Geothermal Resource Prospecting in the Qualibou Caldera Saint

Geothermal Resource Prospecting in the Qualibou Caldera, Saint Lucia By Frank Dale Morgan Geo-Caraibes Technical Team & Massachusetts Institute of Technology March 2006

Outline • • History Summary Brief Review of Four MIT Studies Conclusion Recommendations

History • Serious geothermal resource exploration began in the mid-70 s by the British Geological Survey • After dozens of investigations and nine drilled holes, no real geothermal development has resulted to date.

Historic Drill Site Recommendations Soufrière Cresslands Soufrière Bay 1951 British start formal investigation (Willmore) Ravine Claire 1952 1964 survey Fond St. Jacques 1974 Institute of Geological Sciences (IGS) U. K. resistivity survey 1975 -76 Seven wells drilled by IGS (Wells 1 -7) 1976 Aspinall et al. perform seismic monitoring 1982 Aquater (Italy): Magnetotellurics, gravity, well data evaluation. 1983 -84 Los Alamos (USA): Geology, geochemistry, geophysics UNRFNRE 1987 -88 USAID/UN: Drill two deep wells (SL 1 & SL 2) USAID – DOE & USGS 1992 Geothermal Energy New Zealand: Gravity, resistivity, audio magnetotelluric resistivity 1998 -Pesent M. I. T. : Reinterpretation of British resistivity data, self potential geophysics, decision analysis 2004 -Present United Network of the Eastern Caribbean is commissioned to develop geothermal resources. Diamond Petit Piton Time Line Terre Blanche Sulphur Springs Rabot Anse Des Pitons Belfond Etangs Morne Bonin Belle Plaine Gros Piton USAID – LANL Gov’t of St. Lucia GENZL & Aquater British Drilling Programme GENZL Kilometers 0 0. 5 1 2 3 4 5 6 Tomblin performs detailed geology

Geology

Geothermal Wells & Hot Springs Soufriere Bay Petit Piton Gros Piton

GENZL, 1992 USAID (Aquater), 1987

Summary • Very complex geology and hydrogeology • The chemistry of the geothermal waters beneath the Sulphur Springs is quite severe. • The geothermal reservoir cap rocks are weak. • Exploration is best optimized by exploring for less hot – but less corrosive – waters away from the Sulphur Springs.

Synopsis of Four MIT Studies • Reinterpretation of the British Line 9 resistivity data. • 3 D rendering of 2 D resistivity inversions. • Self Potential surveying. • Geological/Geophysical data integration using a decision analysis method.

Reinterpretation of the British Line 9 Resistivity Data collected in 1974 by Lee and Greenwood, British Geological Survey

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Sulphur Springs (1974) Depth (m) 0 40 1 3 30 5 200 400 6 7 4 5 SL-2 2 50 100 15 200 30 600 5 800 Sulphur Springs (2002) 1 Depth (m) 0 6 7 4 5 SL-2 3 200 400 600 800 0. 5 1 1. 5 2 2. 5 3 Log Resistivity (ohm-m) 3. 5 4

Sulphur Springs 2 1 3 7 4 5 6 SL-2 SL-1 1000 ohm-m 150 o. C 30 ohm-m 250 o. C 30 to 1000 ohm-m

3 D Rendering of 2 D Resistivity Inversions. All the British resistivity lines were inverted into 2 D cross-sections and then rendered into 3 D.

3 D Resistivity Tomogram Southeast -to- Northwest

3 D Resistivity Tomogram Northeast -to- Southwest

Self Potential Surveying Small, millivolt electrical potentials were mapped, processed and interpreted throughout the Qualibou Caldera.

SP Survey Lines Cres slan d Di am on Ma r hu lp Su te tou e r lg d. es cqu t. Ja d d. S Belfon Fon in Ma gs rin Sp 3

Individual SP Lines 200 Self Potential 100 0 -100 Fond St. Jacques Cresslands Diamond Sulphur Springs Rabot Belfond Malgretoute -200 -300 0 2000 4000 6000 Distance 8000 10000 12000

N Correlation of observed SP anomalies and fault locations.

m. V Interpolated SP Data Sulphur Springs

Geological/Geophysical Data Integration Using a Decision Analysis Method. Eleven disparate data sets were jointly analyzed by a decision analysis methodology to determine possible drilling locations.

Method Re-interpreted British Resistivity 700 m BGS 0 km 3 km 6 km Morgan et al. , (2002) Target Region Discretized Caldera Example Data Map Eleven datasets were used: Seismics, self potentials, fault structure, deep resistivity, shallow resistivity, geology, topography, wells/springs/geochemistry, shallow AMT, deep AMT, and residual gravity.

Group Result Cresslands X 4 Diamond X 3 Malgretoute X 6 X 1 Sulphur Springs X 2 Etangs X 5

Conclusion Geothermal resource exploration in Saint Lucia is a very difficult endeavor because of: • Geological complexity • Highly corrosive geothermal waters.

Recommendations • Explore for drilling locations away from the Sulphur Springs to balance improved water chemistry with lower temperatures. • The probability of success will increase substantially by doing 3 D resistivity/selfpotential geophysics to accurately locate drilling positions and to avoid the faux pas of the past.