DEVELOPING REALISTIC MODELS OF HETEROGENEITY FOR FAULT-CONTROLLED HYDROTHERMAL FLUID FLOW

Most hydrothermal systems that discharge at the land surface are fault-controlled; thus, modeling the migration of fluids between the reservoir and the discharge area requires the specification of a realistic set of fault hydraulic properties. Unfortunately, few data exist to constrain fault heterogeneity, and faults are commonly simulated as either high- or low-permeability structures (conduits or barriers) of uniform effective properties. Alternatively, some investigators have made use of “speculative” property distributions to investigate the sensitivity of thermally-driven systems to fault heterogeneity. Although these studies have made important contributions to our understanding of the role of heterogeneity in hydrothermal systems, there is a clear need for better models of the spatial distribution of fault properties. Here we discuss our efforts to develop realistic simulations of heat and fluid flow in the Borax Lake hydrothermal system in southeast Oregon, USA, and present several alternative models of heterogeneity for the Borax Lake fault. The permeability distributions presented are conditioned on field observations at the study area, and the results of coupled thermal-hydrologic simulations are used to identify plausible property sets for the Borax Lake system. In addition, we will discuss potential strategies for applying the results of the Borax Lake study to simulations of mass and energy transport in other fault-controlled hydrothermal systems.