Carbonate Build-Up Sweet Spot Targeting Approach, Central Luconia, Sarawak, Malaysia

Abstract

Sarawak exploration’s creaming curve, mainly dominated by dry natural gas, is still rising from recent discoveries in the Late Miocene platform carbonates and pinnacle reefs of Central Luconia sub-basin. The geological province of Central Luconia extends over 40,000 sq.km with more than 200 carbonate build-ups, which grew on regional and local highs of deep graben structure. PTTEP acquired exploration block namely SK410B in 2016, and completed 3D broadband seismic acquisition in 2017. In order to successfully explore remaining hydrocarbon potential in a mature basin, comprehensive exploration approach for well targeting in carbonate reef is established. The study includes reservoir characterization using seismic quantitative interpretation (rock physics, AVOs, and seismic inversion) integrating with carbonate growth architecture identification subject to sequence stratigraphy context. The carbonate growth architecture, including of pre-growth setting, growth history according to sea-level changes, build-up architecture restoration, facies classification and reservoir quality prediction, is interpreted on 3D seismic that corresponding to sequence stratigraphy context integrating with well data and conventional core interpretation. Diagenesis features, such as tight layer, karst, and cavern, are anticipated to express in this study. The difference of carbonate depositional facies would correspond to different rock properties and reflectivity in seismic. Rock physics, AVOs, and Seismic Inversion are aim to achieve reliable seismic reservoir characterization resulted by applying rock physics analysis and 3D seismic quantitative interpretation techniques. The goal of the inversion is to output volumes of elastic properties, probabilistically identified litho-facies, and petrophysical properties which will help to properly well targeting into the sweet spot of carbonate build-up. Moreover, it is possible to avoid severe drilling fluid losses into the karst and cavern feature. According to drilling history, most of pinnacle reef of Central Luconia, where adjacent to the West Baram line, are situated in the high pressure high temperature environment. Hence pore pressure is the main drilling risks that effect well completion. Integrated Pore Pressure & fracture gradient prediction for wellbore stability analysis study is initiated to achieve the multi-aspects analysis derived from well data and seismic data. The result provide a good understanding of the overpressure generating mechanism as well as its magnitude and distributions spatially and vertically according to 1D analysis at input wells. Furthermore, the study use 3D seismic data to guide the overpressure trends and support well design for minimizing drilling risk and successful exploration. PTTEP purpose integrated and comprehensive geological and geophysical approach to successfully explore and well target for carbonate build-up of a mature basin with high pressure high temperature environment.

AAPG Datapages/Search and Discovery Article #90331©2018 AAPG Asia Pacific Region GTW, Back to the Future – The Past and Future of Oil and Gas Production in the Asia Pacific Region, Bangkok, Thailand, September 26-27, 2018