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Symbols in alphabetical order

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Dimensions: L=length, m=mass, q=electrical charge, t=time, T=temperature, M=money, and n=amount of substance.

Letter Symbol Reserve SPE Letter Symbol Quantity Dimensions
a activity
a Fa air requirement various
a decline factor, nominal
a La,L1 distance between like wells (injection or projection) in a row L
aE FaE air requirement, unit, in laboratory experimental run, volumes of air per unit mass of pack L3/m
aR FaR air requirement, unit, in reservoir, volumes of air per unit bulk volume of reservoir rock
A amplitude various
A S area L2
A atomic weight m
A S cross section (area) L2
A F helmholtz function (work function) mL2/t2
Ac amplitude, compressional wave various
Ar amplitude, relative various
As amplitude, shear wave various
b W breadth, width, or (primarily in fracturing) various
b Y intercept various
b f,F reciprocal formation volume factor, volume at standard conditions divided by volume at reservoir conditions (shrinkage factor)
b W width, breadth, or (primarily in fracturing) thickness L
bg fg,Fg reciprocal gas formation volume factor
bgb fgb,Fgb reciprocal gas formation volume factor at bubblepoint conditions
bo fo,Fo reciprocal oil formation volume factor (shrinkage factor)
B C correction term or correction factor (either additive or multiplicative)
B F formation volume factor, volume at reservoir conditions divided by volume at standard conditions
Bg Fg formation volume factor, gas
Bgb Fgb bubblepoint formation volume factor, gas
Bgb Fgb formation volume factor at bubblepoint conditions, gas
Bo Fo formation volume factor, oil
Bob Fob bubblepoint formation volume factor, oil
Bob Fob formation volume factor at bubblepoint conditions, oil
Bt FT formation volume factor, total (two-phase)
Bw Fw formation volume factor, water
c k,κ compressibility Lt2/m
cf kff compressibility, formation or rock Lt2/m
cg kgg compressibility, gas Lt2/m
co koo compressibility, oil Lt2/m
cpr kprpr compressibility, pseudoreduced
cw kww compressibility, water Lt2/m
C capacitance q2t2/mL2
C Ct capital investments, summation of all M
C coefficient of gas-well backpressure curve L3–2nt4nm2n
C nC components, number of
C c,n concentration various
C σ conductivity (electrical logging) tq2/mL3
C K conductivity, other than electrical (with subscripts) various
C c,n salinity various
C c specific heat (always with phase or system subscripts) L2/t2T
C waterdrive constant L4t2/m
Ca σα conductivity, apparent tq2/mL3
CC1 cC1 concentration, methane (concentration of other paraffin hydrocarbons would be indicated similarly, CC2, C¬C3, etc.) various
CfD conductivity, fraction, dimensionless
Ci capital investment, initial M
Ck capital investment in period k M
CL cL,nL content, condensate or natural gas liquids various
CL waterdrive constant, linear aquifer L4t2/m
Cm cmnm fuel concentration, unit (see symbol m) various
CO2 cO2 concentration, oxygen (concentration of other elements or compounds would be indicated similarly, CCO2, CN2, etc.)
Cpv investment at present value M
Cwg cwg,nwg content, wet-gas various
d decline factor, effective
d D diameter L
d Ld,L2 distance between adjacent rows of injection and production wells L
dh dH,Dh diameter, hole L
di dl,Di diameter, invaded zone (electrically equivalent) L
dp Dp diameter, mean particle L
D deliverability (gas well) L3/t
D depletion, depreciation, or amortization (all nonreal account entries) various
D y,H depth L
D µ,δ diffusion coefficient L2/t
e i encroachment or influx rate L3/t
eg ig encroachment or influx rate, gas L3/t
eo io encroachment or influx rate, oil L3/t
eO2 EO2 oxygen utilization
ew iw encroachment or influx rate, water L3/t
ez exp z exponential function
E η,e efficiency
E V electromotive force mL2/t2q
E U energy mL2/t2
E expense, total (except income taxes) M
E modulus of elasticity (Young’s modulus) m/Lt
EA ηA,eA efficiency, areal (used in describing results of model studies only): area swept in a model divided by total model reservoir area (see EP)
Ec Φc electrochemical component of the SP mL2/t2q
ED ηD,eD efficiency, displacement: volume of hydrocarbons (oil or gas) displaced from individual pores or small groups of pores divided by the volume of hydrocarbon in the same pores just prior to
EDb ηDb,eDb efficiency, displacement, from burned portion of in-situ combustion pattern
EDu ηDu,eDu efficiency, displacement, from unburned portion of in-situ combustion pattern
EI ηI,eI efficiency, invasion (vertical): hydrocarbon pore space invaded (affected, contacted) by the injection fluid or heat front divided by the hydrocarbon pore space enclosed in all layers behind the injected fluid or heat front
Ek Φk electrokinetic component of the SP mL2/t2q
Ek kinetic energy mL2/t2
En Euler’s number
EpSP ΦSP pseudo-SP mL2/qt2
Ep ηP,eP efficiency, pattern sweep (developed from areal efficiency by proper weighting for variations in net pay thickness, porosity, and hydrocarbon saturation): hydrocarbon pore space enclosed behind the injected fluid or heat front divided by total hydrocarbon pore space of the reservoir or project
ER ηR,eR efficiency, overall reservoir recovery: volume of hydrocarbons recovered divided by volume of hydrocarbons in place at start of project (ER=EPEIED=EVED)
ESP ΦSP SP (measured SP) (self-potential) mL2/t2q
ESSP ΦSSP SSP (static SP) mL2/t2q
Eu expense per unit M
EV ηV,eV efficiency, volumetric; product of pattern sweep and invasion efficiencies
EVb ηVb,eVb efficiency, volumetric, for burned portion only, in-situ combustion pattern
−Ei(−x) exponential integral, dt, x positive
Ei(x) x positive
f F fraction (such as the fraction of a flow stream consisting of a particular phase)
f v frequency 1/t
f friction factor
f fugacity m/Lt2
fg Fg fraction gas
fg Fg mole fraction gas, V/(L+V)
fL FL,f (script ℓ) fraction liquid
fL FL,f (script ℓ) mole fraction liquid, L/(L+V)
fs Q,x quality (usually of steam)
fV fVb, Vbf fraction of bulk (total) volume
fsØh Øigfsh fraction of intergranular space ("porosity") occupied by all shales
fØshd Øimfshd fraction of intermatrix space (“porosity”) occupied by nonstructural dispersed shale
fØw Øigfw fraction of intergranular space (“porosity”) occupied by water
F degrees of freedom
F f fluid (generalized) various
F Q force, mechanical mL/t2
F ratio or factor in general (always with identifying subscripts)
FaF air/fuel ratio various
FB factor, turbulence
FR formation resistivity factor—equals R0/Rw
(a numerical subscript to F indicates the value Rw)
Fs Fd damage ratio or condition ratio
(conditions relative to formation conditions unaffected by well operations)
FwF water/fuel ratio various
Fwo water/oil ratio, producing, instantaneous
Fwop water/oil ratio, cumulative
FWV γ specific weight mL2/t2
g acceleration of gravity L/t2
g γ gradient various
gc conversion factor in Newton’s second law of motion
gG gg gradient, geothermal T/L
G F free energy (Gibbs function) mL2/t2
G g gas (any gas, including air) always with identifying subscripts various
G g gas in place in reservoir, total initial L3
G fG geometric factor (multiplier) (electrical logging)
G Es shear modulus m/Lt2
Gan fGan factor, geometric (multiplier), annulus (electrical logging)
Gan fGan geometric factor (multiplier), annulus (electrical logging)
Ge ge gas influx (encroachment), cumulative L3
GFi gFi free-gas volume, initial reservoir (=mNBoi) L3
GFp gFp free gas produced, cumulative L3
Gi gi gas injected, cumulative L3
Gi fGi geometric factor (multiplier), invaded zone (electrical logging) L3
GL gL condensate liquids in place in reservoir, initial L3
GLp gLp condensate liquids produced, cumulative L3
Gm fGm geometric factor (multiplier), mud (electrical logging) L3
Gp gp gas produced, cumulative L3
Gp fGp geometric factor (multiplier), pseudo (electrical logging) L3
Gpa gpa gas recovery, ultimate L3
GpE gpE gas produced from experimental tube run L3
Gt fGt geometric factor (multiplier), true (noninvaded zone) (electrical logging)
Gwgp gwgp wet gas produced, cumulative L3
Gxo fGxo geometric factor (multiplier), flushed zone (electrical logging)
h d,e bed thickness, individual L
h i enthalpy, specific L2/t2
h hh,hT heat-transfer coefficient, convective m/t3/T
h d,e height (other than elevation) L
h hyperbolic decine constant (from equation)
h d,e thickness (general and individual bed) L
hmc dmc,emc thickness, mud cake L
hn dn,en thickness, net pay L
ht dt,et thickness, gross pay (total) L
H I enthalpy (always with phase or system subscripts) mL2/t2
Hs Is enthalpy (net) of steam or enthalpy above reservoir temperature mL2/t2
i discount rate
i injection rate L3/t
i interest rate 1/t
ia injection rate, air L3/t
ig injection rate, gas L3/t
iR rate of return (earning power)
iw injection rate, water L3/t
I I (script i), i current, electric q/t
I I (script i), i electric current q/t
I IT,Iθ heat transfer coefficient, radiation m/t3T
I income (net revenue minus expenses) M
I i index (use subscripts as needed)
I i injectivity index L4t/m
I(z)(script I) imaginary part of complex number z
Ibt income before taxes M
If if,IF,iF fracture index
IFf iFf free fluid index
IH iH hydrogen index
Ipwk income at present value in period k M
IR iR hydrocarbon resistivity index Rt/R0
Is is injectivity index, specific L3t/m
IshGR ishGR shaliness gamma ray index, (γlogγcn)/(γshγcn)
IΦ iΦ porosity index
IΦ1 iΦ1 porosity index, primary
IΦ2 iΦ2 porosity index, secondary
J ω reciprocal permeability 1/L2
J j productivity index L4t/m
Js js productivity index, specific L3t/m
K κ magnetic susceptibility mL/q2
K K permeability, absolute (fluid flow) L2
K r,j reaction rate constant L/t
kg Kg effective permeability to gas L2
kg/ko= Kg/Ko gas/oil permeability ratio
kh λ thermal conductivity (always with additional phase or system subscripts)
ko Ko effective permeability to oil L2
krg Krg relative permeability to gas
kro Kro relative permeability to oil
krw Krw relative permeability to water
kw Kw effective permeability to water L2
kw/ko Kw/Ko water/oil permeability ratio
K Kb bulk modulus m/Lt2
K coefficient in the equation of the electrochemical component of the SP (spontaneous electromotive force) mL2/t2q
K M coefficient or multiplier various
K d dispersion coefficient L2/t
K k,Feq equilibrium ratio (y/x)
K M multiplier or coefficient various
Kani Man anisotropy coefficient
Kc Mc,Kec electrochemical coefficient mL2/t2q
KR MR,a,C formation resistivity factor coefficient (FRΦm)
ln natural logarithm, base e
log common logarithm, base 10
loga logarithm, base a
L s,ℓ (script l) distance, length, or length of path L
L s,ℓ (script l) distance, path length, or distance L
L nL liquid phase, moles of
L s,ℓ (script l) path length, length, or distance L
Lf xf fracture half-length (specify "in the direction of" when using xf) L
Ls s,ℓ (script l) spacing (electrical logging) L
Lv λv heat of vaporization, latent L2/t2
L (y) (script L) transform, Laplace of y, y(t)e-stdt
m cementation (porosity) exponent (in an empirical relation between FR and Φ
m FF fuel consumption various
m mass m
m FFo,Fgo ratio of initial reservoir free-gas volume to initial reservoir oil volume
m A slope various
mE FFE fuel consumption in experimental tube run m/L3
mEg FFEg fuel consumption in experimental tube run (mass of fuel per mole of produced gas) m
k amortization (annual write-off of unamortized investment at end of year k) M
mR FFR fuel consumption in reservoir m/L3
M I Magnetization m/qt
M Fλ mobility ratio, general (λdisplacing/λdisplaced)
M Fλ mobility ratio, sharp-front approximation (λD/λd)
M molecular weight m
M m number of compounding periods (usually per year) m
M mθD slope, interval transit time vs. density (absolute value) tL2/m
Mf Magnetization, fraction
ML molecular weight of produced liquids, mole-weighted average m
M MDd,Msu mobility ratio, diffuse-front approximation [(λD+λd)swept/(λd)unswept]; mobilities are evaluated at average saturation conditions behind and ahead of front
Mt Fλt mobility ratio, total, [(λt)swept/(λt)unswept]; "swept" and "unswept" refer to invaded and uninvaded regions behind and ahead of leading edge of displacement front
n N density (indicating "number per unit volume") 1/L3
n exponent of backpressure curve, gas well
n μ index of refraction
n N number (of variables, or components, or steps, or increments, etc.)
n N number (quantity)
n number of compounding periods 1/t
n saturation exponent
nj Nj moles of component j
nN density (number) of neutrons 1/L3
npj Npj moles of component j produced, cumulative
nt Nt number of moles, total
N n,C count rate (general) 1/t
N neutron[usually with identifying subscript(s)] various
N number, dimensionless, in general (always with identifying subscripts)
N n oil (always with identifying subscripts) various
N n pump strokes, number of, cycles per unit of time
N mθND slope, neutron porosity vs. density (absolute value) L3/m
Ne oil influx (encroachment), cumulative L3
NGR Nγ,CG gamma ray count rate 1/t
Ni ni oil in place in reservoir, initial L3
NN Nn,CN neutron count rate 1/t
Np np oil produced, cumulative L3
Npa npa oil recovery, ultimate L3
NR NF fuel deposition rate m/L3t
NRe Reynolds number (dimensionless number)
p P pressure m/Lt2
p price M
pa Pa pressure, atmospheric m/Lt2
pb ps,Ps,Pb pressure, bubblepoint (saturation) m/Lt2
pbh Pbh pressure, bottomhole m/Lt2
pc Pc pressure, critical m/Lt2
pcf Pcf pressure, casing flowing m/Lt2
pcs Pcs pressure, casing static m/Lt2
pd Pd pressure, dewpoint m/Lt2
pD PD pressure, dimensionless
pe Pe pressure, external boundary m/Lt2
pext Pext pressure, extrapolated m/Lt2
pf Pf pressure, front or interface m/Lt2
pgk price of gas in period k M
pi Pi pressure, initial m/Lt2
piwf Piwf pressure, bottomhole flowing, injection well m/Lt2
piws Piws pressure, bottomhole static, injection well m/Lt2
pk price in period k M
ppc Ppc pressure, pseudocritical m/L2
ppc Ppc pseudocritical pressure m/Lt2
ppr Ppr pressure, pseudoreduced
pr Pr pressure, reduced
psc Psc pressure, standard conditions m/Lt2
psp Psp pressure, separator m/Lt2
ptD PtD pressure function, dimensionless, at dimensionless time tD
ptf Ptf pressure, tubing flowing m/Lt2
pts Pts pressure, tubing static m/Lt2
pw Pw pressure, bottomhole general m/Lt2
pwf Pwf pressure, bottomhole flowing m/Lt2
pws Pws pressure, bottomhole static m/Lt2
pws Pws pressure, bottomhole, at any time after shut-in m/Lt2
p P average pressure m/Lt2
p P pressure, average or mean m/Lt2
pR PR pressure, reservoir average m/Lt2
P phases, number of
P profit M
Pc PC,pC capillary pressure m/Lt2
Ppvat profit at present value after tax M
Ppvatk profit at present value after tax in period k M
q Q production rate or flow rate L3/t
qa Qa production rate at economic abandonment L3/t
qdh qwf,qDH,Qdh volumetric flow rate downhole L3/t
qD QD production rate, dimensionless
qg Qg production rate, gas L3/t
qgD QgD production rate, gas dimensionless
qi Qi production rate at beginning of period L3/t
qo Qo production rate, oil L3/t
qoD QoD production rate, oil, dimensionless
qp Qp production rate or flow rate at mean pressure L3/t
qs Qs segregation rate (in gravity drainage) L3/t
qsc qσ,Qsc surface production rate L3/t
qs qσ,Qsc volumetric flow rate, surface conditions L3/t
qw Qw production rate, water L3/t
qwD QwD production rate, water, dimensionless
production rate or flow rate, average L3/t
Q Q charge q
Q q,Φ heat flow rate mL2/t3
Qi qi pore volumes of injected fluid, cumulative, dimensionless mL2/t3
QLtD QℓtD (script l) influx function, fluid, linear aquifer, dimensionless
Qp QℓtD (script l) fluids, cumulative produced (where Np and Wp are not applicable)
Qp produced fluids, cumulative (where Np and Wp are not applicable) L3
QtD fluid influx function, dimensionless, a dimensionless time tD
QV ZV cation exchange capacity per unit pore volume
r R radius L
r R resistance ML2/tq2
r royalty various
rd Rd drainage radius L
rD RD radius, dimensionless
re Re external boundary radius L
rH RH hydraulic radius L
rR royalty rate various
rs Rs radius of well damage or stimulation (skin) L
rw Rw well radius L
rws Rwa radius of wellbore, apparent or effective (includes effects of well damage or stimulation) L
R ρ,r electrical resistivity (electrical logging) mL3/tq2
R gas constant, universal (per mole) mL2/t2T
R Fg,Fgo gas/oil ratio, producing
R N molecular refraction L3
R reaction rate m/L2
R revenue M
R(z)(script R) real part of complex number z
Ra ρa,ra apparent resistivity mL3/tq2
RF FgF, FgoF free gas/oil ratio, producing (free-gas volume/oil volume)
Ri ρi, ri invaded zone resistivity mL3/tq2
Rm ρm ,rm mud resistivity mL3/tq2
Rmc ρmc ,rmc mudcake resistivity mL3/tq2
Rmf ρmf ,rmf mud-filtrate resistivity mL3/tq2
Rp Fgp,Fgop cumulative gas/oil ratio
Rs Fgs,Fgos solution gas/oil ratio (gas solubility in oil)
Rsb Fgsb solution gas/oil ratio at bubblepoint conditions
Rsh ρsh,rsh shale resistivity mL3/tq2
Rsi Fgsi solution gas/oil ratio, initial
Rsw gas solubility in water
Rt ρt,rt true formation resistivity mL3/tq2
Rw ρw,rw water resistivity mL3/tq2
Rxo ρxo,rxo flushed-zone resistivity (that part of the invaded zone closest to the wall of the hole, where flushing has been maximum) mL3/tq2
Rz ρz,rz apparent resistivity of the conductive fluids in an invaded zone (caused by fingering) mL3/tq2
R0 ρ0,r0 formation resistivity when 100% saturated with water of resistivity Rw mL3/tq2
S Laplace transform variable
S L displacement L
S Σ entropy, specific L2/t2T
S S, σ skin effect various
S standard deviation of a random variable, estimated
s2 variance of a random variable, estimated
S σt entropy, total mL2/t2T
S ρ,s saturation
S s, σ storage or storage capacity various
SfD SD dimensionless fracture storage capacity
Sg ρg,sg gas saturation
Sgc ρgc,sgc gas saturation, critical
Sgr ρgr,sgr gas saturation, residual
Sh ρh,sh saturation, hydrocarbon
Shr ρhr,shr residual hydrocarbon saturation
Siw ρiw,siw irreducible (interstitial or connate) water saturation
SL ρL,sL liquid saturation, combined total
So ρo,so oil saturation
Sog ρog,sog gas-cap interstitial-oil saturation
Sor ρor,sor residual oil saturation
Sw ρw,sw water saturation
Swc ρwc,swc critical water saturation
Swg ρwg,swg interstitial-water saturation in gas cap
Swi ρwi,swi initial water saturation
Swo Swb interstitial-water saturation in oil band
Swr ρwr,swr residual water saturation
T τ time t
t (script t) Δt interval transit time t/L
td τd time, delay t
tdN decay time, neutron (neutron mean life) t
tD τD time, dimensionless
tDm τDm time, dimensionless at condition m
tma (script t) Δtma matrix interval transit time t/L
tN τN,tn neutron lifetime 1/t
tp τp time well was on production prior to shut-in, equivalent (pseudotime) t
tpoat payout time, after tax t
tpypobt payout time, before tax at present value t
ts τs time for stabilization of a well t
tsh (script t) Δtsh shale interval transit time t/L
t1 τ1 relaxation time, proton thermal t
t½ half-life t
t2 τ2 relaxation time, free-precession decay t
T Θ period t
T tax on income various
T Θ temperature T
T T transmissivity, transmissibility various
Tbh θBH bottomhole temperature T
Tc θc critical temperature T
Tf θf formation temperature T
Tk tax in period k various
Tpr θpr pseudoreduced temperature T
Tr θr reduced temperature
TR θR reservoir temperature T
TR tax rate various
Tsc θsc temperature, standard conditions T
u Ψ flux various
u Ψ flux or flow rate, per unit area (volumetric velocity) L/t
u Ψ superficial phase velocity (flux rate of a particular fluid phase flowing in pipe; use appropriate phase subscripts)
U UT,Uθ heat transfer coefficient, overall m/t3T
v V,u acoustic velocity L/t
v vs specific volume L3/m
v value (economic) M
v V,u velocity L/t
vb Vb,ub burning-zone advance rate (velocity of) L/t
vp net present value (NPV) M
V nv moles of vapor phase
V U potential difference (electric) mL2/qt2
V v volume L3
V fvFv volume fraction or ratio (as needed, use same subscripted symbols as for volume; note that bulk volume fraction is unity and pore volume fractions are ø) various
Vb vb bulk volume L3
VbE vbE bulk volume of pack burned in experimental tube run L3
Vbp vbp volume at bubblepoint pressure L3
Ve Vpe,ve volume, effective pore L3
Vgr vgr volume, grain (volume of all formation solids except shales) L3
Vig vig volume, intergranular (volume between grains; consists of fluids and all shales)(Vv−Vgr)
Vim vim volume, intermatrix (consists of fluids and dispersed shale) (Vb-Vma) L3
VM vm molal volume (volume per mole) L3
Vma vma matrix (framework) volume (volume of all formation solids except dispersed clay or shale) L3
Vma vma volume, matrix (framework)(volume of all formation solids except dispersed shale) L3
Vp vp pore volume (Vb−Vs) L3
VpD vpD pore volume, dimensionless
Vpoat vpD payout volume, after tax L3
VRb volume of reservoir rock burned L3
VRu volume of reservoir rock unburned L3
Vs vs volume, solids(s) (volume of all formation solids) L3
Vsh vsh volume, shale(s)(volume of all shales: structural and dispersed) L3
Vshd vshd volume, shale, dispersed L3
Vshs vshs volume, shale, structural L3
w z Arrhenius reaction-rate velocity constant L3/m
w m mass flow rate m/t
w m rate, mass flow m/t
W w water (always with identifying subscripts) various
W w water in place in reservoir, initial L3
W w,G weight (gravitational) mL/t2
W w work mL2/t2
We we water influx (encroachment), cumulative L3
Wi wi water injected, cumulative L3
Wp wp water produced, cumulative L3
x mole fraction of a component in liquid phase
vector of x
tensor of x
mean value of a random variable, x, estimated
X reactance ML2/tq2
y f holdup (fraction of the pipe volume filled by a given fluid: yo is oil holdup; yw is water holdup; sum of all holdups at a given level is one)
y mole fraction of a component in a vapor phase
z Z gas compressibility factor (deviation factor) (z=pV/nRT)
z mole fraction of a component in mixture
Zp Zp gas deviation factor (compressibility factor) at mean pressure
Z atomic number
Z D,h elevation referred to datum
Z D,h height, or fluid head or elevation referred to a datum
Z impedance various
Za impedance, acoustic m/L2t


Letter Symbol Reserve SPE Letter Symbol Quantity Dimensions
α β,γ angle
α Mα attenuation coefficient 1/L
α a,ηh heat or thermal diffusivity L2/t
α reduction ratio or reduction term
α a,ηh thermal or heat diffusivity L2/t
αSPsh reduction ratio, SP, caused by shaliness
β γ bearing, relative
β b thermal cubic expansion coefficient 1/T
γ gamma ray [usually with identifying subscript(s)] various
γ s,Fs specific gravity (relative density)
γ k specific heat ratio
γ εs strain, shear
shear rate 1/t
γg sg,Fgs specific gravity, oil
γw sw,Fws specific gravity, water
δ Δ decrement various
δ deviation, hole (drift angle)
δ Fd displacement ratio
δ drift angle, hole (deviation)
δ rs skin depth (logging) L
δob Fdob displacement ratio, oil from burned volume, volume per unit volume of burned reservoir rock
δou Fdou displacement ratio, oil from unburned volume, volume per unit volume of unburned reservoir rock
δwb Fdwb displacement ratio, water from burned volume, volume per unit volume of burned reservoir rock
Δ difference or difference operator, finite (Δx=x2x1 or x1x2)
ΔGe Δge gas influx (encroachment) during an interval L3
ΔGi Δgi gas injected during an interval L3
ΔGp Δgp gas produced during an interval L3
ΔNe Δne oil influx (encroachment) during an interval L3
ΔNp Δnp oil produced during an interval L3
Δr ΔR radial distance (increment along radius) L
Δtwf Δτwf drawdown time (time after well is opened to production) (pressure drawdown) t
Δtws Δτws buildup time; shut-in time (time afterwell is shut in) (pressure buildup, shut-in time) t
ΔWe Δwe water influx (encroachment) during an interval L3
ΔWi Δwi water injected during an interval L3
ΔWp Δwp water produced during an interval L3
ε dielectric constant q2t2/mL3
ε e,εn strain, normal and general
η hydraulic diffusivity (k/øcμ or λ/øc) L2/t
θ β,γ angle
θ θV strain, volume
Ө αd angle of dip
Өa αda dip, apparent angle of
Өc Гc,γc contact angle
λ C decay constant(1/τd) 1/t
λ mobility (k/μ) L3t/m
λ wavelength(1/σ) L
λg mobility, gas L3t/m
λo mobility, oil L3t/m
λt Λ mobility, total, of all fluids in a particular region of the reservoir [e.g., (λo+ λg+ λw)] L3t/m
λw mobility, water L3t/m
μ M azimuth of reference on sonde
μ m magnetic permeability mL/q2
μ mean value of a random variable
μ υ,σ Poisson’s ratio
μ η viscosity, dynamic m/Lt
μa ηa viscosity, air m/Lt
μc chemical potential
μg ηg viscosity, gas m/Lt
μga ηga viscosity, gas, at 1 atm m/Lt
μo ηo viscosity, oil m/Lt
μp ηp viscosity at mean pressure m/Lt
μw ηw viscosity, water m/Lt
ν N kinematic viscosity L2/t
ν N viscosity, kinematic L2/t
ρ D density m/L3
ρ R resistivity, electrical (other than logging) mL3tq2
ρa Da density, apparent m/L3
ρb Db density, bulk m/L3
ρf Df density, fluid m/L3
ρF DF density, fuel m/L3
ρg Dg density, gas m/L3
ρma Dma density, matrix (solids, grain) m/L3
ρo Do density, oil m/L3
ρsE DsE density of solid particles making up experiment pack m/L3
ρt Dt density, true m/L3
ρw Dw density, water m/L3
ρxo Dxo density, flushed zone m/L3
L L density of produced liquid, weight-weighted average m/L3
σ γ conductivity, electrical (other than logging) various
σ cross section, microscopic 1/L
σ s cross section of a nucleus, microscopic L2
σ y,γ interfacial surface tension m/t2
σ microscopic cross section L2
σ standard deviation of a random variable
σ s stress, normal and general m/Lt2
σ y,γ surface tension, interfacial m/t2
σ wave number(1/λ) 1/L
σ2 variance of a random variable
Σ S cross section, macroscopic 1/L
Σ summation (operator)
τ ss stress, shear m/Lt2
τ τc time constant t
τd td decay time (mean life) (1/λ) t
τd tdt mean life (decay time) (1/λ) t
τe tortuosity, electric
τH hydraulic tortuosity
τH tortuosity, hydraulic
τ t lifetime, average (mean life) t
φ f,ε porosity (Vb−Vs)/Vb
φa faa porosity, apparent
φe fee porosity, effective (Vpe/Vb)
φE fEE porosity of experimental pack
φh fhh porosity, hydrocarbon-filled, fraction or percent of rock bulk volume occupied by hydrocarbons
φig figig "porosity" (space), intergranular(VbVgr)/Vb
φim fimim “porosity” (space), intermatrix
φne fnene porosity, noneffective (Vpne)/Vb
φR fRR porosity of reservoir or formation
φt ftt porosity, total
Φ βd dip, azimuth of
Φ f potential of potential function various
ψ dispersion modulus (dispersion factor)
Ψ stream function various
ψ dispersion modulus (dispersion factor)
ω angular frequency (acentric factor) 1/t


Letter Symbol Reserve SPE Letter Symbol Quantity Dimensions
proportional to
average or mean (overbar)
< smaller than
equal to or smaller than
> larger than
equal to or larger than
~ asymptotically equal to
approximately equal to or is approximated by
del (gradient operator)
divergence operator
Laplacian operator
erf error function
erfc error function, complementary
lim limit
b γ intercept various
En Euler’s number
Ei(x) exponential integral, modified, x positive
–Ei(–x) exponential integral, , x positive
ez exp z exponential function
F ratio
f F fraction
ς(z) imaginary part of complex number z
L (y) Laplace transform of y, y(t)estdt
ln logarithm, natural, base e
log logarithm, common, base 10
loga logarithm, base a
m A slope various
N number, dimensionless
n number (of variables, or steps, or increments, etc.)
P(z) real part of complex number z
s Laplace transform variable
s standard deviation of a random variable, estimated
s2 variance of a random variable, estimated
x mean value of a random variable, x, estimated
vector of x
tensor of x
α β,γ angle
γ Euler’s constant=0.5772
Δ difference (Δx=x2–x1 or x1–x2)
Δ difference operator, finite
μ mean value of a random variable
σ standard deviation of a random variable
σ2 variance of a random variable
Φ f potential or potential function various
Ψ stream function various

See also

Recommended SI units and conversion factors

SI metric conversion factors

Nomenclature for SI metric conversion tables