FUTURE OF GEOTHERMAL ENERGY

Transcription

1 1 FUTURE OF GEOTHERMAL ENERGY by Subir K. Sanyal GeothermEx, Inc. Richmond, California International Symposium on Renewable Energy and Sustainability Morelos, Mexico 9 August 2010

2 2

3 TYPES OF GEOTHERMAL ENERGY 3 Convective ( Hydrothermal ) systems Enhanced geothermal systems ( EGS ) Conductive sedimentary systems Produced water from oil & gas fields Geopressured systems Magma energy

4 4 Beowawe Field - Initial-State Temperature Distribution 5,000 ft. 10,000 ft. Temperature (F) ,000 ft.

5 1. CONVECTIVE ( HYDROTHERMAL ) SYSTEMS 5 Limited distribution worldwide Decades of commercial exploitation history Two basic types - Volcanic - Non-volcanic Current generation capacity: worldwide 10,000 MW, and 958 MW in Mexico

6 6

7 7

8 Number of Active Volcanoes in a Country and the Geothermal Resource Base 8 COUNTRY NO. OF ACTIVE VOLCANOES GEOTHERMAL RESOURCE BASE (MW) U.S.A ,000 Japan ,000 Indonesia ,000 Philippines 53 6,000 Mexico 35 6,000 Iceland 33 5,800 Nicaragua 20 4,350 New Zealand 19 3,650

9 Schematic of a conceptual two-well Enhanced Geothermal System in hot rock in a low-permeability crystalline basement formation. 9

10 10

11 2. ENHANCED GEOTHERMAL SYSTEMS 11 Conductive system Worldwide distribution Still experimental Basic challenges: - Creating a pervasively fractured large rock volume - Securing commercial well productivity - Minimizing cooling - Minimizing water loss

12 3. CONDUCTIVE SEDIMENTARY SYSTEM 12 In sedimentary basins with high heat flow No fracturing needed but deep wells required. Not yet commercially proven but should be feasible if reservoir flow capacity and temperature are high enough

13 13

14 14 4. OIL & GAS FIELD WATERS From deep oil or gas field Hot water produced with oil or gas or from depleted oil/gas wells No technical challenge but power cost may not always be attractive

15 5. GEOPRESSURED SYSTEMS 15 Very restricted distribution Reservoir pressure higher than hydrostatic Kinetic energy, thermal energy and energy from dissolved methane No commercial project to date; one demonstration of technical feasibility Several technical challenges to making power cost commercial

16 16

17 Is Geothermal Energy Renewable? 17 The total heat loss rate from the earth s surface is on the same order of magnitude as the worldwide energy demand (about J/ year). Natural heat loss rate per sq. km of the earth s surface (on the order of 50 KW) is so low that commercial geothermal energy extraction is primarily heat mining. The 6 types of geothermal energy sources are various heat mining schemes, each with a minor contribution from renewable heat flow from the earth s core.

18 How Long Can Geothermal Energy Supply the World? 18 Heat energy stored up to a depth 5 km worldwide is 1.46 x J; about 1% of this energy being minable, the worldwide resource base is on the order of 1.46 x J. At the current annual worldwide energy demand of 4.18 x J, heat mining up to a depth of only 5 km can theoretically supply the world s energy need for about 3,500 years.

19 How Long Can Geothermal Energy Supply the World? (Cont d) 19 Since drilling to at least 10 km depth is technically feasible today, geothermal heat mining can, in theory, supply the world s energy demand for many millennia. If a geothermal project is operated for its typical life of 30 years and then stopped, the resource would be naturally replenished in about a century, when it can be exploited again. Such a scheme can make geothermal power truly renewable, and therefore, practically inexhaustible, akin to sustainable forestry.

20 MW per year 202 MW per year 517 MW per year

21 21

22 22

23 23

24 CONCLUSIONS 24 Of the six types of geothermal energy, the EGS resource base in U.S. is two orders of magnitude higher than in the other types combined; the same is likely to be true for the world. Commercial geothermal energy exploitation is primarily a heat mining operation rather than tapping an instantly renewable energy source, such as, solar or wind energy.

25 25 CONCLUSIONS (Cont d) At the current energy demand level, geothermal heat mining can theoretically supply the world for several millennia. Geothermal energy can be truly renewable and practically inexhaustible if approached like sustainable forestry.

26 CONCLUSIONS 26 Between 2010 and 2050, geothermal power capacity in the world would increase from 11,000 MW to perhaps as high as 58,000 MW. Rate of growth in power capacity can be higher given adequate commercial incentives by governments and international agencies.