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Heat Mining at The Geysers Geothermal Field Using Reclaimed Wastewater Marina Voskanian, P. E. California State Lands Commission Society of Petroleum Engineers Distinguished Lecturer Program The views expressed in this presentation are those of the author, and do not necessarily reflect those of the State Lands Commission or its staff.

Overview History Need for innovative solutions Government-industry collaboration Two injection projects Effect on induced seismicity Environmental benefits Worldwide applications 2

(1000 MWe) The Geysers Geothermal Field 3

The Geysers Geothermal Field History Discovered in 1847 Largest geothermal field in the world Peak field development in 1987 generating 1500 Megawatts Steep production decline:  Reservoir pressure  Steam source 4

450 wells 50 injection wells 18 power plants 1000 Megawatt capacity Equivalent to 60% of the power demand for the Coastal Region Current Status The Geysers Geothermal Field 5

Geothermal Heat Mining System H 2 O Surface Power Plant Microseismic Monitoring Fractured Reservoir Deep Wells Injection Well Production Well 6

Additional Water Injection Need for pressure maintenance Plant condensate not sufficient for heat mining Injection reduces Non-Condensable Gas production (NCG) Tracer tests confirm water injection supplements steam production 7

Government-Industry Collaboration Need for discharge of treated sewage water: Lake County City of Santa Rosa Other Municipalities Environmental benefits of disposing effluent water into the Geysers Partnership between public and private sectors 8

Two Injection Projects Southeast Geysers Effluent Pipeline (SEGEP) Santa Rosa Geysers Recharge Pipeline (SRGRP) 9

The Geysers Geothermal Resource Area with the Lake County and Santa Rosa Injection Zones 10

Southeast Geysers Effluent Pipeline Project (SEGEP) Delivered lake water and secondary treated water from Lake County Sanitation District Increased field wide mass replacement from 28% to 50% Benefit estimated at 69 MWe of additional power 11

Santa Rosa Recharge Geysers Pipeline (SRGRP) Delivered tertiary treated water from treatment plant from City of Santa Rosa for injection Benefit estimated at 85 MWe of additional power Increased mass replacement to 85% Remaining water used for: Agriculture Urban irrigation 12

Calpine Fieldwide Benefits 13

Calpine Geysers Production and Injection History 14

Water Injection Management Where to inject? How much to inject? InjectionProduction 15

Injection Management Techniques Fracture characterization Heat mining modeling Reservoir temperature/pressure Production decline NCG concentration Location and operational efficiencies Proximity to power plant and water pipeline 16

Induced Seismicity Seismically active prior to injection Public concern with increasing micro-earthquakes (MEQ) Ongoing monitoring by two seismic arrays:  United States Geological Survey  Lawrence Berkeley National Laboratory 17

Effect of Water Injection on Seismic Activity 18

Water Injection and Induced Seismicity 19

Summary of “Earthquake Potential” Studies Earthquakes cannot be predicted Earthquake magnitudes depend on surface area of fault that can slip Large earthquakes occur mainly in large faults No large faults mapped at The Geysers It is extremely unlikely that injection activities at The Geysers will lead to large earthquakes 20

Environmental Benefits Clean Energy 13 million gal/day of recycled water injection 100 megawatts 1 million barrels of oil per year 100,000 households 21

Environmental Benefits Clean Energy 49 million liters/day of recycled water injection 100 megawatts 119 million liters of oil per year 100,000 households 21

Conclusion Worldwide Application Successful application of petroleum engineering tools Sustained steam production through heat mining Additional power generation and revenue Identifying opportunities for environmental benefits Successful government-industry collaboration 22

Any Questions 23

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Induced Seismicity Potential in Energy Technologies Published by National Academy of Sciences ecord_id=13355#orgs