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Title: Thin bedded reservoirs in the Plio-Pleistocene of the Columbus Basin, offshore Trinidad : challenges of reservoir architecture, quantification and characteristics
Author: Ramnath, Maria Melissa
ISNI:       0000 0004 5360 3382
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2015
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The Columbus Basin, offshore Trinidad, is a mature gas producing basin with a number of major fields now in decline. Focus for infield exploration and production is shifting, with thin bedded sandstones as a secondary pay target. This basin is exceptional as age equivalent analogues to the subsurface reservoirs are exposed along the south east coast of Trinidad at Mayaro Bay (16 – 25 m sections). This research utilizes these outcrops and integrates findings with subsurface core data to present an improved understanding of thin bedded sandstones in three significant areas: 1) depositional setting on a wave dominated delta through description and interpretation of their large scale architecture and facies associations, 2) reservoir quality and connectivity of the facies and microfacies that comprise these heterolithic units through petrography and pore system characterization and 3) pore scale reservoir quality and connectivity through micro CT imaging and 3D modelling of their pore system morphology. Detailed sedimentological analysis has revealed that thin beds are highly interbedded units with thicknesses of 0.1 – 10 cm and have a lenticular geometry. Their lateral extent, controlled by their exposure, varies from 3 to 10s m in some areas. Field sampling and microfacies analysis, revealed five distinct lithofacies types and five microfacies types that make up two principal facies associations (FA): (FA1) axial distal delta front facies and (FA2) lateral distal delta front facies. The reservoir quality poroperm data achieved for the thin sandstones of these two facies associations are consistent with routine core analysis data from basin core and industry assigned values for conventional thicker bedded sandstones, inferring their secondary reservoir potential. Utilizing new techniques such as X-Ray tomography, a high resolution 3D model of the thin sandstone pore systems has been created for qualitative and quantitative reservoir characterization, especially vertical and lateral connectivity within the thin bedded units. This detailed dataset of 3D pore dimensions that can be used as conditioning data for other reservoir models. The observations and conclusions of this research give an insight into the depositional architecture and thin bedded sandstones on a distal delta front and their associated reservoir properties and connectivity mechanisms that facilitate an effective reservoir. These findings may inform and guide future exploration and appraisal, development and production and well completion and configuration programmes for thin bedded reservoirs as explained by the implications and recommendations at the end of this thesis.
Supervisor: Not available Sponsor: Government of Trinidad and Tobago ; bpTT
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Thin bedded sandstones ; reservoir quality