RESERVOIR DEVELOPMENT STRATEGY Siting Wells for Production and Injection

1
RESERVOIR DEVELOPMENT STRATEGY Siting Wells for
Production and Injection

• Presented by
• Jim Lovekin
• GeothermEx, Inc.

Geothermal Resources Council Workshop on
Geothermal Reservoir Evaluation Reno, Nevada 4
October 2008
2
Overview

• Conceptual models vs hard assets
• Evolution of injection strategy
• Example Coso Geothermal Project

3
Conceptual Models vs Hard Assets
Initial concepts and hopes Thermal anomaly MW
capacity from heat in place Demonstration
of productivity Sweet spots and disappointments
Injection strategy
Public data and fortuitous opportunities Tempera
ture-gradient wells production test
wells Discovery well Confirmation
wells Development wells
4
Conceptual Models vs Hard Assets(continued)
Quantitative model based on actual
performance Modifications to resource
operating strategy Expansion schemes Defined
heat sources and reservoir limits
Operating power plant money coming in Make-up
wells and reconfigured injectors Step-out
wells and deepenings Optimized facility
5
Example Coso
Presented by Jim Lovekin GeothermEx, Inc.
6
Acknowledgement

• Thanks to Terra-Gen Power, LLC
• and to the Geothermal Program Office
• of the Naval Weapons Center for
• permission to present the following
• information on Coso.

7
Coso Chronology

• Pre-history
• Early 20th century
• 1960s and 1970s
• 1981
• 1982-1987
• July 1987
• November 1988
• December 1988
• August 1989
• December 1989
• 1993

Known hot spring area, obsidian quarry Resorts
and mineral prospecting Geothermal test
wells Discovery well at Navy I Confirmation and
development drilling Navy I, Unit 1 start-up
30 MW Navy I, Units 2 3 90 MW
total BLM, Units 7 8 150 MW
total BLM, Unit 9 180 MW
total Navy II, Units 4 6 270 MW
total East Flank gathering system
8
Coso Power Output
Source GeothermEx 2004, CEC PIER Report Phase
I www.geothermex.com/projects-pier.php
9
Coso Lease Map
Source GeothermEx 2006, CEC PIER Report Phase
II www.geothermex.com/projects-pier.php
10
Coso Aerial Photo
Source GeothermEx 2006, CEC PIER Report Phase
II www.geothermex.com/projects-pier.php
11
Early Exploration

• 1966 Coso No. 1 drilled by NWC
• 1970s Geological, geochemical, and
  geophysical studies (NWC, USGS,
  University of Utah)
• 1975-1977 24 heat-flow holes (ARPA, ERDA),
  depths 76 to 438 feet
• 1977 CGEH-1 (Pacific Northwest
• Laboratories), depth 4785 feet

12
Coso thermal anomaly from temperature-gradient
holes
Source Combs, 1980 JGR, Vol 85, No B5, p 2422
13
Discovery, Confirmation and Development Through
1987

• 1981 Navy I discovery well
• 1982-1983 Navy I confirmation drilling
• 1983-1984 Temperature core holes
• 1986 BLM discovery well
• 1986-1987 Navy I development drilling
• Navy I injection strategy decided
• 1987 Navy II discovery well
• BLM confirmation drilling
• East Flank temperature core hole
• Navy I, Unit 1 power plant on line

14
Navy I production test
15
Coso 1987
16
Confirmation and Development 1988

• 46 wells drilled
• Up to 9 rigs simultaneously
• East Flank discovery well
• BLM development drilling
• BLM injection strategy decided
• Navy II confirmation and development drilling
• Navy II injection strategy decided
• Four turbine-generators on line
• Navy I, Units 2 and 3 BLM Units 7 and 8

17
Air photo looking west 5 rigs on Navy II
18
Coso 1988
19
Coso thermal anomaly from development drilling
Source Moore and Erskine, 1990 Coso Field Trip
Guide AAPG EMD1, 2 June 1990
20
Actual Performance Through 1991

• Spring 1989 BLM Units 7 and 8 affected by
  recirculation of NCG from injection ?
  chemical abatement
• Aug 1989 BLM Unit 9 on line
• Dec 1989 Navy II, Units 4-6 on line
• 1987-1991 Observation wells show significant
  pressure declines in reservoir
• Consistent with lower porosity and fluid mass
  in granitic rocks
• Confirmed original expectation of long-term
  fluid mass shortage and future need
  for augmented injection
• Tracer tests show returns of injection fluid
  at
• Navy I and BLM, but not Navy II

21
Modification of Operating StrategyStarting 1992

• Discovery well in 1992 for Navy I deep resource
  in northwest corner
• Step-out well to south confirms southern boundary
• Several injection strategies
• Lateral offset original approach
• Injection below production zone
• Shallow injection at low rates to de-superheat
  steam cap
• Injection around periphery of production zones
• Injection within production zones
• Early priority was to bring Navy II injection
  closer to western production area
• Acquisition of source for future injection
  augmentation

22
Coso 1992
23
Development of East FlankStarting 1992

• Originally contemplated for additional plants
• By 1992, East Flank production was deemed to be
• needed for existing plants
• West-to-East production well drilled in 1992
• Further drilling directly in East Flank in
• 1992-1993
• Definition of East Flank production zone,
• including both Navy I and Navy II wells
• Eastern injection locations to support
• East Flank production

24
Access to Western Leases (BLM North)Starting
1998

• Allowed directional production wells to tap
• additional productive area
• Allowed injection on northern and western
• margins of northern production area

25
Coso 1999
26
WHAT WAS LEARNED?

• Western productive area functions as one
• reservoir, spanning all 3 projects
• One heat source in west is near Navy II / BLM
• boundary, with outflow plume to north
• Second heat source in west is at NW corner of
• productive area
• East Flank has its own heat source, supplying
• deep production near boundary between
• Navy I and Navy II

27
WHAT WAS LEARNED?(continued)

• Initial injection strategy was like Goldilocks
• and the three bears
• Navy II was too far
• BLM was too close
• Navy I was just right
• Injection of NCG became unworkable as
• steam cap evolved and well produced
• less and less liquid-phase water
• This was addressed by conversion to chemical
• systems to control H2S emissions

28
WHAT WAS LEARNED?(continued further)

• Declining reservoir pressures have been
• mitigated by re-distribution of injection
• Further mitigation is planned by use of
• supplemental injection of shallow
• groundwater
• Patterned after successful results at The Geysers
• and Dixie Valley
• Permits are in progress and implementation is
  planned for early 2009
• Tune in next decade to see how it all works out!

29
TAKE-AWAYS

• An optimized strategy for resource
• management takes years to develop
• Understanding heat sources and boundaries
• really only comes with field operation,
• and also typically takes years
• Incremental development works to your
• advantage for resource management
• Get on line early, with the shallowest drilling
• feasible
• Deeper understanding can come later

30
Sunset Shot
31
For Those With Sharp Eyes