Page 333 - Petrophysics 2E

302 PETROPHYSICS: RESERVOIR ROCK PROPERTIES

2. Chemical analysis of an oil reservoir brine yielded the following
results: 50,000 ppm Naf, 60,000 ppm C1-, 15,000 ppm Mg2+,
12,000 ppm SO:+, 8,000 ppm HCO;, Calculate:

(1) the equivalent salinity in ppm sodium chloride, and
(2) the resisitivity of the brine at loo", 175", and 250°F; discuss the
effect of temperature on the resistivity of water.

3. A normally pressured well located in offshore Louisiana is 5,900 ft
deep. The producing interval is completely water-wet. The apparent
porosity of the shale zone is approximately 0.39. The cementation
exponent for shales in this field is 1.57. The true resistivity of the
shale zone is 0.90 ohm-m. Calculate:

(a) water resistivity of the formation at the reference temperature
of 75"F, and
(b) water resistivity at the formation temperature of 140'F.

4. The results of laboratory measurements made on 12 water-wet clean
sandstone rock samples and well log analysis are shown in Table 4A.
The resistivity of a formation-water sample at 25OC is 0.056 ohm-m.
The formation temperature is 89°C.

(a) Calculate the formation resistivity factor for each sample.
(b) Estimate the cementation factor.
(c) Determine the water saturation in each sample.
(d) Find the best representative values of tortuosity.

TABLE 4A

Sample No. Porosity Ro Rt
1 0.204 0.665 30.0
2 0.178 0.830 24.0
3 0.163 0.960 22.0
4 0.201 0.680 21.0
5 0.143 1.190 20.0
6 0.252 0.470 16.5
7 0.254 0.460 20.0
8 0.273 0.410 23.0
9 0.175 0.850 20.0
10 0.200 0.680 16.0
11 0.174 0.860 17.0
12 0.144 1.170 17.0