Water Injection in Brown Field:Never Too Late

摘要

It has been observed that in many brownfields across the world having 25-30 years of production history,water injection projects were not undertaken to maintain pressure in earlier stage of the fields`life while the average reservoir pressure depleted well below the bubble point pressure.Is it too late to initiate water injection?Is it techno-economically justifiable? This paper attempts to explore these questions. 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 of the reservoir might help gain significant incremental oil production.To restore the reservoir pressure back to the original bubble-point pressure might be unnecessary and uneconomical.However,it might be sufficient to pressure up the reservoir to critical gas saturation pressure,enough to arrest the excessive gas production helping more oil to produce. In our case studies,we studied one of the stacked reservoirs of a large(8km x 12 km)oil field in offshore Peninsular Malaysia,at a water depth of about 70 meters.This maturing offshore reservoir with 25 year of production history consists of multiple interdependent closures with relatively thin oil columns and large gas caps with roughly 1.8 BSTB STOIIP.The reservoir communicates with nine neighboring producing fields via a common regional aquifer encompassing an area of more than 7000 square kilometers. As of Q2 2013,the field produced 29%of STOIIP.Gas injection was initiated in some parts of the field.However,no water injection scheme implemented.Simulation studies estimated that no further activity scenario would yield only an additional 1%recovery by year 2021(i.e.EUR 30%).However,initiating selective water injection even at such a late stage can significantly boost the oil recovery by about 5%,making it a viable commercial proposition.