Common variables | |||||||||||||

R_{w} |
Resistivity of formation water | ||||||||||||

R_{t} |
True formation resistivity | ||||||||||||

S_{w} |
Saturation woth water | ||||||||||||

R_{m } |
Mud resistivity | ||||||||||||

R_{mf} |
Mud filtrate resistivity from fluid & mud that filters into the formation invaded zone | ||||||||||||

d_{h} |
borehole diameter | ||||||||||||

R_{mc} |
mud cake resistivity from the side of the borehole | ||||||||||||

R_{xo} |
Flushed zone resisitivity, a portion of the invaded zone | ||||||||||||

R_{i} |
Annulus zone resistivity, the outer portion or transition part of the invaded zone | ||||||||||||

d_{i} |
diameter of flushed zone portion of invaded zone | ||||||||||||

d_{j} |
diameter of complete invaded zone,
includes d_{i} |
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S_{xo} |
water saturation of flushed zone | ||||||||||||

h_{mc} |
thickness of mud cake | ||||||||||||

Dr_{j} |
radius of outer boundary of invaded zone | ||||||||||||

a | tortuosity factor in Archie Equation | ||||||||||||

m | cementation exponent in Archie Equation | ||||||||||||

n | saturation exponent in Archie Equation | ||||||||||||

R_{i} |
invaded zone resistivity | ||||||||||||

R_{mf
>> }R |
resistivity relation for freshwater muds | ||||||||||||

R_{mf
~ }R |
resistivity relation for saltwater muds | ||||||||||||

R_{t} |
true formation resistivity derived from deep resistivity log | ||||||||||||

T_{ms} |
mean surface temperature | ||||||||||||

T_{f} |
formation temperature | ||||||||||||

g_{G} |
geothermal gradient; slope of T_{f}/Depth |
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D | depth | ||||||||||||

SSP | static spontaneous potential, correction from raw SP | ||||||||||||

R_{we} |
equivalent formation water resistivity | ||||||||||||

V_{shale} |
volume of shale | ||||||||||||

SP_{shale} |
SP value of shale generally set to zero | ||||||||||||

PSP | psuedostatic spontaneous potential; maximum SP of a shaly formation | ||||||||||||

f_{s} |
sonic derived porosity | ||||||||||||

Dt_{ma} |
interval transit time in the matrix | ||||||||||||

Dt_{log} |
interval transit time in the formation | ||||||||||||

Dt_{fl} |
interval transit time in the fluid | ||||||||||||

C_{p} |
compaction factor for unconsolidated sands in Wyllie formula for sonic porosity | ||||||||||||

Dt | interval transit time | ||||||||||||

f=f_{s}x.09 |
Hilchie (1978) formula for correction of hydrocarbon effect on sonic porosity log for where oil is present | ||||||||||||

f=f_{s}x0.7 |
Hilchie (1978) formula for correction of hydrocarbon effect on sonic porosity log for where gas is present | ||||||||||||

r_{b} |
Rho b, bulk density | ||||||||||||

r_{ma} |
Matrix density | ||||||||||||

r_{fl} |
density of fluid (salt=1.1 or fresh=1.0 g/cm3; gas=0.7) | ||||||||||||

f_{D} |
density derived porosity | ||||||||||||

f_{N} |
neutron porosity | ||||||||||||

f_{NDgas} |
porosity of the gas bearing formation | ||||||||||||

f_{w} |
water-filled porosity | ||||||||||||

f_{ND } |
neutron density crossplot derived porosity | ||||||||||||

e | dielectric constant from the log | ||||||||||||

e_{w} |
dielectric constant of water | ||||||||||||

e_{ma} |
dielectric constant of rock matrix | ||||||||||||

p | constant that varies with water salinity; value of 1.2 can be used, or can be calculated from nearby H2O zone by substitution of phiND for phiw | ||||||||||||