The deep structures and oil-gas prospect evaluation in the Qiangtang Basin, Tibet

Abstract

The Qiantang Basin is now one of the topics of general interest in petroleum exploration in China. This paper reports a comprehensive study of geophysical and geological survey data recently obtained in this area and, combined with INDEPTH-3 deep survey results, comes to the following conclusions: 1) The hydrocarbon source formations, reservoirs, and overlying strata and their association within the basin are quite good, local structures are developed, and, therefore, the region is favorable for forming and preserving oil and gas accumulations. Faults are not a fatal problem. The future main target strata are the middle-deep structural strata composed of Upper-Triassic and middle Jurassic rocks; 2) A new classification has been made for second-order tectonic sequences inside the basin to disavow the central Qingtang uplift. It is noted that the main structures at the surface are orientated NE-SE and the crustal structure can be described as three depressions, three risees, and one deep depression, of which the prospective zone with the most potential is the inner main subsided belt and its two sides; 3) Comparatively intensive interaction between the crust and mantle and volcanic and thermal activities in the northern basin play a very important role in petroleum evaluation. The southern deeper sedimentation and less thermal activity make this area a more perfect zone for oil exploration; 4) Currently, the most important objective is determining the physical properties of the deep strata, the status of oil and gas accumulations, the source of the hydrocarbons, and the relationship between the upper and lower structures; and 5) The Lunpola Tertiary basin may be favorable for oil accumulations because petroleum may migrate from marine strata on two sides.