US2700593A - Correlation of crude oils - Google Patents

Description

Jan. 25, 1955 J. F. BLACK ET AL 7 2,700,593 CORRELATION 0F CRUDE OILS Filed Dec. 1, 1949 3 Sheets-Sheet l FLOW DIAGRAM FOR FIQACT/ONAT/QN OF CQUDE OILS BY PRECIPITATION METHODS -50 cc. cauoa OIL 500 cc. N- PENTANE eec/ z TA TE 500 cc; N-PENTA NE I PENTANE SOLUBLE FRACT/o/v P/aE-c ZP/ TA TE 500cc. Az-psAn-Aue RES ms page [PITA r5 IOQOCC.IN-=HEPTANE HEPTANE SOLU L PENTA NE IN LU LE CARBCN DIS ULF/DE s ASPHALTENE V susmsavo ED SEDIMNT MM TM Z w 83 /11 mm W Jan. 25, J F. BLACK ET AL 2,700,593

CORRELATION OF CRUDE OILS Filed Dec. 1, 1949 5 Sheets-Sheet 2 RELATIVE EMISSION LINE lNTENS/T/ES OF ELEMENTS oerzcrco 5/ Mg Fe. v 211 N1 ca AZ Ga Mn c'r c2002 OIL A J l a c2005 O/LBJ 3 .51 Mg Fe. V Zn M Ca AI Ga Mn Cr C2005. 0/1. c: I l l I x 5/ My Fe .V Zn /v' Cd AI Ga Mn Cr CR UDE OIL DJ I I Jan. 25, 1955 J. F. BLACK ET AL 2,70

CORRELATION OF CRUDE OILS Filed Dec. 1, 1949 3 Sheets-Sheet 3 SPECTROCHEM/CAL ANALYSES OF PENTANE SOLUBLE FRACTIONS OF CRUDE OILS RELATIVE EMISSION LINE. INTENSIT/ES 4 OF ELEMENTS DETECTED 5/ Mg Fe. V Zn Ni Ca AI Ga Mn Cr IUI I I1 .I

s/ 1 49 Fe'v Zn Ni Ca Al Ga'Mn Cr United States Patent 2,700,593 CORRELATION or CRUDE OILS James F. Black, Roselle, N. .I., and Clara D. Smith,

Columbus, Ohio, assignors to Standard Oil Development Company, a corporation of Delaware Application December 1, 1949, Serial No. 130,496 1 Claim. C1. 23-430) This invention relates to an improved method for determining similarities, or dissimilarities between crude oils. In other words the process of this invention is of application in the characterization or correlation of crude oils. In accordance with this invention, crude oil samples are treated so as to segregate certain particular fractions which may then be subjected to infrared analysis tests, spectrochemical tests, or X-ray diffraction tests to uniquely characterize the crude oil samples from which the fractions were segregated.

In oil exploration activities it is frequently desirable to determine whether or not two oil wells are producing from the same source. To accomplish this it is necessary to characterize the crude oil obtained from the wells. It has been the general practice to work towards this end by determining fundamental inspections of the oils; for example, by determining the A. P. I. gravities, the carbon to hydrogen ratio, the distillationcharacteristics of the oils to be compared, etc. Such techniques are subject to several disadvantages. For one thing it is not possible to obtain information of this type from samples of the oil obtained by core sampling techniques. More fundamentally, methods based on the inspections of crude oils are not sutficiently basic to establish geological relationships between crude oils. This is true for the reason that the crude oil characteristics measured in these inspection tests are markedly affected by incidental and uncontrollable factors existent at a particular locale, such as the gas pressure on the producing horizon; loss of light ends from the crude, etc.

Attempts have been made to more precisely correlate crude oils so as to determine geological relationships between crudes by subjecting total crude oil samples to spectrographic and optical methods of analysis. In some cases it is possible to successfully characterize crudes by this method. For example, it has been found possible to successfully correlate total crude oil samples by the specialized radiation absorption technique disclosed in U. S. application Ser. No. 109,441, filed by Clara D. Smith on August 10, 1949. However, even in this case reliability of correlations established by this method are somewhat doubtful. The method is not applicable to correlations based on core samples and the method is subject to errors caused by loss of light ends from the crude, deasphalting of the crude which may have occurred in the ground, and other factors.

It'is, therefore, the principal object of this invention to provide an improved technique for characterizing crude oils overcoming the disadvantages of the methods heretofore employed, of the nature indicated above.

As indicated by the preceding description, a difliculty of existing crude oil correlation methods relates to the variations in crude oils caused by conditions existing in the oil trap from which the crude oil is drawn. For example, a total crude oil sample withdrawn from one well ascompared to the sample withdrawn from a diiferent well, both fed by the same source and having the same geological history, may differ in sediment content; asphalt content; light hydrocarbon content, etc. Such differences can arise due to a number of factors such as the penetration of salt water to the producing horizon, deasphalting of oil due to light hydrocarbons present, or differences in pressure existing at the particular point from which the crude oil is taken. Consequently, it is the novel concept of this invention to overcome the effect of factors of this nature by subjecting the crude oil sample to be characterized to a particular segregation process so as to gating reproducible fractions for analysis 2,700,593 Patented Jan. 25, 1955 content, etc.

In accordance with this mvention, a crude oil to be characterized is segregated into at least two fractions.

One fraction is a light hydrocarbon soluble fraction, while the second fraction constitutes an asphaltene fraction. The method by which these fractions are obtained is an important feature'of this invention depending upon particular dilution, filtration, and washing techniques. As will be disclosed, by following the segregation process of this invention, a light hydrocarbon soluble fraction and an asphaltene fraction will be obtained which can be examined by conventional analytical methods so as to indicite geological relationships between crude oils being teste The method of this invention may be fully understood by reference to the following detailed description in connection with the accompanying drawings in which:

Figure 1 represents a flow diagram showing a specific segregation process embodying this invention, which is suitable for obtaining reproducible fractions of a crude oil to be analyzed, and;

Figure 2 represents the spectrochemical analysis of the deasphalted fractions of three distinctive crude oils obtained by the process of this invention, and;

Figure 3 similarly represents the spectrochemical analysis of fractions from two geologically related crude oils.

Referring now to Figure 1, a specific manner of segreis represented. As shown by this figure, a sample of crude oil is first subjected to about a 10 to 1 dilution with a light hydrocarbon. It is presently preferred to utilize normal pentane as the dilution agent although the principles of this invention may be adapted to the utilization of normal butane, normal propane and other C3 to C7 paratfinic hydrocarbons. Similarly, the particular extent of dilution is not particularly critical. The addition of normal pentane, or other light normal paraflinic hydrocarbon is effective in precipitating substantially all asphaltenes from the crude oil. This asphaltene precipitate is then washed on a filter, for example, with normal pentane. In the specific case illustrated in Figure 1, when 50 ccs. of crude oil is diluted with 500 ccs. of normal pentane to secure the precipitation of asphaltenes, it is suitable to wash the asphaltene precipitate with an additional 500 ccs. of normal pentane. These steps will yield a washed precipitate containing substantially all of the asphaltenes originally present in the crude oil, and will yield a pentane soluble fraction of the crude oil substantially constituting deasphalted crude oil from which sediment has been removed by the filtration step. As will be brought out, the pentane soluble fraction constitutes a fraction of the crude oil which may successfully be characterized by methods such as infrared absorptive analysis, or spectrochemical analysis so as to effectively characterize the crude oil.

Returning now to the washed precipitate obtained as indicated by dilution of the oil with normal pentane followed by washing with normal pentane, it is necessary to subject this precipitate to further treating steps in order to obtain a reproducible asphaltene fraction. The necessity for further processing of the asphaltene precipitate arises from the fact that the nature, and extent of asphaltene precipitation from the crude oil depends in part upon sediment present in the crude oil, and the specific hydrocarbon composition of the oil. Thus the asphaltene precipitate as heretofore obtained is not a reproducible fraction of the crude oil. For this reason this precipitate is preferably subjected to a further wash with, for example, 500 ccs. of normal pentane. This wash is effective in dissolving a portion of the precipitate to yield a second pentane soluble fraction, including certain resins originally present in the crude oil. The asphaltene precipitate is then subjected to a wash with a hydrocarbon capable of dissolving a portion of the asphaltenes, and other materials still present in the asphaltene fraction. In other words, an agent is employed which is suitable to cause some of the asphaltenes present in the fraction to go back into solution. To achieve this, a paraffinic hydrocarbon may be used having a greater number of carbon atoms than the hydrocarbon formerly used to precipitate the asphaltenes. For example, in the particular process being described, it is suitable to employ about 1000 ccs. of normal heptane, yielding a heptane-soluble, pentane-insoluble fraction consisting as indicated of a portion of the asphaltenes originally present in asphaltene fraction is then dissolved in a solvent such as carbon disulfide capable of dissolving all remaining asphaltenes, but leaving any sediment present in the crude oil undissolved. A variety of asphaltene solvents may be employed such as pyridine, benzene, toluene, carbon tetrachloride, and carbon disulfide. Consequently, by filtering the solution of the asphaltenes, suspended sediment can be removed. As will be brought out, the asphaltene fraction dissolved in a solvent such as carbon disulfide as precipitated, washed and partially redissolved, as described, will constitute a reproducible asphaltene fraction of the original crude oil which may successfully be characterized by conventional analytical procedures such as X-ray diffraction and infrared absorptive analysis.

As heretofore described, the novel crude oil characterization method of this invention depends upon the segregation of a crude oil sample into particular fractions. In particular, it is necessary to precipitate all asphaltenes present in an initial step to obtain a deasphalted fraction of the crude oil, and it is then necessary to particularly treat the asphaltene precipitate to obtain a reproducible asphaltene fraction of the original crude oil. In essence, the necessary segregation process depends upon the initial precipitation of substantially all asphaltenes, followed by the partial solution of a portion of the asphaltenes. By this technique it is possible to eliminate the effect of the original crude oil composition on the fraction of precipitated asphaltenes obtained, and essentially the technique permits obtaining an asphaltene fraction precipitated from a control medium so as to be of a reproducible nature.

In order to demonstrate the utility of the segregation process described for successfully characterizing crude oils, examples will be given showing the manner in which the crude oil fractions may be analyzed. Attention will first be directed to the methods by which the pentane soluble fraction may be examined.

Two methods in particular are suitable for characterizing the pentane soluble fraction. These methods are spectrochemical analysis, and infrared spectrometry. Insofar as both of these analysis methods are well known to the art, no description will be given of the manner in which they are conducted. In the case in which spectrochemical analysis is used the pentane soluble fraction is reduced to an ash which is then analyzed by the methods of spectrochemical analysis to provide the comparative emission line intensities of metallic elements present in the ash. Referring to Figure 2, typical spectrochemical analyses of pentane soluble fractions of three crude oils are indicated, showing the results obtained on three different crude oils. It will be noted that the emission line intensities of crude oils A, B and C, differ widely in character. Thus, for example, the fraction of crude oil B unlike the fractions of crude oils A and C does not contain vanadium, zinc, gallium, manganese, and chromium. Again, the fraction of crude oil C unlike those of crude oil A and crude oil B contains no magnesium. A significant point in regard to the spectrochemical analyses indicated in Figure 2 is that no sodium is present in any of the fractions, while sodium was present in the original crudes from which the fractions were obtained. The absence of sodium from the pentane soluble fraction demonstrates that the filtration step is effective in removing suspended contaminants. Inasmuch as the three crude oils from which samples were taken in preparing Figure 2, 'ere selected from different geographic regions, the data of Figure 2 demonstrates that spectrochemical analysis of the ash from the pentane soluble fraction of crude oils is a sensitive method for comparing crude oils.

Referring now to Figure 3, the spectrochemical analysis of the ash obtained from the pentane soluble fraction of two crude oils chosen from the same geographical location is represented. it will be observed that the emission line intensities for the two crude oils D and E are very similar in nature. This bears out the probability that the two crude oils have a close geological relationship since both of the oils were obtained from neighboring wells at Lower Cretaceous producing horizons.

As indicated by the data presented in Figures 2 and 3, therefore, spectrochemical analysis of the pentane soluble fraction of crude oils provides a suitable manner of characterizing crude oils so as to establish, or disprove geological relationships between the oils.

It may be noted that attempts to obtain similar correlations by conducting a spectrochemical analysis of the total crude oils Without segregation, or fractionation, was unsuccessful in providing comparative data of the nature indicated in Figures 2 and 3.

In the event the pentane soluble fraction of crude oil is subjected to infrared analysis procedures, similar correlations can be established between crude oils from which the pentane soluble fractions are obtained.

Referring now to the examination of the asphaltene fraction derived according to the procedure indicated in Figure 1, this fraction may also be examined by a number of methods. A particularly effective manner is to determine the infrared absorption spectra of the asphaltene fraction. The absorption spectra may be obtained according to conventional infrared procedures. Table I indicates typical data obtained from the infrared spectra of the asphaltene fraction of a variety of crude oils. Oils A through F are Canadian crude oils, while oils G through I are Egyptian crude oils. Table I indicates the relative intensity of the principal absorption maxima for the asphaltene fraction of these oils.

TABLE I Data from infrared spectra of asphaltene fraction from crude oils Frequency of Bend Group C ausing Band G-H (2) Aromatic OHM-CH3 CCH;

Asphaltenes from:

Crude Oil A 2 11 31 11 Crude Oil B 100 3 12 33 11 Crude Oil C 100 2 11 33 10 Crude Oil #1 D 100 8 21 35 10 Crude 100 3 16 34 10 Crude 100 2 18 32 I0 Crude Oil G- 100 5 21 34 11 Crude Oil H 100 1 16 31 10 Crude Oil I- 100 2 16 33 10 Crude Oil J 100 4 17 34 9 (1) Base line densities from each spectrum were multiplied by a factor which would convert the density of the 3400 cm.- absorption band to avalue of 100.

(2) Possibly C=O.

Referring to the Canadian oils (oils A-F), it will be noted that with respect to the 1700 cm." and 1615 cm." maxima, the asphaltenes from oils A, B and C are identical within the experimental accuracy of the intensity measurements. On this same basis oil D is markedly different from oils A, B and C, and finally oils E and F fall between these two extremes. These data are in accordance with spectrochemical analyses of the ash content of pentane soluble fractions obtained from these oilsand bears out the supposed similarity and dissimilarity of geological relationships between the oils. In considering the data relative to the Egyptian crude oils chosen from the Gulf of Suez area; that is, oils G through I, it will be noted that relatively small variations exist among these samples. This result would be expected as the Egyptian oils are believed to be very similar in nature.

Similar infrared absorption comparisons may be made in other regions of the infrared spectra. Thus, while the data of Table I was obtained in the 2.0 to 7.5 micron region of the spectra, if desired similar data may be obtained bearing out these same relationships between the oils in the 7 .5 to 15.0 micron infrared region.

If desired, the asphaltene fraction may also be examined by X-ray diffraction methods. Apparently crystalline material is present in the asphaltenes from all crude oils other than embronic oils which may be too young to have formed crystalline material. Consequently, distinctive X-ray diffraction patterns may be obtained by examining the asphaltenes by conventional X-ray techniques. Referring to typical data obtained by X-ray diffraction methods, it was found that oils chosen from the Devonian belt in Canada are clearly distinguishable from oils found in the Cretaceous belt in Canada. Oils from the Devonian belt are characterized by the presence of two sharp lines in their X-ray ditfraction patterns which are completely absent from the patterns of oils of the Cretaceous belt.

As described, therefore, the present invention comprises a novel method of characterizing crude oils. In accordance with this method a total crude oil sample is fractionated so as to obtain a deasphalted fraction and an asphaltene fraction. As implied, in the preceding description, all steps may be carried out at existing temperatures and pressure although elevated temperatures and pressures may be used if desired. By suitable analysis of either, or both of these fractions it is then possible to uniquely characterize the crude oils from which the fractions were obtained, and to establish any geological relations which may exist between the crude oils.

What is claimed is:

In the correlation of crude oils for the purpose of comparing crude oils from different sources the steps which comprise diluting said crude oil with a C3 to Ca paraifinic hydrocarbon whereby an asphaltene fraction is precipitated and a light hydrocarbon soluble fraction is obtained, thereafter partially dissolving said asphaltene fraction by the addition thereto of a light parafiinic hydrocarbon having a greater number of carbon atoms than in the preceding step, dissolving all the remaining asphaltene fraction and separating this dissolved fraction from sedi' ment and thereafter subjecting said dissolved asphaltene fraction to examination by radiant energy to determine the transmission characteristics of said dissolved asphaltene fraction.

References Cited in the file of this patent UNITED STATES PATENTS 1,868,211 Le Nobel July 19, 1932 2,143,882 Keith, Jr., et al. Jan. 17, 1939 2,158,980 Brundin May 16, 1939 2,213,138 Hayward Aug. 27, 1940 2,257,170 Howell Sept. 30, 1941 2,300,119 Holmes Oct. 27, 1942 2,349,366 Moon May 23, 1944 2,366,657 Sorem Jan. 2, 1945 2,383,535 Dickinson Aug. 28, 1945 2,394,703 Lipson Feb. 12, 1946 2,462,270 Lipson Feb. 22, 1949 2,483,500 Long Oct. 4, 1949 2,500,757 Kiersted, Jr. Mar. 14, 1950 OTHER REFERENCES Abraham: Asphalts and Allied Substances, 4th edition, p. 1008. Published by D. Van Nostrand and Co. Inc., New York, N. Y., 1938. Copy in Div. 31.

Spectrographic Analysis, by A. C. Rice et al., pages 21 and 22, 88-14 S. E.

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