Casing tensile stress distribution in the bending section of a well during hydraulic fracturing

Abstract

Abstract During hydraulic fracturing, there has been little research on casing tensile stress distribution from the tilting area to the horizontal area in the whole string. In order to study the casing tensile stress distribution in the bending sections during hydraulic fracturing, a three-dimensional finite element mechanical analysis model of casing–cement–formation in the bending sections was established. The analysis showed that: When the cement of tilting area was missing, the casing tensile stress decreased with in situ stress difference increasing, and the casing tensile stress increased when the middle area or the target area was missing. When the internal pressure of casing increased continuously, the casing tensile stress decreased first and then increased, and the casing internal pressure was 20 MPa, which was the minimum point. When the casing internal pressure was lower than 20 MPa, the casing tensile stress decreased with Poisson’s ratio of cement increasing. When the casing internal pressure was higher than 20 MPa, the casing tensile stress increased with Poisson’s ratio of cement increasing. Compared with the case where the temperature difference was ignored, the temperature difference below 5 ℃ had little influence on casing temperature stress; however, the temperature difference above 5 ℃ had significant influence on casing temperature stress. Fracturing in the formation where Young’s modulus of elasticity of rock was higher than 15 GPa could reduce the stress failure of casing tensile. The research results had a certain guiding significance for the prevention of casing tensile failure in the bending sections.

Keywords

• Finite element
• Collapse strength
• Bending sections
• Casing tensile stress
• Casing tensile failure