--> ABSTRACT: Use of a Reaction-Transport Model for Assessing the Geochemical Fate of Hazardous Wastes by Deep Well Injection, by Xinghui Liu, Peter J. Ortoleva, Randy Larkin; #91020 (1995).

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Use of a Reaction-Transport Model for Assessing the Geochemical Fate of Hazardous Wastes by Deep Well Injection

Xinghui Liu, Peter J. Ortoleva, Randy Larkin

The injection and migration of hazardous waste fluids in deep formations is an environmental issue of great concern. The Sandia Waste-Isolation Flow and Transport Model (SWIFT) Is often the numerical model of choice since it allows the flow and transport of wastes by including variable pressure, elevation, temperature, fluid viscosity and density. However, the SWIFT model cannot account for chemical reactions between rock, wastes, and formation-fluids and their effects on contaminant transport and rock texture. These reaction and transport processes are incorporated in a numerical code CIRF.A that we have developed and used to analyze the fate of waste fluids as well as other geochemical problems.

In this study, a typical case scenario of waste injection was simulated by both the SWIFT and CIRF.A models. The results carried out by the two models compare favorably without rock-fluid interactions. By allowing chemical reactions in our model, results show that waste fluids dissolve some minerals. This changes the distribution of intrinsic permeability and hence the pattern of fluid migration. Other simulations indicate that precipitation due to reaction may cause severe damage to rock permeability. This can inhibit the injection on the one hand, but may also help to select desirable formations to eventually trap waste fluids by creating environmentally safe, hydrologic seals.

In heterogeneous formations, reaction-transport processes may lead to reaction-front fingering. In multiphase flow, viscosity contrasts can also result in viscous fingering. Examples in this study also address the coupled, nonlinear fingering phenomena occurring in geochemical modeling problems of single- or multi-phase flow.

This study provides valuable insight into the geochemical fate of hazardous wastes disposed by deep well injection. Results presented demonstrate that CIRF.A can be a valuable tool for assessing deep well injection.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995