1. BASIC PETROPHYSICAL FORMULAE
Compiled By:- Muhammad Zahid

2. 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)

3. Sonic Porosity (Wyllie)
PHIS = (DT - DTma) / (DTfld - DTma)
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
SoPhiH = (1-SwA) * PHIA

4. 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)

5. Resistivity Temp Correction
T1 and T2 in 'F
R2 = R1 * (T ) / (T )
T1 and T2 in 'C
R2 = R1 * (T ) / (T )

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

7. 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)) )

8. 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 = ~ * <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)) ))

9. 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 = ( (Vshl+0.7)^2)^0.5
Steiber Shale Correction
Vshl = 0.5 * Vshl / (1.5 - Vshl)

10. 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

11. 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

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