Abstract
Aimed at studying the casing wear in the highly deviated well drilling, the experimental study on the casing wear was carried out in the first place. According to the test data and the linear wear model based on the energy dissipation proposed by White and Dawson, the tool joint–casing wear coefficient was obtained. The finite element model for casing wear mechanism research was established using ABAQUS. The nodal movement of the contact surface was employed to simulate the evolution of the wear depth, exploiting the Umeshmotion user subroutine. In addition, the time-dependent geometry of the contact surfaces between the tool joint and casing was being updated continuously. Consequently, the contact area and contact pressure were changed continuously during the casing wear process, which gives a more realistic simulation. Based on the shapes of worn casing, the numerical simulation research was carried out to determine the remaining collapse strength. Then the change curve of the maximum casing wear depth with time was obtained. Besides, the relationship between the maximum wear depth and remaining collapse strength was established to predict the maximum wear depth and the remaining strength of the casing after a period of accumulative wear, providing a theoretical basis for the safety assessment of worn casing.
Highlights
With the development of petroleum industry, extendedreach well, highly deviated well, ultra-deep well, and horizontal well technologies are widely applied in oil and gas drilling.[1,2,3] The highly deviated well in this article refers to the well with deviation angle greater than 45°.4,5 Because of long drilling cycle, large friction, and big side force acting on the casing, the casing wear phenomenon is very severe
It is worth observing that the wear depth of each point at instant time t is different on the contact surface of the casing inner wall, because of the different instantaneous contact pressures and sliding distances that depend on the time
Based on the finite element model of tool joint–casing wear established in this article, a field condition is analyzed when the rotating speed of the drill string is 60 r/min and side contact force is 25 kN/m; the relationship curve of the maximum wear depth changing with time can be acquired through extensive numerical simulations
Summary
With the development of petroleum industry, extendedreach well, highly deviated well, ultra-deep well, and horizontal well technologies are widely applied in oil and gas drilling.[1,2,3] The highly deviated well in this article refers to the well with deviation angle greater than 45°.4,5 Because of long drilling cycle, large friction, and big side force acting on the casing, the casing wear phenomenon is very severe. Gao and Sun[14] modified the wear efficiency model by considering the change in the contact pressure during casing wear process and developed the nonlinear relationship of the wear depth and time. Lin et al.[17] established a new crescent-shaped wear equation for calculation of worn casing collapse strength considering both non-uniform wear and manufacturing defects. Investigations found that previous researches generally adopted the ‘‘average contact’’ method to assume the contact pressure and total sliding distance in a period of wear.[2,7,14,16,17,18,19,20,21] according to energy principle, the casing wear is a dynamic accumulation process, and the direct contact area between drill string and casing increases continuously and nonlinearly with the running wear. The remaining collapse strength was calculated based on the accumulative worn casing, using the ABAQUS restart function
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