Reservoir Pressure Management Using Waterflooding: A Case Study

Abstract

Abstract As a rule, the reservoir pressure depletion occurs with a continuous production over a period of time. This leads to high Gas-Oil Ratio and low production rates. Thus it is important to manage the pressure of reservoir and stabilize it. For this, certain IOR techniques are employed; waterflooding being one of them. This paper discusses waterflooding as a solution for a pressure management program. This work represents results of the strategic IOR program in a mature field showing importance and influence of each decision made during project implementations. The reservoir into consideration is a sandstone reservoir which was producing under a solution gas drive & a very weak aquifer for about 5 years. During the course of production, reservoir pressure decreased substantially and went below the bubble point pressure. Waterflooding was considered as the most suitable remedy to restore the reservoir pressure and well productivity, considering all the parameters. Various waterflooding plans were designed on the basis of areal & vertical sweep efficiencies and reservoir voidage compensation using material balance. The fractional flow, saturation profiles, mobility ratio and frontal advance equations were kept in mind while proposing these plans. By implementation of the most appropriate plan, the reservoir pressure was maintained 150 psi above the bubble point pressure resulting in daily production rate of about 13000 bopd with water injection rate of about 15000 bpd. The estimated oil recovery is about 52 % and breakthrough is expected to occur about 7 years after the start of waterflood. The results were not only a total reversion but also an increasing production profile that was declining over the years. Introduction This paper discusses about a case study based on the real field data, but the names of the field, different blocks in the field and wells have been changed, due to the restrictions. The Leon field is located in deltaic region of the river Azlean. It is an offshore field with water depth ranging from 20–40 m. This field was discovered in 1985 and put on production in 1993. The field is sub-divided in four blocks namely LA, LB, LC and LD. Blocks LA and LB produce high quality crude oil and they contribute about 73% of total oil production from the field. LD block is mainly a gas producer. The gravity of oil in LA and LB blocks is 35.3 and 37.2 deg API respectively with the solution GOR being 80 sm3/sm3 and 88 sm3/sm3 respectively. The oil and water viscosities are around 0.57 and 0.25 cp at reservoir conditions.