Modeling Aquifer Flow Behavior in Low-Dip Edge-Water Drive Gas Reservoirs

Abstract

Water encroachment from aquifers into hydrocarbon reservoirs plays a crucial role in water production and, consequently, in prediction of hydrocarbon field performance. In this regard, several analytical and numerical models have been introduced to calculate water influx. While many studies have been conducted on water influx calculations in hydrocarbon reservoirs, the authors were unable to find any previous study describing aquifer behavior in relation to low-dip reservoirs. In this study, we investigated aquifer behavior in this specific reservoir type from two perspectives: First, water encroachment mechanisms from an aquifer into a low-dip reservoir were assessed, using a numerical gridded approach. Second, we evaluated the validity of analytical and numerical models used in commercial reservoir simulators for low-dip, edge-water drive (LDEWD) reservoirs. We applied the findings of this study to a LDEWD in a heterogeneous carbonate gas reservoir in the Middle East. This was the first study to identify that the major water influx was from the outer corner of the reservoir in the low-dip, edge-water aquifer. We have referred to this phenomenon as outer corner water encroachment (OCWE). We also showed that commonly available analytical and numerical models could not capture either a precise water movement profile or the water influx volume for LDEWD aquifers. The simulation results from prediction models used with actual field data showed that lateral water movement from the outer corner of the reservoir (OCWE movement) was the main contributor to water encroachment and production—and that the vertical water coning phenomenon was not significant in heterogeneous carbonate reservoirs.