Transient Productivity Index for Numerical Well Test Simulations
G. Blanc, D. Y. Ding, A. Ene, T. Rahon, D. Rahon, 1999. "Transient Productivity Index for Numerical Well Test Simulations", Reservoir Characterization—Recent Advances, Richard A. Schatzinger, John F. Jordan
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The most difficult aspect of numerical simulation of well tests is the treat-ment of the bottom-hole flowing (BHF) pressure. In full-field simulations, this pressure is derived from the well-block pressure (WBP) using a numerical productivity index that accounts for the grid size and permeability, and for the well completion. This productivity index is calculated assuming a pseudo-steady-state flow regime in the vicinity of the well and is therefore constant during the well production period.
Such a pseudo-steady-state assumption is no longer valid for the early time of a well test simulation as long as the pressure perturbation has not reached several grid-blocks around the well. This paper offers two different solutions to this problem:
The first solution is based on the derivation of a transient numerical productivity index (TNPI) to be applied to Cartesian grids.
The second solution is based on the use of a corrected transmissibility and accumulation term (CTAT) in the flow equation.
The representation of the pressure behavior given by both solutions is far more accurate than the conventional one, as shown by several validation examples presented in the following pages.
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Reservoir Characterization—Recent Advances
Optimum reservoir recovery and profitability result from guidance by an effective reservoir management plan. Success in developing the most appropriate reservoir management plan requires knowledge and consideration of (1) the reservoir system, including rocks, fluids, and rock-fluid interactions, as well as wellbores and associated equipment and surface facilities; (2) the technologies available to describe, analyze, and exploit the reservoir; and (3) the business environment under which the plan will be developed and implemented. Reservoir management plans de-optimize with time as technology and the business environment change or as new reservoir information becomes available. Reservoir characterization is the process of creating an interdisciplinary high-resolution geoscience model that incorporates, integrates, and reconciles various types of geological and engineering information from pore to basin scale. The reservoir data are then conceptually and quantitatively modeled and compared to the historical production data and fluid flow distribution patterns within and beyond the limits of the reservoir to match well production histories and predict their behavior. The goals of reservoir characterization are to simultaneously (1) maintain high displacement efficiency, (2) optimize high sweep efficiency, (3) provide reliable reservoir performance predictions, and (4) reduce risk and maximize profits. Notice that in addition to the technical concepts that we normally associate with "characterization," maximizing profits is an essential element of this process. Papers from the Fourth International Reservoir Characterization Technical Conference (1997), sponsored by the U.S. Department of Energy, this publication is a unique compilation of 27 papers covering every aspect of reservoir characterization and has been a popular AAPG publication since that time. Using an interdisciplinary approach, the papers address qualitative information as well as integrated quantified data and culminate in a fully integrated study.