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https://hdl.handle.net/2440/52375
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Type: | Journal article |
Title: | In situ stresses and natural fractures in the Northern Perth Basin, Australia |
Author: | King, R. Hillis, R. Reynolds, S. |
Citation: | Australian Journal of Earth Sciences, 2008; 55(5):685-701 |
Publisher: | Taylor & Francis Ltd. |
Issue Date: | 2008 |
ISSN: | 0812-0099 0016-7614 |
Statement of Responsibility: | R. C. King, R. R. Hillis and S. D. Reynolds |
Abstract: | Present-day stress orientations in the Northern Perth Basin have been inferred from borehole breakouts and drilling-induced tensile fractures observed on image logs from eight wells. Stress indicators from these wells give an east - west maximum horizontal stress orientation, consistent with stress-field modelling of the Indo-Australian Plate. Previous interpretations using dipmeter logs indicated anomalous north-directed maximum horizontal stress orientations. However, higher-quality image logs indicate a consistent maximum horizontal stress orientation, perpendicular to dominant north - south and northwest - southeast fault trends in the basin. Vertical stress was calculated from density logs at 21.5 MPa at 1 km depth. Minimum horizontal stress values, estimated from leak-off tests, range from 7.4 MPa at 0.4 km to 21.0 MPa at 0.8 km depth: the greatest values are in excess of the vertical stress. The maximum horizontal stress magnitude was constrained using the relationship between the minimum and maximum horizontal stresses; it ranges from 8.7 MPa at 0.4 km to 21.3 MPa at 1 km depth. These stress magnitudes and evidence of neotectonic reverse faulting indicate a transitional reverse fault to strike-slip fault-stress regime. Two natural fracture sets were interpreted from image logs: (i) a north- to northwest-striking set; and (ii) an east-striking set. The first set is parallel to adjacent north- to northwest-striking faults in the Northern Perth Basin. Several east-striking faults are evident in seismic data, and wells adjacent to east-striking faults exhibit the second east-striking set. Hence, natural fractures are subparallel to seismically resolved faults. Fractures optimally oriented to be critically stressed in the present-day stress regime were probably the cause of fluid losses during drilling. Pre-existing north- to northwest -striking faults that dip moderately have potential for reactivation within the present-day stress regime. Faults that strike north to northwest and have subvertical dips will not reactivate. The east-striking faults and fractures are not critically stressed for reactivation in the Northern Perth Basin. |
Keywords: | in situ stress natural fractures Northern Perth Basin |
DOI: | 10.1080/08120090801982843 |
Published version: | http://dx.doi.org/10.1080/08120090801982843 |
Appears in Collections: | Aurora harvest Australian School of Petroleum publications |
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