MICROSTRUCTURE FORMED BY FAULT DEFORMATION AND ITS INFLUENCES ON OIL AND GAS FILLING IN THE LUNNAN UPLIFT, TARIM BASIN

Lunnan uplift is a narrow zone formed by two nearly parallel and opposite thrust faults which is formed during Hercynian。Due to the multi-stage tectonic superimposition, oil and gas formed by marine source rocks of Middle-Upper Ordovician migrated upward through thrust faults, and oil and gas reservoir were found from Ordovician to Cretaceous, thus forming the most complex petroliferous area in Tarim Basin。Base on observation of cores ，by using the data of thin section identification (fluorescence and casting thin section) and thermometry of fluid inclusions，51 samples collected from 13 wells in this area were use to study and quantitatively evaluated characteristics of deformation band formed in Triassic reservoir under multi-stage tectonic movement . （1）The interbeds formed by deformation band can be observed in the oil-bearing cores with a width between 1-3 cm，the quantity and distance of thrust faults are in the direct ratio；（2）Microscopically, quartz grains not strongly compacted are mainly point to line contacts. Cataclastic band with reduced grain size and directional microcrack can be observed；（3）Hydrocarbon fluid inclusions can be observed in quartz microcracks and X-shaped conjugated microfractures in fluorescent thin films. By the cutting relationship and mechanical characteristics of fluid inclusion planes, the homogenization temperature of aqueous inclusion formed in same period was determined to be 110-120 degrees Celsius. Therefore, we propose that the Triassic reservoirs in Lunnan uplift are structurally affected to form cataclastic bands, which are characterized by reduced permeability and porosity. The density of cataclastic bands decreases with the increase of distance from the fault core. Microfractures contained hydrocarbon fluid inclusions are formed by compression-shear stress. By judging the mechanical characteristics, the same phase of aqueous inclusion can be distinguished. The homogenization temperature of associated aqueous inclusion is generally characterized by a single peak, mainly 110-120 degrees Celsius, which was formed in the Late Himalayan period (13.8-4.0 Ma).