Influence of Composition and Pore Geometry on Immiscible Fluid Flow through Greensands: Development of Neutron Transmission Methods and Image Analysis

Doktorsavhandling, 2002

The effect of the mineralogical composition and pore geometry of sediments on the distribution as well as the flow of immiscible fluids are of importance when evaluating petroleum reservoirs. Greensand containing the clay mineral glauconite is a complex reservoir rock type. Evaluation of greensand reservoirs can be problematic due to the ductile and micro-porous nature of glauconite. The objectives of this work are to evaluate the feasibility of neutron transmission methods to be used for core analysis and to evaluate to what extent composition and pore geometry affect fluid distribution and fluid flow. Greensand samples from different locations were investigated by means of core analysis, determining fluid saturations and flow properties. Neutron transmission methods were used to resolve the spatial distribution of variations in fluid saturations. The mineralogical composition and pore geometry were determined by petrographical studies and image analysis. This work shows that neutron transmission analyses utilising fast neutrons can be used for determining fluid saturations. Analyses utilising thermal neutrons can resolve the spatial distribution of fluids in two and three dimensions. The mineralogy and pore geometry clearly have an effect on fluid distribution and flow. Most of the irreducible bound water is found within the pores of glauconite and other clay minerals. The non-wetting oil is situated in the intergranular pore space and a weak link between residual saturation and clustering of large pores was found. The image porosity determined by petrographic image analysis represents the effective porosity. The absolute permeability can successfully be estimated using the Kozeny equation and data from petrographic image analysis. Relative permeability and immiscible fluid displacement characteristics were related to pore geometry determined by petrographic image analysis. To sum up the work, it shows that conventional core analyses (gas porosity and permeability) on glauconitic reservoir rocks should be complemented with petrographical studies and image analysis. This would provide a more rational analysis of reservoir volumes as well as conditions for production strategy.