US2280075A - Detection of gas in drilling fluids - Google Patents

Description

ApiilZl, 1942.

J. T. HAYWARD DETECTION OF was In DRILLING FLUIDS? Filed Feb. 23, 1938 INVENTOR I 1 J. "r HAYWARD ATTORNEY 2 Sheet-Sheet 1 TO VACUUM PUMP Agra 21, 1942.

Filed Feb. 23, 1938 J. HAYWARD DETECTION OF GAS IN DRILLING FLUIDS 2 Shets-Sheet 2 M39 M A 4| J. T. HAYW'ARD BY v 4 M 1 J'TORNEY J 'I'hisf invention relatesto amethod ratente'an azl, 19 2; a

UNITED STATES PATENT OFFICE DETECTION OF GAS IN DRILLING FLUIDS John nnaywara, Tulsa, one; Application February 2:, 1932, Serial No. 191,895 r (cue-5 1) 5 Claims.

ofdetecting andijmeasuring the. gas content of hydraulic and recognition of the gas formation must rely wholly upon the prompt detectioriiof this small fluids, and particularly of mud fluids such as are used'in connectionwith thejdrilling' of oil or gas'well In the drilling of oil or {gas wells, whereina hydraulicfluid, such as a suspension of clay or earthym'aterials in water, is'circulated' through the well .during. the drilling theretif, by conventionalpractice, the specific gravity of the cir-- culating-fluid is controlled, ordinarily, so that the in the well is greater than the pressure of oil or gas which itis-expected will be encountered at points in the well. ,This procedure is followed in'order to prevent the presquantity-of gas in the fluid. The-following example will serve to illustrate the "relatively a encountered. The

,minute quantities of gas which willbe-present f in'the mud fluid under a normal set of drilling conditions: A well is being drilled at a depthj,oiij f, v gas-containing iorniaflon .is" formation pressure is ap- 6000 feet where a proximately '3000 mud fluid in the pounds per square inch. The *wellhas a specific gravity of 1.38 producing a fluid column pressure at the bottom of the well of approximately .3600 pounds per square inch or approximately 600 pounds per sure of ,a gas formation, which may be encountered, from, exceeding that of the fluid head pressure and causing blow-outs, whereby thefluid is blown from the well with disastrous consequences, which, in some cases, may result in complete destruction 'of the welLand endanger lives and propertyin the vicinity of the well.

While this procedure is advantageous for protecting the well during drilling, it is disadvantageous inthatthe excess pressure of the hydraulic fluid prevents the entrance into thewell of gas from an encountered gas-containing formation, with the result that such formation'may entirely escape detection of the drill operators and .be-

' come mudded-oif" or sealed by the circulating 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 comprisingthecylinder of the formation being cut out by theidrill bit. Assume the diameter of the bore of the well is nine inches, a conventional The volume of each lineal foot of the cylinder of gas formation drilled will be approximately 735 cubic inches. If we assume a "porosity: of 25 per cent, that is, the pore space mud fluid, and erroneously cause the well to be-' come abandoned as a non-producer. Also, as oil is very often found in immediate-or adjacent association with gas, failure todetect the presence of gas substantially immediately after penetration by the drill into the gas formation, may cause the driller to continue entirely throughthe oil-containing formation and also mud-off that formation. This is particularly true where, as"

is often the case, the oil-containing 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 will be very quickly traversed by the drill unless comparatively exact knowledge of the location of such formations is known-beforehand and the approach of the drill theretovery carefully controlled.

Since asnoted, the pressure. ofthe fluid column in thewell is ordinarily controlled to exinthe formation in which the gas is held constitutes 25 percent of the volume of the formation. then it is evidentthat the'total volume of gas in one lineal foot of the cylinder of forma-' tion willbe approximately 184 cubic inches at a "pressure of 3000 pounds per square inch. When r 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 ata rate of approximately barrels per lineal foot drilled, the-36,800 cubic inches of gas will be distributed through 100 barrels of mud fluid, and upon calculation, itwill 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 ordinaiyinspecceed that of any gas formation which may encountered/only that relativelysmalLquantity-fl of gasg which-is contained in the relatively small 1 cylinder of formation cut outv by the'drill. trayersing the formationfwillescape into-the,fluid, 5-

ftion methods, due to the fact that the mud fluids ordinarily used in drilling are generally very viscous and have gel-like properties which,

cause the minute globules of-gasto be strongly occluded in the fluid to arr-extent, many- "cases, that'substantially .none'gof' the gas will escape from the fluid, evenwhen 'thefluid is al sectional area.

different pressures indicating the presence of gas I in the sample and providing a measure of the amount of gas contained in the liquid. 7

It has been discovered that when gases are 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 percent of gas occupies a volume of 100 cubic centimeters,

at one atmosphere pressure, at one-half atmosphere, the liquid will occupy a volume of 102 cubic centimetera 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 one-half 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. 1

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 specific 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 liquidfrom the column, thereby proportionally reducing the conducting cross-sectional area of theliquid and increasing the electrical resistance approximately in direct proportion to the decrease in this cross- By utilization of suitable electrical apparatus, as will be more fully described hereinafter, the electrical resistance of the fluid valuable in connection with well drilling where, 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 passage through the well. Such a comparison method is referred to in my co-pending application Serial Number 187,619, filed January 29, v

1938, which became Patent No. 2,214,674 September 10, 1940, in connection with the detectionand logging of gas formations and to the extent of such common subject matter, this application is a continuation-impart 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 anydraulic 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 circulated in 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 drawunder different pressures may be measured, and

tent. The latter procedure may be particularly ings, which illustrate forms of apparatus which may be utilized for successfully practicing the new invention. 7

In the drawings:

Fig. 1 illustrates a form of measuring bottle for indicating the presence of, or for measuring directly the volume of gas in a gas-containing Fig. 2 illustrates a form of electrical apparatus for indicating the presence of, or for measuring indirectly the volume of gas in gas-containing 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 measurement tubes utilized in the apparatus of Fig. 3.

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. c. 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 extending hollow measuring tube 5 provided with a downward extension 6, which extends into bottle I to a point near the bottom thereof Th adjacent surfaces of neck 3 and crease in volume will tube 5.

heavy rubber tubing, "generally designated as vacuum'tubing, which leads to a vacuum pump. not shown, of any Iormfsuitable ior producing a low pressure in bottle I. A pressure-vacuum gage, such as a manometer I, is connected into 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 I, until the level of fluid is "at-ring mark- 2, which, as noted,

preferably indicates 100 cubiccentimeters. The

bottle is then filled to the neck with distilled water or other non-expansible liquid to displace air or gas from the space above the sample, and stopper-l is inserted with extension! extending through the liquid in the bottle to a point near the bottom ther'eofi If necessary some additional water is dropped into the open top of measuring tube l until the level of liquid stands at the zero marl: in the measuring tube.

tion applied, until a subatmospheric pressure 01 the desired degree, indicated on manometer I, is

attained in the apparat It gasis present-in the sample in bottle I, the level or liquid will rise in measuring tube I. The mere fact of an inimmediately indicate the presence of gas in the liquid sample. The point to which the level '.will rise will be dependent upon the volume 01' gas in the sample and the vacuum applied thereto, in accordance with the well known principles of Boyle's Law. For ex ample, assumethat suction is applied 'to-reduce the pressure on the sample to onefifth -of an atmosphere, and the volume increases 8 cubic centimeters as shown by the level in measuring The percentage by volume or gas in the original sample will be iound'by simple calculation to be 2 percent.

E'ipe 'I isthen co'n'- nected to the top or measuring tube and suc- 3 stopper 4 are ground to iorrnan airtight seal. commodate four vertically spaced band elec- .Measu'ring tube is calibrated preferably in cubic trodes, 8, It, II and I2, respectively, reading centimeters and has connected to its open. upper fromthe top down. The electrodes are separated and an exhaust pipe I which maybe made of and insulated from one another by the glass walls of the bottle. Insulating material other than glass may be used. The other portions oi 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 I, a measuring tube 5, an extension 6. a suction pipe I and a manometer 8.

The four electrodes I, I0, II and I2 comprise the electrodes for a more or less conventional apparatus used for measuring electrical resistivity of materials.

0 and J2 are placed in circuit. through a lead II with a suitable direct current source, such as battery llyand a milii-ammeter I5 and a variable resistance I connected into the circuit. The two intermediate electrodes III and II are connected together in circuit by means of a lead I1, into which is connected a millivoltmeter It. With this arrangement of apparatus, a suitable current is applied to the fluidin bottle I through Thus, by this simple method andapparatus.

' a mud fluid used in well drilling, the presence and the amount 0! 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 con-' tent oi the exiting mu'd over that of the entering mud will be due to gas introduced into the mud during its passage through the well. Of course, if the entering mud is known to be free 0! gas. then the gas content of the exiting mud will be solely that picked up by the mud in passage through the well. By correlating specific entering and exiting increments of the 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 01 the mud, may be readily logged.

Fig. 2 shows another modification of apparatus for detecting and measuring, by electrical means, the gas content of liquids containing oceluded gas. i

The apparatus is in many respects quite similar to the apparatus of Fig. 1. In this modification, bottle I is elongated sui'nciently to properly acthrough electrodes electrodes I and I2 and the resulting potential diflerences in the iluid between electrodes In and II read on millivoltmeter II. g

This apparatus is utilized in the following mantested is poured completely filled or gas therein.

into bottle I until the bottle is to neck I to displace any air Stopper I is inserted as before and the liquid caused to rise in measuring tube 5 by displacement by extension i. In this instance, no water or other fluid is added in order not to alter the 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 vol- .ume 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 It ,milliamperes, is applied to the sample 9 and I2. Variable resistance It is utilized to regulate the amount of current applied, which will ice-determined to a great extent by the nature of the liquid to be tested. In the event the liquid is an electrolyte, the 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 mini-voltmeter I8.

Pipe 1 is now connected to the top of measur-. ing tube I 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 It and II read.

Since changes in pressure will have no effect upon the resistivity of the sample unless gas is actually present in the liquid, the mere fact that the resistivity of the liquid changes upon The outermost electrodes change in pressure will limmediat'ely indicate the presence of gas in the liquid and will be sufficient for pufp'oseslotdetecting the presence of gas occluded in the liquids.

As-noted above, it' is found that the change in' resistancefof a-mixture of liquid and occluded gas'atrdiiferent-pressures is approximately directly proportional to the change inthe propor- -.tional volume'oji thegas in the mixture at the diligent pressures.

I orifthis relation, ,it is possible to setup a simple, equation for expressing the percentage of; in ,thefluid mixture in ternrsqg change resistance of the mixture at change in pres- "sure,-an'd 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.

. 'O'ne equation suitable for such calculations is as follows:

x 100 a nea.-

P1 and Pz=diflerent, absolute pressures at" which-the sample was tested, and

P2 is less than Pi R1=resistance (voltage) at Pi R2=resistance (voltage) at P2 Ve=volume of gas in the sample measured at P1, and 7 Vt=volume 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: I

The reading of milli-voltmeter 18 at a pressure of 760 mm, of mercury was 525 millivolts, and at a pressure of 190 mm. was 625 millivolts. Substituting in the above formula,

loo

ratus for continuously measuring the volume of gas in well drilling muds by the electrical method described above in connection with Fig. 2. In thisflgure, 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 mud fluid from the casing through riser conduit 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 bottom of the well into contact with the formations being drilled and-picks up the cuttings of theiormation and carries them back to the surface through casing 20, from which the mud and cuttings are discharged through overflow pipe.2l, 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 2l,-is. connected to a pump 24, which continuously withdraws a small stream of the mud fluid as it returns to the surface from thebottom .of the well, and discharges the withdrawn mud through a riser conduitv 25, which extends substantially vertically to asuitable height above the suriace of 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 oi the 25 and down-comer conduit 26, and once the siphon 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 2!, which is connected. to the top of riser conduit 25, to draw the lmud fluid to the top of the riserand so initiate the siphon 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 oi the riserf'will therefore be lower than that infthe lower portion thereof, the diflerence in pressure beingproportional, in general, to the heightor the riser and the weight of the volume of mud fluid therein. 1

' 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 2i, closely adjacent to its extreme upper and lower ends, respectively. A pressure-vacuum gage 3| is connected into the mid-point o1' 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- 38. 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 tubesare connected by suitable leads 36 and 31 to individual voltmeters 38-", whilethe, 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 380. will not require correction for proper correlation.

- of pump 24 or by vacuum jet,'not shown, conthe bottom of the well and has the usual drill 76 nected to nipple 28. When theflow of mud fluid calculated, and from this, knowing the thickis well established, current of suitable density is applied to the measuring tubes and the tential drops in reach resistance tube read from its respective voltmeter. The pressure in each tube is read from the corresponding gage. By substituting these measured 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 resistance 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 1 of about 15 feet between the resistance tubes will produce a pressure of about one fourth of an atmosphere, absolute, in tube "and approxi-- mately one atmospherein tube It. 1

When the well fluid entering the well is known to be gas-free, a difference in the readings between voltmeters 33-38 will immediately indiness of the formation and its area, the gas co tent 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 detecting gas in well drilling mud containing gas introduced therein solely from the drill cuttings which comprises, subjecting said well drilling mud to a-change in pressure from substantially atmospheric to sub-atmospheric, and observing the resulting change in volume thereof;

2. The method of testing well drilling mud for the presence of small amounts or gas introduced therein solely from the drill cuttings which comprises, placing a measured quantity of mud in a vessel, subjecting the mud to two different pressures, one of. which is sub-atmospheric, observing the resulting increase in volume of said mud, and computing the percentage of c0mpressible fluid 'in said mud in accordance with the cats the presence of gas in the outgoing fluid and willthus immediately apprise the well operator that a gas formation has been penetrated by the drill. proper inspection ofthe 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 per- Ordinarily' this is all that is desired for cent of gas in the entering mud determined thereby. By then measuring the gas content oi the mud leaving the well after theelapse of a period of time required for the. mud to reach the bottom of the. well and return to the top, and comparing the twomeasurements, the increase in gas con-v tent, if any, can be readily determined. 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 nulda such as well drilling muds. It will also be seen that"the invention consists broadly in measuring the v'splumetric 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 specificresistivity of the gas-containing liquids at different pressures. V f

It will be understood that while in theabove description the measurements are obtained at two pressures one of which is prererably1 atm pheric or super-atmospheric, whil'efthe otliuis nute amounts of gas occludedv therein which com-r prises placing a measured quantity of said mud fluid in a vessel, subjecting the mud fluid to two different pressures one of which is sub-atmospheric, observing the resulting increase in volume of said mud fluid. and computing the percentage oi compressible fluid in the mud fluid in accordance with the known laws of the behavior of gaseous fluids, to thereby obtain an indication of the presence of gas in the mud fluid and an indica'tion of the amount of gas therein.

4. Apparatus for detecting gas in well drilling mud comprising, a-container having an opening therein, and adapted to receive a measured volumeof mud, an air-tight closure for said opening, an elongated hollow tube extending through said closure to a point adjacent the bottom of said container and in open communication therewith, and having an extensionabove said container,

. means connected to said extension to apply a vacuum through said tube to the mud within said container, gage'means for measuring the pressubatmospheric, both pressures may auperatmospheric or both may be sub-atmospheric.

This invention may be. advantageously em'- ployed in connection with well drilling for estimating the gas reserves, that is the gas content.

Of a sub-surface formation. 'Since theivolume o! well drilling mud circulated per foot or 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 sure in said container, and means cooperating with said extension to indicate changes in volume of said mud responsive to. the change in pressure in said container.

- 5. An apparatus according to claim 4 wherein said extension-is provided with a transparent sight portion a calibrated scale thereon,

whereby a'vl'sual indication is provided of the change in levelof said mud in said extension in response to thechange .in ,pressure.

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