Recent Advances in Casing Wear Technology

Abstract

Abstract Casing wear is often a problem in deep wells where doglegs and large tension loads on the drill string combine to produce high lateral loads where the drill string contacts the casing. Casing wear can result in blowouts, lost production, and other hazardous and expensive problems. A mathematical model which describes casing wear in terms of hole geometry, casing/tool-joint material, mud system, and drilling program, has been developed and verified. Over 300 laboratory wear tests have provided wear factors which allow the model to be applied to a wide range of drilling situations. The model has been incorporated into a computer program, CWEAR. The prediction of dogleg severity and casing wear is seriously compromised by directional surveys in which the station spacing is 100 ft or greater. Through the laboratory test program, means to reduce casing wear rate have been demonstrated and applied in the field. Mud lubricants, tool-joint materials, pipe protectors, and casing materials and internal coatings have all been examined as possible means to reduce casing wear. Some mud lubricants significantly reduce frictional drag; others do not. Because a mud lubricant significantly reduces frictional drag does not imply that it will also reduce the casing wear rate. Newer, proprietary tool-joint coating materials have proven effective in reducing casing wear, while continuing to protect the tool joints in open hole. Pipe protectors have proven to be one of the better means of reducing casing wear. Laboratory experiments have demonstrated severe operational difficulties of these protectors. Several of the protector manufacturers are now engaged in development programs to improve their products. Inadequacies in the available methods of measuring casing wear in the field have been demonstrated. As a result of this work, at least two new casing wear measurement tools are under development. GOALS OF THE PROJECT The goals of our casing wear technology project are to:Predict Casing WearMeasure Casing WearReduce Casing WearPredict Burst and Collapse of Worn Casing To predict casing wear requires a mathematical description of the casing wear process. To implement this model requires experimental determination of the wear factors which are an integral part of the casing wear model. Such a model has been developed and verified. The model has been incorporated into a computer program, CWEAR, which has been used as both a planning and operational tool. More than 300 laboratory tests have been performed to determine wear factors which allow the model to be applied to a wide range of well geometries and drilling programs. Measurement of casing wear in the field has proven to be poor at best. Experimental evaluation of casing wear logging tools showed the need for improvement.