Page 205 - Basic Well Log Analysis for Geologist

JG INTERPRETATION CASE STUDIES

CALIPER oiam on incses : POROSITY INDEX %_S.S. maTRIx
cp cepeeeape np se peserpeenepeenpeeey 6" : COMPENSATED FORMATION DENSITY POROSITY
30 20 lO
GAMMA RAY ae Units
COMPENSATED NEUTRON POROSITY

th
Rmf at meas.
7 7/8
Bit Sire
mc at meas. temp
Max Rec. Temp
Type Fluid in hole | F GM
Rm at meas. temp. | 2.53 at 65° F

Figure 93. Combination Neutron-Density Log with gamma ray log and caliper, Cretaceous Pictured Cliffs Sandstone, San Juan
basin.
Note:
1. Decrease in hole diameter (1,926 to | 958 ft) on caliper log in track #1 indicating mudcake (permeability).
2. Neutron porosity is higher than density porosity in tracks #2 and #3. But in a gas-bearing sand, the neutron
porosity should be less than density porosity (gas effect). It can be surmized that the reason for the high neutrot
porosity values in the Pictured Cliffs Sandstone is the high shale content of this sand. Shale has a high
hydrogen concentration and therefore has high neutron porosity values.

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