Enhanced oil recovery solutions and technologies for final phase of granite basement reservoir of Bach ho field Chapter 1: Granite fractured basement reservoir of Bach Ho field and production performance
Abstract
The granite fractured basement reservoir of Bach Ho field is widely known for its big reserves. After more than 30 years of production, the remaining recoverable reserve of this reservoir mainly exists in: (i) fracture system at the top of the basement, (ii) macro fracture system in the middle of oil column (saturated oil residues), (iii) micro fracture and disconnected fracture system, (iv) the top of the basement which is still unperforated, and (v) the undetermined and unreachable fracture zones.
Secondary recovery with water injection system has been implemented and is still the most effective way to boost production performance, control gas-oil ratio, improve oil recovery and especially maintain the stable oil production rates of the central dome of the basement reservoir. However, water flooding has also been limiting its effectiveness to the areas with high tectonic activities, which reflect in large breccia zones with high connectivity and high permeability. For any low breccia zones with poor connectivity and permeability, water injection rarely shows any effect. Besides, keeping the reservoir above bubble point with water injection is also difficult, especially near the last stage of field life since the injection rate is normally reduced to control water cut.
The major challenges of production management for the basement reservoir of Bach Ho field are: high water cut increment even in the main producers; the current dynamic oil-water contact has been raised to around 100m from the top of reservoir, even 18m at some areas; the current oil recovery factors in the South and North East domes are ultra low, at only 1.9% and 1.3%, respectively; oil production and improved recovery from micro fracture system are still very limited.
Therefore, the study will then concentrate on analysing the fractured basement structural geology, petrographic and rock properties, fluid properties, oil reserves, production performance and recovery mechanism in order to propose technological solutions for enhanced oil recovery of matured basement reservoir of Bach Ho field.
References
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