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184 WELL LOGGING
9.8 The scale of reservoir sampling can be estimated by comparing the ratio of the
area sampled to the drainage area of a well. The fraction of area sampled (f )
AS
can be written as the ratio f AS = area sampled/well drainage area.
a. What is the area of a vertical, circular wellbore that has a 6″ radius?
b. If the drainage area of a well is 40 acres, what fraction (f ) of this area is
AS
directly sampled by the wellbore?
C. Suppose a well log signal penetrates the formation up to 5 ft from the
wellbore. What fraction of area is now sampled?
