Directional Survey and Proximity Log Analysis of a Downhole Well Intersection

Abstract

A relief well was drilled to intersect the casing of a blowout well at 13,500 ft (4115 m) total vertical depth (TVD). During drilling, numerous directional surveys were run on the relief well. These surveys have been analyzed to determine the error associated with each. Both systematic and random errors were found in the surveys. The systematic errors caused much larger position errors than did the random errors. Magnetic and resistivity proximity logs were run to determine the distance between the blowout well and the relief well. Comparison with the directional survey data indicated that the magnetic proximity log could detect casing at least 42 ft (13 m) away and gave reasonably accurate distance and direction to it. The resistivity logs gave qualitative indications of casing when the wells were 100 ft (30 m) apart, but the quantitative interpretation was not as good as the magnetic log.

Borehole magnetometry; detection of a steel liner from a nearby observation borehole

“…In the subsurface, the magnetic effect of casing has been used to estimate the proximity of a relief well being drilled to intersect and extinguish a blowout well (Warren, 1981). The magnetic effect of a drill string upon a directional survey compass housed in a non-magnetic drill section is examined by Scott and MacDonald (1979).…”