Field Testing of an Advanced LWD Imager for Oil-Based Mud Applications

摘要

Microresistivity and acoustic-borehole imaging encounters many challenges in oil-based mud (OBM). Although several wireline OBM imaging tools are commercially available, thus far there has been no equivalent LWD device. In this paper, we introduce a new tool that addresses this gap in LWD formation-evaluation technology. Existing wireline oil-based imagers use four-point resistance measurement methods. These devices require good and stable coupling to the formation. This is typically achieved by mounting the sensors on pads, which are forced against the formation wall by hydraulically activated arms. Such a solution is impractical in the LWD environment in which rotation and lateral movement of the drillstring prevents reliable contact with the borehole wall. Moreover, the additional friction caused by firm pad contact with the borehole wall would reduce the rate of penetration and could result in tool sticking or failure.