Diagenesis and sequence stratigraphy of Miocene, Nyalau Formation, Sarawak, Malaysia: A case study for clastic reservoirs

The link between sequence stratigraphy and diagenetic alterations is quite familiar for the last two decades in different types of reservoir rocks. Understanding the lithologic characteristics and diagenetic alterations is key to deciphering the various complex controls on porosity and permeability. Although, the sandstone heterogeneity is a product of a complex history of depositional and diagenetic modifications. However, much deeper augmentation is required to achieve the desired resolution and precision to fill this research deficit. This case study focuses on the diagenesis and reservoir potential of the early Miocene, Nyalau Formation. This study is based on conventional sedimentological and sequence stratigraphical measurements, petrographic observations, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) images and Energy dispersive X-ray spectroscopy (EDS) analysis. The main diagenetic processes are compaction, dissolution and cementation. The Transgressive System Tract (TST) is dominated by iron oxide, calcite cementation, and mechanical compaction in eodiagenesis. In HST (Highstand System Tract), the principal diagenetic signatures are iron oxide cements and/or grain dissolution. In sandstones primary porosity is controlled by deposition and is in the form of interparticle pores. Later, secondary pores become more significant with help of grain dissolution. Diagenetic alterations, e.g. cementation, compaction, dissolution are discussed in the sandstone reservoir within an outcrop sequence stratigraphic framework. Our conceptual model shows that the porosity is controlled by deposition and is preserved in the form of interparticle porosity and later enhanced by secondary grain dissolution. Diagenetic alterations presented here in sandstone reservoir in a sequence stratigraphic framework can help in other similar tectono-sedimentary basins, globally.