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Mineral Dissolution and Precipitation Rate Laws Predicted from Reactive Pore Scale Simulations
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, IOR 2017 - 19th European Symposium on Improved Oil Recovery, Apr 2017, Volume 2017, p.1 - 15
Abstract
When injecting water into an oil reservoir for pressure support, during an EOR operation or in well treatment operations, the injected water will interact with the formation and the equilibrate with the formation at a distance from the injection point. For some operations the exact composition of the pore water is crucial, and it is of importance to know how fast the chemical interactions are. This is of particular importance when injecting a low salinity brine or optimised brine to improve the microscopic sweep. Normally one uses mixed flow reactors to determine the reaction rates of minerals, in our experience these experiments greatly overestimate the reaction rates compared to core flooding experiment. Core scale simulations, used to interpret the experiment, also showed that the precipitation pattern of secondary minerals must be such that they allow for contact between the original mineral phase and the pore fluid. Thus allowing for a complete alteration of the primary mineral. In this work we present a pore scale reactive flow simulations using a lattice Boltzmann advection diffusion solver coupled with a geochemical solver to study the effect of uneven precipitation and nucleation of secondary minerals and how this alters the effective reaction rates on the Darcy scale. The dissolution of primary minerals and precipitation of secondary minerals alter the pore space and the changes in permeability and porosity are predicted from the pore scale model. We apply the model to chalk, and use chalk geometries obtained from three types of outcrop chalk: Stevns-Klint, Kansas and Liege. The pore geometries have been obtained by FIB-SEM techniques that has been segmented into binary images. The samples have sizes ranges of from 6 to 8 micrometer and a resolution of 10x10x10 nanometers. The pore scale simulations and up scaled rate laws are compared with core scale flooding experiments on the same type of outcrop chalk.