US3174910A - Microbial oil prospecting method - Google Patents

Description

3,174,910 MICROBHAL OIL PROSPECTENG METHOD Donald G. Hitzman, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed Nov. 14, 1962, Ser. No. 237,732 4 Claims. (Cl. 195-4035) This invention relates to an improved method of prospecting for deposits of hydrocarbons heavier than methane by measuring the quantity of at least a second oxidizable gas, other than methane, oxidized simultaneously as the methane is consumed by bacteria in soil samples. In another aspect, it relates to a novel method of prospecting for oil in which the microbial action of pairs of samples of earth from each of a plurality of sample points are measured for the consumption of methane in one sample of each pair as compared to the consumption of the same concentration of methane and a hydrocarbon gas or gases heavier than methane in the other sample.

In the prior art, such as US. patent to Taggart, Jr., 2,349,472, May 23, 1944, each soil sample was divided into two portions, one of which was exposed to a methanecontaining atmosphere and the other to a heavier hydrocarbon gas-containing atmosphere. On page 2, column 1, lines 24-44, this patent states that by comparing the results obtained by the action of the respective gases one can determine with certainty the amount of bacteria contained in the soil sample which is propagated by heavier hydrocarbons. I have found, however, that there are many instance in which the method outlined by this patent is inoperative as a prospecting method to determine the presence or absence of hydrocarbons heavier than methane in some underground formations, because some organisms which chiefly and preferably utilize methane may also use the higher hydrocarbon gases if no methane is present, so that confusion results because of consumption of the heavier hydrocarbon by the organisms that normally thrive on methane.

In the novel process of the present invention, the said confusion which would result in the process of said patent by the consumption of the heavier hydrocarbons by the organisms that normally thrive on methane is avoided by supplying respectively to each of a pair of soil samples taken at the same point a first methanecontaining atmosphere to the first sample of each pair and a second methane-containing atmosphere also containing a heavier hydrocarbon gas to the second sample of each pair, so that the organisms that normally and preferably thrive on methane will consume the methane in both atmospheres, while the organisms that normally thrive on heavier hydrocarbons will do so only in the atmosphere containing said heavier hydrocarbons. Then, by subtracting the percent of total gas absorbed by the first sample of each pair from the first methane-con- EJMEW Patented Mar. 23, 1965 taining atmosphere from the percent of total gas absorbed by the second sample of each pair from the second heavier hydrocarbon and methane-containing atmosphere of each pair of samples, a numerical value is arrived at which eliminates the etfect of organisms which normally thrive on methane, and represents the amount of heavier hydrocarbons consumed by organisms which normally thrive on heavier hydrocarbons.

While a theoretical basis is not necessary to establish the present invention, it is believed wherever hydrocarbons heavier than methane are accumulated by nature in underground formations, that small amounts of these heavier hydrocarbons will gradually leak out of storage and Work their way directly upward to the surface of the ground above the storage area. the surface of the ground over both said areas storing said heavier hydrocarbons and over areas which contain no heavier hydrocarbons, there is vegetable material present in the soil which is decaying and partially breaking down into methane. The decay of this vegetable material always produces methane, but will not produce hydrocarbons heavier than methane. Microorganisms of all types have a power of spreading widely and are present in the soil, regardless of whether the soil is over a heavier hydrocarbon storage area or not. But during the years, microorganisms that normally thrive on hydrocarbons heavier than methane will multiply and become concentrated in areas overlying underground storage of hydrocarbons heavier than methane, and will almost die out completely in areas which are not over such underground storage, because in the latter areas they never are supplied any heavier hydrocarbons than methane. At the same time, organisms that normally thrive on methane will be present in any soil containing decaying vegetation, whether the soil is over heavier hydrocarbon storage areas or not, and therefore will be present in both types of areas in large numbers. When a sample is exposed to an atmosphere containing relatively large amounts of a specific hydrocarbon, the amount of the specific hydrocarbon consumed in a period of one to two weeks is directly dependent on the concentration of microorganisms that will consume and thrive on that particular specific hydrocarbon. Also, said concentration of the specific microorganisms in the sample is directly dependent on the presence, 'or absence, of exposure of said sample in situ in the ground over a large number of years to said specific hydrocarbon. The situation is complicated by the fact that in any area survey there is always a background value of methane, which may be high or low depending on factors not relating to oil but to things such as moisture, temperature, and mineral nutrients in the soil, which factors vary the amount of vegetation present and its rate of decay, which vegetation supplies organic matter which will decay to form methane. Obviously, there is more methane in the soil in a swamp than in a desert region.

At the same time, near' feet being more preferred.

J The processes of the prior art have no means for distinguishing or allowing for this background value of methane.

By use of the present invention this variable background value, due to different amounts of methane in the swampy soil and in drier soil, is substantially eliminated. By using pairs of samples from each point and exposing one set of samples to methane alone and the other set to methane and heavier hydrocarbons, the background value due to the methane is canceled out.

One object of the present invention is to provide a novel and improved process of microbial prospecting for oil or hydrocarbons heavier than methane.

Another object is to provide a novel microbial prospecting process in which the background effect of methane is eliminated and the results are dependent on the effect produced by hydrocarbons heavier than methane.

Another object is to provide an improved process of prospecting for hydrocarbons heavier than methane by measuring the quantity of a second oxidizable gas other than methane, oxidized simultaneously as the methane is consumed by methane-consuming bacteria.

Numerous other objects and advantages will be apparent to those skilled in the art upon reading the accompanying specification and claims.

In practicing the present invention, soil samples are collected from each of a plurality of spaced sampling stations, as taught by my prior U.S. Patent 2,880,143 of March 31, 1959. The soil samples are preferably gathered below the level of surface contamination.

This patent states that depths from six inches to three feet are usually preferred, with depths from two to three In taking the samples, it is important that the soil sample be a sample of undisturbed soil at the desired depth. One convenient method of sampling is to dig a hole with the aid of an ordinary posthole digger to approximately the desired depth and then,

by the use of a hand auger, take a sample of undisturbed soil from the side of the hole at the desired depth. The area under investigation is usually sampled according to a prearranged plot of said area. Obviously, any desired plot can be employed. While one sample at each sampling station can be used in the practice of this invention, in order to reduce the possibility of a poor sample it is preferred to take two samples at each station. Therefore, preferably at each sampling station two holes spaced ten feet apart are dug and samples collected from each hole. The samples are preferably placed in suitable sterile glass containers and suitably labeled to prevent confusion.

One hundred grams of soil from each of said two holes at each sample station are blended to give a two hundred gram sample for each sampling station. The two hundredgram sample of soil is then blended in a Waring Blendor or other suitable mixing device for approximately one minute with one liter of a sterile mineral medium preferably having the following composition:

Mineral medium N0. 1: Grams NH NO 1.0 MgSO 0.1 K HPO 0.5 CaSO 0.1

Distilled water to make 1 liter total.

The pH of the soil suspension is then adjusted to 7 while the suspension is being agitated.

Mineral medium No. l is satisfactory if the samples treated with it will consume gas from the first atmosphere containing only methane as its only hydrocarbon. If this does not occur, then other mineral mediums should be tried until one that will do so is found. However, it is extremely unlikely that any one of the three mineral mediums disclosed above and below will ever fail to give good results in the practice of this invention.

The mineral medium which is used in preparing the above-described soil suspensions and dilutions can be varied widely, as is well known to bacteriologists. Two other such mineral mediums which can be used consist of:

Mineral medium No. 2: Grams NH Cl 1.0 K HPO 0.5 MgNHAJPO4 CaSO 0.1 Distilled water to make 1 liter total.

Mineral medium No. 3:

KNO 1.0 MgSO -7H O 0.2 KZHPOL 0.5 FeCl -6H O 0.05

Distilled water to make 1 liter total.

While the soil suspension is being agitated with the mineral medium, a sample of about cc. is withdrawn by a hypodermic syringe and injected into an evacuated bottle, which has been scaled by a rubber gasket, by forcing the needle through the rubber gasket, discharging the contents into the bottle and removing the needle from the gasket, whereupon the hole in the rubber closes and the bottle retains its vacuum. The vacuum can be established before or after adding the sample by withdrawing air through a hypodermic needle inserted and withdrawn in the same manner. The bottle should have a volume of about 200 cc. and should be filled about half full of the soil sample slurry, leaving about 100 cc. space under vacuum over the liquid slurry sample. After the soil suspension has been added, the bottle is filled with a selected gas mixture containing predetermined percentages of methane and air for one set of samples, and predetermined percentages of methane, air and one or more heavier hydrocarbons, such as butane, propane or ethane, in the case of the other set of samples. The addition of the gas is also through a hypodermic needle inserted through the rubber gasket and then removed with the rubber gasket closing the hole again. The gas mixtures can be enriched with oxygen and/ or carbon dioxide, but in the runs in Table I only air, methane and/ or propane was used. While ethylene, acetylene, propene, butene, butadiene and other unsaturated gaseous hydrocarbons may be used successfully in the practice of this invention, it is preferred to use saturated paraffinic hydrocarbon gases 7 because connate oil and heavier hydrocarbon gases are generally saturated in natural storage, and they are what the bacterial organisms have been exposed to over the period of years that produced the population present in the undisturbed sample of soil.

One way in which the pressure of gas in the sample bottles can be equalized immediately after the gas has been injected is to place all the bottles in a water bath at the same temperature and bleed ofi any pressure over atmospheric by a hypodermic needle. Or the gas can be added and its pressure measured and regulated at that time.

The sample and gas-containing bottles are incubated at room temperature (about 27 C.) and preferably started with atmospheric pressure'in the bottles (about 780 mm. of mercury absolute gas pressure). After one to two weeks has passed (in TableI below, after 10 days), the pressure in the bottles is either measured by pressure measurement through a hypodermic needle, or by allowing water to be drawn into the bottle through a hypodermic needle until the pressure inside is atmospheric and then measuring the added volume of water by comparing liquid levels before and after. The bottles can be graduated with a suitable volumeric scale for the later purpose, such bottles being available on the market and used by drug stores for medicine bottles. 0

TABLE I Sample values in percent of total gas absorbed after days incubation at 27 C. and starting with 780 mm.

of mercury absolute gas pressure Content of Culture Armosphere AO Sample A B C BA (Process Point Type of Location (Present B-C of Invention) 2,349,472) 20% CH4, 20% CH4, 20% 0 11 80% Air 20% CSHE, 80% Air 60% Air 1 In Oil Field 32 10 17 22 5 d 8 29 21 9 -12 10. 5 24 9 13.5 15 1. 5 11. 5 23 6 11.5 17 5. 5 7 17 10 10 7 -3 10. 5 27 20 7. 5 7 5 11 13 3 2 10 8 15 13. 5 5 -1. 5 8. 5 10 19. 5 20. 5 13 1 7.5 6.5 15 13 4 2 9 11 In order to compare the results of the process of the present invention with the process of U.S. Patent 2,349,- 472, cited above, in column 1, second paragraph, a series of triple samples was taken at 10 sample points, 1-10, at location intervals of 0.1 mile on a line running into a known producing oil field from an area which had been tested by drilling oil wells which turned out to be dry holes. In that way, it was positively known that sample points 1-4 should indicate the presence of oil, whereas samples points 5-10 should only indicate the presence of methane from decaying vegetation. The three cultures using the same soil slurry of 250 gm. of soil to 1 liter of mineral medium #1 were prepared for each soil sample. One hundred cc. of each culture was put into a bottle having a volume of about 200 cc. and the remainder of the bottle was charged with gas. In Table I above, bottles of Series A were charged with 20 percent methane and 80 percent air, while bottles of Series B were charged with 20 percent methane, 20 percent propane and 60 percent air, and bottles of Series C were charged with 20 percent propane and 80 percent air. The bottles were incubated for ten days at about 27 C. (room temperature) and all the bottles started out with atmospheric pressure in the bottles. At the end of ten days, each bottle was inverted and a hypodermic needle connected with a source of water Was forced through a rubber gasket over the mouth of the bottle, allowing air pressure of the atmosphere to force water into the bottle until the pressure therein was atmospheric. From the change in liquid level the total amount of gas utilized by the bacteria or absorbed in the sample was calculated as a percent of the original total amount of gas.

The values obtained in columns A, B and C were then subtracted to give the values shown in columns B-A, B-C and A-C. Obviously, by subtracting the values A from B in column B-A, the process of the present invention is followed, Whereas if the values in column C are subtracted from those in column A, as done in column A-C, the process of U.S. Patent 2,349,472 (cited above) is being followed. It will be noted that only in column B-A, the process of the present invention, is there consistently a higher value for Samples 1-4 in the oil field than for Samples 5-10 taken in the dry area. Only in the column of the present invention is there no overlapping of values, and therefore only the present invention distinguishes between areas underlain by commercial amounts of hydrocarbons heavier than methane from areas in which any wells drilled would be dry holes.

Furthermore, it should be noted that in each of columns A, B and C taken alone, there is overlap between the values of Samples 14 in the oil field and Samples 5-10 in the dry area, so no one of columns A, B and C alone would distinguish between the oil field and the dry area. 7

There are three ways in which two of columns A, B and C can be combined, namely, B-A of the present invention, A-C of U.S. Patent 2,349,472 (cited above), and B-C which is not suggested by anyone. Of these three possible ways, that of the present invention is the only one which consistently distinguishes between the values obtained in the oil field samples and in the dry area samples, without over-lapping values.

While this invention has been described with reference to particular examples given for illustrative purposes, 0bviously this invention is not limited thereto.

Having described my invention, I claim:

1. A method for prospecting for petroleum deposits which comprises collecting a plurality of samples of soil at each of a plurality of points over an area under investiga tion, admixing a known portion of each of said samples with aqueous inorganic salt medium for hydrocarbon-consuming bacteria, subjecting at least one sample from each point to the action of a first atmosphere consisting essentially of a free oxygen-containing gas and methane, subjeoting at least one other sample from the same point to the action of a second atmosphere consisting essentially of a free oxygen-containing gas, an unsubstituted hydrocarbon gas heavier than methane, and substantially the same amount of methane as in said first atmosphere, and comparing the amounts of the hydrocarbon gas heavier than methane taken up by the samples from the difierent points exposed to said second atmosphere for a selected time in the range of about 1 to 2 weeks, after subtracting from the total gas taken up the amount of methane taken up by samples at the same respective points exposed to said first atmosphere in about the same selected time, to determine at which preferred points more hydrocarbon gas heavier than methane was taken up as an indication of the likely presence of petroleum deposits underneath said preferred points.

2. A method for prospecting for petroleum deposits which comprises collecting a plurality of samples of soil at each of a plurality of points over an area under investigation, admixing a known portion of each of said samples with aqueous inorganic salt medium for hydrocarbon-consuming bacteria, subjecting at least one sample from each point to the action of a first atmosphere consisting essentially of a free oxygen-containing gas and methane, subjecting at least one other sample from the same point to the action of a second atmosphere consisting essentially of a free oxygen-containing gas, a hydrocarbon gas heavier than methane, and substantially the same amount of methane as in said first atmosphere, and comparing the amounts of the hydrocarbon gas heavier than methane taken up by the samples from the different points exposed to said second atmosphere for a selected time between about 1 and 2 weeks, after subtracting from the total gas taken up the amount of methane taken up by samples at the same respective points exposed to said first atmosphere in about the same selected time, to determine at which preferred points more hydrocarbon gas heavier than methane was taken up as an indication of the likely presence of petroleum deposits underneath said preferred points.

3. A method for prospecting for petroleum deposits which comprises collecting a plurality of samples of soil at each of a plurality of points over an area under investigation, admixing a known portion of each of said samples with aqueous inorganic salt medium for hydrocarbonconsuming bacteria, subjecting at least one sample from each point to the action of a first atmosphere consisting essentially of air and methane, subjecting at least one other sample from the same point to the action of a second atmosphere consisting essentially of air, a hydrocarbon gas heavier than methane, and substantially the same amount of methane as in said first atmosphere, and comparing the amounts of the hydrocarbon gas heavier than methane taken up by the samples from the different points exposed to said second atmosphere for a selected time between about 1 and 2 weeks, after substracting from the total gas taken up the amount of methane taken up by samples at the same respective points exposed to said first atmosphere in about the same selected time, to determine at which preferred points more hydrocarbon gas heavier than methane was taken up as an indication of the likely presence of petroleum deposits underneath said preferred points.

4. A method for prospecting for petroleum deposits which comprises collecting a plurality of samples of soil at each of a plurality of points over an area under investigation, admixing a known portion of each of said samples with aqueous inorganic salt medium for hydrocarbonconsuming bacteria, subjecting at least one sample from each point to the action of a first atmosphere consisting essentially of air and methane, subjecting at least one other sample from the same point to the action of a second atmosphere consisting essentially of air, propane, and substantially the same amount of methane as in said first atmosphere, and comparing the amounts of propane taken up by the samples from the different points exposed to said second atmosphere for a selected time between about 1 and 2 weeks, after subtracting from the total gas taken up the amount of methane taken up by samples at the same respective points exposed to said first atmosphere in about the same selected time, to determine at which preferred points more propane was taken up as an indication of the likely presence of petroleum deposits underneath said preferred points.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A METHOD OF PROSPECTING FOR PETROLELUM DEPOSITS WHICH COMPRISES COLLECTING A PLURALITY OF SAMPLES OF SOIL AT EACH OF A PLURALITY OF POINTS OVER AN AREA UNDER INVESTIGATION, ADMIXING A KNOWN PORTION OF EACH OF SAID SAMPLES WITH AQUEOUS INORGANIC SALT MEDIUM FOR HYDROCARBON-CON SUMING BACTERIA, SUBJECTING AT LEAST ONE SAMPLE FROM EACH POINT TO THE ACTION OF A FIRST ATMOSPHERE CONSISTING ESSENTIALLY OF A FREE OXYGEN-CONTAINING GAS AND METHANE, SUBJECTING AT LEAST ONE OTHER SAMPLE FROM THE SAME POINT TO THE ACTION OF A SECOND ATMOSPHERE CONSISTING ESSENTIALLY OF A FREE OXYGEN-CONTAINING GAS, AN UNSUBSTITUTED HYDROCARBON GAS HEAVIER THAN METHANE, AND SUBSTANTIALLY THE SAME AMOUNT OF METHANE AS IN SAID FIRST ATMOSPHERE, AND COMPARING THE AMOUNTS OF THE HYDROCARBON GAS HEAVIER THAM METHANE TAKEN UP BY THE SAMPLES FROM THE DIFFERENT POINTS EXPOSED TO SAID SECOND ATMOSPHERE FOR A SELECTED TIME IN THE RANGE OF ABOUT 1 TO 2 WEEKS, AFTER SUBTRACTING FROM THE TOTAL GAS TAKEN UP THE AMOUNT OF METHANE TAKEN UP BY SAMPLES AT THE SAME RESPECTIVE POINTS EXPOSED TO SAID FIRST ATMOSPHERE IN ABOUT THE SAME SELECTED TIME, TO DETERMINE AT WHICH PREFERRED POINTS MORE HYDROCARBON GAS HEAVIER THAN METHANE WAS TAKEN UP AS AN INDICATION OF THE LIKELY PRESENCE OF PETROLEUM DEPOSITS UNDERNEATH SAID PREFERRED POINTS.