Integrated Interpretation of Galvanic and Induction Measurements by Inversion Methods

Accurate estimation of residual and movable hydrocarbon requires precise estimation of the formation resistivities in the flushed and uncontaminated zones. The estimation of formation resistivities is commonly done by interpreting the data provided by galvanic (mainly laterolog) and induction devices. Conventional interpretation methods of electromagnetic measurements use approximate and independent techniques for galvanic and induction logging measurements. These techniques provide some means to correct the resistivity measurements for borehole, shoulder, and invasion effects. Since the charts are typically designed for the interpretation of the measurements that correspond to a single suite of logs, individual results may differ when different sets of measurements available in a particular borehole are used in the interpretation. The interpretation, i.e., finding an earth model consistent with all measurements, is then left to the skill of the log analysts. This work demonstrates how the interpretation is improved by suing an algorithm that simultaneously considers all available resistivity measurements. The work also shows the importance of the inversion process in extracting the information content from the data in cases that would not be possible by using conventional interpretation methods, as well as the use of statistical results to assess the quality of the interpretation. Several field casesmore » are presented that show the importance of unified interpretations in improving the accuracy of the formation resistivity estimation, and the enhancement of radially and vertically layered earth models that result.« less