Malaysian Journal of Geosciences (MJG)

This study focusses on geological modelling of a fluvial outcrop analogue, illustrating the impact of stratigraphic architecture on sand-body distribution, internal geometry, and stacking on sedimentary heterogeneity and static properties. Outcrop measurements and sedimentological logs generated from a 4.8 km2-section provide data for modelling two lithostratigraphic zones from the three zones recognised. The model consists of a Cartesian grid with 576 cells and 544 cells in the horizontal directions. Each cell is 5 m x 5 m along horizontal directions and 4.3 m along depth. Facies object method was used for modelling lithology and Sequential Gaussian Simulation for modelling porosity and permeability data sourced from a subsurface analogue. The results reveal that a major channel element in Zone 1 has complex ribbon geometry marked by upward thinning and fining sequences. In this zone, intraformational mudrock rip-up clasts form channel lags with potential as flow baffles in pebbly sandstone intervals while thick floodplain mudrock limits lateral continuity of interbedded sandstone, posing huge risks to lateral sweep. Crevasse splays in Zone 2 improve lateral continuity of interbedded sandstone. However, mud-prone heterolithic deposits may pose a significant risk to vertical sweep in poorly connected splay intervals. Therefore, drilling horizontal laterals from existing wells into such intervals and/or adopting a gas-based depletion strategy may improve areal sweep in previously bypassed low-connectivity zones. In hydrocarbon fields where overbank sheets are sandwiched between thick floodplain fines, exemplified by Zone 3, in-place volume may be uneconomic to warrant development.