American Association of Petroleum Geologists

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Enhanced Geothermal Systems

A Joint AAPG/SPE/SEG Hedberg Research Conference organized through the AAPG Research Committee
March 14-18
Napa, California
Conference Conveners
Gary H. Isaksen
ExxonMobil Exploration Company
Dag Nummedal
Colorado Energy Research Institute, Colorado School of Mines
Peter Malin
Institute of Earth Science and Engineering, University of Auckland

Watch here for Abstracts

Improved understanding of geothermal resources and recent advances in exploitation technologies offers the possibility of a much broader use of geothermal energy sources on a global scale. The principal purposes of this conference was to facilitate knowledge sharing, enhance science and technology networks, foster cooperation among geothermal experts from industry, academia, and government, and identify technology gaps and economic barriers to project implementation. The goal was to develop clarity around recent advances, identify technology gaps, and discuss scenarios and strategies to help develop enhanced geothermal systems in economically viable ways.

Background

Our earth is a bountiful source of heat. Over the last decade, we have greatly improved our understanding of subsurface heat flow and our ability to engineer systems to exploit geothermal reservoirs. As petroleum reserves become more difficult to replace, alternative energy sources, such as enhanced geothermal systems, hold increasing promise for local and regional use as a renewable and sustainable energy source. In this context we are primarily interested in enhanced geothermal systems (EGS), also known as deep geothermal systems. These are defined as engineered reservoirs where a system of fractures is created in an area with elevated heat, water injected through injection wells, and heat is extracted through production wells.

Much of the know-how and many of the technologies required to develop enhanced geothermal systems are well known in the oil and gas industry. These include operating in a safe and environmentally responsible manner, subsurface imaging and mapping, rock properties under different PT conditions, drilling, creation of fracture zones, injector-producer wells, reservoir management, and project economic stewardship. However, many challenges still exist, including controlled fracture pathways, long term pressure maintenance, and project stand-alone economics and risk assessments.

Format

The meeting took place over three days and included single session oral and poster presentations, along with an optional post-conference field trip to the Geysers/Calpine Geothermal Center in Middletown, California. Oral presentations were 30 minutes in length, with discussion by all attendees following each presentation. The poster sessions were linked to the oral presentations and featured prominently in the discussions. The results of the conference will be published in a compendium research volume, hopefully as an AAPG Memoir.

Themes:

The conference covered these major topics:

  1. Recent Advances that address (a) improved understanding of worldwide subsurface heat flow and geothermal reservoirs, (b) links between geothermal reservoir models, heatflow, geodynamics, pressure cells, structural and stratigraphic models, fracture technologies (e.g. fluids in closed and open systems), prediction of migration pathways, charge, stimulation (hydraulic, chemical), and probabilistic approaches to fluid migration and risk analysis.
  2. Subsurface Imaging and Modeling, specifically addressing properties of rocks, faults, and fractures, as well as water and other fluids. Research included reservoir diagenesis and porosity/permeability alteration, artificial fracturing, fracture propagation, PVT, stress and deformation, multi-phase flow, heat flow evolution, fault behavior, and low- and high-temperature processes.
  3. Uncertainty and Risk associated with rock volume interpretations, structural interpretation, migration/flow fairways, resource volume assessments. Project Economics: drilling and completion costs, costs for energy conversions, energy forecasts.
  4. Energy Conversion and Recovery from Enhanced or Engineered Geothermal Systems. What are the technology gaps we need to fill in order to ensure economic viability for EGS? What EGS technology challenges exist for academia and industry? How can we best engineer the system to emulate the productivity of a hydrothermal reservoir? What do regulators and policy makers need to understand to help promote use of EGS?
  5. Environmental Considerations, addressing water use, land use, artificial reservoir fracturing, supplies to the electric grid.

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