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

Is it necessary to install a downhole safety valve in a subsea oil/gas well?
Contents
Preface.........................................................................................................................................I
Summary and conclusions......................................................................................................... II
List of Acronyms and Abbreviations ........................................................................................ V
Contents...................................................................................................................................VII
List of figures ...........................................................................................................................IX
List of tables .............................................................................................................................IX
1 Introduction ........................................................................................................................ 1
1.1 Objectives................................................................................................................... 1
1.2 Limitations .................................................................................................................2
1.3 Report structure.......................................................................................................... 3
2 Rules and regulations .........................................................................................................4
2.1 Norway....................................................................................................................... 4
2.2 United Kingdom......................................................................................................... 4
2.3 United States of America ........................................................................................... 5
2.4 Standard organizations ............................................................................................... 5
2.5 Regulatory challenges ................................................................................................ 5
3 Use of acceptance criteria .................................................................................................. 7
3.1 The ALARP principle ................................................................................................ 8
3.2 Safety integrity level (SIL)......................................................................................... 9
4 Overall risk assessment .................................................................................................... 11
4.1 Consequences........................................................................................................... 11
4.1.1 Economic.......................................................................................................... 12
4.1.2 Blowouts........................................................................................................... 12
4.2 Installation related risk............................................................................................. 14
4.3 Production related risk ............................................................................................. 14
4.4 Workover related risk............................................................................................... 15
5 Risk reducing effect of a DHSV ...................................................................................... 17
5.1 Case example............................................................................................................ 17
5.1.1 Production tree ................................................................................................. 17
5.1.2 Production well ................................................................................................ 18
5.2 Barrier analysis......................................................................................................... 21
5.2.1 Case example.................................................................................................... 21
5.3 Fault Tree Analysis .................................................................................................. 25
5.3.1 Case example.................................................................................................... 25
5.4 Unavailability calculations....................................................................................... 26
5.4.1 The Mean Fractional Dead Time calculation model........................................ 26
5.4.2 Calculations done in CARA............................................................................. 28
5.4.3 Calculations done by hand ............................................................................... 28
5.4.4 CARA calculation results................................................................................. 29
5.4.5 Hand calculation results ................................................................................... 30
5.5 Risk reducing findings in the Case example ............................................................ 33
5.5.1 Comments to the risk reducing findings .......................................................... 35
6 Well intervention.............................................................................................................. 36
6.1 Intervention types..................................................................................................... 36
6.1.1 Light intervention............................................................................................. 36
6.1.2 Heavy intervention (workover) ........................................................................ 36
6.1.3 Workover equipment........................................................................................ 36
Diploma thesis, NTNU 2002 VII