Page 110 - Principles of Applied Reservoir Simulation 2E

Conceptual Reservoir Scales

One of the most important goals of modeling is to reduce the risk
associated with making decisions in an environment where knowledge is limited.
The range of applicability of acquired data and the integration of scale-dependent
data into a cohesive reservoir concept are discussed below.

11.1 Reservoir Sampling and Scales

A sense of just how well we understand the reservoir can be obtained by
considering the fraction of reservoir area sampled by different techniques. As
an example, suppose we want to find the size of the area sampled by a wellbore
that has a six-inch radius. If we assume the area is circular, we can calculate the
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area as TC r where r is the sampled radius. The resulting sampled area is less than
a square foot. To determine the fraction of area sampled, we normalize the
sampled area with respect to the drainage area of a well, say a very modest five
acres. What fraction of the area is directly sampled by the wellbore? The drain-
age area is 218,000 square feet. The fraction of the area sampled by the well is
three to four parts in a million. This is a tiny fraction of the area of interest.
A well log signal will expand the area that is being sampled. Suppose a
well log can penetrate the formation up to five feet from the wellbore, which
is a reasonably generous assumption. The fraction of area that has been sampled
is now approximately four parts in ten thousand. The sample size in a drainage
area of five acres, which is a small drainage area, is still a fraction of a percent.

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