US2370793A - Geochemical prospecting - Google Patents

Description

Billion March 6, 4 L. oRvrrz 2,370,793

' GEOCHEMICAL PROSPECTING Filed Match 10, 1941 4 Sheets-sheaf. 1

4 7 Port: Heavy Hydrocarbons par :0

30. par Gem per 2000. Nulluon poo per Mil

" looo- I N VENTOR ATTORNEY March 6,1945. 7 L,IHORIVITZI 2,370,793

GEOCHEMICAL PROSPECTiNG Filed March 10, 1941 4 Sheets-Sheet 2- Heavy Hydrocarbons Parts w per Billlon m carbonates per cent w l3; 0 l J Pam per

Million 4'3, INVENTOKJ per I00 I} Billion March 6, 1945. L. Hoiwn'z 2,370,793

' GEOCHEMICAL PROSPECTING Filed March 10, 194a. 4 sheets-sheet 3 Pam \ IS l6 l1 l0 I9 20 ll 22 23 24 2B 20 21. 20 '29 30 than Hy drncarbons Parts P" 200 Billion I5 l6 I! I! lo 20 :l 22 as 2415 26 a! as 29 3o.

. I lnorq umc carbonates per 0on1 t INVENTQR.

' BI 32 33 34 35 I. S! 30 3. J4

ATTORNEY Mmh'6; 1945. I 1.. HORVITZ -2,37Q,793

GEOCHEMICAL PRdSPECTINQ Fileduapch 10, 1941 4 Sheets-Sheet 4 INVENTOR.

v Arm n-L Patented M. e, 19 5 t UNITED STATES PATENT OFFICE 2,:m;'19a v am Horvltz,

Houston, Tex asslgnor Rosaire, Honston "lex to Esme E.

Application March 10, 1941, Serial No. 382,606 a at Claims. (oi. 23-230 The present invention relates to a process of geochemical prospecting.

More specifically, the, present invention relates to geochemical prospecting for carbonaceous deposits, such as oil, gas, coal and the like, and for structures in which such deposits may occur by the quantitative detection of leakage from the deposits themselves and from the'rocks in which.

they are contained. Such leakage results in a deposition in the soil of evidence of the leakage and such evidence may be detected and measured by analysis of the soih This invention relates "to the broad subject matter of copending applica tion Serial No. 107,497, filed October 24, 1936, and

entitled Geophysical prospecting method.

The search for oil fields by geochemistry has heretofore been conducted by seeking actual evi-., dence' of leakage from the-deposits themselves.

It has been found, however, that inorganic substances not heretofore regarded as being related to the deposits themselves are indicative of prox-' imity to buried structures which l'nay'contain the sought deposits. Thus, analyses of soil samples taken near the surface of theearth have resulted in finding variable concentrations, 01' chlorides,

the variations corresponding generally with a known structure; Many other inorganic sub' stances are similarly indicative. Actual investigation has revealed that carbonates, bicarbonates, sulfates, sulfides,..halides, b'asicit acidity, total acid soluble and total water soluble constituents,

etc., are suitable indicators. Practically any in'-- organic soil constituent may be'selected as the significant constituent. The soil maybe exainined quantitatively for cations or anions. In certain'locations examination of the soil for yields-significant data; In other locations, some other ion may. prove significant and this. will ordinarily be relied upon for purposes of interpretation. Usually the content of a number of' ing which may economically be employed to evaluate large areas relative to future exploration programs.

Usually, the halo phenomenon originally observed in connection with analyses for the con-' around the producing area. Thus, when a halide profile is obtained having a single hump rather than the double hump, which usually characterizes a profile which is taken across an area which yields the halo pattern, it will be found that the hump on the halide profile will fit in the low space between the double hump on the profile shown by Y hydrocarbons and other constituents. On infrequent occasions this departure from the convena. rule give the-conventional pattern. This deviation in pattern emphasizes the desirabilityin- -practice of analyzing the soil samples over a given area for a plurality of constituents so that the anomalies appearing in the pattems resulting from the individualconstituents can be compared and interrelated to produce acomplete picture of the area.

' In some areas it has been found that certain constituents do not yield distinctive patterns.

' Usually this failure to give a pattern over a proinorganic constituents in soil samples from a given area is determined and ordinarily corre- 'lationbetween the majority of the constituents determined will be found.

-vide a method of surface soils for-evidence therein of anomalous mineralizationand secondary salt deposition.

' Anpbiect, of the present invention is to progeochemical prospecting for buried structurecapable of containing valuable deposits by the examination of surfaceandnear technique would be in order.

ducing area will be "confined to one' inorganic constituent and the characteristic pattern will be shown by any number of other constituents which may be determined.- .Thus, in prospecting according to .the present method it would beunwise to condemn an area because one inorganic constituent failed to give a characteristic pattern, but the patterns of other -constituents should be obtained so that it can be determined whether or not'a significant pattern is obtained with the majority of the constituents. Evenif a, significant pattern is obtained with only one'constitu-i ent, :which would indeed be a rare case, further exploration of thearea by' the hydrocarbon general nature. facehave such a small dip that collection of the Generally, it has been found that the consistency of ,results is better in samples of soil taken at a depth of several feet since topsoil samples are affected by leaching by meteoric waters, local fertilization, and the like. A compromise between the economy demanded by a reconnaissance method and the reasonable accuracy demanded by any exploration method indicates that a preferred form of the inventionis practiced by the collection of samples from a depth of about ten feet, though, of course, the depth may be varied depending upon general conditions-of climate, nature of soil, vegetation and agricultural utilization. It will be understood that all samples in a given area should preferably be collected at the same depth. I 1

In actual practice the soil samples are'eollected at the same depth over a given area where this is possible. In some/areas where there. are outcroppings of rock or other'natural impediments it often happensthat the sampling depth selected cannot be continued throughout the whole area.

For example, where samples are taken at eight feetnt the start, it might develop later that in some certain spot it is only possible to penetrate six feet. In such cases it is preferred to take the majority of samples at the depth originally selected and take the remaining samples at as great a depth as they can be obtained. In any case, the depth at which each sample is taken is noted on the sample container for the information of the interpreter. y

.l'he practice is often followed of determining the variation with depth of the significant constituent in the sample holes at selected points along a profile. For example, in scattered holes in the area under investigation, samples are taken so as to determine the variation of the si gniflcant constituent with depth. Then if all the atone or two foot intervals in the sample hole P asvoaes Analyses 1. Halides:

o. Leach (or extract) with (distilled) water; a

/ (refluxing known weight of any volume of H20). b. Measure theHaO extract.

soil with c. Titrate with standard AgNOa solution using potassium chromate (K2CI'O4) as an indicator. 2. Bicarbonates:

' {1. Heat and dry sample. i

I). eat at higher temperature below decomposition temperature of carbonates. say 300 C. to decompose bicarbonates.

0. Measure CO: evolved; or titrate with standard HCl to phenolphthalein endpoint, and then titrate to methyl orange end-point. Where samples shownegligibie quantities vof soluble carbonates, titration to phenolphthalein may be omitted.

3. soluble sulfates: I

0. Extract with distilled water.

and-titrate unused Each with NaeCOs. using phenolphthalein as indicator; or c. 'Iitrate water extract with BaCla usin tetra-hydro-quinone as indicator. 4.; Sulfites:

a. Titration of water extract with standard potassium iodate and KI mixture, starch 8. carbonates (and bicarbonates):

minations will aid the operator in deciding at what depth less than 12 feet he can safely take samples where they cannot be obtained at 12 feet.

\ Where there is along a profile passing through the well. In this way the best depth at which to collect samples in already a producing well in an ,area under investigation it is advantageous to make depth determinations in each sample hole Where are is not excessive dippin'g of the formations it lends to uniformity to collect the samples out of the same formation so that the samples will have, as nearly as possible, the same Ordinarily strata nearthe sursamples at a uniform depth will result incollection of the samples in the same strata. Should it transpire that, wherethe samples are being analyzed for a constituent, such as calcium, and

during the collection of the samples 3. deposit high in calcium, such as limestone. is encountered, thev operator will naturally take this into account and large incressein the calcium content in samples taken in this depodt will be taken into consideration injhe interpretation of the results; The actual analysis of the collected soil samples may follow any acceptable quantitative procedure,

a. Decompose with acid and .measure C0:

evolved by volume or weight.

,9. sulfides:

o. Decompose with-acid and measure the evolved H28 as by precipitating the sulfide of a selected metal from a solution of one of its salts I and weighing the precipitate.

The constituent selected for determination usually occur as a minor constituent-of the soil sample, and may be present only in minute amounts." In some areas, however, the constituent selected as the significant constituent may constitute a very substantial-portion of the. soil sample. For example,-inone main-which the samples were collected'from caliche deposits and the variations in acid-soluble constituents, largely carbonates, were determined, an-anomaly was obtained' on the basis of the 'acid-soluble'content which corresponded substantially with the anomaly prepared byanalysesof samples for hydrocarbons. In many of these samples the acid-soluble components constituted more than by weight of the sample. It is preferable to examine. the

samples for those constituents which are readily soluble in. water or common inorganic acids.

A feature of considerable importance of the i present invention a the discovery of the fact that a in soil samples containing" carbonates, it appears matter but also inorganic compounds. For ex-' that the carbonates envelope not only organic ample, when it is desired to soil samples fol-chlorides, ordinary extraction of the sample end-point b. Add excess-Bach to extract to ppt. S04

. from the method ators of the present method samples were taken about 1,000 feet apart and a samples were taken at a depth of twelve feet. The samples were ,collected by field men who,

measured to determine the carbonate content or followed by titration, as indicated above, may

revealonly negligible amounts of chlorides. If

the sample. Another- 25 grams or so was digested with water and .allowed to stand for 12 to 24 hours and the extract'so obtained was titrated, separate portions being used, for halides and sulphates. Theportion which had. been treated with acid for the carbonate determination was then washed with water by a series of mixings 'and decantations until the finely divided mateof the type desired. This same acid treatment is advantageous for analyses for all inorganic constituents.

The usefulness of this method has been demonstrated in practice in that when exploration has been conducted in areas also explored by other methods, the method was found to give information 'similarto that obtained by other f methods. It is not intended to imply that it gives substantially the same information in all cases as geochemical exploration by analysis of soil samples forQsay, ethane. The patternsresulting of the present invention thus; far Beara similarity to those resulting from the hydrocarbon technique.

In order to demonstrate the resemblance between the patterns obtained-by the procedure of the-preseiit invention and those obtained by the rial, representing clay, was removed and the remainder was dried and weighed to give a measure of the sand content of the soil.

A separate portion of the original sample was then subjected to analysis for hydrocarbons ineluding ethane and heavier by the method described in copending application Serial 'No. 183,960, filed January 8, 1938. The hydrocarbons so determined were expressed in parts'per billion by weight of the sample. I

The profiles shown in Fig. 2 were made by plotting content of the significant constituent against hydrocarbons sample locations. Profile No. I is the hydrocar-- bon profile designated onthe drawings as. Heavy to. mean ethane, propane, butane, etc., profile No. 2 is the'carbonateprofile, profile No. 3 is the sulphate profile, and profile No. 4 "is the halide profile. It will be noted that in profile'No. I the first hump starts between analysis of samples for hydrocarbons, profiles of areas obtained by actual exploration bylthesemethods are shown in the accompanying drawings in which-- I r Fig. 1 is a plan showing the sample locations along two lines, A-A' and 3-3, in an area explored and the portion or the halobrought out a by these two lines;

Fig. 2 is a series of profiles obtained by analyses Of the samples taken along the line A-A' by determination of various constituents; Fig. 3 is a similar set of profiles obtained by of; the background samples, that samples, were all 10 or lower.

corresponding analyses. of the samples taken along the line 3-8"; Fig. 4 shows two profiles obtained by analyzing samples collected along parallel lines in a given area for ethane and higher hydrocarbons;

Fig. 5 is a pair of profiles obtained by analyzing the sanie samples for carbonates;

Fig. 6 is a map of an area which was 'prospected to determine the limits of production in a known field by collecting samples and analyzing them .for their content of bicarbonates.

rin is shown in Fig. 1 a plurality of sample locations along two lines,,

Refer g to Figs. 1-3, there A'-A' and B'B', the former being numbered 1-16 inclusive, and the latter 17-32 inclusive. These samples were taken in which there had been no drilling and in which there was no known anomaly so far as the (mardrilled holes twelve -feet deep, 'sco oped about a thereof. :For examplefa portiorthaving a weight ot'about grams was subjected to a series of analytical steps to determine the inorganic constituents.- This portion was first dried and about 10- grams 01' it was treated with hydrochloric acid and the volume oi carbon dioxide given cit was virgin territory in were aware. These sample 3 and 4 and endsbetween samples 6 and 7, while the second hump starts between samples 11 and Hand ends between samples 15 and 16. In making this profile, samples containing more than 10 parts per billionby weight of hydrocarbons were considered high, while samples containing less than 10 parts per billion by weight were conside ed low. It may be mentioned here that the valu 10 was selected because the values is, of the low The profile of the carbonates corresponded closely to that of hydrocarbons.- 'Here, the ordinates are expressed as percentage by weight of the sample. 'Ihe'signiflcant quantity may be considered as anything in excess of 5%, and in lion by weight of the sample. Herethe general pattern'of the other profiles is followed but it is bons and carbonates, however, is larger than that compacted toward the center. It will be noted that samples 7 and 11 are high, and it is between these samples that production isindicated by the hydrocarbon and carbonate profiles. The area of production indicated-by the hydrocarindicated-by the sulphates. a

lgaimin the case of the halides, a departure from the conventional pattern is found. vIn this case also, the ordinates are expressed in parts .of halides per million-by weight of the sample.

pint of soil from the bottom of the hole, placed It will beobserved that high concentrations of halides seem tofall in the zone of low hydro-v carbon. concentrations, with the exception of sample 10.- It is noteworthy that inv this'profile also the space between samples 7 and 11 is anomalous. Taken by itself, the halide profile would not be cohclusive, but would indicate-a.

zone of interest and, whentaken in conjunction with the hydrocarbon and carbonate profiles, serves to define that zone. Experience has demonstrated that withiphloride profiles, either a high over production or a highin a halo zone around the production may be expected. This gravity meter maps.

. second hump part of a halo.; Accordingly, the

and 19 andends between samples 21 and 22.

the right side begins between and, ends between samples 3 be observed that sample 8 is while the bump on samples 2'? and 28 and 31. It is to conimon to lines A;-A and 3-3. Numeral 8 designates the'carbonate profile along 3-3, in

whichthe ordinates represent percent by weight. of the sample. As was the case with respect to carbonate profile bears a close profile A-A', the resemblance to the hydrocarbon profile. shifted slightly to the Ian, as a whole.

Numeral I designates the sulphate profile It is pattern as the carbonate and hydrocarbon profiles. The ordinates in this case represent parts per million by weight. It will be observed that the halo is slightly displaced to the right with respect to the hydrocarbon profile.

Numeral 8 designates the halide profile along BB', in which the ordinates'represent parts per million by weight of, the sample. This profile bears the same relationto the hydrocarbon profile as exists between profile 4 and profile i. It

indicates an area of interest between samples 22 and 27-. In these profiles along the abscissa correspond to the distances between. sampling points'inFlg. 1. On the basis of the contour similar values in much the same way as equivalues obtained fromthe various samples,

potential lines are drawn on potential maps 01,.

the earth's surface, and isogr ams are drawn on By connecting the point at which the first hump in profile I began with the point at which the first bump in profile 5' began, line B'was drawn. Similarly, line Ill connects the pointat which the first hump ends in profile l with the corresponding'point in profile 5. Again, line ll connects the point at which the began in profile I with the corresponding point in profile ii, and line H connects the point at which the second hump ended in profile I with the corresponding point on profile 5.

It will be seen that lines 3 and I0 appear to be boundary lines of one part oi a halo, and lines H and 12 appear to-be boundary lines of another' the line 3-3. Here per billion by weight of the. distances between points producing area asvaves north and south over a given area. Sample locations are indicated by the. numbered points along the abscissa. The ordinates represents parts per billion by weight of the samples of hydrocarbons, including ethane, propane, butane, etc. (referred to collectively on the carbons). These samples were all taken at a depth of 12 feet, in the manner previouslyidescribed.

In the profile designated by numeral 41 the value selected as the dividing line between sig- 7 along 3-3, which follows the same general nificant and nonsignificant quantities of hydrocarbons was 50 quarts per billion. On this basis, it will be seen that, from a point between samples 17. and 18 to a point between samples 20 and 21, there is a hump, followed by a depression, and then a second hump beginning at point '26 and extending. to a point somewhat beyond sample 30. From this it would be expected that in the area between sample 20 and sample 26 there would be production. It may be noted that the profile shows an initial hump X which may indicate. a second producing horizon because this humpX has a counterpart in profile 49 to be described hereafter.

Referring to profile 43, it will be notedthat, taking 50 parts per billion as the dividing line,

there is a hump which starts some place south ofsample 15 and extends to a point between profile 48 begins close lines are drawn on Fig. 1 connecting Xi in profile 4T. samples 24 and 25 and returns to normal value" atisaimple 26, irom which samples 36 and 3'7, corresponding almost precisely to the terminal point of the hump between samples 20 and 21. Likewise, the secondhump in to sample 42, corresponding ,to sample 26 in profile", and extends to a point north of sample 46-. The upward trend at either end of this profile, strongly suggests a: second producing horizon, Inany event, there is a definite indication of a producing zone between sample 36 and sample 43. A distillate well 5| was situated between samples 21 and 22, correspondi'ng to samples 37 and 33. 7

Referring to Fig. 5, the first profile 49 was obtained by analyzing samples 15 to for carbonates in the manner heretofore described. In this profile, the ordinates represent percentage by weight of carbonates in each sample. Taking 5% as the dividing .line between anomalous and ordinary concentrations, it is found that there is a hump beginning between samples 17 and 18 and ending between samples 20 and 21. There. is also an initial h'ump Y, corresponding to hump A third hump begins between point it increases progtssively. It may be noted at this point that,

i-while the corresponding hump in profile 41 was should be between lines 10 and I I. In cases where the distance'between lines 9 and ill or between ll; and l2 is great,'it often happens there are two or more producing horizons, so that production might actually be found between lines 9 and I0, for example, at a depth greater than produc tion between lines Ill and II.

- ing samples taken, 1000 feet apart, along two parallel lines one quarter of a mile apart running 3. A sec said to begin at sample 26, the hydrocarbon concentration actually crossed the SO-part-per-billion line between samples 24 and 25, and returned tothe fill-part point at sample 26, from which point it increased progressively. Thus, there is a strong resemblar'ice between tile carbonate profile and the hydrocarbon profile, even to the suggestion of a second producing horizon.

carbonate profile and the corresponding hydrocarbon profile 48.

drawing as Heavy hydro- Profile was made by conducting the carbonate analysis on samples 31 to 46, inclusive. I

- and forwarded to the laboratory.

sample wasanalyzed for bicarbonates by the,

Referring to Fig. 6 numeral 55 designates the edge or production as it existed in a known field prior to the application of the method of the' present 1 vention. The black dots indicate producing w s, while the black dots with a cross in dicate abandoned producers. In this case soil following procedure: digest sample with.distilled water 12-24 hours, titratealiquot portion withstandardized H01 acid using methyl orange as indicator-amount of l-lCl required to neutralize is measure'oi bicarbonate present. The parts per million by weight oibicarbonate in each sample is shown by the larger number adjacent each sample location. Contents of 200 parts per million and greater were taken as significant. On

' this basis, contourlines were drawn, .with the result that an inner line 52 was obtained representing' the inner. boundary of a halo, the outer boundary of which-was defined by a line 53. The black circular dots between lines 55 and 52 represent the producing wells which have been drilled since the aforesaid work was done. The small circles indicate locations for new wells. The

wells drilled closest to boundary line 52 have been found to yield barely their allowable and, in some cases,'1ess than this, indicating that the edge of 40 and 41 as contrasted with the values of samples 42 and 48. Sufi'icient samples to determine the direction in which this line would go were not taken. v

' 'ganic constituents mentioned on these profiles constitute only a small part of the-many inorganic constituents the variations in which have been observed.\- ,-It is not to be assumed that in every .case the measurement of the inorganic constituents in soil samples will yield the precise; patterns shown in the drawings. It may be said that, for the most part, the patterns obtained by 5 my copending application ser. is. 304,141. fil d measurement of the inorganic constituents have the same general nature as the hydrocarbon patv terns. In any case, the inorganic pattern will have a anomalous portion which can-be correlated w ththesignificant' portion of the hydrocarbon pattern. 7

Naturally, the results of. the method ,0! the present invention leave something to the Judgment of the interpreter. ,Should the interpreter find that a particular in low for a large number of samples and then suddenly increases'to a high level, which is also maintained for a large number 01" samples, he will investigate to-determine the nature of the formations irom' which the samples. were procured. 7

Likewise, when the interpreter finds a single high sample among; a grouper low samples, he will investigate the circumstances to determine what significance, if anynhuuld be. slv ntc h i m indication.,-

As in established geophysical'practice, where,

' 'for example, gravitational and magnetic data are used to determine the economic feasibility of,

further work by seismic or other more expensive methods, the present invention offers an inex pensive technique useful in ascertaining the economic feasibility of further exploration of a given area. In this respect, it is in a position to be compared directly with the torsion balance, gravity meter, magnetometer, resistivity and electrictransient method which measure indirect evi- 'dence of the presence of structure, with thedata yielding a basis ior economic exploitation with 'more-expensivemethods, like the seismic which 5 measures the structure directly, or a geochemical method which measures the direct leakage products vfor the sought deposits.

While the method of prospecting herein disclosed can be used as the basis 'for a drilling pro-' gram, it appears to best advantage when used as region by the disclosed method, determining the areas which may economically be exploited by a prospecting method of higher resolving'power,

and further exploring the thus limited areas by such methods of higher resolving power.

" The methods of higher resolving power include the seismic which under favorable conditions is capable of delineating structure favorable to the method of; copending application Serial No. 103,129, which is generally applicable to the prob lem of determining the existence and the real extent, of such accumulations.

do not fall in the class of methods of higher resolving power asthey are generally conceded to be reconnaissance methods incapable of accurate g power," as-used method and the above mentioned soil analysis method with any improvement thereon. Asthis invention is a surface method and con-.

"method of higher resolving power."

This application is a continuation in part of Nove ber 13, 1939, and entitledMethod of prosnec Y In addition to the species 0 drogen ion concentrationfoi the soil samples, in

, Ser. No. 451,629, .flled July 20,1942, the'determi-q nation of the total water'soluble content of the soil. samples, in ser. No. 451,630, filed July organic constituent runs .65 1942, the determination or the total acid soluble o determination of the content or bicarbonate radim he soilsamples.

I Thenature and objects orthe presentinvemtion having been thus described, what is claimedas new and useful and is desired to be secured 7| bylettersPatent is: r

The gravimetric, m magnetometric, resistivity methods and the like 'The profiles described above and illustrated in production was approached. Line 54 is a contour accumulation of Oil and gas a he 8111118518 line necessitated by the high values of samples and detailed structural analy is. Therefore-the 45 term method of higher resol in this specification, is limited to the seismic I templates surface methods oi higherresolving power, prospecting with the drill, as by core drilling, is excluded from the definition of the I i med in this an,- plication there are claimed in Ser. No. 451,628, so flled July 20, 1942', the determination or thehyk other.

1. A method of geochemical exploration for subterranean petroliferous deposits which comprises collecting samples of soil at spaced points component ions thereof and correlating the con-- tents of the substance so determined in the re-;

spective samples with the locations of the samples so that the possible existence ,of an area of petroleum deposit may be ascertained from the.

orientation of samples having anomaious contents "of said substance.

2. A method of geochemical subterranean petroliferous deposits which comprises collecting samples of soil at spacedpoints in an area to be investigated at a depth several feet below the surface, said depth being sufilcient to eliminate the effect of surface conditions, subjecting each sample to an analysis forthe determination of the content thereof per unit weight of each of a plurality of substances .selected from the group consisting of ionizable inorganic salts and the component ions thereof and correlating the contents of the respective samples so determined with the "sample locations so that the possible existence of an area of petroleum deposit may be ascertained by theorientationof samples having anomalous contents of said substances. 3. A method according to claim 1'in which the sample locations are laterally spaced from each other. i

4. A method according to claim 2' in which the sample locations are laterally spaced from each other. I

feet below the surface, said depth being sufiicient to eliminate the effect of surface conditions, subjecting the individual samples to an analysis for the determination of the content per unit weight exploration for leum deposit may'be ascertained from the orientation of the samples containing anomalous contents of said acid radical,

10. A method according to claim 9 in which, in the treatment of the soil samples referred to, each sample is extracted with a dilute acid, and

the radical selected for determination om.

which is not contained in said acid.

11. A method according to claim 9 in which 12. A method according to ,claim 1 in which A the radical selected for determination is a halide.

, 13. A-method according to claim -1 in which the radical selected for determ ination'is the carbonate radical.

14. A method according to claim 9 in which the sample locations are laterally spaced from each other.

15. A-method according to claim 9 in'which the sample depth is at least tenfeet.

16. 'l'he method of geochemical exploration to subterranean petrcliferous deposits which comprises collecting samples of soil at spaced points in an areato be investigated at a depth several feet below the surface, said depth being suflicient to eliminate the effect of surface conditions, subjecting each sample toa. treatment capable of, releasing therefrom inorganic acid radicals in aqueous solution, determining the quantity of each of a plurality of selected acid radicals in the extract from each sample per unit weight of said sample and correlating the quantities of the selected radicals in the respective samples with the sample locations so that the possible exist once of. an area of petroleum deposit may be as- 7 capable of decomposing carbonates to evolve carthereof of a selected inorganic acid radical and correlating the contents so determined in the re spective samples withthe sample locations so that the possible existence of an area of petroleum deposit may be ascertained by the orientaticn of samples having anomalous contents of I said acid radical. c c 6. A method according toclaim 1 in whichthe sample depth is'at least ten feet.

7. A method according to claim 5 in sample depth is at least ten feet.

'5 in which the sample locations are laterally spaced from each which the 8. A method according to claim \9. The method of geochemical exploration in an area to be investigated at adepth several M bondioxide.

for' -sul'iterraiiean petroliferous deposits which comprises collecting samples of soil at spaced points certained from the orientation of samples having anomalous uantities of said acid'radicals.

17. Them thod of geochemical exploration for i subterranean petroliferous deposits which com prises collectingsamples of soil at spaced points in an area to be investigated-at a depth several feet below the surface, said depth being sufficient to eliminate the eflect of surface conditions, sub iecting each sample to a treatment with an acid bon dioxide, determining the amount of carbon dioxide evolved from each sample per unit wcight' V of' each sample and correlating the quantities of carbon dioxide so determined in the respective -samples with the sample locations so that thepossible existence of anarea of petroleum deposit may be ascertained from the orientation of" samples liberating anomalous'quantities of car- 18. A method to claim 17 in which the samples are collected at laterally spaced points at a depth of at least ten feet. 19. A method of geochemical exploration for 5 termining the chloride content. per unit weight feet below the surface, said depth being sufllcient to eliminate the effect of surface conditions, subaqueous solution, determining the quantity of a selected acidmadical in the extract from each that the possible existence of an area of.

iecting each' sample to a treatment capable of lasing therefrom inor anic acid radicals in g 7 tions at which of each of the respective samples, and determining the location of petroliierous deposits by selecting the-significant high chloride values and correlating the high values were cbtained.

20. A inethgdaccordlng to claim 19 icwiiicii' thesam'ples are-laterally spaced from each other; and are colleciedatfa depth. of about ten feet.

- LEO. HORV'ITZ.

the radical selected for determination is a halide.

c with reference to the loca-'- samplesyielding such significant

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