ABSTRACT:

Since the introduction of logging techniques, resistivity measurements, both while drilling and wireline, are widely used for the determination of water saturation profiles, net pay and hydrocarbon-in-place in hydrocarbon-bearing reservoirs. Nevertheless, due to a number of environmental effects (borehole, shoulder beds, invasion, dipping beds, anisotropy), the measured resistivity may differ from the true resistivity (Rt) required for the correct evaluation of these important petrophysical parameters. In order to remove these alterations, the industry has developed sophisticated techniques that simultaneously correct the measurements for a number of environmental effects. This paper discusses the results obtained in a clastic, thinly-bedded reservoir in the Mediterranean area, where the reservoir characterization has been done by applying resistivity modelling and inversion techniques. The methodology, developed by Schlumberger in cooperation with ENI-AGIP as an outcome of a joint R&D project, is based on an iterative modelling and inversion process and gives the best results when applied in difficult drilling and production optimisation environments, such as complex heterogeneous reservoirs. The most important results are:

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    the reconciliation between LWD and wireline resistivity measurements;

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    the reconciliation between saturation profiles derived from resistivity/porosity data and direct down hole nuclear magnetic resonance logging measurements;

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    the determination of more accurate water saturation profiles in both thin bedded intervals and dipping sandstone beds.

These results, when compared with those obtained using standard interpretation techniques, confirm the effectiveness of the developed methodology in improving the quality of the reservoir characterization and in maximizing the return of the investments in logging and well data measurements.

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