Hydrodynamic Analysis on the Depletion and Recovery Behavior of a Geopressured Aquifer

Using established petroleum reservoir engineering techniques as applied to a geopressured system, this paper presents results from analysis on the Gladys McCall geopressured aquifer, located in Cameron Parish, Louisiana, U.S.A. Analysis of the flow data has led to the assessment of important formation parameters, evaluation of aquifer drive mechanism, and development of conceptual aquifer model that accounts for pressure behavior observed during both depletion and recovery phases. This paper contains results from studies conducted in two parts. First purpose of this study is to summarize and analyze results of the eight transient tests. This analysis provided data needed for a quantitative description on the characteristics of the aquifer, including: a) connected pore volume, b) formation transmissivity and skin, c) the size and possible shape of the main producing aquifer, and d) characteristics of the pressure support mechanism. The second part is an evaluation of the aquifer drive mechanism using long-term pressure data. Based on results obtained from the pressure transient analysis and material balance calculations, a fault-controlled influx model has been proposed. The model was derived from a conceptual model of water leakage through a partially sealing fault into the aquifer under steady-state conditions. In addition, the stress-induced hysteresis in the formation rock was highlighted by the differences between aquifer unloading (depletion) and loading (recovery) fault conductivities. An influx calculations based on the model provides an excellent match to the detailed downhole pressure buildup measurement made during aquifer tests.