Geothermal Energy is the Ethical Energy Source for the Future Will Gosnold Dept. of Geology and Geological Engineering Donald Poochigian Dept. of Philosophy and Religion

Geothermal Energy Generation in Oil and Gas Settings Conference March , 2006 Southern Methodist University Gas/presentations.htm

Outline Heat flow and subsurface temperatures Thermal blanketing effect of shales and heat advection in regional groundwater flow systems Thermostratigraphy Bottom hole temperatures and equilibrium temperatures Estimates of the energy resource

21st Century Global Warming Climate Simulations for IPCC 2007 Report ► Climate Model Sensitivity ~ 2.7ºC for 2xCO2 (consistent with paleoclimate data & other models) Source: Hansen et al., to be submitted to J. Geophys. Res. The energy source we choose for the future must be as free as possible from detrimental environmental impact.

Normal continental heat flow regions can have good geothermal resource potential. The thermal blanketing effect of low conductivity rocks such as shales focused distribution of heat by advection in regional groundwater flow systems enhance geothermal potential. Heat Flow

Geothermal Map of North America, 2004 D. Blackwell and M. Richards, Eds.,

Most of the heat flow sites in Nebraska and South Dakota were drilled with funding from the US Department of Energy’s geothermal programs.

T-z profiles in Nebraska from DOE Geothermal Program

T-z profiles in South Dakota from DOE Geothermal Program

D.D. Blackwell, 2006

Favorable conditions for EGS resources are: Depths less than 7 km Temperatures >150°C. There are at least 17 million km 2 with these requirements Total thermal energy potential ix 8.6 x Joules.

The EGS resource base for Texas alone (temperature above 150°C(300°F) and depths less than 7 km ) is 255,000 EJ, or 4.1x10 8 MW secs-20yrs. If a recovery factor of 1% is used there is still 4.1x10 6 MW sec for 20 years available (the present installed electrical power capacity in Texas of 0.1x10 6 MWe). The US Geological Survey has estimated the resource in the geopressured setting in Texas and Louisiana to be 1.74x10 14 MW-20 yrs plus the dissolved gas (109 mcf). The geothermal estimate of the USGS is in addition to the EGS component of the resource. The dissolved gas geopressure also is an additional resource that would be otherwise uneconomical to produce.

Heat flow contours of South Dakota and Nebraska showing the effects of regional groundwater flow

The site at Burton, NE provided the crucial piece of evidence for groundwater flow as the source of the thermal anomaly.

A simple geological profile tested a model of the thermal effects of water flow from the Black Hills eastward.

Geothermal Map of North America, 2004 D. Blackwell and M. Richards, Eds.,

Thermostratigraphy is the application of Fourier’s law of heat conduction to calculate temperature at depth Determine Q from equilibrium T-z and K. Assume Q is constant, K and dz are known

Estimate geothermal energy in ND and SD

Colors are temperature, contours are depth (m), lines are county boundaries

BHT’s and Observations Although BHT data are useful, they often do not indicate actual temperatures at depth. The example from the Williston Basin is typical.

q r = ρc v ad(t-t ref ) The energy resource in Joules is calculated by Surfer © GRID routines were used to calculate the volume of the formation above the reference temperature, e.g. 90 °C Madison Fm = 1476 EJ

Energy estimates for the Williston Basin Coal ~ 118 EJ Geothermal ~23 EJ Oil ~ 20 EJ

Summary Normal continental heat flow and subsurface temperatures characterize most of the region. Thermal blanketing effect of shales and heat advection in regional groundwater flow systems cause regional thermal anomalies. Heat flow, thermal properties, and stratigraphy can be used to determine subsurface temperatures with good accuracy. Bottom hole temperatures and equilibrium temperatures may differ. Temperatures of 180 °C can be found in the deeper regions of the Williston Basin and temperatures greater than 90 °C occur widely in the basin. In general, the recoverable stratabound geothermal resource in the region exceeds the energy that could be recovered from oil.

Philosophical Questions How long will oil last? When does the world cross the threshold for disastrous climate change? What can the scientific community do?

North Dakota morning commute “If you consider it a sport to gather your food by drilling through 8 inches of ice and sitting there all day hoping that the food will swim by, you might live in North Dakota.” Jeff Foxworthy