THE REGIONAL TECTONO—STRUCTURAL FEATURES AND TRAP TYPES IN SOUTHEASTERN SZECHUAN AND THEIR RELATIONS WITH THE DISTRIBUTION OF GAS POOLS

Interpretation of Landsat images has indicated four westeastward hidden fractures and nine concealed structural traps, some of which are proved to be gas pools.There is evidence that a major hidden fracture exists below the high, steep, narrow anticlinal belt. since the late paleozoic time, as a result of the mutual subduction and collision of the Indian-Australian plate, the Asian plate and the Pacific plate, large amount of wrench series have developed within Szechuan Basin. These fracture series of horizontal displacement have involved the creeping of the low volocity beds or the upper mantles and the deep seated beds as well as the activation of the magma, resulting in strong faulting and folding and deformation of the crust. The horizontal displacements of several deep fractures that are located between Huaying Shan and Qian Jiang have given rise to large amount of torsionanticlinal traps in the sedimentary cover. At the time of the formation of these traps, the primary and secondary hydrocarbons migrated to and accumulated in these traps, while hardly any gas pools occurred in the high, steep, narrow anticlinal belt due to its poor conditions for gas preservation. Therefore the low anticlines and/or the hidden structural traps are essentially the sites for gas accumulation. The gas pools are rather dispersed both geographically and stratigrap-hically and the traps are poorly filled.