BASIC PETROPHYSICAL FORMULAE

Compiled By:- Muhammad Zahidpetrophysicist786@hotmail.com

POROSITY• Effective Porosity

• PHIE = PHIA * (1-Vshl)

• Density Porosity

• PHID = (RhoM - RHOB) / (RhoM - RhoF)

• Average Neutron Density Porosity

• PHIA = (PHID + PHIN) / 2

• Gamma Ray Neutron Porosity

• Enter Values for PorMax, PorMin...

• PorMax = 0.35

• PorMin = 0.02

• Enter Values in Counts Per Second or API...

• CPS_PorMax = 75

• CPS_PorMin = 600

• B = 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 = 1.0• PHIS = (1/Cmp) * (DT - DTma) / (DTfld - DTma)• Sonic Porosity (Empirical)• PHIS = 0.67 * (DT - DTma) / DT• Apparent Sonic Matrix• DTma = ( DT - PHIA * DTfld ) / (1 - PHIA)• Apparent Density Matrix• RHOMa = (RHOB - PHIA * RhoF) / (1 - PHIA)• Bulk Volume Water• BVW = PHIA * SwA.• Hydrocarbon Pore Volume• HCPV = (1-SwA) * PHIA • Hydrocarbon Pore Volume• SoPhiH = (1-SwA) * PHIA

WATER RESISTIVITY• Archie Ro• Ro = a * Rw / (PHIA^m)• Apparent Water Resistivity• Rwa = RT * PHIA^m• Conductivity• COND = 1000/RT• Rw from Dual Water• RwDW = Rw * RwBnd / (Rw * Vshl + (1-Vshl) * RwBnd)• Ro from Dual Water• RoDW = (1 / (PHIA^m)) * (Rw * RwBnd / (Rw * Vshl + RwBnd * (1 -

Vshl)))• Modified Simandoux Ro• If (Vshl < 1)• RoMS = 1/(PHIE^m / (a* Rw*(1-Vshl)) + Vshl/Rshl)

• Resistivity Temp Correction

• T1 and T2 in 'F

• R2 = R1 * (T1 + 6.77) / (T2 + 6.77)

• Resistivity Temp Correction

• T1 and T2 in 'C

• R2 = R1 * (T1 + 21.5) / (T2 + 21.5)

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

• Dual Water SwT & SwE• Calculate SwT Total Porosity• Y = Vshl * ( RwBnd - Rw ) / ( 2 * RwBnd )• SwT = Y +( (Rw / ( RT * PHIA^2 ) ) + Y^2 )^.5• SwT = min( 1, max( Vshl, SwT ) )• Calculate SwE Effective Porosity• If ( Vshl < .75 )• SwE = ( SwT - Vshl ) / ( 1 - Vshl )• Modified Simandoux SwMS• If (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 SwI• SwI = sqrt(1/RT) / ( Vshl^(1- 0.5*Vshl) /sqrt(Rshl) + sqrt( PHIE^m /

(a*Rw)) )• Ratio Method Sw• Requires normalized SP,• Rmf/Rw ratio from SP...• K = ~ 61 + 0.1333 * <Temp>• K = -71• RmfRwRatio = 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 VOLUME• Calculate Vshl from Minimum of GR, SP & N/D

• Vshl_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 Correction

• Vshl = 1.7 - (3.38 - (Vshl+0.7)^2)^0.5

• Steiber Shale Correction

• Vshl = 0.5 * Vshl / (1.5 - Vshl)

DT EQUATIONS• Faust's Equation for DT• DT_F = 1000/(2 * (DEPTH * RT) ^(1 / 6))• Gardner's Equation for DT• DT_G = ((25 / RHOB) ^4) /140• Sonic from Apparent Porosity• DT_P = DTma + PHIA * ( DTfld - DTma)• Sonic 3pt Average Curve• DTAve = (DT [-1] + DT + DT[1])/3• Sonic 5pt Average Curve• DTAve = (DT[-2] + DT[-1] +DT + DT[1] + DT[2])/5• Sonic 7pt Average Curve• DTAve = (DT[-3] + DT[-2] + DT[-1] +DT + DT[1] + DT[2]+ DT[3])/7

PERMEABILITY• Tixier Permeability

• K = (250 * PHIE^3/SwIrr)^2

• Timur Permeability

• K = (100 * PHIE^2.25/SwIrr)^2

• Coates Permeability

• K = (70 * PHIE^2 * (1- SwIrr)/SwIrr)^2

MISCELLANEOUS• Oil in Barrels; Depth in Feet• BBL = 7758 * Acres * PHIA * (1 - SwA)• Gas in Mcfd; Depth in Feet• MCF = 43.560 * Acres * PHIA * (1 - SwA)• Oil in Barrels; Depth in Meters• BBL = 25450 * Acres * PHIA * (1 - SwA)• Gas in Mcfd; Depth in Meters• MCF = 142.9 * Acres * PHIA * (1 - SwA)• Oil in Barrels; Depth in Meters• BBL = 62890 * Hectares * PHIA * (1 - SwA)• Gas in Mcfd; Depth in Meters• MCF = 353.1 * Hectares * <Step> * PHIA * (1 - SwA)• Oil in Barrels with Pay criteria• If (PAY >0)• BBL = 7758 * Acres * PHIA * (1 - SwA)• Gas in Mcfd with PAY criteria• If (PAY >0)• MCF = 43.560 * Acres * PHIA * (1 - SwA)