A Precious Achievements Review of Geological Development and IOR Application from 20 Successful Years in High Temperature Fractured Granite Reservoir
Authors: Dang Cuong Thanh Quy , Nguyen Ngoc Thi Bich , Bae Wisup , Jung Byounghi , Lee Jeonghwan 
Published: March 2015

Natural fractured petroleum reservoirs represent over 20% of the world's oil and gas reserves. It plays an obvious role in oil exploration and makes a large contribution toward oil and gas production worldwide. The research tendency for natural fractured reservoir NFR has become more apparent in the last five to ten years because more fractured reservoirs are being developed as production from conventional reservoirs is declining. However, characterization of fractured reservoir is complex and presents unique challenges in comparison with conventional reservoir. There are several uncertainties in NFR characterization in exploration and field development strategies, especially in the early stages when little or even no data is available. Thus, it is urgent and necessary to collect the experiences from previous successful research to reduce risky level in such reservoir.

White Tiger is the biggest fractured basement reservoir up to now on the continental shelf of Viet Nam This reservoir has a complicated geological structure, very high heterogeneity, high temperature (more than 2750F) and closure stress (more than 8,000 psi); the collector model is quite different from that of conventional oil reservoirs in sediments rocks. The total OIIP of this field reached nearly 4 billions barells with 2000 meters of the oil bearing thickness and has been produced by more than 100 wells, tens of which flow at the rate of approximately one thousand barrels per day. Thus White Tiger has become one of the rarest oil fields worldwide. A huge volume of science researches has been done with great success. Many specify software, and calculation models, simulation geophysics and seismic interpretation have been successfully studied and applied to the basement reservoir. Based on experiences from White Tiger, a significant number of other oil fields in the fractured basement were discovered such as Rang Dong, Phuong Dong, Ruby, series of Black Lion, Yellow Lion, Brown Lion, Yellow Tuna, Southern Dragon and Turtle. The discovery of the oil reservoir in White Tiger fractured basement has changed the concept of oil and gas prospecting, exploration and development in Viet Nam and the region, being a considerable contribution to the world's oil and gas science.

This paper reviews significant events in geological development and achievements in improved oil recovery by special methods for fractured granite basement reservoirs such as slant directional drilling, acid formation treatment, hydraulic fracturing of formation, polymer and surfactant flooding etc. With rich experience in exploration and production of hydrocarbon in fractured granite basement rocks over the past 20 years, it is worthy case study for both current and future development planning of NFR in the world.

Introduction

The continental shelf of Viet Nam was undergone many deformation stages. Since then, some basins were formed in which oil was accumulated in both sedimentary and granite basement rock reservoirs. Figure 1 shows the distribution of basins in the Viet Nam continental shelf and field location of Cuu Long basin. Authors mainly study a basement rock reservoir in Cuu Long basin, especially White Tiger and Dragon oil field which was produced with the huge oil amount.