30 years of tongonan-1 (leyte, philippines) … years of tongonan-1 (leyte, philippines) sustained...
TRANSCRIPT
Proceedings World Geothermal Congress 2015
Melbourne, Australia, 19-25 April 2015
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30 Years of Tongonan-1 (Leyte, Philippines) Sustained Production
Marie Hazel C. Uribe, Danilo B. Dacillo, Lorena M. Dacoag, Romeo P. Andrino, Jr. and Edwin H. Alcober
Energy Development Corporation, Brgy. Tongonan, Ormoc City, Leyte, Philippines
Keywords: Sustainability, Production, LGPF
ABSTRACT
Tongonan-1 in Leyte, Philippines has achieved a milestone for sustainable production for 30 years. Reservoir management played a
key role in the continuous power generation and in conquering the challenges since the commissioning of the Tongonan-1 power
plant in 1983. The series of challenges in its 30-year history has been a source of lessons and the reason for the sound production
and injection strategies that have been implemented.
Cooler injection returns, blockages, erosion and pressure drawdown are among the challenges that have been met squarely by the
early and present resource managers. Technological knowledge and developments in field management, geochemistry and reservoir
engineering were crucial in analyzing and addressing these challenges. Likewise, experiences in targeting M&R wells proved to be
significant in achieving the sustained production.
1. INTRODUCTION
The Leyte Geothermal Production Field (LGPF), located in the province of Leyte in the Eastern Visayas region of the Philippines,
is known as one of the largest liquid dominated reservoir in the world. It is comprised of two distinct hydrothermal systems -
Tongonan to the north and Mahanagdong to the south, separated from each other by the low permeable Mamban block.
Figure 1: Location Map of the Leyte Geothermal Production Field
The Tongonan geothermal system encompasses four (4) sectors – Upper Mahiao, Tongonan-1, Malitbog and South Sambaloran,
over a total resource area of 15km2. The Tongonan baseline hydrological flow model identified a convective upflow centered in the
area bounded by wells in Upper Mahiao and Tongonan-1. Major outflow was identified towards the Malitbog sector and some
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minor outflows towards the north, northwest and northeast directions in Upper Mahiao. Noteworthy of the field is a natural
recharge in the form of a cooler fluid in the eastern region of the Upper Mahiao sector.
Figure 2: Tongonan Hydrological Flow Model
The experience of LGPF in the geothermal industry has come over from a long journey and can be considered one of the pioneers
in this ground. Field surveys started as early as in the 1950’s where the Commission on Volcanology completed a geothermal
feasibility study that led to conception of the PNOC-EDC in the 1970’s, tasked to develop the geothermal resources in the country.
This paper will focus on the journey of the Tongonan resource, where it all began for EDC, making the 30 years of Tongonan-1
Power Plant sustainable production possible – and the rest is history.
2. TONGONAN RESOURCE RESPONSE TO PRODUCTION
Commercial operation in the Leyte Geothermal Production Field started with the commissioning of the 112.5MW Tongonan-1
power plant in 1983. Twelve production wells were initially hooked - up to the system to provide the steam supply requirement of
the power plant. Mass extraction in the Tongonan resource further increased with the commissioning of additional power plants -
232MW in Malitbog and 132MW in Upper Mahiao during operational expansion in 1996 to 1997. This also leads to the increase in
brine injection to the resource.
Figure 3: Tongonan Production History
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Initial response of the Tongonan field after the start of large-scale production showed a large decline in the reservoir pressure
between the periods of 1996 to 2002. Likewise, discharge enthalpy of most production wells across the Tongonan field began to
increase, transforming liquid producing zones to highly two phase producers. However, discharge enthalpy declined in dry area
encroached with injection returns and is most notably at the wells in proximity to the injection sinks. Injection management
strategies were then implemented that stabilized field enthalpy in Upper Mahiao, Tongonan-1 and Malitbog sectors. Also, the
drilling of new deep low enthalpy wells affected field enthalpy trends.
Figure 4: Tongonan Pressure and Enthalpy with Time
The pressure decline during increase in commercial operation resulted to secondary reservoir processes that affected steam supply
of production wells with time. These encouraged solids problem – erosion, surface scaling and wellbore blockage. It also
enhanced flow of cooler fluids from the outskirt to the production sectors such as brine-condensate returns in the north and
groundwater inflow in the east of the Upper Mahiao, brine from Tongonan-1 injection sinks, and groundwater inflow in the east and
west of MBSS sectors. Dried wells encroached with brine mists have silica deposition in the formation. Feed or output sharing
was also observed in some wells. Feed refers to the source which maybe a fault or structure intersected wherein geothermal fluids
enter the well thru the permeable zone/s for production. Feed or output sharing are observed in wells drilled in an area with close
distances from each other. Such is the incident in one of the production pads in the Malitbog-South Sambaloran sector wherein
after cut-in of a new well, existing online wells showed decline in their output. The observed total decline in output was almost
equivalent to the output of the new well suggesting output sharing between the wells in the pad likely due to the high intra-
formational permeability and close distances between their permeable zones. While in the Upper Mahiao sector, output sharing
was best observed between the two wells in the same pad. During output measurements, the output of one well will decline in an
amount equivalent to the increase in the output of the other well, and vice-versa. It was discovered during evaluation that the two
wells shared a common structure in the openhole section and were drilled relatively close to each other.
Below is the summary of reservoir process observed in the production wells of the Tongonan geothermal field.
Reservoir Process Tongonan - 1 Upper Mahiao Malitbog – South Sambaloran
Silica Scaling
Solids Problem
Brine Returns
Condensate Returns
Peripheral Groundwater Inflow
Feed / Output Sharing
Table 1: Summary of Tongonan Reservoir Processes
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Hydrological connection between the injection sink and the production sector become apparent in all the Tongonan sectors.
Recharge of cooler peripheral fluids has become prevalent in the east of the South Sambaloran and in the eastern section of Malitbog sectors. The western part of the South Sambaloran sector has also exhibited signs of relatively cooler fluid
incursion. Another reservoir process which contribute mostly to decline in production well steam flow is possible silica depositions either in the formation or wellbore. Majority of the production wells observed to have this condition are those located in the periphery of “dried-up” zone and injection sink. Silica deposition is enhanced by continuous flashing and casing breaks. Some dry wells began discharging significant suspended solids that caused erosion damage to some FCRS facilities. Cases of mixing production well with dry and watery discharges have caused deposition / scaling along their common branchline.
3. RESOURCE CHALLENGES AND RESOLUTIONS
Resource management in the Leyte Geothermal Production Field is a great challenge given the condition of the reservoir from long
term utilization. The major challenges encountered to sustain production are presented as follows,
(1) Steam Availability
(2) Injection Management
(3) Critical Wells
(4) Age Categorization of Wells
(5) M&R Pads Development and Planning
Some management strategies to address these concerns are the implementation of optimization of steam supply distribution to
maximize generation, brine injection transfer and conversion/development of non-utilized pads, monitoring of wells considered
critical due to casing break and erosive-corrosive nature, and sequencing of future M&R pads developments to be tapped for
production. Wells that have been in the service for above 25 years, with already minimal output and poor casing condition, have
also been identified for possible replacement of future drilling.
Generating the current temperature contours in Tongonan geothermal field was a challenge since most data from old wells were no
longer obtainable due to continuous expansion of the upper two-phase layer and inaccessibility to bottom due to wellbore
obstructions such as mineral or casing / liner damage. However, new wells drilled deep in the Tongonan-1 sectors have still tapped
the >300°C zone which is within the upflow region of the system. Latest temperature data showed that most of the production
wells in the Tongonan sectors are still within the 280°C contour. Temperature declines towards the identified outflows of the
resource and temperature dents observed at the injection sinks in Upper Mahiao, Tongonan-1 and Malitbog areas are now more
evident.
Figure 5: Tongonan Temperature Contour
160
170
180
190
200
210
220
230
240
250
260
270
280
290
300
4 5 7 0 0 0 4 5 8 0 0 0 4 5 9 0 0 0 4 6 0 0 0 0 4 6 1 0 0 0 4 6 2 0 0 0 4 6 3 0 0 0 4 6 4 0 0 0 4 6 5 0 0 0
EASTING (m)
5R45R5D
5R6D
5R1D
5R7D5R2D
5R9D
5R8D
5R3D
5R10D
5R11D
TGE6
TGE1
TGE11
TGE4
LM1
TGE5A
LM2
MN3RD
4R7D4R10D
4R9D
4R14R2D
408
405
4R4D
4R3D
4R5D
4R6D
4R12D4R11D
4R13D4R14D
109D
214
110D
111D
215
217D
218D
219D
115D
221D
223D
208A
202
' 209A105D
108
106
101
103
102
114D
222D
113D
213212
212AD
216D
112D220D
411D
402
414D
410
401
403
406412D
404409
407
415D
416D
421D
413D
428D417D
423D
427D
424D418D
422D 425D
426D
419D
420DA
1R3
2R4D1R10
1R4DA
1R6D
1R7D
1R8D2R3D
2R2
1R9D
1R11D
1R5D
301D 304D
303
302
312
318D
306D
305D
314D 315D317D
307D309D
310D
308D311D
313D
316D
511D
513D
514D
501
505D
506D
518D
519D508D
510D
503
509
515D
517
520D
502
516D
U p p e r M a h ia o
T o n g o n a n -1
M a litb o g
S o u th S a m b a lo ra n
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In the same way, update on the pressure contour has shown lowest downhole pressure at ~5MPa to enclose the central production
sectors of Tongonan-1 and South Sambaloran. High downhole pressures are still observed in northern periphery of the Upper
Mahiao sector and along Malitbog wells where recharge is available either in the form of injection returns or groundwater inflow.
Figure 6: Tongonan Pressure Contour
4. FUTURE OUTLOOK
Continuous extraction and commercial expansion of the Tongonan Geothermal Field resulted to decline in pressure and boiling of
the central production field. At the start of utilization of the three sectors, boiling occurred in the reservoir as evidenced by the
sudden surge of steam flow as initial response and then followed with a sharp decline. Field-wide extraction has enhanced inflow of
peripheral cooler fluids, brine returns and mineral deposition in the drawn-down area which contributed to the steam flow decline.
However, the rate of decline was arrested when mitigating measures such as optimized brine loading and strategic injection
locations were implemented.
Aside from the strategic injection utilization, drilling of M & R wells and work-over of old wells were also undertaken to sustain
steam supply to the power plants. Amongst the latest interventions is the Leyte Steam Augmentation Project (LSAP). LSAP started
in 2008 with the aim of drilling 19 production wells and 2 injection wells to replace steam decline and augment steam available.
Drilling of LSAP wells with a target output of 105.5MW achieved 98.4% success after obtaining a total of 103.8MW after
completion in 2011.
Figure 7: Tongonan-1 Field Enthalpy Trend
1980 1985 1990 1995 2000 2005 2010
1200
1600
2000
2400
2800
Enthalpy
(kJ/kg)
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In Tongonan-1 alone, the field experienced initial sudden surge in enthalpy during commercial expansion in 1996-1997 due to
pressure decline which resulted to initial increase in steam fraction from drying up of the wells. The increase was not sustain due to
secondary reservoir processes such as blockages and cooler fluids inflow which in turned decrease the steam production. However,
when resource management strategies were implemented beginning of 2002, the Tongonan-1 sector was able to sustain steam
supply requirement to the power plant making it operational until now even after about thirty years of utilization.
REFERENCES
Dacillo, D.B., et. al.: Tongonan Geothermal Field: Conquering Challenges of 25 Years of Production, Philippines, Proceedings,
World Geothermal Congress, Nusa Dua Bali, Indonesia (2010).
Sta. Ana, F.X.M., et. al.: Increased Production Load in Tongonan Geothermal Field, Philippines: Reservoir Response and Field
Management Strategies, Proceedings, 24th Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford,
CA (1999).