Hydrocarbon Accumulation in Meso-Cenozoic Lacustrine Remnant Petroliferous Depressions and Basins, Southeastern China
Li Desheng, Luo Ming, 1990. "Hydrocarbon Accumulation in Meso-Cenozoic Lacustrine Remnant Petroliferous Depressions and Basins, Southeastern China", Lacustrine Basin Exploration: Case Studies and Modern Analogs, Barry J. Katz
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More than 140 small lacustrine Meso-Cenozoic remnant petroliferous depressions and basins are distributed along deep fault zones in southeastern China. Some contain abundant oil and gas reserves in high-yield traps, although areal extent of this type of petroliferous basin is only 800-1000 km2. Among the structural and lithologie characteristics of hydrocarbon accumulations in these depressions and basins are (1) distribution along deep fault zones, (2) widely distributed, thick source rocks, (3) well developed sand bodies, (4) high geothermal gradient, and (5) multiple-trap styles.
Meso-Cenozoic remnant depressions and basins in southeastern China contain thick, deep-water lacustrine shale, the primary source rocks for the region's hydrocarbon accumulations. These dark, organic-rich, fine-grained strata were deposited in the deeper parts of lake depressions and basins. Consequently, the principal source rocks have been well preserved over much of their original extent, although uplift and erosion following shale deposition have resulted in the destruction of depression and basin margins.
Most of these small remnant structures occur as half-grabens resulting from successive development of faults along one side of the basin; however, some also may appear as full grabens. Well developed remnant depressions and basins consist of three characteristic structural elements—(1) step-faulted belt on the steep flank, (2) central, low buried-hill belt, and (3) monoclinal slope belt on the gentle flank. Examples of these types of depressions and basins include the Damintun, Lanpu, and Sulu depressions, and the Baishe and Sanshui basins. Poorly developed remnant basins consist of (1) a step-faulted belt on the steep flank, (2) central trough, and (3) monoclinal slope belt on the gentle flank. Examples of these types include the Biyang, Changwei, Qianjiang, and Yuanjiang depressions, and the Maoming basin.
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Lacustrine Basin Exploration: Case Studies and Modern Analogs
Lacustrine environments are a major contributor of petroleum source rocks. Lacustrine source rock prediction is, however, influenced by numerous, complex variables governing lake sedimentation. Current predictive capability can be improved by attempting to map essential climatic variables to limit in space and time the area of lacustrine source rock exploration. Climatic characteristics that govern lake occurrence and the potential for stratification have been investigated with a General Circulation Model of the atmosphere for the present and for the mid-Cretaceous. In this analysis, the distribution of areas with a positive water balance first is used as an indicator of the distribution of areas conducive to lake formation. Second, the distribution of areas that experience large annual climatic variations is used as an indicator of the distribution of lakes that are less likely to be stratified and, hence, less likely to be sites of high organic-carbon preservation. Four factors used to define large climatic variations include (1) seasonal temperature cycle in excess of 40°C; (2) seasonal temperature extreme of less than 4C°; (3) average seasonal differences in precipitation minus evaporation balance in excess of 5 mm/ day; and (4) distribution of mid-latitude winter storms. Evidence is presented to support the capability of climate models that add insight into lacustrine source rock prediction by simulating geographic regions conducive to lake development and to stratification and organic-carbon preservation