Prevailing Geological Controls on the Petroleum Accumulations in the Foreland Basins of Western China

Yan Song, Mengjun Zhao, Shaobo Liu, Shengfei Qin, and Feng Hong
RIPED, PetroChina Company Limited, Beijing, China

Foreland basin represents one of the most important petroleum habitats, and the recent discovery of Kela 2, a giant gas field in the Tarim Basin, has promoted the integrated effort of geological research and petroleum exploration in foreland basins. Important features of the foreland basins in western China include their complex tectonic development involving superimposed basins and hence the formation of multiple hydrocarbon source rock and reservoir combinations. Detailed examinations of major Mesozoic foreland basins in western China reveal that the occurrence of abundant natural gas resources in these basins is primarily related to the presence of thick coal measures as gas-prone source rocks. The coal-bearing strata represent the most significant detachment zones in the foreland basin development. The distribution of different structural belts is critical in controlling the oil and gas occurrence in a foreland basin, which will be demonstrated using several case studies from western China. Below the major detachment zone, oil pools are distributed in the thrust belts and fore-bulge zone, whereas oil pools are located mainly in the depressional area above the major detachment zone. Earlier formed oil traps tend to be destroyed and become oil seepages, asphalt or residual oil reservoirs in the piedmonts; relatively more matured gas is often accumulated in the foreland thrust belts and depression; the slope zone and fore-bulge belts are favorable localities for the accumulation of early generated oil and gas and late stage gases.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005