This paper proposes analysis techniques for post-transient, flow at constant bottomhole pressure. Rate-time decline curves approximate this flow regime. Reservoir characteristics for homogeneous reservoirs, vertically-fractured reservoirs, and naturally-fractured reservoirs can be obtained using these techniques. These analysis techniques are based on the exponential, post-transient, constant-pressure radial flow solutions for each case. We show that theory predicts a linear relation between log (rate) and time for these curves. Thus, a straight line on a semi-log rate vs. time plot may be the line predicted by the analytical solution for that reservoir. If so, important formation characteristics can be estimated analytically. Reservoir pore volume is determined directly while other reservoir characteristics are calculated indirectly. These new techniques are a very powerful extension of transient well testing.

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