Menzies- Sustaining Long-Term Production at Chevron Tiwi Field

Experiences, Successes and
Challenges in Sustaining Long-Term
Production at the Tiwi Geothermal
Field
Anthony (Tony) Menzies
Chevron Geothermal Services Company
IEA–GIA/EDC Joint Seminar
© Chevron 2005 September 21, 2013
Drilling of Nag-1 (1972)
© Chevron 2005
Credit: Bernie Tolentino
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Presentation Outline
Introduction
Field Location and Regional Setting
Summary Fact Sheets
•
•
•
Power Plants and Production
Resource Description
Challenges and Responses
Meteoric Recharge (MR)
Matalibong Steam Zone and Rising Liquid Levels
Concluding Remarks
© Chevron 2005
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Introduction
Development of the Tiwi geothermal field was notable for
the installation of 330MW over three years (1979 to 1982)
•
This was and still is one of the most aggressive development
schedules seen in the geothermal industry
The aggressive development was a consequence of the
situation in the Philippines at the time, with a 95%
dependence on imported oil, three fold increases in oil
prices and surging demand for electricity
There was obviously risk associated with the speed of this
development and also that of Mak-Ban (330MW; 1979 –
1984), with both fields reacting quite differently to the
imposed level of extraction
This presentation will review two of the major challenges
that have occurred in Tiwi and how they were or are being
managed to reach a successful outcome
© Chevron 2005
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Location and Geologic Setting
Tiwi is located in the Bicol
Region of Southern Luzon,
≈350 km SE of Manila on the
northeast flank of Mt. Malinao
Mt. Malinao is part of a
chain of andesitic,
composite volcanoes
associated with SW
subduction of the Pacific
Plate, which include Mt.
Mayon and Mt. Bulusan
which continue to be active
© Chevron 2005
Topographical Map and
Production Sectors
NAG PARK
MATALIBONG
1&2
BARIIS
3&4
KAPIPIHAN
5&6
1&2
3&4
5&6
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Power Plants and Production
Power Plants:
Initial installed capacity: 330 MW
•
Units 1 and 2 (55 MW each) - 1979
•
Units 3 and 4 (55 MW each) - 1980
•
Units 5 and 6 (55 MW each) - 1982
Partial Re-hab (re-rated to 234 MW)
•
Units 1 and 2: 60.0 MW each
•
Units 5 and 6: 57.0 MW each
•
Unit 3: standby in 2005
•
Unit 4: decommissioned in 2001
Overall Generation
•
49.04 TWh gross generation as of Aug 2013
•
Average 161 MWe gross (1979 – 2013)
Production Facilities:
81 equivalent km of pipeline
10 separator vessels and 6 scrubbers
≈40 production / ≈20 injection wells
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Resource Description
Production Area: 18 km2
Initially over-pressured and artesian
with small shallow steam zone in
outflow
Max. resource temperature: ≈ 340ºC
Reservoir fluids generally benign
•
≈ 5,000ppm Cl; avg 2.5 wt-% NCG
Reservoir changes due to production
•
Formation of steam caps in Naglagbong and
Matalibong
•
Influx of meteoric water (different depths)
•
Influx of peripheral acid fluids
Wide variation in well discharge
characteristics
•
Discharge enthalpy: from liquid water (1,050
kJ/kg) to steam (with up to 30ºC superheat)
•
Steam production: from 2.5 to 40+ kg/s
Present resource challenges
© Chevron 2005
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Rising liquid levels below steam zone
•
Maintaining injection capacity
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Challenges and Responses
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Challenge
Signature
Response
Meteoric water influx in
Nag resulting in Calcite
scaling and thermal decline
Declining Cl, excess stm,
NCG, increasing Tritium
Moved production further
west
Injection of waste brine /
injection breakthrough
Increasing Cl, Si and lower
excess stm, NCG
Drilled more distal
injectors
Well / Pipeline Scaling
Well production/injection
declines, blockages
SDO and acidization,
reconfiguration of well
tie-ins, hot brine injection
Acid-sulfate / Corrosive
Fluids
Declining pH, increasing
sulfate, Mg
Recompleted wells or
changed targets
Downhole chemical
mitigation
Deeper casing in new
wells
Steam Cap “Dryout”
Superheat, excess Cl, Fe in
steam condensate
Pilot infield injection,
Brine scrubbing
(MatRidge Upgrade)
Steam wells turn wet and
lose productivity
Step change in enthalpy and
productivity caused by rising
liquid level
Divert injection from Matridge area to the south
east
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Meteoric Recharge (MR)
© Chevron 2005
Impact of “MR” on Production
Tiwi started commercial production in 1979 – 1982 with
the available steam supply from the Naglagbong sector
being more than sufficient to fully load all units
(330MW)
Initial production caused high pressure drawdown and
formation of an extensive steam zone, particularly in
shallow outflow region
© Chevron 2005
•
Production discharge enthalpies increased, with most
wells turning to all steam
•
Shut-in wellhead pressures increased as the steam
zone expanded downward
•
Increased shallow steam formation and associated
heat flow resulted in a number of hydrothermal
eruptions from 1977 to 1984 in the area of the hot
springs
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Impact of “MR” on Production
Steam zone formation was followed by an influx of
groundwater (MR), leading to productivity declines in
Naglagbong wells due to:
•
•
Cooling and enthalpy decline
Increased occurrence of calcite scaling
Various ideas were put forward to stop the influx,
including grouting and injecting seawater to initiate
anhydrite scaling. These were not successful
With the declining productivity of the Naglagbong wells,
make-up wells were drilled progressively to the west;
initially in the Kapipihan area and later in the Matalibong
and Bariis areas
•
© Chevron 2005
Only one of the original Naglagbong wells is still producing
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Impact of “MR” on Production
Loss of production in the Naglagbong area required replacement
wells to be drilled in the Western sectors (Kap-Mat-Bar)
© Chevron 2005
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The Attack of the “Blue Blob” ……
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Monitoring “MR” Movement
Chloride
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Monitoring “MR” Movement
Tritium
© Chevron 2005
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Tiwi Production Area and Well
Locations
2008
1&2
5&6
1978
3&4
3&4 Power Plant Units
© Chevron 2005
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Matalibong Steam Zone and Rising
Liquid Levels
© Chevron 2005
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Tiwi Field Map Showing Present
Production and Injection Areas
© Chevron 2005
Matalibong Production/Injection
Sector
Matalibong
Sector
© Chevron 2005
Matalibong Production/Injection
Sector
Important area of the field as it provides 30 – 40% of the
total steam production, with a significant proportion from
the overlying steam zone, with a number of wells
producing superheated steam
Steam zone production has declined since 2004 by 26MW
due to a rising liquid – steam interface that has “flooded”
the deeper steam production zones in some wells
•
Rising interface is caused by combination of increasing deep
liquid zone pressures and declining steam zone pressures
If the interface continues to rise, it is anticipated that a
further 34MW will be lost over the next 10 years, in
addition to normal decline
Understanding how and why the deep liquid and overlying
steam zone pressures are changing is therefore important
to the long term management of the resource
© Chevron 2005
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Steam/Water Interface Changes
Pressure (MPa.g)
600
Pressure @ 1,000m bsl
Pressure @ 600m bsl
Steam-Water Interface
8
6
800
4
900
2
1000
0
1100
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700
80
82
84
86
88
90
92
94
96
98
00
02
04
06
08
10
Steam/Water Interface (m bsl)
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The relative change in deep liquid and shallow steam zone pressures since the
mid-1990’s has resulted in a continuous rise in the steam-water interface from
945m bsl in 1995 to 700m bsl in 2009 and this has continued
Downhole PT logs confirm that the rise in water level has “flooded” deeper
production zones in some steam wells that had previously produced dry or
superheated steam
When the flooding occurs, the wells quickly change from producing steam
(2,800+kJ/kg) to liquid (1,160kJ/kg) and productivity declines or the well dies
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Well Mat 23 Downhole Data
-250
Satn T: Flowing
Satn T: Shut-in
0
Elevation (m bsl)
250
500
Production Zone
Steam/Water Interface
750
1000
1250
1500
Flowing Press
Flowing Temp
Shut-in Press
Shut-in Temp
1750
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0 2 4 6 8 10
Pressure (MPa.a)
150 200 250 300 0 10 20 30 40
Temperature (deg C)
SH (deg C)
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Simple Conceptual Model and Net
“Voidage” Concept
Production from the deep liquid zone is independent of production from
the overlying steam zone
Net “voidage” in the liquid zone is defined as:
Net “voidage” = deep injection – deep production
© Chevron 2005
Correlation Between Deep
Pressure Changes and “Voidage”
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Observations
The data indicate that the pressure increase in the deep
reservoir is caused by injection to Mat-21 and 33 and this
has caused the steam-liquid interface to rise and
negatively affect the shallow steam wells
Based on the net “voidage” analysis, reducing deep
pressures will require >125kg/s injection flow to be
diverted to another area of the field
•
This information was used to justify the building of an
injection line linking WS-7 to the SE injection system
•
Diversion of brine through this line was recently started
The liquid-steam interface also depends on pressure
changes in the overlying steam zone. Hence it will be
necessary to maintain negative “voidage” to get the
interface to descend. If this occurs, it may allow previously
flooded production zones to flow again
© Chevron 2005
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Concluding Remarks
© Chevron 2005
Resource Challenges Going
Forward
The historical issues are still with us and hence we need
to continue to be vigilant
Major resource challenges going forward continue to
include:
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•
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Difficulty in forecasting well and field decline;
•
Managing injection
Stabilizing the Matalibong steam zone;
Potential thermal degradation of deep reservoir due to
continuing meteoric recharge;
— Maintaining capacity
— Where to inject and how much?
— Monitoring for possible thermal breakthrough
© Chevron 2005
Concluding Remarks
Tiwi has presented many challenges over the years for
resource management and no doubt it will continue to do so
in the future
The meteoric influx to the Nag area during the first 3 years of
operation was a huge challenge that required relocation of the
entire production system and has continued to influence
resource management to the present time
Tiwi generation for the past 34 years has averaged 161MWe
(gross) and has provided 45.76 TW.hrs (net) electricity to the
Philippine national grid
In 2008, Bar-11 and Kap-35 were successfully drilled and
opened up additional production areas to the south and
southwest of Bariis and Kapipihan that will help maintain
production in the future
Today we are producing ≈140MWe and there are plans to drill
© Chevron 2005
additional wells in the future to increase capacity
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The End
Thank you
© Chevron 2005