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Rock Properties Equations

Browse 76 rock properties petroleum engineering equations with formulas, inputs, outputs, units, and sources.

Rock-property calculations support porosity, density, sonic, neutron, gamma-ray, photoelectric, wettability, and core-log interpretation checks.

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PetrophysicsRock Properties

Acoustic Transit Time

Δt=106v\Delta t=\frac{10^6}{v}
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PetrophysicsRock Properties

Adhesion Tension from Water-Oil Interfacial Tension

τ=σwocos⁡θ\tau=\sigma_{wo}\cos\theta
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PetrophysicsRock Properties

Air Density for de Nouy Upper Phase Correction

ρair=4.324×10−2PT\rho_{air}=4.324\times10^{-2}\frac{P}{T}
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PetrophysicsRock Properties

Amott-Harvey Wettability Index

IAH=Iw−IoI_{AH}=I_w-I_o
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PetrophysicsRock Properties

Amplitude Transmission Coefficient in Seismic Reflection and Refraction

T=2Z1Z2+Z1T=\frac{2Z_1}{Z_2+Z_1}
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PetrophysicsRock Properties

Apparent Gamma Ray Recorder Intensity

Ja(t)=J1+(J2−J1)(1−e−t/rc)J_a(t)=J_1+(J_2-J_1)(1-e^{-t/r_c})
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PetrophysicsRock Properties

Apparent Interfacial Tension - de Nouy Ring Method

S=mg2lS=\frac{mg}{2l}
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PetrophysicsRock Properties

Atlas Wireline Neutron Lifetime Log

Σ=3.15τ\Sigma=\frac{3.15}{\tau}
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PetrophysicsRock Properties

Clavier Shale Volume from Gamma Ray Index

Vsh=1.7−3.38−(IGR+0.7)2V_{sh}=1.7-\sqrt{3.38-(I_{GR}+0.7)^2}
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PetrophysicsRock Properties

Coates NMR Permeability from Free-Fluid Ratio

k=(ϕNMRC)4(FFIBVI)2k=\left(\frac{\phi_{NMR}}{C}\right)^4\left(\frac{\mathrm{FFI}}{\mathrm{BVI}}\right)^2
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PetrophysicsRock Properties

Composite Capture Cross Section of the Formation Schlumberger Thermal Decay Time Tool

Σ=4.55τ\Sigma=\frac{4.55}{\tau}
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PetrophysicsRock Properties

Contact Angle from Interfacial Tensions

θ=cos⁡−1(σso−σswσwo)\theta=\cos^{-1}\left(\frac{\sigma_{so}-\sigma_{sw}}{\sigma_{wo}}\right)
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Reservoir EngineeringRock Properties

Core Bulk Volume from Saturated and Immersed Weights

Vb=Ws−WiρsV_b=\frac{W_s-W_i}{\rho_s}
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Reservoir EngineeringRock Properties

Core Pore Volume from Saturated and Dry Weights

Vp=Ws−WdρsV_p=\frac{W_s-W_d}{\rho_s}
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PetrophysicsRock Properties

Corrected Interfacial Tension - de Nouy Ring Method

σ=SC\sigma=SC
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PetrophysicsRock Properties

de Nouy Ring Interfacial Tension Correction Factor

C=0.7250+0.01452Sl2(ρD−ρd)+0.04534−1.679rRC=0.7250+\sqrt{\frac{0.01452S}{l^2(\rho_D-\rho_d)}+0.04534-\frac{1.679r}{R}}
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PetrophysicsRock Properties

Density Log Porosity from Bulk Density

Φ=ρma−ρbρma−ρf\Phi=\frac{\rho_{ma}-\rho_b}{\rho_{ma}-\rho_f}
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PetrophysicsRock Properties

Effective Photoelectric Absorption Cross Section Index

Pe=(Z10)3.6P_e=\left(\frac{Z}{10}\right)^{3.6}
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Reservoir EngineeringRock Properties

Effective Porosity from Connected Pore Volume

ϕe=VconnectedVb\phi_e = \frac{V_{connected}}{V_b}
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PetrophysicsRock Properties

Electron Density Index for Gamma-Gamma Absorption Logging

ρe=2NeNA\rho_e=\frac{2N_e}{N_A}
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PetrophysicsRock Properties

Epithermal Neutron Diffusion Coefficient

De=ξLe2ΣeD_e=\xi L_e^2\Sigma_e
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PetrophysicsRock Properties

Epithermal Neutron Flux Distribution

ψe=NN4πDee−r/Ler\psi_e=\frac{N_N}{4\pi D_e}\frac{e^{-r/L_e}}{r}
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PetrophysicsRock Properties

Error Percentage of Porosity Measurements

Eϕ=ϕm−ϕpsϕm100E_\phi=\frac{\phi_m-\phi_{ps}}{\phi_m}100
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Reservoir EngineeringRock Properties

Exponential Pore Volume from Rock Compressibility

PV=PVrefexp⁡(cr(P−Pref))PV = PV_{ref}\exp(c_r(P-P_{ref}))
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Reservoir EngineeringRock Properties

Exponential Porosity from Rock Compressibility

ϕ=ϕrefexp⁡(cr(P−Pref))\phi = \phi_{ref}\exp(c_r(P-P_{ref}))
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PetrophysicsRock Properties

Fraction of Total Porosity Occupied by Clays

q=ΦS−ΦDΦSq=\frac{\Phi_S-\Phi_D}{\Phi_S}
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PetrophysicsRock Properties

Fresh Water-Filled Porosity - Limestones

Φ=ρls−ρbρls−ρw\Phi=\frac{\rho_{ls}-\rho_b}{\rho_{ls}-\rho_w}
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PetrophysicsRock Properties

Gamma Ray Log Shale Index

IGR=GR−GRclGRsh−GRclI_{GR}=\frac{GR-GR_{cl}}{GR_{sh}-GR_{cl}}
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PetrophysicsRock Properties

Gas-Effect Corrected Porosity from Neutron-Density Logs

Φcorr=(ΦD2+ΦN22)0.5\Phi_{corr}=\left(\frac{\Phi_D^2+\Phi_N^2}{2}\right)^{0.5}
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PetrophysicsRock Properties

Half Thickness Value

h1/2=0.693αlh_{1/2}=\frac{0.693}{\alpha_l}
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Reservoir EngineeringRock Properties

Ineffective Porosity from Disconnected Pore Volume

ϕin=VdisVb\phi_{in}=\frac{V_{dis}}{V_b}
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PetrophysicsRock Properties

Integrated Radial Geometric Factor

G(r)=1−e−r/hˉG(r)=1-e^{-r/\bar{h}}
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PetrophysicsRock Properties

Larionov Older-Rock Shale Volume from Gamma Ray Index

Vsh=0.33(22IGR−1)V_{sh}=0.33\left(2^{2I_{GR}}-1\right)
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PetrophysicsRock Properties

Larionov Tertiary-Rock Shale Volume from Gamma Ray Index

Vsh=0.083(23.7IGR−1)V_{sh}=0.083\left(2^{3.7I_{GR}}-1\right)
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Reservoir EngineeringRock Properties

Leijnse Porosity from Rock Compressibility

ϕ=1−(1−ϕref)exp⁡[−cr(P−Pref)]\phi = 1-(1-\phi_{ref})\exp[-c_r(P-P_{ref})]
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Reservoir EngineeringRock Properties

Leverett J-Function from Capillary Pressure

J=Pcσcos⁡θ(kϕ)0.5J=\frac{P_c}{\sigma\cos\theta}\left(\frac{k}{\phi}\right)^{0.5}
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PetrophysicsRock Properties

Linear Absorption Attenuation Coefficient

αl=σN\alpha_l=\sigma N
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PetrophysicsRock Properties

Liquid Permeability - Permeameter Lab Measurement

k=μVLAPtk = \frac{\mu V L}{A P t}
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Reservoir EngineeringRock Properties

Maximum Oil Column Height in Cap Rock

H=Pa−Pw+Gohα+Pcρ−GoH=\frac{P_a-P_w+G_oh\alpha+P_c}{\rho-G_o}
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PetrophysicsRock Properties

Mean Free Path Photon Absorption

h=1αlh=\frac{1}{\alpha_l}
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PetrophysicsRock Properties

Neutron Lethargy Logarithmic Energy Decrement

u=ln⁡(EoE)u=\ln\left(\frac{E_o}{E}\right)
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PetrophysicsRock Properties

Neutron Porosity in a Shaly Formation

ΦN=ΦT+VshΦNsh\Phi_N=\Phi_T+V_{sh}\Phi_{Nsh}
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PetrophysicsRock Properties

NMR Free-Fluid Index from Porosity Partition

FFI=MPHI−BVI\mathrm{FFI}=\mathrm{MPHI}-\mathrm{BVI}
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PetrophysicsRock Properties

Pair Production Gamma Ray Interactions

Ee=Ec−EE_e=E_c-E
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PetrophysicsRock Properties

Photoelectric Absorption Cross Sectional Area

αpe=12.1Z3.6Eγ3.15\alpha_{pe}=\frac{12.1Z^{3.6}}{E_\gamma^{3.15}}
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PetrophysicsRock Properties

Poissons Ratio Seismic Arrival Time Method

ν=Vp2−2Vs22(Vp2−Vs2)\nu=\frac{V_p^2-2V_s^2}{2\left(V_p^2-V_s^2\right)}
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Reservoir EngineeringRock Properties

Pore Throat Sorting from Capillary Pressure Quartiles

PTS=(Q3Q1)0.5PTS=\left(\frac{Q_3}{Q_1}\right)^{0.5}
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PetrophysicsRock Properties

Porosity from Neutron Flux Response

ϕ=α−βlog⁡10(N)\phi=\alpha-\beta\log_{10}(N)
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PetrophysicsRock Properties

Pycnometer Volume Correction

Vg=Vk[1+Ω(Tt−Tk)]V_g=V_k\left[1+\Omega(T_t-T_k)\right]
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Reservoir EngineeringRock Properties

Quadratic Porosity Multiplier from Rock Compressibility

ϕ=ϕref(1+X+X22)\phi = \phi_{ref}\left(1+X+\frac{X^2}{2}\right)
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PetrophysicsRock Properties

Rate of Radioactive Decay

N=Noe−CdtN=N_o e^{-C_d t}
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PetrophysicsRock Properties

Raymer-Hunt Transform - Porosity Transit Time Relationship

Δt=((1−ϕ)2Δtma+ϕΔtf)−1\Delta t=\left(\frac{(1-\phi)^2}{\Delta t_{ma}}+\frac{\phi}{\Delta t_f}\right)^{-1}
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PetrophysicsRock Properties

Relation Between Concentration of K Th or U and Recorded Total Gamma Ray Signal

γ=4CTh+8CU+CK\gamma=4C_{Th}+8C_U+C_K
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PetrophysicsRock Properties

Relative Centrifugal Force

RCF=(RPM265)2dRCF=\left(\frac{RPM}{265}\right)^2d
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PetrophysicsRock Properties

Reservoir Wettability Characterization Rise-in-Core Method

cos⁡θ12=μ1ρ22−μ2ρ12ρ12ρ22CγL2L1m2t\cos\theta_{12}=\frac{\mu_1\rho_2^2-\mu_2\rho_1^2}{\rho_1^2\rho_2^2C\gamma_{L2L1}}\frac{m^2}{t}
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PetrophysicsRock Properties

SDR NMR Permeability from T2 Geometric Mean

k=aϕNMR4T2gm2k=a\phi_{NMR}^4T_{2gm}^2
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PetrophysicsRock Properties

Shale Index from Gamma Ray Spectrometry - Potassium

Ish,K=CK,log−CK,minCK,sh−CK,minI_{sh,K}=\frac{C_{K,log}-C_{K,min}}{C_{K,sh}-C_{K,min}}
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PetrophysicsRock Properties

Shale Index from Gamma Ray Spectrometry - Thorium

Ish,Th=CTh,log−CTh,minCTh,sh−CTh,minI_{sh,Th}=\frac{C_{Th,log}-C_{Th,min}}{C_{Th,sh}-C_{Th,min}}
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PetrophysicsRock Properties

Shale Index from Gamma Ray Spectrometry - Uranium-Free Gamma

Ish,Uf=GUf,log−GUf,minGUf,sh−GUf,minI_{sh,Uf}=\frac{G_{Uf,log}-G_{Uf,min}}{G_{Uf,sh}-G_{Uf,min}}
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PetrophysicsRock Properties

Slowness of the Formation

Δt=tlLs−DbΔtm2(Ls2+Db2)−tl2Ls2+Db2\Delta t=\frac{t_lL_s-D_b\sqrt{\Delta t_m^2(L_s^2+D_b^2)-t_l^2}}{L_s^2+D_b^2}
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PetrophysicsRock Properties

Sonic Compaction Correction Factor from Shale Transit Time

Cp=Δtshc100C_p=\Delta t_{sh}\frac{c}{100}
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PetrophysicsRock Properties

Sonic First-Arrival Time in a Borehole

tlog=Lsvf+dh−(dt+2lc)vm1−(vmvf)2t_{log}=\frac{L_s}{v_f}+\frac{d_h-(d_t+2l_c)}{v_m}\sqrt{1-\left(\frac{v_m}{v_f}\right)^2}
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PetrophysicsRock Properties

Sonic Porosity Raymer-Hunt-Gardner Method

Φsonic=CRHGΔt−ΔtmaΔt\Phi_{sonic}=C_{RHG}\frac{\Delta t-\Delta t_{ma}}{\Delta t}
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PetrophysicsRock Properties

Spacing Between Transmitter and Receiver

(Ls)c=2soff1+Cmf1−Cmf(L_s)_c=2s_{off}\sqrt{\frac{1+C_{mf}}{1-C_{mf}}}
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PetrophysicsRock Properties

Stieber Shale Volume from Gamma Ray Index

Vsh=IGR3−2IGRV_{sh}=\frac{I_{GR}}{3-2I_{GR}}
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Reservoir EngineeringRock Properties

Total Pore Volume Compressibility

cf=1PVi(PVi−PVpPi−P)c_f = \frac{1}{PV_i}\left(\frac{PV_i - PV_p}{P_i - P}\right)
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Reservoir EngineeringRock Properties

Total Porosity from Bulk and Grain Volume

ϕt=Vb−VgVb\phi_t=\frac{V_b-V_g}{V_b}
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Reservoir EngineeringRock Properties

Total Porosity from Pore and Bulk Volume

ϕt=VpVb\phi_t=\frac{V_p}{V_b}
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Reservoir EngineeringRock Properties

Total Porosity from Pore and Grain Volume

ϕt=VpVp+Vg\phi_t=\frac{V_p}{V_p+V_g}
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PetrophysicsRock Properties

Total Porosity from Pore Volumes

ϕ=Vi+VdVb\phi = \frac{V_i + V_d}{V_b}
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PetrophysicsRock Properties

True Sonic Porosity from Compaction Correction

Φt=ΦaCp\Phi_t=\frac{\Phi_a}{C_p}
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PetrophysicsRock Properties

USBM Wettability Index

IU=log⁡10(A1A2)I_U=\log_{10}\left(\frac{A_1}{A_2}\right)
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PetrophysicsRock Properties

Volumetric Photoelectric Absorption Cross Section

U=PeρeU=P_e\rho_e
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PetrophysicsRock Properties

Wavelength Equation

λ=Cf\lambda=\frac{C}{f}
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PetrophysicsRock Properties

Wyllie Time-Average Sonic Porosity - Compacted Formations

Φs=Δt−ΔtmaΔtf−Δtma\Phi_s=\frac{\Delta t-\Delta t_{ma}}{\Delta t_f-\Delta t_{ma}}
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PetrophysicsRock Properties

Wyllie Time-Average Sonic Porosity - Uncompacted Formations

Φs=(Δt−Δtma)/(Δtf−Δtma)Bcp\Phi_s=\frac{(\Delta t-\Delta t_{ma})/(\Delta t_f-\Delta t_{ma})}{B_{cp}}
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