David Muchmore
Oryx Energy Co.
Dallas
Nomenclature (57595 bytes) A toolkit consisting of macros provides petroleum engineers an easy method for incorporating petroleum fluid properties into spreadsheets. Published correlations were used to write the macros, defined as Microsoft Excel functions.
Engineers can call these functions when constructing spreadsheets and eliminate having to access external sources for many common fluid property correlations. The Excel functions also allow the correlations to be easily incorporated into existing spreadsheets.
A collection of spreadsheets is included with the toolkit that use these functions for the solution of common petroleum engineering problems.
Functions, terms, spreadsheets are listed in the accompanying box.
This toolkit was written using Excel 4.0 and Windows 3.1. The programs use 300K of disk space and require either Excel 4.0 or 5.0.
To use the spreadsheets:
- Open the spreadsheet.
- Change the values as needed.
- Print table by clicking the print tool.
- Print graphs by double clicking to select them and then printing them with the print tool.
WATER PROPERTIES
Water properties of reservoir brines are calculated for a range of pressures. The spreadsheet, Watprop.xls, produces a table of fluid proper ties-vs.-pressure and four graphs which show individual fluid properties-vs.-pressure (Fig. 1)(219148 bytes).
The gas-water ratio (RSW) function calculates the dissolved gas-water ratio for reservoir brines using correlations developed by Craft and Hawkins, and Ramey.1 A correction is applied for the salinity of the water.
The function is entered as:
RSW(PER_NaC1,TEMP, PRESS)
The reservoir brine formation volume factor (BW) is calculated using correlations developed by Numbere, Brigham, and Standing? Corrections are applied for gas saturation and salinity.
The function is entered as:
BW(GAS_SAT,PER_NaCI, TEMP,PRESS)
The isothermal compressibility (CW) for reservoir brines uses correlations developed by Numbere, Brigham, and Standing, and Meehan.3 Corrections are applied for gas saturation and salinity. This function uses the RSW function as a subroutine.
The function is entered as:
CW(GAS_SAT,PER_NaCI, TEMP,PRESS)
The UW function calculates the viscosity of reservoir brines using correlations developed by Numbere, Brigham, and Standing.4 A correction is applied for the salinity of the water.
The function is entered as:
UW(PER_NaC1,TEMP, PRESS)
GAS PROPERTIES
The spreadsheet, Gasprop.xls, calculates the fluid properties of wet and dry gas for a range of pressures. The spreadsheet produces a table of fluid proper-ties-vs.-pressure and four graphs which show individual fluid properties vs. pressure for both wet and dry gas (Fig. 2)(211142 bytes).
Wet gas is defined as the dry gas plus the vapor equivalent of the produced condensate. Water is not considered. The formation factor for wet gas has been corrected for the vapor equivalent of condensate. It is defined as the volume of wet gas at reservoir conditions divided by the volume of dry gas at standard conditions.
The Z-factor spreadsheet, Z.xls, calculates the Z-factor of hydrocarbon gases for a range of pressures and temperatures. It produces one table and one graph.
The Z-function calculates the Z-factor (real gas deviation factor) for hydrocarbon gases using the Dranchuk, Purvis, and Robinson technique.5 This technique uses pseudocritical temperature and pressure based on correlations developed by Standing with the Wichert-Aziz correction for sour gases applied.6
The function is entered as:
Z(GAS_GRAV,COND_MIS, TEMP,PRESS,PER_N2,PER_CO2,PER_H2S)
The BG.xls spreadsheet calculates the formation volume factor of hydrocarbon gases for a range of pressures and temperatures. It produces one table and one graph.
The BG function calculates the formation volume factor of hydrocarbon gases.7 It uses the Z-function as a subroutine. The function is entered as:
BG(GAS_GRAV,COND_MIS,TEMP,PRESS,PER_N2, PER_CO2,PER_H2S,STD_P, STD_T)
This CG.XLS spreadsheet calculates the isothermal coefficient of compressibility of hydrocarbon gases for a range of pressures and temperatures. It produces one table and one graph.
The CG function calculates the isothermal coefficient of compressibility for hydrocarbon gases.5 8 It uses the Z-function as a subroutine.
The function is entered as:
CG(GAS_GRAV,COND_MIS,TEMP,PRESS,PER_N2, PER_CO2,PER_H2S)
The UG.xls spreadsheet calculates the viscosity of hydrocarbon gases for a range of pressures and temperatures. It produces one table and one graph.
The UG function calculates the dynamic viscosity of hydrocarbon gases using a method devised by Gonzalez and Lee.9 The calculation is based on the density of the gas. The Z-function is used as a subroutine.
The function is entered as:
UG(GAS_GRAV,COND_MIS,TEMP,PRESS,PER_N2, PER_CO2,PER_H2S)
GAS WELL DELIVERABILITY
Gas well deliverability spreadsheets calculate the absolute open-flow potential of gas wells as required by the Texas Railroad Commission. 1Point.xls is for tests with only one flow rate and 4Point.xls is for tests with four flow rates. The spreadsheets produce a table with all of the information necessary to fill in the G1 form required by the Railroad Commission. They also produce a back-pressure curve which is submitted to the Railroad Commission with the G1.
The gas volumes calculated by this spreadsheet consist of dry gas plus the vapor equivalent of the produced condensate. Water is not included in the calculated volume.
The spreadsheet uses the data entered in the last-test box to calculate the gravities and correction factors to apply to the meter coefficient, therefore it is important to enter good data in the last-test box. A meter coefficient is not entered. The spreadsheet looks up the meter coefficient and corrects it for water production.
The spreadsheet assumes the meter run has flange taps.
The gravity used for the volume calculations is calculated based on the gas measurement, and last-test entries. If a separator gas is being measured, 0 should be entered for gas measurement. The program will then use the dry-gas gravity to calculate a dry-gas volume and correct the volume for the vapor equivalent of condensate. If the gas is measured full well stream, 1 should be entered for GAS measurement. The spreadsheet will then used the full wellstream, gravity (G-mix) calculated from the last-test entries to calculate a gas volume. In either case, be sure to enter a separator gas gravity for gravity (dry gas).
This spreadsheet is designed for dry, sweet gas wells. It uses the Z function with 0 entered for PER_N2, PER_H2S, and PER_CO2. Significant liquid production will result in calculated bottom hole pressures that are lower than actual. This can result in either a too high or too low calculated AOF. Sour gases may cause inaccurate volume calculations.
BOTTOM HOLE PRESSURE
This spreadsheet, BHP.XLS, calculates the static and flowing bottom hole pressures for dry gas wells using the Cullender and Smith method.
The calculations assume no liquids are present in the well bore. If the well makes water or condensate, the actual bottom hole pressures will be higher than calculated.
OIL PROPERTIES
OILPROP.XLS calculates the fluid properties of oil for a range of pressures and produces a table of fluid properties vs. pressure and four graphs which show individual fluid properties vs. pressure (Fig. 3)(255321 bytes).
The table of fluid properties uses the gas gravity corrected for separator conditions. If you do not want to correct the gas gravity for separator conditions, enter a separator temperature between 76 and 100 F., and a separator pressure of 114.7 psia.
Kartoatmodjo's10 correlations were used to find:
- GASGS function for correcting gas gravity for separator conditions.
- PBP function for calculating the bubble point pressure
- RSB function for calculating the gas-oil ratio below the bubble point
- BO for calculating the oil formation volume factor
- CO for calculation of oil compressibility
- UO for calculating the live oil viscosity at pressures above and below the bubble point.
The GASGS is entered as:
GASGS(GAS_GRAV,OIL_GRAV, SEP_T,SEP_P)
The PBP correlation uses the gas gravity corrected for separator conditions, which is a separate function (GS). In most cases, you can enter a measured gas gravity and obtain good results.
The function is entered as:
PBP(GAS_GS,OIL_GRAV, TEMP,RS)
The RSB function also uses GS. In most cases, you can enter a measured gas gravity and obtain good results. The PBP function is used as a subroutine.
The function is entered as:
RSB(GAS_GS,OIL_GRAV, TEMP,PRESS,RSi)
The BO function also uses GS. In most cases, you can enter a measured gas gravity and obtain good results. The RSB function is used as a subroutine.
The function is entered as:
BO(GAS_GS,OIL_GRAV, TEMP,PRESS,RSi)
The CO function uses the RSB function as a subroutine and also GS. In most cases, you can enter a measured gas gravity and obtain good results.
The function is entered as:
CO(GAS_GS,OIL_GRAV, TEMP,PRESS,RSi,COND_MIS,PER_N2,PER_CO2,PER_H2S,STD_P,STD_T)
The UO function uses the RSB function as a subroutine.
The function is entered as:
UO(GAS_GS,OIL_GRAV, TEMP,PRESS,RSi)
This BT function calculates the two-phase oil formation volume factor at pressures above and below the bubble point.11 It uses the RSB, BO, and BG functions as subroutines.
The function is entered as:
BT(GAS_GS,OIL_GRAV, TEMP,PRESS,RSi,COND_MIS,PER_N2,PER_CO2, PER_H2S,STD_P,STD_T)
TOTAL SYSTEM COMPRESSIBILITY
Spreadsheets Totcompo.xls and Totcompg.xls calculate the fluid, formation, and total compressibility for a range of pressures for oil reservoirs and gas reservoirs. Both spreadsheets produce one table and one graph.
The rock compressibility is calculated using Hall's correlation.12 The compressibility correlations for water have a much narrower valid pressure range than the compressibility correlations for oil or gas.
The isothermal compressibility of water is much smaller than the isothermal compressibility of oil or gas and changes only slightly with pressure. For most reservoirs it makes up only a small portion of the total reservoir compressibility. To allow the calculation of the total system compressibility for a wider pressure range, this program allows a value of CW to be calculated outside the valid pressure range of the correlation. For pressures below 1,000 psia, CW is calculated at 1,000 psia. For pressures above 6,000 psia, CW is calculated at 6,000 psia.
A message will appear in the spreadsheet If either of these conditions occurs.
RESERVES DATA SHEET
Reserves.xls spreadsheet calculates the original hydrocarbons in place and reserves for oil and gas reservoirs using the volumetric equation.
Editor's note: To obtain these spreadsheet macros, Journal subscribers can send a blank 5 1/4 or 3 1/2 diskette formatted to MS DOS and a self-addressed, postage paid or stamped return diskette mailer to: Production Editor, Oil & Gas Journal, 3050 Post Oak Blvd,, Suite 200, Houston, TX 77056, USA.
Subscribers outside the U.S. should send the diskette and return mailer without return postage to the same address. This mail offer will expire Feb. 28, 1996.
REFERENCES
1. Hewlett-Packard, Hewlett-Packard HP-41C Petroleum Fluids Pac, Hewlett-Packard, Singapore, 1984, p. 108.
2. Hewlett-Packard, Hewlett-Packard HP-41C Petroleum Fluids Pac, Hewlett-Packard, Singapore, 1984, pp. 98-99.
3. Meehan, D.N., "A Correlation For Water Compressibility," Petroleum Engineer International, November, 1980, pp. 125- 126.
4. Hewlett-Packard, Hewlett-Packard HP-41C Petroleum Fluids Pac, Hewlett-Packard, Singapore, 1984, pp. 102-104.
5. Abou-Kassem, J.H., Mattar, L., and Dranchuk, P.M., "Computer Calculations of Compressibility of Natural Gas," Journal of Canadien Petroleum Technology, September-October 1990, Volume 29, No. 5, pp. 105-108.
6. Agrawal, B., "Spreadsheet Program File Quickly Evaluates Gas Properties," OGJ, Oct. 18, 1993, pp. 52-55.
7. Craft, B.C., and Hawkins, M.F., Applied Petroleum Engineering, Prentice Hall, 1959, p. 24.
8. Trube, A.S., "Compressibility of Natural Gases," Trans. AIME, Volume 210, No. 261, 1957, pp. 355-357.
9. Lee, A.L., Gonzalez, M.H., and Eakin, B.E., "The Viscosity of Natural Gases," JPT, August 1966, pp. 997-1000.
10. Kartatmodjo, T. and Schmidt, Z., "Large Data Bank Improves Crude Physical Property Correlations," OGJ, July 4, 1994, pp. 51-55.
11. Craft, B.C., and Hawkins, M.F., Applied Petroleum Engineering, Prentice Hall, 1959, p. 24.
12. Hewlett-Packard, Hewlett-Packard HP-41C Petroleum Fluids Pac, Hewlett-Packard, Singapore, 1984, p. 112.
Copyright 1995 Oil & Gas Journal. All Rights Reserved.
