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Assessment of Well Tubing with Ovality in Cross Section by Numerical Modeling from the Perspective of Integrity Management

Tarami, Behrad | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53453 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Raie, Mohammad
  7. Abstract:
  8. This study investigates the ovality on the burst pressure of the pipe inside the well. In the last decade, the use of natural offshore oil and gas resources has increased, and as a result, the importance of well integration as a major part of offshore platforms is clear. At the same time, accidents at oil and gas wells have economic and environmental consequences that underscore the importance of ensuring safe operation. Integrity management of fluid pressure wells has been developed to ensure the safe operation of wells. The functional area of integrity management begins with planning, then inspects and then evaluates, and eventually leads to corrective action, and this loop is repeated on a regular basis. In this loop, evaluation requires structural analysis. In Tubing, external pressures caused by salt dome layers or factors such as ovality as a primary manufacturing can be the main causes of tubing bursting and production interruption. In this regard, the relationships in the regulations to assess burst pressure due to simplification are in some cases inaccurate and do not cover some of the actual conditions. In addition, relationships in some load combinations produce non-conservative results. Bending anchorage can occur due to the external pressure caused by the salt layer on the wall pipe and the wall pipe pressure on the pipes inside the well. This external pressure together with the ovality of the cross section of the pipe inside the well creates a critical situation. In this study, finite element analysis has been used to investigate the effect of the oval cross section of the pipe, the final strength of the pipe material, the ratio of diameter to pipe thickness and also the bending in the pipe on burst pressure. The results of the present study show that with increasing the ratio of diameter to thickness, increasing the amount of bending anchor and increasing the amount of cross-sectional ovality and decreasing the final strength of pipe materials, the burst pressure of the pipe decreases. It was observed that the rupture site of the pipe due to burst pressure was along the long axis of the oval cross section parallel to the longitudinal axis of the pipe. Finally, a relation for the burst pressure of the tubing inside the well is presented based on the parameters of rupture stress, the amount of cross-sectional ovality, the ratio of diameter to pipe thickness and the amount of bending anchor applied. It was also found that in tubing with an ovality of 10%, the difference between the finite element method and the relation of the British standard regulations is up to 50 % and mean of 30%, and this difference is a maximum of 46 % and mean of 28% for the API Guideline and in both of the guidelines the burst pressure which we get from the equations is higher than burst pressure that we get from FEM modeling and this means that both of the guidelines are not conservative. Also, increasing the ratio of diameter to thickness(Diameter to Thickness ratio of 29 to 60) increases the error from 2% to 23%, increases the ovality(Ovality 5% to 10%) from 0 to 5 %, decreases the rupture stress (Ultimate stress 550 to 431 MPa) from 2% to 31% can cause a difference in burst pressure between code relationships and numerical modeling (burst pressure of guidelines are higher than FEM numerical Modeling). Due to the difference between the results of the above-mentioned guidelines and the results obtained from FEM modeling, to improve the relationship between the above guidelines in the study domain, including (Diameter to Thickness ratio of 29 to 60) and (Ultimate stress 431 to 550 MPa) and (Ovality 5% to 10%) A relation for Tubing burst pressure in the well based on the parameters of ultimate stress, cross-sectional ovality ratio, diameter to thickness ratio and amount of bending anchor is presented in the study domain will be usable
  9. Keywords:
  10. Finite Element Analysis ; Burst Pressure ; Well Integrity Management System ; Ovality in Cross Section ; Well Tubing ; Bending Moment

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