Abstract
Gas injection has been widely used for Improved Oil Recovery (IOR)/ Enhanced Oil Recovery (EOR) processes in oil reservoirs. Unlike the conventional gas injection (CGI) modes of CGI and Water Alternating Gas (WAG), the Gas-Assisted Gravity Drainage (GAGD) process takes advantage of the natural segregation of reservoir fluids to provide gravity stable oil displacement. It has been proved that GAGD Process results in better sweep efficiency and higher microscopic displacement to recover the bypassed oil from un-swept regions in the reservoir. Therefore, dry gas has been considered for injection in fractured basement reservoir, Bao Den (BD) oil field located in Cuu Long basin through the GAGD process application. This field, with a 5-year production history, has nine production wells and is surrounded by a strong active edge aquifer from the North-West and the South East flanks. The depth of basement granite top is about 2,800 mTVDss with a vertical oil column of 1,500m. The pilot GAGD project has been designed to test an isolated domain in the BD fractured basement reservoir where there is favorable reservoir conditions to implement GAGD. Both reservoir simulation and Lab test have been run and confirmed the feasibility and the benefit of GAGD project in the selected area.The Dry gas will be periodically injected through existing wellwith high water cut production that located in the isolated area. As the injected gas rises to the top to form a gas zone pushing GOC (gas oil contact) downward, and may push WOC (water oil contact) to lower part of this producer (or even away from bottom of the well bore) could lower down water cut when switch this well back to production mode. The matched reservoir model with reservoir and fluid properties have been used to implement sensitivity analysis, the result indicated that there is significantly oil incremental and water cut reduction by GAGDapplication. Many different scenarios have run to find the optimal reservoir performance through GAGD process. Among these runs, the optimal scenario, which has distinct target, requires high levels of gas injection rate to attain the maximum cumulative oil production.
Highlights
The Bao Den field is located in the Cuu Long Basin offshore southern Vietnam, 120 miles (180 kilometers) southeast of Ho Chi Minh City
A typical phenomenon of water development in fractured basement is that once water appears, water cut will increase quickly and natural flow ceased after several weeks
This paper proposes the implementation of an Improved Oil Recovery (IOR) technique known as Gas-Assisted Gravity Drainage (GAGD) in fractured basement reservoir (FBR), BD oil field with the ability to accelerate field production and increase oil recovery
Summary
The Bao Den field is located in the Cuu Long Basin offshore southern Vietnam, 120 miles (180 kilometers) southeast of Ho Chi Minh City. The reservoir pressure is 4,400 psia at 2,800 mTVDss, reservoir temperature is 270 oF (130oC) and very low hydrogen Sulphide content in associated gas The production from this reservoir started in 2010 and all wells flowed under natural depletion.water breakthrough happened very soon just after one year of production. With increasing water cuts and depleting reservoir energy, currently the lift gas capacity is insufficient to optimized field production. This paper proposes the implementation of an IOR technique known as Gas-Assisted Gravity Drainage (GAGD) in fractured basement reservoir (FBR), BD oil field with the ability to accelerate field production and increase oil recovery. Gas-Assisted Gravity Drainage (GAGD) is a simple IOR/EOR technique in which a gas is injected into the reservoir and the in-situ oil swells until it is fully saturated, until a separate gas-cap is created. The periods of gas dissolution / migration will vary according to the vertical connectivity within the fracture system
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