Abstract

Mofete and San Vito geothermal fields are tapping hot fluids, hosted in a quaternary volcanic area, still subject to volcanic and tectonic activities.

Seven wells have been drilled, ranging in depth from 700 to 2200 m in Mofete field and three wells, ranging in depth from 2300 to 3050 m have been drilled in San Vito field.

The wells have been the basis for physical-chemical analyses of the fluids and petrographic analyses of the rocks, which permitted the individualization of an argillitic upper zone, acting as cap rock, overlying altered and metamorphosed zones, acting as reservoirs.

The wells have been tested for production both on a short and a long term basis, giving the information needed for developing the fields. The development of Mofete field is foreseen in two stages: first the installation of a small power plant (3 MW) and second the intallation of an industrial power plant (say 15-30 MW). The first stage is considered a testing period for a better development of the second one.

The power plant will be installed on the platform common to the wells MF-2, 9d, 3, 8d. The first stage power plant will be fed by the wells MF 1, 7d and 8d, reinjecting the waste water into well MF-2. As regards the reservoirs, the producing wells tap a horizon shallower than the reinjection level avoiding direct mixing of the fluids.

The three producing wells yield an excess flow rate, so that they will be throttled to cope with turbine requirements. The waste water flow rate is on the order of 150 t/h, which is handled by a single 8" pipe, in a "Z" shape to allow for thermal expansion.

During the production an extensive monitoring programme is foreseen to improve the knowledge of the field.

The development of San Vito field is still at a preliminary stage, since the production of one well is poor, one well is dry and one well is waiting for a new wellhead, due to its unusual temperature (420°C) and pressure (22.5 MPa) at bottomhole.