BASIC PETROPHYSICAL FORMULAE Compiled By:- Muhammad Zahidpetrophysicist786@hotmail.com

POROSITYEffective PorosityPHIE = PHIA * (1-Vshl)Density PorosityPHID = (RhoM - RHOB) / (RhoM - RhoF)Average Neutron Density PorosityPHIA = (PHID + PHIN) / 2Gamma Ray Neutron PorosityEnter Values for PorMax, PorMin...PorMax = 0.35PorMin = 0.02Enter Values in Counts Per Second or API...CPS_PorMax = 75CPS_PorMin = 600B = log(PorMax/PorMin) / (CPS_PorMax - CPS_PorMin)A = PorMax / 10 ^ (B*CPS_PorMax)PHIGRN = A * 10 ^ (B * CPS)

Sonic Porosity (Wyllie)PHIS = (DT - DTma) / (DTfld - DTma)Sonic Porosity (Wyllie)Enter Compaction Coefficient below,Cmp = 1.0PHIS = (1/Cmp) * (DT - DTma) / (DTfld - DTma)Sonic Porosity (Empirical)PHIS = 0.67 * (DT - DTma) / DTApparent Sonic MatrixDTma = ( DT - PHIA * DTfld ) / (1 - PHIA)Apparent Density MatrixRHOMa = (RHOB - PHIA * RhoF) / (1 - PHIA)Bulk Volume WaterBVW = PHIA * SwA.Hydrocarbon Pore VolumeHCPV = (1-SwA) * PHIA Hydrocarbon Pore VolumeSoPhiH = (1-SwA) * PHIA

WATER RESISTIVITYArchie RoRo = a * Rw / (PHIA^m)Apparent Water ResistivityRwa = RT * PHIA^mConductivityCOND = 1000/RTRw from Dual WaterRwDW = Rw * RwBnd / (Rw * Vshl + (1-Vshl) * RwBnd)Ro from Dual WaterRoDW = (1 / (PHIA^m)) * (Rw * RwBnd / (Rw * Vshl + RwBnd * (1 - Vshl)))Modified Simandoux RoIf (Vshl < 1)RoMS = 1/(PHIE^m / (a* Rw*(1-Vshl)) + Vshl/Rshl)

Resistivity Temp CorrectionT1 and T2 in 'FR2 = R1 * (T1 + 6.77) / (T2 + 6.77)Resistivity Temp CorrectionT1 and T2 in 'CR2 = R1 * (T1 + 21.5) / (T2 + 21.5)

WATER SATURATIONArchie Water SaturationSwA = sqrt( Rw / (RT * PHIA^2) )Archie Water SaturationSwA = (a * Rw / ( RT * PHIA^m) )^(1/n)Archie Water Saturation (Humble)SwA = sqrt( .62 * Rw / (RT * PHIA ^2.15) )Archie Water SaturationSwA = sqrt( Rw / (RT * PHID ^m) )Archie Water SaturationSwA = sqrt(Ro / RT)Archie Water SaturationSwA = sqrt(Rw / Rwa)SwA = min( 1, max( 0, SwA )

Dual Water SwT & SwECalculate SwT Total PorosityY = Vshl * ( RwBnd - Rw ) / ( 2 * RwBnd )SwT = Y +( (Rw / ( RT * PHIA^2 ) ) + Y^2 )^.5SwT = min( 1, max( Vshl, SwT ) )Calculate SwE Effective PorosityIf ( Vshl < .75 )SwE = ( SwT - Vshl ) / ( 1 - Vshl )Modified Simandoux SwMSIf (Vshl < 1)SwMS = (sqrt( (Vshl/Rshl)^2 + 4*PHIE^m/(a*Rw*(1-Vshl)*RT) ) - Vshl/Rshl)/(2*PHIE^m/(a*Rw*(1-Vshl)) )

Indonesian SwISwI = sqrt(1/RT) / ( Vshl^(1- 0.5*Vshl) /sqrt(Rshl) + sqrt( PHIE^m / (a*Rw)) )Ratio Method SwRequires normalized SP,Rmf/Rw ratio from SP...K = ~ 61 + 0.1333 * K = -71RmfRwRatio = 10 ^ (SP / K)Sw = Min( 1, ( (ResS/ResD) / (RmfRwRatio) ) ^(5/8) )Vshl = min(1, max(0, (GR-GRcln) / (GRshl-GRcln) ))Vshl = min(1, max(0, (SP-SPcln) / (SPshl-SPcln) ))Vshl = min(1, max(0, (RHOB - RhoM + PHIN * (RhoM - RhoF)) / (RhoShl - RhoM +HIshl * (RhoM - RhoF)) ))

SHALE VOLUMECalculate Vshl from Minimum of GR, SP & N/DVshl_GR = (GR-GRcln) / (GRshl-GRcln) )Vshl_SP = (SP-SPcln) / (SPshl-SPcln) ))Vshl_ND = (RHOB - RhoM + PHIN * (RhoM - RhoF)) / (RhoShl - RhoM +HIshl * (RhoM - RhoF)Vshl = Min(Vshl_GR , Min( Vshl_SP , Vshl_ND ))Clavier Shale CorrectionVshl = 1.7 - (3.38 - (Vshl+0.7)^2)^0.5Steiber Shale CorrectionVshl = 0.5 * Vshl / (1.5 - Vshl)

DT EQUATIONSFaust's Equation for DTDT_F = 1000/(2 * (DEPTH * RT) ^(1 / 6))Gardner's Equation for DTDT_G = ((25 / RHOB) ^4) /140Sonic from Apparent PorosityDT_P = DTma + PHIA * ( DTfld - DTma)Sonic 3pt Average CurveDTAve = (DT [-1] + DT + DT[1])/3Sonic 5pt Average CurveDTAve = (DT[-2] + DT[-1] +DT + DT[1] + DT[2])/5Sonic 7pt Average CurveDTAve = (DT[-3] + DT[-2] + DT[-1] +DT + DT[1] + DT[2]+ DT[3])/7

PERMEABILITYTixier PermeabilityK = (250 * PHIE^3/SwIrr)^2Timur PermeabilityK = (100 * PHIE^2.25/SwIrr)^2Coates PermeabilityK = (70 * PHIE^2 * (1- SwIrr)/SwIrr)^2

MISCELLANEOUSOil in Barrels; Depth in FeetBBL = 7758 * Acres * PHIA * (1 - SwA)Gas in Mcfd; Depth in FeetMCF = 43.560 * Acres * PHIA * (1 - SwA)Oil in Barrels; Depth in MetersBBL = 25450 * Acres * PHIA * (1 - SwA)Gas in Mcfd; Depth in MetersMCF = 142.9 * Acres * PHIA * (1 - SwA)Oil in Barrels; Depth in MetersBBL = 62890 * Hectares * PHIA * (1 - SwA)Gas in Mcfd; Depth in MetersMCF = 353.1 * Hectares * * PHIA * (1 - SwA)Oil in Barrels with Pay criteriaIf (PAY >0)BBL = 7758 * Acres * PHIA * (1 - SwA)Gas in Mcfd with PAY criteriaIf (PAY >0)MCF = 43.560 * Acres * PHIA * (1 - SwA)