Late Permian Palaeogeography of the Myall Creek Area, Roma Shelf, Queensland: Application of Palaeocurrent Analysis of Core and AST Image Logs from the Tinowon Formation.
Honours Degree, 2003
University if Adelaide
Production data from the Myall Creek area suggests a significant stratigraphic trapping component, that is yet to be constrained, is required to quantify calculated reserves. Analysis of palaeocurrent data from Acoustic Scanning Tool (AST) image logs and core goniometry significantly assisted the high resolution palaeogeographic reconstruction of the Late Permian Tinowon Formation within the Myall Creek area, Bowen-Surat Basin. Consequently fluvial reservoir facies provenance, development and destination were able to be locally constrained.
Although well and seismic data allowed accurate interpretation of an initially southerly trending fluvial system draining the Gambier Park, Horseshoe and northern palaeo-highs within the Myall Creek area of the Roma Shelf, a lack of outlying data initially prevented extrapolation regarding the development of reservoir facies distal to the Myall Creek area. This also hindered the interpretation of fluvial system development throughout the three dominant sequence stratigraphic cycles. However, core facies morphology within Myall Creek-3 suggested a meandering fluvial system deposited the Lower Tinowon Formation and a moderate to high energy, laterally mobile (braided) fluvial style was responsible for the Upper Tinowon channel facies. Palaeocurrent analysis of both AST image logs and core goniometry results from Myall Creek-3 allowed the quantitative assessment of these interpretations. The two independent palaeocurrent data sets exhibited good vector mean azimuth correlation. This resulted in a large palaeocurrent data set that could be confidently analysed.
Palaeocurrent distribution within the Lower Tinowon exhibited an operational range of 152° around a vector mean azimuth of 081°N. As suggested by well and seismic data this is indicative of meandering fluvial system with low sinuosity. Channel belt azimuth and fluvial style are relatively unconstrained for the reservoir facies of the Intra-Wallabella Formation as Myall Creek-3 only intersects overbank sediments within this interval. Fluvial facies of the Upper Tinowon indicate a mean channel belt azimuth of 344°N but within a 360° operational range. This is indicative of a highly meandering fluvial system as opposed to a braided style interpretation. Within the Myall Creek area this is attributed to lateral constraint due to differential compaction around coarse channel facies of the Intra-Wallabella sandstone.
Overall the fluvial system within the Myall Creek area is characterised by a larger fluvial system whose overall vector mean azimuth develops upsection from from east to north, and a smaller tributary system trending south, draining the northern palaeohighs.