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1 Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, People's Republic of China; yqjiao{at}cug.edu.cn
2 Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, People's Republic of China
3 Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, People's Republic of China
4 Institute of Petroleum Exploration and Development, Xinjiang Petroleum Administration Bureau, Karamay 834000, People's Republic of China
5 Institute of Petroleum Exploration and Development, Xinjiang Petroleum Administration Bureau, Karamay 834000, People's Republic of China
6 Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, People's Republic of China
Jiao Yangquan is a professor of geology in the Faculty of Earth Resources, China University of Geosciences in Wuhan. He received his B.S. degree in 1986, his M.S. degree in 1993, and his Ph.D. in 2001 from the China University of Geosciences. His research focuses on basin analysis, sedimentology, and geology of energy resources.Yan Jiaxin has been granted a B.S. degree from Wuhan College of Geology and an M.S. degree and a Ph.D. from China University of Geosciences (Wuhan). Since 1983, he has worked at the China University of Geosciences. His research interests are sequence stratigraphy, paleoecology, and paleoclimatology.
Li Sitian is a professor and director at the Institute of Sedimentary Basin and Mineral Resources, China University of Geosciences (Wuhan). He is an active member of AAPG and a member of the American Geophysical Union. He has long been engaged in sedimentology, basin analysis, and coal geology, particularly in the integrated analysis of the Mesozoic and Cenozoic hydrocarbon-bearing basins in eastern China. His recent interests are in the study of the geodynamics of sedimentary basins.
Yang Ruiqi graduated from Xinjiang Petroleum College with a petroleum geology degree. Since 1959, he has worked in the Exploration and Development Institute, Xinjiang Management Bureau of Petroleum. His major academic job as senior engineer is to research petroleum exploration and development in the Tarim and Junggar basins.
Lang Fengjiang graduated from the community college affiliated to the Xinjiang Petroleum Management Bureau. Since 1980, he has worked as an engineer in petroleum development at the Exploration and Development Institute of the Xinjiang Petroleum Management Bureau.
Yang Shengke, an engineer, graduated from China University of Geosciences (Wuhan). Since 1978, he has been involved in teaching and research work in the Sedimentology and Energy Geology Laboratory, China University of Geosciences (Wuhan).
Reservoirs of the Karamay Formation occur as oil sandstones in outcrop in the Karamay oil field. Two types of high-quality reservoirs are present in this field: low-sinuosity channel sandstones and distributary-channel sandstones, each having different sediments, bounding surfaces, and architectural units.
The low-sinuosity channel has coarse-grained sediments, a smaller scale, and relatively simple architectural units composed of intrachannel units and lithofacies that occur in a vertically stacked pattern. The distributary channel has fine-grained sediments, a larger scale, and relatively complex architectural units, which are reflected in the following three ways. (1) The distributary channels have three multiorder architectural units: an intrachannel unit, a macroform accretion unit, and a lithofacies unit. (2) Isolated barrier beds, whose permeability is lower, occur near third-order and fifth-order surfaces. (3) The evolution of the distributary channels has two stages. In the flooding stage, the sediments were coarse grained, and the intrachannel units were in a vertically stacked pattern. In the waning stage, the sediments were fine grained, and the intrachannel units were in a laterally stacked pattern.
Reservoir heterogeneity of distributary-channel sandstones is revealed in the following three scales. (1) In a microscale range, the growth of pores is associated directly with lithofacies. The pore diameter and the throat width both increase with the coarsening of the grain size in the sediments. The anisotropic pore structure is reflected in the variation of permeability. The horizontal permeability parallel to the paleocurrent is the largest; the horizontal permeability perpendicular to the paleocurrent is intermediate; and the vertical permeability is the smallest. (2) At a channel scale, the fluid-flow units are demarcated according to the isolated barrier bed and porosity and permeability inside the distributary channel. The fluid-flow unit, distributed mainly in the middle–lower interval of the distributary channel or the intrachannel unit, is associated closely with third-order or fifth-order surfaces. The porosity and permeability inside the fluid-flow unit decrease gradually from its center to the margin and upper interval, depending on the spatial distribution of lithofacies. In this kind of lithofacies, which is characterized by a low matrix content and by coarse-grained sediments with large trough cross-beds, high porosity and permeability are commonly found. (3) In a lacustrine delta system, the distributary-channel sandstone has the best porosity and permeability and is the best reservoir.
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