Optimum Means of Protecting Casing and Drillpipe Tool Joints Against Wear
Authors: True Martin E. , Weiner Peter D. 
Published: December 2007

Drilling of deeper wells and the use of directional drilling has increased the frequency of casing failures caused by drillpipe and tool-joint wear. Laboratory investigations of various hardfacings and protectors indicate that plain tool joints, smooth-ground tungsten carbide hardfacing, and rubber protectors can diminish the problem.

Introduction

During recent years there has been a marked increase in the number of holes that have been drilled to greater depths. Many of these are drilled directionally from an offshore platform and from small areas where surface locations are expensive, such as those in the Arctic and in congested areas. In these directional wells, deviations of 13 degrees/100 ft are typically produced. In addition, while drilling nondirectional wells, the borehole sometimes spontaneously deviates as much as 8 degrees/100 ft from the vertical. These hole deviations cause the drillstring to undergo cyclic bending and apply high pressure between the drillstring and the well casing, resulting in wear of both casing and tool joints.

In general, hard metal is applied to a section of drillpipe tool-joint boxes to reduce wear of drillpipe connections through deviated sections. Although most of the hardfacing materials protect the drillpipe tool joints from wear, the casing is severely worn by many of these because of rotation or movement of the drillstring through the well casing. Also, rubber protectors that have a diameter greater than the tool protectors that have a diameter greater than the tool joint are installed on some drillpipe strings to prevent contact between the casing and tool joints.

Prevention or a major reduction of the damage to casing together with the selection of a material or method for protecting or minimizing drillpipe wear would save the industry millions of dollars annually. A project was conducted by Texas A and M U. under contract to Exxon Co. U.S.A. to evaluate the effect of various drilling assemblies on the wear of casing while drilling oil and gas wells. Also, an evaluation was made of the wear of tool joints, drillpipe rubbers, and experimental metal tool-joint protectors. The program provided for evaluating the effect of hardfacing on drillpipe tool joints vs plain tool joints, and the effect of rubber and experimental metal protectors that prevent drillpipe tool joints from protectors that prevent drillpipe tool joints from contacting casing during drilling operations. The investigation was carried out in water, in two weights of water muds, and in oil-base mud. The tests in muds were made with and without sand. The tool joints, rubber protectors. and metal protectors were operated in three grades of pipe.

This paper describes the laboratory tests and presents the results of the project, which included 347 presents the results of the project, which included 347 tests. These tests included 267 tool-joint tests, 66 rubber-protector tests, and 14 experimental metal tooljoint box protectors. The tool joints, casing, and drillpipe protectors, and the casing specimens used in these tests, are shown in Fig. 1.

Material Used in Conducting Drillpipe Tool-joint and Casing Wear Tests

The following drillpipe tool joints, pipe protectors, casing, and drilling fluids were used in conducting tests of tool joints and casing.

JPT

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