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ABSTRACT: Contemporary stress orientation and structural permeability in the Petrel Sub-basin

Mildren, Scott D.1, Richard R. Hillis2, and Richard Jones3
(1) National Centre for Petroleum Geology and Geophysics, South Australia, Australia 
(2) Adelaide University, Adelaide, Australia 
(3) National Centre for Petroleum Geology and Geophysics, University of Adelaide, Adelaide, Australia

Four-arm dipmeter logs from six wells in the Petrel Sub-basin (southern Bonaparte Basin) were interpreted for borehole breakouts. Results of the analysis reveal a consistent NE-SW contemporary SHmax orientation (055°N). This orientation is parallel to the average SHmax determined further north in the Timor Sea area (northern Bonaparte Basin) and the adjacent onshore Canning Basin. The data supports the interpretation that the NE-SW SHmax direction in the area reflects a first-order stress pattern controlled by plate boundary forces along the northeastern margin of the Indo-Australian Plate. Numerical modelling of the stress field in response to plate boundary forces suggests that the divergence of SHmax from a plate motion parallel direction can be explained by the heterogeneous nature of the northeastern plate boundary.

A new fault-seal integrity rapid evaluation tool has been developed to integrate the contemporary stress field with structural information to produce a structural permeability risk map. Fault-seal integrity is colour mapped along fault strike according to orientation and dip for a given stratigraphic horizon. This technique has been applied to the Petrel Sub-basin using the newly interpreted stress orientations and stress magnitude estimates. The dominant NW-SE structural grain of the sub-basin has a relatively low risk of seal breach with respect to the development of structural permeability within the contemporary stress field. However, changes in dip along fault strike do significantly vary the risk of failure and therefore it is critical to undertake the assessment using 3D stress and fault orientation data.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia