Numerical Welltest Analysis

Abstract

The importance of reservoir and well parameters estimated from BHP analysis, has made it necessary to analyze field pressure data as practically as possible. This has lead to the application of numerical solutions to BHP analysis. It involves the proper griding of reservoir and subsequent numerical solution of the resulting partial differential equation. This incorporates heterogeneity of reservoir properties into BHP analysis, thereby broadening its applicability to reservoir description, unlike analytic solution, which does not offer the details it requires. Although, analytical methods give reasonable estimate for simple cases, they are not suitable for real complex cases, due to the limiting assumptions inherent in their development. This paper assessed the applicability of numerical solution to BHP analyses. It solved some field examples analytically and numerically, first for a known simple case and then for real complex cases. Furthermore, test design data were generated using field data in a heterogeneous system. The test was analyzed using both analytical and numerical approaches. The results obtained show that although analytical solutions can be employed for some heterogeneous systems, they are highly idealistic and limited to some convenient cases and that numerical solution models field data realistically. Introduction Welltest analysis involves the interpretation of bottomhole pressure (BHP) data to estimate well and reservoir parameters like permeability, skin, average pressure, etc. The analysis of BHP has been increasingly vital in reservoir management, due to the importance of reservoir and well parameters it offers. Petroleum engineers have since made extensive use of analytical solutions to BHP analyses. This method presents a wide range of models for analyzing BHP tests in homogenous and heterogeneous reservoirs. Although this method is fast, reliable and applicable to a wide range of models, it is developed based on idealized well and reservoir configurations and as such has a limited scope. It's solution presents accurate analysis for some simple cases and highly approximate analysis in modeling real complex geology. In the bid to integrate reservoir heterogeneities into BHP analyses, it became necessary to model field BHP using numerical approach. The application of numerical Welltest analysis solutions has made it possible to model complex cases of BHP analysis. This is based on finite element modeling which is a method of solving partial differential equations in heterogeneous and complex geometry domains.

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