Understanding The Reservoir Heterogeneity In Southern Gulf Of Thailand For Optimal Development: Integration Of Borehole Image Logs And Core For High Resolution Static Model

Abstract

Optimal development of a Southern Gulf of Thailand hydrocarbon field requires the best possible placement of wells accommodating the reservoir heterogeneity inherent of the gross fluvial sedimentary environment where challenges are aplenty with lateral facies variations and compartmentalization. Integration of borehole image logs and core helps in understanding the architectural elements of the sediment deposition style at highest resolution, thereby providing robust understanding of reservoir heterogeneity and extent of the channelized sands helping better planning of infill producers and injectors. The study well was logged with borehole images for ~3400-ft (1036 m. equivalent) and drill-core was taken in an interval of 60-ft (18 m. equivalent). The common interval of image log and core helped in achieving the core-image calibration, and using the understanding developed to extrapolate for the whole logged interval to develop a single-well sedimentary interpretation. Different facies like massive sands, cross-bedded sands, ripple cross-laminated sands, parallel laminated shale and bioturbated shale were identified in the limited cored interval, associated with fluvial and lacustrine environments. The dimensions of individual units, like a 10-ft (3 m.) cross-bedded channel-sand helped in developing a conceptual model for the possible lateral extent, away from the borehole well that further helps in updating the static model for sub-seismic events. The regional structural dip was almost flat (~2-deg) with a south-westerly azimuth whilst the cross-bedded sands were low-angled, averaging around 10-deg towards north-west. Also, a strong structural grain of NW-SE strike was observed and possible sub-seismic faults were interpreted that tend to offset the sand-bodies. It is imperative to understand the connectivity of sands both structurally and facies-variation wise as they are often separated by lacustrine shale, thereby providing barriers during water injection. Single-well sedimentological interpretations built with core and image logs is further incorporated in the static model of the field. The core-image calibration done in a well or two not only reduces the need of full coring later on, but also with image logs in few more wells helps in delineating the high resolution reservoir heterogeneity of the depositional architecture for optimal field development. This can further help in injection planning hinging upon the connectivity or lack of that within individual sub-elements.

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