Exploration History of the Liuhua 11-I-1A Discovery, Pearl River Mouth Basin, China
Authors: Christian H.E. , Tyrrell W.W. 
Published: October 2008

ABSTRACT
Stratigraphic analysis of sparse seismic data in 1981 indicated the presence of a lower Miocene carbonate bank complex over the western part of the Dongsha Massif, 220 kilometers southeast of Hong Kong. A large carbonate bank closure was mapped in deep water 38 kilometers south of the most probable Paleogene source basin. The stratigraphic study also predicted the presence of a widespread, thick, basal sandstone below the carbonate complex that could serve as a conduit for long distance migration of hydrocarbons into the closure. After drilling by other companies demonstrated that oil had migrated well out of the source basin (Huizhou Sag), Amoco negotiated for Contract Area 29/04. The first well, Liuhua ll-1-1A, tested 2,240 BOPD of 21 degree API oil from a 75 meter pay section in a highly porous and permeable carbonate bank sequence topped at 1197.5 meters. A 400 meter lower carbonate section and a 150 meter sandstone sequence resting on basement were water bearing. Additional drilling has confirmed a giant in place oil accumulation, but commerciality is yet to be determined.

INTRODUCTION
In January 1987, Amoco Orient Petroleum Company tested 2,240 BOPD in its first China well 220 kilometers offshore in the Pearl River Mouth Basin. The location of Contract Area 29/04 and the discovery well for a giant in place oil accumulation are shown on Figures 1 and 2. Although smaller accumulations in the basin had tested higher flow rates nearer shore, Amoco's Liuhua (LH) l1-1-1A was the first discovery from a large carbonate complex. Discoveries and relative field sizes in the eastern part of the basin are shown on Figure 2. The ACT Group has begun development of its Huizhou (HZ) 21-1 and 26-1 oil fields, and JHN will develop its Lufeng (LF) 13-1 field. Development of the other discoveries is under consideration. Our paper will concentrate on the exploration history of the Liuhua 11-1 field and the discovery well. It provides a good example of the "ups and downs" of exploration in a frontier basin. A recent paper by R. N. Erlich, S. E. Barrett and B. J. Guo (1990) discusses the drowning of the Liuhua carbonate bank and a presentation by N. L. Turner (1990) dealt more specifically with the carbonate reservoir geology. These papers are also included in this volume. R. S. Paces (1990) discussed an extended well testing program including horizontal drilling in the field.

EXPLORATION HISTORY, BLOCK 29/04

Preparation for 1982 First Round Bids
In 1979-80 approximately 40 companies participated in joint geophysical surveys in the Pearl River Mouth Basin area outlined on Figure 3. Another survey area covered portions of the Beibu Wan and Yinggehai Basins west of Hainan Island. The People's Republic of China had drilled Zhu wells 1-7 offshore Guangzhou (Canton) and Hong Kong within the Pearl River Mouth Basin survey area. They had also drilled several wells north and south of Hainan Island and a Xisha Islands shallow test. Conoco-Amoco and others had drilled" several wells east of the survey area in Taiwanese waters. All of these other wells were 400 to 600 kilometers from the Zhu wells. Zhu 5 and Zhu 7 tested waxy oil from upper Oligocene-lower Miocene sandstone reservoirs.