Deliberate Search for Stratigraphic Traps: A Success Story from Sabah Offshore

Abstract

This article briefly discusses the workflow through which a gas discovery was made within the Late Miocene interval (Lower and Upper Stage IVD) from the structurally down-flank of a three-way fault closure, where previously an unsuccessful campaign was carried out in the structurally higher location. The causes for the failure were attributed to reservoir absence and trap incompetency. An attempt was made to understand the causes of facies variations and their limits through an integrated sequence stratigraphic approach. This model was further concretized through post-stack attributes where the limits of the seismic facies were prominent. A quantitative interpretation (QI) study coupled with forward modelling helped de-risk the reservoir presence and fluid types. Rock physics modelling work, including shear log prediction, rock property modelling, depth -trend analysis, followed by simultaneous inversion and sand probability volume generation, reveals that the deeper part of Upper Stage IVD and Lower Stage IVD intervals were shale-out and pinch-out, respectively, for the earlier campaign. Likewise, sand-dominated facies are likely at the down-dip for both intervals with an effective lateral seal up-dip (due to facies change and pinch out). Finally, this integration led to a hydrocarbon discovery in a previously written-off fault block and proved a potential stratigraphic trap presence in this area. The well encountered 50 m of net gas-bearing sand within both intervals. This approach could further facilitate exploring stratigraphic play (s) in a similar geological setup.