Analysis of Salt Effects on the Depletion of Fractured Reservoir Blocks

Abstract

To simulate flow problems in which the transport of a variable salinity hrine occurs, the TOUGH2 code with an equation-of-state module able to handle three-component mixtures of water, sodium chloride, and a gas has been used. This EOS module can describe liquid and gas phases, and includes precipitation and dissolution of solid salt. The reduction of rock porosity because of salt precipitation is also considered, as well as the related decrease of formation permeability. We have simulated fluid production from tight matrix blocks under conditions considered representative of systems to examine some effects of permeability reduction and vapor pressure lowering due to salinity. Block depletion occurs by a "well on deliverability" placed in the fractures, and cases with different initial NaCl concentration and matrix permeability have been studied. We find that for initial NaCl mass fractions above threshold values, "sealing" of the block occurs and large amounts of fluid may not be recovered. As sealing occurs in the outermost grid element, the matrix block partitioning according to the MINC method has been varied to analyze discretization effects.