D EEP P ERMEABLE S TRATA G EOTHERMAL E NERGY A Means To Extend Geothermal Energy Production To Deep Sedimentary Basins Dr. Richard J. Erdlac, Jr. The University of Texas of the Permian Basin Center for Energy & Economic Diversification Douglas B. Swift Petroleum Consultant Concept Devised & Initiated By: Mr. Douglas B. Swift Dr. Richard J. Erdlac, Jr. West Texas Earth Resources Institute

World Geothermal Provinces

U.S. Geothermal Provinces

United States Geothermal Electric Power Generation Potential (GeoPowering The West - DOE, 2000) Top 3 States: Nevada, California, Utah Other High Potential States: Idaho, Hawaii, New Mexico, Oregon, South Dakota, Texas, and Wyoming

“Texas does not have the sort of readily accessible high-temperature hydrothermal resource that can be used to generate electricity.” “Geysers, hot springs, volcanoes, and seismic activity, all of which are noticeably absent in Texas, mark such regions.” Texas Renewable Energy Resource Assessment, 1995 Statement did not envision DPSGE.

Deep sedimentary basins, (e.g the Delaware, Val Verde, Anadarko, Appalachian) contain high thermal reservoirs which can be tapped for geothermal power generation. Structures in the Delaware and Val Verde Basins have been prolific for natural gas production. These wells demonstrate extensive, highly porous and permeable strata. Geothermal grade temperatures are readily apparent from DST data, BHT tests, and less reliable electric log measurements.

Potential U.S. DPSGE Sedimentary Basins

Texas Oil And Gas District Boundaries

Deep wells (Ellen>15,000’) in central Delaware Basin. Well control courtesy of GDS; Mapped with Geographix.

Subsurface map of borehole temperature (BHT) data from oil and gas wells in the Permian Basin. Black dots: BHT 150 o F (65 o C). Blue dots: BHT = 151 o F to 179 o F (66 o C to 81 o C). Green dots: BHT = 180 o F to 280 o F (82 o C to 142 o C). Red dots: BHT 290 o F (143 o C). Isotherm contours are in thousands of feet below surface. The dark gray area represents the 150 o F isotherm. Adapted from Subsurface Temperature Map of North America (1976).

The basic requirements for an exploitable DPSGE geothermal region are similar to those for oil and gas exploration: 1) a sufficiently high geothermal gradient ; 2) A significantly large, porous and permeable reservoir to receive and heat injection fluids; 3) A seal to contain the system.

Distribution of temperature gradient for wells within the Permian Basin (New Mexico and Texas). Values given in degrees F/100 feet. Data source from the Geothermal Survey of North America. AAPG, 1976.

Distribution of temperature gradient for wells within the Delaware and Val Verde Basins. Values given in degrees F/100 feet. Data source from the Geothermal Survey of North America. AAPG, 1976.

Deep Ellenburger Formation gas fields with BHTs ranging from 115 o to > 160 o C ( 239 o to >320 o F ) are well documented. These temperatures are sufficiently high to generate live steam. A number of the fields studied are prospective for flash power generation. Most are particularly attractive as sources for fueling binary systems.

Distribution of temperature gradient for wells within the Trans-Pecos region of Texas. Values given in degrees F/100 feet. Data source from the Geothermal Survey of North America. AAPG, 1976.

Geothermal Delivery Systems Existing Plant Designs  Dry Steam Power Plants – use steam directly.  Flash Steam Power Plants – hot water under pressure (most common).  Binary Cycle Power Plants – hot water through heat exchanger.  Feedstock Systems – incremental heat in elevated water temperatures. New Plant Designs  Power Tube – iso-pentane & iso-butane into subsurface.

Water temperature (optimum range) 230 o to 380 o F ( 110 o to 193 o C ) Construction costs ~ $1500 per kW including exploration and drilling. 10 Mw plant $15,000,000 (National Renewable Energy Laboratory, 1999)

Canyon Diablo Binary Geothermal Plant Mammoth, California

Alternate Geothermal Technology – Power Tube

D EEP >4 KM (>13,000’) P ERMEABLE S TRATA G EOTHERMAL E NERGY

A N E W D A W N !