Western Atlas International, Inc.

Izhar Ahmad

Randy Gold

Richard R Pemper

James E Brewer

An apparatus and method for detecting the location of subsurface markers in a formation proximate to a borehole. The apparatus includes marker detectors in a housing having at least two housing sections attached in an initial orientation. The distance between the detectors is measured under controlled conditions with a calibration bar. The initial attached orientation between the housing sections is identified with a calibrator, and deviations from the initial attached orientation are identified by the calibrator after the housing sections are detached and reattached. The calibrator permits well site corrections to be made to the housing sections without recalibration. Gauges permit corrections for temperature and pressure fluctuations, and the corrected distances between the housing detectors is computed. Detectors in the housing generate signals when each detector is proximate to a marker in the formation, and such signals can be processed to identify the elevation of a marker in the borehole, or the distance between markers in the borehole, to determine formation compaction or settlement. In an apparatus having two detectors separated by a spacer, flexible retainers can be positioned between each detector and the spacer to permit thermal expansion or contraction of the detectors relative to the spacer.

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League City, TX, United States of America

Izhar Ahmad