Lori Manoukian

1st Class Honours

            Reservoir characterization through the identification of flow units is an important step in resolving challenges faced in the production of oil and gas.  This study investigated the vertical variations in reservoir quality and heterogeneity of the Lower Mississauga Formation, penetrated by the Venture B-13 Well of the Sable Subbasin, offshore Nova Scotia.

            Core logging, thin section analysis, permeability and porosity data were used to:  1) identify lithofacies and microlithofacies within the Venture B-13 Well, 2) identify and analyse factors that lead to reservoir heterogeneity, and 3) recognize vertical permeability variations.  Flow units could be defined on the basis of measurements of permeability and porosity corresponding to grain size, bioturbation, lithology cementation, and clay content.  A semi-quantitative system was designed to allow the factors to be rated relative to each other.  Application allowed for detection of potential flow units and their individual strengths.

            The Lower Mississauga Formation at Venture B-13 corresponds to four depositional environments.  Lithofacies 1 consists of oolitic limestone interpreted to be of a shallow marine sub-tidal zone.  Microlithofacies subgroups of lithofacies 1 include bio-oosparite and oobiosparite.  Facies 2 contains shales of an interpreted shallow marine setting.  Lithofacies 3 comprises interbedded sandstone and shale of a tide-influenced nearshore shallow marine setting.  Lithofacies 4 consists cross-stratified calcareous and micaceous sandstone.  Its depositional environment is interpreted as a low-energy shoreface.  Associated microlithofacies range from medium-grained sandstone to fine grained silt, with a slight variation in mineralogy.  A steady increase  in porosity and permeability values from lithofacies 1 to 4 is observed.  Facies 4 micaceous sandstones have the highest potential for reservoir rocks.

            Fifty-six potential flow units and 48 major flow units were identified with a wide range of preferential flow values.  Changes in permeability and porosity are attributed to a change in depositional environment, diagenetic processes and activity of paleo-organisms.  Enhanced flow unit definition could allow for strategic drilling in order to improve long term hydrocarbon production rates.

Keywords: Lower Missisauga Formation, Sable Subbasin, Offshore Nova Scotia, permeability, diagenesis, lithofacies, microlithofacies
Pages: 130
Supervisor: Grant Wach