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This paper presents a new method for determining formation resistivity via sequential interpretation of the LWD and Wireline (WL) resistivity logs. The LWD logs can be used to determine the Rt, but they may not contain enough information to accurately determine parameters of invaded zones. The inversion-based interpretation of the WL Array resistivity logs provides a direct way of determining the hydrocarbon-bearing formation model. However, interpretation of WL data may be unstable and provide an incorrect equivalent solution due to a strong non-uniqueness of the inverse problem. To find the true model from an unlimited number of equivalent solutions, we propose a stable method that leads to a gradual increase of the formation model complexity. The major steps are: Estimation of Rt using deep-reading LWD data inversion.Estimation of Rxo using an Rxo WL log.Estimation of Lxo using WL data inversion.Simultaneous corrections of the final model parameters using WL data inversion. To establish the effectiveness of our method, we first successfully tested it on 2-D and 3-D benchmark models. To examine the practical validity of the method, we applied it to LWD induction data and the Array Lateral Log WL data acquired in a salt-saturated mud environment in a deviated well located in the South China Sea. Our objective was accurate determination of hydrocarbon saturations. Application of our method allowed us to accurately determine the formation resistivity and translate it directly to accurate Sw estimates. We demonstrate that the suggested method provides a lower Sw saturation than the sole WL data interpretation. |
