ALBERT

Description: Hydrocarbon reservoirs in the Oulituozi area of the Liaohe basin, northeastern China, occur within a subvolcanic trachyte porphyry intrusion. This intrusion was emplaced at a depth of less than 1 km during the Paleogene. The prevalent reservoir porosity is in explosive breccias, fracture networks, steeply dipping cracks, and dilational microfractures in the apical zone of the intrusion. These voids were formed by underground explosion during magma solidification and by postsolidification volume contraction. Minor oil and gas volumes are trapped also in fractures in the overlying brittle beds. The massive rocks in the lower part of the porphyry body serve as hydrocarbon seals for reservoir beds lateral to the intrusion. We propose a model for reservoir formation related to a subvolcanic intrusion that includes three types of reservoirs: (1) reservoirs in the apical zone of the intrusion, (2) reservoirs in the upper wall of the intrusion, and (3) reservoirs lateral to the intrusion. Attention should be paid to all the three reservoir types during exploration around a subvolcanic intrusion. Lianxing Gu received a B.Sc. degree from Peking University in 1967 and then worked as an exploration geologist until 1978 in Geological Company No. 814. He obtained his M.Sc. degree and Ph.D. from Nanjing University in 1982 and 1985, respectively, and is currently a professor in the Department of Earth Sciences, Nanjing University. His principal research interests are massive sulphide ores, mineral deposits related to granites and volcanic rocks, and the formation mechanism of oil and gas reservoirs in volcanic rocks.Zuowei Ren received a B.Sc. degree in geophysics in 1988 from Qingdao Ocean University. He then worked as a geologist with the Exploration and Development Research Institute (E&D Institute) of Liaohe Oilfield Branch Company, PetroChina. He is now the director of the Basin Exploration Research Department of the E&D Institute, Liaohe Oilfield Branch Company, PetroChina and is also a Ph.D. student in the Department of Earth Sciences, Nanjing University. His current research deals with the formation mechanism of oil and gas reservoirs in volcanic rocks. Changzhi Wu received a B.Sc. degree from Changchun University of Science and Technology in 1999 and is currently a Ph.D. student at Nanjing University. His current research deals with petrogenesis of Cenozoic volcanic rocks in the coastal areas of eastern China. Ming Zhao received B.Sc. and M.Sc. degrees from Nanjing University in 1978 and 1997, respectively. She has been a staff member of Nanjing University since 1978 and is now an associate professor in mineralogy and petrology. Her main research area is the mineralogy and petrogenesis of volcanic rocks. Jin Qiu received a B.Sc. degree in petroleum geology in 1989 from Chengdu Geology Institute. She has been working as a geologist with the E&D Institute of Liaohe Oilfield Branch Company, PetroChina since graduation and is now engaged in petroleum geology research.