The activities of deep fluid are regionalized in the Tarim Basin. By analyzing the REE in core samples and crude oil, carbon isotope of carbon dioxide and inclusion temperature measurement in the west of the Tazhong Uplift in the western Tarim Basin, all the evidence confirms the existence of deep fluid. The deep fluid below the basin floor moved up into the basin through discordogenic fault and volcanicity to cause corrosion and metasomatosis of carbonate rock by exchange of matter and energy. The pore structure and permeability of the carbonate reservoirs were improved, making the carbonate reservoirs an excellent type of deeply buried modification. The fluorite ore belts discovered along the large fault and the volcanic area in the west of the Tazhong Uplift are the outcome of deep fluid action. Such carbonate reservoirs are the main type of reservoirs in the Tazhong 45 oilfield. The carbonate reservoirs in well YM 7 are improved obviously by thermal fluid dolomitization. The origin and territory of deep fluid are associated with the discordogenic fault and volcanicity in the basin. The discordogenic fault and volcanic area may be the pointer of looking for the deep fluid modified reservoirs. The primary characteristics of hydrocarbon accumulation in deep fluid reconstructed carbonate rock are summarized as accumulation near the large fault and volcano passage, late-period hydrocarbon accumulation after volcanic activity, and subtle trap reservoirs controlled by lithology.
Ordovician carbonate buried-hill reservoir beds in the Hetianhe (和田河) gas field, located in the Mazhatage (玛扎塔格) structural belt on the southern margin of the Bachu (巴楚) faulted uplift, southwestern Tarim basin, were studied. Based on field survey, core and slice observation, the general characteristics of carbonate buried-hill reservoir beds and specifically Ordovician carbonate buried-hill reservoir beds in the Hetianhe gas field were discussed. The karst zone of the reservoir beds in Hetianhe gas field was divided into superficial karst zone, vertical infiltration karst zone, lower sub- surface flow karst zone, and deep sluggish flow zone from top to bottom. The effects of faulting on Or- dovician carbonate buried-hill reservoir beds in the Hetianhe gas field were obvious. The faulting in- tensified the karstification and increased the depth of denudation. Faulting and subsequent fracture growth modified the reservoir beds and improved the physical property and quality of the reservoir beds. Moreover, faulting enhanced the development of the dissolution holes and fractures and increased the thickness of the effective reservoir beds. Meanwhile, faulting made the high porosity-permeability carbonate belts, which created conditions for the hydrocarbon accumulation, develop near the fault zone.
