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Fractured Basement Reservoirs and Oil Displacement Mechanism in White Tiger Field, Offshore Vietnam

Nguyen, Huy X.¹; Wisup, Bae¹; Tran Van, Xuan²
¹Energy and Mineral Resources Engineering, Sejong University, Seoul, Korea, Republic of.
²Petroleum Geology Engineering, Ho Chi Minh City University of Technology, Ho Chi Minh City, Viet Nam.
³Petro Vietnam, Ho Chi Minh City, Viet Nam.

Over 85% OOIP of oil fields are producing in fractured basement reservoirs. However, the formation mechanism of petroleum deposits caused still questionable with the different evidences in outlining the basin history and tectonic development of Cuu Long basin.

Fractured basement reservoirs as high heterogeneity and complex geological characteristics always face a major challenges and high risk in exploration and production phases. These reservoirs were discovered twenty three years ago. High water cut presented in reservoirs because unable to control the amount of water injection during a long time and complicated hydrodynamic mechanism. There is an urgent need to study procedures for an increased and maximum oil recovery. A clear geological understanding of the relationship between faults, fractures and micro-fractures have changed our view of reservoirs connection and hydrodynamic distribution to determine the optimal recovery method for this oil reservoir.

The porosity and permeability distributions are irregular with depth, laterally anisotropic in fractured basement reservoirs. The production rate recovered a good flow in deeper and the differences from wells to wells in structure. The dynamic oil/water contact could not be maintained at the same depth. In particular, the flow behaviors of dual porosity, permeability, and the inter-porosity have significant impacted oil recovery associated macrofractures of hydrodynamic permeability and microfractures of permeability capillary. When the reservoir pressure is higher than bubble point pressure, macrofractures play important role as channels of oil flow. When the reservoir pressure is decreasing continuously to the saturation pressure, oil is accumulated in microfractured matrix as storage to supply to the macrofractures network.

The results presented the brecciated zones and associated fractures recognized with high oil rate, hence, the need to operate appropriately for maintaining reservoir pressure and improving hydrocarbon recovery in fractured basement reservoir. In addition, an understanding of faults and big fractures can help on prediction of hydrodynamic paths from injection wells to production wells and reasonable planning for waterflooding .

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012