Assessment of Similarity Between Well Logs Using Synchronization Measures

In oil exploration, studying the similarity between patterns of the same geophysical properties in different wells is essential for making early decisions on future planning as well as for assessing the lithology of the area under survey. Geoscientists either rely on visual tools or resort to correlation studies between the different wells to match portions of the well logs. This is a tedious process involving several trial and error runs, which includes shifting, stretching, and sometimes preprocessing of the well logs by experienced geoscientists. However, this can be simplified by automating the process of matching. The well logs, a measure of the lithology, fall under the class of nonlinear signals. Therefore, linear methods are inadequate for matching these sequences. In this letter, we introduce similarity measures based on the concept of synchronization as used in matching nonlinear signals such as chaotic time series data. Two recently proposed methods, i.e., synchronization likelihood (SL) and visibility graph similarity (VGS), have been applied on the gamma-ray and porosity logs along different wells. These are considered as depth sequences, which can also be converted to suitable time series with the availability of the velocity profile. The data for this study originate from 12 existing wells in the western coast of India. The values of SL and VGS as well as the correlation are computed between these wells. Higher values indicate the existence of similarities. This has also been verified from the overlapped plots of well-log data.