Analysis of convective heat transfer in deformed and stratified aquifers associated with Frasch thermal mining

This paper presents numerical experiments designed to simulate heat transfe r in deformed, stratified geologic formations during Frasch thermal mining operations in the Delaware Basin. In such operations, superheated water (16 3 degrees C) is injected into permeable ore zones to melt and mobilize sulf ur, The efficiency of Frasch mining depends largely on various aspects of h ydrologic controls and geologic factors, such as directing heat flow toward target areas and minimizing heat dissipation through advection and conduct ion in ore zones. Numerical modeling techniques were used in the search of an optimum thermal mining strategy for maximum sulfur recovery in various g eologic settings present at the Culberson Mine, west Texas. The sample calc ulations illustrate heat transfer patterns in inclined, folded, and fractur ed geologic formations. Important results presented include the controls of geologic structures on directions and rates of heat transfer and ground wa ter flow a display of field evidence for the occurrence of thermal convecti on in permeable ore zones, and a depiction of heat transfer during a therma l mining operation proceeding down-dip along an inclined geologic unit. Mod eling results and field data strongly support the hypothesis that thermal c onvection occurs and controls the heat transfer process in inclined ore zon es. Simulations further suggest that the current thermal mining practice, w hich proceeds down-slope along an inclined ore zone, may result in lowered ultimate sulfur recovery. In this mining approach most heat migrates up-slo pe where the rock's permeability is enhanced by previous sulfur extraction, rather than down-dip toward the target area.