Structure Character And Petroleum Exploration Of Jiuquan Basin

The first oil field in china was discovered in Jiuquan basin, and a series of important results about structure study of the basin have been achieved. Due to the limitation of complex geologic condition, lots of question are still leaved over, which influence the drilling effects. Through dissecting the superposition and tectonic evolution of the basin, the relationship between structural character and the distribution of reservoirs were studied in the paper which will guide the exploration to discover various new reservoirs, and the result of the study gives the enlightenment to understand the tectonic evolution of the north section of Qingzang plateau.Based on various data and unifying the seismic-geologic strata, It is revealed that Hongnan and Chijin sub-depressions reflected by gravity data are Cenozoic depression. Most of lower cretaceous data are missing in Hongnan sub-depression. Lower cretaceous strata are absent in Chijin sub-depression and distributed locally in Dahongquan area.The method of unconformity-depositional cycle analysis was used to analyze the proto-basins in Jiuquan area, and more attention was paid on the proto-basins of early cretaceous and their extension. By the study of superposition and tectonic evolution of the basin, It is recognized that originally Jurassic and cretaceous basins in Jiuquan were resulted from thermal uplift The distribution and characters of early cretaceous, late cretaceous, and Cenozoic fracture systems were studied, and the result shows that all of the major fracture systems in Jiuquan area underwent the superposition of fracture system in various tectonic regimes,Mountain front thrust and fold belts bordered by the north boundary fault of the northern Qilian in southern Jiuquan basin can be divided into two sub-belts in their dip direction. The strike orientation of two sub-belts are controlled by transfer faults, and the structures are characterized with segmented deform. The structural deform characters of multiple thrust nappes in the south margin of the basin are the result of multiple periods compressive structure movement acted from Devonian to Cenozoic time. Neotectonics in Jiuquan basin resulted in thick-skinned deformation. Order of the deformation is that up-warping fold took place first, and the thrusting followed.