitablc interconncction wili then producc a si~nal from whîcll the interfering mud pump pressure signals are cl iminatcd .
Thc forc~oina disclosurc and tile showings madc in the drawillas arc mcrcly illustrativc of the principlcs of ~his inven~ion an-l ~re not ~o bc in- -terprctcd in a limitillg scnsc.

- ~8 _

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A measurement while drilling apparatus for use in a borehole down through which drilling fluid is forced to flow in a circulation system and having a restriction in said system causing a high fluid pressure zone and a low fluid pressure zone, said apparatus comprising a valve interposed between said zones, said valve being moveable to open a passage for flow of drilling fluid from said high pressure zone to said low pressure zone and to close said passage, means for detecting the magnitude of a downhole parameter and for producing electrical signals repre-senting said magnitude, an electromagnetic solenoidal means comp-rising a source of electrical energy and responsive to said electrical signals for generating an electromagnetic force for controlling the opening of said passage, and a means independent of electrical energy for causing the closure of said passage whereby the openings and the closures of said passage are effect-ive in generating pressure variations in the drilling fluid, said pressure variations representing the magnitude of said para-meter and a means at the earth's surface to detect said pressure variations to provide a measure of said magnitude.

2. The apparatus of claim 1 wherein a pump is provided for forcing drilling fluid through said passage and back to the sur-face through an annulus thus defining said circulation system, wherein said restriction produces substantial difference of pres-sure between the interior of said string which comprises said high fluid pressure zone and annulus which comprises said low pressure zone, and wherein said valve is interposed between the interior of said string and said annulus.

3. The apparatus of claim 1 wherein said means independent of electrical energy utilizes pressure difference between said high pressure zone and said low pressure zone for causing the closure of said passage.

4. The apparatus of any of claims 1 to 3 wherein said valve comprises a valve seat having an inlet extending to said high fluid pressure zone and an outlet extending to said low fluid pressure zone and a valve stem moving from the inlet of said valve seat to open said passage and to the inlet of said valve seat to close said passage.

5. A measurement while drilling apparatus for use in a borehole down through which drilling fluid is forced to flow in a circulation system and having a restriction in said system causing a high fluid pressure zone and a low fluid pressure zone, said apparatus comprising a valve interposed between said zones, said valve being movable in a first direction to open a passage for flow of drilling fluid from said high pressure zone to said low pressure zone, and moveable in a second direction to close said passage, means for detecting the magnitude of a downhole parameter and for producing electrical signals representing said magnitude, an actuating means for moving said valve in said two directions, said actuating means comprising:
a source of electrical energy, an electromagnetic solenoidal means deriving electrical energy from said source and responsive to said electrical signals for developing an electromagnetic force in said first direction, a means independent of electrical energy for developing a mechanical force in said second direction, whereby the motion of said valve in said two directions is effective to cause pres-sure variations in the drilling fluid, and a means at the earth's surface to detect said pressure variations to provide a measure of the magnitude of said para-meter.

6. The apparatus of claim 5 wherein said means independent of electrical energy is a hydraulic means for developing a force in said second direction.

7. The apparatus of claim 5 wherein said means independent of elec-trical energy utilizes pressure difference between said high pressure zone and said low pressure zone for developing a force in said second direction.

8. A measurement while drilling apparatus for use in a borehole down through which drilling fluid is forced to flow in a circulation system and having a restriction in said system causing a high fluid pressure zone and a low fluid pressure zone, said apparatus comprising a valve interposed between said zones, said valve being moveable in a first direction to open a passage for flow of drilling fluid from said high pressure zone to said low pressure zone, and moveable in a second direction to close said passage, means for detecting the magnitude of a downhole parameter and for producing an electrical signal representing said magnitude, an actuating means for moving said valve in said two directions, said actuating means comprising:
a source of electrical energy, a first, electromagnetic solenoidal means deriving electrical energy from said source and responsive to said electrical signal for developing an electromagnetic force in said first direction, a second means independent of said electrical energy for developing a second force in said first direction, and a third means for developing a third force in said second direction whereby the motion of said valve in said two directions is effective to cause pressure variations in the drilling fluid, said pressure variations representing the magnitude of said parameter, and a means at the earth's surface to detect said pressure variations to provide a measure of said magnitude.

9. The apparatus of claim 8 wherein said second means is a hydraulic means for developing said second force in said first direction.

10. An apparatus of claim 8 wherein said second means comprises a volume element in which drilling fluid is maintained at a pressure intermediate between that in said high pressure zone and said low pressure zone, and utilizes the difference in pressure between that in said high pressure zone and that in said volume element to generate said second force in said first direction.

11. The apparatus of claim 5 wherein said valve comprises a valve seat and a valve stem moveable away from said valve seat in a first direction to open said passage and moveable towards said valve seat in a second direction to close said passage.

12. The apparatus of claim 5 wherein a pump is provided for forcing drilling fluid through said passage and back to the surface through an annulus thus defining said fluid circulation system, wherein said restriction produces substantial difference of pressure between the interior of said string which comprises said high pressure zone and annulus which comprises said low pressure zone, and wherein said valve is interposed between the interior of said string and said annulus.

13. A method of making measurements in a borehole in which drilling fluid is forced to flow in a circulation system having a restriction in the system causing a high fluid pressure zone and a low fluid pressure zone, and including a valve interposed between said zones, said valve being moveable to open a passage for flow of drilling fluid from said high pressure zone to said low pressure zone and to close said passageway, including a source of elec-trical energy, comprising the steps of:

determining the magnitude of one or more selected para-meters in the borehole and generating electrical signals repre-senting said magnitude, applying electrical energy in response to said electri-cal signals to open said valve, closing said valve in absence of the application of electrical energy, the openings and closings of said valve serv-ing to create pressure pulses in said drilling fluid; and detecting said pressure pulses at the earth's surface to provide a measure of said magnitude.

14. The method of claim 13 wherein the step of closing said valve in the absence of the application of electrical energy includes utilizing the pressure differential between said high pressure zone and said low pressure zone.