Page 207 - Fundamentals of Reservoir Engineering

STABILIZED INFLOW EQUATIONS 145

structural contour maps are available for the reservoir, then the areas so determined
can be roughly matched to the reservoir geometry to obtain a reasonable estimate of
the shape of the drainage area. Fig. 6.4 should then be consulted to determine the
shape factor C A which can be seen to be dependent not only on the drainage shape
but also upon the position of the well with respect to the boundary. For irregular
shapes, interpolation between the geometrical configurations presented by Dietz may
be necessary. Naturally it is never possible to obtain the exact shape of the drainage
volume but a reasonable estimate can usually be made which, when interpreted in
terms of a shape factor and used in equ. (6.22), can considerably improve the
accuracy of calculations made using the inflow equation.

Also listed in fig. 6.4 is the dimensionless time group t DA = kt/φµcA, in which t is the
time for which the well has been producing at a reasonably steady rate of production.
Unless the calculated value of t DA exceeds the figure quoted for each geometrical
configuration then the well is not producing under semi-steady state conditions and the
Dietz shape factors cannot be used.