SIMPLIFIED MODELING TOOLS TO ESTIMATE CO2 AND BRINE LEAKAGE AND THE AREA OF REVIEW

Injection of CO2 into deep formations leads to a multi-phase flow problem that may involve important mass exchange between phases, non-isothermal effects, and complex geochemical reactions. In addition, because enormous quantities of CO2 must be injected to have any significant impact on the atmospheric carbon problem, the spatial scale of the problem becomes very large. Broad questions involving the fate of the injected CO2, including possible leakage of CO2 out of the formation, as well as the fate of displaced fluids like resident brines, lead to very challenging modeling and analysis problems. Furthermore, important leakage pathways can be very localized, and their properties can be highly uncertain, with an example being the very large number (millions) of old oil and gas wells in North America which can serve as potential leakage pathways. With leakage pathways like old wells included in the problem definition, an overall analysis of the system requires complex multi-phase flow physics to be resolved over multiple length scales. The high uncertainty associated with the condition of old wells leads to the need for a probabilistic approach. These requirements render standard numerical simulators ineffective due to excessive computational demands. A series of simplifying assumptions may be proposed to provide more efficient numerical calculations, even to the point of allowing for analytical or semi-analytical solutions. Such simplifications, while restrictive in their assumptions, allow for large-scale analysis of leakage in a probabilistic framework while capturing much of the essential physics of the problem. These simplified models also allow for the development of relatively simple user interfaces, including web-based tools, which can provide very fast estimates for plume extent, leakage out of the target formation along a "typical" leaky well, and extent of pressure perturbation in the domain. Example calculations illustrate the utility of these methods, and show how general multi-scale approaches can provide solutions for important practical problems. In this presentation we will focus on the use of a web-based interface that allows simplified but practical calculations to be performed, including sensitivity analyses and studies of system response to different injection scenarios.