Study on structural feature and its oil and gas geologic conditions of A Well Area, North of Awati Sag, Tarim Basin

Few large oil and gas fields have been presently discovered around the Awati Sag in western Tarim Basin. However, in recent years, with both the improvements of drilling technology and level of understanding, it is obviously urgent to carry out related re-evaluation upon those potential favorable structural traps or zones. In this paper, based on previous studies, using both pre-existing and newly-obtained 2D seismic data covering the A structure together with drilling data, we firstly conduct seismic data interpretation and delineate structural maps of key reflector layers (the bottom surface of the Tertiary and the top surface of the mid-upper Ordovician limestones). The results show that the A structure is an integrated compressional anticline trending NW-SE within the Mesozoic-Cenozoic interval, but within Palaeozoic interval it is a large-scale thrust-diapir domal anticline structure, which is quietly different from previous understanding. Further analysis on oil and gas conditions indicate that the thrust-diapir domal structure possesses some essential elements for forming potential giant reservoir, including: 1) a large-scale trap with an area of 260 km 2 and a closure height of 1100 m; 2) location beside available source rocks of the mid-upper Ordovician blocked-trough; 3) fractured reservoir of the Upper Cambrian-Middle Ordovician carbonate rocks; 4)late Hercynian paleostructural trap condition together with continuous hydrocarbon charging from Cretaceous to the present; 5) massive shale sealing condition as well as the fault sealing condition within the shale beds. The adverse factors for this structure are its depth of burial with target layers up to 6400~7500 m, and may be affected by the neighboring large-scale volcanic intrusion to its northeast.