T.P. 2931 CORRELATION OF BOTTOM- HOLE SAMPLE DATA GUY BORDEN, JR. AND MICHAEL J. RZASA, STANOLIND OIL AND GAS CO., TULSA, OKLA., MEMBERS AI ME Laboratory data on bubble point pressures and reservoir volume factors have been correlated as functions of solution gas-oil ratio, calculated gas gravity of the pentanes-and-lighter fraction of the entire fluid, differential residual oil gravity, and reservoir temperatures. INTRODUCTION Several correlations of crude oil properties have appeared in the literature. D. L. Katz' in 1942 presented five methods of predicting oil shrinkage, these being of decreasing accuracy for decreasing amounts of information available. M. B. Standing· in 1947 published three correlations of laboratory flash vaporization data of California crudes. From values' of GOR (gas-oil ratio), gas gravity, liquid gravity, and temperature, his correlations will predict bubble point pressure, formation volumes of bubble point liquids, and twophase formation volumes. Curtis and Brinkley' in 1949 presented several correlations. From the gas-oil ratio, an approximation of reservoir volume factor and barrels of condensate recoverable per barrel of reservoir space may be obtained; along with liquid gravity and reservoir temperature, the GOR will allow prediction of bubble point pressure. These last corlReferences given at end of paper. Manuscript received in the office of the Petroleum Branch May 29, 1950. Paper presented at the Mid-Continent Joint Meeting in Tulsa, Okla., May 12-13, 1950. Vol. 189, 1950 relations seem to be more qualitative than quantitative. Generally, laboratory bottom hole sample tests furnish information on solution gas-oil ratios, residual oil gravities, bubble point pressures, viscosities of oils, liquid shrinkages, and occasionally gas gravities. Each of these data has its own applications and use in reservoir engineering calculations. The particular uses of correlated bottom hole sample data are found in (1) Providing a basis for obtaining estimates of formation crude properties in fields where bottom hole sampling is impractical or impossible. (2) Greatly reducing the time in obtaining the desired information. (3) Determining the applicability of the results from various bottom hole samples to particular field problems. (4) Avoiding, in many cases, the uncertainties of sampling by replacing it with an element over which greater control can be exercised. (5) Permitting use of preliminary field data in application of production procedures before a bottom hole sample can be obtained and analyzed in the laboratory. (6) Serving as a check on data which may appear out of line. (7) Estimating for a particular type crude the appropriate equilibrium constants by working backward from the bubble point pressure. (8) Estimating original or other past history properties of reservoirs that were not sampled in the past. PETROLEUM TRANSACTIONS, AIME , PROCEDURE Application of the published correlations'" to Stanolind laboratory data indicated that the general scheme presented by Standing' could give de3irable results if changes were made in parameter positions and scales. The correlation curves were drawn with all the variables having consistent gradations except the temperature increments which were drawn in to best fit the· data. The variables from available Stanolind laboratory data are defined below: (1) Gas-oil Ratio: Gas is liberated at reservoir temperature by differential vaporization (or rather by a series of flashes, approaching differential vaporization) and measured at atmospheric pressure and temperature, at which the compressibility factor is assumed to be unity. The oil is the residual liquid remaining after the pressure has been reduced to atmospheric. For the gas-oil ratio both volumes are corrected to standard conditions of 14.7 psia and 60°F. (2) Gas Gravity: It was decided to arbitrarily divide the hydrocarbons of the entire bottom hole sample into pentanes-and-lighter and hexanes-and-heavier, and use a calculated gas gravity of the pentanesand-lighter for a correlating variable. (Sample calculation is shown in Table III.) (3) Liquid Gravity: This is the API IIravity of 'the residual liquid from the differential vaporization. The gravity is measured at room temperature and corrected to 60°F. 345 Downloaded from http://onepetro.org/JPT/article-pdf/2/12/345/2239302/spe-950345-g.pdf/1 by guest on 31 July 2023 ABSTRACT T.P. 2931 CORRElATION OF BOTTOM HOLE SAMPLE DATA (4) Temperature: This is the temperature at which the differential vaporization and bubble point pressure determinations are carried out, and is usually the bottom hole (reservoir) temperature. EXAMPl£ CRUDE eAG.O.R.-S25 G- .79 (5) Bubble Point Pressure: This is the pressure at which there is a break in slope of the pressure-volume curve; that i~, the pressure at which gas starts to evolve as pressure is decreased. This bubble point pressure is at the test temperature. -API -27.4 T -2IS-F FROM CHART BPP·3260 ~\..' •- .0 USE OF CORRELATION CHARTS o £ Prediction (Jf Bubble Point Pressure and Reservoir Volume Factor . ..g g .,g o 00 ~.,. FIG. 1 - BUBBLE POINT PRESSURE CORRELATION. Published data of three samples were used to test the correlations. Table II shows the properties of these crudes and the comparisons of predicted and experimental bubble point pressures and reservoir volume factors. Example uses of the correlation charts are shown in Figs. 1 and 2. The method of calculating gas gravity is shown in Table III. Use of Bubble Point Pressure Correlation Chart to Predict Saturation of Reservoir Crude "A"a was sampled at 3,600 psia and 218°F. The tank oil gravity was 27.4° API. Calculated gravity of pentanes-and-lighter is 0.79. By entering Fig. 1 at 3,600 psia for bubble' point pressure and ending up with gas-oil ratio, while using the above quantities for the variables, a gas-oil ratio of 615 cu ft/bbl is predicted. This means that Crude "A" can hold in solution approximat~ly 615 cu ft/bbl of .79 gravity pentanes-and-lighter gas at 3,600 psia and 218°F and be at its bubble point. Comparing 615 with 525 cu ft/bbl shows that the oil is undersaturated at the sampling conditions. Extrapolating experimental data on Crude "A" shows that 575 cu ft/bbl could be in solution at the sampling conditions. Thus, the undersaturation of the oil is correctly predicted. 346 EXAMPLE CRUDE "A" G.o.R." 525 G" .79 -API -27.4 T-218"'f FIG. 2 - RESERVOIR VOLUME FACTOR CORRELATION .. PETROLEUM TRANSACTIONS, AIME Vol. 189, 1950 Downloaded from http://onepetro.org/JPT/article-pdf/2/12/345/2239302/spe-950345-g.pdf/1 by guest on 31 July 2023 (6) Reservoir Volume Factor: This is the barrels Qf bubble point oil per barrel of residual oil at 60°F and atmospheric pressure. Separation of gas is by differential vaporization at reservoir temperature. GUY BORDEN, JR. AND MICHAEl J. RZASA Table I - Range of Data on Bottom Hole Samples from Correlations Were Made Company Operating Divisions Division 1 Division 2 Division 3 Min. Max. Min. Max. Min. Max. Bubble Point Pressure psia 1187 4650 246 3625 514 3551 Reservoir Vol. Factor, bbljbbl* 1.082 1.745 1.054 1.610 1.098 1.678 Gas·Oil Ratio, cu ft/bbl* 156 1165 151 1246 94 1383 Oil Gravity, °API* 23.8 49.6 29.1 42.6 22.7 49.9 Calculated Gas Grav. .56 (Air = 1) 1.21 .92 1.30 1.66 .837 Reser:voir Temp., °F** 126 236 82 159 101 236 DISCUSSION Which Division 4. Min. Max. 292 1239 1.037 1.217 50 24.8 318 31.5 1.09 122 1.36 156 Table II - Properties of the Crudes Analysis, Mol Fractions Crude "Am Component Crude "W'" Crude "B'" Methane .4404 .5345 .4573 Ethane .0432 .0636 .1032 Propane .0405 .0466 .0665 Butanes .0284 .0417 .0379 Pentanes .0297 .0174 .0274 Hexanes .0290 .0341 Heavier .4011 .2559 .3016 Crude "W'" Crude Crude "B"3 "A"3 Flash Differen- Field Data tial Data Data Reservoir Temperature, OF 218 243 145 145 145 525 1078 921 959 Lab. Flash GOR, cu ft/bbl* Differential Vaporization GO R 1065 27.4 34.5 Residual Oil Gravity, °API 42.0 40.3 42.4 .812 Calculated Gas Gravity of C•. .790 .886 .886 .797 3305 4470 2952 2952 2952 Experimental Bubble Pt Pr, psia 4620 2640 2960 Correlated Bubble Pt Pr, psia (Fig. 1) 3260 2730 Experimental Res Vol Fac, bbljbbl 1.305 1.64 1.477 1.550 1.477 1.306 1.700 1.490 1.541 Correlated Res Vol Fac (Fig. 2) 1.450 -150 -312 -8 -222 Differences: BPP psi 45 -.001 -.013 RVF bbljbbl -.060 .009 .027 1.4 3.2 11.8 .3 8.1 Per Cent Difference: BPP .9 .6 1.9 RVF .1 3.7 'Standard conditions for volume<> are 14.7 psia, 60·F Table III - Calculation for Gas Gravity of Pentanes-and-Lighter (Crude "A"3) Mol Fraction Molecular Weight MolFrxM W Component .4404 16.04 7.064 Methane 1.299 .0432 30.07 Ethane .0405 44.09 1.786 Propane 58.12 .0284 1.651 Butanes .0174 72.15 1.255 Pentanes 13.055 .5699 13.055 = --= 22.91 .5699 Molecular weight of air = 29 Molecular weight C,. Gas Gravity C._ Vol. 189, 1950 22.91 = --= .790 29 PETROLEUM TRANSACTIONS, AIME Accurate predictions of reservoir fluid properties are of great importance in reservoir engineering studies. It was for this purpose that this investigation was begun and correlations determined. Published correlations"· aided the course of action and suggested the forms of the correlations. Laboratory data for correlation purposes were obtained from bottom hole sample reports filed at t}Ie Stanolind Oil and -Gas Co. Research L~boratory. These data are from samples from the company's wells extending from the Gulf Coast to the Rocky Mountains. Standing used California oils and gases for his correlations· which may account for the differences in the correlations. Table IV shows the precision of the correlations with the data from which they were made . The samples of Table II were chosen to show the use of the correlations because their data have been published.'" The correlations were made from differential vaporization data only. It is realized, however, that the usefulness of this type of correlation would be greatly increased if crude properties and conditions as determined from flash vaporization and field data might also be correlated by the same charts. Flash vaporization data of Crudes "A" and "B" are fairly well correlated by Figs. 1 and 2. The flash and field data of Crude "W" are not as well fitted to the correlations as are the differential va. porization data. Normally, flash vaporization will show greater gas release than differential if both are conducted at the same temperature. The reason for the lower gas-oil ratio in Crude "W," Table II, is became the- flash was conducted in two stages and the second stage temperature was 60°F, which allowed less gas evolution than the higher temperature. These differences in the types of vaporization and the temperatures will necessitate judgment in the use of flash data with the presented correlations. The use of these correlations with field data may be hazardous, inasmuch as laboratory data were used to develop the charts. However, a rough estimate of bubble point pressure and relative volume factor using field data with these correlations may be of some usefulness . It was found that the geographical location of the Stanolind wells sampled made little difference in the prediction of bubble point pressures and reservoir 347 Downloaded from http://onepetro.org/JPT/article-pdf/2/12/345/2239302/spe-950345-g.pdf/1 by guest on 31 July 2023 "From laboratory differential vaporization. ""Division 2 data dominated the temperature range up to 105°F; Division 3, the range 105· to 126° F; Division 4, the range 125· to 145°F; and Division 1, the range from 145°F, up. SUMS T.P. 2931 T.P. 2931 CORRelATION OF BOTTOM HOLE SAMPLE DATA volume factors. Recombination samples were not well predicted by the correlation for bubble point pressure. Four samples at lower temperatures (95°F to 127°F) had bubble point pressures predicted from 12 per cent to 53 per cent low; two at higher temperatures (208°F and 230°F), 10.8 per cent and 18.37 per cent high. CONCLUSIONS Figs. I and 2 will permit estimation of bubble point pressures and reservoir volume factors from laboratory solution gas-oil ratios, calculated specific gravities of the pentanes-and-lighter fraction of the entire fluid, residual oil gravities, and reservoir temperatures. It shpuld be possible, in many instances, to determine if a reservoir is saturated or un· dersaturated. ACKNOWLEDGMENT The authors wish to express their appreciation to the management of the Stanolind Oil and Gas Co. for permis. sion to present and publish this paper. 348 Precision of Correlated Data Bubb!e Point Correlation, Fig. 1 Total Points from Bottom Hole Sample Data______ _________ 188 Total Points from Recombination Sample Data______________ _____________ 6 Average Per Cent Prediction High______________________ __________________ 8.16% Average Per Cent Prediction Low__________________________________________________ 10.50% Average Per Cent Prediction TotaL_________________ ________________________ ___1.84% Low Per Cent of Data Points Within 10% of Predicted BPP ___________ 65.5% Per Cent of Data Points Within 15% of Predicted BPP _________________ 84.5% Maximum % Deviation (True Value 1437, Predicted 863) ____________ 66.5% Maximum psia Deviation (True Value 3760, Predicted 4600) _______ 840 psia Divi~ion Total Samples Within 15% Predicted Division 1 77 72 Division 2 81 61 Division 3 19 15 Division 4 17 16 No. of Samples with Predicted BPP More than 200 psi High ______ 23 No. of Samples with Predicted BPP More than 200 psi Low_ 30 Reservoir Volume Factor Correlation, Fig. 2 Total Points from Bottom Hole Sample Data_______ _____________ 172 Total Points from Recombination Sample Data__ _________________ 6 Average Total Deviation __ ______________________-__________________________________ :_______ 1.0% Per Cent of Points within 2.6% of Predicted Value ____________________ 95.5% Average Deviation High (bbl/bbl) _________________________________________________ .015 Average Deviation Low (bbl/bbl) ______________________________________________ . ________ .014 Maximum % Deviation (True Value 1.445, Predicted 1.605) ________ 10% Maximum Deviation bbl/bbl (True Value 1.445, Predicted 1.605) .160 REFERENCES J. Dewees and H. M. Harris: "Bureau of Mines Analysis of Subsurface Oil S·amples," Petroleum Engineer, (May, 1945) 85. 2. R. C. Curtis and T. W. Brinkley: "Calculation of Natural Condensate Recovery," Presented API Div~ of Prod., Tulsa, Okla., March 23-25, 1949. 3. C. R. Dodson and M. B. Standing: "Prediction of Volumetric and Phase Behavior of Naturally Occurring Hy· drocarbon Systems," API Drill. and Prod. Prac., (1941) 326-340. 4. D. L. Katz: "Prediction of Shrinkage of Crude Oils," API Drill. and Prod. Prac., (1942) 137-147. S. B. H. Sage and H. Reamer: Trans. AIME, (1941) 170, 179. 6. M. B. Standing: "A Pressure-Volume --Temperature Correlation for Mixtures of California Oil and Gases," API Drill. and Prod. Prac., (1947) 275-287. PETROLEUM TRANSACTIONS, AIME Vol. 189, 1950 1. A. B. Cook, E. * * * Downloaded from http://onepetro.org/JPT/article-pdf/2/12/345/2239302/spe-950345-g.pdf/1 by guest on 31 July 2023 Differences in reservoir volume factors for samples at bubble point pressures and at pressures higher than the bubble point are due to the liquid compressibility. Compressibilities range from 5 x lO-6 to 18 X 10- 6 bbl/bbl/psi for Stanolind samples with most falling in the 7 x 10- 6 to II X 10- 6 bbl/bbl/psi limits. Therefore, the reservoir volume factor will decrease by approximately 0.001 for every hundred psi above the bubble point pressure. Table IV -