Post-depositional controls on siliciclastic tight reservoirs: Implications from the Oligocene Nyalau Formation (Cycle 1), onshore Central Sarawak, Borneo

Abstract

Abstract Subsurface tight reservoir sandstones of the Oligocene Nyalau Formation (Cycle I), NW Borneo were studied to understand the variability of its reservoir quality with depth, determine major controls responsible for porosity loss, identify reservoir facies and reconstruct paragenetic sequence. Core samples representing an estimated 125 Feet (38.1 m) interval from an onshore well in Central Sarawak were subjected to thin section, Helium porosimetry, inductively coupled plasma mass spectrometry, x-ray powder diffractometry, scanning electron microscopy and energy diffractive x-ray spectroscopy. The sandstones are fine-to-medium grained and comprise of sublithearenite and subarkose primarily sourced from recycled orogenic sources. Four lithofacies base on textural composition and diagenetic events were identified: (A) matrix dominated sandstone, (B) matrix-free sandstone, (C) quartz-cemented sandstone and (D) clay-coated sandstone. Obtained helium porosity, 0.90–11.52% (Average 4.27%) and Klinkenberg permeability,