Page 157 - Basic Well Log Analysis for Geologist

LOG INTERPRETATION CASE STUDIES

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You are now preparing to calculate, and then assess. the when R, nin formula and tornado chart R, are compared.
log parameters necded to determine whether the Atoka
8-925
Ry,
Swr = [Ryo/ R/C Ring
Sandstone might produce.
You have the following information: (1) resistivity of Moveable Hydrocarbon Index:
formation water (Ry) = 0.065 at T; from vour logging
Sy/Syo = [Ryo/RD/(Rimt/ Ry]?
engineer: (2) resistivity of mud filtrate (Rap) = 0.65 at Ty
from the log header and corrected to formation temperature Water Saturation Corrected:
by the Arps equation (see Chapter 1); (3) temperature of the
Swa \025
formation (T,) = [87°F from the estimation of formation
Svc corr = Swa x So
WE
temperature chart (see Chapter I): and (4) the surface

temperature = 75°F from an estimation by the well site Bulk Volume Water—Porosity (@) in this example is
geologist. neutron-density porosity (dy_p).
Complete the following Pennsylvanian Atoka Sandstone
BVW = & X Sya
Log Evaluation Table (work Table A). Five depths were
selected for your convenience and are listed in the table. Residual Oil Saturation—S,, ts water saturation of
You may find this list of formulas helpful as you pursue flushed zone calculated by: S,, = [0.81/62 x (Ra Ryo)}!?
your calculations:
ROS = 1.0 — S,,
Neutron Density Porosttv— Values for neutron (N) and
density (D) porosity read on neutron-density log (Fig. 55). Moveable Oil Saturation:
vv = y [iy + bn? MOS = S,, — Sy,
2
Irreducible Water Saturation—Formation factor (F)
R, Minimum—-Value for LL-8* from Jog reading (Fig. 54) equal to 0.81/d? in consolidated sands (see Table |). This
used to correct Ry y* to R, in thin, resistive zones (Chapter formula calculates an approximate value for irreducible
Hl). water saturation. It should be used only in crossplots where
you are trying to determine the relative permeabilities: K,,.
Ry min = (LL-8* or SPL*) * (Ry/Rmy)
tmin
K,,. and K,y.

Water Saturation Archic—Here, o is the value of by, Swin = VW F/2000
from the neutron-density formula. Also, in this example, R,
is equal to either R,,,,, orf to R, from the tornado chart in Volumetric Recoverable Gas Reserves—Variables defined
Appendix 6 (page 212). in introduction to case studies.
0.3} R G, = 43,560 x drainage area (DA) X reservior
— x w
Ywal 2 R, thickness (h) X porosity (@) X hydrocarbon
fie ass saturation (S,) X gas volume factor (B,i)
Water Saturation Ratio—Value for R,, is from the
shallow Laterolog* (Fig. 54). R, value is the larger value recovery factor (RF)

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