An iterative approach to reservoir characterization, conducted by an integrated work team, proved to be essential to adequately understand and manage the late life production of the Trinity Shoal "N" Sand Reservoir. This paper describes the approach taken by the team in obtaining a superior simulation history match, which resulted in a more complete understanding of the reservoir, lead to the identification of successful infill well locations, and improved long term reservoir management plans.
Introduction
Production from the Trinity Shoal "N" Sand Reservoir represents a significant portion of the total liquid and gas production for Texaco E&P Offshore Division; accordingly, proper reservoir management is essential for maintaining tactical and strategic goals for the division. A simulation study was undertaken to fulfill the following objectives:develop long term reservoir management strategy;identify potential drilling/workover opportunities to increase production; andrevise oil and gas reserve estimates.
The reservoir can be characterized as a moderate water drive reservoir with a large gas cap and oil rim. The aquifer is infinite acting and is believed to be linear in geometry, having limited access to the reservoir in the center of the sand body. The oil rim in the center of the reservoir is moving up-dip, while on the western flank, the gas cap is expanding and drives the oil column down-dip. To date, 25 MMSTB have been produced, leaving an estimated 6 MMSTB of recoverable oil yet to be produced. Gas cap blowdown is scheduled for the year 2000. Twenty-four wells have been drilled in the reservoir, with seven still producing (see Fig. 1). During the study, it was observed that simulation results provided valuable clues to clarifying reservoir properties infered from other interpretations, i.e., well log analysis, seismic interpretation, pressure transient analysis, material balance, etc., and that many of the initial petrophysical interpretations had to be revisited and revised as the history matching procedure progressed. While several authors report the advantages of working within an integrated team, this paper focuses on the iterative aspect of reservoir characterization.
Integrated vs. Sequential Approach to History Matching Traditionally, reservoir simulation has been viewed as the last link of a sequential reservoir characterization chain, preceded by seismic interpretation, well log analysis, core analysis, depositional and structural geology, mapping, decline curve analysis, material balance, pressure transient analysis, nodal analysis, etc. Several tasks were often completed by company specialists, consultants, or vendors, external to the asset management team (AMT), and sometimes without knowledge of other reservoir information. While this arrangement was adequate in many field studies, it did not work well in this case. Basicly, the reservoir engineer was given the unenviable job of history matching production data using predetermined geophysical and engineering interpretations.
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