TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAn algorithm has been developed for computing the pressure response for a well with constant wellbore storage and non-Darcy skin factor across the completion. The algorithm has been used to generate type curves for drawdown and buildup tests. The buildup pressure derivative response for a well with non-Darcy flow across the completion exhibits a much steeper slope during the transition out of wellbore storage than that of a well with constant skin.No reservoir model with constant wellbore storage and skin can reproduce this steep derivative. Thus, if it is present in a buildup test, the well is experiencing either decreasing wellbore storage or decreasing skin factor, or both.With the new type curves, under favorable conditions, both Darcy and non-Darcy skin components may be estimated from a single buildup test following constant rate production. The new algorithm may also be used to model a test sequence comprising multiple flow and buildup periods.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper introduces the concept of the transient hyperbolic exponent b. The transient hyperbolic exponent may be used to derive values for b for use in Arps' equations for a variety of drive mechanisms. For a coalbed methane reservoir, b is shown to be a function of the ratio of the average reservoir pressure to the Langmuir pressure, with b approaching 1.5 at pressures much higher than p L , 1.0 when the pressure is equal to p L , and approaching 0.5 at pressures much lower than p L . For wells producing from finite, transient dual porosity reservoirs, the b value may be as high as 2, during a flow period characterized by steady state flow in the natural fracture system, and transient linear flow in the matrix. A coalbed methane well and two Antrim Shale wells are presented as examples.