A Simplified Approach to Geochemical Modeling and Its Effect on Well Impairment

Abstract

Abstract Solids can easily cause impairment of wells by plugging flow channels. A source of these solids is the dissolution and subsequent precipitation of minerals caused by transport of fluids out of equilibrium with the host formation. To model these geochemical processes, allowing for the transport of fluids with kinetic reactions, it is necessary to solve the mass balance equations for each component flowing in the medium. This work presents a new approach, based on the method of characteristics (MOC), to greatly simplify these solutions. Based on this solution technique, we build a model that includes kinetic (aqueous-solid) as well as equilibrium (aqueous-aqueous) reactions. We define new dimensionless groups to scale the solution. Unlike many previous geochemical models, we focus on flow that is substantially out of local thermodynamic equilibrium. The MOC model has been tested against results from the more general geochemical KGEOFLOW simulator and against experimental literature data. Results match the KGEOFLOW solution closely, but computing time is reduced at least 50 times. The MOC model can run quite general geochemical problems on a desktop personal computer. We applied the MOC model to a radial flow around a well to study the effect of precipitation, supersaturation, and dissolution on injection well impairment. We focussed on cases in which there was substantial well impairment in calculations based on local thermodynamic equilibrium. Results show that, at certain rates, a well's injectivity can be impaired, though the damage will be less severe than when local thermodynamic equilibrium is assumed. However, injection rates must be unrealistically large to completely prevent damage.