关键词: 复杂断块, 低渗储层, 成藏条件, 勘探开发关键技术, 乌石油田, 北部湾盆地

Abstract: Wushi oilfield is a Cenozoic complex fault block oilfield developed in the eastern part of Wushi sag in Beibuwan Basin. It is also the third largest oil production base in the western part of the South China Sea, with the total proven reserves of 100 million tons and daily production of more than 1 000 m³. By reviewing the exploration and development history of Wushi oilfield, this paper systematically summarizes the geological conditions and characteristics for hydrocarbon accumulation, and key exploration and development technologies of the oilfield. On this basis, the following achievements and understandings are obtained. (1)The organic-rich lacustrine shale and oil shale of Liushagang Formation, which are widely distributed in the eastern part of Wushi sag, have laid a good material foundation for the formation of oil field. (2)Owing to the multi-source, multi-period and multi-stage tectonic-sedimentary evolution, many sets of favorable reservoir-cap assemblages are formed in the sag. (3)Several sets of regional stable mudstone caprocks were developed in the whole area during the lacustrine transgression period, providing favorable conditions for oil and gas preservation. (4)Multi-level oil source faults, sand body, structural ridges and unconformity surface constitute favorable hydrocarbon migration pathways. (5)Based on the dynamic and static accumulation factors, three typical hydrocarbon accumultion patterns are clarified in Wushi oilfield, including the lateral step-type in slope zone, three-dimensional composite type in uplift zone of the sag, and pumping type with fault-sand coupling in steep slope zone. (6)A series of supporting technologies with a focus on the high-resolution seismic data acquisition and processing technology, fine interpretation and evaluation technology for complex fault blocks, fine carving technology for large-scale reservoirs, and water flooding compatibility evaluation technology for offshore waterflooding oil fields have been established, which provide a technical guarantee for efficient exploration and production as well as capacity construction in Wushi oilfield. The research results are expected to provide some guidance and reference for the exploration and development of similar reservoirs in other basins at home and abroad.

Key words: complex fault block, low permeability reservoir, accumulation condition, key exploration and development technology, Wushi oilfield, Beibuwan Basin