Numerical and Analytical Well Test Analysis: A Case History

In this paper, we present a case history of integrating numerical and analytical well test analysis methods to interpret the pressure and production history'of a complex, multilayer, multiphase reservoir. Some engineers believe that recent improvements in analytical models have made numerical modeling for well test interpretation all but obsolete. Others believe just as strongly that numerical models should be used for routine well test interpretation. Still others believe that both tools are useful, and that a combination of the two approaches provides the best general strategy for reservoir characterization. This field case focuses on the Gas Research Institute (GRI) Staged Field Experiment (SFE) No. 2. This well was hydraulically fractured. A variety of different analysis techniques were applied in order to evaluate the consistency between reservoir and fracture properties estimated by the different methods of analysis. Analysis methods applied to the flow and buildup tests performed on this well include type curve matching using analytical solutions, numerical modeling with single-phase, multi-layer radial and Cartesian grids, and numerical modeling with multi-phase, multi-layer radial and Cartesian grids. The simpler models were able to match segments of the production and pressure history; only the full multiphase, multilayer model was able to satisfactorily match the complete production and pressure history. We have found that an approach combining analytical and numerical models has been the most successful strategy in our work. As in this field case, analysis begins with the simple models and proceeds through more complex models as necessary to match the reservoir behavior in the desired detail.