In the past, the reservoir material balance (voidage) effects occurring between the end of the measured (known) production history and future Inflow Performance Relationship (IPR) time levels have been commonly ignored in the computation of the future IPR behavior. Neglecting the reservoir voidage that occurs during the time interval between the end of the known production history and the future IPR time levels results in erroneous estimates of the future IPR behavior.

A detailed description is given of the mathematically rigorous technique that has been used in the development of a multilayer well performance simulator that properly accounts for the reservoir voidage effects. Some of the more significant results are also presented of an extensive effort to develop an accurate and computationally efficient well performance simulation model.

The reservoir can be considered to be multilayered, with mixed reservoir layer completion types and outer boundary shapes, drainage areas and boundary conditions. The well performance model can be used to simulate performance in three different operating modes: (1) constant wellhead rate, (2) constant bottomhole pressure, and (3) constant wellhead pressure. The transient performance of vertical, vertically fractured and horizontal wells can be simulated with this well performance model. The well performance model uses mathematically rigorous transient solutions and not simply the approximate solutions for each of the well types, as do most of the other commercially available well performance models.

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