Feasibility Study of Electromagnetic Telemetry System for Offshore Drilling

Abstract

Abstract Electromagnetic telemetry (EMT) system uses a downhole source inserted near the drilling bit to send out real-time measurements via low frequency electromagnetic waves. A surface antenna picks up the transmitted signal by measuring the potential difference of two locations. Compared with onshore drilling, EMT system for offshore drilling has two major differences: there exists one layer of conductive seawater and one endpoint of the surface antenna anchors near the seabed. An integral-equation-based simulation algorithm was developed for fast and accurate simulation of EMT system in oil and gas exploitation. How the conductive seawater affects electromagnetic wave propagation is studied by modeling different scenarios by changing water depth, well trajectory, downhole source type, and operating frequency. The success of EMT application is strongly dependent on the formation resistivity between the downhole tool and the surface antenna used to monitor the transmitted signal from the downhole tool. Therefore, it’s important that an accurate prediction of the EMT system performance is performed before planning and performing an EMT job. Theoretical and numerical analysis suggests that EMT technology for offshore drilling behaves differently from onshore drilling because there exists a layer of conductive seawater and the surface antenna must traverse through the seawater to the seabed.