Oil – Gas – Geothermal – An Energy Triad Part II: Heat Energy And Risk Mitigation In Delaware-Val Verde Basin Reservoirs
Douglas B. Swift1, Richard J. Erdlac2, and Subir K. Sanyal3
1 Swift-Arrow Geological Consulting; Midland, Texas
2 The University of Texas of the Permian Basin Center for Energy & Economic Diversification; Midland, Texas
3 GeothermEx, Inc.
Studies in the Delaware-Val Verde Basins suggest the potential for generating electrical power from deep sedimentary strata. The regional temperature gradient is complex in form, as demonstrated by lognormal, dual linear, and combined shallow lognormal and deep linear thermal gradient analysis. Calculations suggest an average deep temperature gradient of 29oC/km, with a possible deep strata heat flux of 100 mW/m2.
Devonian, Fusselman, and Ellenburger formations are target reservoirs for heat extraction. Local fracture permeability that reach 2,000 md or more in the Devonian and Ellenburger are higher than the 200 md range at Pleasant Bayou #2 geothermal well in Brazoria, Texas. Temperature measurements between 110 and 180°C are common and appropriate for binary or hybrid power plant development.
Preliminary reservoir engineering and economic study of a Delaware Basin 18,000-foot gas well suggests that as water cut increases, on-site generation for either local use or sale to the grid can offset declining gas revenues and provide an income stream of its own. A hybrid power scheme is envisaged with a gas engine or turbine and a binary-cycle geothermal plant. The studied well had a flowing wellhead temperature of 135°C, and a conservatively estimated payout time of about 6 years. Besides active producers, abandoned wells may be considered for this process. Although project economics depend on temperature and the hydraulic characteristics of the water and gas producing zones, this analysis indicates the potential for generating geothermal electricity from previously unwanted hot brines that accompany gas production in Texas and deep basins elsewhere.