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The Keys to New Gas Discovery of Deeply Buried Hill in Depression in Offshore Bohai Bay Basin,China

Zhang, Rucai *1; Peng, Wenxu 1; Xinhuai, Zhou 1; Wang, Baoquan 1
(1) Exploration & Production Research Institute, CNOOC LTD.-TianJin Bohai Oilfield, TianJin, China.

The oil and gas exploration to buried hill in offshore Bohai Bay basin began in the late 1970s, a series of buried hill reservoirs such as Bozhong 28-1, Jinzhou 25-1 / South, Penglai 9-1 have been found, these reservoirs mainly distributed in uplifts and around depression. However, oil and gas haven’t been discovered in deeply buried hills in depression before 2011. Recently, the gas got industry production rate in Bozhong 21-1 structure of deeply buried hills, the proved OGIP exceed 10 billion cubic meters. The key factors to the breakthrough discovery of gas mainly rest with the following aspects: 1. Bozhong 21-1 structure is located in Bozhong hydrocarbon-rich depression, the gas which generated in Dongying and Shahejie formation migrates top-down vertically or laterally into the buried hill reservoir along the unconformity, faults and permeability rocks, the lateral charging “window” for gas migration is the key to the formation of interior reservoirs and its extent determinates the vertical range of gas pools; 2.High quality carbonate reservoirs were formed along the unconformity, faults and activity areas of fluid under the control of the original depositional environment and later reconstruction of diagenesis; 3.The thick mudstone of Dongying formation was deposited on the top of buried hill, which is the regional seal.

Bohai Bay basin is typical rift basin, strong activity of the faults caused differential depression of the base, the buried hill structures are easy to form in Pre-Tertiary basement of basin, many deeply buried hill have developed in depression except in uplifts and around depression. So the breakthrough of gas discovery in Bozhong 21-2 structure of deeply buried hills provides a reference to oil and gas exploration in buried hills with similar reservoir forming conditions.


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California