Summary
Pressure-rate deconvolution provides equivalent representation of
variable-rate well-test data in the form of characteristic constant rate
drawdown system response. Deconvolution allows one to develop additional
insights into pressure transient behavior and extract more information from
well-test data than is possible by using conventional analysis methods. In
some cases, it is possible to interpret the same test data in terms of larger
radius of investigation.
There are a number of specific issues of which one has to be aware when
using pressure-rate deconvolution. In this paper, we identify and discuss
these issues and provide practical considerations and recommendations on how to
produce correct deconvolution results. We also demonstrate reliable use of
deconvolution on a number of real test examples.
Introduction
Evaluation and assessment of pressure transient behavior in well-test data
normally begins with examination of test data on different analysis plots
[e.g., a Bourdet (1983, 1989) derivative plot, a superposition (semilog) plot,
or a Cartesian plot]. Each of these plots provides a different view of the
pressure transient behavior hidden in the test data by well-rate variation
during a test. Integration of these several views into one consistent
picture allows one to recognize, understand, and explain the main features of
the test transient pressure behavior. Recently, a new method of analyzing
test data in the form of constant rate drawdown system response has emerged
with development of robust pressure-rate deconvolution algorithm. (von
Schroeter et al. 2001, 2004; Levitan 2005).
Deconvolved drawdown system response is another way of presenting well-test
data. Pressure--rate deconvolution removes the effects of rate variation from
the pressure data measured during a well-test sequence and reveals underlying
characteristic system behavior that is controlled by reservoir and well
properties and is not masked by the specific rate history during the test. In
contrast to a Bourdet derivative plot or to a superposition plot, which display
the pressure behavior for a specific flow period of a test sequence,
deconvolved drawdown response is a representation of transient pressure
behavior for a group of flow periods included in deconvolution. As a result,
deconvolved system response is defined on a longer time interval and reveals
the features of transient behavior that otherwise would not be observed with
conventional analysis approach.
The deconvolution discussed in this paper is based on the algorithm first
described by von Schroeter, Hollaender, and Gringarten (2001, 2004). An
independent evaluation of the von Schroeter et al. algorithm by Levitan (2005)
confirmed that with some enhancements and safeguards it can be used
successfully for analysis of real well-test data. There are several
enhancements that distinguish our form of the deconvolution algorithm. The
original von Schroeter algorithm reconstructs only the logarithm of
log-derivative of the pressure response to constant rate production. Initial
reservoir pressure is supposed to be determined in the deconvolution process
along with the deconvolved drawdown system response. However, inclusion of the
initial pressure in the list of deconvolution parameters often causes the
algorithm to fail. For this reason, the authors do not recommend determination
of initial pressure in the deconvolution process (von Schroeter et al. 2004).
It becomes an input parameter and has to be evaluated through other means. Our
form of deconvolution algorithm reconstructs the pressure response to constant
rate production along with its log-derivative. Depending on the test sequence,
in some cases we can recover the initial reservoir pressure.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
4 June 2004
- Revised manuscript received:
23 August 2005
- Manuscript approved:
28 August 2005
- Version of record:
20 March 2006
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