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The Business Of Geothermal Power: From Conventional To Unconventional… ‘Sedimentary Basins’

Richard J. Erdlac, Jr., Ph.D., P.G. (TX, PA)
Erdlac Energy Consulting EEC

Existing geothermal power production in the U.S. has focused on western states like California and Nevada. This has resulted in over 2800 MW of online geothermal electrical power being produced every hour. Over a one year period this production is the equivalent to over 15.2 million bbls of oil or over 83.7 million mcf of gas. As of May of 2007, new reported additional geothermal power development activity was over 2400 MW.

However, past investigations by the AAPG, USGS, and the DOE have shown the presence of an untapped geothermal resource ignored in sedimentary basins. This potential stretches from the Gulf Coast north through many of the other oil and gas producing states into the Williston Basin. Existing turbine technologies, such as a flash steam or binary power plant, make acquisition of this resource from wells drilled in sedimentary basins a known straight forward process. The advent of skid-mounted micro-turbines less than 1 MW in size allows for expanding the amount of production to lower temperatures a lower water flow rates.

Various temperatures and flow rates can be used to generate power of 25 kW/hr to around 2.5 megawatts/hr from a single well. This power can be used for offsetting electric demands at a field or it may be of sufficient production to be sold into the power grid as a base load renewable resource. Two example wells, from the Permian Basin and the Texas Gulf Coast, suggest net power outputs of 1.4 MW and 3.1 MW respectively from hot water, entrained natural gas, and horsepower from the fluid flow.

Exploration and development costs vary depending on the size of the resource, the availability of the electrical delivery infrastructure, and the location of the resource. In general, the larger the resource the less expensive the development cost. Similarly a hotter resource (i.e. 284oF) will result in lower capital costs than a resource that has a lower temperature (i.e. 212oF). Proximity to an existing electrical infrastructure decreases development cost, especially when cost for high voltage lines can be $1 million per mile.

Location of the resource may have the greatest overall impact on the project cost. Existing geothermal power projects have been in the western states in arid areas where the resource can at times be blind with little to know surface manifestation. Federal lands are often involved, along with the need to build a delivery infrastructure. Time between initial explorations, to capitalization, to final production can take 5 years. The prime advantage to these areas has been heat reservoirs of several 10’s of MW at shallow (i.e. 5,000 ft) depths. Capital costs in a sedimentary basin for geothermal production will be very different. Sedimentary basins that have been explored for oil and gas generally have a readily available electrical delivery system already established. The size of the resource may be similar to the western states, but the depth is substantially greater, easily on the order of 18,000 feet in some areas. However large amounts of data already exist from oil and gas drilling that can be used for geothermal evaluation in an area. Consideration of the available hot water in the subsurface can improve overall economics in a mature basin by providing production of three energy resources…oil, gas, and hot water for geothermal electrical power. Much of the existing oil and gas infrastructure will thus reduce the overall cost of such an energy development. The payoff is a renewable resource whose produced value can be in the several billions of dollars just in Texas alone.

Geothermal energy development allows the existing oil and gas industry to move into renewable energy production using the personnel, data, and technology already in existence. It offers the opportunity for improving company PR and offsetting of future potential carbon taxes that would affect fossil fuel production. As fossil fuel production continues to decrease over time, energy production and financial stability can be found by managing the production of an energy resource that will continue to renew itself…Geothermal.

AAPG Search and Discovery Article #90089©2009 AAPG Southwest Section Meeting, Midland, Texas, April 26-29, 2009

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