Unique Application of EM LWD Casing Antenna System to Rocky Mountain Drilling

摘要

Certain formations in the Rocky Mountains preclude the use of electromagnetic(EM)telemetry due to their inherent resistivities.A new system has been developed that extends the use of EM telemetry systems where they were previously not usable.The system involves installing a special downhole antenna when surface or intermediate casing is run to improve EM signal to noise ratio.The casing antenna system not only allows operators to take advantage of the benefits of EM logging- while-drilling(LWD)systems but also extends the drilling depth range where data can be provided. Drilling wells in the Powder River Basin often requires heavy mud weights and the extensive use of lost circulation material (LCM).Unfortunately,these types of muds play havoc on standard mud pulse telemetry systems.Washed equipment and downhole failures related to plugged pulsers often result in multiple trips for failures and excessive nonproductive time (NPT).This new EM LWD system,by contrast,has no moving parts and a through-bore,which allows for higher concentrations of LCM and heavy weighting materials to pass easily through the bottom hole assembly(BHA).The system is combinable with a variety of LWD sensors so the telemetry type proves especially useful in areas that experience high LCM incidents.A key aspect of this system is that it also extends the depth range of where EM LWD systems can operate. Along with a compensated resistivity tool,a unique LWD spectral azimuthal gamma ray(SAGR)sensor,which provides accurate formation evaluation data,high quality gamma ray images and spectral elemental analysis,was used to help geosteer the well to stay in the zone of interest in the reservoir.This paper will examine a case study where the new system was used in an area where drilling with EM was not previously possible.It will describe the basic system design,key operating parameters,provide insight on the drilling problems,and address formation evaluation challenges and solutions.