Success Story of a Waterflood Project in a Geologically Complex, High-Viscosity Oil Reservoir in a Major Brownfield in South Oman

Abstract

Summary This paper presents the success story of waterflooding in a geologically complex reservoir that contains high-viscosity (90 cp) oil. This reservoir is part of a large brownfield in south Oman and has been on production for more than 25 years. The reservoir comprises glacial sandstones of Palaeozoic age and is highly heterogeneous, with wide variation in reservoir characteristics at scales smaller than well spacing. The reservoir geology is complicated because of the presence of faults and fractures. The reservoir has been subdivided into different areas that we call "catchments," characterized by their geological setting and dynamic reservoir behavior. Full-field water injection was started in the field after approximately 18 years of primary depletion. Different water-injection philosophies for different areas of the field have been adopted with consideration to factors such as primary drive mechanism operative in the reservoir, presence or absence of vertical-flow barriers; pre-existing field-development pattern; and more importantly, future development beyond waterflood to maximize the value of the reservoir in its entire life cycle. The paper illustrates that the success of a waterflood in a complex reservoir relies on the implementation of a tailor-made development plan with flexibility to be changed on the basis of data from reservoir surveillance. The importance of well and reservoir management (WRM) to improve the value of waterflood is emphasized.