Facies Characteristics and Static Reservoir Connectivity of Some Siliciclastic Tertiary Outcrop Successions in Bintulu and Miri, Sarawak, East Malaysia

Abstract

Abstract – 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 extend of the studied outcrops were 200 – 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, pore-perm and static connectivity) of different sandstone facies to construct 2-D intermediate-scale model from outcrop. Techniques involve field description in terms of facies distribution, measurements of dimensions of sand bodies & rock sample for grain-size analysis (Folk and Ward methods), petrographic analysis (by point count method for porosity, sorting, grain-size and sand-mud%) and poro-perm (for porosity and permeability) 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) wavy- to 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, the depositional pattern with 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 poro-perm. On the bases of these results, a 2-D outcrop model is constructed, thus providing additional insight into the significance of small-scale heterogeneity and static connectivity of shallow marine sandstone deposits.

AAPG Datapages/Search and Discovery Article #90194 © 2014 International Conference & Exhibition, Istanbul, Turkey, September 14-17, 2014