Improving dual-porosity simulation of waterflood performance in the naturally fractured Spraberry Trend area

Abstract

In this thesis we have discussed the methods of analyzing the waterflood performance of the O'Daniel waterflood pilot in the Spraberry Trend Area with the help of reservoir simulation. Spraberry Trend Area is considered to be one of the richest oil fields in the world. However, out of 6-10 billion bbls of original oil only 700 million bbls have been produced. In an effort to increase recovery, several waterflood pilots were conducted in Spraberry beginning in the late 1950's. Because of profoundly complicated nature of the reservoir, waterflooding has been only moderately successful, and billions of barrels of hydrocarbons remain unrecovered. A recent waterflood pilot study started in 1995 with dramatically different results. The pilot was conducted in the O'Daniel unit of the Spraberry. The recovery in this lease has exceeded 25% of the original oil in place, compared to only 10% recovery in the entire Spraberry. Data from the current waterflood clearly shows that on-trend wells which are outside the pilot and along the major fracture trend responded favorably. In the previous waterflood pilots in Spraberry, the producer located off-trend from the water injectors received all the attention and the response in the on-trend wells was overlooked. In this study, we have developed a waterflood pattern for Spraberry where the target wells for waterflood response will be the on-trend producers. A successful waterflood depends on properly positioning the injectors and producers. In fractured reservoirs, fracture location, orientation and permeability dictates the placing of injection and production wells. So, to understand the fracture distribution, the main intention behind this thesis is to develop a method to determine location, orientation and permeability of fractures in Spraberry by using reservoir simulation. We performed three simulation studies: Humble pilot waterflood, O'Daniel tracer analysis and O'Daniel pilot waterflood. The first two simulation studies were performed with simple two-well models. The fracture orientation and permeability ratio obtained in these models were applied to the full field O'Daniel pilot that consists of 59 wells in about 8500-acre area. Our simulation model shows that a concept of fracture enhancement (grid-blocks with high fracture permeability) in the dual-porosity model is necessary to capture the effect of heterogeneity of fracture network. The major fracture orientation obtained from the simulation is very close to the one obtained from the interference test and horizontal core analysis. The results of this study could be used in determining an optimum waterflood pattern suitable for that area to forecast oil production with different scenarios such as, infill drilling, CO2 injection, horizontal wells etc. Finally, the results of this work will provide a method to assess the economic feasibility of large-scale water injection in the remainder of the field.