An integrated geologic and engineering reservoir characterization of the North Robertson (Clear Fork) Unit, Gaines County, Texas

An integrated geological, petrophysical and reservoir engineering study has been performed for a large, mature waterflood project (>250 wells, ∼80% water cut) at the North Robertson (Clear Fork) Unit, Gaines County, Texas, Shallow-shelf carbonate (SSQ reservoirs such as the North Robertson (Clear Fork) Unit (NRU) share a number of common characteristics, including: (1) Such reservoirs have a high degree of areal and vertical heterogeneity, and relatively low porosity (3 to 8 percent) and permeability (0.01 to 1 md). (2) The degree of reservoir compartmentalization is significant and results in poor vertical and lateral continuity of the reservoir flow units and poor sweep efficiency. (3) High permeability intervals and poor vertical continuity within the productive interval result in poor balancing of injection and production rates, and early water breakthrough in the most continuous reservoir intervals. (4) Porosity and water saturation (as determined from analysis of well logs) do not always accurately reflect reservoir quality and performance.; Given these reservoir characteristics, the ability to accurately target infill well opportunities is critical since blanket infill drilling will be uneconomic in most cases. The primary goal of this study is to develop a cost-effective integrated reservoir description for “targeted” (economic) 10-acre infill drilling and future recovery operations in a low permeability carbonate reservoir. Integration of the results from geological and petrophysical studies as well as reservoir performance analyses provide a rapid and effective method for developing a comprehensive reservoir description.; Our hypothesis is that focusing on reservoir surveillance and the optimization of completion and stimulation techniques can optimize future reservoir performance. It is our objective to demonstrate that a comprehensive analysis, interpretation, and prediction of well and field performance can be completed quickly, at a minimal cost, and that these analyses can be used to directly improve our understanding of reservoir structure and performance behavior in complex, low permeability formations.