EFFECT OF CASING TUBING WEAR ON BURST STRENGTH

Casing wear has recently become one of the areas of research interest in the oil and gas industry. Casing wear is mainly caused by the rotation of the drill string, bending actions during directional drilling and due to the chemical composition of drilling fluid. The decrease in the thickness of the casing wall results in the weakness of the mechanical strength of the casing. The burst strength of a worn out casing is one of the affected mechanical properties and yet an area less researched.
Studies had been conducted to come up with the most reliable theoretical methods to estimate the resulting burst strength of a worn out casing. The most commonly used equation is Barlow’s equation. However, this equation is considered to be more conservative as it incorporates high safety factor which in the long term results in more economic expenditure. In addition to Barlow’s equation, the initial yield burst, the full yield burst and the rupture burst equation are other equations that are used to estimate casing burst strength.
The objective of this project is to estimate casing burst strength after wear through Finite Element Analysis (FEA) method and compare the results with theoretical values. The project work includes building various models with different defect shapes and depths to represent wear on a casing and simulating the models using linear and nonlinear analysis methods. The von Misses stress is used in the estimation of the burst pressure. The result obtained confirms that casing burst strength decreases as the wear depth percentage of the casing increases. Moreover, the burst strength value of the casing obtained from the FEA yields a higher value compared to the theoretical burst strength values. Casing with crescent shaped wear gives the highest burst strength value when simulated under nonlinear analysis.