This paper is part of my thesis, which uses the concept of stratigraphy sequence to model the heterogeneous facies of Upper Lakat and Tualang sand-reservoirs. Upper Lakat and Tualang Formations consist of alternating sandstones, siltstones and shales, deposited in fluvial to transitional continentalmarine environment during Late Oligocene to Early Miocene. They are well-known as reservoir rocks, comprise 8 (eight) sand-reservoirs productive in Bengkalis oil-fields. Based on the unit genetic, we suggest 8 (eight) Flooding surfaces (FS) as sand-reservoir marker and 12 (twelve) sub-flooding surfaces (sub-FS) as stratigraphic marker to distinguish body facies of Upper Lakat and Tualang sand-reservoirs, namely Fluvial Channel, Distributary Channel, Distributary Mouth Bar, Mouth Bar, Tidal Estuarine and Storm Deposit. In general, geometry of the sands-reservoir facies are elongate and perpendicular to shoreline influenced by tidal. Southern Bengkalis paleogeography at Upper Lakat and Tualang time interpreted from fluvial to delta systems, which the sediments provenance are quartz recycled, dominated by subarkose sandstones consist of quartz rich, probably derived from Malacca Terrane basement high in northern part of Bengkalis Trough, controlled by sea-level change transgression when tectonic quiescence during Late Oligocene to Middle Miocene.
Author : Fitriani Indah Pratiwi, V. Bonny Indranadi, Budianto Toha