The Structural Envolution And Favorable Exploration Areas In JiangHan Basin

Jianghan Basin is a representative inland salt-lake fault basin with an unique structural evolution history and petroleum geologic conditions. More than forty years of exploration activities have found over a hundred millions of proved reserves in place, and nearly two thirds of hydrocarbon resources to be proved. With the increasingly maturative exploration, the exploration direction research should be done as soon as possible. In this paper, focusing on re-analysis of basin-scale structural evolution, the exploration potential is assessed and the exploration direction is proposed for exploration disposition, by studying effects of the structural evolution on depositional filling, hydrocarbon formation and accumulation in various-period basin configurations, which is established by detailed analysis of the distribution of major faults over the basin and its periphery, systematic description of the textural and structural characteristics and division of the structural evolution phases, using such methods as basin-based structural analysis, belt-based structural description, reconstruction and structural modeling of eroded strata, based on the basin formation theory with respect to extension, strike-slip, compression, and reversal.This study suggests that the Pre-Cretaceous fault system below Jianghan Basin was formed into the southern and northern arc systems by the Qinling-Dabie Orogeny Belt, Jiangnan-Xuefeng Uplift and Huangling Anticline, and four fault trend systems from west to east, forming an eastward-converging horn-like configuration. In the basin, four NW-oriented depressions alternated with three NW-oriented uplifts comprise a generally SW-NE trending structural framework, where four patterns of structural-stratigraphic frameworks occur. NW, NNE, NE-NEE and approximately EW-trending faults occur in the basin, which can be subdivided into two broad types including 13 faulting-assemblage styles. In structural evolution, the basin can be divided into 6 episodes of 3 structural cycles under a stress background transmitting from rift (basin-range) to transtension and compression periods. It is suggested that old to young faulting activities over the basin show a clockwise transformation trend in order, and that the syn-deposition faults control and influence formation of localtraps, which were shaped during the compression through reconstruction, resulting in a typical tectonic style of different-strike-layers-stacking composite basin;The periodical, selective pre-existing faulting activities control the basin filling, forming a gross west-faulting-east-overlapping, and north-faulting-south-overlapping filling patterns. During various periods of the rift and transtension, two main periods for the basin development, such three types of sedimentary systems in terms of filling pattern as alluvial plain-shore shallow water rift lake basin, deltaic-bathyal depression, rift-depression lake basin, alluvial plain, delta and shallow-water depression occur.In the basin occur the Lower member of the Xingouzui and Qianjiang Formations of the palaeogene source rocks, as well as three reservoir-seal associations of the Cretaceous, the Lower member of the Xingouzui and Qianjiang Formations of the palaeogene. The modeling analysis of burial history using a new technology, various-episode rift structure-thermal evolution model reveals the burial histories and hydrocarbon generation and expulsion processes for the all depressions. Eight favorable exploration belts are proposed in the palaeogene Xingouzui and Qianjiang Formations and the Cretaceous by comparison of conditions for hydrocarbon accumulation and analysis of the exploration degree in the basin. Exploration has already reached important progress and discovered 4 commercial value belts (blocks) in the periphery of the Banghu Syncline, Laoxin-Jianxin Structural Belt , Balingshan-Chi'anjie Structural Belt and the Eastern of Baimiao Syncline.This study is closely related to the production practice, playing an important guidance role in the disposition of petroleum exploration in the study area.