Stress Analysis of Internal Wall Worn Casing String under Uniform Earth Pressure Based on ANSYS

Abstract:

Wear of casing string is a common phenomenon in the process of oil and gas exploitation, and it reduces collapse and burst strength of casing string. Stress of internal wall worn casing string must be analyzed to ensure strength of casing string. In the paper, wear form of casing string is assumed as a crescent-shape, and a half finite element model (FEM) of worn casing string, cement-loop and earth combined system is established using the symmetry. Geometry relationships of wear ratio (or wear depth) and the centre of drill pipe are established. Effects of variables such as wear ratio of casing string, magnification factor of wellbore, elastic modulus of cement-loop and working conditions on casing string stress are discussed respectively. Some conclusions are drawn: maximum stress in casing string increases with increased wear ratio of casing string, and ultimately exceeds the yield limit. Increase of magnification factor of wellbore will improve bearing capacity of casing string, but maximum stress in casing string decreases slower and slower with further increase in magnification factor of casing string, at the same time, stress decreases more in casing string than in cement-loop. Minimum stress in cement-loop increases and maximum stress in cement-loop fluctuates with increased elastic modulus of cement-loop, while both minimum and maximum stress in casing string first increases then decreases, the turning point is related to elastic modulus of casing string and earth, as well as the geometry relationships among them. The bigger pressure difference, the larger maximum stress exists in casing string.

• Periodical: Applied Mechanics and Materials (Volumes 152-154)
• Pages: 912-919
• DOI: https://doi.org/10.4028/www.scientific.net/AMM.152-154.912
• Online since: January 2012
• Authors: Yin Ping Cao, Yi Hua Dou, Yang Yu
• Keywords: Elastic Modulus of Cement-Loop, Magnification Factor of Wellbore, Wear Ratio of Casing String, Worn Casing String

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