Geothermal Exploration On Nevis- A Caribbean Success Story

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Conference Paper: Geothermal Exploration On Nevis- A Caribbean Success Story

The island of Nevis is in the northern part of the Lesser Antilles volcanic island arc in the Caribbean. It is the next island northwest of Montserrat at a distance of approximately 35 miles (56 km). Nevis has a primary central cone, Nevis Peak, which had its last major eruption about 100,000 years ago. West Indies Power (WIP) initiated a geothermal exploration program on Nevis in January 2007. Previous studies had been conducted but no extensive geophysical surveys had been run and no exploration drilling had taken place. Although the entire island was evaluated for geothermal potential, it was apparent from geothermal indicators that the western side of the island is where detailed exploration activities should be conducted. The first phase of the exploration program for West Indies Power consisted of field mapping, geochemical sampling, sampling of noncondensible gasses, a digital elevation model analysis, and remote sensing analysis of satellite imagery and airphotos. These data were used to delineate the areal extent of the geothermal system and to map the apparent faulting on the flanks of the island's central volcano, Nevis Peak. The second phase consisted of magnetotelluric (MT) and controlled-source audio-frequency magnetotelluric (CSAMT) geophysical surveys. Transects were run in order to map the subsurface clay cap, delineate the reservoir, identify fault and fracture zones, and to estimate the orientation and dip of these structures. Drill sites were selected near faults that appeared to be conduits for ascending hydrothermal fluids. Drilling next to upflow faults improves the chances of identifying high-temperature resources at shallower depths. The third phase consisted of drilling three slimholes to depths of 2,500 to 3,700 feet and elevations below sea level (bsl) of 1,800 to 3,200 feet. Fluid samples and temperature measurements from the top of the reservoir were obtained. These holes identified a hydrothermal system with temperatures of over 500°F (260°C) that extends for at least 3.5 miles in a north-south direction on the western side of the island. Chemical analyses of the reservoir show it to be a mixture of meteoric water and seawater with fairly neutral pH and relatively moderate noncondensible gas content for a young volcanic system. This may reflect passive degassing since the last eruption. Subsequent production wells will be drilled directionally to target suspected 'upflow' faults at depths of approximately 5,000 to 6,000 feet. Our drill sites were selected on the basis of regional faulting, surface manifestations, thermal domestic wells, geophysical surveying, and conceptualization of the potential configuration of the hydrothermal system. All three slim-holes measured temperatures near 500°F (260°C). Two of the three slim-holes flow on their own, one quite impressively. Nevis-3 was estimated to flow 76,000 lb/ hr through a 3-_ inch drill pipe. It's a screamer.

Joe LaFleur and Roland Hoag

GRC, 2010

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Joe LaFleur,Roland Hoag. 2010. Geothermal Exploration On Nevis- A Caribbean Success Story. In: (!) ; (!) ; (!) . (!) : GRC; p. (!)