Structural and Palaeocurrent Analysis from Image Log Data for the Patchawarra Formation, Cooper Basin, South Australia
Holden, Darren John
Honours Degree, 2001
University of Adelaide
FMS and FMI image log data coverage in the southwest Cooper Basin has aided in testing the previous interpretations made on the Patchawarra Formation.
The Patchawarra Formation is an early Permian fluvio-lacustrine sequence lying within the Cooper Basin. It consists of a cyclical succession of sandstones, siltstones, shales, and coals and is a known source and reservoir target. This study complements a broader study on the palaeogeography of the Patchawarra Formation and verifies previous mapping. Compilation of palaeocurrent data identified the principal sediment transport from west to east along palaeo-channel belts for several chronostratigraphic intervals in the formation picked using sequence stratigraphic criteria.
Interpretation of breakouts and drilling induced tensile fractures from image logs show that the present day in situ stress field orientation for the southwest corner of the Cooper Basin has an average maximum horizontal stress oriented around 109o. The most important implication is that fracture networks close to this direction are likely to be hydraulically conductive and open. If horizontal wells could be designed to exploit both the optimal channel belt orientation and fracture network orientations, then increased hydrocarbon recovery from the Patchawarra Formation may result. Favourable targets in the Patchawarra Formation include areas where channel orientations are in the minimum horizontal stress direction and horizontal wells oriented to such channel sands are also optimally oriented to intersect any natural fractures that are open and hydraulically conductive within in situ stress field. Several leads are suggested where optimal reservoir quality and fracture intersections occur where horizontal drilling may be a possible exploitation strategy. These include areas southwest of Big Lake 54, Wooloo South1, and around Barina and Farina wells.