Elsevier Editorial System(tm) for Geothermics Manuscript Draft
Manuscript Number: GEOT-D-08-00009
Title: Overview of the Wayang Windu Geothermal Field, West Java, Indonesia
Article Type: Indonesian Geothermal Fields
Section/Category:
Keywords: Geothermal reservoirs; Vapor-dominated; Liquid dominated; Wayang Windu; Java; Indonesia
Corresponding Author: Dr Ian Bogie,
Corresponding Author's Institution:
First Author: Ian Bogie
Order of Authors: Ian Bogie; Yudi I Kusumah; Merry C Wisnandary
water level at an elevation as high as 1700 m asl. Subsequent boil off may reflect low recharge rates due to hydrological isolation at depth. To the south, the vapor-dominated vapor-dominated reservoirs decrease in thickness and are characterized by progressively higher pressures, temperatures and gas contents, suggesti ng that the southernmost vapor-dominated zone is the youngest and that these reservoirs become increasing older toward the north.
water level at an elevation as high as 1700 m asl. Subsequent boil off may reflect low recharge rates due to hydrological isolation at depth. To the south, the vapor-dominated vapor-dominated reservoirs decrease in thickness and are characterized by progressively higher pressures, temperatures and gas contents, suggesti ng that the southernmost vapor-dominated zone is the youngest and that these reservoirs become increasing older toward the north.
Cover Letter
Dear Sue, Attached are seven files corresponding to the Bogie et al. manuscript. The paper is for the special issue on Indonesia and has been handled outside EES. Title of the manuscript: West Java, Indonesia Authors:
Overview of the Wayang Windu Geothermal Field,
Ian Bogie, Yudi Indra Kusumah and Merry C. Wisnandary
Corresponding author:
Ian Bogie
Mailing address: Ian Bogie Sinclair, Knight Merz Ltd PO Box 9806, Newmarket Auckland, New Zealand Other contact information: Tel.: +64 9 913 8900; fax: +64 9 913 8901 E-mail address:
[email protected] Manuscript received on:16 April 2007 Manuscript accepted on 20 March 2008 The file labeled “GEOT-D-08-Bogie-text.doc” has 38 pages of text, including two tables and the figure captions. The paper has a total of six figures, all in JPEG format. Note that I have already sent an e-mail message and a letter to Ian Bogie informing him of the acceptance. Please let me know if you have any questions about the manuscript or
* Manuscript
GEOT-D-08-Bogie Overview of the Wayang Windu Geothermal Field, West Java, Indonesia 1*
2
2
Ian Bogie , Yudi Indra Kusumah and Merry C. Wisnandary
1. Sinclair, Knight Merz Ltd, PO Box 9806, Newmarket, Auckland, New Zealand. 2. Mandala Nusantara Ltd., Wisma Mulia 50th Floor, Jl. Jend. Gatot Subroto no. 42, Jakarta 12710, Indonesia.
Received: 16 April 2007; accepted 20 March 2008
Abstract
The Wayang Windu geothermal field, West Java, Indonesia, is interpreted to be transitional between vapor-dominated and liquid-dominated conditions with four coalesced fluid upwelling centers that generally become younger and more liquiddominated towards the south. Two of these centers are associated associated with the large Gunung Malabar andesite stratovolcano and the other two with the smaller aligned Gunung
The deep liquid reservoir is overlain by three separate vapor-dominated reservoirs. The northernmost is the largest as it is coalesced over two separate fluid upwelling centers. Its low gas content, size, prolonged productivity and constant pressure at a given elevation preclude it from being a parasitic steam zone. Mineralogical relationships demonstrate that the northern vapor zone was originally liquid-dominated with its water level at an elevation as high as 1700 m asl. Subsequent boil off may reflect low recharge rates due to hydrological isolation at depth. To the south, the vapor-dominated reservoirs decrease in thickness and are characterized by progressively higher pressures, temperatures and gas contents, suggesting that the southernmost vapor-dominated zone is the youngest and that these reservoirs become increasing older toward the north.
Keywords: Geothermal reservoirs; Vapor-dominated; Liquid dominated; Wayang Windu; Java; Indonesia
and Tangkuban Perahu (Wibowo, 2006). These fields lie within andesitic, volcanic highlands formed by a concentration of volcanic centers in this part of the Sunda Arc.
The city of Bandung is located in a basin (Dam, 1994) near the center of the volcanic highlands. That basin does not appear to be a back-arc basin, as it has arc volcanics on either side, but may owe its origin to flexure from varying rates of subduction roll back along the Sunda Arc. This arc has formed in response to the subduction of the AustralianIndian Plate beneath the Eurasian Plate.
It has been active since the Cretaceous
(Whittaker et al., 2007), but has undergone changes as increasing amounts of Australian continental crust have become involved in the collision and it is undergoing roll back. The dominant strike directions of the major faults in West Java are 40° and 340° (Wibowo, 2006; Fig.1), forming a conjugate pair of strike-slip faults, consistent with compression due to near-perpendicular subduction.
1
Wayang and G. Windu in 1991 (Budiardjo, 1992; Ganda and Hantono, 1992; Ganda et al., 1992). Well data showed that a perched steam-heated groundwater aquifer overlies a two-phase vapor-dominated zone that in turn overlies a neutral-Cl liquid-dominated reservoir. This was the discovery well for the Wayang Windu field and for transitional liquid-vapor type geothermal systems. A 600-m deep slim hole (MSH-1) drilled by Pertamina in 1993-1994 on the southern slopes of G. Malabar also provided indications of the existence of a shallow two-phase zone, overlain by a steam-heated perched aquifer further to the north.
2.1. Thermal manifestations and surficial hydrothermal alteration The most intense surficial hydrothermal activity occurs adjacent to the small G. Wayang and G. Windu volcanic centers (Fig. 3). Fumaroles, steaming and altered ground, and acid-sulfate springs occur in the Wayang thermal area, which lies within a sector collapse, with the current peak of G. Wayang representing an eastern remnant of a much
Smaller areas of altered ground with acid-sulfate springs and weak fumarolic activity are found on the southern slopes of G. Malabar, while warm, neutral-bicarbonate-sulfate springs are present south of G. Malabar and to the south, west and east of the smaller volcanic centers (Fig. 3). The springs have temperatures ranging from 25° to 66°C and are notable for their lack of Cl (Sudarman et al., 1986). The Cibolang spring in the south has an elevated B content (16 ppm). As its other constituents indicate that it discharges steam-heated groundwater, the high B content is suggestive of high-temperature boiling at depth, because B is volatile at high temperatures (Ellis and Mahon, 1977).
The northernmost area of hydrothermal alteration is exposed on the southwest rim of the Malabar Caldera complex and there is strong alteration in the cirque of the Wayang sector collapse. Small patches of altered ground are scattered around the area, although the overall extent of the hydrothermal alteration is only apparent where deep cuts have been made for roads and drill pads as much of the hydrothermal alteration is covered by a
evidence from the MT surveys for the field to extend beneath these areas.
As the
prevailing weather during the rainy season is from the north, a “rain curtain” may be obscuring thermal activity where precipitation rates are highest.
3. Field development
The Wayang Windu field was developed by MNL (Magma Nusantara Ltd.) beginning in 1996 as a fast track development that started in the logistically easier areas in the south and east with a combination of 1500-m deep slim holes (WWC-SH, WWJ-SH, WWL-SH and WWR-SH; Nurruhliati, 1996; Thaysa, 2003) and deeper production drilling. The existence of a large thermal anomaly was established, but initially productive wells were restricted to sites immediately beneath and southwest of the yo ung volcanic centers.
Wells drilled north of G. Bedil encountered a shallower, two-phase, vapor-dominated reservoir than the one found in the first well (WWA-1). These new wells confirmed the
The initial 110 MWe (gross) development obtained its main steam supply from the northern two-phase reservoir, with some deep northern production and a combination of shallow and deep production from wells further to the south, on the WWA pad upon which the Pertamina discovery well was located. Two-phase fluid transmission pipelines from these drill pads feed a central separator station with steam passing through a scrubber before entering the dual inlet, 110 MWe Fuji turbine in the power plant. This unit, which was installed in 1999, is one of the world’s largest operating geothermal turbines (Murakami et al., 2000). As a result of this turbine installation, Wayang Windu holds the distinction of being the most rapidly developed geothermal field of its size. Both condensate and separated brine are reinjected by gravity in the southernmost part of the known resource.
Unocal Indonesia became a 50% shareholder of the Wayang Windu project in 2001. The
The Wayang Windu field was acquired by Star Energy Holdings Pty Ltd in 2004. A new drilling program began in August 2006 to supply steam for a second 110 MWe Fuji turbine at the existing power plant. The first well completed under this program (MBD5) produces the steam equivalent of 40 MWe making it at the time it was drilled the largest dry steam well in the world. The whole eight-well program realized a total of 180 MWe and included make up wells for the existing turbine. The northern extension of the field is currently being explored with the ultimate goal of obtaining steam to generate 440 MWe (gross), which on the results of reservoir modeling studies (Asrizal et al., 2006) is eminently achievable.
3.1. Extent of the Wayang Windu geothermal field Only the southern part of the western boundary of the Wayang Windu geothermal field is
MT data indicated a deep base of the conductor with no doming or ridging. Since there are indications that the southern area is the youngest part of the system (see below), the position of the conductor is likely to have been dictated by earlier geothermal activity when the deep liquid reservoir reached higher elevations. The conductor in the south now appears to be too impermeable for the alteration mineralogy to re-equilibrate and allow formation of a dome or ridge in its base, although the resistivity in the area of productive wells southwest of G. Windu is slightly higher than where the non-productive WWE-1 and WWA-1ST were drilled.
Combining new well data with those of recent MT surveys, which have a greater station density and have yielded better quality information, the bulk of the field is interpreted to lie beneath G. Malabar, the andesite stratovolcano now centred at Puncak Besar (Fig. 3). The potential resource in the north is estimated to be approximately 4 km wide in an E-W direction and to extend approximately 14 km to the south beneath a series of aligned,
suggested for Karaha-Telega Bodas (Nemčok et al., 2007) and two geothermal centers were recognized at Awibengkok (Hulen and Anderson, 1998).
4. Geology of the field
The stratigraphy of Wayang Windu has been discussed by Bogie and MacKenzie (1998) who applied volcanic facies models to subdivide the various volcanic units at depth, which define a series of overlapping andesitic piles. extended in Fig. 4; its the trace is shown in Fig. 2.
Their cross section has been
Microdiorite, dolerite and diorite
porphyry dykes are found, but blind drilling and very limited coring have prevented the clear recognition of any major intrusives. Andesitic lavas, pyroclastic and epiclastic deposits predominate in the volcanic units with dacite only occurring at G. Gambung. Quartz found in rocks of the other smaller volcanic centers is xenocrystic, and geochemically these rocks are andesites.
interlayered smectite-illite.
As these clays are usually found at temperatures below
200°C (Anderson et al., 2000), we suggest the beds must have very low permeability, since measured temperatures at the corresponding depths (> 300°C in some instances) are much greater than the typical stability limit of the clay.
Gunung Malabar sits on the boundary fault of the Bandung Basin (Figs. 1 and 3; Dam, 1994).
There is a multiphase summit caldera complex on G. Malabar. Rocks from the
volcano summit (east of the calderas), Puncak Besar (a prominent peak south of the caldera complex directly above the Bandung Basin boundary fault) and G. Gambung (a parasitic dacite dome to the southeast), all have K-Ar da tes of 0.23 Ma and have bulk and trace element chemistries of a differentiated series (Bogie and Mackenzie, 1998). Gunung Bedil, the next volcanic center to the south, was dated at 0.19 Ma, and G. Windu, the southernmost volcanic center at 0.10 Ma. A 0.49 Ma date for G. Wayang breaks the trend of having younger centers towards the south. While the other young volcanic
from the wells concluded that they are geochemically similar to the Malabar rocks (Asrizal et al., 2006).
Structurally the field conforms best to regional patterns in the south, with faulting exhibiting steep dips (> 80°) and strikes of 30-40° and 330–340°. In the north, along the southern boundary of the Bandung Basin, further deformation results from movement along the boundary fault. Gunung Malabar is actively subsiding into the basin and is deforming the basin fill, as can be seen by the presence of upthrust Tertiary sediments (Alzwar et al., 1992) as northern foothills to G. Malaba r.
The rocks penetrated by the wells have highly localized structural permeability; with the most permeable geologic structures following the regional 40° strike. As these structures have trends similar to regional faults, then it is likely they are strike-slip faults, which would tend to have lower permeabilities than normal faults because of shearing and
stress field) as determined from the caliper measurements obtained from micro-resistivity formation imaging logging. They found that the calculated stress field did not correspond to the regional orientation, but had the least principal stress striking at 310°, with an overall normal faulting regime. The NE-striking faults are thus likely to have been regional strike-slip faults reactivated as more permeable normal faults due to a change from a regional compressive to a local extensional regime.
Further to the north,
extension may be even stronger at the boundary and inside the Bandung Basin.
4.1. Hydrothermal alteration at depth
Hydrothermal alteration (Table 1) at depth is most strongly developed in the pyroclastic deposits with more structurally limited alteration zones in the lava flows.
Shallow
alteration (above and locally within the conductor), is marked by the presence of kaolinite, alunite, natroalunite, and rare native sulfur. This alteration is associated with
by smectite along with near ubiquitous quartz, chlorite, calcite and pyrite with zeolites, including heulandite, mordenite, clinoptilolite, stilbite, analcime and laumontite. Kaolinite, calcite, anhydrite and quartz are found within parts of the conductor occurring as an overprint.
With increasing depth, interlayered illite-smectite rather than smectite is found, until there is a transition to a propylitic assemblage with its top marked by the presence of corrensite and epidote.
At greater depths, illite becomes the main sheet silicate.
Secondary amphibole, orthoclase and magnetite making up a high-temperature potassic assemblage are encountered still deeper. The formation of secondary amphibole appears to be related to dike emplacement. A contact metamorphic assemblage of diopside, oligoclase and magnetite has been observed in well WWA-4.
In the deep liquid
reservoir, wairakite and prehnite, along with epidote, are common as alteration and vein minerals, with less frequent adularia.
pyrophyllite, diaspore, woodhouseite and dickite, with accompanying quartz, anhydrite and pyrite. As these hydrothermal minerals are created under high-temperature, acid conditions, and considering that the reservoir pH is now near neutral, and has temperatures below those at which these minerals formed (Reyes et al., 1993), we consider this deep advanced argillic alteration to be relict. This may possibly reflect the earlier presence of acidic condensed magmatic volatiles, particularly since woodhouseite (CaAl3PO4SO4(OH)6; Stoffengren and Alpers, 1987) has an exclusively magmatic association (Bogie and Lawless, 2000).
In the northern part of the Wayang Windu geothermal field, hydrothermal epidote is found at elevations up to 1330 m asl. The shallowest appearance of this mineral is above the vapor-dominated reservoir, and all its first occurrences in well samples are above the deep liquid reservoir (Figs. 4 and 6). Since generally in this type of geothermal reservoir epidote forms at temperatures above 240°C under near neutral pH conditions (Browne,
the conductor is at 1400 m asl, and there is a concurrent deepening to the first appearance of epidote (Fig. 4). Thus, the top of the conductor to the south can be considered to correspond to the original water level.
The top of the epidote zone is very close to the tops of the Waringin volcanic unit (Fig. 4) and of the vapor-dominated reservoir (Fig. 6) reflecting, perhaps, a porosity variation. In the northern part of the field, the Malabar volcanic unit consists mainly of lavas whose average porosity is ~1% (Asrizal et al., 2006). The underlying Waringin unit consists mainly of lapilli tuffs with an average porosity of ~8% (Asrizal et al., 2006).
It is
possible that the original porosity of the pyroclastic deposits was higher prior to alteration, but this would not be the case for the lava flows.
Therefore, the thick
sequence of lava flows could have acted as the initial caprock of the geothermal system. The permeability associated with vertical faults that cut these flows may have been restricted by the presence of the regional ash deposits, which because of their high clay
In some places the original conductor has been overprinted by hydrothermal alteration caused by perched steam-heated aquifers that, where topography allows, extend to higher elevations and above topographic highs in the conductive layer. However, these aquifers have higher resistivities (~ 5 Ωm) than the main conductor (~ 2 Ωm), due to the presence of kaolinite, which is more resistive than smectite, as the predominant clay mineral.
The areas of the conductor that have slightly higher resistivity more clearly define the four fluid upwelling centers at the Wayang Windu geothermal field (i.e. where productive wells have been drilled; Fig. 3) than the elevation of the base of the conductive layer. Presumably this is because the higher resistivity areas in the conductor reflect near present conditions, whereas its base was defined during an early stage in the development of the system. Similar higher resistivities in the conductor have been reported at KarahaTelaga Bodas (Raharjo et al., 2002), and may generally serve, in combination with the
above the vapor-dominated zones is now above the water level and must be relict. That is, the alteration, which includes the electrically conductive argillic zone, must have formed early in the development of the system. This zone, which is characterized by a conductive temperature profile indicative of low permeability, now constitutes the caprock of the geothermal reservoir. On the margins of the field, where the base of the conductor deepens, these clay-rich altered rocks form the lateral hydrological boundaries of the vapor-dominated resource, at least in its upper parts. This may explain why this steam zone is best developed in the north where there is the steepest drop off in the depth of the margin of the conductor, forming a dome which encloses the vapor-dominated reservoir.
Hydrothermal alteration in two-phase, vapor-dominated reservoirs that have formed above the deep water is only weakly developed. Epidote is partially replaced by calcite, white clay (possibly kaolinite), pyrite and anhydrite, a further indication of its relict
Fluid inclusion work has been limited by the amount of suitable sample material. Abrenica (2007) reports homogenization temperatures between 228° and 255°C, with the mode at 235°C, in primary fluid inclusions in quartz from a vein at 590 m asl in well MBD-5; the current estimated temperature is 246°C (the downhole logging tool did not reach this depth). Melting point measurements for these inclusions indicate salinities of 0.53 to 1.05 wt% NaCl equivalent (Abrenica, 2007), reflecting both the dissolved salt and gas contents of the trapped fluids. The present-day salinities, calculated on a gas-free basis, of the deep liquid reservoir is ~2 wt% NaCl equivalent. Therefore, these inclusion results likely reflect early liquid reservoir conditions.
Secondary fluid inclusions in that quartz sample are vapor-rich and have higher vapor/liquid ratios in successive generations, consistent with the presence of increasing vapor-dominated conditions with time. Homogenization temperatures of the secondary inclusions range from 241° to 334°C, but since it is unlikely that a single-phase fluid was
Epidote from 542 m asl in MBA-1 was observed to contain liquid-dominated fluid inclusions (Abrenica, 2007), although homogenization temperatures could not be obtained. As vapor-dominated conditions now prevail at that depth, it is inferred that the liquid level was previously higher and that the epidote is relict.
5. Reservoir characteristics and geochemistry
The Wayang Windu geothermal resource has a deep, hot, neutral pH, liquid reservoir that, in the area drilled, is overlain by perched vapor-dominated, two-phase reservoirs (Fig. 6). Throughout the field within the deep liquid reservoir, pressures and temperatures versus elevation are similar (Table 2; Fig. 5). In the north its top is at 400 m asl, and it deepens towards the south where it is found near sea level elevation. Since under naturalstate (pre-exploitation) conditions the reservoir had almost the same vertical pressure distribution throughout, it can be considered to be a continuous body, and since it was
reservoir are cooler than elsewhere in that reservoir, but without actual temperature inversions deeper in the well, indicating some limited ingress of meteoric waters into the shallow zones.
Overlying the deep liquid-dominated zone we find two-phase vapor-dominated reservoirs. The largest in the north appears to be coalesced over two fluid upwelling centers (associated with Puncak Besar and G. Gambung), while the two farther south (associated with G. Wayang and G. Windu) appear to be separate. In other words, the Wayang Windu geothermal system seems to present three vapor-dominated reservoirs that are located over four fluid upwelling centers.
The characteristics of the vapor-
dominated zones change progressively towards the south; i.e. their pressures, temperatures and gas contents increase, their thicknesses decrease, and are found at greater depths.
distribution of impermeable, regional ash deposits that restrict vertical permeability (and fluid flow), and the distribution of the more porous pyroclastic-rich deposits that host the two-phase zones.
Interpretation of the MT surveys indicate that the Wayang Windu geothermal field may extend approximately 7 km to the north of MBE-2 and that this well is located south of two domed structures in the base of the conductor (Fig. 3), while MBE-2 and the major producing wells on the MBA and MBD drill pads are associated with the southern dome. In the north, a fourth area related to the northernmost domed structure in the base of the conductor has now been drilled and found to be productive [well MBB-1 (see Figs. 2-4) produces enough steam to generate 23 MWe].
The four possible fluid upwelling centers areas in the field are spatially associated with four eruptive centers (Puncak Besar, G. Gambung, G. Wayang and G. Windu, going from
3
The waters of the deep reservoirs in the G. Gambung and G. Wayang areas have similar Cl/B ratios than those from the G. Windu region, but are much more saline and have lower gas contents suggestive of boiling at high temperatures, with very limited mixing with groundwaters (a process that requires continuous heat recharge to maintain reservoir temperatures). Parts of the system where the deep liquid reservoir is more saline would therefore have to be older than those at G. Windu in order to provide time for this extent of boiling off to occur, which is consistent with the age of the fluid upwelling centers (i.e. generally getting younger towards the south). The variation in gas content between the areas (Table 2) may reflect a lower gas flux from the older centers, and may be responsible for the deepening of two-phase conditions as the increase in gas content towards the south increases the depth of first boiling.
7. Discussion
As the pre-exploitation pressure-versus-elevation in the deep Wayang Windu liquid
Wayang Windu also mean that the field cannot be strictly compared to the solely vapordominated systems of Darajat or Kamojang. Wayang Windu must therefore be regarded as a new type of geothermal field, transitional between liquid-dominated and vapor dominated. This transition is most advanced in the northern parts of the field where the drop in the deep water table has been largest. Towards the south, the vapor-dominated zones are thinner and deeper and make up proportionality less of the resource. This relationship implies a series of steps in the transition from liquid- to vapor-dominated conditions represented in the geothermal field.
The Wayang Windu system is largely sealed off from surrounding and overlying coldwater aquifers, but still receives deep heat and fluid recharge from possibly four fluid upwelling centers that are inferred to be progressively younger to the south. Vapordominated reservoirs have developed over the fluid upwelling centers, with a vapordominated reservoir in the north coalesced over the fluid upwelling centers associated
The locations of the four fluid upwelling centers could overlie shallow apophyses of the larger intrusive body, which have been fractured by a combination of secondary boiling and thermal contraction, to provide conduits that channel steam and gas flow from a much larger intrusive source at depth. If the ages of the eruptive centers can be related to the fluid upwelling centers, it would explain how the geothermal system has been active for possibly 0.23 Ma.
Early pulses of acidic, magmatic condensates produced from the intrusive apophyses may be responsible for the formation of the rare advanced argillic alteration observed deep in the Wayang Windu field. The deep liquid reservoir now has a neutral pH; thus there is no evidence for the presence of acidic fluids produced by the condensation of magmatic volatiles reaching shallow levels of the geothermal system.
The deep magmatic degassing is now heating and partially recharging a large exploitable
The Wayang Windu field is part of a cluster of Indonesian high-temperature geothermal fields, which include the vapor-dominated reservoirs of Darajat and Kamojang that may represent the end point of the liquid-to-vapor transition.
Vapor-capped reservoirs at
Patuha (Layman and Soemarinda, 2003) and Karaha Telaga Bodas (Moore et al., 2002, 2004) exhibit magmatic vapor cores as defined by Reyes et al. (1993), and may represent an earlier stage of transition than found in the Windu part of the Wayang Windu geothermal field; the Wayang and Gambung-Puncak Besar areas being successively further advanced in that transition.
A common feature of some of these Indonesian geothermal fields is that they underlie sector collapses; this is most strongly the case at Darajat, where it includes most of the field. This may possibly also be the situation at Kamojang, where a partially circular collapse feature is reported, although this has been previously interpreted to be a caldera (Healy and Mahon, 1982). Moore et al. (2002, 2004) consider that the sector collapse of
alteration and activity have not been reported from these areas and it is more difficult to relate them to changes in the hydrology of the system.
This concentration of vapor-dominated and transitional resources associated with andesite stratovolcanoes in the Bandung area is yet to be satisfactorily explained given their apparent dearth in the rest of Java, or elsewhere in the world.
Allis (2000)
suggested that the perpendicular subduction beneath Java produced compressive deformation in the upper plate restricting the recharge from depth, but this applies all along Java, not just to the Bandung region.
This compression is enhanced by the
subduction of the Roo Rise (Whittaker et al., 2007), a thickened section of oceanic crust of the down-going Australian Plate. However, there is a break in the Roo Rise in the Australian Plate immediately adjacent to the Bandung area, which is marked by a large bulk-sound velocity anomaly of the down going slab (Gorbatov and Kennett, 2003), with a gravity high directly above it (Newcomb and McCann, 1987).
of the upper crustal plate and the deep magma source will vary with time as rollback proceeds.
The fields around Bandung are in terrains of sufficient elevation for there to be room for steam reservoirs to form above the general level of deep meteoric recharge.
This
recharge may be limited by the poor permeability at depth as the faults in the basement had an initial strike-slip movement that reduced fault permeability due to prolonged shearing. The subsequent fault movement within the volcanic deposits was normal (at least at Wayang Windu) resulting in higher rock mass permeabilities, thus favoring the formation of highly productive vapor-dominated reservoirs.
Acknowledgements
The authors wish to gratefully acknowledge the permission and support of the management of Mandala Nusantara Ltd. to publish this paper and the help of Manfred
Engineering Department, Faculty of Engineering, Gadjah Mada University, Yogyakarta, Indonesia, 151 pp.
Allis, R., 2000. Insights on the formation of vapor-dominated systems. In: Proceedings of the World Geothermal Congress 2000, Kyushu-Tohoku, Japan, pp. 2489-2496.
Allis, R., Moore, J.N., McCulloch, J., Petty, S., DeRocher, T., 2000, "Karaha-Telaga Bodas, Indonesia: A Partially Vapor-Dominated Geothermal Systems”, Geothermal Resources Council Transaction 24, 217-222.
Alzwar, M, Akbar, N., Bachri, S., 1992.
Geology of the Garut and Pameungpeuk
Quadrangle, Jawa. Geologic map issued by Republic of Indonesia, Department of Mines and Energy, Directorate General of Geology and Mineral Resources, Geological Research and Development Centre.
Asrizal, M., Hadi, J., Bahar, A., Sihombing, J.M., 2006. Uncertainty quantification by using stochastic approach in pore volume calculation, Wayang Windu Geothermal Field, W. Java, Indonesia. In: Proceedings of the Thirty-First Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, CA, USA, pp. 235-242.
Bandyopadhay, I., Juandi, D., Baroek, M., Hadi, J., Pramono, B., 2006. In situ stress analysis in deviated wells using inversion method – A case study from volcanic pyroclastics of Wayang Windu Field, Java, Indonesia. In: Proceedings of the Jakarta 2006 International Geosciences Conference and Exhibition, 11 pp.
Bogie, I., Lawless, J.V., 2000. Application o f mineral deposit concepts to geothermal exploration. In: Proceedings of the World Geothermal Congress 2000, Kyushu-Tohoku, Japan, pp. 1003 – 1009.
Bogie, I., Mackenzie, K.M., 1998. The application of a volcanic facies model to an andesitic stratovolcano hosted geothermal system at Wayang Windu, Java, Indonesia. In:
Budiardjo, B., 1992. Petrographic study of cores and cuttings from drillhole WWD-1. Geothermal Diploma Project Report 92.04, Engineering Library, University of Auckland, New Zealand, 43 pp.
Dam, M.A.C., 1994. The Late Quaternary evolution of the Bandung Basin, West-Java, Indonesia. Dissertation, Free University of Amsterdam, The Netherlands, 252 pp.
Ellis, A.J., Mahon, W.A.J., 1977. Chemistry and Geothermal Systems. Academic Press, New York, NY, USA, 392 pp.
Fournier, R.O., Truesdell, A.H., 1973. An empirical Na-K-Ca geothermometer for natural waters. Geochim. et Cosmochim. Acta 37, 1255-1275.
Giggenbach, W.F., 1992. Magma degassing and mineral deposition in hydrothermal systems along convergent plate boundaries. Economic Geology 87, 1927-1944.
Ganda, S., Hantono, D., 1992. Alteration mineralogy of the Wayang Windu geothermal
Hadi, J., Harrison, C., Keller, J., Rejeki, S., 2005.
Overview of Darajat reservoir
characterization; a volcanic hosted reservoir. In: Proceedings of the World Geothermal Congress 2005, Antalya, Turkey, 11 pp.
Healy, J., Mahon, W.A.J., 1982. Kawah Kamojang Geothermal Field, West Java, Indonesia. In: Proceedings of the. Pacific Geothermal Conference incorporating the 4th New Zealand Geothermal Workshop, University of Auckland, Vol. 2, pp. 313-319.
Hochstein, M.P., Sudarman, S., 2007. History of geothermal exploration in Indonesia from 1970 to 2000. Geothermics (this issue)
Hulen, J.B., Anderson, T.D., 1998. The Awibengkok Indonesia, geothermal research project. In: Proceedings of theTwenty-third Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, CA, USA, pp. 256-263.
Moore, J.N., Allis, R., Renner, J.L., Mildenhall, D., McCulloch, J., 2002. Petrological evidence for boiling to dryness in the Karaha-Telega Bodas geothermal system, Indonesia. In: Proceedings of the Twenty-seventh Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, CA, USA, pp. 223-232.
Moore, J.N., Christenson, B., Browne, P.R.L., Lutz, S.J., 2004.
The mineralogic
consequences and behavior of descending acid-sulfate waters: an example from the Karaha-Telaga Bodas geothermal system, Indonesia. Canadian Mineralogist, 42, 14831499.
Murakami, H., Kato, Y., Akutsu, N., 2000. Construction of the largest geothermal power plant for Wayang Windu project, Indonesia. In: Proceedings of the World Geothermal Congress 2000, Kyushu-Tohoku, Japan, pp. 3239-3244.
Nurruhliati, R., 1996. Hydrothermal alteration of well WWR-SH, Wayang Windu geothermal field, West Java, Indonesia. Geothermal Diploma Project Report 96.18, University of Auckland, New Zealand, 52 pp.
Raharjo, I, Wannamaker, P., Allis, R., Chapman, D., 2002. Magnetotelluric interpretation of the Karaha Bodas geothermal field, Indonesia. In: Proceedings of the Twenty-seventh Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, CA, USA, pp. 388-394.
Reid, M, 2004. Massive collapse of volcano edifices triggered by hydrothermal pressurization. Geology 32, 373-376.
Reyes, A.G., Giggenbach W.F., Saleras, J.R.M., Salonga, N.D., Vergara, M.C., 1993. Petrology and geochemistry of Alto Peak, a vapor-cored hydrothermal system, Leyte Province, Philippines. Geothermics 22, 479-519.
Suminar, A., Molling, P., Rohrs D., 2003. Geochemical contributions to a conceptual model of Wayang Windu field, Indonesia. Geochimica et Cosmochimica Acta Supplement 67 (18), Abstract, pp. 454.
Thaysa, A., 2003. Hydrothermal alteration and geochemistry of geothermal fluids study of the Wayang Windu field, West Java, Indonesia. Final Project Report, Department of Geology, Faculty of Sciences and Technology, Bandung Institute of Technology, Indonesia, 74 pp.
Utami, P., 2000. Characteristics of the Kamojang geothermal reservoir (West Java) as revealed by its hydrothermal alteration mineralogy.
In: Proceedings of the World
Geothermal Congress 2000, Kyushu-Tohoku, Japan, pp.1921-1926.
Whittaker, J.M., Muller, R.D., Sdrolias, M., Heine, C., 2007.
Sunda-Java trench
Table 1 Alteration mineralogy (Possible relict phases shown in italics) Location Above Conductor
Conductor
Vapor-Dominated Reservoirs
Initial Alteration Opal, cristobalite, kaolinite, alunite, natro-alunite and sulphur Smectite, illite-smectite, quartz, chlorite, albite, calcite, pyrite, heulandite, mordenite, clinoptlolite, stilbite, analcime, laumonite Quartz, chlorite, calcite, albite, pyrite, illite-smectite, corrensite, epidote, illite, chalcedony, wairakite Amphibole Pyrophyllite, diaspore, quartz, anhydrite Quartz, chlorite, illite, pyrite, wairakite, epidote, prehnite, adularia, albite, tourmaline
Deep Liquid Reservoir Dickite, pyrophyllite, quartz, woodhouseite, pyrite Amphibole, orthoclase, magnetite Diopside, oligoclase, magnetite
Over Print
Kaolinite, anhydrite, calcite, quartz
Anhydrite, calcite, pyrite
Table 2. Geochemical and pressure-temperature properties of Wayang Windu reservoir areas prior to production
Deep Liquid Reservoir
Two-Phase Reservoirs
Area Reservoir Cl
3
1
NaKCa Temp.
(ppm) Puncak Besar
4
(°C) 4
Gambung
12, 000-13,000
295 - 300
Wayang Windu
12,000–13,000 6000-8000
295 - 308 285 - 300
NCG
2
2
NCG (Wt (Wt %) %)
Measured 3 Temp. (°C)
Measured 3 Pressure
Elevation
(bar)
(masl)
4
4
4
4
0.3 0.6 0.5 0.6 3.5
0.6 2.6
250 - 260
35 - 45
? - 1120 400 1100
2 - 4.5 10
255 - 267 260 - 290
50 - 55 80 -85
200 - 700 80 - 400
Notes 1 2 3 4
NaKCa geothermometer of Fournier and Truesdell (1973). Non-condensable gases in weight percent. Prior to production. Well MBB-1 drilled in this area produces 20 MWe o n initial discharge. It did not penetrate into the deep liquid reservoir and fully stabilised gas,
Figure captions
Fig. 1: The distribution of Quaternary volcanic rocks and high-temperature geothermal fields in West Java, Indonesia.
Fig. 2: Topographic map of the drilled portion of the Wayang Windu geothermal field; contour interval: 100 meters; bold contour: 2000 m asl. Also shown are the locations of drill pads, well tracks and of section A-B described in Figs. 4 and 6.
Fig. 3: Location of geothermal wells, thermal features, volcanic summits, calderas, and sector collapses in the Wayang Windu geothermal field in relation to the base of the conductor.
Fig. 4: Section across the Wayang Windu geothermal field showing well tracks, geological units (extended north and south from that of Bogie and Mackenzie, 1998) and the top of epidote (section location is given in Fig. 2).
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