An approximate and efficient electromagnetic (EM) telemetry 3D modeling method is presented that can provide prejob and on-site support of an EM telemetry tool, usually a component in a measurement-while-drilling (MWD) or logging-while-drilling (LWD) operation. This method can handle vertical, curved, and lateral sections during drilling a well in which an EM gap-transmitter sub is added in the borehole assembly (BHA). In addition, both surface stakes (SS) and deep electrodes (DE) in adjacent steel-cased wells can be used as an antenna to receive EM signals transmitted from the gap-sub source. The most fundamental concept is that pipe currents flowing along the drillpipe are the basis for successful EM telemetry communication. To capture these pipe currents and be able to perform 3D EM modeling in an efficient way, three innovative ideas supporting this method rely on: firstly, efficient computation of pipe currents in a vertical well through 2D axisymmetric finite-element (FE) modeling and its extension to a deviated well; secondly, an equivalent source method treats each pipe current element as an electric dipole source, and then sums all dipole responses to obtain EM fields at any receiver location. With 1D formation resistivity, these dipole fields can be computed efficiently by running a 1D EM solver, and thirdly, for DE reception, an additional EM reciprocity principle can be invoked by treating the DE well as an artificial source and the same 2D axisymmetric modeling algorithm can be applied. Finally, this approximate 3D method is verified and validated by comparing it with rigorous COMSOL 3D modeling, as well as with a real EM telemetry data set acquired in a lateral section with a 19,000-ft total depth (TD).
Presentation Date: Wednesday, September 18, 2019
Session Start Time: 8:30 AM
Presentation Time: 9:20 AM
Presentation Type: Oral