Electromagnetic well logging. Models for MWD/LWD interpretation and tool design / Электромагнитный каротаж скважин. Модели для интерпретации MWD/LWD и проектирования инструментов

Electromagnetic wave resistivity methods in Measurement-While-Drilling and Logging-While-Drilling applications, or simply MWD/LWD, are now approaching their fourth decade of practice. Th ey are instrumental in anisotropy determination, dip angle analysis, bed boundary detection, fl uid identifi cation, and so on, and are important to economic analysis, stimulation planning, geosteering, unconventional resources and numerous exploration challenges. Essentially, phase delays and amplitude changes measured at (one or more) coil receivers relative to (one or more) transmitters are interpreted using Maxwell’s equations to provide clues related to vertical and horizontal resistivities Rv and Rh. Th at said, the objectives are well-defi ned and easily understood. However, the general modeling problem is diffi cult and mathematical challenges persist.

Fift y years ago, induction logging practice and interpretation were straightforward. Formations were thick and homogeneous. Wells were vertical. Tools were concentrically placed. Azimuthal symmetry was the rule. Coils wound around fi berglass mandrels, with their planes perpendicular to the axis, implied that only Rh was available from measurements. But that was fi ne – fl uid fl owed only radially toward the well so only horizontal (or radial) properties mattered. Like everything else back then, life was simple in the slow lane, and well logging and math modeling were no exception. Th e simple dipole model taught in physics suffi ced for most purposes and log analysis was elementary. <...>