Calibrating predictions of fault seal reactivation in the Timor Sea

Abstract

Predictions of the likelihood of fault reactivation for five fault-bound prospects in the Timor Sea are made using the FAST (Fault Analysis Seal Technology) technique. Fault reactivation is believed to be the dominant cause of seal breach in the area. Calculations are made using a stress tensor appropriate for the area, a conservative fault–rock failure envelope and the structural geometries of each prospect. A depth–stress power relationship defines the vertical stress magnitude based on vertical stress profiles for 17 Timor Sea wells. Empirical evidence of hydrocarbon leakage at each trap is used to investigate the accuracy of the fault reactivation–based predictions of seal integrity. There is a good correlation between evidence of leakage and the risk of reactivation predicted using the FAST technique. Risk of reactivation is expressed as the pore pressure increase (ΔP) that would be required to induce failure. This study allows the fault reactivation predictions to be calibrated in terms of risk of seal breach. Low integrity traps are associated with ΔP values less than 10 MPa, moderate integrity traps correspond with values between 10 and 15 MPa and high integrity traps correspond with values greater than 15 MPa. Faults with dip magnitudes greater than 60° in the Timor Sea area are likely to have a high risk of reactivation and shear failure is the most likely mode of reactivation.