Stress estimation in faulted regions: the effect of residual friction

摘要

This paper presetns relationships for estimating horizontal stresses hased on the assumptions that the in situ stress state in a petroleum basin is controlled by the bounding normal or thrust faults at a limit equilibrium and that the fault block is linear elastic and plane strain conditon applies in the direction parallel to the strike of the fault. These relationships are an extension of an earlier study and include the effect of residual friction angles onthe estimation of horizontal stresses at depth. The result shows that re-orientation of the minimum principal stress is possible after faulting depending on the Poisson's ratio of the formation. Predictions based on the relationships are compared with the stress data obtained in normal and thrust fault conditions as well as with the change in the miniumum horizontal stress induced by the pore pressure depletion. The results show that to match the field stress data, a relatively low residual friction angle (10 degree-30 degree) on the fault is required. This is further supported by the mumerical modelling of the in situ stresses in the Cusiana field in Colombia, and is consistent with the residual friction angles measured in laboratory or back-calculated based on earthquake mechanism.