Development of the optimized waterflooding pattern for the naturally fractured Spraberry Trend area

Abstract

The Spraberry Trend area has produced oil since 1949 with a history of low productivity and unresponsive waterflooding within areas of interest in the field. It has been shown over the years that the conventional line drive waterflooding approach is highly ineffective in this field and there is a need to develop unique ways in which the reservoir can be waterflooded and produced. The reservoir model used for this study was developed in two distinct steps to speed up the development and ascertain the accuracy of the model. The preliminary model introduced only a single water injector while the final model included all the injectors around the area of interest. In developing the model, we found that the conventional simulation grid orientation which is normally employed in dynamic model building could not be applied to the Spraberry. Rather, fracture enhancements were introduced into the model to represent and model the complex fracture network. This proved valuable in validating the final reservoir model which was used for the various studies in this research. This thesis examined the influence of the distance and orientation of producers to injectors, water injection rate, fracture spacing and reservoir wettability in the effectiveness of waterflooding in the Spraberry with the hope that the distance and orientation of producers to injectors as well as the water injection rate can be optimized and implemented in the field. Furthermore it is hoped that this research will throw more light on how fracture spacing and matrix wettability affect the response of producers to water injectors. Reservoir simulation work contained in this thesis was performed on an 800 acre area of the O'Daniel pilot. Some of the results obtained validated earlier studies while other results provided new insights into the behavior of waterflooding in this reservoir. By systematically using the developed simulation model to confirm the production pattern observed in the field, the results obtained show that attention has to be paid to the orientation of the production wells relative to the water injectors and the dominant fractures. The effects of the fracture orientation and fracture spacing at various distances from the water injector were also investigated and it was concluded that if the producer is close to the water injector, the fracture orientation will dominate fluid movement while the farther the injector and producers are placed apart, the greater the influence of the fracture spacing on the fluid movement. Investigating the wettability, we found that with a high water matrix wettability, it was possible to optimize the injection rate. At low wettability however, we found that it is not possible to optimize the injection rate since the water injection rate has a somewhat inverse relationship with oil production. Finally, the result obtained by this research shows that fracture spacing of 10ft could be considered as the critical spacing, above which there is an insignificant effect of fracture spacing on the performance of the waterflooding in the Spraberry.