Water Injection in Brown Field: Never Too Late

It has been observed that in many brownfields across the world having 25-30 years of production history, waterinjection projects were not undertaken to maintain pressure in earlier stage ofthe fields' life while the average reservoir pressure depleted well below thebubble point pressure. Is it too late to initiate water injection? Is ittechno-economically justifiable? This paper attempts to explore thesequestions. It may be uneconomical and ineffective to carry out full field water flooding project in a marginal brown field. However, selective water injection to boost up pressure in carefully selected pockets ofthe reservoir might help gain significant incremental oil production. Torestore the reservoir pressure back to the original bubble-point pressure might be unnecessary anduneconomical. However, it might be sufficient to pressure up the reservoir tocritical gas saturation pressure, enough to arrest the excessive gas productionhelping more oil to produce. In our case studies, we studied the J-sandreservoir of the Seligi Field, the largest oilfield in Peninsular Malaysia, located approximately 280 kilometers off the eastcoast of Peninsular Malaysia, at a water depth of about 70 meters (230 feet). In this large (8km × 12 km) maturing offshore reservoir (30 year of production history)comprising multiple interdependent closures with relatively thin oil columnsand large gas caps, contains roughly 1.823 BSTB STOIIP. The reservoircommunicates with nine neighboring producing fields via a common regional aquiferencompassing an area of more than 7000 square kilometers. As of Q4 2011, the field produced 532 MSTBor yielded a recovery of 29%. Gas injection was initiatedin some parts of thefield. However, water injection has not been commenced. Simulation studiesestimated that no further activity scenario would yield only an additional 18MSTB (~ 1% Recovery) by year 2021. However, initiating selective waterinjection even at such a late stage can significantly boost the oil recovery byabout 5%, making it a viable commercial proposition.