Laplace-Transform Finite-Difference and Quasistationary Solution Method for Water-Injection/Falloff Tests

Authors
Azeb D. Habte (Universiti Teknologi PETRONAS) | Mustafa Onur (Istanbul Technical University)
DOI
http://dx.doi.org/10.2118/168221-PA
Document ID
SPE-168221-PA
Publisher
Society of Petroleum Engineers
Source
SPE Journal
Volume
19
Issue
03
Publication Date
June 2014
Document Type
Journal Paper
Pages
398 - 409
Language
English
ISSN
1086-055X
Copyright
2013.Society of Petroleum Engineers
Disciplines
6.6 Reservoir Monitoring/Formation Evaluation, 6.6.3 Pressure Transient Testing, 6 Reservoir Description and Dynamics
Keywords
Variable-rate test, Laplace transform finite difference method, Wellbore storage, Injection/Falloff tests, Skin
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Summary

In this work, we present a method for efficiently and accurately simulating the pressure-transient behavior of oil/water flow associated with water-injection/falloff tests. The method uses the Laplace-transform finite-difference (LTFD) method coupled with the well-known Buckley-Leverett frontal-advance formula to solve the radial diffusivity equation describing slightly compressible oil/water two-phase flow. The method is semianalytical in time, and as a result, the issue of time discretization in the finite-difference approximation method is eliminated. Thus, stability and convergence problems caused by time discretization are avoided. Two approaches are presented and compared in terms of accuracy for simulating the tests with multiple-rate injection and falloff periods: One is based on solving the initial-boundary-value (IVB) problem with the initial condition attained from the end of the previous flow period, and the other is based on the conventional superposition on the basis of the single-phase flow of a slightly compressible fluid. The former is shown to always provide a more accurate and efficient solution. The method is quite general in that it allows one to incorporate the effect of wellbore storage and thick-skin and finite outer-boundary conditions. The accuracy of the method was evaluated by considering various synthetic test cases with favorable and unfavorable mobility ratios and by comparing the pressure and pressure-derivative signatures with a commercial black-oil simulator, and an excellent agreement was seen.

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