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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  F_{a}  air requirement  various 
a  decline factor, nominal  
a  L_{a},L_{1}  distance between like wells (injection or projection) in a row  L 
a_{E}  F_{aE}  air requirement, unit, in laboratory experimental run, volumes of air per unit mass of pack  L^{3}/m 
a_{R}  F_{aR}  air requirement, unit, in reservoir, volumes of air per unit bulk volume of reservoir rock  
A  amplitude  various  
A  S  area  L^{2} 
A  atomic weight  m  
A  S  cross section (area)  L^{2} 
A  F  helmholtz function (work function)  mL^{2}/t^{2} 
A_{c}  amplitude, compressional wave  various  
A_{r}  amplitude, relative  various  
A_{s}  amplitude, shear wave  various  
b  W  breadth, width, or (primarily in fracturing)  various 
thickness  
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 
b_{g}  f_{g},F_{g}  reciprocal gas formation volume factor  
b_{gb}  f_{gb},F_{gb}  reciprocal gas formation volume factor at bubblepoint conditions  
b_{o}  f_{o},F_{o}  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  
B_{g}  F_{g}  formation volume factor, gas  
B_{gb}  F_{gb}  bubblepoint formation volume factor, gas  
B_{gb}  F_{gb}  formation volume factor at bubblepoint conditions, gas  
B_{o}  F_{o}  formation volume factor, oil  
B_{ob}  F_{ob}  bubblepoint formation volume factor, oil  
B_{ob}  F_{ob}  formation volume factor at bubblepoint conditions, oil  
B_{t}  F_{T}  formation volume factor, total (twophase)  
B_{w}  F_{w}  formation volume factor, water  
c  k,κ  compressibility  Lt^{2}/m 
c_{f}  k_{f},κ_{f}  compressibility, formation or rock  Lt^{2}/m 
c_{g}  k_{g},κ_{g}  compressibility, gas  Lt^{2}/m 
c_{o}  k_{o},κ_{o}  compressibility, oil  Lt^{2}/m 
c_{pr}  k_{pr},κ_{pr}  compressibility, pseudoreduced  
c_{w}  k_{w},κ_{w}  compressibility, water  Lt^{2}/m 
C  capacitance  q^{2}t^{2}/mL^{2}  
C  C_{t}  capital investments, summation of all  M 
C  coefficient of gaswell backpressure curve  L^{3–2n}t^{4n}m^{2}n  
C  n_{C}  components, number of  
C  c,n  concentration  various 
C  σ  conductivity (electrical logging)  tq^{2}/mL^{3} 
C  K  conductivity, other than electrical (with subscripts)  various 
C  c,n  salinity  various 
C  c  specific heat (always with phase or system subscripts)  L^{2}/t^{2}T 
C  waterdrive constant  L^{4}t^{2}/m  
Ca  σ_{α}  conductivity, apparent  tq^{2}/mL^{3} 
CC_{1}  c_{C1}  concentration, methane (concentration of other paraffin hydrocarbons would be indicated similarly, C_{C2}, C¬_{C3}, etc.)  various 
CfD  conductivity, fraction, dimensionless  
C_{i}  capital investment, initial  M  
C_{k}  capital investment in period k  M  
C_{L}  c_{L},n_{L}  content, condensate or natural gas liquids  various 
C_{L}  waterdrive constant, linear aquifer  L^{4}t^{2}/m  
C_{m}  c_{m}n_{m}  fuel concentration, unit (see symbol m)  various 
CO2  c_{O2}  concentration, oxygen (concentration of other elements or compounds would be indicated similarly, C_{CO2}, C_{N2}, etc.)  
C_{pv}  investment at present value  M  
C_{wg}  c_{wg},n_{wg}  content, wetgas  various 
d  decline factor, effective  
d  D  diameter  L 
d  L_{d},L_{2}  distance between adjacent rows of injection and production wells  L 
d_{h}  d_{H},D_{h}  diameter, hole  L 
d_{i}  dl,Di  diameter, invaded zone (electrically equivalent)  L 
d_{p}  D_{p}  diameter, mean particle  L 
D  deliverability (gas well)  L^{3}/t  
D  depletion, depreciation, or amortization (all nonreal account entries)  various  
D  y,H  depth  L 
D  µ,δ  diffusion coefficient  L^{2}/t 
e  i  encroachment or influx rate  L^{3}/t 
e_{g}  ig  encroachment or influx rate, gas  L^{3}/t 
e_{o}  io  encroachment or influx rate, oil  L^{3}/t 
e_{O2}  E_{O2}  oxygen utilization  
e_{w}  i_{w}  encroachment or influx rate, water  L^{3}/t 
e^{z}  exp z  exponential function  
E  η,e  efficiency  
E  V  electromotive force  mL^{2}/t^{2}q 
E  U  energy  mL^{2}/t^{2} 
E  expense, total (except income taxes)  M  
E  modulus of elasticity (Young’s modulus)  m/Lt  
E_{A}  η_{A},e_{A}  efficiency, areal (used in describing results of model studies only): area swept in a model divided by total model reservoir area (see EP)  
E_{c}  Φ_{c}  electrochemical component of the SP  mL^{2}/t^{2}q 
E_{D}  η_{D},e_{D}  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  
E_{Db}  η_{Db},e_{Db}  efficiency, displacement, from burned portion of insitu combustion pattern  
E_{Du}  η_{Du},e_{Du}  efficiency, displacement, from unburned portion of insitu combustion pattern  
E_{I}  η_{I},e_{I}  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  
E_{k}  Φ_{k}  electrokinetic component of the SP  mL^{2}/t^{2}q 
E_{k}  kinetic energy  mL^{2}/t^{2}  
E_{n}  Euler’s number  
E_{pSP}  Φ_{SP}  pseudoSP  mL^{2}/qt^{2} 
E_{p}  η_{P},e_{P}  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  
E_{R}  η_{R},e_{R}  efficiency, overall reservoir recovery: volume of hydrocarbons recovered divided by volume of hydrocarbons in place at start of project (ER=EPEIED=EVED)  
E_{SP}  Φ_{SP}  SP (measured SP) (selfpotential)  mL^{2}/t^{2}q 
E_{SSP}  Φ_{SSP}  SSP (static SP)  mL^{2}/t^{2}q 
E_{u}  expense per unit  M  
E_{V}  η_{V},e_{V}  efficiency, volumetric; product of pattern sweep and invasion efficiencies  
E_{Vb}  η_{Vb},e_{Vb}  efficiency, volumetric, for burned portion only, insitu 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/Lt^{2}  
f_{g}  F_{g}  fraction gas  
f_{g}  F_{g}  mole fraction gas, V/(L+V)  
f_{L}  F_{L},f_{ℓ} (script ℓ)  fraction liquid  
f_{L}  F_{L},f_{ℓ} (script ℓ)  mole fraction liquid, L/(L+V)  
f_{s}  Q,x  quality (usually of steam)  
f_{V}  f_{Vb}, V_{bf}  fraction of bulk (total) volume  
f_{sØh}  Ø_{igfsh}  fraction of intergranular space ("porosity") occupied by all shales  
f_{Øshd}  Ø_{imfshd}  fraction of intermatrix space (“porosity”) occupied by nonstructural dispersed shale  
f_{Øw}  Ø_{igfw}  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)  
F_{aF}  air/fuel ratio  various  
F_{B}  factor, turbulence  
F_{R}  formation resistivity factor—equals R_{0}/R_{w} (a numerical subscript to F indicates the value R_{w}) 

F_{s}  F_{d}  damage ratio or condition ratio (conditions relative to formation conditions unaffected by well operations) 

F_{wF}  water/fuel ratio  various  
F_{wo}  water/oil ratio, producing, instantaneous  
F_{wop}  water/oil ratio, cumulative  
F_{WV}  γ  specific weight  mL^{2}/t^{2} 
g  acceleration of gravity  L/t^{2}  
g  γ  gradient  various 
g_{c}  conversion factor in Newton’s second law of motion  
g_{G}  g_{g}  gradient, geothermal  T/L 
G  F  free energy (Gibbs function)  mL^{2}/t^{2} 
G  g  gas (any gas, including air) always with identifying subscripts  various 
G  g  gas in place in reservoir, total initial  L^{3} 
G  f_{G}  geometric factor (multiplier) (electrical logging)  
G  E_{s}  shear modulus  m/Lt^{2} 
G_{an}  f_{Gan}  factor, geometric (multiplier), annulus (electrical logging)  
G_{an}  f_{Gan}  geometric factor (multiplier), annulus (electrical logging)  
G_{e}  g_{e}  gas influx (encroachment), cumulative  L^{3} 
G_{Fi}  g_{Fi}  freegas volume, initial reservoir (=mNBo_{i})  L^{3} 
G_{Fp}  g_{Fp}  free gas produced, cumulative  L^{3} 
G_{i}  g_{i}  gas injected, cumulative  L^{3} 
G_{i}  f_{Gi}  geometric factor (multiplier), invaded zone (electrical logging)  L^{3} 
G_{L}  g_{L}  condensate liquids in place in reservoir, initial  L^{3} 
G_{Lp}  g_{Lp}  condensate liquids produced, cumulative  L^{3} 
G_{m}  f_{Gm}  geometric factor (multiplier), mud (electrical logging)  L^{3} 
G_{p}  g_{p}  gas produced, cumulative  L^{3} 
G_{p}  f_{Gp}  geometric factor (multiplier), pseudo (electrical logging)  L^{3} 
G_{pa}  g_{pa}  gas recovery, ultimate  L^{3} 
G_{pE}  g_{pE}  gas produced from experimental tube run  L^{3} 
G_{t}  f_{Gt}  geometric factor (multiplier), true (noninvaded zone) (electrical logging)  
G_{wgp}  g_{wgp}  wet gas produced, cumulative  L^{3} 
G_{xo}  f_{Gxo}  geometric factor (multiplier), flushed zone (electrical logging)  
h  d,e  bed thickness, individual  L 
h  i  enthalpy, specific  L^{2}/t^{2} 
h  h_{h},h_{T}  heattransfer coefficient, convective  m/t^{3}/T 
h  d,e  height (other than elevation)  L 
h  hyperbolic decine constant (from equation)  
q=q_{i}  
h  d,e  thickness (general and individual bed)  L 
h_{mc}  d_{mc},e_{mc}  thickness, mud cake  L 
h_{n}  d_{n},e_{n}  thickness, net pay  L 
h_{t}  d_{t},e_{t}  thickness, gross pay (total)  L 
H  I  enthalpy (always with phase or system subscripts)  mL^{2}/t^{2} 
H_{s}  I_{s}  enthalpy (net) of steam or enthalpy above reservoir temperature  mL^{2}/t^{2} 
i  discount rate  
i  injection rate  L^{3}/t  
i  interest rate  1/t  
i_{a}  injection rate, air  L^{3}/t  
i_{g}  injection rate, gas  L^{3}/t  
i_{R}  rate of return (earning power)  
i_{w}  injection rate, water  L^{3}/t  
I  I (script i), i  current, electric  q/t 
I  I (script i), i  electric current  q/t 
I  I_{T},I_{θ}  heat transfer coefficient, radiation  m/t^{3}T 
I  income (net revenue minus expenses)  M  
I  i  index (use subscripts as needed)  
I  i  injectivity index  L^{4}t/m 
I(z)(script I)  imaginary part of complex number z  
I_{bt}  income before taxes  M  
I_{f}  i_{f},I_{F},i_{F}  fracture index  
I_{Ff}  i_{Ff}  free fluid index  
I_{H}  i_{H}  hydrogen index  
I_{pwk}  income at present value in period k  M  
I_{R}  i_{R}  hydrocarbon resistivity index R_{t}/R_{0}  
I_{s}  i_{s}  injectivity index, specific  L^{3}t/m 
I_{shGR}  i_{shGR}  shaliness gamma ray index, (γ_{log}–γ_{cn})/(γ_{sh}–γ_{cn})  
I_{Φ}  i_{Φ}  porosity index  
I_{Φ1}  i_{Φ1}  porosity index, primary  
I_{Φ2}  i_{Φ2}  porosity index, secondary  
J  ω  reciprocal permeability  1/L^{2} 
J  j  productivity index  L^{4}t/m 
J_{s}  j_{s}  productivity index, specific  L^{3}t/m 
K  κ  magnetic susceptibility  mL/q^{2} 
K  K  permeability, absolute (fluid flow)  L^{2} 
K  r,j  reaction rate constant  L/t 
k_{g}  K_{g}  effective permeability to gas  L^{2} 
k_{g}/k_{o=}  K_{g}/K_{o}  gas/oil permeability ratio  
k_{h}  λ  thermal conductivity (always with additional phase or system subscripts)  
k_{o}  K_{o}  effective permeability to oil  L^{2} 
k_{rg}  K_{rg}  relative permeability to gas  
k_{ro}  K_{ro}  relative permeability to oil  
k_{rw}  K_{rw}  relative permeability to water  
k_{w}  K_{w}  effective permeability to water  L^{2} 
k_{w}/k_{o}  K_{w}/K_{o}  water/oil permeability ratio  
K  K_{b}  bulk modulus  m/Lt^{2} 
K  coefficient in the equation of the electrochemical component of the SP (spontaneous electromotive force)  mL^{2}/t^{2}q  
K  M  coefficient or multiplier  various 
K  d  dispersion coefficient  L^{2}/t 
K  k,F_{eq}  equilibrium ratio (y/x)  
K  M  multiplier or coefficient  various 
K_{ani}  M_{an}  anisotropy coefficient  
K_{c}  M_{c},K_{ec}  electrochemical coefficient  mL^{2}/t^{2}q 
K_{R}  M_{R},a,C  formation resistivity factor coefficient (F_{RΦm})  
ln  natural logarithm, base e  
log  common logarithm, base 10  
log_{a}  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  n_{L}  liquid phase, moles of  
L  s,ℓ (script l)  path length, length, or distance  L 
L_{f}  x_{f}  fracture halflength (specify "in the direction of" when using x_{f})  L 
L_{s}  s,ℓ (script l)  spacing (electrical logging)  L 
L_{v}  λ_{v}  heat of vaporization, latent  L^{2}/t^{2} 
L (y) (script L)  transform, Laplace of y, y(t)estdt  
m  cementation (porosity) exponent (in an empirical relation between F_{R} and Φ  
m  F_{F}  fuel consumption  various 
m  mass  m  
m  F_{Fo},F_{go}  ratio of initial reservoir freegas volume to initial reservoir oil volume  
m  A  slope  various 
m_{E}  F_{FE}  fuel consumption in experimental tube run  m/L^{3} 
m_{Eg}  F_{FEg}  fuel consumption in experimental tube run (mass of fuel per mole of produced gas)  m 
k  amortization (annual writeoff of unamortized investment at end of year k)  M  
m_{R}  F_{FR}  fuel consumption in reservoir  m/L^{3} 
M  I  Magnetization  m/qt 
M  F_{λ}  mobility ratio, general (λ_{displacing}/λ_{displaced})  
M  F_{λ}  mobility ratio, sharpfront approximation (λ_{D}/λ_{d})  
M  molecular weight  m  
M  m  number of compounding periods (usually per year)  m 
M  m_{θD}  slope, interval transit time vs. density (absolute value)  tL^{2}/m 
M_{f}  Magnetization, fraction  
M_{L}  molecular weight of produced liquids, moleweighted average  m  
M_{ }  M_{Dd},M_{su}  mobility ratio, diffusefront approximation [(λ_{D}+λ_{d})_{swept}/(λ_{d})_{unswept}]; mobilities are evaluated at average saturation conditions behind and ahead of front  
M_{t}  F_{λt}  mobility ratio, total, [(λ_{t})_{swept}/(λ_{t})_{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/L^{3} 
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  
n_{j}  N_{j}  moles of component j  
n_{N}  density (number) of neutrons  1/L^{3}  
n_{pj}  N_{pj}  moles of component j produced, cumulative  
n_{t}  N_{t}  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  m_{θND}  slope, neutron porosity vs. density (absolute value)  L^{3}/m 
N_{e}  oil influx (encroachment), cumulative  L^{3}  
N_{GR}  N_{γ},C_{G}  gamma ray count rate  1/t 
N_{i}  n_{i}  oil in place in reservoir, initial  L^{3} 
N_{N}  N_{n},C_{N}  neutron count rate  1/t 
N_{p}  n_{p}  oil produced, cumulative  L^{3} 
N_{pa}  n_{pa}  oil recovery, ultimate  L^{3} 
N_{R}  N_{F}  fuel deposition rate  m/L^{3}t 
N_{Re}  Reynolds number (dimensionless number)  
p  P  pressure  m/Lt^{2} 
p  price  M  
p_{a}  P_{a}  pressure, atmospheric  m/Lt^{2} 
p_{b}  p_{s},P_{s},P_{b}  pressure, bubblepoint (saturation)  m/Lt^{2} 
p_{bh}  P_{bh}  pressure, bottomhole  m/Lt^{2} 
p_{c}  P_{c}  pressure, critical  m/Lt^{2} 
p_{cf}  P_{cf}  pressure, casing flowing  m/Lt^{2} 
p_{cs}  P_{cs}  pressure, casing static  m/Lt^{2} 
p_{d}  P_{d}  pressure, dewpoint  m/Lt^{2} 
p_{D}  P_{D}  pressure, dimensionless  
p_{e}  P_{e}  pressure, external boundary  m/Lt^{2} 
p_{ext}  P_{ext}  pressure, extrapolated  m/Lt^{2} 
p_{f}  P_{f}  pressure, front or interface  m/Lt^{2} 
p_{gk}  price of gas in period k  M  
p_{i}  P_{i}  pressure, initial  m/Lt^{2} 
p_{iwf}  P_{iwf}  pressure, bottomhole flowing, injection well  m/Lt^{2} 
p_{iws}  P_{iws}  pressure, bottomhole static, injection well  m/Lt^{2} 
p_{k}  price in period k  M  
p_{pc}  P_{pc}  pressure, pseudocritical  m/L^{2} 
p_{pc}  P_{pc}  pseudocritical pressure  m/Lt^{2} 
p_{pr}  P_{pr}  pressure, pseudoreduced  
p_{r}  P_{r}  pressure, reduced  
p_{sc}  P_{sc}  pressure, standard conditions  m/Lt^{2} 
p_{sp}  P_{sp}  pressure, separator  m/Lt^{2} 
p_{tD}  P_{tD}  pressure function, dimensionless, at dimensionless time t_{D}  
p_{tf}  P_{tf}  pressure, tubing flowing  m/Lt^{2} 
p_{ts}  P_{ts}  pressure, tubing static  m/Lt^{2} 
p_{w}  P_{w}  pressure, bottomhole general  m/Lt^{2} 
p_{wf}  P_{wf}  pressure, bottomhole flowing  m/Lt^{2} 
p_{ws}  P_{ws}  pressure, bottomhole static  m/Lt^{2} 
p_{ws}  P_{ws}  pressure, bottomhole, at any time after shutin  m/Lt^{2} 
p  P  average pressure  m/Lt^{2} 
p  P  pressure, average or mean  m/Lt^{2} 
p_{R}  P_{R}  pressure, reservoir average  m/Lt^{2} 
P  phases, number of  
P  profit  M  
P_{c}  P_{C},p_{C}  capillary pressure  m/Lt^{2} 
P_{pvat}  profit at present value after tax  M  
P_{pvatk}  profit at present value after tax in period k  M  
q  Q  production rate or flow rate  L^{3}/t 
q_{a}  Q_{a}  production rate at economic abandonment  L^{3}/t 
q_{dh}  q_{wf},q_{DH},Q_{dh}  volumetric flow rate downhole  L^{3}/t 
q_{D}  Q_{D}  production rate, dimensionless  
q_{g}  Q_{g}  production rate, gas  L^{3}/t 
q_{gD}  Q_{gD}  production rate, gas dimensionless  
q_{i}  Q_{i}  production rate at beginning of period  L^{3}/t 
q_{o}  Q_{o}  production rate, oil  L^{3}/t 
q_{oD}  Q_{oD}  production rate, oil, dimensionless  
q_{p}  Q_{p}  production rate or flow rate at mean pressure  L^{3}/t 
q_{s}  Q_{s}  segregation rate (in gravity drainage)  L^{3}/t 
q_{sc}  q_{σ},Q_{sc}  surface production rate  L^{3}/t 
q_{s}  q_{σ},Q_{sc}  volumetric flow rate, surface conditions  L^{3}/t 
q_{w}  Q_{w}  production rate, water  L^{3}/t 
q_{wD}  Q_{wD}  production rate, water, dimensionless  
production rate or flow rate, average  L^{3}/t  
Q  Q  charge  q 
Q  q,Φ  heat flow rate  mL^{2}/t^{3} 
Q_{i}  q_{i}  pore volumes of injected fluid, cumulative, dimensionless  mL^{2}/t^{3} 
Q_{LtD}  Q_{ℓtD} (script l)  influx function, fluid, linear aquifer, dimensionless  
Q_{p}  Q_{ℓtD} (script l)  fluids, cumulative produced (where Np and Wp are not applicable)  
Q_{p}  produced fluids, cumulative (where Np and Wp are not applicable)  L^{3}  
Q_{tD}  fluid influx function, dimensionless, a dimensionless time tD  
Q_{V}  Z_{V}  cation exchange capacity per unit pore volume  
r  R  radius  L 
r  R  resistance  ML^{2}/tq^{2} 
r  royalty  various  
r_{d}  R_{d}  drainage radius  L 
r_{D}  R_{D}  radius, dimensionless  
r_{e}  R_{e}  external boundary radius  L 
r_{H}  R_{H}  hydraulic radius  L 
r_{R}  royalty rate  various  
r_{s}  R_{s}  radius of well damage or stimulation (skin)  L 
r_{w}  R_{w}  well radius  L 
r_{ws}  R_{wa}  radius of wellbore, apparent or effective (includes effects of well damage or stimulation)  L 
R  ρ,r  electrical resistivity (electrical logging)  mL^{3}/tq^{2} 
R  gas constant, universal (per mole)  mL^{2}/t^{2}T  
R  F_{g},F_{go}  gas/oil ratio, producing  
R  N  molecular refraction  L^{3} 
R  reaction rate  m/L^{2}  
R  revenue  M  
R(z)(script R)  real part of complex number z  
R_{a}  ρ_{a},r_{a}  apparent resistivity  mL^{3}/tq^{2} 
R_{F}  F_{gF}, F_{goF}  free gas/oil ratio, producing (freegas volume/oil volume)  
R_{i}  ρ_{i}, r_{i}  invaded zone resistivity  mL^{3}/tq^{2} 
R_{m}  ρ_{m} ,r_{m}  mud resistivity  mL^{3}/tq^{2} 
R_{mc}  ρ_{mc} ,r_{mc}  mudcake resistivity  mL^{3}/tq^{2} 
R_{mf}  ρ_{mf} ,r_{mf}  mudfiltrate resistivity  mL^{3}/tq^{2} 
R_{p}  F_{gp},F_{gop}  cumulative gas/oil ratio  
R_{s}  F_{gs},F_{gos}  solution gas/oil ratio (gas solubility in oil)  
R_{sb}  F_{gsb}  solution gas/oil ratio at bubblepoint conditions  
R_{sh}  ρ_{sh},r_{sh}  shale resistivity  mL^{3}/tq^{2} 
R_{si}  F_{gsi}  solution gas/oil ratio, initial  
R_{sw}  gas solubility in water  
R_{t}  ρ_{t},r_{t}  true formation resistivity  mL^{3}/tq^{2} 
R_{w}  ρ_{w},r_{w}  water resistivity  mL^{3}/tq^{2} 
R_{xo}  ρ_{xo},r_{xo}  flushedzone resistivity (that part of the invaded zone closest to the wall of the hole, where flushing has been maximum)  mL^{3}/tq^{2} 
R_{z}  ρ_{z},r_{z}  apparent resistivity of the conductive fluids in an invaded zone (caused by fingering)  mL^{3}/tq^{2} 
R_{0}  ρ_{0},r_{0}  formation resistivity when 100% saturated with water of resistivity Rw  mL^{3}/tq^{2} 
S  Laplace transform variable  
S  L  displacement  L 
S  Σ  entropy, specific  L^{2}/t^{2}T 
S  S, σ  skin effect  various 
S  standard deviation of a random variable, estimated  
s^{2}  variance of a random variable, estimated  
S  σ_{t}  entropy, total  mL^{2}/t^{2}T 
S  ρ,s  saturation  
S  s, σ  storage or storage capacity  various 
S_{fD}  S_{D}  dimensionless fracture storage capacity  
S_{g}  ρg,s_{g}  gas saturation  
S_{gc}  ρ_{gc},s_{gc}  gas saturation, critical  
S_{gr}  ρ_{gr},s_{gr}  gas saturation, residual  
S_{h}  ρ_{h},s_{h}  saturation, hydrocarbon  
S_{hr}  ρ_{hr},s_{hr}  residual hydrocarbon saturation  
S_{iw}  ρ_{iw},s_{iw}  irreducible (interstitial or connate) water saturation  
S_{L}  ρ_{L},s_{L}  liquid saturation, combined total  
S_{o}  ρ_{o},s_{o}  oil saturation  
S_{og}  ρ_{og},s_{og}  gascap interstitialoil saturation  
S_{or}  ρ_{or},s_{or}  residual oil saturation  
S_{w}  ρ_{w},s_{w}  water saturation  
S_{wc}  ρ_{wc},s_{wc}  critical water saturation  
S_{wg}  ρ_{wg},s_{wg}  interstitialwater saturation in gas cap  
S_{wi}  ρ_{wi},s_{wi}  initial water saturation  
S_{wo}  S_{wb}  interstitialwater saturation in oil band  
S_{wr}  ρ_{wr},s_{wr}  residual water saturation  
T  τ  time  t 
t (script t)  Δt  interval transit time  t/L 
t_{d}  τ_{d}  time, delay  t 
t_{dN}  decay time, neutron (neutron mean life)  t  
t_{D}  τ_{D}  time, dimensionless  
t_{Dm}  τ_{Dm}  time, dimensionless at condition m  
t_{ma} (script t)  Δt_{ma}  matrix interval transit time  t/L 
t_{N}  τ_{N},t_{n}  neutron lifetime  1/t 
t_{p}  τ_{p}  time well was on production prior to shutin, equivalent (pseudotime)  t 
t_{poat}  payout time, after tax  t  
t_{pypobt}  payout time, before tax at present value  t  
t_{s}  τ_{s}  time for stabilization of a well  t 
t_{sh} (script t)  Δt_{sh}  shale interval transit time  t/L 
t_{1}  τ_{1}  relaxation time, proton thermal  t 
t_{½}  halflife  t  
t_{2}  τ_{2}  relaxation time, freeprecession decay  t 
T  Θ  period  t 
T  tax on income  various  
T  Θ  temperature  T 
T  T  transmissivity, transmissibility  various 
T_{bh}  θ_{BH}  bottomhole temperature  T 
T_{c}  θ_{c}  critical temperature  T 
T_{f}  θ_{f}  formation temperature  T 
T_{k}  tax in period k  various  
T_{pr}  θ_{pr}  pseudoreduced temperature  T 
T_{r}  θ_{r}  reduced temperature  
T_{R}  θ_{R}  reservoir temperature  T 
T_{R}  tax rate  various  
T_{sc}  θ_{sc}  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  U_{T},U_{θ}  heat transfer coefficient, overall  m/t^{3}T 
v  V,u  acoustic velocity  L/t 
v  v_{s}  specific volume  L^{3}/m 
v  value (economic)  M  
v  V,u  velocity  L/t 
v_{b}  V_{b},u_{b}  burningzone advance rate (velocity of)  L/t 
v_{p}  net present value (NPV)  M  
V  n_{v}  moles of vapor phase  
V  U  potential difference (electric)  mL^{2}/qt^{2} 
V  v  volume  L^{3} 
V  f_{v}F_{v}  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 
V_{b}  v_{b}  bulk volume  L^{3} 
V_{bE}  v_{bE}  bulk volume of pack burned in experimental tube run  L^{3} 
V_{bp}  v_{bp}  volume at bubblepoint pressure  L^{3} 
V_{e}  V_{pe},v_{e}  volume, effective pore  L^{3} 
V_{gr}  v_{gr}  volume, grain (volume of all formation solids except shales)  L^{3} 
V_{ig}  v_{ig}  volume, intergranular (volume between grains; consists of fluids and all shales)(V_{v}−V_{gr})  
V_{im}  v_{im}  volume, intermatrix (consists of fluids and dispersed shale) (V_{b}V_{ma})  L^{3} 
V_{M}  v_{m}  molal volume (volume per mole)  L^{3} 
V_{ma}  v_{ma}  matrix (framework) volume (volume of all formation solids except dispersed clay or shale)  L^{3} 
V_{ma}  v_{ma}  volume, matrix (framework)(volume of all formation solids except dispersed shale)  L^{3} 
V_{p}  v_{p}  pore volume (Vb−Vs)  L^{3} 
V_{pD}  v_{pD}  pore volume, dimensionless  
V_{poat}  v_{pD}  payout volume, after tax  L^{3} 
V_{Rb}  volume of reservoir rock burned  L^{3}  
V_{Ru}  volume of reservoir rock unburned  L^{3}  
V_{s}  v_{s}  volume, solids(s) (volume of all formation solids)  L^{3} 
V_{sh}  v_{sh}  volume, shale(s)(volume of all shales: structural and dispersed)  L^{3} 
V_{shd}  v_{shd}  volume, shale, dispersed  L^{3} 
V_{shs}  v_{shs}  volume, shale, structural  L^{3} 
w  z  Arrhenius reactionrate velocity constant  L^{3}/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  L^{3} 
W  w,G  weight (gravitational)  mL/t^{2} 
W  w  work  mL^{2}/t^{2} 
W_{e}  w_{e}  water influx (encroachment), cumulative  L^{3} 
W_{i}  w_{i}  water injected, cumulative  L^{3} 
W_{p}  w_{p}  water produced, cumulative  L^{3} 
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  ML^{2}/tq^{2}  
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  
Z_{p}  Z_{p}  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  
Z_{a}  impedance, acoustic  m/L^{2}t 
Greek
Letter Symbol  Reserve SPE Letter Symbol  Quantity  Dimensions 
α  β,γ  angle  
α  M_{α}  attenuation coefficient  1/L 
α  a,η_{h}  heat or thermal diffusivity  L^{2}/t 
α  reduction ratio or reduction term  
α  a,η_{h}  thermal or heat diffusivity  L^{2}/t 
α_{SPsh}  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,F_{s}  specific gravity (relative density)  
γ  k  specific heat ratio  
γ  ε_{s}  strain, shear  
shear rate  1/t  
γ_{g}  s_{g},F_{gs}  specific gravity, oil  
γ_{w}  s_{w},F_{ws}  specific gravity, water  
δ  Δ  decrement  various 
δ  deviation, hole (drift angle)  
δ  F_{d}  displacement ratio  
δ  drift angle, hole (deviation)  
δ  r_{s}  skin depth (logging)  L 
δ_{ob}  F_{dob}  displacement ratio, oil from burned volume, volume per unit volume of burned reservoir rock  
δ_{ou}  F_{dou}  displacement ratio, oil from unburned volume, volume per unit volume of unburned reservoir rock  
δ_{wb}  F_{dwb}  displacement ratio, water from burned volume, volume per unit volume of burned reservoir rock  
Δ  difference or difference operator, finite (Δx=x_{2}−x_{1} or x_{1}−x_{2})  
Δ_{Ge}  Δ_{ge}  gas influx (encroachment) during an interval  L^{3} 
Δ_{Gi}  Δ_{gi}  gas injected during an interval  L^{3} 
Δ_{Gp}  Δ_{gp}  gas produced during an interval  L^{3} 
Δ_{Ne}  Δ_{ne}  oil influx (encroachment) during an interval  L^{3} 
Δ_{Np}  Δ_{np}  oil produced during an interval  L^{3} 
Δ_{r}  Δ_{R}  radial distance (increment along radius)  L 
Δ_{twf}  Δ_{τwf}  drawdown time (time after well is opened to production) (pressure drawdown)  t 
Δ_{tws}  Δ_{τws}  buildup time; shutin time (time afterwell is shut in) (pressure buildup, shutin time)  t 
Δ_{We}  Δ_{we}  water influx (encroachment) during an interval  L^{3} 
Δ_{Wi}  Δ_{wi}  water injected during an interval  L^{3} 
Δ_{Wp}  Δ_{wp}  water produced during an interval  L^{3} 
ε  dielectric constant  q^{2}t^{2}/mL^{3}  
ε  e,ε_{n}  strain, normal and general  
η  hydraulic diffusivity (k/øcμ or λ/øc)  L^{2}/t  
θ  β,γ  angle  
θ  θ_{V}  strain, volume  
Ө  α_{d}  angle of dip  
Ө_{a}  α_{da}  dip, apparent angle of  
Ө_{c}  Г_{c,γc}  contact angle  
λ  C  decay constant(1/τ_{d})  1/t 
λ  mobility (k/μ)  L^{3}t/m  
λ  wavelength(1/σ)  L  
λ_{g}  mobility, gas  L^{3}t/m  
λ_{o}  mobility, oil  L^{3}t/m  
λ_{t}  Λ  mobility, total, of all fluids in a particular region of the reservoir [e.g., (λ_{o}+ λ_{g}+ λ_{w})]  L^{3}t/m 
λ_{w}  mobility, water  L^{3}t/m  
μ  M  azimuth of reference on sonde  
μ  m  magnetic permeability  mL/q^{2} 
μ  mean value of a random variable  
μ  υ,σ  Poisson’s ratio  
μ  η  viscosity, dynamic  m/Lt 
μ_{a}  η_{a}  viscosity, air  m/Lt 
μ_{c}  chemical potential  
μ_{g}  η_{g}  viscosity, gas  m/Lt 
μ_{ga}  η_{ga}  viscosity, gas, at 1 atm  m/Lt 
μ_{o}  η_{o}  viscosity, oil  m/Lt 
μ_{p}  η_{p}  viscosity at mean pressure  m/Lt 
μ_{w}  η_{w}  viscosity, water  m/Lt 
ν  N  kinematic viscosity  L^{2}/t 
ν  N  viscosity, kinematic  L^{2}/t 
ρ  D  density  m/L^{3} 
ρ  R  resistivity, electrical (other than logging)  mL^{3}tq^{2} 
ρ_{a}  D_{a}  density, apparent  m/L^{3} 
ρ_{b}  D_{b}  density, bulk  m/L^{3} 
ρ_{f}  D_{f}  density, fluid  m/L^{3} 
ρ_{F}  D_{F}  density, fuel  m/L^{3} 
ρ_{g}  D_{g}  density, gas  m/L^{3} 
ρ_{ma}  D_{ma}  density, matrix (solids, grain)  m/L^{3} 
ρ_{o}  D_{o}  density, oil  m/L^{3} 
ρ_{sE}  D_{sE}  density of solid particles making up experiment pack  m/L^{3} 
ρ_{t}  D_{t}  density, true  m/L^{3} 
ρ_{w}  D_{w}  density, water  m/L^{3} 
ρ_{xo}  D_{xo}  density, flushed zone  m/L^{3} 
_{L}  _{L}  density of produced liquid, weightweighted average  m/L^{3} 
σ  γ  conductivity, electrical (other than logging)  various 
σ  cross section, microscopic  1/L  
σ  s  cross section of a nucleus, microscopic  L^{2} 
σ  y,γ  interfacial surface tension  m/t^{2} 
σ  microscopic cross section  L^{2}  
σ  standard deviation of a random variable  
σ  s  stress, normal and general  m/Lt^{2} 
σ  y,γ  surface tension, interfacial  m/t^{2} 
σ  wave number(1/λ)  1/L  
σ^{2}  variance of a random variable  
Σ  S  cross section, macroscopic  1/L 
Σ  summation (operator)  
τ  s_{s}  stress, shear  m/Lt^{2} 
τ  τ_{c}  time constant  t 
τ_{d}  t_{d}  decay time (mean life) (1/λ)  t 
τ_{d}  t_{dt}  mean life (decay time) (1/λ)  t 
τ_{e}  tortuosity, electric  
τ_{H}  hydraulic tortuosity  
τ_{H}  tortuosity, hydraulic  
τ  t  lifetime, average (mean life)  t 
φ  f,ε  porosity (V_{b}−V_{s})/V_{b}  
φ_{a}  f_{a},ε_{a}  porosity, apparent  
φ_{e}  f_{e},ε_{e}  porosity, effective (V_{pe}/V_{b})  
φ_{E}  f_{E},ε_{E}  porosity of experimental pack  
φ_{h}  f_{h},ε_{h}  porosity, hydrocarbonfilled, fraction or percent of rock bulk volume occupied by hydrocarbons  
φ_{ig}  f_{ig},ε_{ig}  "porosity" (space), intergranular(V_{b}−V_{gr})/V_{b}  
φ_{im}  f_{im} ,ε_{im}  “porosity” (space), intermatrix (V_{b}−V_{ma})/V_{b} 

φ_{ne}  f_{ne},ε_{ne}  porosity, noneffective (V_{pne})/V_{b}  
φ_{R}  f_{R},ε_{R}  porosity of reservoir or formation  
φ_{t}  f_{t},ε_{t}  porosity, total  
Φ  β_{d}  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 
Math
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  
curl  
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  
e^{z}  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  
s^{2}  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=x_{2}–x_{1} or x_{1}–x_{2})  
Δ  difference operator, finite  
μ  mean value of a random variable  
σ  standard deviation of a random variable  
σ^{2}  variance of a random variable  
Φ  f  potential or potential function  various 
Ψ  stream function  various 
See also
Recommended SI units and conversion factors
Nomenclature for SI metric conversion tables