The Research On The Tectonic Stress Field Numerical Simulation Of Middle-lower Ordovician, In Tazhong Area, Tarim Basin

Tectonic stress field is one of the important factors which affect the oil and gas migration, accumulation, preservation and destruction. Moreover, tectonic stress field can form the channel of hydrocarbon migration and the trap of hydrocarbon accumulation. Instantaneous tectonic stress of discontinuous state and long-term tectonic stress of continuous state can also provide hydrocarbon migration with a driving force. In this paper, according to fracture characteristics of Tazhong uplift and its evolution, with middle-lower Ordovician limestone as main study object, large-scale finite element analysis software (ANSYS) was applied to simulate tectonic stress field of Late Ordovician, Devonian, Triassic and Neogene by contact algorithm. The research on the stress distribution characteristics of Tazhong area can apply to crack prediction and hydrocarbon migration and accumulation.Corresponding to the three phase crack, four tectonic movements-the late Caledonian movement, the early Hercynian movement, Indo-Chinese Movement and Himalayan Movement-seriously affected hydrocarbon formation and accumulation in Tazhong area. The tectonic evolution history of Tazhong uplift is divided into four stages. By analysis of the main fault structure in Tazhong area, Tazhong uplift has three structure situations including vertical stratification, north-south sub-zone and east-west subsection.On the base of structural analysis, four geological models in four different periods were established corresponding to four tectonic movements, and different boundary conditions were imposed according to different periods. Multi-stages fault structure of Tazhong area disturbed tectonic stress field strongly. By contrast and repeated calculation, the contact algorithm can simulate the dynamic characteristics of faults preferably. Due to multi-fraction have the character of pressure-twisting and strike-slip, reducing friction coefficient and normal stiffness, and increasing tangential stiffness and maximum value of allowable penetration were used to represent strike-slip faults. In the process of simulation, basin-model software TSM, modeling software AutoCAD and large-scale finite element analysis software Ansys were firstly combined to use and made a progress in conversion of vector information during three software.By simulating tectonic stress field of middle-lower Ordovician carbonate rocks in four different periods, principal compressive stress field, which was affected markedly by the eastern strike-slip fault named Cherchen-xingxingxia, presented strip-shape and low-value distribution along fault zone in uplift area. Tazhong 1st fault in different periods were all at the minimum value area of main press stress field, which reflected Tazhong fault zone, especially the 1st fault was a well directed area for hydrocarbon migration. The main tensile stress field was banded distribution of high-value along fault zone. The hanging wall of fault was the high-value area of tensile stress and easy to form a tensile crack. The change area of fracture trend and trip fracture were also the high-value area of tensile stress and important structure area developing tensile crack. The affection on main tensile stress and shear stress field was weakened from Cherchen-xingxingxia strike-slip fault.Based on the analysis of simulation, the favorable area of hydrocarbon migration was the 1st fracture in Tazhong uplift, while the favorable areas of crack developing were the east of 1st fault, Tazhong 26 well area, Tazhong 45 well area and the junction by the 2nd trip fault and Tazhong 5-48 well faults.