In-situ stress field and fault reactivation in the Mutineer and Exeter Fields, Australian North West Shelf

摘要

This study evaluates the in-situ stress field and the potential risk of fault reactivation and seal breach in the Mutineer and Exeter fields, Australian North West Shelf. Stress determinations are undertaken using pumping pressure test, rock mechanical, and log data from twelve wells. Subsequent geomechanical modelling uses the stress data to assess pore pressure changes that may induce slip on mapped faults cutting the region. The principal stresses are assumed to be the vertical stress (S_V), and a maximum and minimum horizontal stress, S_H and S_h respectively. Borehole breakouts and drilling-induced tensile fractures (DITFs) interpreted from image logs indicate S_H has an average orientation of 107°N and S_h is orientated 017°N. Leak-off test data compiled from well completion reports reveal the magnitude of S_h increases with depth at a rate of 17.1 MPa/km. Density log data show S_V can be approximated by a power law function. An upper bound to S_H is calculated using the frictional limit to stress beyond which faulting occurs when using a frictional coefficient of 0.6. Better constraints on the magnitude of S_H are gained using rock mechanical data, knowledge of S_h and S_V, mud weights, and the occurrence of borehole breakouts and DITFs. Stress magnitudes show that the tectonic regime is strike-slip (S_h < S_V < S_H).