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? question any proposal without a DHSV, but if the inclusion was not “reasonably practicable” an assessment should be done. The author sees an opportunity to persuade the authorities if a proper documentation of the needlessness of a DHSV is provided. In Norway the regulations do, however, also require a minimum of two independent and tested barriers between the reservoir and the environment. The DHSV is considered to be the primary barrier and the xmas tree to be the secondary barrier. A revision of the barrier formulation must be done if the DHSV is to be removed from the completion. Considerations of making the x-mas tree either the only barrier or implementing another and more reliable downhole barrier solution should be taken. This thesis will consider the first alternative, making the x-mas tree the only barrier. Diploma thesis, NTNU 2002 6
Is it necessary to install a downhole safety valve in a subsea oil/gas well? 3 Use of acceptance criteria To gain an impression of the risk an event represents, the consequence of and the probability for the event must be considered. The assessment may be based on a load of different developed risk assessment tools. Finding the right measurement for risk and by what criterion it is acceptable may be tricky. An acceptable level of risk in an activity is described by acceptance criteria. The criteria are either based on standards, experience or theoretical knowledge. Acceptance criteria express the probability and consequence of a hazardous event, and may either be qualitative or quantitative. In a risk assessment the use of acceptance criteria is important to identify areas that need risk reducing efforts. Acceptance criteria should be expressed in a way that makes them applicable to the different areas of the assessment. The criteria should reflect the safety goals of the operator and requirements set by the authorities. For an installation the acceptance criteria perform a basis for what is consider acceptable at the present time. Formulation accuracy may vary in accordance with the demand set by authorities and the operating company. To verify whether the contents of the acceptance criteria are met, the values have to be quantitative. In other cases the use of qualitative criteria are acceptable. Acceptance criteria are established according to the extent and purpose of the assessment. There are mainly three different ways to establish acceptance criteria. A comparison with established and accepted methods By the use of risk-matrixes and the ALARP-principle By the use of predefined criteria for qualitative analysis In the Norwegian sector of the North Sea, all operators have to define risk acceptance criteria according to requirements by the NPD. Different regulations are issued to standardize acceptance criteria. Many interest are involved when discussing acceptable risk problems: the interest of society, the interests of employees, and the interests of the oil company [32]. An important issue of risk analysis is to determine what hazards present more danger than society is willing to accept. A level of acceptable risk can be hard to find. To find a balance between having guarantee for a safe, environmental friendly and healthy focus and making a reasonable profit is sometimes difficult. The use of the ALARP-principle (“As Low as Reasonable Practicable”) is one method to set acceptance criteria. Personnel risk is often subject to the use of the ALARPprinciple. A further description of The ALARP-principle is given in section 3.1. When dealing with quantitative criteria are set by different methods of measurement. The Norwegian Oil Industry Association has in the latter times standardized acceptance criteria for certain operations in the North Sea. A Safety Integrity Level (SIL) to provide a basis for the evaluation of appropriate risk levels for different events. SIL will be discussed further in section 3.2. Human risk The most common rating when dealing with personnel risk is the fatal accident rate (FAR) and the PLL-rate (Potential Loss of Life). The PLL-rate presents the average fatal accident per year. The FAR value is the most common and represents the predicted number of fatalities per 100 million hours exposed to the hazard [7]. The FAR value is a reasonable measure for risk Diploma thesis, NTNU 2002 7
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APPENDIX A A1 Subsea production sys
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A1.3 Well completion A1.3.1 Tubing
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A1.5.2 Guidelineless system Several
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Appendix B In this appendix a figur
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Appendix C Fault trees constructed
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Production Wing valve ITL WV Produc
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Component: Production Packer Failur
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Reliability data dossier Component:
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Component: Production wing valve Fa
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Component: Crossover line Failure r
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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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