Understanding Fluvial Sand-Body Size For Modelling And Development Planning In The Lower Toolachee Formation Of The Moomba Field, Central Cooper Basin, South Australia
Bennett, Alexandra S.
Geoscience Honours Degree, 2011
University of Adelaide
Predicting the likely reservoir sand-body dimensions or lateral extent in a fluvial succession has the ability to improve and assist in reservoir modelling and development planning e.g. well placement. Gaining the knowledge of a sand bodies’ likely geometry has the ability to improve hydrocarbon production and reduce company costs.
Interpreting channel body thicknesses in the subsurface can provide a means for estimating likely channel belt widths within a formation. Forty wells in the Toolachee Formation, Cooper Basin, South Australia, were studied with access to core samples and wireline log data. Core analyses led to an interpreted depositional environment and subsequent interpreted facies associations for this formation e.g. full channel cycles, crevasse splays, mudstone/shale, and coal. Full channel cycles meant that the bankfull thicknesses could be measured through core and wireline log studies, and applied to a series of empirical equations to estimate the upper and lower limits of channel belt widths. Measurements of cross-set thicknesses are useful in backing up bankfull thickness measurements where there are no full channel cycles. The channel belt width results present wide ranges, from tens of metres to thousands of metres; however the study recognises that a narrow width range is optimal. The datasets used in obtaining these estimates were found to have limitations. The wide ranges make it difficult to assess the extent of connectivity in the formation, which was concluded to be variable. Variogram modelling also plays a role in predicting likely channel belt widths from thickness data.
It was recognised that a better understanding of modern river systems and the external factors that affect them is needed in order to reduce uncertainty when it comes to making interpretations in the subsurface. However, the use of all available forms of data constitutes more reliable subsurface interpretations.