The Lower Miocene Liuhua Carbonate Reservoir, Pearl River Mouth Basin, Offshore People's Republic of China: ABSTRACT

Abstract

Since the drilling in January 1987 of the Amoco Liuhua 11-1-1A discovery well located 220 km southeast of Hong Kong, five additional wells have drilled and tested this lower Miocene Zhujiang Formation carbonate reservoir. Deposition of upper Zhujiang carbonates in the Liuhua area took place in an isolated platform environment. Major facies are (1) a platform-rim reef composed of red algae and coral boundstones, (2) a back-reef lagoon of fine-grained carbonates, (3) a large interior platform bank dominated by red algae but with a red algal-coral fringe on the south and southwest sides, (4) platform grainrocks, and (5) platform to lagoonal mud-supported carbonates. A paleo-water table surface present in every well represents a time of regional exposure. The reservoir is subdivided into five diagenetic carbonate units that are correlated across the platform and that cross facies boundaries and inferred time lines. 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% and several darcys comprise most of the reservoir. They are separated by a thin (7 m) tighter interval that formed by cementation below the water table ofmore » an exposure surface. The less porous unit at the base of the reservoir formed as a result of interaction between oil and water causing calcite cementation. Leaching continued in the carbonate below the reservoir and biodegradation occurred after oil had filled the structure. Further drilling and testing will determine the limits of the diagenetic units and whether the reservoir has commercial potential.« less