Is it necessary to install a downhole safety valve in a subsea ... - NTNU

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Is it necessary to install a downhole safety valve in a subsea oil/gas well? The consequences of a bad reputation are hard to estimate. If a boycott of the operating company is carried out it could lead to greater economic losses. Negative publicity not only affects the concerned company but the entire oil industry. Diploma thesis, NTNU 2002 54
Is it necessary to install a downhole safety valve in a subsea oil/gas well? 7.2 Recommendations for further work This thesis is carried out within a limited period of time and with limited access to data. It is recommended that the conclusion of the thesis be explored further. A range of tasks may be carried out to provide an even better basis in deciding whether or not a downhole safety valve (DHSV) should be present in a subsea oil/gas well Improved calculation model In the calculation model of this thesis the blowout frequency during production is based on the assumption that all leakage classifies as a blowout. This generates a very conservative value. The leakage may in some cases be very small and not classify as a blowout. The model used in the fault tree calculations assume that a leakage in closed position and fail to close failure of the wing valve leads directly to sea. If the safety barriers in the flow direction fail there are still barriers further up the line that may prevent a blowout, e.g. the manifold, separator or other equipment. A better and improved model could generate a better and more realistic blowout frequency result. Data accuracy The author has limited access to valid data. The reliability data used in the calculations is gathered for both platform and subsea wells. Valid data only for subsea wells should be applied in the calculations. Another problem is the age of the applied data. All data in this thesis is more than five years old due to the confidentiality of the operating companies. Implementing new up-to-date data may change the outcome of the total blowout frequency and is recommended. The presented approach is, however, valid and applicable when new data is found. Including the consequence The calculations done in this thesis do not consider the blowout consequences. Although a blowout occurs it may not always cause severe pollution. None of the blowouts in the production, workover or installation phase, recorded in ref. [7], has caused severe pollution. During the production phase only one of seven blowouts caused small pollution; the other six caused no pollution. A workover blowout is more likely to cause severe pollution than the other stages of the well. An evaluation of the consequences of a blowout at the different well life phases should be included in a further evaluation of the risk reducing effect of the DHSV. Economic cost evaluation In this thesis some of the economic aspects related to the DHSV are discussed. Due to a lack of cost information from operating companies an evaluation of the reduced cost a removal of the DHSV would represent is not included. A total economic evaluation of the costs related to the DHSV for the operating company should be performed. The findings in this thesis have revealed that a substantial amount of money may be saved. Alternative solutions In some cases alternative solutions may be more reliable than a DHSV. A further study developing new solutions and examining other existing solutions is recommended. The economic cost and the environmental risk related to a frequent workover rate caused by the DHSV may be reduced. Diploma thesis, NTNU 2002 55
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Page 69 and 70: APPENDIX A A1 Subsea production sys
Page 71 and 72: A1.3 Well completion A1.3.1 Tubing
Page 73 and 74: A1.5.2 Guidelineless system Several
Page 75 and 76: Appendix B In this appendix a figur
Page 77 and 78: Appendix C Fault trees constructed
Page 79 and 80: Production Wing valve ITL WV Produc
Page 81 and 82: Component: Production Packer Failur
Page 83 and 84: Reliability data dossier Component:
Page 85 and 86: Component: Production wing valve Fa
Page 87 and 88: Component: Crossover line Failure r
Page 89: Appendix F The guide-words used in
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Is it necessary to install a downhole safety valve in a subsea ... - NTNU

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