US2362805A - Method and apparatus for detecting hydrocarbons - Google Patents

Description

Nov. 14, 1944. v R DOAN 2,362,805

METHob AND APPARATUS FOR DETECTING HYDROCARBONS Filed June 17, 1940 aw 'dWOD STORAGE TANK 1 h g 3 q gr! 4% 2 INVENTORI R.L.DOANY ATTEi z to several per cent.

Patented Nov; 14, 1944 METHOD AND APPARATUS FOR DETECTING HYDROCARBON S Richard L. Doan, Bartlesville, kla., assignor to Phillips Petroleum Company, a corporation of Delaware Application June 17, 194-0, Serial No. 341,031

Claims. (Cl. 23-232) This invention relates to the detection and location of gas and oil bearing. strata intersected by a bore hole during the course of drilling operations.

With the introduction of rotary equipment and continuous mud circulation into drilling practice the problem of invasion of porous formations by drilling fluid and the consequent mudding oil of potentially productive zones. assumed a much greater importance than it had when cable tools only were employed. In many cases the pressure head of mud in the hole is considerably greater than the gas pressure in the reservoir which it traverses so that very little, if any, of the reservoir fluid escapes'into the hole and hence tothe surface where it could be observed by the driller. Since direct evidence of oil and gas has always been, and, still is, the most dependable criterion of where to test for commercial production it is highly desirable to retain this avenue of exploration which, for reasons cited, has been almost closed so'far as visual evidence is concerned by the methods of rotary drilling. To do this it is necessary to make use of instruments and techniques capable of revealing much smallerquantities 01' oil and gas than can be detected visually and to conduct routine tests on drilling mud during the time that the well is drilling through the section of'hole it is desired to investigate.

It is an object of the present invention to provide a method of extracting dissolved and ad- 'sorbed gases from drilling mud and testing them for combustible content. It is a further object to provide a method of accurately determining the depth from which the gas originated.

- The volume content of combustible gas in drilling mud may range from negligible amounts lip If the gas pressure in a petroleum reservoir traversed by a bore hole is much less than the hydrostatic head of mud,,no seepage intothe hole can take place and the the method which would prevent its use in the upper ranges for such a purpose as, say, the routine testing of mud in high pressure areas to detect dangerous rises in gas concentration which might, if allowed to go uncontrolled, result in a blowout. It is the range of lower concentrations where the greatest benefits are to be derived from mud analysis because of the impossibility of get-- ting direct evidence of oil and gas any other way except bycoring, which is costly and limited in application. In the present specification the term occluded is used to describe the conditions of retention of the hydrocarbons in the earth sample whether such form of retention be absorption. adsorption, or merely structural envelopment. Electrical logs at best give only indirect evidence and are subject to numerous interpretation hazards which, however, should be only addition of hydrocarbons to the mud will be v due to the actual volume of gas andoil contained in the cuttings removed by the drill bit. 'On the other hand, where the reservoir pressure approximates or is higher than the mud ressure, seepage can and does occur and in extreme cases may be sumcient to bring about a gas-cut condition of the mud or even blow it out of the hole.

This invention is primarily concerned with those cases in which the gas content of the mud is too small to be noticeable by visual inspection, although there is nothing in the application of reduced considerably by being used in conjunction with the data obtained from mud analysis. It is realized, of course, that not all gas-bearing strata will be commercially productive but information on the location of such'zones obtained through routine mudtesting in accordance with this invention should result in much better knowledge of where to test.

Mud discharged from the hole in drilling may carry gas in excess of that which it can hold in a dissolved or adsorbed state at atmospheric pressure. In this case the excess will be given off into the air as the mud emerges from the hole. It would thus bepossible to obtain some information of value by testing the air above the mud stream in the discharge line for hydrocarbon content. However, this method is subject to the disadvantage that it is not applicable when the ga content is below the point at which the gas' breaks out of the mud readily and it is probable that most of the cases of importance may fall in this category.

To make use of the dissolved and adsorbed gas as an index of formations traversed by the drill it is first necessary to extract the gas from the mud and it is one of the objects of the present invention to describe a process for accomplishing this in a rapid and eflicient manner. After extraction, a number of diilerent'methods might be used for determining the hydrocarbon content the contained gas for purposes of analysis, a considerable amount of aeration and loss of gas from the main body of mud undoubtedly occurs in circulating through the pits at the surface. However, some will remain in the mud and be carried on a return trip down the hole. The effect of this is to raise the general background of gas content against which new increases must be observed. The thing that makes it possible to obtain useful information on the petroleum content of subsurface strata by analysis of the discharge mud is that there is apparently little mixing of the mud in coming up the hole so that the gas travels eflectively in slugs whereas in circulating through the mud pits enough mixing occurs to blend the residual gas into the general background. For analytical purposes it may be desirable to know what the backgroundis from time to time and tests on suction mud just before it enters the mud hog will furnish the information.

The general analytical procedure to be described comprises pumping mudfrom eitherthe discharge or suction lines on the rig through a supply linetraversingv the field laboratory, bypassing a definite volume of mud into the extraction unit, heating this mud in a closed reservoir to an elevated temperature and pressure, flashing the heated content to a water-cooled evacuated chamber, diluting the extracted gas with hydrocarbon-free air to restore the pressure to atmospheric, pushing the diluted gas mixture out of the extraction apparatus through suitable drying tubes and into the analytical apparatus by the use of water, and finally measuring the combustible content of the mixture by an electrical method. A schematic diagram of the equipment layout is shown in the annexed drawing to which the following details are referred. I

Mud from the discharge pipe on the rig enters the intake of pump III through the line I I and is forced out through the line 12. vA test sample is taken by opening valves l3 and I4 and partially closing valve l5 which causes a portion of the mud stream in l2 to by-pass through the pressure reservoir l6 until it overflows through line 11 to drain l8. A sample of suction mud may be taken in a similar manner through line i 9.

The sample comprising a known volume of mud is isolated in the pressure reservoir l8 by closing all valves leading to the chamber. This chamber is then heated by the gas flame from burner 20, supplied with fuel which may be liquefied petroleum gas contained in tank 2|. To improve the heating conditions a jacket of thermal insulation 22 surrounds chamber IS. The pressure inside reservoir I6 is registered on gauge 23 and the heating is continued until it reaches some predetermined value preferably between 30 and 55 pounds gauge corresponding to a temperature range of approximately 135 and 150 C. Such a temperature is high enough to be effective in driving off adsorbed gases and low enough to avoid cracking any oil that may be present. Valve 24 in line 25 is then opened, connecting chamber [3 with a chamber 26 which has previously been pumped to a vacuum by pump 21 acting through valve 28, line 29 and valve 30. Thedegree of vacuum desired is attained by observing gauge 3|. The rush of steam and mud into the vacuum chamber carries a large amount or heat which is rapidly dissipated by water circulating in a copper coil 32 surrounding chamber 23 and soldered to it for good thermal contact. Vacuum chamber 26 should have a volume several times as large as the heated reservoir l6 and should be located abov it in order that mud and water can run back after the first rush has subsided and the stream condensed.

The foregoing procedure fulfills the three essential requirements for rapid and thorough extraction of dissolved and adsorbed gases from the mud-high temperature, agitation, and vacuum. The next step is to raise the pressure in the vacuum chamber to atmospheric in order that the gas mixture may be transferred conveniently to the analytical unit, This is don by admitting hydrocarbon-free air from cylinder 33 through valves 34 and 30. The sample is diluted in so doing but this is not important since the analytical method possesses ample sensitivity to measure the combustible content after dilution. Since the volume of gas extracted from the mud is negligible as compared to the volume of the vacuum chamber the dilution factor is essentially constant for all samples.

The method of analysis comprises forcing the gas-air mixture out of the vacuum chamber, through drying reagents contained in tube 35 and into the combustion unit' 36 of an electrical analyzer. This is accomplished by admitting water through the valve 31. To indicate the water level in the vacuum chamber'as the gas is bein forced out, the glass gauge 39 is provided and is connected to the chamber by ordinary packing glands. The danger of accidentally overflowing this chamber by failing to turn off the water at the proper time is eliminated by a float 39 in the top of the chamber which closes valve 31 before the water rises high enough to do any damage.

The combustion unit contains two essentially identical platinum filaments in separate enclosed chambers one of which is sealed in air at atmospheric pressure while the other can be flushed out and filled with the sample of gas to be tested. The two filaments are heated to incandescence by passing an electric current through them, and diiferential changes in resistance due to burning the combustible gas on one of them are measured by means of a bridge circuit. This apparatus has been described in applicant's co'pending application, Serial Number 298,708 filed October 9, 1939. Calibration of the unit is checked from time to time by means of a synthetic combustible gas-air mixture of v known proportions contained in tank 41.

Facilities provided on the apparatus for washing out the mud after analysis and for testing the pressure and vacuum chambers for leaks ar as follows: When'the test of a given sample is completed, valve 13 at the bottom of the lower reservoir is opened and the mud and water from both chambers are flushed out through the drain at the bottom of air pressure applied through 29. A water jet 42 in the lower chamber connecting to the main supply through valve 43 aids in sweeping out any especially heavy or viscous muds. High pressure air may be admitted to this chamber through valve 44 for the purpose of testing for leaks. The receptacle 5 at the top of the pressure reservoir and connecting with it through valve 46 is provided as an emergency measure so that mud samples may be poured into the extraction apparatus if the mud pump should fail.

The percentage of gas in the mud is calculated in terms of the standard gas (either propane or butane) used in calibrating the electrical analyzer unit. The reading obtained for a test sample on this unit gives the percentage of combustible gas in the diluted mixture from the vacuum chamber. The actual volume of gas extracted from the mud is equal to the observed will be a sufliciently good approximation to conpercentage multiplied by the volume of the vacuum chamber. This in turn divided by the known volume of mud used in the test gives the volume percentage of the gas present in the mud.

The comparison sample is obtained by admitting into tank 41 a measured quantity of gas from container 2| reduced in pressure at valve 48 to atmospheric pressure and measured in calibration cylinder 49. Storage tank 41 is previously evacuated and the 'hydrocarbonegas in calibration cylinder 49 is swept into the storage tank by air from compressed air source 33 thereby forming a synthetic combustible gas-air mixture of known proportions in the storage tank.

The method of utilizing the data on gas content in locating gas and oil bearing strata intersected by the drill is as follows, Each time a mud sample is taken for analysis the depth of the drill bit and also the rate of drilling are noted. A method of continuous recording whereby both of these factors may be conveniently and accurately obtained at any time is described in co-pending application Serial Number 385,942 filed March 29, 1941, by the applicant and Francis W. Crawford. The point of origin of the gas carried by the mud is assumed to coincide with the position of the drill bit at the time the test sample passed it. To

determine this point it is necessary to deduct from the observed depth at the time the sample is taken a footage correction which is obtained by multiplying the drilling rate in feet per hour by the time in hours required for the mud to travel from the bit to the top of the hole. Various methods have been proposed for determining the circulation time of the mud from the known pumping rate of the mud hog, size of the pipe and v annular space between pipe and walls of the hole, etc. and by direct experiment through the addition of dyes or certain light materials such as oats or fibrotex to themud and watching for it to come back. Such methods are fairly satisfactory for determining total circulation time but I give no information on how much of this time is spent on the down trip and how much in coming up. It is the latter that is of importance in calculating the depth correction for mud samples and it is one of the objects of the present invention to provide a method of determining the time required for mud and cuttings to travel from the bottom to the top of the hole.

The foundation of the method is the drilling chart referred to above on which is recorded the progress of the bit at all times during the drilling operations. The slope of the line on this chart represents the drilling speed, which is determined to a considerable extent by the nature of the formation being drilled. When the bit moves out of a hard layer such as limestone into one where the drilling is easy and rapid, such, as an unconsolidated sand, the fact will at once become evident on the drilling chart by a sharp change in slope of the line. Both the time and the depth at which this change occurred will be accurately marked. If, when such a change of slope occurs,

samples of cuttings are collected at closely spaced intervals and examined under the microscope, the time at which the first traces of the newly penetrated layer appear can be noted. The difference between this time and the time shown on the drilling chart for the break in the curve will be an accurate measure of the length of time required for the mud to travel up the hole. Ordinarily there will be a number ofopportunities to determine the travel time as the hole is being drilled and in between such determinations it sider the circulation time as equal to a constant multiplied by the depth of the hole, the value of the constant being redetermined each time an observation is actually made. i

The most convenient method of interpreting the data obtained from mud analysis is to plot them in the form of a depth log with gas content as abscissa and corrected depth as ordinate. Such a log will show peaks of higher gas content marking the position of gas bearing strata, providing these strata are mudded off sufliciently to stop gas seepage after the bit has passed them, otherwise only the top will be marked and the background gas content will be permanently increased.

Even after making the best possible correction for circulation time, the depth determination in mud analysis has a greater element of uncertainty than have direct measurements with the drill pipe or steel line. I have found, however, that this uncertainty as to the depth of the formation responsible for the gas can be reduced considerably in those cases where the gas-bearing zone is also one of easy drilling compared to neighboring strata. The method used is to plot a drilling-rate log to the same scale as the gascontent log and compare the two. A high correlation between certain peaks on both logs will be noted and for such peaks the depth of the top and bottom of the gas bearing stratum will be accurately defined by drill pipe measurement on the drilling-rate chart. This is an important concept in the present invention, since it places the depth determination in mud analysis on a more quantitative basis than is possible by any method which depends on a measurement of mud circulation time.

I claim:

1. A method of treating drilling fluid comprising confining a sample of the drilling fluid in a closed vessel, heating the sample in the vessel to a temperature above the boiling point of the same whereby a superatmospheric pressure in the vessel results, flashing the heated drilling fluid under pressure into a lower pressure zone, cooling the vaporous eflluent of the flashing step sufliciently to condense water vapor present, adding an oxygen containing gas to the remaining vaporous eflluent to form a mixture, and passing the mixture to a combustion zone to measure the combustible content.

2. A method of treating drilling fluid comprismg confining a sample of the drilling fluid in a closed vessel, heating the sample in the vessel to a temperature above the boiling point of the same whereby a superatmospheric pressure in the vessel results, flashing the heated drilling fluid under pressure into a lower pressure zone, coolmg the vaporous eilluent of the flashing step sufficiently to condense water vapor present, further dehydrating the remaining vaporous efliuent, and passing the remaining vaporous eflluent to a combustion zone to measure the combustible content. 3. A method of treating drilling fluid comprising confining a sample of the drilling fluid in a closed pressure vessel, heating the sample in the vessel to a temperature above the boiling point of the same whereby a. superatmospheric pressure in the vessel results, evacuating a second vessel establishing communication between the vessels:

wherebythe vaporous eiiluent of the pressure VapOrolls eflluent, and passing the remaining vaporous effluent to a combustion zone to measure the combustible content.

4. Apparatus for testing aqueous drilling i'iuid -for volatile combustible constituents comprising a pressure vessel constructed to withstand superatmospheric internal pressures, means to heat the vessel, a chamber arranged to collect vapor from the vessel, evacuating means, valved conduit means connecting the evacuating means with the chamber, a valved conduit connecting the upper part of the vessel'with the interior of the chamber, an analyzer for combustible gases, and means including valved conduit means connected to the chamber for supplying water thereinto and valved conduit means connecting the chamber with the analyzer whereby combustible gases segregated in the chamber from the vessel may be displaced by the water and passed to the analyzer for analysis.

5. Apparatus for testing aqueous drilling fluid for volatile combustible constituents comprising a pressure vessel constructed to withstand superatmospheric internal pressures, means to heat the vessel, a chamber arranged to collect vapor from the vessel, means for cooling the chamber sumciently to condense water vapors, evacuating means, valved conduit means connecting the evacuating means with the chamber, valved conduit means connected to th chamber for supplying air thereinto to increase the pressure therein, a valved conduit connecting the upper part or the vessel with the interior of the chamber, an analyzer for combustible gases, and means including valved conduit means. connected to the chamber for supplying water thereinto and valved conduit means connecting the chamber with the analyzer whereby combustible gases segregated in the chamber may be displaced by the water and passed to the analyzer for analysis.

, RICHARD L. DOAN.

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