Burial Diagenesis of Coal-Bearing Mudrock and Its Relationship to The Evolution of Pore Types and Abundance Rosmalia Dita NUGRAHENI*, CHOW Weng Sum*, ABDUL HADI bin A. Rahman*, *Geoscience and Petroleum Engineering Department Universiti Teknologi PETRONAS, Tronoh, 31750, Perak, Malaysia Corresponding author : [email protected] Keywords – mudrock, burial diagenesis, pore-types, pore-network, pore-distribution Abstract- The coastal region of Sarawak is primarily covered by thick Neogene coal-bearing mudrocks. The mudrocks are composed of shale or mudstone, alternating with sandstone layers and locally intercalated with coal beds. Carbonaceous material in the mudrocks in the form of maceral vitrinite is substantially important to generate gas. The study of pore-types and networks in mudrocks related to burial diagenesis provides the framework on how gas can be stored and flow through the pores. Nano- to micrometer-sized pores were observed in the matrix-related pore network of the mudrocks. These pores together with natural fractures form the flow path network that allows gas flow from the mudrock. The pore types associated with mineral particles are subdivided into interparticle and intraparticle. During burial, mudrocks undergo compaction that decreases substantial pore volume and it also causes thermal hydrocarbon maturation, where organic matter (OM) changes to kerogen. As such, the porosity and gas content is directly associated with the TOC content. INTRODUCTION The types of pores in the rocks are determined based on the relationships to particles as mentioned by Pittman, 1979. Pores formed by the arrangement of mineral grains can be interparticle (interP) and intraparticle (intraP). Organic matter also has intraparticle pores (intraP OM). Fracture also contribute to the rock porosity. Identification of pores, such as type, size, arrangement of pore, connectivity and wettability provides an insight to reservoir properties. Micro- to nano- scaled pore spectrum is easily recognized using scanning electron microscope (SEM), whilst macro-scaled pore can be seen under polarized microscope. The porosity of the mudrocks of the Balingian and Begrih Formation, Sarawak were studied in this project. RESULTS and DISCUSSION Typical interparticle pores are commonly found in the young or shallow-buried sediments of the Balingian and Begrih Formation with characteristics of well-connected and permeable layers. Subsequent overburden stress and diagenesis occurred during burial and closed the InterP pore spaces and plugged the pore throats. Ductile or plastically deformable grains (e.g. clay floccules, mica and organic matter) exacerbate the rate of porosity loss. The age of the