Long-Term Monitoring with Fiber Optics Distributed Temperature Sensing at Campi Flegrei: The Campi Flegrei Deep Drilling Project

Abstract

Monitoring volcanic phenomena is a key question, for both volcanological research and for civil protection purposes. This is particularly true in densely populated volcanic areas, like the Campi Flegrei caldera, which includes part of the large city of Naples (Italy). Borehole monitoring of volcanoes is the most promising way to improve classical methods of surface monitoring, although not commonly applied yet. Fiber optics technology is the most practical and suitable way to operate in such high temperature and aggressive environmental conditions. In this paper, we describe a fiber optics Distributed Temperature Sensing (DTS) sensor, which has been designed to continuously measure temperature all along a 500 m. deep well drilled in the west side of Naples (Bagnoli area), lying in the Campi Flegrei volcanic area. It has then been installed as part of the international ‘Campi Flegrei Deep Drilling Project’, and is continuously operating, giving insight on the time variation of temperature along the whole borehole depth. Such continuous monitoring of temperature can in turn indicate volcanic processes linked to magma dynamics and/or to changes in the hydrothermal system. The developed monitoring system, working at bottom temperatures higher than 100 °C, demonstrates the feasibility and effectiveness of using DTS for borehole volcanic monitoring.

Review of Recent Drilling Projects in Unconventional Geothermal Resources at Campi Flegrei Caldera, Cornubian Batholith, and Williston Sedimentary Basin

“…Following the results of the pilot hole, a further well, specifically aimed to find the areas of highest temperature gradients at very shallow depths, and hence the most suitable for inexpensive and powerful geothermal exploitation, was drilled in the Agnano-Pisciarelli area (red triangle in Figure 1). The measured temperature-depth profiles of the two wells are shown in Figure 5 [39]. The Agnano borehole samples the area of highest shallow geothermal gradient, with temperature exceeding 110 • C found at only 88 m of depth, showing the very high potential of this area, already quantified by Reference [19], even at very modest and inexpensive depths.…”

Fiber optic sensing for volcano monitoring and imaging volcanic processes

“…DTS finds most of its applications in ground water temperature projects, such as coal, oil and gas, and geothermic studies. There are few examples of DTS applications in volcanology, such as at Mount Erebus, Antarctica (Curtis & Kyle, 2011), at Campi Flegrei (Southern Italy) with submarine temperature profiling (Carlino et al, 2016) and borehole temperature monitoring (Somma et al, 2019).…”

Inquiry into the Temperature Changes of Rock Massif Used in Energy Production in Relation to Season

“…Initial testing of long-term temperature measurement using DTS systems was carried out in the area of Campi Flegrei caldera which includes a part of the large city of Naples (Italy). 500 m deep wells with high temperatures of about 100 • C were measured in an area with volcanic activity [24]. The installation for 8 days and temperature measurement using the DTS system were carried out in geothermal wells in the production state.…”