The challenge of model identification in well test interpretation - A unique build up analysis case study

Reservoir engineers are frequently faced with a very difficult question, thought to be a simple one, when attempting to analyze pressure transient test data. Correct model identification that can be used to analyze test data is ought to be a very simple exercise due to numerous analytical models, which are published in the literature. However, dealing with almost a black box situation "Underground Reservoir," it is still difficult today to identify a reservoir model that represents a particular test. In fact, the pressure derivative technique in identifying flow regimes that pressure behavior undergoes during the well testing has introduced another dimension and is considered to be an important step in analyzing pressure transient tests. However, the non-uniqueness in model responses, which produces similar pressure derivatives, hinders the engineers, and most often causes in taking a wrong decision. This study looks into non-unique model response, introduces a simplistic method using numerical simulator and any reservoir information available in eliminating non-realistic solutions. Analysis of actual well test data, to obtain the very basic properties, and integrating any other available data, one can build different model realizations. An actual model was build by history matching the pressure derivative that helped reducing the problem of non-uniqueness response.