OBM Resistivity Imaging in Formations with Wide Resistivity Range, Multi-Frequencies Acquisition to Identify Features of Different Characteristics

Several challenges were encountered to obtain good quality of high-resolution resistivity images in oil-based mud (OBM) borehole environment. Technology development incorporated innovative designs of multi-arm, multi-frequency resistivity imaging pads to mitigate some of these challenges. This article will demonstrate the achieved benefits of deploying two OBM wireline (WL) resistivity images in addition to ultrasonic imager, in a large and intermediate vertical borehole through mixed lithologies with wide range of Formations resistivities and to provide recommendations for future deployments. Pre-planning is emphasized for achieving good results; expected lithologies, resistivity ranges, OBM components, etc. Accordingly, frequencies selection and required logging passes can be advised. During image acquisition, raw data processing takes place instantaneously to maintain real-time quality control and perform interactive changes as required for logging optimization. Customized composite plots are produced to compare between processed images from different frequencies to visualize the variable definition of borehole features between frequencies in ascending order. At this stage, dielectric effects on higher frequencies can be observed clearly when the Formation's resistivity range comes out of limits for these frequencies. In different Formations resistivity ranges, Low-Resistivity-Low-Contrast (LRLC), medium and high, it was proven that implementing multiple frequencies from OBM resistivity imaging technologies significantly reduce the probability of missing the definition of fine features such as thin-bedding sequences or natural fractures those existed in Formations of wide resistivity range (0.2 ~ 1500 ohm.m). Multiple frequencies from OBM resistivity imagers plus one from the ultrasonic imager were processed, compiled and analyzed to conclude that using of multiple frequencies is far superior than single-frequency OBM resistivity imager in similar environment, confirming the need to combine technologies to cover wider range of measurement specifications and to urge the industry towards the innovation of a single new technology that incorporates wider range and number of frequencies covering the measurement range and required environmental corrections in one platform. Eventually, OBM resistivity imagers of multiple frequencies deployment is becoming more proven approach after studying this case, and way important to achieve the deployment objective of high-resolution borehole imaging service(s) in OBM borehole environment. Future technology development is intended to correct for measurement artifact.