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The Keys to New Sub-Igneous Oilfield Discovery in Offshore Bohai Bay Basin, China


The oil and gas exploration to sub-igneous structure in offshore Bohai Bay basin began in the 1970s, a series of oil and gas bearing structures have been found in forty years, but no commercial sub-igneous reservoir has been discovered until 2015. In recent years, commercial sub-igneous reservoir was firstly discovered in the southern slope of Huanghekou sag, with the reserves of 80 million cubic meters. The key factors to the breakthrough discovery of gas mainly rest with the following aspects: (1)The background of uplift was formed under the action of magmatic diapir and strike slip extrusion in the slope, which is a favorable direction of hydrocarbon migration and accumulation. (2)As the activities of magmatism in the late Oligocene, a large scale of basalt and tuff distributed widely, which is a good regional capping layer of oil and gas. (3)The volcanic channel facies developed in fissure eruption mode is a good lateral sealing layer of oil and gas, which is extremely favorable to form a high hydrocarbon abundance zone. (4)Early magmatic activity formed an alkaline water environment, which was favorable to preserve primary pores, while late hydrocarbon generation and expulsion of organic acid fluid formed an acidic water environment, which was favorable to the development of the secondary pores. The igneous rock developed widely in Bohai Bay basin, with the distribution area of more than 60%, which is good for looking for sub- igneous reservoirs. Therefore, the breakthrough discovery of commercial sub-igneous oil and gas provides a great reference to oil and gas exploration.