Publication Date:
2007-08-01
Description:
Xihu Basin is one of the Cenozoic sedimentary basins within the continental shelf of the East China Sea, within which eight oil and gas fields and four hydrocarbon-bearing structures have been found. Our systematic analysis of potential petroleum systems in the basin has identified the Eocene Pinghu Formation as the most important source rock in the basin. The Eocene Pinghu Formation consists of mudstone and coal deposited in an embayment and tidal-flat environment and is characterized as containing type III kerogen. The Pinghu Formation is mature and, at the present time, is within the oil and wet-gas windows with determined vitrinite reflectance values in the range of 0.55–2.2% measured vitrinite reflectance (Rom). Modeling results suggest that the main stage of hydrocarbon expulsion occurred during the Miocene. The main reservoir consists of fine-grained sandstones of the Huagang and Pinghu formations deposited within shallow lacustrine and estuarine environments. The measured porosity from core samples of reservoir rock ranges from 10 to 35%, whereas permeability values range from 1 to 4000 md; both porosity and permeability decrease with depth. The mudstones of the upper Huagang and Longjing formations also occur as regional seals, which developed overpressure zones as determined by two-way sonic transit times. The overburden includes all the Oligocene, Miocene, Pliocene, and Quaternary strata. The hydrocarbon traps in the basin are mainly structural traps, including faulted blocks, faulted structural noses, and anticlines. Most traps were developed at the ends of the Eocene or Oligocene. Hydrocarbons produced from the Xihu Basin are predominantly natural gases with minor amounts of crude oil. The crude oil in the basin is characterized by a low density, low sulfur, low wax, low vanadium/nickel ratio, a low resin and asphaltene content, and a high proportion of saturated hydrocarbons. The natural gas in the basin is composed predominantly of methane, with an average C1/∑C1–5 ratio of 0.89 and a C1/∑C2–5 ratio of 8.6. Two petroleum systems have been identified in the basin: the known Pinghu-Huagang and the hypothetical Huagang-Huagang systems. The Pinghu-Huagang is the major petroleum system and most important for oil and natural gas exploration in the basin. Jiaren Ye received a B.Sc. degree (geology) in 1986, an M.Sc. degree (petroleum geology) in 1989, and a Ph.D. (mathematical geology) in 1996 from the China University of Geosciences (Wuhan). He is currently a professor in the Faculty of Earth Resources at the China University of Geosciences (Wuhan). His present research interests include petroleum resource assessment, basin modeling, and petroleum systems. Hairuo Qing is a professor at the University of Regina. His research interests include characterization of carbonate reservoirs, geochemistry and diagenesis of dolomites, and secular variation of isotopic composition of seawater in geologic history. He received a bachelor's degree in petroleum geology from Chengdu University of Technology and an M.Sc. degree and a Ph.D. (Dean's honor list) from McGill University. Stephen L. Bend is also a faculty member of the Department of Geology, University of Regina. He received a bachelor's degree in geology from the University of Keele and an M.Sc. degree and Ph.D. from the University of Newcastle upon Tyne, United Kingdom. He previously worked in industry as a field geologist and geochemist for 5 years. His current research interests include oil-source rock characterization and fossil fuel studies. Huirong Gu graduated from the China University of Geosciences (Wuhan) with a B.Sc. degree in petroleum geology in 1986. He is currently a senior geologist of Shanghai Offshore Petroleum Bureau, China Petroleum and Chemical Corporation. His present research interests are basin analysis and petroleum systems.
Print ISSN:
0149-1423
Electronic ISSN:
1943-2674
Topics:
Geosciences
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