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

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.
Publisher:
Stanford Univ., Stanford, CA (United States)
Country of Publication:
United States
Language:
English
Subject:
15 GEOTHERMAL ENERGY; TIWI GEOTHERMAL FIELD; GEOLOGIC STRUCTURES; WELL DRILLING; DRILL CORES; PETROGRAPHY; GEOLOGIC FRACTURES; PHILIPPINES