Montserrat geothermal system: A 3D conceptual model

Abstract

[1] We constructed a three-dimensional conceptual model of a geothermal system on the Caribbean island of Montserrat. The model was generated using magnetotelluric resistivity data, earthquake hypocenter data, and a three-dimensional P wave velocity model, all plotted using a shared geographical reference. The results of the study suggest a high-temperature fracture-controlled geothermal system at the intersection of two faults in the SW of the island. We also present a "prospectivity index" map that represents a proxy of the spatial variation in harvestable heat flux at 1500 m depth. The index is the product of relative permeability around modeled faults and a proxy for the subsurface temperature calculated using P wave velocity anomalies. Citation: Ryan, G. A., J. R. Peacock, E. Shalev, and J. Rugis (2013), Montserrat geothermal system: A 3D conceptual model, Geophys.

Seismic Velocity/Temperature Correlations and a Possible New Geothermometer: Insights from Exploration of a High-Temperature Geothermal System on Montserrat, West Indies

“…Looking closely at the well temperature logging results shown in Figure 6 we can see features in the data which support the general model of Ryan et al [9].…”

“…The current study indicates that rather than a direct dependence on temperature, seismic velocity is likely mediated by temperature dependent variations in the hydrothermal mineral assemblage. The data show that while seismic velocity anomaly increases with temperature below 220 °C, above this temperature the relationship reverses in a way that was not anticipated by Ryan et al [9]. Figure 6 shows the variation in measured temperature with normalized seismic velocity anomaly (Vpn) as derived from the tomographic model of Shalev et al [13] (appendix).…”

“…Extrapolating from the work of Kristinsdottir [10], Ryan et al [9] hypothesised that the magnitude of the seismic anomaly would be proportional to the reservoir temperature. The current study indicates that rather than a direct dependence on temperature, seismic velocity is likely mediated by temperature dependent variations in the hydrothermal mineral assemblage.…”

“…The detailed spatial inter-relation between the low velocity and low resistivity zones was explored by Ryan et al [9] who determined that there was an offset between the two anomalies with the low velocity zone sitting just beneath the low resistivity zone. Ryan et al [9] proposed the hypothesis that the seismic velocity anomaly was related to temperature variations in the geothermal reservoir as suggested by laboratory experiments on reservoir rocks presented by Kristinsdottir et al [10]. This current study suggests that this initial hypothesis should be superseded by the hypothesis that velocity in the reservoir is largely controlled by temperature dependent variations in the hydrothermal mineral assemblage.…”

“…Using these data, and data from previous studies, high priority areas for exploratory drilling were proposed by EGS Inc. [6] (Figure 1). In 2013, the geophysical data were reanalyzed to better pinpoint drilling targets within the priority zones [9]. In this study, geophysical data; magnetotelluric, earthquake hypocenters and seismic tomography data were used in conjunction with other geological information to construct a 3D conceptual model of the reservoir.…”