Modified salinity water (MSW) core flooding tests conducted in carbonates often exhibit a delay in the additional oil recovery. It has been suggested that the ionic adsorption process controls this delay. In this study, we examine the adverse effect of the adsorption process on the performance of MSW flooding in various models categorized as layered and heterogeneous reservoirs and a North Sea field sector model. To evaluate the impact of porous media's heterogeneity on the delay caused by the adsorption, we introduce the net present volumetric value based on which the cost of delay is calculated. This evaluation is achieved by comparing the calculated cost of delay for heterogeneous systems and that of their equivalent homogeneous porous media. It is found that, as the level of reservoir heterogeneity increases, the adverse effect of ionic adsorption on the improved oil production decreases. Further, computational results suggest that the connectivity index, which is defined as the effective permeability between injection and production wells divided by the average permeability, is a better alternative to the vorticity index to describe the impact of the delay of additional oil recovery in heterogeneous reservoirs subjected to MSW flooding.
Water weakening effect in the chalk reservoir causes additional compaction due to the interaction between the rock and injected water. To consider the impact of the coupled interactions on the fluid transport (e.g., production) and reservoir deformation due to the seawater injection into the chalk reservoirs, in this study, a wrapper is developed in Matlab that combines Eclipse 100 reservoir simulator and Visage geomechanics simulator to capture the induced alteration of mechanical and petrophysical properties of chalk. Here, we utilize the history-matched reservoir model of the Halfdan sector model to investigate the impact of the temperature-dependent fluid-rock interactions induced by sulfate adsorption on the surface of calcite grains on the deformation behavior of the reservoir during waterflooding. Our sector-scale simulation results show that while considering the geomechanics model has a considerable impact on calculated reservoir pressure and recovery, the impact on history matched data due to water weakening is not significant when yield stress and bulk modulus are expressed as functions of temperature and sulfate concentration for the Halfdan model. We argue that the minor contribution of the water weakening effect at in situ conditions is due to 1) the relatively high initial water saturation in the water flooded section of the reservoir and 2) the low initial temperature (70 ˚C) of Halfdan reservoir, especially towards the northern part of the Danish North Sea.
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