Assessment of reservoir clay heterogeneity in subsurface clastic sandstones: Toward enhanced reservoir quality in Nyalau Formation, East Malaysia

Abstract

The Nyalau Formation in onshore Central Sarawak, NW Borneo correlates to the petroliferous Cycles I and II in the offshore. Significant poro-perm loss in the subsurface siliciclastic sandstone of this formation has been recently documented. Unfortunately, available data are insufficient to draw conclusions on the diagenetic signatures that resulted into this anomaly. Without this certainty, production from the Nyalau Formation in the onshore central Sarawak will be problematic, as useful enhanced oil recovery techniques cannot be administered with high degree of confidence. Hence, this research seeks to integrate bulk mineralogy, clay size mineralogy and subsurface high resolution imaging to understand fluid flow parameters, pore geometry, mineralogical behaviour and percentage mineral composition in the sandstone reservoirs. A total of 188 subsurface samples (14 cores samples and 174 ditch cuttings) retrieved from the onshore “Kaku-1” well will be sedimentologically described to deduce textural parameters, presence or absence of glauconite, carbonaceous detritus and sand/shale ratio. Disaggregated bulk samples and clay size fraction will be subjected to X-ray diffractometer analysis. Polished and unpolished core samples will be viewed using the variable pressure scanning electron microscopy (VPSEM) coupled with energy dispersive x-ray (EDX). Downhole profiles of bulk and clay mineralogy, as well as clay morphological behaviours will be integrated with secondary poro-perm data to draw inference on the relationships between bulk mineralogy, clay morphology, clay types, clay composition and poro-perm values. Integration of the occurrences and/or absences of glauconite and carbonaceous detritus alongside textural parameters will provide clues on downhole depositional conditions in the well.

AAPG Datapages/Search and Discovery Article #90351 © 2019 AAPG Foundation 2019 Grants-in-Aid Projects