Modeling the Effects of Geochemistry on Well Impairment

by
Aura Nicolasa Araque Martinez, Ph.D.

University of Texas at Austin, 2001
Supervisor: Larry W. Lake

Solids can easily cause flow restrictions by plugging flow channels. A source of these solids is the dissolution and subsequent precipitation of minerals caused by transport of fluids not in chemical 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, 3 computer simulators were developed, UTKFLOW1, UTKFLOW2 and UTKFLOW3, that includes kinetic (aqueous-solid) as well as equilibrium (aqueous-aqueous) reactions for different field applications (production wells, hot or cold water injection and push-pull cycles). This work also defines new dimensionless groups to scale the solution and solves for the specific equilibrium velocity. Unlike several previous geochemical models, this work focuses on flow that is substantially out of local thermodynamic equilibrium.

The UTKFLOW models have been tested against results from the more general geochemical KGEOFLOW simulator and against experimental literature data. Results match the KGEOFLOW solution closely, but with at least 50 times less computing time. In addition, these models can run quite general geochemical problems on a desktop personal computer.

The UTKFLOW models were applied to radial flow around a well to study the effect of dissolution, supersaturation, and precipitation on seawater injection in carbonate reservoirs, water injection in a sandstone reservoir, production from carbonate reservoirs and production from a sandstone reservoir after hot water injection. In general, results show that at nearly all injection rates, mineral precipitation can occur, though the amount will be less than when local thermodynamic equilibrium is assumed. However, injection rates must be unrealistically large to completely prevent precipitation. In the case of production wells, results show that mineral precipitation can occur in the wellbore region. However some water flow is needed to cause significant precipitation to plug the flow channels.

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