Haijun Yang

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 O1y1, the lower O1y2 and the O3l3. 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.

The Genesis and Prospecting Significance of High-sulfur Gas Condensates in the Deep Dolomite Reservoirs Beneath Gypsum Rocks: A Case Study of the Cambrian Reservoir in Tarim Basin

Comprehensive two-dimensional gas chromatography (GC×GC-TOFMS) was used to detect recently discovered condensates in the Cambrian dolomite reservoir beneath gypsum rocks of Tarim Basin. It was found that the thioadamantane and dibenzothiophene compounds are rich in the dolomite reservoirs, which indicates that the gas condensates have undergone hydrocarbon charging with TSR genesis. Based on the contents of SO42− and Mg2+ in the formation water of the Well ZS-1 reservoirs, the dolomite reservoirs and gypsum caps of intraplatform tidal flat facies sediments have been proven to be an effective geological combination to provide sulfate contact-ion pairs for TSR initiation. Compared with typical high-sulfur gas reservoirs with TSR throughout the world, the TSR extent in the Lower Cambrian dolomite reservoirs of ZS-1 is lower, and the liquid hydrocarbons in the Lower Cambrian of Well ZS-1 at the buried depth close to 7,000 m have not intensively cracked. Therefore, it is speculated that abundant cracking gas may occur in deeper slopes and basins (about 9,000 m) with high content of H2S and CO2. It is also revealed that deep dolomite reservoirs beneath gypsum rocks are the actual geological conditions for the accumulation and preservation of secondary H2S-bearing gas condensates.