SUBROUTINE oilsep(z,M7Plus,SG7Plus,NumSep,Pres,Tres, 1 PSep,TSep,Psc,Tsc,x,ysepgas,FVF,API,GOR,GG,GHV) c*********************************************************************** c This subroutine calculates the formation volume factor, API c gravity, gas-oil ratio, separator gas gravity, separator gas c gross heating value, oil composition, and gas composition c resulting from an oil flashed thru a specified number of c separators. These calculations are described in Amyx, James c W.,Bass, Daniel M., Jr., and Whiting, Robert L., Petroleum c Reservoir Engineering, McGraw-Hill, 1960, pp.352-356. c Author: Scott K. Laudeman c Date: June 20, 1987 c Input Variables. c z: Array containing mole fraction of each component in feed c mixture. Components are assigned subscripts as shown below. c 1: carbon dioxide c 2: hydrogen sulfide c 3: nitrogen c 4: methane c 5: ethane c 6: propane c 7: isobutane c 8: n-butane c 9: isopentane c 10: n-pentane c 11: n-hexane c 12: heptanes plus c M7Plus: Molecular weight of heptanes plus, lbs/lb*mole. c SG7Plus: Specific gravity of heptanes plus, lbs/lb*mole. c NumSep: Number of stages including stock tank. c Pres: Reservoir pressure, psia. c Tres: Reservoir temperature, Deg. F. c PSep: Array containing separator pressures, psia. c TSep: Array conataining separator temperatures, Deg. F. c Psc: Pressure at standard conditions, psia. c Tsc: Temperature at standard conditions, Deg. F. c Output Variables. c x: Array containing mole fraction of each component in c separator liquid. c ysepgas: Array containing mole fraction of each component in c separator gas. c FVF: Oil formation volume factor, bbl/STB. c API: API gravity of stock tank oil, Deg. API. c GOR: Total gas-oil ratio, scf/STB. c GG: Gas Gravity. c Other Variables. c cvCf: Conversion factor for cf, cf/bbl. c cvRankine: Conversion factor for degrees Rankine, Deg. R. c DenRes: Density of reservoir oil, scf/STB. c DenST: Density of stock tank oil, scf/STB. c DenWater: Density of water, scf/STB. c F: Function to be solved for mole fraction of vapor phase. c GHV: Gross heating value of separator gas, BTU/scf. c H: Array containing gross heating values for each component, c BTU/scf. c i: Loop counter. c j: Loop counter. c K: Array containing equilibrium ratios. c M: Array containing molecular weights for each component, c lbs/(lb*mole). c MAir: Molecular weight of air, lbs/(lb*mole). c MaxError: Error tolerance for vapor phase mole fraction. c molgas: Moles of separator gas for 1 mole of feed. c molgstage: Moles of separator gas at specified stage. c molsepgas: Array containing accumulated moles for each c separator gas component. c molvol: Molar volume of gas at standard conditions, scf. c MWres: Molecular weight of reservoir oil, scf/STB. c MWST Molecular weight of stock tank oil, scf/STB. c NumIter: Iterations required for flash calculation. c moloil: Moles of stock tank for 1 mole of feed, STB. c P: Pressure, psia c R: Universal gas constant, cf*psi/(Deg. R.). c T: Temperature, Deg. F. c V: Total mole fraction of vapor phase. c volg: Volume of separator gas for 1 mole of feed, scf. c volmol: Molar volume of gas, cf. c volres: Volume occupied by 1 mole of reservoir oil, bbl. c volST: Volume of stock tank oil for 1 mole of feed, STB. c x: Array containing mole fraction of each component in liquid c phase. c y: Array containing mole fraction of each component in vapor c phase. c zsep: Array containing mole fraction of each feed component. c Subprograms Used c flash: Calculates the compositions of the liquid and vapor c phases resulting when a mixture is flashed. c kvalue: Calculates equilibrium ratios. c oildensity: Calculates oil density. c*********************************************************************** c*********************************************************************** c Declarations c*********************************************************************** c======================================================================= c Constants c======================================================================= REAL MAir,MaxError PARAMETER (cvCf=5.615,cvRankine=459.67,DenWater=62.365, 1 MAir=28.9625,MaxError=1E-06,NumComp=12,R=10.73) c======================================================================= c Variables c======================================================================= REAL H(NumComp),K(NumComp),M(NumComp),molgas,molgstage,moloil, 1 molvol,molsepgas(NumComp),MWRes,MWST,M7Plus, 1 PSep(NumSep),TSep(NumSep),x(NumComp),y(NumComp), 1 ysepgas(NumComp),z(NumComp),zsep(NumComp) c======================================================================= c Initialize Arrays c======================================================================= DATA M/44.010,34.076,28.013,16.043,30.070,44.097, 1 58.124,58.124,72.151,72.151,86.178,0.0/ DATA H/0.0,0.0,0.0,1010.0,1769.6,2516.1,3251.9, 1 3262.3,4000.9,4008.9,4655.9,6248.9/ c---------------------------------------------------------------------- c Molecular weights and gross heating values are from Gas c Processors Suppliers Association, Engineering Data Book, c Volume II (1987) 23-2:4. Gross heating value for octane is c used for heptanes plus. c---------------------------------------------------------------------- c*********************************************************************** c Main Program c*********************************************************************** M(12) = M7Plus molgas = 0.0 moloil = 1.0 volg = 0.0 volmol = R*(Tsc + cvRankine)/Psc DO 10 i = 1,NumComp zsep(i) = z(i) molsepgas(i) = 0.0 10 CONTINUE c======================================================================= c Calculate moles and composition of stock tank oil and separator c gas resulting from multiple separator flashes. c======================================================================= DO 20 i = 1,NumSep CALL kvalue(PSep(i),TSep(i),K) CALL flash(NumComp,zsep,K,MaxError,V,x,y,NumIter,F) molgstage = V*moloil molgas = molgas + molgstage volg = volg + volmol*molgstage moloil = (1.0 - V)*moloil DO 30 j = 1,NumComp zsep(j) = x(j) molsepgas(j) = molsepgas(j) + y(j)*molgstage 30 CONTINUE 20 CONTINUE c======================================================================= c Calculate molecular weight of reservoir and stock tank oil. c Calculate separator gas composition and properties. c======================================================================= MWRes = 0.0 MWST = 0.0 GG = 0.0 GHV = 0.0 DO 40 i = 1,NumComp MWRes = MWRes + z(i)*M(i) MWST = MWST + x(i)*M(i) ysepgas(i) = molsepgas(i)/molgas GG = GG + ysepgas(i)*M(i)/MAir GHV = GHV + ysepgas(i)*H(i) 40 CONTINUE c======================================================================= c Calculate formation volume factor, stock tank gravity, and c gas-oil ratio. c======================================================================= CALL oildensity(z,Pres,Tres,M7Plus,SG7Plus,DenRes) CALL oildensity(x,Psc,Tsc,M7Plus,SG7Plus,DenST) volres = MWRes/DenRes volST = moloil*MWST/DenST FVF = volres/volST API = 141.5/(DenST/DenWater)-131.5 GOR = volg*cvCf/volST RETURN END