Pressure Transient Testing Using Surface Based Measurements

Abstract Proper reservoir management and production optimization require timely knowledge of formation pressure, permeability and well bore skin factor. To this effect, pressure transient tests using wireline conveyed pressure gauges are commonly run in flowing wells. The presence of artificial lift equipment complicates and often precludes the use of wireline conveyed devices so that conventional pressure transient tests are seldom performed in these wells, resulting in poor reservoir and production management. Since the 1980s, the industry has used programmable equipment for calculation of bottomhole pressure from surface pressure and acoustically measured liquid level data in pumping wells. Advances in electronics, computer software and transducer technology have vastly improved the data quality and the usability of this equipment to the point that routine determination of BHP using surface measurements is reliable, cost effective and provides real-time data with the quality necessary for pressure transient analysis. Seven field cases are presented to illustrate application of the acoustic pressure transient system in different wells and to illustrate best practices that results in high quality data. Introduction The present economic climate in the oil industry requires that maximum production efficiency be achieved with minimum engineering and technical manpower. Considering that the majority of US and Canada land oil wells are produced through artificial lift and the majority of these by means of beam pumping systems, there exists a need to easily monitor and analyze the performance of beam pumped and other artificially pumped wells. Flowing bottom hole pressure surveys, pressure buildup tests, pressure drawdown tests, and inflow performance analyses are the principal tools available to determine reservoir pressure, formation permeability, productivity index, pump efficiency, skin factor, as well as other indicators can be used in the optimization of producing well operations. These techniques are widely used in flowing wells and in some gas lift wells, where the pressure information is easily obtained from wireline conveyed bottomhole pressure recorders. The presence of the sucker rods in beam pumped wells essentially precludes practical, routine, direct measurement of bottomhole pressure, thus eliminating the single most important parameter for well analysis. Permanent installations of surface indicating bottomhole pressure gages have not become cost effective or reliable over long periods of time. Wire line measurements through the annular space between the tubing and casing involve operational difficulties, risk and high cost. The solution of this problem has been found through calculation of the bottom hole pressure from casinghead pressure measurement and determination of the annular fluid head from echometric surveys that yield the depth of the gasliquid interface.1,2,3 A microcomputer-based system for automatic acquisition of pressure transient data was developed in 1987 as a hybrid system using analog filtering and recording of the acoustic signal 4,5. Such system still depended in some measure on the operator's interpretation of the acoustic chart recordings to determine the average acoustic velocity in the annular gas.

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