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
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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
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(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
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"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.
* * *
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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 -