Reservoir Characterisation of Tenggiri Blocks through Rock Physics, AVO Analysis and Neural Network

Abstract

Extended Abstract The study area is located in the shallow water of Tenggiri Basin, a region where numerous gas fields have been discovered and which has a great deal of remaining potential. In order to fully evaluate the area a new broadband seismic dataset was acquired and an integrated subsurface study was initiated. The goal of the study was to evaluate the discovered fields and new development area for prospective hydrocarbon potential. Furthermore the study sought to gain deeper understanding of the stratigraphic architecture and insight into how to optimally develop these complex reservoirs. This study consisted of a detailed integration of modern broadband seismic data, rock physics, AVO, attribute studies and seismic facies classification. The reservoir characterization study has improved our understanding on the lithological distribution and increase the confidence of the established depositional model for the Miocene reservoirs. Introduction The Miocene reservoirs of Tenggiri Block are challenging to characterize as they are arealy discrete, close to or below tuning and geologically complex. The reservoirs are interpreted to have been deposited in a low relief fluvial-estuarine to shallow marine setting. This paper documents three intervals, presented in order of increasing geological and geophysical complexity, named: Miocene C-10, Miocene C-20 and Miocene B-10. All 3 intervals are penetrated by 4 existing wells. The wells contain an excellent data base including checkshot survey and shear logs; for the generation of synthetic seismograms and AVO modeling. The block is fully covered by a recently acquired modern broadband 3D seismic survey shot in 2012 and processed through VTI anisotropic Pre-Stack Depth Migration in 2013. The study area has significant occurrence of coal and carbonaceous shale throughout. Coals and carbonaceous shale can mask bright amplitude hydrocarbon reservoirs and the effect is especially prominent for thin bedded reservoirs. Interval C-10 is characterized by NW-SE trending channel system penetrated by one well with approximately 50 feet of gas sand. According to wedge modelling 50 feet is approximately close to tuning. Interval C-20 is another adjacent event situated directly below Interval C-10, none of the existing wells have penetrated any of the prospective seismic anomalies. Based purely on available seismic extractions, it is suggested that Interval C-20 shows smaller channels also trending NW-SE while the majority of the southeastern area is covered with coal. Additionally Interval C-20 appears to contain a perpendicular NE-SW channel system that is interpreted to be shale-filled. Based on well data, Interval B-10 is characterized with moderate quality thin sands intercalated between the presences of laterally extensive coal layer and carbonaceous material patches. Interval B-10 has many channel-like features however they are significantly more esoteric and lack the obvious orientations of the C-10 and C-20 Intervals.