Abstract: Direction of in-situ stress near a fault is significantly different with that far away from the fault.Experimental approaches and finite element simulation method were previously used to study the patterns of faults acting on in-situ stress field direction,but these patterns were never explained in respect of mechanical mechanism.The regularity of elasticity mechanical mechanism were reveals by using the analytical solution of elliptic orifice problems based on study of the change patterns of the maximum horizontal principal stress direction near a single fault.And a block was taken as an example to study the change of the direction of maximum principal stress along fault strike in areas with multiple faults.The results show that the maximum horizontal principal stress deviates to the fault strike at the ends of faults.The phenomenon can be well explained with the aid of orifice problem of elastic mechanics analytical solution.The calculation results of in-situ stress in one unit of Tahe oilfield also verify the rule.

Key words: elliptic orifice problem, in-situ stress, fault, Tahe oilfield