With the recent advancement of directional drilling technology and the use of rotary steerable systems, more deviated and horizontal wells are being drilled and evaluated around the world and especially in Saudi Arabia. In these complex reservoirs, logging while drilling (LWD) wave propagation technology allows accurate geosteering and well placement. Such a technology often exhibits boundary related artifacts (horns) at formation boundaries between beds having different resistivities, particularly where the borehole penetrates formations at an angle. This makes resistivity interpretation difficult and creates a challenge for determining true formation resistivity that is essential for determining hydrocarbon saturation.

This paper presents a processing methodology for the elimination and reduction of horns and shoulder bed effects. Logs processed using this method are more accurate and easier to interpret. This new technique solves the forward and inverse problems using a simplified approach. The forward problem is solved using a fast analytical technique that generates synthetic logs. The inverse problem is solved using the forward problem solution iteratively and minimizing a cost function that measures the discrepancy between the generated synthetic logs and the field data in a Gauss-Newton fashion.

Data processing and inversion of examples from fields in Saudi Arabia are presented to illustrate the usefulness of this methodology. For the examples, the values of formation resistivity and distances to bed boundaries are obtained. These results indicate that the processing method provides a reliable technique for evaluating the true formation resistivity of LWD logs in deviated and in horizontal wells for both well placement and formation evaluation.

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