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Basic symbols in alphabetical order

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Letter Symbol English 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 production) in a row L
A amplitude various
A atomic weight m
A F Helmboltz function (work function) mL2/t2
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 thickness (primarily in fracturing) L
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
c k, κ compressibility Lt2/m
C capacitance q2t2/mL2
C capital costs or investments M
C coefficient of gas-well backpressure curve L3−2nt4n/m2n
C nC components, number of
C c,n concentration various
C σ conductivity (electrical logging) tq2/mL3
C c,n salinity various
C c specific heat capacity (always with phase or system subscripts) L2/t2T
C waterdrive constant L4t2/m
CƒD fracture conductivity, dimensionless
CL cL,nL condensate or natural gas liquids content various
d decline factor, effective
d D diameter L
d Ld,L2 distance between adjacent rows of injection and production wells L
D deliverability (gas well) L3/t
D y,H depth l
D µ,δ diffusion coefficient L2/t
e i influx (encroachment) rate L3/t
eO2 EO2 oxygen utilization
ez exp z exponential function
E η,e efficiency
E V electromotive force mL2/t2q
E U energy mL2/t2
E Y modulus of elasticity (Young’s modulus) M/Lt2
EA ηA,eA areal efficiency (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
Ek Φk electrokinetic component of the SP mL2/t2q
En Euler number
ESP ΦSP SP (measured SP) (self potential) mL2/t2q
Ei (−x) exponential integral, , dt, x positive
Ei (x) exponential integral, modified, 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
fs Q,x quality (usually of steam)
F degrees of freedom
F A,R,r factor in general, including ratios (always with identifying subscripts) various
F ƒ fluid (generalized) various
FR formation resistivity factor—equals R0/Rw (a numerical subscript to F indicates the value Rw)
FWV γ specific weight mL2/t2
g γ gradient various
g gravity, acceleration of L/t2
gc conversion factor in Newton’s second law of Motion
G g gas in place in reservoir, total initial L3
G g gas (any gas, including air), always with identifying subscripts various
G ƒG geometrical factor (multiplier)

(electrical logging)||

G Es shear modulus m/Lt2
GL gL condensate liquids in place in reservoir, initial L3
h i enthalpy, specific L2/t2
h hh,hT heat transfer coefficient, convective m/t3T
h d,e height (other than elevation) L
h hyperbolic decline constant (from equation)
h d,e thickness (general and individual bed) L
H I enthalpy (always with phase or system subscripts) mL2/t2
i injection rate L3/t
i interest rate 1/t
iR rate of return (earning power)
I income (net revenue minus expenses)
I i (script i), i current, electric q/t
I IT,I¬θ heat transfer coefficient, radiation m/t3T
I i index (use subscripts as needed)
I i injectivity index L4t/m
ς (z)(script I) imaginary part of complex number z
IR iR resistivity index (hydrocarbon)—equals Rt/R0
j iR reciprocal permeability 1/L2
J j productivity index L4t/m
k κ magnetic susceptibility mL/q2
k K permeability absolute (fluid flow) L2
k r,j reaction rate constant L/t
kh λ thermal conductivity (always with additional phase or system subscripts) mL/t3T
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)
Kani Mani anisotropy coefficient
Kc Mc, Kec electrochemical coefficient mL2/t2q
KR MR,a,C formation resistivity factor coefficient (FR Φm)
ln natural logarithm, base e
log common logarithm, base 10
loga logarithm base a
L nL moles of liquid phase
Lf xf fracture half-length (specify "in the direction of" when using xf) L
Ls ss,ls (script l) spacing (electrical logging) L
Lv λv latent heat of vaporization L
L (y) (script L) Laplace transform of y, y(t)e-stdt
m FF fuel consumption various
m mass m
m porosity exponent (cementation) (in an empirical relation between FR and )
m FFo,Fgo ratio of initial reservoir free-gas volume to initial reservoir oil volume
m A slope various
M I magnetization m/qt
M Fλ mobility ratio, general (λdisplacing/λdisplaced)
M molecular weight m
M mθD slope, interval transit time vs. density (absolute value) tL2/m
M volumetric heat capacity m/Lt2T
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, components, steps, increments, etc.)
n n number (quantity)
n saturation exponent
n number of compounding periods 1/t
nt Nt moles, number of, 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 m ND slope, neutron porosity vs. density (absolute value) L3/m
NGR Nγ,CG gamma ray count rate 1/t
NR NF fuel deposition rate m/L3t
O operating expense various
p P pressure m/Lt2
p price M
P phases, number of
P profit total M
Pc Pc ,pc capillary pressure M/Lt2
q Q production rate or flow rate L3/t
Q q charge (current times time) q
Q q,Φ heat flow rate mL2/t3
Qi qi pore volumes of injected fluid, cumulative dimensionless
QLtD Ql tD (script l) fluid influx function, linear aquifer, dimensionless
Qp Ql tD (script l) fluids, cumulative produced (where Np and Wp are no applicable)
QtD fluid influx function, dimensionless, at dimensionless time tD
QV ZV cation exchange capacity per unit pore volume
r R radius L
r R resistance mL2/tq2
R ρ,r electrical resistivity (electrical logging) ml3tq2
R gas constant, universal (per mole) mL2/t2T
R Fg,Fgo gas/oil ratio, producing
R N molecular refraction L3
R(z) (script R) real part of complex number z
s L displacement L
s σ entropy, specific L2/t2T
s Laplace transform variable
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
t τ time t
tma(script t) Δtma matrix interval transit time t/L
t½ half-life t
T Θ period t
T θ temperature T
T T transmissivity, transmissibility various
u ψ flux various
u ψ flux or flow rate, per unit area (volumetric velocity) L/t
U UT,Uθ heat transfer coefficient, overall m/t3T
v V,u acoustic velocity L/t
v νs specific volume L3/m
v V,u velocity L/t
V R,Vt,Rt gross revenue ("value"), total M
V moles of vapor phase
V U potential difference (electric) mL2/q2
V v volume L3
V ƒV,FV volume fraction or ratio (as needed, use same subscripted symbols as for "volumes"; note that bulk volume fraction is unity and pore volume fractions are Φ) various
w z Arrhenius reaction-rate velocity constant L3/m
w m mass flow rate 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
x mole fraction of a component in liquid phase
vector of x
tensor of x
xD dimensionless quantity proportional to x
X reactance mL2/tq2
y ƒ 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 vapor phase
z Z gas compressibility factor (deviation factor) (z=pV/nRT)
z mole fraction of a component in mixture
z valence
Z atomic number
Z D,h elevation (height or fluid head) referred to datum L
Z impedance various
α β, γ angle
α 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
β γ bearing, relative
β b thermal cubic expansion coefficient 1/T
γ Euler’s constant=0.5772
γ gamma ray [usually with identifying subscripts(s)] various
γ s,Fs specific gravity (relative density)
γ k specific heat ratio
γ εs strain, shear
ė shear rate 1/t
δ Δ decrement various
δ deviation, hole (drift angle)
δ Fd displacement ratio
δ rs skin depth (logging) L
Δ difference or difference operator, finite

x=x2−x1 or x1−x2)

Δ r Δ R radial distance (increment along radius) L
ε dielectric constant q2t2/mL3
ε e,εn strain, normal and general
η hydraulic diffusivity (k/Φcμ or λ/Φc) L2/t
θ β,γ angle
θ θV strain, volume
θ αd angle of dip
θ c Γc,γc contact angle
λ C decay constant (1/τd) 1/t
λ mobility (k/μ) L3t/m
λ wave length (1/σ) L
μ v, σ Poisson’s ratio
μ m azimuth of reference on sonde
μ m magnetic permeability mL/q2
ν N kinematic viscosity L2/t
ρ D density m/L3
ρ R electrical resisivity (other than logging) mL3/tq2
σ γ electrical conductivity (other than logging) various

Letter Symbol Greek

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
τ ss stress, shear m/Lt2
τ τc time constant t
τ tortuosity
lifetime, average (mean life) t
τd td decay time (mean life) (1/ λ) t
ø f, ε porosity (VbVs)/Vb
Φ βd dip, azimuth of
Φ f potential or potential function various
ψ dispersion modulus (dispersion factor)
Ψ stream function various
ω angular frequency 1/t