In order to evaluate the effectiveness of a hydraulic fracture treatment, one must be able to correctly analyze post-fracture production and pressure buildup data. In many cases, conventional analysis techniques or simple single-phase, two-dimensional models are all that is required to obtain satisfactory results. However, in complex reservoir systems, such simplified techniques may provide incorrect solutions. As part of a research program sponsored by the Gas Research Institute (GRI) a substantial engineering effort is being exerted towards better understanding of complex reservoir systems. The thrust of this work has been in the Travis Peak formation of east Texas which is a multi-layered reservoir that normally produces both gas and water. To properly analyze this formation, a three-dimensional and/or two-phase reservoir simulator is needed.

This paper presents a thorough discussion of the problems associated with the analysis of complex reservoirs and illustrates these problems with numerous field examples. Examples are included in which short, high conductivity fractures are calculated when conventional analysis techniques are used. However, a longer, more realistic estimate of fracture length is computed when one uses a multi-phase, multi-dimensional reservoir model to accurately history match the gas and water flow rates as well as the wellbore pressures.

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