THE ELECTROMAGNETIC PREDICTION OF THE OPEN POROSITY BEYOND BOREHOLES
V.V. Spichak, O.K. Zakharova
Geoelectromagnetic Research Centre of the Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Troitsk, Russia
Keywords: Prediction, porosity, specific electrical resistivity, magnetotelluric sounding, electromagnetic resistivity pseudolog, artificial neural network, Archie formula
Abstract
Prediction of the open porosity factor below boreholes and in the interwell space, from electromagnetic sounding and electrical logging data, has been studied. Modeling porosity data are synthesized from laboratory studies on the samples of two boreholes drilled in the Bishkek geodynamic site. The porosity prediction is carried out using specific electrical resistivity data obtained from 1D inversion of magnetotelluric sounding data collected in the vicinities of these wells. A new approach to predict porosity is suggested, based on the constructing of electromagnetic resistivity pseudologs at the target location. The comparison of this technique with other options indicates that its application results in substantial improvement of the predicted accuracy (in particular, relative errors of prediction in double depth of the borehole and in the interwell space could be 2 and 8 %, respectively). In general, the porosity predictions, based on Archie formula, give worse results.
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