Abstract
We monitor the seismic signal emitted from a rotating drill bit in real time with an array of seismic sensors at the seafloor. Drill-bit seismic signals provide information to locate the drill-bit position itself and to image geological objects ahead and around the drill bit for geosteering purposes during drilling operations. The data can be obtained in real time without the need to stop drilling for logging and without any additional downhole instrumentation in the bottom hole assembly. Drill-bit positioning accuracy is independent of measured depth and with meter level lateral precision. This is significantly better than conventional downhole gyro-based methods, especially for long horizontal wells. With sources along the drilled well path approaching a target reservoir we obtain a 3D reverse VSP (RVSP) image around the well for prediction ahead of the drill bit. This paper presents a case study from the Grane reservoir in the North Sea, where we utilize a permanent reservoir monitoring (PRM) array for listening to signals emitted from drilling with a PDC bit. We present imaging results from a highly deviated well and compare them to 3D seismic. The field example shows the ability to look ahead several hundreds of meters below the drilled well trajectory.
