RESERVOIR GEOMETRY IDENTIFICATION OF TIDE DOMINATED ESTUARINE ENVIRONMENT DEPOSITS AND ITS IMPLICATION TO RESERVOIR QUALITIES: CASE STUDY WITHIN THE UPPER SAND OF BEKASAP FORMATION, GADANG FIELD,CENTRAL SUMATRA BASIN, INDONESIA

摘要

Gadang Field is one of hydrocarbon field which located in Central Sumatra Basin. The production in sand reservoir of the upper part of Bekasap Formation in this field identified is still not optimum. Because of this term, need a geological understanding of reservoir body for future potential development by generate a redefinition of reservoir to understand the condition of reservoir, such as geometry, distribution, and quality of reservoir for proper plan/method in the future development. The methods that are being used in this study are depositional environment interpretation by core data in the sand body of the upper part of Bekasap Formation; understanding geometry and distribution of reservoir by analysis from gross facies unit map and net sand unit map; and characteristics of reservoir determination by using vshale and effective porosity. This study is using 83.5 feet core data from 2 wells and well log data from 16 wells. Core detail description was end up with two facies associations identified, named cross-bedded - coarse sandstones facies association (estuarine channel) and flaser-laminated - fine sandstones facies association (tidal sand flat/sand bar). This two facies associations were interpreted as tide dominated estuarine environment deposit consider with estuarine depositional environment model developed by Dalrymple (1992). By geometry analysis, there are two different geometry of reservoir from this one reservoir zone, such as "channel" sand body (estuarine channel) and "tidal sand flat/sand bar" sand body (tidal sand flat/sand bar), which influenced by mechanism of depositional environment from each facies. Reservoir characteristics analysis based on vshale and effective porosity, indicate that the sand body which deposited in estuarine channel relatively has a better reservoir quality than the sand body which deposited in tidal sand fLat/sand bar.