METHOD AND APPARATUS FOR DETECTING BOUNDARY STRATUM

摘要

Methods and apparatus for detecting the approach of a boundary stratum (5) while drilling in a substantially horizontal subsurface zone (4) using sensor tools having sensors (6, 7) with different depths of investigation. The two depths of investigation signals are used to reduce spurious signals. In some cases, dips or angles of the boundary strat with the borehole may be determined. In alternative embodiments, one or more electromagnetic energy transmitters (16', 18', 20') are used with a single receiver (R1, R2) to generate a characteristic signature of approaching boundary stratum.