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Effect of Particle Erosion on the External Collapse Pressure of a Steel Production Casing Used in Oil and GasWells

Boer, N. (2018) Effect of Particle Erosion on the External Collapse Pressure of a Steel Production Casing Used in Oil and GasWells.

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Abstract:In the oil industry it is of great importance to accurately predict the external collapse pressure of the Oil Country Tubular Goods (OCTG) used in well applications as the collapse of a casing tube used in an oil well can lead to important economic losses and serious ecological damages. In this study the effect of solid particle erosion on the external collapse pressure of a production casing is evaluated by the use of FEA collapse simulations. In the literature study, two analytical models are proposed to calculate the external collapse pressure: the Shell Collapse Pressure Formula and the American Petroleum Institute Collapse Equations. The API equations provide accurate results and are used in well design, so these formulas are used for model validation in this research. The particle material, angle of impingement, particle impact velocity and particle size determine which erosion mechanism is active. In addition to these factors, there are other factors that influence the erosion rate, of which a list is provided and the effect of each factor on the erosion rate is discussed. No general erosion prediction model is present in literature that is suitable for practical use. This is because some aspects of the erosion mechanism are not fully understood yet and further research is required to develop a consistent set of physical parameters that can describe the erosion situation. A uniform cross-section model with a nominal outside diameter of 177.8 mm, a wall thickness of 9.36 mm and an ovality of 0.18% is used to represent the production casing. The perforation design is as follows: 26 SPM, 90 degree phasing, 13 mm tunnel diameter. The used material is Grade L80 steel. Simulations are done with common steel casing geometries (without the perforation tunnels) to examine the validity of the FEA model. The FEA collapse pressure is compared to the API collapse pressure. Three steel casing geometries are used for model validation, which results in FEA collapse pressure over API collapse pressure ratios of 1.23, 1.52 and 1.33. The effect of six erosion profiles on the external collapse pressure is evaluated using FEA simulations: three profiles with a maximum erosion depth of 10% and three profiles with a maximum depth of 25%. For both erosion intensities, the separate effect of erosion profile characteristics is evaluated using the following profiles: a profile with both wall thickness decrease and perforation tunnel diameter increase, a profile with wall thickness decrease only and a profile with perforation tunnel diameter increase only. The effect of the erosion profiles on the external collapse pressure is evaluated by comparing the FEA collapse pressure with the FEA collapse pressure of the uneroded casing. As expected, the erosion profiles with both the wall thickness decrease and the tunnel diameter increase show the largest drop in collapse pressure (decrease of 5% for the 10% profile and 11% for the 25% profile). Furthermore, it can be concluded that the effect of decreased wall thickness on the external collapse pressure is bigger than the effect of the increased tunnel diameter.
Item Type:Internship Report (Master)
Faculty:ET: Engineering Technology
Programme:Mechanical Engineering MSc (60439)
Keywords:solid particle erosion, local buckling, production casing, OCTG, collapse pressure, FEA, FEM
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