A Means of Increasing Drill Collar Connection Life

Drill collar connection failures have increased as oil and gas wells are drilled to greater depths requiring the use of smaller collars. The high cost resulting from these failures prompted a project to develop means of reducing the drill collar connection failures. This paper discusses laboratory investigations and the results of a development program conducted by Texas A&M University Research Foundation to determine the magnitude of drill collar connection stresses and the selection of a collar modification to reduce connection stresses. Full-scale laboratory fatigue tests of drill collar connections and subsequent field service demonstrated that the use of exterior stress relief grooves on each side of the connection materially increased connection life before failure occurred. Field Service tests following fuel scale laboratory fatigue tests show increased drill collar connection life resulting from use of exterior stress-relief grooves.