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Title: Fracture permeability in the Matalibong-25 corehole, Tiwi geothermal field, Philippines

Abstract

The Tiwi geothermal field is located in southern Luzon on the northeast flank of Mt. Malinao, an andesitic volcano that was active 0.5 to 0.06 Ma. Matalibong-25 (Mat-25) was drilled through the Tiwi reservoir to investigate lithologic and fracture controls on reservoir permeability and to monitor reservoir pressure. Continuous core was collected from 2586.5 to 8000 feet (789 to 2439 meters) with greater than 95% recovery. The reservoir rocks observed in Mat-25 consist mainly of andesitic and basaltic lavas and volcaniclastic rocks above 6600 feet depth (2012 meters) and andesitic sediments below, with a transition from subaerial to subaqueous (marine) deposition at 5250 feet (1601 meters). The rocks in the reservoir interval are strongly altered and veined. Common secondary minerals include chlorite, illite, quartz, calcite rite, epidote, anhydrite, adularia and wairakite. An {sup 39}Ar/{sup 40}Ar age obtained on adularia from a quartz-adularia-cemented breccia at a depth of 6066 feet (2012 meters) indicates that the hydrothermal system has been active for at least 320,000 years. Fractures observed in the core were classified as either veins (sealed) or open fractures, with the latter assumed to represent fluid entries in the geothermal system. Since the core was not oriented, only fracture frequency andmore » dip angle with respect to the core axis could be determined. The veins and open fractures are predominantly steeply dipping and have a measured density of up to 0.79 per foot in the vertical well. Below 6500 feet (1982 meters) there is a decrease in fracture intensity and in fluid inclusion temperatures.« less

Authors:
;  [1];  [2]
  1. Univ. of Utah, Salt Lake City, UT (United States)
  2. Philippine Geothermal, Inc., Metro Manila (Philippines) [and others
Publication Date:
OSTI Identifier:
472077
Report Number(s):
CONF-960124-
TRN: 96:005767-0029
DOE Contract Number:
AC07-95ID13274
Resource Type:
Conference
Resource Relation:
Conference: 21. Stanford workshop on geothermal reservoir engineering, Stanford, CA (United States), 22-24 Jan 1996; Other Information: PBD: 1996; Related Information: Is Part Of Proceedings of the twenty-first workshop on geothermal reservoir engineering; PB: 595 p.
Country of Publication:
United States
Language:
English
Subject:
15 GEOTHERMAL ENERGY; TIWI GEOTHERMAL FIELD; GEOLOGIC STRUCTURES; WELL DRILLING; DRILL CORES; PETROGRAPHY; GEOLOGIC FRACTURES; PHILIPPINES

Citation Formats

Nielson, D.L., Moore, J.N., and Clemente, W.C. Fracture permeability in the Matalibong-25 corehole, Tiwi geothermal field, Philippines. United States: N. p., 1996. Web.
Nielson, D.L., Moore, J.N., & Clemente, W.C. Fracture permeability in the Matalibong-25 corehole, Tiwi geothermal field, Philippines. United States.
Nielson, D.L., Moore, J.N., and Clemente, W.C. Tue . "Fracture permeability in the Matalibong-25 corehole, Tiwi geothermal field, Philippines". United States. doi:.
@article{osti_472077,
title = {Fracture permeability in the Matalibong-25 corehole, Tiwi geothermal field, Philippines},
author = {Nielson, D.L. and Moore, J.N. and Clemente, W.C.},
abstractNote = {The Tiwi geothermal field is located in southern Luzon on the northeast flank of Mt. Malinao, an andesitic volcano that was active 0.5 to 0.06 Ma. Matalibong-25 (Mat-25) was drilled through the Tiwi reservoir to investigate lithologic and fracture controls on reservoir permeability and to monitor reservoir pressure. Continuous core was collected from 2586.5 to 8000 feet (789 to 2439 meters) with greater than 95% recovery. The reservoir rocks observed in Mat-25 consist mainly of andesitic and basaltic lavas and volcaniclastic rocks above 6600 feet depth (2012 meters) and andesitic sediments below, with a transition from subaerial to subaqueous (marine) deposition at 5250 feet (1601 meters). The rocks in the reservoir interval are strongly altered and veined. Common secondary minerals include chlorite, illite, quartz, calcite rite, epidote, anhydrite, adularia and wairakite. An {sup 39}Ar/{sup 40}Ar age obtained on adularia from a quartz-adularia-cemented breccia at a depth of 6066 feet (2012 meters) indicates that the hydrothermal system has been active for at least 320,000 years. Fractures observed in the core were classified as either veins (sealed) or open fractures, with the latter assumed to represent fluid entries in the geothermal system. Since the core was not oriented, only fracture frequency and dip angle with respect to the core axis could be determined. The veins and open fractures are predominantly steeply dipping and have a measured density of up to 0.79 per foot in the vertical well. Below 6500 feet (1982 meters) there is a decrease in fracture intensity and in fluid inclusion temperatures.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Dec 31 00:00:00 EST 1996},
month = {Tue Dec 31 00:00:00 EST 1996}
}

Conference:
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  • The Tiwi geothermal field is located in southern Luzon on the northeast flank of Mt. Malinao, an andesitic volcano that was active 0.5 to 0.06 Ma. Matalibong-25 (Mat-25) was drilled through the Tiwi reservoir to investigate lithologic and fracture controls on reservoir permeability and to monitor reservoir pressure. Continuous core was collected from 2586.5 to 8000 feet (789 to 2439 meters) with greater than 95% recovery. The reservoir rocks observed in Mat-25 consist mainly of andesitic and basaltic lavas and volcaniclastic rocks above 6600 feet depth (2012 meters) and andesitic sediments below, with a transition from subaerial to subaqueous (marine)more » deposition at 5250 feet (1601 meters). The rocks in the reservoir interval are strongly altered and veined. Common secondary minerals include chlorite, illite, quartz, calcite, pyrite, epidote, anhydrite, adularia and wairakite. An 39Ar/ 40Ar age obtained on adularia from a quartz-adularia-cemented breccia at a depth of 6066 feet (2012 meters) indicates that the hydrothermal system has been active for at least 320,000 years. Fractures observed in the core were classified as either veins (sealed) or open fractures, with the latter assumed to represent fluid entries in the geothermal system. Since the core was not oriented, only fracture frequency and dip angle with respect to the core axis could be determined. The veins and open fractures are predominantly steeply dipping and have a measured density of up to 0.79 per foot in the vertical well. Below 6500 feet (1982 meters) there is a decrease in fracture intensity and in fluid inclusion temperatures.« less
  • Geochemical modeling simulations are being used to examine the source of the reservoir fluids in the Tiwi geothermal field and to evaluate the chemical and physical processes responsible for producing observed vein parageneses. Such information can be used to trace the evolution of the Tiwi geothermal field through time. The React geochemical modeling code was used to simulate the effects of isothermal and isoenthalpic boiling, conductive cooling and heating, and incorporation of condensed steam, on fluids from the Matalibong area. Predicted mineral stabilities were used to identify mineral indicators for each process. Calcite and anhydrite precipitation were favored by conductivemore » heating, while illite precipitation was favored when condensed steam was added to the reservoir fluid. Reconstructed downhole fluids from borehole Mat-25 are acidic and are consistent with the presence of illite as the latest alteration mineral in veins. The processes of isothermal and isoenthalpic boiling could be differentiated from conductive cooling by the presence of epidote and/or calcite during boiling, and illite during cooling. Both boiling and cooling favored precipitation of quartz, K-feldspar, wairakite, and pyrite. Ratios of Na, Cl, and Br in waters from the Matalibong are relative to seawater indicate a significant component of seawater in reservoir fluids.« less
  • Commercial-scale geothermal development in the Philippines began i n 1972 with the completion of the discovery well in the southeastern portion of Luzon Island. A second geothermal anomaly was discovered i n 1975 on the southern flank of Mt . Makiling, forty miles south of Manila. Both fields are being developed and operated by Philippine Geothermal, Inc. (PGI) , a wholly-owned subsidiary of Union Oil Company of California. Currently the Philippines ranks second worldwide in installed geothermal-powered electrical generation capacity with 443 MW and PGI has developed 440 PW of the 443 MW country total. Additional generation capacity is plannedmore » or under construction in both fields. Over 1.9 billion kilowatt-hours of electrical power have been produced to date. This represents a savings of approximately three million barrels of imported fuel oil for power generation.« less
  • Commercial production of electricity from the Tiwi geothermal system began in 1979. In 1982, Tiwi became the world`s first water-dominated system to produce more than 160 MWe. Today the field supplies about 11% of Luzon`s electricity. Initially, the reservoir was single-phase liquid with a small, shallow steam zone on the east side. Temperature reversals in the first wells showed the east to be an outflow zone. As production began, reservoir pressure declined, two-phase conditions developed, and groundwater entered the reservoir from the east. As many productions wells cooled, brine production increased and generation decreased from about 280 MWe in 1983more » to about 190 MWe in 1986. Improvements to surface facilities and new wells drilled farther west raised generation to about 280 MWe by mid-1993. Separated brine was first injected into the reservoir, but this lowered steam production; injection is now outside the field.« less
  • Wellbore image data recorded in six wells penetrating a geothermal reservoir associated with an active normal fault at Dixie Valley, Nevada, were used in conjunction with hydrologic tests and in situ stress measurements to investigate the relationship between reservoir productivity and the contemporary in situ stress field. The analysis of data from wells drilled into productive and non-productive segments of the Stillwater fault zone indicates that fractures must be both optimally oriented and critically stressed to have high measured permeabilities. Fracture permeability in all wells is dominated by a relatively small number of fractures oriented parallel to the local trendmore » of the Stillwater Fault. Fracture geometry may also play a significant role in reservoir productivity. The well-developed populations of low angle fractures present in wells drilled into the producing segment of the fault are not present in the zone where production is not commercially viable.« less