Automatic Pressure Buildup Data Acquisition and Interpretation Using a Microcomputer-Based Acoustic Liquid Level Instrument

Abstract

ABSTRACT Production is lost when skin damage restricts fluid flow into the wellbore. The presence and degree of skin damage is most commonly determined through analysis of pressure buildup tests. This forms the basis for selecting wells as candidates for stimulation, workovers and recompletion. Traditionally these tests have been conducted using downhole pressure bombs or in the case of most pumping wells through the use of acoustic annular fluid level data which was processed off-site. The logistical complexities and high cost of these methods have limited the extent and frequency of well testing. Given the present need for production optimization and operating cost reduction, the development of a cost effective method for buildup testing represents a major advance in petroleum technology. This paper describes the design, implementation and application of a microcomputer-based system for automatically performing pressure buildup tests in pumping wells, from surface measurements, and analyzing the data in realtime at the wellsite. The system is based on a portable PC which controls the operation. A solenoid-actuated acoustic source, powered with compressed gas, generates accurately repeatable acoustic pulses at variable programmable intervals. Acoustic echo travel time is interpreted in terms of position of the liquid level in the wellbore. Simultaneously the computer acquires wellhead pressure and temperature data, using high precision transducers, from which bottomhole pressure is calculated. Strip chart recordings of the acoustic signals are also made to periodically control the quality of the data. At any time during the test the operator can obtain standard graphical display of the buildup test ( Horner plot, dP vs. dT, MDH, etc. ) as well as conventional interpretation in terms of skin, afterflow rates and duration. Results from three field tests of the system are presented. They indicate that the system was used successfully in fairly harsh environmental conditions and was able to acquire buildup data of quality comparable to that obtainable with bottomhole pressure bombs. Interpretation of the results are in agreement to those obtained independently by DST.