US2373323A - Process and apparatus for pressure core drilling - Google Patents

Description

April 10, 1945. G; A. MACREADY PROCESS AND APPARATUS FOR PRESSURE CORE DFILLING 1941 r 2 Sheets-Sheet 1 Filed Nov. 21

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Application November 21, 19415, serial No. 619,884

' 6 Claims. (oi. sss- -i's) My invention relates to a method and apparatus for obtaining core drill samples from bore" holes and bringing them to the surface sealed against loss of pressure so that the liquid and gaseous substances contained in the pores or interstices of the formation sampled are recovered for inspection. v

An object of my invention is a process and apparatus for preventing contamination of the fluids originally contained in the formation sampled by the mud laden circulation fluid used for drilling the well.

Another object of my invention is a process and apparatus by which liquid and gaseous subwith the core or the bottom of the well to contaminate the sample.

Frequently the purpose of drilling wells is to discover or to produce liquid and gaseous substances, such as petroleum and natural gas, which occur in the interstices or pore spaces of the rock formations. I

In the art of drilling wells it has been good practice for many years to take core samples of formation to ascertain the typeof formation encountered during drilling- But in ordinary coring and exude from the core lower pressure at the top of a well so that the sample is of spent formation with the pay fluids lost.

\In order to take a more truly representative core I provide a core drill in which the. tube containing the core is sealed before it leaves the practice fluids expand bottom of the well and is brought to the surface with thefiuld 'still contained within the tube'under pressure. I further provide a measuring process and apparatus by which the pressure and quantity of gas brought up with the core can be quantitatively measured. By chemical analysis the quantity of petroleum in the core can also be determined. Since the gas is usually in solution in the petroleum as a homogenous liquid underground the'data obtained gives an accurate deas it ascends to the termination of the gas-oil ratio ofthe formatlon.

Another objectionable accompaniment of rotary core drilling is caused by the use of mud laden circulation fluid under higher hydrostatic pressure than the formation pressure. from this fiuid forms Ta cake or plaster on the side wall of a well which prevents caving and excesslve loss of circulation fluid into the formation. But on the very bottom of the well the rotating bit continuously scapes off the mud cake so that circulation fluid is free to percolate into the formation, particularly if the formation is porous and permeable. The result is that in permeable formations the circulation fiuid acts as a water flushing driveto push through the interstices oi the formation such fluids as would subsequently be produced. The extent of this drive is not sumcient to impair subsequent production but it is sufiicient to contaminate the formation directly in the path of the drill so that core drill samples are contaminated before enter.- ing the core tube by displacement of original formation fluid with circulation fluid.

In order to obtain an even more representative core sample than my samples in the preceding paragraphs, although at greater expense, llprovide a novel process for separating the circulating fluid from contact with the bottom of the well and also from the core within the core receiving tube. To do this I employ a pool of molten'alloyon the bottom of the well as a barrier between the circulation fluid and the formation, andI prime the core receiving tube with gl'ycerine or other distinguishable liquid as a barrier between the core and the-circulation fluid. The core is taken under pressure as previously mentioned.

As a result of my new process circulation fluid 'cannotpenetrate ahead of the drill to contaminate the formation, and neither can it enter the core receiving tube to contaminate the core.

Chemically giycerine is distinct and not miscible with gas or petroleum. It is chemically distinct although misicible with water. The percentage of glycerine in the mixture can be determined by its specific gravity, glycerine beingheavier than water.

- With the foregoing and other objects in view which will be made manifest in the following detailed description and especially pointed out in the appended claims, reference is had to the accompanying drawings on which similar numerals refer to similar parts throughout the several views,

for illustrative embodiment of my invention wher in:

The mud core tube on larger scale to show bit as shown in Figure 4 but barrel type illustrated in Figures 1 barrel is provided with the end as illustrated in Fisure 2.

Figure 1 is a longitudinal section or one form my core drill, illustrated as in a well, ior recovering the core under pressure but in which there is no provision for maintaining a pool or molten metal on the bottom of the well,

Figure 2 is a longitudinal section of the inner in more detail the construction oi' the valves and inner core shoe.

Figure S is an elevational view oi'the inner 0 core tube with the apparatus that Iprovide for measuring the pressure and quantity or gas recovered with a core,

Fisure i is a longitudinal ection 0! 'a modification or the drill shown by Figure l but with is the inner barrel shown in elevation and with the additional provision for maintaining a pool of molten metal on the bottom of the well during coring, this section 22 and 28,

Figure 5 is an elevation oi the bit shown in Figure 4 for providing the pool oi molten metal. I Figure 8 is a longitudinal section or the same taken in plane 6-8 being on plane t-t of Figures of Figures 22 and 23,

Figure 7 is a longitudinal section 0! the bit shown in Figure 6 along the same plane but shown to illustrate the position of the molten metal during coring, v

Figure 8 is a cross section oijmy core drill at so plane 8-8 or Flsures 1 and s.

. Figure 9 is a section at plane s-s oi Figures '1 and 4, s Figure 10 is a section at plane iii-iii of Figures 1 and 4:, 35

Flsure 11 is a section at plane H-ii of Figures 1 and s. i

Figure 12 is a section at plane iZ-il of Figure 13 is a section at plane it -l8 of 40 Figure 1. I

Figure la is a section at plane i iis or Figure}, I

Figure 15 is a section at plane it-ib oi Fisure 2. as Figure 16 is a section at plane-ltis of Figure 2.

Figure 17 is a section at plane il-i'l of Figure 2. y

Figure 17 is a section at plane ie-m oi so Figure 2, V

Figure 19 is a section at plane lE-JE of Figure 20 is a section at plane Eli-2o or Figure 2. so Figure 21 is a section atplane 2i-2i of Figure 2.

Figure 22 is a section at plane, 22--2s of Figure 4 through the inner core tube and the bit with meltable metal attached, and P 0 Figure 23 is a section at plane 28-23 oi Figure 4 throush the inner core shoe, bit blades. and meltabie metal of the modification shown 'in Figure 22. v v

Referring to the drawings. my apparatus conco sists or the rotary core drill oi the swivelled inner and 4. and the gas measuring apparatus shown in co-operation with the inner barrel in- Fisure 8. The inner valve assembly at 70 the upper end'and the inner shoe: at thelower 1he outer barrel oi the core drillconsists-oi an upper sub I threaded as at ,2 for connection to the lowest member 3 of the drill string. A cou- 2B; Sleeve member as is slidably spindle 23 28 on sleeve member box 39 with packing stem. The upper end ofthe needle valve stem pling d is connected as by threads 5 to sub I or both may be made integrally as one piece. The

coupling or piece 4 is threaded as at 8 ior connection to the upper end piece I 0! the outer tube 6. The lower piece 8 is threaded as at ill for attachment of the bit H or H.

The upper end of the inner barrel assembly is tipped by the thrust ignob it which mates against the dished bearing seat M of lose that during-drilling the outer barrel to rotate without rotating the inner barrel and weight can be applied from the drill pipe to push the inner barrel down over the core.

Coupling i8 is provided with laterally proiectins lugs II by which the inner barrel is suspended from piece 1 during raising and lowering of the drill. Bar coupling is is attached at its upper end to coupling l9 and at its lower end by coupling IE to member 20' of the valve assembly. It is is free 0 important with this type of drill that the relative lengths of outer and inner barrels be properly adjusted which is done by inserting shims 2| of selected thickness in threaded recess 22.

The valve assembly includes the central tubular spindle 23 attached at its upper and to member mounted about and is rigidly attached by an accurately finished pressure tight threaded joint 25 to inner core receiving tube 26.

Spindle 28 is provided at its lower end with an enlarged boss 21 which mates against valve seat as. A rubber or composition ring 29 in a groove seats over the annular crack vof the seat to completely close same in the event close.

grit'lodges on seat 28 so that the valve can oil high pressure within core tube it.

Spindle 28 is also provided with a central ion-p eitudinal passage Bil having a lateral port 8!, a constricted portion 82. and a threaded lower end as for attachment of case as containing a maximum registering thermometer illi. Rubber. metal or composition shock absorbers til protect the thermometer. k

' At the upper end of spindle 23 is a needle valve 3'! threaded into guide bonnet as having a stuiilng so tojseal around the valve ii to mate a wrench l2 has a notch or square (Figure 8) so that the point iii can be screwed against or away from its seat to close or open passage 82. Side outlets to are threaded for attachment of tubes for gauges or flow tubes.

Sleeve member seat 28 at its lower end and a counterbore 6B beside the constriotedportion 66 of spindle 28. Lateral vent openings 61 provide for venting of liquid displaced by the incoming core into tube.

at when valve '28 is held open-by drilling weight as illustrated in Figure 1.

A key way and key as may optionally be used to prevent relative rotation between spindle 23 .and sleeve at which is desirable when a core is oriented under pressure.

A Bins Ell abuts coil compression spring Bl which urges boss 21 against seat 28 to normally close the valve. Spring Bi also abuts shim ring 52 through which are holes 58 which can be turned into alignment with outlets it when tubes are attached. The length of 'travel of spindle 28 in sleeve-2d is limited by sleeve M contacting between rings Bil and 82 as illustrated in Fig. 1.

Attached to the lower end of core receivin tube 28 is the inner core shoe It. The threaded Joint U6 is accurately made so as to seal against high pressures. The shoe BB is provided with thrust spider at is provided with the valve should be left to freely .55.

an annular chisel edge 51 to punch and cut over the core and the bore 58 is slightly tapered to enlarge upward away fromedge 51. Before taking each core a plug 59 of plaster of Paris or similar medium is cast in shoe 58 so that the inner barrel will retain the priming of glycerine or whatever other distinctive liquid is used.

Two forms of bit for the outer barrel are illustrated.

In Figures 1 and 13, bit II is illustrated where it is desired to recover a core under pressure with no special effort to prevent contamination of the formation below the bit. Bit II consists of a tubular'shell 88 from which cutting blades GI and 62 project externally and with internal uide ribs 83 for centering the inner core tube. The blades may all be of equal full gauge shape .or they may be of the pilot and reamer form illustrated in which pilot blades 8| dig a short pilot hole to be reamed byreamer blades 82 of wider diameter. In this form of bit circulation fluid pumped down the drill pipe flows downthe annular space between barrels 8 and 28 and discharges between guide-ribs 83 against the bot-' tom of the well where it is deflected upward to pass to the top of the well outside the drill string.

The more elaborate and expensive bit I 2. illustrated in Figures 4 to 7, not only recovers a core under pressure as does bit II but it performs the additional function of preventing contamination of the formation fluid by circulation fluid permeating down into formation ahead of the core drill.

Bit 12 consists of a tubular shell 84 provided with blades 65 projecting externally and guide ribs 66 projecting internally similar to bit II but with the following additions. The four equal blade form is preferable because of space limitations.

Surrounding the shell 84 and spaced from it is a shield 81 extending from blade to blade and from the top of the blades to a central aperture closely fitting around inner shoe 55. Bracer ribs 88 between shield 81 and shell 88 prevent the shield collapsing onto the shell.' The function of the shield is to prevent the stream of circulation fluid discharging against the bottom of the well and to deflect it upwardly to discharge above the bit blades. Circulation flows between shell 64 and shield 81.

A fusible alloy-88 is attached as by casting to the lower end'of bit I2. The diameter of this alloy is less than that of the blades and the lower edge is beveled as illustrated in Figures 4 and 5 so that it will easily pass down the well bore. The alloy may extend completely across its lower facing leaving no central aperture through which heavy mud may be forced into and prematurely plug the inner core receiving tube 28. Space Surface irregularities of the steel bit and rough projections or welded adhesions 18 pr vide for attachment of the alloy to the bit. The fusible alloy 89 may beselected from among many combinations of bismuth, leadgtin and cadmium melting between 150 and 350 degrees Fahrenheit. Y

After the core has been taken and brought to the surface the gas recovered with the core is measured by the'apparatus illustrated in Figure 3. Briefly the gas measm'ing apparatus consists of a tank H for measuring gas at atmospheric temperature after water displacement, a separator 81 for separating gas from liquid and stepaccommodate core shoe The gas measuring apparatus includes a closed inverted conical measuring tank 1| filled with water to be displaced by the gas sample. Depth of undisplaced water, or volume of gas sample is measured by a glass gauge and graduated scale 12. Pressure of the gas sample is brought to atmospheric by use of leveling bottle 13 attached to rubber hose 14. Valves 15, 18 and 11 control gauge and bottle. Funnel 18 and valve 18 provides-for preliminary filling of the tank with water. Funnel 88 and valve 8i and pipe outlet 82 provide for draining the tank 1I. Valve 83 provides for release of air when filling tank H with water and also for attachment of a sample bottle if it be desired to retain a. samfunnel 941 and valve ple of the measured gas for analysis. Union 88 is convenient for assembly. Pipe T 85 connects pipes to peak of cone tank 1I.

Valve 88 separates the low pressure measuring cone tank 1| from the high pressure separator 81.

The high pressure separator or trap consists of a pipe chamber 81 to which is attached a conventional boiler gauge glass 88 through which the level of liquid in the separator trap can be observed. At the top of chamber 81 is a pressure gauge 89 controlled by valve 98. At the bottom of chamber 81 is a valve 9| for draining liquid from the chamber into a sample can 92.

Tank 93 provides an auxiliary storage supply of glycerine or other liquid and is filled through 85. Valve controls flow of liquid from tank 93 to chamber 81. Hand pump 91 provides air pressure which can be applied through valves 98 and 99m tank 93 or chamber 81. Glycerine is very viscous and slug- 1 until lugs I rest on tached to the outer is useful in speeding its fiow.

A bracket I88 above cone tank 1I provides a support for core receiving tube 26 during measuring operations. Valve controlled pressure gauge IM and valve I82 are screwed onto outlets of the inner barrel. Union I88 connects valves I82 leads to the middle of chamber 81.

The entire measuring apparatus may be mounted on a portable floor I88 with tank 98 and chamber 81 supported on legs I81 and I88. Or the small parts may be bracketed to a frame attached to the side of cone tank II.

The field assembly of the core drill is. as follows.

The plaster of Paris plug 58 is cast in shoe 55 which in turn is attached to inner barrel 28.

The core tube or inner barrel 28 is supported in an inclined position with shoe 55 lowest and the upper valve assembly removed. The core tube 28 is then primed or other distinctive liquid as is desired. Thermometer 35 is shaken down and placed in its case 38. With needle valve 88 securely attached to core tube 28 and the needle valve closed tight. The thrust bearing is then attached making the inner barrel assembly complete.

The proper bit II or I2 is selected and atbarrel 8 which is then set in the top'of the well bore. The inner barrel assembly is then lowered into the outer barrel top member 1, couplings I and l are attached, and the drill pipe connected. he drill is then lowered into the well.

ping down pressure, and auxiliaries 93 to 91 for and I84 controlling tube I which filled with glycerine or such I open the valveassembly is The circulation pumps are started and-the circulation fluid brought to proper condition before the drill is lowered completely to the well bottom. When bit l2 with fusible alloy is used the drill must be lowered slowly because there is no downward jet to stir f out heavy 'mud settlings.

During drilling the circulation fluid is pumped down through the drill pipe, passing between the fins I09 of spider l5, between lugs ll around coupling l 6, and down the annular space between outer and inner barrels to the bit. Usually the fluid used for circulation consists of water weighted with mud and frequently chemicals in suspension and solution. Occasionally an oil -base mud free from water is used. After passing the bit the circulation fluid ascends between the drill pushed over the core standing between bladeswith edge 51 shaving the core to smaller diameter. reduced core H0 with plaster .plug 59 resting on top. of the core. The glycerine, or other fluid, with which the core tube was primed is displaced Core tube 26 then passes down over the by incoming core H0 and vented through valve 28 and side openings ll into the circulation stream and lost.

-Where drilling is done with bit ll illustrated in Figure 1 it will be noted that the circulation fluid discharges against the bottom of the well. This combined with the scraping by the bit and high pressure by the circulation column prevents formation of a mud cake and permits circulation fluid to flow into the formation ahead of the drill. A core sample thus obtained is contaminated by drilling fluid. Consequently, while a pressure core with this bit determines the gasoil ratio of the formation it does not determine the total original fluid in the formation.

When a more complete determination is desired the more expensive and elaborate bit H.

sure. It has been found wedges in the tapered bore illustrated on Figures 4 to 7 may be used. When bit I2 is rotated on bottom the blunt end of the alloy 69 rubs on the bottom of the well and the heat of friction melts the fusible alloy to form a molten pool 69a on the bottom of the well extending as high as the top of shield 61 as illustrated in Figure 7; Circulation fluid instead of jetting against the bottom of the .well strikes shield 61 and'unable to escape between shield 61 and shoe 55 because of the close fit, which may be improved by a packing ring H4, is deflected up through the passage between shield 61 and screwing members l9 from be known or predictable. In California most well temperatures range between 100 and 250 degrees Fahrenheit. An alloy should be selected'which melts a few degrees above the formation temperature. Alloys melting. within ten degrees of any desired temperature. can be selected from a large number of well known combinations of hismuth, lead, tin and cadmium which melt between 150 and'350 degrees Fahrenheit. The proper alby will remain molten'by friction heat of drilling. But unlike water it freezes 'or congeals before it can be forced an appreciable depth into the formation. Therefore it does not contaminate the formation fluid and is drilled up to remelt in the molten pool. The alloys used have a specific gravity of about 10 compared to 1 for water and 2.7 for formation cuttings. Cuttings therefore float quickly to the top of the molten pool to be picked up and carried out of the well by the circulation stream.

By raising the bit a few inches off bottom just before coring is completed a layer of molten metal flows completely over the well bottom. By quickl resuming coring before it solidifies and coring a few inches more the core recovered has a break of metal across pletely seal the bottom plug should the last formation chance to be very permeable.

When sufllcient depth has been drilled the drill string is raised. Spring 5lexpands I is lifted from it to close valve 28 and seal the upper end of the core'tube; against escape of presof inner shoe breaks the core oil flush with its lower edge 51 and that the lower piece of core 58 so tightly that it resists very high pressure and makes a simple and efficient pressure seal for the lower end of core tube 26.

The drill withits core is then pulled from the well and in ascending the external hydrostatic pressure on the core tube 26 and the temperature of the tube decrease. 'The decreasing temperature causes a greater contraction in thevolu'me of the liquid within the core tube than of the metal or core 50 that the actual pressure within the barrel decreases.

Whenthe drill reaches the top of the well the inner barrel assembly is removed from the outer barrel and th thrust bearing removed by un- 20. The'inner core tube 26 is then placed in an inclined position in bracket l-Ill over the measuring apparatus as ilshell 54 so that circulation fluid does not contact the formation until above the bit blades. It may be pointed out here that the passage between shell M and shield 61 may be a space between fabricated pieces, a hole cored in a castin a.

hole drilled thru metal, or other suitable pas- Q sage. Above the bit blades the mud cake is not scraped off and quickly plasters th well wall so that only an insignificant quantity of circulation fluid enters the formation andwhat little that does so remains above the bit; 7

Not only is bit l2 more expensive but selection of the proper alloy requires engineering knowled e of the well and alloys. The temperature of the formation at depthof coring should flush air pockets out of ,tl'e

- lustrated in Figure 3.

with valve 86 closed and valves 19 and 83 open the gas measuring cone TI is filled with water from funnel 18 until it overflows through valve 83. Gauge glass 12 and leveling bottle I3 are also filled with water. All valves on com tank H are then-closed. Air pressure is applied by pump 51 to glycerine All valves are then closed and gauge 89 replaced;

This preparation of the gas measurin apparatus can be done while the core drill is being pulled T from the well with some advantage in time sav ing- with -the innercore tube 26 supported in bracket lllll valve I82 'is attached to threaded opening 44 of the valve assembly and. to union Ill as illustrated. Valve. is again opened to last connection and it near bottom to comwhen weight I by usage that the form tank 93, gauge 89 is re- "moved, and valves 50,- 96 and I04 are opened.

; T y asvaaesY the valve controlled pressure gauge llll attached All valves are closed and the apparatus is'ready to proceed with measurements as follows.

First, needle valve 31 is opened wide by turning wrench 42. The valve of pressure gauge Illl is opened and the initial pressure recordedas well as the temperature at putty covered thermometerlll.

Valves 9!), 9i and lot are next opened wide. Valve I02 is then opened and manipulated cautiously while observing the pressure on gauge 89. and the liquid level H3 in glass 88. Valve 9! is opened and closed to keep liquid level H3 visible in the g1ass 88 and the drainings are saved in sample can 92. Valve )2 i closed before pressure on gauge 89 reaches 100 pounds per square inch The moderate pressure gas sample in chamber bl is then stepped down to atmospheric pressure into cone tank H by cautiously manipulating valves 86 and 8!. With valves i5, 18 and ll open the pressure in measuring cone H is brought .to atmospheric by using leveling bottle E3. The volume of gas above and displacing water in the cone The total volume of gas in measuring cone ll is then read on graduated scale 12 and recorded and the temperature shown by putty covered thermometer H2 also recorded. To this is added the small volume of ,gas in chamber d! which should have'been calibrated. The volume of gas can be designated as sample G" and all or part of it transferred through valve 83 to a sample bottle for subsequent analysis.

All valves are closed except 9| and be .which are opened and air pressure from pump 9'! is ap-.

pressure. Quantities can be determined by anal-" ysis. In addition tests can be made to determine what additional production might be obtained by water flushing drive.

From'the foregoing it will bereadily under stood that I have disclosed a new anduseful processand apparatus for determining the fluid content of formation and avoiding their contamination by circulation fluid.

Iclaim asmyinvention: Y Y l. A process for preventing contamination by circulation 'fluid of core sam les taken from bore holes which includes placing on the bottom of the well afusible alloy having a melting point .slightly higher than .*the temperature of the formation cored, melting said alloy by friction generated heat to form a barrier of molten metallic alloy on the bottom of the well between the circulation fluid and'the formation during coring,

maintaining a barrier betweenthe core and the circulation fluid by receiving the core in a tube filled with glyoerine, and closing the core receiving tube against escape of its contentswhile it i being lowered and raised in the bore hole.

- 2. An apparatus for recovering cores from bore holes under pressure consisting of an outer rotatable barrel, a rotary bit on the lower endthereof, an inner core receiving tube swiveled within said outer barrel and spaced therefrom, a thrust bearing between said outer barrel and inner tube, an annular bit on the lower end. of the inner tube provided with a tapered upwardly expanding bore and an annular cutting edge at the lower end of its bore, a poppet type valve at the upper end of said tube, a compression spring urging said valve to close and compressible by weight from the drill string to open said valve and vent the tube into the spacebetween' inner'tube and outer plied to force all liquid remaining in chamber 87 into can 92 to be saved for analysis as sample L." With the pressure in core tube 26 now atmospheric, valves lflz and Hit are removed and the main valve assembly cautiously-detached from core tube 26. Temperature of thermometer 35 is recorded as the maximum on the core tube. lAll,

liquid surrounding the core is poured into a, can

and saved for analysis as sample M.

The core is then removed from core tube 2eby; usual means but preferably without use of water and 'saved for analysis as sample 03' m From the coring operation we now have as am pies: I

Sample G is ameas'ured quantity of aur s mined by analysis. a e

Sample "L" is glycerine from chamber 81 with Q the addition of'a small quantity of liquid from the core. I a

Sample M is liquid and chipsexuded from the core and mixed with the glycerine or other -yielded by the core. -Its character can be deterbarreLand a manually operable valve controlling a passage through the stem of the poppet valve to communicate the interior of the core receiving tube with side connection outlets.

3. An apparatus for recovering core from bore holes under pressure consisting of an outer rotatable barrel, a rotary bit on the lower end thereof, an inner core receiving tube swiveled within said outer barrel and spaced therefrom, a thrust bearing between said outer barrel and inner tube,

an annular bit'on the lower end of the inner tube provided with a tapered upwardly expanding bore and an annular cutting edge at the lower end of its bore. a p ppet type valve at the upper end or said tube; a compression springurg'ing said ponmt valve to close and compressible by weight from the drill string to open said valve and vent the inner tube into theannular, ace between inner tube and outer barrel, a manually operable valve controlling a passage through the stem of the. poppet valve to communicate the interior of the innertube with side connection outlets, said rotary bit being provided with a shield close- 1y surrounding the annular bit and with a'passage to deflect the circulation stream upwardly to the top of the rotary bit, and a supply of fusible metallic alloy'attached to said bit below said shield.

ducing the formation sampledto atmospheric pressure.

'- Sample C is the solid core sample containing in its pores such petroleum and water as remains when the formation is reduced to atmospheric 4. a bit to prevent contamination of well cores by circulation fluid consisting of. a tubular body, cutting blades projecting longitudinally at One end-to tips and laterally from said body, a shield between the body and the tips of the blades.

'- provided with a'central aperture of smaller inte'mal diameter internal diameter ot'the body. andasupply or-tusible metallic central aperture of the shield to external discharses adjacent the threaded end of the body. 6-. A valve for a pressure core drill consisting i a tubular spindle having an enlarged boss ad- Jacent one end and a passage longitudinally throuah thespindle. a. tubular sleeve mounted about said spindle andhavina aseat to engage passage adjacent the end farthest iron: the boss, a coupling attached to the needle valve end of the spindle. and a compression spring surroundsage throueh saidspindle heine provided with said boss, a needle valve.eontroiiin: the spindle in: the spindle between said coupling and said sleeve urging the boss against its seat, the pasthreaded lateral outlets and with a seat ior the needle valvebetween said outlets and said boss, and said tubular sleeve being provided with a eounternorehavinz lateral vent ports communieating with the passase. between the boss and its seat when opened and with means for attachment to the core receiving ltube oi a core drill. 6. .An apparatus for recovering well cores under pressure which includes the combination-oi a core receiving tube having an upper and a lower end, a valve controlling the upper end of the tube to resistinternal pressure. and an internally upwardly expanding tapered cutting shoe at the lower end oi. said tube in which a core-can wedge to resist internal pressure.

I GEORGE A. MAcREapY.

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