Facies Characteristics and Static Reservoir Connectivity of Some Siliciclastic Tertiary Outcrop Successions in Bintulu and Miri, Sarawak, East Malaysia, #51035 (2014)

A significant percentage of the world's hydrocarbon reserves are found in shallow marine sandstone rocks. Understanding the outcrop geometry and static connectivity of these shallow marine sandstones in terms of reservoir model, is a challenging task. This research work focuses on outcrop analysis and characterization of six well-exposed marginal to shallow marine succession in Bintulu and Miri area, Sarawak, East Malaysia. The lateral extents of the studied outcrops are 200 to 500 m, consisting mostly of siliciclastic Tertiary sandstone with mud-rich interval deposits and some isolated sand bodies. The main objective of this study is to characterize the reservoir properties (grain size, petrography, poroperm, and static connectivity) of different sandstone facies to a construct 2-D intermediate-scale model from outcrop. Techniques involve field description in terms of facies distribution, measurements of dimensions of sand bodies and rock sample for grain-size analysis (Folk and Ward methods), and petrographic analysis (by point count method for porosity, sorting, grain-size and sand-mud percent) and poroperm (for porosity and permeability). These were used to quantify and examine seven different types of sandstone facies; i) hummocky cross-stratified sandstones (HCSS), thickness varies from 0.5 4 m, ii) herringbone cross-bedded (HBSC), thickness from 1 7 m, iii) trough cross-bedded sandstones (TCB), thickness from 0.5 2 m, iv) wavyto flaser-bedded (W-FBS), thickness varies from 2–9 m, v) cross-bedded sandstone (CS), thickness from 0.5–3 m, vi) bioturbated sandstone (BS), thickness from 1 – 5 m, and vii) massive sandstone (MS), thickness from 1–5 m. These results show that sandstones of HCSS and HBSC are better sorted, with minimal mud content, and the depositional pattern indicates increasing vertical and lateral connectivity, even in bioturbated rich sand, as compared to other sandstone facies. On the other hand, sandstones of BS and CB are of poor quality in terms of grain sorting and poroperm. Based on these results, a 2-D outcrop model is constructed providing additional insight into the significance of small-scale heterogeneity and static connectivity of shallow marine sandstone deposits.