The Prediction and Control of Casing Wear (includes associated papers 6398 and 6399 )
Authors: Bradley William B. , Fontenot John E. 
Published: December 2007

Casing wear is a problem in many wells and can cause abandonment of a wellbefore reaching total depth, or can lead to a blowout. Procedures forestimating casing wear caused by rotating, tripping, and running wirelinehave been developed. Based on results of extensive laboratory study, theyallow consideration of, among other things, dog-leg severity, coupled withdrillstring tension, mud solids, and drillpipe protectors.

Introduction
Casing wear is a problem in many wells. In directionalholes, very deep holes, and medium-depthabnormally pressured holes, it can become a criticalproblem. It can cause the abandonment of a well beforereaching total depth or, in certain cases, it can leadto a blowout.The objective of the work reported here was todevelop better methods for the prediction andcontrol of casing wear. To develop better predictivemethods, casing wear rates were measured undercontrolled conditions. Laboratory measurements weremade to define the major factors in rotating, tripping, and wireline wear. This paper compares the variousmodes of casing wear and develops procedures forestimating field wear rates.

Background
Although casing wear has been a problem for manyyears, published literature on the subject is meager.In the United States, tests have shown the value offine-particle tungsten carbide hardbanding on thereduction of casing wear by rotating tool joints.The remaining body of literature on casing wearcomes primarily from Russia. Laboratory tests havebeen run there to determine casing wear ratesby drillpipe rotation. Unfortunately, they were runin drilling muds without abrasives. Russianinvestigators have also studied the wearing mechanismsof abrasives, but their studies were not done withcasing.The effects of other variables on the casing wearprocess have also been studied by Russianinvestigators. Theoretical calculations of wear becauseof drilling, tripping, and connecting were made.But, without experimentally determined wear rates, these calculations are of little value. Test resultsalso show that the hardness of the casing doesnot greatly affect its wear resistance. Analysis ofrecovered casing has indicated that, in manyinstances, temperatures of the wear surfaces reach 900to 1,000 degrees C. Wearing under these conditions canproduce significant cracking of the casing wall anda substantial reduction in casing strength. Casingdamage by drill bits during tripping has also beenreported by the Russian investigators.The ability of drillpipe rubbers to prevent contactbetween the drillstring and casing is discussed in Ref.15. Tests to determine the deflection of the protectorsunder various conditions of load, mud, and temperatureare reported. These results are similar to the results reported in Ref. 1. Physical damage to theprotectors from casing joints during tripping is alsodiscussed.Calculations and casing-design considerations tominimize failure of casing because of wear arereported in Refs. 5, 10, 16, and 17. Measurement ofdrag forces at points of contact in wells is reportedin Ref. 16.
JPT
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