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1 NOTICE CONCERNING COPYRIGHT RESTRICTIONS This document may contain copyrighted materials. These materials have been made available for use in research, teaching, and private study, but may not be used for any commercial purpose. Users may not otherwise copy, reproduce, retransmit, distribute, publish, commercially exploit or otherwise transfer any material. The copyright law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted material. Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. One of these specific conditions is that the photocopy or reproduction is not to be "used for any purpose other than private study, scholarship, or research." If a user makes a request for, or later uses, a photocopy or reproduction for purposes in excess of "fair use," that user may be liable for copyright infringement. This institution reserves the right to refuse to accept a copying order if, in its judgment, fulfillment of the order would involve violation of copyright law.

2 GRC Transactions, Vol. 33, 2009 Rapid Exploration of the Tolhuaca Prospect, Southern Chile Glenn Melosh, William Cumming, David Sussman, Dick Benoit, Elizabeth Soto, Anna Colvin, Max Wilmarth, Jeff Winick, and Luis Fredes GeoGlobal Energy LLC Keywords Exploration, Drilling, Geophysics reservoir. Drilling was suspended for winter on April 29, 2009 and the rig demobilized. Abstract GeoGlobal Energy LLC (GGE) performed detailed exploration and then drilled and tested a 1073 m deep core hole in southern Chile in a period of 5 months. The successful well test demonstrated discovery of a geothermal system in the Tolhuaca Prospect. Following earlier reconnaissance exploration and several years of surface access negotiations, a detailed geophysical resistivity survey was completed and immediately followed by helicopter-supported core hole drilling during the period from December 2008 through April The resistivity survey imaged a >10 km 2 low resistivity clay cap that extended beyond the two known fumaroles on the lower flanks of Tolhuaca volcano. Geologic mapping and detailed geochemical sampling were run in parallel with the other work. Initially the well was targeted between the two fumaroles. However, early geophysical results showed that the fumarole to the south was in a broader and more intensely altered part of the clay cap. Details of the low resistivity pattern in this area along with the gas chemistry suggested the possible occurrence of a permeable steam cap. As staging for the rig mobilization began, a revised well target was selected near the southern fumarole on February 26. The well Tolhuaca-1 spudded on March 9 and was continuously cored from the surface to total depth. A 160 C dry steam reservoir entry was flow tested on March 25. Drilling continued to Hot Springs 1073 m and reached a maximum temperature Fumaroles of 289 C, with the temperature gradient and propylitically altered rocks suggesting that the well was very close to a permeable ~300 C Introduction The Tolhuaca Prospect is located on the NW flank of the heavily glaciated, inactive Tolhuaca Volcano in southern Chile (Figure 1). Reconnaissance exploration conducted in 2005 revealed two previously unknown fumaroles separated by about 1.8 km on a NNW trend of eruptive vents on the NW flank of the volcano. The active Lonquimay Volcano, which last erupted in 1988, occurs along this same trend 12 km to the SE. Fluid chemistry suggested that a neutral geothermal system might occur along Don Fuad Heliport Tolhuaca National Park Termas Tolhuaca Sola Fumarole TOLHUACA-1 Muro Fumarole Chile Pacific Ocean Argentina Map Area Curacautín Tolhuaca, Chile Legend Newly Discovered Thermal Features Gravel Road np Wellsite Camp Concession San Gregorio Overview Map Dirt Roads Rivers ÑÔ Don Fuad Heliport Horse Trail 0 Ü Contours: 50m Region IX WGS UTM Zone 19S GIS: Adam Peretz 1:82,000 4Kilometers Figure 1. Location Map of the Tolhuaca Geothermal Prospect. Temuco Santiago Kilometers

3 this overall trend with reservoir temperatures estimated from gas geothermometry of 220 to 250 C. In early December, 2008, after surface rights agreements seemed close to resolution, GGE embarked on a plan to demonstrate a geothermal resource at Tolhuaca before the winter snows closed access. Over the next 5 months a remarkably time-effective and successful exploration campaign demonstrated the occurrence of a 160 C reservoir and revealed the high probability of encountering a ~300 C resource at a depth of about 1200 m at the drilled location. Project History On December 5, 2008 GGE initiated detailed planning for exploration including, if possible, drilling during the 2009 southern hemisphere summer-fall field season at Tolhuaca. The climate in the area is temperate but subject to heavy rains and extensive snowfall in early winter, which usually begins in May. Consequently the entire project had to be completed by early May. This led to an exploration plan where the geophysics was run first followed immediately by drilling with additional geological and geochemical exploration run in parallel. Once the decision to proceed was made in early December, project work started immediately to complete surface access agreements and plan the geoscience work and drilling. The project scope included negotiating final surface access agreements, executing a MT/AMT survey, completing surface fluid sampling, creating a 1:50,000 geologic map, mobilizing a drilling rig and camp, and drilling an exploration core hole. During the planning process an option to extend a road into the area was considered and postponed due to the cost and time required to complete the road. Consequently the drilling rig had to be transported and supported by helicopter with some minor horse transport of personnel and supplies. Resource and schedule constraints dictated that the drilling rig be capable of safely drilling to at least 500 m depth, at temperatures up to 300 C, and be finished within 10 weeks. The single most effective data set for targeting a well in this situation was likely to be a fast, reliable, single site resistivity method. By early February 2009 access and logistics issues had been addressed and contracts for the geophysical work were complete and field work began. During the geophysical survey preliminary well targets were reviewed for the potential to hand excavate the 2 meter deep cellar so that valves and a low profile annular blowout preventer could be installed under the rig floor. This eliminated the requirement for a rig substructure. Several locations were found in volcanic ash deposits overlying the glaciated lavas and were tested with a hand auger. The final cellar location was selected based on the early results of the resistivity survey. The initial magnetotelluric (MT) and audio MT (AMT) station locations were sited to characterize a low resistivity clay alteration zone associated with the observed surface hydrothermal alteration in the area. Following a review of the initial MT data, a final well target location was selected and a cellar excavated while the geophysical survey continued to detail the subsurface conductors. Meanwhile GGE contracted helicopter transport with Inaer, Inc., and field camp facilities and the drilling rig with Geotec/ Boyles Brothers SA. The drilling rig was a Boyles B-20 with a capacity of taking NQ (2.98") core to a depth of 1000 m and smaller BQ (2.187") core to a depth of 1350 m. This rig was completely refurbished and tested in the few weeks between the signing of the drilling contract and mobilization. The rig and camp facilities were mobilized to the site beginning on February 26. Rig mobilization used a combination of two helicopters. A Kamov with a 4000 kg lift capacity was used for 1 day to mobilize the heavy pieces of the rig, drill pipe, casing, mud and cement, and the camp generator. A smaller Bell 407 helicopter with a capacity of 600 kg at an altitude of 2000 m was utilized for a period of 9 days to mobilize most of the other materials, supplies, and staff. Similar Bell helicopters were also used for weekly support during drilling activities. Helicopter trips of about 6 minutes (one way) were routed from a staging area contracted from a local landowner in a nearby valley bottom with good road access. The camp site took advantage of one of the local hot springs to provide a continuous supply of hot water. Drilling started on March 9 with a HQ bit (3.782") in a pilot hole through a shallow lava flow that was later opened up with a 7 7/8" rotary bit. The initial PW (5.5") diameter casing was set at 20.1 m. After drilling out with HQ, intense alteration and a well kick were encountered. This zone was plugged with 3 sacks of cement and HWT casing (4.5") was cemented at m. This provided secure well control. This early indication of resource potential led to accelerated design and construction of a flow line assembly and wellhead using drilling rods and 2" fittings from a local hardware store. After drilling out cement, total lost circulation was encountered at 121 m. The hole was deepened to 161 m with HQ sized tools and then tested. Maximum reading thermometers indicated this shallow resource had a temperature of at least 150 C. A 90 psi compressor was airlifted to the site to support well stimulation. The first part of the well test produced a small amount of gas that had accumulated at the top of the wellbore, elevating wellhead pressures while shut in prior to the test. The compressor was then used to pump air down the annulus and airlift water from the well through the HQ rods. Within about 3 minutes of starting the compressor it was apparent that the well would flow on its own, so the compressor was turned off. For the first 80 minutes the well unloaded drilling fluid and then began producing pure steam at an initial pressure of 20 psi (Figure 2). At the end Figure 2. Tolhuaca #1 flowing pure steam at 3 am on March 26,

Type Depth (m) Cl Ca Qtz Py Ch Ep TOLHUACA-1 SLIM WELL Rock Type Intense Intense Mineralogy Trace (1 or more) Rare (~1%) Com mon (~5%) Abundant (10%+) Casing Change S li g htl y Rock Type Andesite

Conductance is shown in map view while resistivity is shown on the cross-section. This is done to provide a sense of the thickness of the conductor when using the map.

No flow rate measurements were made at that time due to lack of suitable test equipment, but a suite of non-condensable gas samples were collected from the flowline.

4 Type Depth (m) Cl Ca Qtz Py Ch Ep TOLHUACA-1 SLIM WELL Rock Type Intense Intense Mineralogy Trace (1 or more) Rare (~1%) Com mon (~5%) Abundant (10%+) Casing Change S li g htl y Rock Type Andesite Lava Flow Com pletely Moderately A ndesite B re c ci a Sediments Slightly Propylitic Com pletely P ro py l it ic Moderately Propylitic Figure 3. Conductance to 400 m depth in the Tolhuaca Prospect. Conductance is shown in map view while resistivity is shown on the cross-section. This is done to provide a sense of the thickness of the conductor when using the map. of the 8 hour flow test a maximum flowing pressure test showed that the well was capable of stable flow at 120 psi. No flow rate measurements were made at that time due to lack of suitable test equipment, but a suite of non-condensable gas samples were collected from the flowline. Once the well test had proven that a shallow potentially commercial resource existed, the hole was deepened using an HQ Figure 4. Resistivity Cross-Section aligned NNW showing the well trajectory Figure 5. Tolhuaca #1 Well Lithology and. bit to 503 m depth to seek higher temperatures. By this time a Kuster K-10 memory logging tool had been obtained and arrived on location so the first of a series of temperature and pressure logs were run beginning on April 2. HQ diameter casing was set at this depth and cemented from the bottom up to about 130 m depth to retain the opportunity to recover the shallow entry at a later date. Drilling then proceeded with NQ (2.75") to 1003 m where NQ rods were cemented in a similar way. The final section of the well was drilled with BQ (2.187") tools to 1073 m. The total depth was reached on April 23, The rig was released on April 29 following additional logging and testing and demobilized by May 2. Drilling was terminated because of concerns over approaching winter weather and consistently poor performance of the BQ size drilling. The primary drilling problems were difficulty in getting the inner core barrel to go through the BQ rods so it could lock in place inside the core barrel and an inability to keep core inside the inner barrel. Once core was left inside the main core barrel the inner barrel would not properly seat and this resulted in repeatedly tripping out the entire drill 507

string and returning to grind up the lost core. The last four days of drilling added only 57 m to the total depth. During drilling the geochemical exploration continued.

5 string and returning to grind up the lost core. The last four days of drilling added only 57 m to the total depth. During drilling the geochemical exploration continued. Geologic mapping and sampling of surface rocks proceeded for interpretation of alteration styles and volcanic age dates. Samples of the core were collected for thin sections, x-ray diffraction, fluid inclusions, and oxygen isotope analyses. Exploration Results Early fumarole and hot spring analyses in the prospect area showed evidence of a neutral high temperature reservoir although the gases do not show equilibration with methane and have significant H 2 S content (Melosh, 2005). Follow-up work in 2009 included sampling of two more fumaroles and nine hot springs. Hot spring observations suggest broad occurrence of heated meteoric water locally mixed with steam condensate based on field ph and conductivity. The new fumarole gas analyses more accurately constrain the expected range of high temperature reservoir conditions. The MT survey indicated that low resisitivity clay alteration underlies more than 10 km 2 in an area with common outcrops of intense hydrothermal alteration (Figure 3). A simple cross-section shows a low resistivity distribution that is consistent with a typical geothermal alteration pattern (Figure 4). About a third of the conductor underlies active surface thermal areas. The well was drilled in the heart of the conductor 275 m from the highest elevation fumarole and between two 49 C thermal springs. Observations of the core showed that the well was drilled through volcanic flows and breccias, a sedimentary section, and back into volcanic rocks near TD. Hydrothermal alteration grade increased consistent with measured temperatures from argillic to propylitic facies (Figure 5). intensity indicated two zones of intense argillic alteration that showed an impressive correlation with the MT results. Propylitic alteration characterized by quartz, calcite, chlorite, and epidote occurred below a depth of about 730 m. Well temperatures monitored while drilling included use of maximum registering thermometers up to a temperature of 260 C and nine digital Kuster logs. Measured temperatures revealed a shallow reservoir at about 160 C between 120 and 320 m underlain by rapidly increasing temperatures to TD where the maximum temperature of 289 C was recorded (Figure 6). The shallow reservoir was sampled during the flow test and is expected to be directly related to the fumarolic system. Another possible reservoir may occur just beyond the well TD. The decrease in the temperature gradient at the bottom of the well from 200 C to 80 C/km (11 to 4.5 F/100') was confirmed with repeated temperature logs over a period of 4 days and is not Figure 6. Tolhuaca #1 Measured Temperatures. Individual points show MRT data, and solid lines show Kuster logs. Temperatures were generally increasing with time. a transient effect. The decrease in gradient appears much too large to be due solely to a change in rock conductivity, although this will be tested by core analyses. Permeability at the contact with an expected Tertiary intrusive or on one of the north trending faults in the area is possible. The design of this well obviates the possibility of deepening although extensive work on the core is planned. Another exploration well is planned for late 2009 or early 2010 to determine the productivity of a deeper high-temperature reservoir and perform longer term flow testing. Acknowledgement Drilling equipment and effective operations were provided by Geotec Boyles Bros Ltda. including significant efforts by Mauricio Cruz, James Stefanic, and Bernardo Osorio. Geophysical acquisition services were supplied by Wellfield Services. References Melosh, G.; 2005; Region IX Geothermal Exploration Project Technical Report, Geotermia Del Pacifico internal report, 63 pgs. Cumming, W.; 2009; Chile Exploration 2009; GeoGlobal Energy internal document, 16pgs 508

Exploration results and resource conceptual model of the Tolhuaca Geothermal Field, Chile

Proceedings World Geothermal Congress 2010 Bali, Indonesia, 25-29 April 2010 Exploration results and resource conceptual model of the Tolhuaca Geothermal Field, Chile Glenn Melosh 1, William Cumming 2,