Abstract

Since the drilling in January 1987 of the Liuhua 11-1-1A discovery well, six additional wells, four on the primary structure and one each on two satellite structures, have drilled and tested this lower Miocene reservoir carbonate.

Deposition of the carbonates took place in isolated platform environment. Major facies are (1) a platform-rim reef, (2) a backreef platform-rim reef, (2) a backreef lagoon of fine grained carbonates, (3) a large interior platform algal bank, (4) platform coarse grained carbonates, and (5) platform to lagoonal fine-grained carbonates. A paleo-water table surface represents paleo-water table surface represents a time of regional exposure. The reservoir is subdivided into five diagenetic carbonate units. The uppermost unit is a thin, tightly cemented carbonate formed at the time of drowning of the platform. Two thick highly leached carbonate units with porosities and permeabilities as high as 30 percent and several darcies comprise most of the reservoir. They are separated by a tighter interval which formed by cementation below the water table of the exposure surface. The less porous unit at the base of the porous unit at the base of the reservoir formed as a result of interaction between oil and water caused calcite cementation. Leaching continued in the carbonate below the reservoir and biodegradation occurred after oil had filled the structure.

Introduction

Amoco in partnership with Nanhai East Oil Corporation discovered Liuhua Field in January 1987. The field is located offshore China about 220 kilometers (135 miles) southeast of Hong Kong in the Pearl River Mouth Basin of the South China Sea (Figure 1). This field was the first discovery of oil from a large carbonate complex in the basin and is located in Contract Area 29/04 and in water depths over 305 meters (1000 feet).

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