ABSTRACT: Natural fracture plays in an early Palaeozoic Frontier (Eastern Warburton) Basin, South Australia

Sun, Xiaowen , Sun Petroleum Geoservices, Adelaide, Australia

A detailed fracture study confirms that natural fracture plays exist in the under-explored, Cambro-Ordovician Warburton Basin and at the interface between it and unconformably overlying hydrocarbon productive Cooper Basin. Considerable information has been gathered from a detailed core study of 91 wells in conjunction with the use of dipmeters, formation micro-scanner (FMS) logs from 27 wells. Absolute orientation data are obtained from measurements of cores and logs from 23 wells and additional relative orientation data are collected from 24 wells. Two systems of orthogonal fracture sets have been identified for the first time across local structures, and extend beneath the Cooper Basin in South Australia. System I has a pair of orthogonal fractures, striking NNE-SSW (20-200°) and ESE-WNW (110-290° ). System II has a pair of orthogonal fracture sets, striking NE-SW (60-240°) and NW-SE (150-330° ). Open and partially open fractures striking WNW and NW within systems I and II, and dipping SW, are interpreted from both core and FMS data in several wells. Tectonic fractures are believed to be superposed over regional fracture system II as a result of thrusting and reverse faulting. The results suggest that an optimum well trajectory designed to maximise intersection with open natural fractures should be 200-210° and 240-250°, and possibly also 270-290°. The deviation angle should be approximately 30° from horizontal in the fracture zone to maximise the likelihood of such wells encountering high angle open fractures. A semi-quantitative estimate of fracture density has been determined for 91 wells, and the greatest fracture density is located in major fault zones or structural culminations.

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