US2393092A - Apparatus for gas analysis of drilling mud - Google Patents

Description

Jan. 15, 1946. R. L. DOAN APPARATUS FOR GAS ANALYSIS OF DRILLING MUD Filed March 18, 1941 INVENTOR R.L.DOAN

5 a ATTORZQSEYG a Patented Jan. 15, 1946 APPARATUS FOR GAs ANALYSIS or name MUD Richard L. Dean, Bartlesvllie, kla., assignor to Phillips Petroleum Company, a corporation of Delaware Application March 18, 1941, Serial .No. 384,014

3 Claims. (Cl. 23-255) This invention relates to the analysis of rotary drilling mud for entrained combustible gases.

The analysis of drilling mud for entrained hydrocarbons serves two important functions. In rotary drilling, there is a circulating column of fluid which is pumped down the inside of the drill "pipe, through the bit at the bottom of the hole and up again to the surface in the annular space between the drill stem and the walls of the bore hole. The drilling fluid serves several functions, among which the two most important are carrying to the surface the cuttings removed by the bit and providing a fluid valve to hold in control any rock fluid encountered, whether oil, gas or water, in porous strata traversed by the bit. Ordinarily, the hydrostatic head of mud in the hole exceeds the rock pressure of porous reservoirs opened up by the bit and in this case the only reservoir fluids that get into the mud stream are those contained in the interstices of the material removed by the bit plus an additional amount forced out of the porous medium surrounding the I bore hole by infiltration of drilling fluid. It is thus possible to go through a commercially important petroleum bearing zone without having any considerable amount of gas or oil enter the mud stream and unless suitably delicate and quantitatlve means are available for detecting the presence of gas in the mud, the fact that the bit has entered a petroleum bearing formation may go unobserved at the surface. It is one of the functions ofhydrocarbon analysis of drilling mud to detect and locate such zones. On the other side of the picture, there is a possibility that the gas may enter the mud so fast or over such a long period of time that the normal hydrostatic head of mud in the hole is materially reduced and in the extreme case, the well will either kick or blow out. A second function of the analysis of drilling mud for entrained hydrocarbons is to detect rapid and excessive increases in the gas content of the mud suiiiciently in advance of extreme conditions to permit the application of preventative measures.

An object of this invention is to provide an improved apparatus for extracting dissolved and absorbed hydrocarbons from drilling mud.

A further object of this invention is to provide an apparatus for analysis of drilling mud for combustible hydrocarbons.

A still further object of this'invention is to provide suitable apparatus for the rapid analysis of drilling mud.

For complete extraction of the dissolved and absorbed hydrocarbons from the drilling mud, it

is desirable to heat samples to a temperature in excess of 125 C. and to subject the samples to a vacuum either during or subsequent to the heating. Such methods are disclosed in the patent applications of Richard L. Doan, Serial No. 341,- 031, flied June 17, 1940, and of Francis W. Crawford, Serial No. 341,047, filed June 17, 1940. The time required for heating the samples is such that about four samples can be run per hour. If the drilling rate exceeds 30 or 40 feet per hour the depth interval between samples becomes too large for good coverage. It is not unusual in the Gulf Coast for drilling speeds to go as high as or more feet per hour. It is obvious that under such conditions a rapid analytical procedure is required if the samples are to be spaced closely enough in depth to be of real value. The most time consuming operation in the analytical procedure is heating the sample to effect release of the hydrocarbon gases.

It is known that where the original gas content of the mud is high, much of the gas escapes by aeration at atmospheric pressure when the mud arrives at the surface. This is especially true of the highly volatile gases such as methane. It is also known that mechanical agitation of the mud assists in the release of absorbed and entrained gases. Even when the percentage of the gas entrained in the mud is relatively small. some is released into the air at normal temperatures. The quantity of gas given off per unit volume of mud under given conditions is proportional to the total amount in the mud and is significant for exploration purposes.

Previous attempts by others to measure the quantity of gas given up by the drilling mud as it leaves the bore holes have sufiered from two disadvantages. One disadvantage is that the sampling conditions have been neither sufllciently constant nor sufliciently thorough to insure that the gas which passes into the analytical unit has a fixed relation to the gas content of the mud.

The other is that the analytical method employs body of gas to be analyzed is completely isolated priorto ignition oi the filament. The technique is described in my patent application Serial No. 298.708.

The extraction and sampling procedure herein disclosed comprises passing a portion of the mud from the discharge line in a continuous stream through an extraction unit consisting of a vertical standpipe from 20 to 30 feet high in which a vacuum is continuously maintained 'at a fixed value by a pumping arrangement which permits sampling oi the gas breaking out of the mud. Both sampling and testing are accomplished automatically on a definite time schedule approximating three minutes per sample and the results recorded on a clock driven chart. The apparatus arrangement is shown schematically in the accompanying sketch to which reference is now made for the details of operation.

The figure is a diagrammatic elevational view of apparatus suitable for carrying out thepresent invention. Mud from the mud discharge line leading from the bore hole is continuously sampled by the apparatus shown'in the accompanying drawing. The drilling mud sample from the discharge line fiows through the pipe I to the pump I which delivers a continuous stream or mud at a fixed volume rate through the pipe 8 to the top of the extraction chamber 8. The extraction chamber 9 is provided with agitators ll, shown in the drawing as a series or bailles, to break up the mud stream and release occluded gases. The extraction chamber 9 is set at a height of 15 to 25 or more feet above the level or the mud pits to allow separation of the gaseous hydrocarbons irom the mud stream under a vacuum. 'A section of pipe It connects the ex-- traction chamber with the slush pit. Degassed drilling mud irom the extraction chamber flows through the pipe H to the slush pit by the force of gravity.

The gas extracted from the drilling mud in the extraction chamber a fiows through the pipe l2 to a reservoir II. A vacuum pump ll, operating continuously, maintains an absolute pressure or to pounds per square inch in the reservoir i3 and the extraction chamber I. The pressure is regulated to the desired value as indicated on the gauge ll attached to the reservoir II by adjustment of the valve It interposed between the vacuum pump and the reservoir. The gauge "is so constructed and arranged as to protect the vacuum pump from damage by in-.

terrupting the power supply to the pump it the pressure in the reservoir and extraction chamber drops below 5 pounds per square inch absolute. Well known gauges of this type include a pressure operated switch which can be connected to the motor circuit for opening the circuit at a predetermined low pressure value. This obviates the possibility of mud being drawn over from the extraction chamber into the pumping system. The vacuum maintained on the extraction unit supports a column of drilling mud several feet in height which acts as a seal to prevent the entrance oi atmospheric air into the system.

To insure a suppl of oxygen sufllcient to burn the combustibles in the gas extracted from the drilling mud, oxygen from a source of supply I! is admitted to the reservoir through the valve II. The valve It may be adjusted by any of several well known means to give the desired,

now or oxygen.

The mixture or gas and oxygen in the reservoir analyzed to determine the quantity of combustible gases extracted from the drilling mud. A pipe is connects the reservoir l3 to the maniiold so through the solenoid operated valve 2|. The manifold 20 communicates with a sample tank 22. The sample tank is evacuated by means of the vacuum pump 23 which is connected to the manifold 20 through the solenoid operated valve 24. When the sample tank is evacuated to the desired degree, as indicated by the gauge 2!, the valve 24 is closed and a sample 'of the gases irom the reservoir I3 is admitted to the sample tank by opening the valve 2|. When the desired sample has been drawn into the sample tank 22, the valve 2| is closed and the pressure in the sample tankis brought up to atmospheric pressure or higher by admission or water to the tank through the solenoid operated valve 28. The solenoid operated valve 21 is opened and the gas displaced from the sample tank by the water then passes through the U-tube drier a into the combustion unit 2! of an electrical analyzer. The float ll in the sample tank operates to close the valve 2| upon the water reaching a predetermined level. This prevents overfiowing oi the sample tank and flooding of the apparatus with water.

The combustion unit contains two essentially identical platinum filaments in separate enclosed chambers, one oi? which is sealed in air at atmospheric pressure while the other canbe flushed and filled with the sample mixture or gas and oxygen admitted to the analyzer through the valve 21 and the drier 2!. when the combustionunit of the analyzer is filled with the sample. the valve 21 is closed and the two filaments are heated to incandescence by passing an electric current through them. The diflerential changes in resistance due to burning of ccmbustibles on the filament exposed to the gaseous mixture are measured by use of a bridge circuit. This apparatus has been described in the application by Richard L. Doan, Serial No. 298,708. filed October 9, 1939. The change in resistance or the filament is a measure or the hydrocarbon content of the gas-air mixture sin-rounding the filament. This is recorded by the recording meter ll attached to the analyzer. The record made by the recording meter II is interpreted by reference to the zero meter reading or the reading of the meter when both chambers are filled with hydrocarbon-free air. The zero reading varies with use or the instrument and is recorded from time to time by admitting hydrocarbon-free air from the source 32 into the analyzer through the solenoid operated valve 33 and the valve 21.

Water is expelled from the sample tank 22 through the valve ll. To facilitate emptying the sample tank, compressed air irom the tank 32 is admitted to the sample tanklby opening of the valve 38. After the sample tank isemptied, thevalves 32 and 34 are closed and the sample tank may be again evacuated by opening 01' the valve 24 leading to the vacuum pump 23.

The various operations performed in sampling and testing the gases traversing the reservoir It is governed by the commutator l6 driven by the motor 36. The commutator controls the sequence in which the various solenoid operated valves 21, 2|, 2, 21, I8, and It are opened and closed during the cycle of sampling and testing. The commutator also acts as a timing device and is driven minute during which time a complete cycle of it is sampled periodically and the sample sampling andtestlng operationsiscarried out. It

is obvious that the length of time required for sampling and analyzing gases may vary according to the characteristics of the various pieces oi" mutator acts as a switching device to energize the solenoid operating valves with electrical energy at the proper time and for-the period determined by the angular contact length of the various commutator elements 31. The brushes 33 make contact with the various commutator elements 31 and energize the corresponding valve solenoids.

Since the meter readings are referred to a zero reading, obtained by passing hydrocarbon-free air to the analyzer, it is desirable that the zero reading be recorded by the recording meter 3i from time to time for comparison. This is accomplished by means of a sequence switch 33. The position of the moving contact arm 43 o the stationary segments ll determines whether the valve 2! or the valve 33 is opened when the appropriate commutator element is contacted. The contact arm in of the sequence-switch is advanced one segment for each revolution of the commutator. By connecting one or the segments to the valve 33 and the remainder to the valve 2| every flith sample tested is hydrocarbon-free air instead of gas from the reservoir l3. Other combinations are obviously possible.

The operation of the apparatus will be more readily understood by considering a complete cycle. Starting with the sample tank 22 empty at atmospheric pressure with all solenoid operated valves closed and with the commutator and brushes in the position shown in the drawing, a complete cycle of operations is as follows. The first contact to be closed is that which operates and opens valve 24 leading to the vacuum pump. When the brush 38 controlling the solenoid of the valve 24 contacts the corresponding commutator element 31 the solenoid of the valve is energized, opening the valve. The valve remains open as long as the brush is in contact with the commutator element and is closed again when the contact is broken. The valve 24 remains open v a predetermined point, thus closing 08 the valve 23 even though the contact is still closed on the commutator. when the commutator elements controlling the'valves 23 and 21 pass the brushes these valves close and the next commutator element switches on the filaments in the analyzer unit 23. The unbalancing of the bridge circuit in the analyzer'is recorded by the recording meter 3| and the amount by which the bridge is unbalanced, suitably measured by a milliammeter. indicates the amount of combustibles in the gaseous sample. Only a short period of time is required for the combustion in the analyzer. The final commutator segment opens valves 33 and 34 allowing the compressed air from the tank 32 to enter the sample tank and displace the water through the drain valve 33. Upon further rotation of the commutator to its ori inal position, the valves 33 and 34 are closed completing the cycle of sampling andanalyzing gases from the reservoir 12.

I claim:

1. In a gas analysis system for analyzing gaseous material entrained in well-drilling fluids, the

almost half of the entire cycle since the time required for evacuation is longer than for any other operation.

During this time the sample tank 22 and the manifold 20 are evacuated. When the revolving commutator 35 breaks the contact between the commutator element and the brush, the valve 24 closes and another commutator element contacts the brush controlling the operation of the valve 2 I. Upon opening of the valve 2|, gases from the reservoir [3 flow through the manifold 20 into the sample tank 22. The time interval required for the sampling period is short. Following the sampling, the valve 2| closes and'the valve 26 opens to admit water, under a pressure head of 15-20 pounds per square inch gauge, to the sample chamber. The water displaces the gases in the sample tank and raises the pressure to atmospheric or higher. At a time interval sumciently later to insure that the pressure in the tank is atmospheric or higher, the solenoid of the valve 21 is energized. The gas displaced by the water in the sample tank flows through the valve 21 and drier 23 into the combustion unit of the analyzer 29 flushing the combustion unit and leaving it filled with the gas sample. To insure that the water will not overflow the sample tank 22, the float 30 interrupts the current to the solenoid of valve 28 when the water level reaches a combination comprising an extraction chamber, containing baflles arranged for the continuous flow of said fluid therethrough, an inlet thereto for thefluid from the well, an outlet conduit connected to the upper portion of the extraction chamber for drawing off disentrained gases, a gas accumulator chamber connected to said extraction chamber through said conduit and to a vacuum pump, a gas sample chamber connected to said accumulator chamber, a gas analyzer connected to said gas sample chamber, auto matically operating valves included in the connections between the gas sample chamber and the gas accumulator chamber and between the analyzer and the gas sample'chamber, means for evacuating the. gas sample chamber, alternately operating means for subjecting the gas sample chamber to vacuum and for displacing and forcing the gases therein into the analyzer, and timing mechanism so constructed and connected as to automatically alternately control the opening and closing of said valves, to alternately establish passage from the accumulator chamber to the sample chamber and from the sample chamber to the analyzer.

2. In a gas analysis system for analyzing gaseous material entrained in well-drilling fluids, the combination comprising an extraction chamber, containing .baiiles arranged for the continuous flow of said fluid therethrough, an inlet thereto for the fluid from the well, an outlet conduit connected to the upper portion of the extraction chamber for drawing ofi disentrained gases, 9. gas accumulator chamber connected to said extraction chamber through said conduit and to a vacuum pump, a gas sample chamber connected to said accumulator chamber, a gas analyzer connected to said gas sample chamber, magnet valves included in the connections between the gas sample chamber and the gas accumulator chamber, and between the analyzer and the gas sample chamber, means for evacuating the gas sample chamber, alternately operating means for subjecting the gas sample chamber to vacuum and for displacing and forcing the gases therein into the analyzer, and commutator means in electrical circuit with said magnet valves and arranged to selectively and alternately operate the valves for predetermined intervals of time.

3. In a gas analysis system for analyzing gaseous material entrained in well-drilling fluids, the combination comprising anextraction chamber. containing baiiies arranged for the continuous flow or said fluid therethrough, an inlet thereto for the ii-uid from the well, an outlet conduit connected to the upper portion 01' the extraction chamber for drawing of! disentrained gases, a as accumulator chamber connected to said extraction chamber through said conduit and to a vacuum pump, a source of oxygen and a valved connection from said source to said gas accumulator chamber, a gas sample chamber connected to said accumulator chamber, a gas analyser connected to said gas sample chamber, automatically 10 alternately control the opening and closing of said valves to alternately establish passage from the accumulator chamber to the sample chamber and from the sample chamber to the analyzer.

RICHARD L. DOAN.

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