The Geological Characteristics of Reservoirs and Major Controlling Factors of Hydrocarbon Accumulation in the Ordovician of Tazhong Area, Tarim Basin

The ancient deep-buried marine carbonate reservoir takes on strong heterogeneity and fluid complexity, and features large acreage and low abundance. For the ancient deep carbonate exploration in China now, it is challenging to find accumulating positions with high abundance and deploy high-efficiency wells. Based on the E&D practices of Ordovician carbonate reservoir and the high-efficiency well correlation in the Tazhong area, Tarim Basin, it is found that the high-efficiency wells distribute along the peaks of third-order structure zone and the relative high parts of platform, about 0.31.5km away from the strike-slip fault, and longitudinally, mainly in large unfilled Ordovician fracture-cavity reservoirs in the lower O 1 y 1 , the lower O 1 y 2 and the O 3 l 3 . The large scale unfilled fracture-cave system (as favorable reservoir space), the strike-slip fault (as pathway for efficient hydrocarbon charge in late stage) and the sufficient hydrocarbons (charged intensively in multi-stages) contribute to the high abundance hydrocarbon enrichment in the Ordovician karst carbonate reservoir across the Tazhong area. This research recommends to use precise structure interpretation and palaeogeomorphic and palaeotectonic reconstruction to identify the gas source faults and favorable charging position, use precise fracture-cavity description to assess the cavity quantitatively, and use seismic wave impedance inversion and hydrocarbon detection to predict the distribution of large unfilled cavity reservoirs, in order to effectively estimate the high-abundant oil/gas area, locate the high-efficiency well area and improve the E&D performance in ancient deep carbonate rocks.