New Mexico Geological Society Annual Spring Meeting — Abstracts

We are in the process of creating a methodology to identify blind geothermal resources in southwestern New Mexico and assess the risk associated with the exploration for these resources. The presence or absence of a hydrogeologic window through Paleozoic, Mesozoic, and Paleogene confining units and younger, fine-grained basin fill forms the basis of the play fairway framework. Hydrogeologic windows are zones where regional or local aquitards are breached by faulting, erosion, or intrusions, allowing relatively rapid vertical flow of heated groundwater toward the surface; this heated water might become trapped below fine-grained facies in the basin fill, resulting in a blind system. A variety of data sets including temperature-depth profiles, bottom-hole temperatures, heat flow, subsurface formation tops, aqueous geochemistry, fault location, and earthquake location have been gathered and organized into ArcGIS layers that can be superimposed to identify signatures of known geothermal systems and to use those same signatures to explore for unknown systems. The formation top data are used to create a series of subcrop maps below the basin fill to locate bedrock highs and syndeformational lows that formed during Ancestral Rockies, Jurassic Bisbee rift, Laramide, and Neogene Rio Grande rift deformation. These maps are the key to defining the hydrogeologic windows.
Conservative element tracers that are commonly associated with geothermal systems (e.g., lithium, boron, bromide, chloride) are used to locate geothermal outflow plumes in shallow aquifers, following an approach first used by Neupauer and Wilson (1999) to identify the location of up-gradient contaminant sources using contaminant concentrations in down-gradient wells. This new exploration concept considers the dynamics of fluid flow and geochemical tracer transport. The up-gradient path of conservative ions from each borehole in the Socorro-La Jencia and Albuquerque basins is calculated using water table contours and a simple particle tracking algorithm. The flow vectors based on Darcy law are used to “upwind” particles across the basins. The calculated paths are then compared to Quaternary and older fault ArcGIS layers to try to identify the source of waters with elevated conservative ion concentrations. Several known and previously unknown geothermal areas have been identified using this approach.

Neupauer, R. M, and Wilson, J. L., 1999, Adjoint method for obtaining backward-in-time location and travel time probabilities of a conservative groundwater contaminant: Water Resources Research, v. 35, p. 3389-3398.