Heavy Oil Development and Reserve Addition Potentials: The Abura-6ST Case

Abstract

This paper evaluates the effect of the increment in recovery factor of the Abura Heavy Oil reservoirs on the heavy oil portfolio of NNPC E&P Limited and, ultimately, the reserve valuation of Nigeria as a country, considering that the Niger Delta basin has a significant amount of heavy oil reservoirs. The Abura field has three (3) heavy oil reservoirs (1AB6, 2AB6 and 3AB6) with viscosity ranging between 10-17cp. These reservoirs were booked as contingent resources owing to sub-optimal production using conventional techniques and sub-commerciality. An FDP study in 2018 revealed that the heavy oil reservoirs could not sustain production and hence, are uneconomically viable to develop. The initial reservoir simulation results showed flow assurance issues mainly due to the high oil viscosity and consequently poor production rate, high water cut, and high-pressure drawdown due to unfavorable mobility ratios and flow assurance challenges caused by the high oil viscosity. Improved Oil Recovery (IOR) techniques were designed to combat the highlighted issues. The combination of IOR techniques employed includes deploying a Single Well Multiple completion which allowed the completion and commingling of 2 reservoirs (1AB6 and 2AB6) in the same tubing for increased oil production, deploying an Electrical Submersible Pump (ESP) to solve vertical lift challenges, installing Autonomous Inflow Control Devices (AICDs) to allow the preferential flow of oil, hydrocarbon fingerprinting for reservoir management and production allocation, and Micro Emulsion Based (MEB) stimulation post-completion, to reduce skin due to formation damage. The results led to a significant increase in the forecasted production and, therefore, an increase in the reservoirs’ Expected Ultimate Recovery (EUR). This led to an eventual improvement of recovery factors for both reservoirs, positive migration of the contingent resources to reserves, increased revenue for the company, and a positive outlook for the numerous heavy oil resources in the company portfolio.