Page 98 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

86 Reservoir Engineering

Table 5-19
Saturation Exponents in Teflon Cores Partially Saturated
with Nonwetting Conducting Liquid
Air-NaCI solutlon Oil-NaCI solutlon
Brine Brlne
saturation saturation
% PV n % PV n
66.2 1.97 64.1 2.35
65.1 1.98 63.1 2.31
63.2 1.92 60.2 2.46
59.3 2.01 55.3 2.37
51.4 1.93 50.7 2.51
43.6 1.99 44.2 2.46
39.5 2.11 40.5 2.61
33.9 4.06 36.8 2.81
30.1 7.50 34.3 4.00
28.4 8.90 33.9 7.15
31 .O 9-00
~_____
From Reference 178.
were treated so that they were mildly oil-wet. From their data, plotted in Figure
5-6 1, the saturation exponent increased as the extent of oil-wetting increased.
The foregoing data suggest that unless the reservoir is known to be water-
wet, the saturation exponent should be measured with native-state (preferably)
or restored cores. If the reservoir is oil-wet and clean cores are used that may
be water-wet, the saturation exponents that are obtained can lead to an under-
estimate of connate water saturation in the formation tested.
FORMATION EVALUATION
Formation evaluation, as applied to petroleum reservoirs, consists of the
-quantitative and qualitative interpretation of formation cores, geophysical well
logs, mud logs, flow tests, pressure tests, and samples of reservoir fluids. The
goal of the interpretation is to provide information concerning reservoir
lithology, fluid content, storage capacity, and producibility of oil or gas reser-
voirs. The final analysis includes an economic evaluation of whether to complete
an oil or gas well and, once completed, an ongoing analysis of how to produce
the well most effectively. These interpretations and analyses are affected by
geological complexity of the reservoir, rock quality, reservoir heterogeneity, and,
from a logistical standpoint, the areal extent and location of the project of
interest. In the early stages of development, the purpose of formation evaluation
is to define reservoir thickness and areal extent, reservoir quality, reservoir fluid
properties, and ranges of rock properties. The key rock properties are porosity,
permeability, oil, gas, and water saturations. Because of space limitations and
the importance of these properties, methods of measuring porosity, permeability,
and fluid saturations will be emphasized.
Coring and Core Analysis

Routine or conventional core analyses refer to common procedures that
provide information on porosity, permeability, resident fluids, lithology, and