US2280086A

US2280086A - Gas detection

Info

Publication number: US2280086A
Application number: US287299A
Authority: US
Inventors: John T Hayward
Original assignee: Individual
Current assignee: Individual
Priority date: 1938-02-23
Filing date: 1939-07-29
Publication date: 1942-04-21
Anticipated expiration: 1959-04-21

Description

April 21, 1942- J. T. HAYWARD GAS DETECTION v 2 Sheets-Sheet l 75Kcuum Originl Filed Feb. 25, 4958 J. 7. HAYWARD u. I II lll|||l||||||||||||llllcllllllv 7?) Vacuum Pump INVENTOE ll l ll III ATTORNEY April 21, 1942- J. T. HAYwARb 2,280,086

GAS DETECTION 7 Original Filed Feb. 25, 1938 2 Sheets-Sheet 2 29 FIG. 4-

FIG. 3 INYENTOR J. Z'HAYWARO ATTORNEY "Patented Apr. 21, l142 U T S A ES PATENT OFFICE GAS DETECTION 7 John T. Hayward, Tulsa, Okla.

, Originalapplication February 23,1938, Serial No.

191,895. Divided and this application 1939, Serial No. 287,299 13 Claims. (01. 175-183) tional practice, the specific gravity of the circu-" lating fluid is controlled, ordinarily, so that the head of fluid in the wellisgreater than the pres sure of oil or gas which it is expected will be encountered at points-in mewen. Thisprocedure July 29,

which is contained in the relatively small cylinder of formation cut out by the drill traversing the formation, will escape into the fluid, and

recognition of the gas formation must rely wholly upon the prompt detection of this small quantity of gas in the fluid. The following example will serve to illustrate the relatively minute quantities of gas which will be present in the mud fluid under a normal setof drilling condiis followed in order to prevent the pressure of a gas formation, whichmay be encountered, from exceeding that of the fluid head pressure and causing blow-outs, whereby the fluid is blown from the well with disastrous; consequences, which, in some cases, may result in complete destruction of the well and endanger lives and property in the vicinity of the well. I

While thisprocedure is advantageous for pro tectlng the'well during drilling, it is disadvantageous in that the excess pressure of the hydraulic fluid prevents-the entranceinto the well of gas from an encountered gas-containing formation, with the result that such formation may entirely escape detection of the drill operators and become mudded-off or sealed by the circulating mud fluid, and erroneously cause the well to become abandoned as a non-producer. Also, as oil is very often found in 'immediate-or adjacent association with gas, failure to detect the presence of gas substantially immediately after penetration by thedrillinto the gas formation, may cause the driller to continue entirely through the oil-containing formation and also mud-off that formation. This is particularly true where as is often ,the case, the oilcontaining formation is quite'thin, that, is, only a few feet thick. The danger is heightened greatly by the fact that oil and gas formations are usually sandy formations, which are relatively soft and willv be very quickly traversed by the drill unless comparatively, exact. knowledge of the location of such formation is known beforehand and the approach of the drillthereto' very carefully controlled.

Since as noted, the pressure of the fluid column in the well is ordinarily controlled to exceed that of any gas formation which may be encountered, only that relatively small quantity of gas,

' tions: A well is being drilled at a depth of 6,000

feet wherea gas-containing formation is encountered. The "formation pressure is approximately 3,000 pounds per square inch. The mud fluid in the well has a specific gravity of 1.38 producing a fluid column pressure at the bottom of the well of approximately 3,600 pounds per square "inch or approximately 600 pounds per square inch greater than that of the gas formation. Obviously under these conditions, substantially no gas will escape into the well from the gas formation and the only gas entering the circulating fluid will be that relatively small amount-of 'gas present in the cuttings comprising the cylinder of the formation being cut out by the drill bit. Assume the diameter of the bore of the well is nine inches, a conventional size. The volume of each lineal foot of the cylinder of gas formation drilled will be approximately 735 cubic inches. cent, that is, the pore'space in the formation in which the gas is held constitutes 25 per cent of the volume of the formation, then itis evident that the total volumeof gas in one lineal foot of the cylinder of formation will be approximately 184 cubic inches at a pressure of 3,000 pounds per square inch. When the fluid containing this quantity of gas reaches the surface of the ground, the pressure will be reduced to substantially atmospheric pressure, and disregarding the factor of temperature, the gas will expand roughly 200 volumes, or to a volume of 36,800 cubic inches. However, as the mud fluid is ordinarily circulated through the well at the rate of approximately 100 barrels per lineal foot drilled, the

36,800 cubic inches of gas will be distributed through 100 barrels of mud fluid, and upon calculation, it will be found that the mud fluid, when it reaches the top of the well, will contain only about 3.8% by volume of gas. Such a small quantity of gas is practically impossible to detect by ordinary inspection methods, due to the fact that the mud fluids ordinarily used in drilling are generally very viscous and have gellike properties which cause the minute globules of gas to be strongly occluded in the fluid to an If we assume a porosity of 25 per extent, in many cases, that substantially none of the gas will escape from the fluid, even when the fluid is allowed to stand for hours in the open air. As a result of such conditions, the

drill may completely traverse the gas formationgas formation by the determine by difference, the increase in gas content. The latter procedure may be particularly valuable in connection with well drilling where suspended or occluded within liquids, the liquids will expand or contract under changes in pressure applied thereto, in substantially direct relation to the amount of gas contained within the liquid. Thus, if a liquid containing 2 per cent of gas occupies a volume of 100 cubic centimeters at one atmosphere pressure, at onehalf atmosphere, the liquid will occupy a volume of 102 cubic centimeters, that is, the gas occluded within the liquid will expand to twice its volume, namely 4 cubic centimeters, and in expanding, will displace an equal amount of liquid, thereby increasing the apparent volume of the liquid by the amount of the increase in volume of the gas contained therein. By measuring the volume of the gas-containing liquid at normal atmospheric pressure and again at onehalf atmosphere pressure, then starting with an initial volume of 100 cubic centimeters of the liquid, the increase in volume read in cubic centimeters will give directly the approximate percentage of gas in the sample.

The change in volume of a gas-containing liquid under changes in pressure, may be measured directly, as above described, or may be measured indirectly by electrical methods by measuring the electrical speciflc resistivity of a sample of the gas-containing liquid at different pressures. It has been found that the electrical resistivity of an incompressible conductor liquid, such as well mud, containing a compressible nonconducting gas, such as petroleum gases, is approximately proportional to the volume of such gas in the liquid. By reducing the pressure on a column of gas-containing liquid of unit length and cross-sectional area, the gas will expand in accordance with the decrease in pressure and displace a proportional amount of liquid from the column, thereby proportionally reducing the conducting cross-sectional area of the liquid and increasing the electrical resistance approximately in direct proportion to the decrease in this crosssectional area. By utilization of suitable electrical apparatus, as will be more fully described hereinafter, the electrical resistance of the fluid under different pressures may be measured, and the measurements so obtained utilized to determine the percentage of gas in the fluid.

The method of this invention may be utilized for merely detecting the presence of gas liquids, without measuring the volume of gas, or it may be used for measuring quantitatively the volume of gas contained within the fluid. Where the original fluid may contain gas, the methodof this invention maybe utilized to measure the' gas content of the original fluid and the gas content after contact with gaseous fluids and to due to the viscous nature of the well fluid, gas, which may have been previously introduced into the fluid, remains occluded in the fluid, even after the same is removed from the well, and is settled, agitated or treated. Under these conditions, the detection or measurement of the gas content of the fluid leaving the well must be referred to or compared with that of the fluid entering the well in order to determine whether 'or not the gas content has increased during pas,- sage through the well. Such a comparison method is referred to in my co-pending application Serial Number 187,619, filed January 29, 1938, in connection with the detection and logging of gas formations and to the extent of such common subject "matter, this application is a continuation-in-part of my co-pending application.

It is, therefore, a principal object of this invention to provide a method for detecting the presence of gas occluded in liquids.

Another object is to provide a method for. measuring the quantity of gas occluded in hydraulic liquids.

Still another object is to provide a method for measuring the quantity of gas contained in a hydraulic fluid, by measuring the volumetric changes in the fluid at different pressures.

A further object is to provide a method for measuring the quantity of gas contained in a hydraulic fluid by measuring the electrical specific resistivity of the fluid under different pressures. Another and more specific object is to provide a method for detecting and measuring the gas contained in a mud fluid circulatedin a well during the drilling thereof.

Additional and important objects and advantages .of this invention will become apparent from the following detailed description, when read in conjunction with the accompanying drawings, which illustrate forms of apparatus which may be utilized for successfully practicing the new invention.

In the drawings:

Fig. 1 illustrates a form of measuring bottle for indicating the presence of, or for forming directly the volume of gas in a gas-containing fluid, or both.

Fig. 2 illustrates a form of electrical apparatus for indicating the presence of, or for measuring indirectly the volume of gas in gascontaining. fluids.

Fig. 3 illustrates an assembly of apparatus for continuously indicating and measuring gas in well drilling muds.

Fig. 4 is a detail 'of one of the resistance gn ieasirement tubes utilized in the apparatus of l Fig. 1 illustrates a simple form of measuring apparatus for measuring the change in volume of a gas-containing liquid under different pressures. The apparatus comprises a glass bottle I adapted to contain somewhat more than cubic centimeters of the fluid to be tested. Bottles of other volumetric capacities may be used, the 100 c. 0. size being preferred for simplifying calculations. The bottle is marked with a ring mark 2 to denote the level to which the bottle is to be filled. Bottle I is provided with a wide mouth neck 3 into which is inserted a stopper 4 in which is mounted an upwardly exground to form an air-tight seal.

tending hollow measuring tube provided with a downward extension 6, which extends into bottle I to a point near the bottom thereof. The adjacent surfaces of neck 3 andstopper 4 are Measuring tube 5 is calibrated preferably in cubic centimeters and has connected to its open upper end an exhaust pipe I which may be made or heavy rubber tubing, generally designated as vacuum tubing, which leads 'to a vacuum pump, not shown, of any form suitable for producing a low pressure air bottle I. A pressure-vacuumgage, such as a manometer8,.is oonnectedinto pipe I to indicate .the pressure in the apparatus.

This apparatus is utilized in the following manner: A sample of the liquid to be examined is poured into bottle I, through neck 3, until the level of fiuidis at ring mark 2, which, as noted, preferably indicates I08 cubic centimeters. The bottle is then filled to the neck with distilled water or other non-expansible liquid to displace airor gas from the space above the sample, and stopper 4 is inserted with extension 6 extending through the, liquid in the bottle to a point near the bottom thereof. If necessary some additional water is'dropped into the open top ormeas uring tube 5 until the level of liquid stands at the zero mark in the measuring tube. Pipe I is then connected to the top of measuring tube 5 and suction applied, until a sub-atmospheric pressure of the desired degree, indicated on manometer 8, is attained in the apparatus. If gas'is present in the sample in bottle I, the level of liquid will, rise in measuring tube 5. The mere fact of an increase in volume will immediately indicate the presence of gas in the liquid sample. The point to which the level will rise will be dependent upon the volume'of gas in the sample and the vacuum applied thereto, in accordance with the well known principle of Boyles. Law. For ex- I ample, assume that suction is applied to reducethe pressure on the sample to one-fifth of an atmosphere, and the'volume increases 8 cubic centimeters as shown by the' level in measuring tube 5. The percentage by volume of gas inthe original sample will be found by simple calculation to be 2 percent. r

Thus, by this simple method and apparatus, both a qualitative and a quantitative measurement of the gas occluded in a liquid may be quickly determined.

By applying this methodto a well fluid such as a mud fluid used in well drilling, the presence and the amount of gas occluded in the fluid can be readily and easily determined. By measuring the quantity of gas in the well mud leaving a well. and comparing it with the quantity of gas, measured in the same manner, contained in the mud entering the well, any increase in gas content of the exciting mud over that of the entering mud will be due to gas introduced into the mud'during its passage through the well. Of course, it the entering mud is known to be free-of gas, then the gas content of the exciting mud will be solely that picked up by the mud in passage through the well. By correlating specific entering and exciting increments ofthe mud and by relating them to the depth of the bottom of the well, as explained in my co-pending application, referred to above, the sub-surface formation, which was responsible for the increased gas content of the mud, may be readilylogged.

Fig. 2 shows another modification of apparatus for detecting and measuring, by electrical mean'athe gas content of liquids containing oceluded gas.

The apparatus is in many respects quite similar to the appaiatusof Fig. 1. In this modification, bottle I is elongated suflicie-ntly to properly accommodate four vertically spaced band electrodes, 9, II), II and I2, respectively, reading from the top down. The electrodes are separated and insulated from one another by the glass walls of the bottle. Insulating material other than glass may be used. The other portions of the apparatus are substantially the' same as those utilized in the measuring bottle of Fig. 1. Namely, a ground glass stopper 4 fitting in a ground neck 3, a meauring tube 5, an extension 6, a suction pipe I and a manometer 8.

The four electrodes 9, I8, II and I2 comprise the electrodes for a more or less conventional apgether in circuit by means of a lead I'I, into which is connected a milli-voltmeter I8. With this arrangement of apparatus, a suitable current is applied to the fiuid in bottle I through electrodes 9 and I2 and the resulting potential difierences in the fluid between electrodes I8 and I I read on milli-voltmeter I8. v

This apparatus is utilized in the following manner: A sample of liquid to be testedis poured into bottle I until the bottle is completely filled to neck 3 to displace any air or gas therein. Stopper 4 is inserted as before and the liquid caused to rise in measuring tube 5 by displacement by extension-6. In this instance, no water or other fluid is added in order not to alter the '1. electrical resistivity of the sample. It is unnecessary to measure the changes in volume directly in this modification, since the gas content of the liquid will be determined by the electrical measurements to be described, and, therefore, no specific volume of sample need be used. However, for purposes of comparison, the measuring tube in this modification may be calibrated to measure directly the change in volume while the change is also being measured indirectly by electrical means, and in such a case a sample of known initial volume is placed in the bottle.

With the sample of liquid in place in bottle I, and while under atmospheric pressure, a current of suitable amount, generally small, such as I II milliamperes, is applied to the sample through electrodes 9 and I2. Variable resistance I8 is utilized to regulate the amount of current applied, which will be determined to a great extent. by the nature of the liquid to be tested. In the event the liquid is an electrolytathe amount of current will preferably be quite small to avoid polarization, or alternating instead of direct current may be used. When the current has been applied, as described, the potential drop between electrodes I0 and II is read on milli-voltmeter I8.

Pipe I is now connected to the top of measuring tube 5 and suction applied to the sample to reduce the pressure thereon to the desired degree of sub-atmospheric pressure. The pressure is noted and the same amount of current again applied to electrodes 9 and I2 and the resulting potential drop between electrodes I8 and II read.

Since changes in pressure will have no effect upon theresistivity of the sample unless gas is actually present in the liquid, the mere fact that the resistivity of the liquid changes upon change of gas in the fluid mixture'in terms of change in resistance of the mixture at change in pressure, and by substituting the measured values of resistance of the fluid at the different measured pressures, the percentage by volume of gas in the fluid may be readily calculated within a reasonable degree of accuracy.

One equation suitable for such calculations is as follows: Vq R R P X100 approxi- 1 100= 2 1 2 mately' Where: P1 and P2=diilerent, absolute pressure at which the sample was tested, and P2 is less than Pr R1=resistance (voltage) at P1 Rz=resistance (voltage) at P2 VG=volume of gas in the sample measured at P1, and VL=VO1UII1B of the liquid in the sample. Since the relationship between potential drop and resistances is a direct one, volts may be substituted in place of ohms in the above formula without altering the final proportion of volume of gas to volume of liquid in the fluid.

The following is an example of the way in which the equation is used in calculating the percentage volume of gas in a gas-containing liquid:

V 525-525 190 VL 625 )(760-190 The fluid mixture contained 5.35% of gas.

As will be noted, the result of the above equation gives directly the percentage, by volume, of the gas in the fluid sample. The size of the sample is, therefore, largely immaterial except as it may be regulated for convenience in handling and in keeping the measuring apparatus within reasonable limits of size. Practically speaking, the resistivity of the liquid portion ofthe fluid need not be known, as it does not enter directly into the above equation.

'Figure 3 illustrates an arrangement of apparatus for continuously measuring the volume of gas in well drilling muds by the electrical method described above in connection with Fig. 2. In

this figure, the numeral l9 indicates the upper end of a well bore in which is inserted the usual surface casing 20 having a mud overflow pipe 2|. Numeral 22 indicates the conventional hollow drill pipe which extends through the casing to the bottom of the well and has the usual drill bit, not shown, attached to the bottom end thereof. The well drilling mud is circulated in the usual manner through drill pipe 22 to the bottomof the well into contact with the formations being drilled and picks up the cuttings of the formationand carries them back to the surface through casing 20, from which the mud and cuttings are discharged through overflow pipe 2|, the mud then being returned to the drill pipe after being subjected to such usual settling, screening and treating operations, as may be required to maintain the mud at the desirable consistency for drilling purposes.

A pipe 23, which communicates with the casing 20 at a point below the level at which the mud fluid overflows'from pipe 2|, is connected to a pump 24, which continuously withdraws a small stream of the mud fluid as it returns to the surfacefrom the bottom of the well, and discharges the withdrawn mud through a riser conduit 25, which extends substantially vertically to a suitable height above the surface of Y the ground, thence through a down-comer conduit 26 into a liquid-seal trap 21. The pump 24 is utilized primarily to start a siphonic flow of the mud fluid from the casing through riser conduit 25 and down-comer conduit 25, and once the syphon flow is established, the pump need not be used. Instead of the pump, a vacuum jet, not shown, may be connected to a valved nipple 28, which is connected to the top of riser conduit 25, to draw the mud, fluid to the top of the riser and so initiate the syphon flow.

The siphonic flow of the mud fluid through riser 25 and down-comer 26 creates a vacuum in riser 25 and the pressure in the upper portion of the riser will therefore be lower than that in the lower portion thereof, the difference in pressure being proportional, in general, to the height of the riser and the weight of the volume of mud fluid therein.

Resistance measuring tubes

28 and 30, of the four electrode type-described above in connection with Fig. 2, (see Fig. 4), are inserted in riser 25, closely adjacent to its extreme upper and lower ends, respectively. A pressure-vacuum gage 3| is connected into the mid-point of each of the

tubes

29 and 30 to record the respective pressures in these tubes. The outer electrodes of each tube are numbered 32 and 33, while the intermediate electrodes are numbered 34 and 35. The body of the tubes is constructed preferably of Bakelite or similar insulating materials having suflicient structural strength to withstand the required pressures.

Intermediate electrodes

34 and 35 of each of the resistance tubes are connected by suitable leads 36 and 3'! to individual voltmeters 33 and 38a, while the

outer electrodes

32 and 33 are connected in series in a circuit consisting of a lead 39 connecting electrode 33 of one resistance tube to electrode 32 of the other, and a second lead 4!) connecting the remaining electrodes, an ammeter 4|, variable resistance 42 and current source 43 are connected into lead 40. By connecting the outer electrodes of both resistance tubes in series, the same amount of current can be passed through both tubes and the resulting voltage readings of voltmeters 38 and 3811 will not require correction for proper. correlation.

The apparatus is utilized as follows: A siphonic flow of mud fluid from casing 20 is initiated through riser 25 an down-comer 26 by means of pump 24 or by vacuum jet, not shown, connected to nipple 28. When the flow of mud fluid is well established, current of suitable density tial drops in each resistance tube read from its respective voltmeter. Thepressure in each tube is read from the corresponding gage. By substituting themeasured values of pressure and voltage in the above, or an equivalent formula,

the percentage, by volume, of gas in the mud fluid can be quickly calculated.

To reduce any error in the readings, the height of riser 25 and the distances between the-rcsistl ance tubes is proportioned in accordance with the specific gravity of the fluid to produce a substantial decrease in pressure in tube 29 over that in tube 30. For example, with a mud fluid of approximately 1.4 specific gravity, a distance of about one fourth of an atmosphere, absolute, in tube 29 and approximately one atmosphere in tube 30.

When the well fluid entering the well is known to be gas-free, a difference in the readings between voltmeters 38 and 38a will immediately indicate the presence of gas in the outgoing fluid and will thus immediately apprise the well operator that a gas formation has been penetrated by the drill. Ordinarily this is all that is desired for proper inspection of the drilling operation. If the entering well'fluid contains gas, apparatus similar to that last described may be connected to the pipe supplying mud fluid to the well, and the percent of gas in the entering mud determined thereby. By then measuring the gas content of the mud leaving the well after the elapse of a period of time required for the mud to reach the bottom of the well and return to the top, and comparing the two measurements, the increase in gas content, if any,,can be readily determined. I

From the foregoing, it will be seen that this invention provides a simple and novel method for detecting and measuring gas occluded in liquids and one which is particularly valuable for detecting and measuring relatively small percentages of gas which is occluded in very viscous fluids, such as well drilling muds. It will also be seen that the invention consists broadly in measuring the volumetric change of a gas-containing liquid at different pressures; that the volumetric change may be measured directly or the volumetric change may be measured indirectly,

by measuring the electrical specific resistivity of the gas-containing liquids at different pressures. It will be understood that while in the above description the measurements are obtained at two pressures one of which is preferably atmospheric or super-atmospheric, while the other is sub-atmospheric, both pressures may be superatmospheric or both may be sub-atmospheric.

This invention may be advantageously employed in connection with well drilling for estimating the gas reserves, that is the gas content, of a sub-surface formation. Since the volume of well drilling mud circulated per foot of well drilled may be readily measured or calculated, by measuring the percentage of gas contained in the mud leaving the well, the volume of gas per cubic foot of the sub-surface formation can be calculated, and from this, knowing the thickness of the formation and its area, the gas content of the formation may be estimated within reasonable limits of accuracy. What I claim and desire to secure by Letters Patent is:

1. The method of measuring gas in gas-containing liquids which comprises, subjecting a gascontaining liquid to two different pressures, at

least one of which is sub-atmospheric, measuring the electrical specific resistivities of said liquid at said pressures, and determining the gas content of said liquid from the difference in said specific resistivities.

2. The method of detecting gas in well drilling liquids containing gas which comprises, subjecting said well drilling liquid leaving a well to two different pressures, measuring the electrical resistivities of said liquid at both said pressures, and detecting the presence of gas in said liquid by the change in said resistivities.

'3. The method of measuring gas in well drilling liquids containing gas which comprises, subjecting said well drilling liquid leaving a well to different pressures, measuring the electrical resistivities of said liquid at said pressures, and determining the gas content of the liquid from the difference in said resistivities.

4. The method of measuring gas in well drilling liquids containing gas which comprises, subjecting a well drilling liquid to two different pressures. at least one of which is sub-atmospheric, measuring the electrical resistivities of said liquid at said pressures, and determining the gas content of said liquid from the difference in said resistivities.

5. In the method of drilling wells wherein" a hydraulic fiuid is continuously circulated through a well, the method of continuously detecting the presence of gas in said fluid which comprises,

flowing said fluid in .a confined stream, maintaining difierent pressures on said fluid at spaced points in said stream leaving the well, measuring the electrical resistivities of said fluid at said spaced points, and detecting the presence of gas in said fluid by the change in said electrical resistivities.

6. In the method of drilling wells wherein a hydraulic drilling fluid is continuously circulated through a well, the method of continuously measuring gas contained in said fluid, which comprises, flowing said fluid in a confined stream, maintaining different pressures on said fluid at spaced points in said stream leaving the well, measuring the electrical resistivities of said fluid at said spaced points, and quantitatively determiningthe gas contained in said fluid from the difference in said electrical resistivities.

'7. In the method of drilling wells wherein a hydraulic drilling fluid is continuously circulated through a well, the method of continuously measuring the gas contained in said fluid which comprises, flowing said fluid in'a confined stream, maintaining different pressures on said fluid at spaced points in said stream, one of said pressures being sub-atmospheric, measuring the electrical resistivities of said fluid at said spaced points, and quantitatively determining the gas contained in said fluid from the difference in said electrical resistivities.

8. The method of quantitatively measuring the gas in a gas-containing liquid which comprises, flowing said liquid in a confined stream, maintaining different pressures on said liquid at spaced points in said stream, at least one of said pressures being sub-atmospheric, measuring the electrical resistivities of said liquid at said spaced points, and quantitatively determining the gas contained in said liquid from the difference in said electrical resistivities.

9. The method of detecting gas in gas-containing liquids which comprises, subjecting a gas containing liquid to two different pressures, measuring the electrical resistivities of said liqthe percentage of gas in said gas-containing liquid in accordance with the relative resistivities of said gas-containing mud at said different pressures and with the known laws of behavior of gaseous fluids.

11. The method of testing well drilling mud for the presence of small amounts of gas therein which comprises, subjecting said mud to two different pressures, measuring the electrical specific resistivities of said mud at both said pressures, and computing the approximate percentage of gas in said mud in accordance with the formula:

where: P1 and P2 are said different absolute pressures, and P2 is less than Pi; R1=resistance in ohms (voltage) at P1; R2=resistance in ohms measured at P1 and Vi.=volume of the liquid in the sample.

12. Apparatus for testing well drilling muds for the presence of gas therein comprising in combination with the drilling mud system of a well, a conduit through which drilling mud leaving the well is caused to flow, means for measuring the electrical resistivity of said mud at spaced points in said conduit, means for varying the pressure on said mud at said spaced points, and means for measuring the pressure at said spaced points.

13. Apparatus for testing drilling mud for the presence of gas therein comprising in combination with the drilling mud system of a well, a conduit through which a stream of drilling mud is caused to flow, a syphon positioned in said conduit whereby a variation in pressure is obtained at spaced points in said conduit, means '(voltage) at P2; VG=volume of gas in the sample for measuring the pressure at said spaced points,

[and electrical means positioned at said spaced points for measuring the electrical resistivity of said mud at said spaced points.

14. Apparatus for testing drilling mud for the presence of gas therein comprising in combina- 7 tion with the drilling mud system of a well, a

horizontal conduit through which a stream of drilling mud isssuing from the well is caused to flow, means for creating a siphonic flow of mud through said conduit including a vertical riser extending from said conduit, a down-comer pipe connected to the upper portion of said riser and extending downwardly below the levelot said conduit, means for measuring the pressures at spaced points in said riser, and means for measuring the electrical resistivity of said mud at said spaced points.

15. The method of detecting gas which has become dilutedly occluded in the circulating mudladen fluid employed in the drilling of an oil or gas well by the drilling of a stratum while the fluid column is maintained at a head'exceeding the head of the stratum, comprising, causing the occluded gas in the drilling fluid leaving the top of the well to expand and testing for the gas by measuring the change in electrical resistivity of the fluid caused by the expansion of the fluid.

16. The method of detecting gas which has become dilutedly occluded in the circulating mudladen fluid employed in the drilling of an oil or gas well by the drilling of a stratum while the fluid column is maintained at a head exceeding the head of the stratum, comprising, applying a negative pressure to the drilling fluid leaving the top of the well, and testing for the gas by measuring the change in electrical resistivity of the fluid caused by the expansion of said fluid under said negative pressure.

17. The method of detecting gas which has become dilutedly occluded in the circulating mudladen fluid employed in the drilling of an oil or gas well by the drilling of astratum while the fluid column is maintained at a head exceeding the head of the stratum, comprising, subjecting the drilling fluid leaving the top of the well to a change in pressure and testing for the gas by measuring the change in electrical resistivity of the fluid caused by the change in volume of the fluid under the change in pressure.

18. The method of quantitatively measuring the gas in gas-containing liquids which comprises, flowing said liquid in a confined stream, maintaining diflerent pressures on said liquid at spaced points in said stream by establishing a siphonic flow of said liquid in the portion of said confined stream which includes said spaced points, measuring the electrical resistivities of said liquid at said spaced points, and quantitatively determining the gas contained in said liquid from the difierence in said electrical resistivities.

JOHN T. HAYWARD.