Electrical behaviour of rock samples from Puglia 1 borehole (South Italy): from 20°C to 1000°C

Abstract

During 1992, at the Applied Geophysics Laboratories of Florence (I) and Prague (CS) some electrical measurements were made on deep rock samples to understand the source of low resistivity values measured by logs.The studied samples were sandstones (6380 m depth) and dolomites (6070 m depth) coming from the borehole AGIP-PUGLIA 1 (South Italy). The electrical parameters were the real part of the complex resistivity, the loss tangent and the total harmonic distortion. They were measured as functions of temperature (20 £ T £ 1000°C),confining and internal pore pressure (3 £ p £ 33 MPA), and frequency (0.002 £ f£ 1000 Hz). For the measurements, two different apparatus were used: the Florence apparatus working up to T= 200°C conditioning internal pore fluid, and the Prague apparatus working in temperature (200°÷1000°C). Both the literature and laboratory research confirm that the electrical results at our experimental physical conditions remain unchanged. The obtained results confirmed that deep rocks can show low resistivity valued at special internal fluid pressures and temperatures, according to their mineralogical composition and petrographic structure.