Formation Evaluation Using Acoustic Pressure Buildup Data
Augusto L. Podio, Keneth L. Huddleston, James N. McCoy
Production is lost when skin damage restricts fluid flow into the well
bore.
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 petrol
um 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 real time
at the well
site. 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
well
bore. Simultaneously, the computer acquires wellhead
pressure and temperature data, using high precision transducers, from which
bottom hole pressure is calculated. Strip chart recordings of the acoustic
signals are periodically made to 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,
Log
-
Log
, 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 bottom hole
pressure bombs. Interpretation of the results are in agreement to those obtained
independently by DST.
AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.