The Impacts on Waterflood Management of Inducing Fractures in Injection Wells in the Prudhoe Bay Oil Field

Abstract

ABSTRACT The induced fracturing of water injection wells in the Prudhoe Bay Oil Field has been of concern since original waterflood pilot tests were conducted in 1978. Early step-rate tests showed that, as a result of the injection of cold (80°F) seawater into the 200°F Ivishak reservoir, the formation fracture gradient was significantly reduced. Interest peaked with the need to develop a water-flood management strategy soon after waterflooding commenced in the second half of 1984. In order to address the fracturing question, in-depth studies of field injection trends, innovative pressure transient analyses of step-rate data, interpretation of specially designed injection well tests, and several simulation studies were conducted. The results from these independent approaches provided definitive and confirming evidence on the extent of fracturing; this was a crucial prerequisite to the definition of a long-term injection strategy. Subsequently, the impact of formation breakdown on areal and vertical sweep and on oil production rates was evaluated, and it has been concluded that potential negative effects of inducing fractures with clean water injection into the Ivishak formation are minimal, while benefits include accelerated oil production. As a result, an injection pressure limit above the thermally reduced formation fracture gradient has been defined and adopted.