Potential New Method for Paleostress Estimation by Combining Three-dimensional Fault Restoration and Fault Slip Inversion Techniques: First Test on the Skua Field, Timor Sea

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This pilot study indicates that estimating paleostress orientations and magnitudes from seismic data, through analysis of fault slip data obtained using three-dimensional restoration techniques, is possible, and the results generated are consistent with regional observations. The results suggest that the stress regime responsible for late Miocene fault activity in the vicinity of the Skua oil field in the Timor Sea differs from the present-day stress regime. An extensional stress regime, having the maximum principal stress axis (1) oriented vertically, the intermediate principal stress axis (2) oriented approximately east–west, the minimum principal stress (3) oriented approximately north–south, and a stress ratio (R) of about 0.3, was calculated for the late Miocene. In contrast, measurements of the present-day stress field indicate a transtensional stress regime in which 2 is vertical, 1 is horizontal and trends east-northeast–west-southwest, 3 trends north-northwest–south-southeast, and R = 0.8. Estimation of the magnitudes of the principal stresses indicate that the differential stress operating in the late Miocene was similar to the present, but that greater mean stress in the present-day stress state results in a lowering of reactivation risk with time. These results are consistent with regional observations of widespread late Tertiary extensional faulting, with decreasing fault activity to the present day. The work also suggests that the majority of hydrocarbon leakage associated with fault reactivation in this region is less likely to be associated with the present-day stress regime than with the paleostress regime.