A NOVEL FORMATION IMAGING METHOD BASED ON MULTISCALE INVERSION OF ARRAY RESISTIVITY DATA

摘要

Accurate interpretation of modern array resistivity log data is critical to drilling, formation evaluation, and reservoir characterization. Multidimensional inversion-based array data interpretation methods are often used for this purpose. These methods commonly employ a single formation model for the entire interpretation process. Here we present an inversion-based imaging method that uses logresolution- dependent multiscale formation models. The method works as follows: First, we estimate shallow near-borehole resistivity. Then, we generate an image on a coarse spatial grid, inverting the logs with the lowest resolution. After that, we perform iterative image refining using multiscale formation models and logs of a higher resolution as input. The resulting model generated at each step is used as a starting model for the subsequent step. We present the test results using synthetic and field array lateral logs. Synthetic data was simulated by means of benchmark models containing small local anomalies and thin layers of different resistivities. Field data was acquired in an offshore Mediterranean well. In both synthetic and field cases, our method proves to be an efficient log data interpretation instrument that effectively images fine formation features.