Waterflood in a Tight, Heterogeneous, Water-Sensitive, and Massively Fractured Reservoir

The T-K Formation is a tight, heterogeneous, and water-sensitive sandstone formation. To enable production, most wells in this reservoir are hydraulically fractured. After a successful massive fracturing campaign, which boosted the production up to 7,500 BOPD, the exploitation led to a dramatic pressure decline. The reservoir pressure had declined from initial value of 1,230 psi down to 450 psi in only six years. A waterflood project was then prepared and implemented in 2009, by converting watered-out producers into injectors, to increase the reservoir pressure as well as to improve recovery factor. Comprehensive studies and thorough surveillance activities were carried out to ensure the success of the project. As results of the on-going operation, the reservoir pressure is increased, enabling more infill drillings and hydraulic fracturing programs to be performed. Field annual decline rate is decreased from 63% to 32%. In addition, some wells that were dead due to insufficient reservoir pressure are brought back to production after the threshold bottomhole pressure is exceeded. To date, recovery factor is 14% and has surpassed the predicted ultimate waterflood recovery factor of 13.4% by the pre-injection simulation study; the pre-injection simulation study indicated a depletion RF of 9%. In terms of cumulative oil production, the waterflood is expected to contribute around 11.4 MMstb of oil. This paper summarizes the journey of T-K waterflood development. This includes pre-injection reservoir characterizations, formation damage mechanism analyses, and practical surveillance activities performed. The workflow and analyses presented in this paper can be used as a benchmark for managing a waterflood project, especially in reservoirs with similar challenges.