Abstract: The state of terrestrial stress changes because of the effects such as water injection and insitu combustion during the exploitation in the oil and natural gas fields, which influence the yield of oilgas relatively seriously. In this paper, based on the theory of liquidsolid coupling, the mathematical model of the terrestrial stress field is established which takes the pourpluck relations into consideration. The finite element model is developed in three dimensional stress field with the pore pressure changing by using the finite element method, the dyscalculia with the discrepancy between the stratum size and the mouth of a well size is solved by using the method of composite grid. The input is geologic and practical exploitative data, fluid pressure, saturation, solid distortion and the spatial distribution and the change with time of stress field are calculated through threedimensional stress field numerical simulation system. The result offers reliable basis for using appropriate measures to optimum development; meanwhile，it offers theoretical basis for exploitation adjustment, refracturing, forecasting the damage of casing etc. in anaphase.
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Key words: composite grid, liquidsolid coupling, finite element, threedimensional terrestrial stress field, numeral simulation