US2371637A - Method of prospecting for buried deposits - Google Patents

Description

March 2o, 1945. n E 'MC'DEgMcSTf 2,371,6377

METHOD OF PROSPECTING FOR BURIED DEPOSITS FiledJan. 22, 1940l 2 sheets-sheet 1 vez@ Z 5 March zo, 1945. E; MCDERMOT'T `2,371,637

' METHOD AOF PROSPECTlfNG FOR BURIED DEPOSITS Filed Jan. 22, 1940 2 Sheets-Sheet 2 Z4 ZZ Z2 Z6 i m ssame Irffregmzd wat Pafen'ied Mar.20,1945

METHOD oF .PnosPEcrrNG ron Binnen nEPosrrs l. Eugene McDermott, Dallas, Tex.

Application January 22, 1940, Serial No. 315,061

11 Claims.

This invention relates to a method of prospecting for buried deposits such as oil orgas. This application is acontinuation-in-part of my application Serial No. 257,328 filed February 20,

The invention is based on the discovery that high concentrations of combustible carbon exist in the earth near its surface'over buried accumulations of oil and gas.

I have found that the concentration of certain combustible carbon (as later defined) near the surface of the earth bears a significant relation to the location and size of buried oil and gas deposits. By determining the quantity of such combustible carbon present in the earth near the surface, and plotting the relationship of such determinationsit is possible to locate buried oil or gas deposits.

Prior investigators have determined the hydrofcarbon content of soil and preferably the gaseous hydrocarbon content. The particular meth-` ods used by such investigators, however, have been subjected to a number of disadvantages. In the first place they have been complicated and expensive to carry out. Moreover, such investigators failed to take'into account the fact that such hydrocarbons are generally liberated from vegetable matter. from the Vegetable matter are not first eliminated, thenI no true significant results can be obtained. Even if soil samples are taken at a distance of tengfeet or even more, it is still not certain that tbe soil sample will stillnot contain some vegetable matter carbon content. Moreover, according to prior investigators, the results obtained are rather difficult of measurement since quantities such as methane measure in parts per billion by weight.

The present invention avoids these disadvantages and constitutes a simple and inexpensive method of prospecting for buried oil deposits.

`'I'he method takes into account the presenceof vegetable matter carbon content in the soil samples and then eliminates such vegetable matter carbon content before the results are plotted.

v Moreover, according to the present invention it is possible to take yoursample at a much sha1- lower depth Which results in a great saving of time and expense. g Still further, the measurements in accordange with the present invention are made not in parts per billion but in parts per thousand.

Furthermore, if measuring for the gaseous content.' as some prior investigators have, there .is no feasible manner known whereby the vegetadeposited. .Where the rate of leakage from the If the hydrocarbons liberated K occurrence.

ble content may be removed from the sample without removing at least the major proportion of the gases. l It has been found that there are mineral concentrations near the surface of the earth which are caused in part by migration from greater.

depths. The gases` leaking to the surface will carry with them sorne water which is present in the substructure of the earth. In passing through a water rich in minerals appreciable quantities of these will be carried to the surface of the earth. En route some of the minerals will be buried deposit is greatest,- the concentration of minerals at or near the surface will also be greatest. This applies to the significant combustible carbon indicated above as Well as to mineral concentrations, it being understood that, strictly speaking, carbon is not classified as a mineral.

Because of the fact that heavier hydrocarbons accumulate in the cap rock, usually sha1e,'above the oil or gas deposit, the cap rock becomes less permeable to the passage of the hydrocarbon gases. This is especially so where chlorine is present as it tends tooxidize and polymerize the hydrocarbon gases which leak from the deposit and migrate to the surface, and thereby produces liquid and solid hydrocarbons which ll thev pores of the rocks just above the oil or gas deposit andrender such rocks impervious. This causes the migration to move to the edge of such impervious section, and then upwardly. The resultant effect is that the concentration of the significant combustible carbon near the surface directly above the oil or gas deposit may be normal, while around the edges there will be a band pattern of high concentration. There is a high probability that the oil or gas deposit would thus be located .at a central point spaced inwardly from the inner edges of the band pattern.

In some cases, however, the greatest concentration at the surface will be directly over the oil or gas deposit. This situation occurs, for example,lwhen folds in rock shale have caused fissures over the top of the accumulation. This is a rare It is. of course, true that there will be small variations in; the concentrations" at the surface in a given -locality which mayresult from recent leaching such s may occurl from drainage because of the particular topography of the area,

in many areas to be due to the presence of buriedV petroleum deposits and as a rule the small variations due to leaching are -negligible as compared to the larger variations resulting from the presence of buried petroleum deposits.

I have discovered that by systematically taking a plurality of samples of the earth near the surface at predetermined locations and then analyzing each sample for its significant combustible carbon content, and then plotting the results, either in prole or plan, or both, it is possible to determine the probable location of a vburied deposit. Such a procedure in most instances will disclose a band pattern of a high concentration area, as mentioned above, or occasionally a high concentration area directly above the oil or gas deposit, in cases where the folding is rather intense. v

Generally speaking, I analyze the soil samples for their significant combustible carbon content, after which I plot the results of such analyses. Where the results of the plotting, either in plan or in profile, or both, show a band pattern of high concentration surrounding an area of low concentration, or a high concentration area bounded by areas of low concentration as caused by a fissure, it is highly probable that anA oil or gas deposit can be located. In the yfirst instance the oil or gas deposit should be located in the area of low concentration which is surrounded by the band pattern of high concentration. In the second instance, the oil or gas deposit is probably directly beneath or directly adjacent the area of high concentration.

'In accordance with the invention I have de points may be one-eighth mile.. In some cases it may be desirable to use a smaller or larger interval. The vertical scale in the figure indicates the concentrations of significant combustible carbon in one-tenth of a percent by weight of sample. High concentrations are shown to occur at two spaced intervals. The proper location of a well to test the results would be between these two high concentration areas. v

In Fig. 2, the results of a survey are shown in plan. The numbers represent concentrations in one-tenth of a percent by weight of soil samples. The area of high concentration shown in Fig'. 2 forms a band pattern of the type discussed above. In accordance with the theory of the invention, Aand asveried by actual surveys made in accordance with the invention, since the area of high concentration shown in Fig. 2 will occur l over the edges of the buried deposit, it is obvivised a method which is simple and comparatively accurate. The invention takes into account that near the earths surface there may be carbon present in vegetable matter, the presence vof which carbon,'of-course, is not indicative of an oil or gas deposit. Such carbon content is negligibly small in some areas if thesoil sample is taken deep enough, say ten feet, but even if there be some there in vegetable matter the method employed by me eliminates any such carbon and results in a true reading .of the significant combustible carbon due to the presence of buried oil or gas deposits only. In accordance with the above dictates, th principal object of my invention is to provide a convenient method of prospecting for buried oil and gas deposits by measuring soil samples for their significant combustible carbon content and then plotting the results in prole and plan to indicate the probable location of such deposits.

Another object of my invention is to provide such a method which will eliminate from conslderation any vegetable matter carbon and still permit the measurement of appreciable quantities of the significant carbon content.

Still another object of theinvention is the provision of such a method as'will permit the use of samples taken from holes of shallow depth.

These and other objects and advantages will be more apparent from the followingA description and claims when read in'conjunction with the accompanying drawings in which:

. Fig. 1 is a diagrammatic representation of an area which has been plotted in prole.

Fig. 2 is a diagrammatic representation of an area which has been plotted. in plan.

Figs. 3.and 3a together comprise a diagram.

matic showing .of an apparatus for testing soll samples for their significant combustible carbon content in accordancewith the invention.

In Fig. 1, the location of the samples is shown horizontally where the interval between sampling ous that the proper location for a test well should be in-the low concentration area which is inside the high concentration area. In the area of high concentration, values of greater than 5, 6 and 7 tenths of a percent are frequently found, whereas outside of this area values of l and 2 tenths of a percent usually exist. The ratio of the values in the high concentration area to those outside of it is, therefore, very appreciable.

v For a reconnaissance survey samples may be taken at approximately one-eighth mile intervals along approximately parallel lines about one mile apart. Fordetail work lines one-half mile apart will generally suffice. It is not requisite, of course, to take the samples at regular intervals. In general for reconnaissance surveys, a density of four points per s quare mile will be sufficient.

By soil sample is meant any sample of the earth taken near its surface. It has been found that a depth of ten feet is quite satisfactory, though samples may be taken at a smaller or greater depth.- The exact depth of sampling is not critical, but where, because of the particular topography drainage has been heavy, or where there has been excessive weathering or leaching, the samples should be taken a sulicient distance below the surface 'to obtain soil not materially aiected by such conditions. The same holds true where the earth at or near the surface may contain surface vegetable matter carbon, although themethod I employ eliminates this carbon from consideration while permitting the measurement of appreciablequantities of the signcant carbon content. Vegetable matter carbon as herein referred to is carbon contained in the parts of plant growths as severed from a plant or as found in the soil in various stages of decomposition. It may be free carbon or chemically combined carbon of vegetable origin.

. The chemical or physical natures of the other significant or combustible carbon in the soil, from whichv carbon determinations are made for obtaining plotting data, are not denitely known or understood. It is merely known that in the present process the latter carbon, combined or uncombined, whichever it may be, is apparently less readily combustible and is removable from a soil sample at a higher temperature than that required to remove vegetable matter carbon or the 'more readily removable carbonaceous matter.

Y preferred.

eliminatedfrom the sample between' .500 andl cases ltemperatures up to 550 C. may be employed. The oxygen is blown overthe sample in carbonate,. sodium bicarbonate or potassiumbi- 4 carbonate that may be. present. The C02 lib, 'erated thereby will thus be removed. Usually these materials are present in negligible quantiv ties, but if present they will be eliminated.

In some areas the surface vegetable contami- V nation is negligible, and in such areas the pre-v heating need not be employed, though generally.

it is advisable to preheat since it is never certain thata sample taken at ten feet or below may not .have some vegetable contamination therein. The reason for raising the temperature on preheating as high as possible is to make sure that magnesium carbonate aswell as the end products of vegetable matter such as coal are removed. While ,such preheating may remove some of the signincant carbon, this preheating makes the final determination more definite as such determination will not include a determination of the signicant carbon which hasl been removed.

A fter being treated as described above for approximately one hour (the time maybe varied) the sample is next placed in an oven at a temperature in the neighborhood of 600 C. and a gentlel current of oxygen circulated over it for a period of about one hour. Here again the time may be varied. The range between 500 C. and 600 C. has been found to -be quite satisfactory, though it is understood'that reasonable'variations are permissible. Preferably the range should be between 550 C. and 600 C., and as a practical matter temperatures nearer to 600 C. are The significant carbon content is 600 C. 600 C. is the practical upper limit because above that temperature calcium carbonates and the other' carbonates may be liberated.

The stream of oxygen will combust the re, maining significant carbon in the sample and willv carry the C02 formed with it. This stream of oxygen carrying the CO2 is then passed through a tube containing ascarite which will adsorbthe CO2. The ascarite tube is weighed before and after the passage to determine the CO2 formed lfrom which the significant carbon content ofthe sample may be determined.

If there is water vapor in the sample, it may be removed by passing the stream through a tube containing a desiccating agent such as calcium chloride before passing through the ascarite tube.

Instead of combusting at the higher temperature, the'same sample that has been combusted at the lower temperature, duplicates may be used combusting one at 'the lower temperature and the other at the higher temperature, and computing the difference in the ICO2 determinations.

It has beenl found that different types of soil 1 will adsorb and polymerize the hydrocarbon gases at diierent' rates and therefore it is desirable in some cases to make a correction for the com lcorrection is'desirable.V i n One way, though-not the only way, of accomplishing this is to place a measured quantity of they sample in a tube and pass a measured quantity of a hydrocarbon gas, preferably an unsat- 'urated gas such as ethylene, through the sampleV in a measured time. A gently moving stream for a days time will suffice. This gas will be adsorbed and polymerizedto heavier hydrocarbons in the liquid phase. The quantity of such heavier hydrocarbons formed will 'be a measure of the combined adsorption and polymerization abilities of the samples. The quantity of hydrocarbons heavier than ethane and ethylene formed may be measured in a standard gas fractionating appa-- ratus. In such an apparatus the sample is heated at approximately 100 C. to drive off theA hydrocarbons formed. Water vapor and CO2 are removed. Those-heavier than ethane may be condensed in a trap at a temperature of minus 150 C. By .reducing the temperature of the trap they will evaporate into the evacuated apparatus. They may then be burned and the quantity of CO2 formed may be measured. This quantity will be a direct measurement of the heavier hydrocarbons formed and consequently of the combined adsorption and polymerization ability of the sample. Before the above measurement is made, the sample should be heated at a temperature of 600 C. to remove any hydrocarbons present.

If some sample is taken as a base of reference other samples may be corrected by multiplying the significant carbon content measurement of the various samples by a factor which is the ratio of the heavier than ethane hydrocarbons formed in this reference sample to those formed in any of the others'ample's to be corrected.

In Figs, 3 and 3a there has been illustrated diagrammatically an apparatus for testing the soil samples for the significant combustible carbon content. In this figure the reference numeral ,I0 Aindicates an electric oven which is connected by wires I2 to a suitable control mechanism I4 connected with asource of current. A temperature indicating-instrument IB is connected by wires I8 to a thermo-couple 20 disposed in the oven.

The oven has a large tube 22 passing therethrough and in this tube is disposed the Soil sam- SOUS.

ple in a receptacle 24. Also in the tube is a piece of copper oxide gauze 26 and a piece of asbestos 28 impregnated with FeSOi, `which has previously been ignited to FezOs. The elements 26 and 28 act asl a catalyst to assure the complete combustion of Athe material in the sample. Y

Leading to the tube 22 from the left is a conduit 30 adapted to be connected to a` source of oxygen not shown.l A manometer 32 and a valve 34 are 4disposed in the conduit for obvious rea- The conduit 30 is connected by a removable tube 36 to a U-shaped tube 38 which in turn leads directly to and is removably connected with the tube 22 which passes through the oven. The U-tube 38 has ascarite and calcium chloride therein separated by layers of cotton (see the legend) .l The ascarite and the calcium chloride is for the purpose of lremoving water and any COz which may be present in the oxygen supply.

It is assumed that prior yto treatment in this apparatus the' soil sample has rst been pre heated in the manner described `above to remove the carbon contained in the vegetable matter and also to remove the CO2 contained in anymagnesium carbonate. sodium bicarbonate or potassium bicarbonate thatmay be present.

It will be manifest from the drawings that when the valve 34 is opened oxygen will now through the conduit 30, the tube 36, the tube 38 and then into the tube 22 passing through the oven. In the tube 22 the oxygen passes through the copper oxide gauze 26 and thence over the soil sample in the receptacle 2G. Theoxygen then passes the impregnated asbestos 28.

The sample should remain in the oven for approximately an hour although the time may be varied. The temperature should be in the neighborhood of 600 C. As stated above, if a temperature greater than 000 C. vis used, CO2 from the calcium carbonates and other carbonates may be liberated. The stream of oxygen will combust the remaining significant carbon in the sample and will carry the CO2 formed with it as it leaves the tube 22.

To the right of the oven i in the drawing gures (see Fig. 3a), there are a series of connected but individually removable U-shaped tubes 40, 42, M, 4E and 48. These tubes are supported` from a support 50. The arrangement is such that oxygen, with the CO2 leaving the oventhrough the tube 22, passes successively through these U-tubes. sage is a liquid seal 52.

In the first of the tubes, namely, tube 110, the oxygen and CO2 contacts with zinc particles disposed in the tube. The zinc particles remove acid fumes. The next tube l2 is lled with calcium chloride which removes water vapor. 'I'he third tube Q6 and the fourth tube t6 are each lledwith ascarite and calcium chloride to take up the CO2. The last tube 08 has calcium chloride therein to prevent water vapor from the liquid seal 52 from` reaching the tubes it and 5.

At the end of thev pas- In carrying out an analysis of a sample, thev U-tubes 44 and 06 are weighed before and after the stream of oxygen carrying the CO2 has been passed therethrough. It is thus possible by computing the diierence to obtain an indication of the amount of CO2 present in the sample being tested. This indication is then plotted in the manner described above. The CO2 values which which is in such form as to be oxidizable to car bon dioxide. This, of course will not include the carbon contained 1n carbonatos.

. procedure may be made while still remaining within the invention. Other methods and apparatus for testing the individual soil samples may be employed. The invention should not be limited to the exemplary disclosure given except withinthe scope outlined by the .following claims.

I claim:

1. In the art of exploring for buried oil or gas deposits from which leakage occurs, the method of prospecting for the location of such deposits which comprises, taking a soil sample from each of a plurality of points spaced a predetermined distance apart over a predetermined area of the earths surface at depths depending upon local conditions and suicient to obtain soil not materially aiected by excessive drainage, weathering or leaching, heating the samples, substantially free from vegetable matter carbon and containing otherv less readily combustible carbon matter found in said soil, in the presence of oxidizing gas containing free oxygen, converting to carbon dioxide by the resulting combustion substantially only said less readily combustible carbon matter in a measurable quantity in a sample, determining substantiallyonly .carbon so converted, applying to the carbon values thus determined a correction for the adsorption abilities of the respective samples, and plotting from the results of the corrected determinations contrasting high and low values representing relative measures of said latter carbon content against distances between corresponding sample locations to show a configuration indicatingl the probable location of the buried deposits.

2. In the art of exploring for buried oil or gas deposits from which leakage occurs, the method of prospecting for th-e location of such deposits which comprises, taking a soil sample from each of a plurality of points spaced a predetermined distance apart over a predetermined area of the earths surface at depths depending upon local conditions and sufficient to obtain soil not materially affected by excessive drainage, weathering or leaching, heating the samples, freed from vegetable matter carbon and containing other less readily combustible carbon found in said soil, in the presence of oxidizing gas containing free oxygen at a temperature at which said latter carbon is removed by oxidation from the soil samples but; below the temperature of decomposition of calcium carbonate, and determining the latter carbon content, whereby valuable information is obtained concerning the location of said buried oil or gas deposits.

3. In the art of exploring for buried oil or gas deposits from which leakage occurs, the m'ethod of prospecting for the location of such deposits which comprises, taking a soil sample from each of a plurality of points spaced a predetermined distance apart over a predetermined area of the earths surface at depths depending upon local conditions and suicient to obtain soil not materially affected by excessive drainage, weathering or leaching, subjecting the samples containing vegetable matter carbon and other less readily combustible carbonaceous matter to apreliminary heating in the presence o f oxygen gas at a temperature at which Vegetable matter carbon is oxidized and removed from the samples but at which said other less readily combustible carbonaceous matter remains in said samples, removing thereby said vegetable matter carbon substantially completely, subjecting the said samples to further heating in the presence of oxygenat a higher temperature than in said vpreliminary heating but below the temperature of decomposition of calcium carbonate, thus removing carbon of said other carbonaceous matter from the'samples and determining the latter carbon content, whereby valuable information isobtained concerning the location of said buried oill or gas deposits.

4. In the art of exploring for buried oil or gas deposits from which leakage occurs, the method of prospecting for the location of such deposits which comprises, taking a soil sample from each of a plurality of points spaced a predetermined distance apart over a predetermined area of the earthssurface at depths depending upon local conditions and suicent to obtain soilnot mate- .combustible carbonaceous matter to a preliminary heating in the presence of oxygen gas at a temperature up to but not exceeding substantially 550 C. at which vegetable matter carbon is oxidized and removed from the samples but at which said other carbonaceous matter remains in said samples, removing thereby said vegetable matter carbon substantially completely, subjecting the said samples to further heatingin the presence of oxygen at a higher temperature than in said preliminary heating but below the'temperature of decomposition of calcium carbonate, thus removing carbon of said other carbonaceous matter from ythe samples and determining .the latter carbon content, whereby valuable information is obtained concerning thelocation of said buried oil or gas deposits.

5. In the art of exploring for buried oil or gas deposits from which leakage occurs, ,the method of prospecting for ,the location of such-V depositsl which comprises, taking a soil sample from each of a plurality of points spaced a predetermined distance apart over a predetermined area of the earths surface at depths depending upon local conditions and suflicient to obtain soil notmaterially affected byexcessive drainage, weathering or leaching, subjecting the samples to a preliminary heating in the presence of oxygen at a 8. In the art of exploring for buried oil or gas deposits from which leakage occurs, the method of prospecting for the location of such deposits which comprises, taking a soil sample from each of a plurality of points spaced a predetermined distance apart over a predetermined area ofthe earths surface at depths depending upon local conditions and sufficient to obtain soil not materially affected by excessive drainage, weathering -or leaching, heating the samples, substantially freeffrom vegetable mattercarbon andcontaining other lessreadily combustible carbon matter found in said soil,V in the presence of oxidizing gas containing free oxygen, and converting to carbon dioxide by the resulting combustion substantially only said less readily combustible carbon matter in a measurable quantityin a sample, and determining substantially only carbon so converted,

whereby valuable information `is obtained concerning the location of said buried oil or gas de- 9. In the art of exploring for buried oil orgas 'deposits from which leakage, occurs, thel method of prospecting for the location of such depositsV which comprises, taking 'a soil sample' from each of a plurality of points spaced a predetermined distance apart over a predetermined area ofthe earths surface at depths 'depending upon local conditions' and suflicient to obtain soil not matemperature ranging substantially from 400 C. 'I

to 500 C. to. removeA vegetable matter carbon, subjecting the said samples to further heating in the presence of oxygen at a temperature ranging -substantially from 500 C. to 600 Cr, to remove carbon remaining after the rstheating from the samples and determining this carbon content, whereby valuable information is Aob-v tained concerning the location of said buried oil or gas deposits.

6. In the art of exploring for buried oil or gas deposits from lwhich leakage occurs, the method of prospecting for the location of such deposits whichcomprises, taking a soil sample from each of a plurality of points spaced a predetermined distance apart over a predetermined area approximately ten feet below the surface of the earth, subjecting the samples to a preliminary heating in the presence of oxygen gas at a temperature of substantia1ly`500 C. for approximately one hour at which vegetable matter carbon is oxidized and removed from the samples- 4but at which other less readily combustible carbon remains in said samples, removing thereby said vegetable matter vcarbon substantially completely, subjecting the said samples to further heating inthe presence of oxygen at a tempera- Y ture of substantially 600 C., thus removing said other less readily combustible carbon from the samples and determining this carbon content, whereby valuable information is obtained concerning the location of said buried oil or gas deposits. y

7. In a method of prospecting for petroliferous deposits in which samples of soil are collected in the area to be investigated and are analyzed for combustible carbon content of less readily combustible carbon matter than vegetable vmatter carbon in said samples and which is indicative of the presence of oil in a subterranean formation in said area, the step of determining the relative sorptivity of the various samples, whereby the data. obtained from such determinations may be utilized in the interpretation of the results.

vter'ially affected by excessive drainage, weathering or leaching, heating the samples, freed from vegetable matter carbon and containing other less readily combustible carbon foundin said soil, while oxidizing the latter carbon in the samples to convert substantially only the latter carbon to carbon dioxide in a measurable quantity, determining quantitatively the carbon dioxide emanating directly from the samples, whereby valuable information is obtained concerningthe location of said buried oil or gas deposits.

10. In the art of exploring for buried oil or gas deposits" from which leakage occurs, the method of prospecting for the location of such' deposits which comprises, taking a soil sample from each of a plurality of pointsspaced a predetermined distance apart over a predetermined area of the earths surface at depths depending upon local conditions and suflcient to obtain soil not materially affected by excessive drainage, weathering or leaching, subjecting at least a portionof each sample containing vegetable matter carbon and other less readily combustible carbonaceous matter toa preliminary heating in' the presence of oxygen gas at a temperature at which vegetable matter carbon is oxidized and vremoved from the samples but at which said other less readily combustible carbonaceous matter remains in said samples, removing thereby said vegetable matter carbon substantially completely, subjecting at least a portion of each sample to heating in the presence of oxygen at a higher temperature than in said preliminary heatingbut below the decomposition temperature of calcium carbonate, thus 11. In the art of exploring for buried oil or gas I deposits from which leakage occurs, the method of prospecting for the location of suchl deposits which comprises, taking a soil sample from each of a. plurality of points spaced apredetermined distance apart over a predetermined area of the earths surface at depths depending upon localconditions and sufiicient to obtain soil not materially aiTected by excessive drainage, weathering or leaching, subjecting a first portion of each sample containing vegetable matter carbon and other less readily combustible carbonaceous matter to a heating in the presence of oxygen gas at a temperature at which vegetable matter carbon is oxidized and removed from said rst portion but at which said other less readily combustible carbonaceous matter remains in said samples, removing thereby from said rst'portion said vegetable matter carbon substantially completely, subjecting a second portion of each sample to a

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