Breaking Oil Recovery Limit in Malaysian Thin Oil Rim Reservoirs: Force Balance Revisited

Abstract

The goal of an oil field development project is to accelerate the hydrocarbon production and optimize the recovery at the lowest cost. For a thin oil rim reservoir with a large gas cap on top and a strong aquifer below, achieving such goal can be very challenging since recovery of both oil and gas needs to be optimized. A successful project may entail plan first to accelerate the oil production with re-injection of the produced gas at the gas cap, maximizing the oil recovery prior to the start-up of the gas cap blow-down (Ref. 1-2).The maximum oil recovery factor achievable in thin oil rim reservoirs was evaluated for a Malaysian thin oil rim reservoir based on dynamic flow properties. The force balance between the gas cap expansion, aquifer expansion and viscous withdrawal (volumetric fluid production) was demonstrated by showing the model simulated water-oil and gas-oil contact movement. The understanding of the force balance progressively guided the field development project team to selectively re-activate some of the idle wells, to selectively place new additional infill horizontal wells, and to plan selective water and gas injection in key reservoir sectors.In this paper, the impact of changing force balance on oil recovery by increasing viscous withdrawal with increasing idle well re-activation and infill horizontal well drilling at their respective optimum produced gas re-injection was reported. This effort showed a potential of improving the current recovery factor from 35% up to 48%, at and above the estimated theoretical maximum oil recovery efficiency.

Risk of Losing Oil Reserve by Gas-Cap Gas Production in Malaysian Thin Oil Rim Reservoirs

“…For the subject reservoir, it had been studied and discussed (Ref. 3). It was concluded that the art of maximizing oil recovery of a thin oil rim reservoir is to keep oil rim in contact with producing wells at all time and that this could be achieved by balancing the WOC and GOC movement by controlling produced gas injection in the gas cap.…”

“…During this oil rim oil production period, the Gas Injection/Gas Production ratio (GIGP) has to be kept at high values although it depends on aquifer strength and fluid production (viscous withdraw) volume and rate (Ref. 3). …”

Integrated reservoir management in a Niger Delta oil rim field

“…In a study on production optimization, Hasan et al (2009) indicated a significant increase in oil recovery factors in an oil rim reservoir when a binary integer programming, a production optimization technique was used to determine the choke and rate settings in production and injection wells. Razak et al (2010) reported improved oil recovery factors (by 35-48%, which is higher than the theoretical recovery efficiency) in their work by understanding water and gas coning tendencies in thin oil rim reservoirs. They highlighted the impact of force balance changes (coning tendency) by increasing the viscous withdrawal with the use of horizontal wells, coupled with gas re-injection to obtain higher recovery efficiency.…”

Research on rational development mode of gas cap marginal water reservoir

“…When using ordinary directional wells for development, the energy in the gas area and the marginal water area is bigger than the energy in the oil ring. During the exploitation process, the top natural gas and the marginal water are driven by the formation pressure difference [2]. These development characteristics lead to the characteristics of rapid growth in the early development phase and a short water-free recovery period for gas caps and marginal water reservoirs.…”