The report gives a summary of the background and motivation for the audit activity and summarizes the observations made at the meetings.

Transcription

1 Audit Report AUDIT REPORT (UNOFFICIAL TRANSLATION) AUDIT OF USE OF ANNULAR SAFETY VALVES IN GAS LIFT COMPLETIONS SUMMARY During the period from June 2003 to September 2004, the Petroleum Safety Authority Norway (PSA) conducted an audit with the topic Use of annular safety valves in gas lift completions The audit was organised as a transverse activity targeting several operating companies that operate gas lift wells on their facilities. The audit was based on a meeting with the operators that took place on 5 June During 2003 and 2004 the PSA attended meetings with the authorities of other countries (Minerals Management Services, USA and Health Safety Executive, UK), as well as with equipment suppliers for well completions and consultancy firms specialising in risk and reliability analyses. The report gives a summary of the background and motivation for the audit activity and summarizes the observations made at the meetings. The audit work resulted in amendments of the HSE regulations from 2005, and in recommendations for further work on technical safety in gas lift wells, especially regarding the use of annular safety valves. The audit and the results were presented at the 17 th Drilling and Well Technology Conference in Kristiansand on September 2004 and at the Well Regulators Meeting in Aberdeen on November 2004

2 2 1.1 Introduction 1.2 Background Conventional gas lift wells are characterised by a large volume of gas in the annulus under high pressure. In the event of accidental flow, this gas volume can increase the overall risk to facilities with regard to fire or explosions (Gresslok et al. (1992)). Annular safety valves (ASV) are used to reduce this risk. The Norwegian petroleum regulations (Regulations relating to health, environment and safety in the petroleum activities ) stipulated detailed requirements for the use of these types of valves in gas lift completions. This is stated in Section 53 of the Facilities Regulations relating to equipment for completion and controlled well flow. The regulatory requirements relating to ASV originated after the Piper Alpha accident (Leismer (1993)). ASV are primarily used as safety valves against the flow of a large gas volume from the annulus. In cases where no other safety valves, or other types of barrier elements, are used to secure the well against accidental flow from the reservoir, ASV are also employed as independent barrier elements against the reservoir. This function of the ASV is, however, related to compliance with Section 47 of the Facilities Regulations on well barriers. After the implementation of the revised HSE regulations (Regulations relating to health, environment and safety in the petroleum activites ) in 2002, the PSA/Norwegian Petroleum Directorate (NPD) has received several applications for exemptions from the regulations relating to ASV. These applications were motivated by the Increased risk level associated with workover on gas lift wells completed with ASV. Increased risk level associated with supplementary completion of gas lift wells with ASV when the well is characterised by low production and expected short lifetime, for instance, in the field s tail production phase. Problems with the operation, testing and maintanance of ASV Development of alternative, risk-reducing completion methods The operators have chosen different ways of analysing issues relating to technical safety and risk evaluation. Also, different technical approaches were used. Applications were supported by quantitative risk analyses. These analyses have shown that the total risk associated with the completion and maintenance of gas lift wells with ASV can be affected negatively under special conditions. Consequently, the following issues were raised with regard to the current regulations: 1. Does the large number of applications for exemptions reflect a chronic problem? 2. Can the regulatory requirements be achieved using today s technology? 3. Do the risk analyses presented by the operators accurately portray reality? 4. Should the regulations be adapted to the conditions given in the consents?

3 3 Issues relating to ASV were initially discussed by the section for Drilling and Well Technology at the NPD/PSA. Also, the supervisory team for ConocoPhillips started discussions based on a relevant issue that emerged on the Ekofisk Field. A transverse audit activity was defined including all operators that operate gas lift wells on their fields. The PSA involved also the supervisory teams that follow up other operators than ConocoPhillips. The audit was based on a work meeting with the operators that took place on 5 June 2003, where several field cases were presented and discussed. Furthermore, the PSA participated in meetings with equipment suppliers for well completions (Baker Oil Tools, PTC as) and consultancy firms (Exprosoft) specialising in risk and reliability analyses within well technology. The PSA also contacted foreign authorities (Minerals Management Service, USA, and Health and Safety Executive, UK) in order to familiarise itself with other countries regulations regarding the issues at hand. 1.3 Regulatory framework The HSE regulations (Regulations relating to health, environment and safety in the petroleum activities ) stipulated detailed requirements with regard to ASV in Section 53 of the Facilities Regulations relating to equipment for completion and controlled well flow. The guidelines to this Section refer to an accepted standard (2nd revision of NORSOK D-010 Well integrity in drilling and well operations of 1998) and also recommend criteria regarding the setting depth of safety valves. According to this Section the main function of the ASV is to avoid an accidental flow of lift gas from the annulus. ASV in gas lift completions must, in addition to the main function mentioned above, be regarded as well barrier elements, cf. Section 47 of the Facilities Regulations relating to well barriers, first subsection, if the well is not completed with other safety valves between the reservoir and the ASV (see also chapter 5.8). If the ASV is used as a well barrier element, the valve s performance must also be verified, cf. Section 47 of the Facilities Regulations, third subsection. In the event of a failure of the ASV in a gas lift well, or if there were plans for gas lift completion without an ASV, the regulations provide for exemption applications from the detailed requirements, cf. Framework Regulations, Section 59 relating to Exemptions. In the guidelines to this section it is stated that an account should be given as to the non-conformity's individual and total risk for both one s own and others petroleum activities, and it is thus linked to the Framework Regulations, Section 9 relating to Principles for Risk Reduction. In connection with risk reduction the responsible party is obliged to document the risk effect in the form of a quantitative risk analysis, cf. the Management Regulations, Section 14 relating to analysis of major accident risk and Section 15 relating to Quantitative risk analyses and emergency preparedness analyses. Quality requirements for the risk analysis are stipulated in the Management Regulations, Section 13 relating to General requirements to analyses.

4 4 2 Objectives The objective of the audit activity was to Establish a common interpretation of relevant regulations and standards in the industry Identify needs for potential adjustments of the regulations and standards Provide input for continued work on the issue under the direction of the industry. This audit follows up the PSA's strategies in relation to technical and operational integrity on the offshore facilities, as well as to reducing the risk of major accidents. As a transverse activity aimed at several operators, the task also promotes the PSA's priorities as regards comprehensive enforcement of the HSE regulations in the petroleum activities. The activity contributes directly to the PSA's performance targets of contributing to reduce the risk level in the petroleum activities, as well as establishing suitable regulations and frameworks for the activities. 3 Observations 3.1 Industry meeting, 5 June 2003 The participating companies presented examples from their gas lift operations. The main focus was on gas lift wells that had secured exemptions from regulatory requirements. The minutes of the meeting and presentations have been appended to this audit report (see appendices/the PSA's website). The examples presented differed on many aspects. The differences demonstrate the difficulty of stipulating a simple regulatory requirement for safety valves in gas lift wells. For example, the differences include: Subsea completions versus well completions from fixed facilities. Type of facility (steel jacket, gravity based, tension leg, production ship or semisubmersible) The operational purpose of the facility (wellhead platform, process facility combined with wellhead deck, drilling facilities and living quarters modules) Production volume and production phase (plateau or tail), remaining reservoir energy in relation to the reservoir's natural lift capacity Annulus volume and injection pressure factors. With regard to the last item, the setting depth of the valves is influenced by the geological conditions and technical factors with regard to the well completion. This relates mainly to: Crater depth in connection with blowout Hydrate formation, temperatures and fluid composition Kick-off depth and angle for directional wells The industry presented the following alternative, compensatory measures with risk-reducing effect: Reinforced double block valves Check valves integrated in the wellhead Shorter test intervals for double block or check valves

5 5 Deep-set safety valves (below production packer) Automatic depressurization system Use of inert lifting gas (particularly relevant for intermittent gas lift) Dual string completions Gas cap gas lift 3.2 Contact with authorities in other countries (MMS and HSE) Meeting with Minerals Management Service, USA, 17 February 2004: The US regulations Code of federal regulations (Title 30, Subchapter B offshore parts 250 to 282) stipulate no specific requirements for ASV that are to prevent accidental flow of lift gas in gas lift completions. However, requirements (Section ) are stated in general for subsurface safety devices. This generally includes safety valves, plugs or gaskets. The assumption is then that a pipe or annulus is in open communication with hydrocarbon-bearing zones. This also includes tubing/annulus subsurface safety devices, which may be ASV or annular packers. The annulus valve/annular packer will in this constellation have a function equivalent to that of a well barrier in accordance with Norwegian regulations. Exemptions from the regulations (departures) may be granted if an MMS district supervisor ascertains that the well cannot flow by itself, i.e. the reservoir pressure is too low to flow without artificial lift. Communication with HSE (David Scott, Fred Algie), via 13 October 2003 With regard to well safety in gas lift wells, the British authorities focus their audit activities on manned production facilities that use gas lift to maintain production, and challenge operators particularly if they use artificial lift to increase production. The number of gas lift wells per facility is also a factor that determines the scope of an audit. In general, the HSE does not have any detailed requirements for ASV in gas lift completions. However, the following regulatory requirements apply: Offshore Safety Case Regulations 1992(SCR) Reg 8 relates to the requirement for major accident analyses Offshore Installations and Wells (Design & Construction etc) Regulations 1996 (DCR) Reg 13(1) well design and construction is linked to the ALARP principle over the lifetime of the well. Offshore Installations (Prevention of fires and Explosions, and Emergency Response) Regulations 1995 (PFEER) Reg 4(1) Design of fire and explosion protection. Reg 5 Fire and explosion analyses Reg 9(1) Prevention of accidental gas leaks and accumulation of flammable substances.

6 6 The HSE's team for drilling and well technology expects that an operator will study the following factors before making a decision regarding gas lift as a method of artificial lift: a) technical requirements in relation to permanent or periodic gas lift b) other alternative solutions for artificial lift c) use of inert gas The operator must demonstrate that the ALARP principle is safeguarded in the selection of methods and measures to reduce the risk to the crew. 3.3 Meeting with ExproSoft 28 August 2003 ExproSoft is a service company based in Trondheim and offering services in connection with quantitative risk analyses and reliability analyses. The firm was involved in two risk analyses that were conducted in connection with applications for exemptions on Varg (NPD case 2001/2652) and Ekofisk (NPD case 2003/510). The company presented business conditions with particular emphasis on competence and historical project portfolio. They then presented both of the above-mentioned risk analyses. After the meeting with ExproSoft, the NPD/Petroleum Safety Authority Norway was left with the impression that the quality of risk analyses can vary. Some of the differences include: Selection of parameters to quantify risk, i.e. probability and consequence. Consultants who offer commercial risk analyses specialize in various areas and have varying competence. There are no clear guidelines for what type of information is to be exchanged between the consultant company and the operator. Contributions of empirical values can vary in quality from case to case. The consultant may have an incomplete picture of the operational situation. Therefore, discussion and analysis of input data and assumptions should be given particular attention. 3.4 Meeting with Baker Oil Tools, 2-4 September 2003 The company gave an account including structural characteristics of ASV, setting procedures, maintenance and valve technology. 3.5 Meeting with PTC as, 25 September 2003 This service company develops and manufactures process equipment for the oil industry. The company gave an account of the development of a new type of check valve that is installed in gas lift injection lines to gas lift wells, so-called Annular Safety Check Valves. The valves are set in the wellhead of platform wells with the aid of a specially-developed setting tool. The valves and the tool were developed in cooperation with ConocoPhillips.

7 7 4 New version of the Facilities Regulations, Section 53 (valid from 1 January 2005) The Petroleum Safety Authority Norway, the Norwegian Board of Health and the Norwegian Pollution Control Authority have proposed certain amendments and corrections to the joint regulations in the health, safety and environment area in the petroleum activities, with effect from 1 January Among other things, a change has been proposed in the Facilities Regulations, Section 53 relating to equipment for completion and controlled well flow. The new text for the regulatory requirement reads as follows: Equipment for completion shall provide for controlled influx, well intervention, backup well barrier elements and plug back activities. The second subsection shall read: Completion strings shall be equipped with necessary downhole safety valves (SCSSV) in the well flow line and in the production annulus. The second and third sentences in the second subsection will be deleted. The guidelines to Section 53 of the Facilities Regulations will be amended as follows: The new third paragraph will read: In order to fulfil the requirement to necessary downhole safety valves in the production annulus as mentioned in the second paragraph, an overview of barriers should be established, cf. Section 47 on well barriers. See also the Management Regulations Section 14 on analysis of major accident risk and Section 15 on quantitative risk analyses and emergency preparedness analyses. The current third paragraph will become the fourth, etc. In practice, the amendment means that the operator selects and analyzes its technical, operational and organizational solutions with a basis in a decision tree as shown in figure 1. The decision tree can be explained as follows: In connection with well safety issues, before completion of a gas lift well the responsible party should ask the following questions: 1. Is the production annulus in the well used for other production or injection-related purposes? If the answer is Yes, this is followed by a well safety requirement in relation to well barriers and barrier independence. This is normally resolved through the installation of an ASV. If the annulus is only used to inject lift gas, then the next question is: 2. Are there additional qualified barrier elements in the primary barrier below the ASV? If there are other qualified barrier elements, then the next milestone is an analysis of the risk of major accidents. If there are no other barrier elements, then the solution is

8 8 again use of the ASV. 3. If, on the basis of an overall assessment, a well completion without ASV is regarded as having an unacceptably high risk of major accidents, then the operator must select a safer completion solution with an ASV. 4. Finally, the operator must analyze the risk in relation to other completion alternatives. Only when this analysis, after a review of all three preceding stages shows overall reduced risk in selection of an alternative completion solution, shall the operator then choose this solution. Figure 1. ASV requirement flowsheet 5 Barrier requirements, qualification of gas lift valves After internal discussions, the PSA has arrived at the following conclusion surrounding the use of gas lift valves (GLV) as qualified barrier elements: An operator that wants to use GLV as satisfactory barrier elements against the reservoir must consider these valves to be downhole safety valves. The PSA's perception is that, in such a case, the valves will be used beyond their standard/design function, and that they must be qualified cf. the HSE regulations in the Facilities Regulations, Section 8 relating to Qualification and use of new technology and new methods. This qualification is required for various types and models of GLVs. Today, qualification of well barriers and barrier elements is linked to the requirements in the Facilities Regulations, Section 47 relating to well barriers. This section recommends NORSOK D-010 for fulfillment of the detailed requirements. NORSOK D-010, both in its

9 9 old and new versions, refers to API RP 14B and ISO with regard to operation and testing of downhole safety valves. The problems that the PSA believes it has are, that it is difficult to test GLV in relation to critical leak criteria for oil, particularly oil with low gas in oil ratios and/or oil with a high water content. Both factors are relevant for gas lift wells. The industry or the operators that want to use GLV as a barrier element should join forces and closely examine factors such as measurement accuracy and measurement time, also in relation to the composition of the oil produced. Therefore, the PSA will follow up the operator's requirements as regards testing of gas lift valves and use of gas lift valves as qualified barrier elements. 6 Result The audit resulted in an amendment to the regulations which enters into force on 1 January Under certain conditions, alternative technical, operational and organizational solutions can be used in gas lift comletions instead of the use of ASV. The amendment is in line with the third and most recent revision of NORSOK-standard D- 010 Well integrity in drilling and well operations and it entails that the necessity for ASV is now assessed on a case by case basis in relation to the following aspects: 1. General barrier requirements in accordance with Section 47 of the Facilities Regulations relating to well barriers. An ASV is ascribed a function as primary barrier element against the reservoir (and simultaneously as a safety valve against the gas volume in the annulus) if the well is planned without other qualified barrier elements below the ASV. 2. The risk of major accidents, cf. the Management Regulations, Section 6 relating to Acceptance criteria for major accident risk and environmental risk, as well as Section 14 of the Management Regulations relating to Analysis of major accident risk. 3. Risk level affected by the ASV compared with alternative solutions over field life, cf. Section 1 of the Management Regulations relating to Risk reduction and Section 15 relating to Quantitative risk analyses and emergency preparedness analyses. Based on these observations and experiences, the PSA is considering intensifying its efforts with regard to well safety in gas lift wells, particularly for facilities with dedicated wellhead decks, on multi-purpose facilities, and on fields with high reservoir and well pressure. Moreover, the PSA will follow up the operator's requirements in relation to testing of gas lift valves (GLV) and use of GLV as qualified barrier elements. 7 References to literature 1. Gresslok et al. (1992) Blowout Risk Analysis of Gas-Lift Completions, SPE Production Engineering, May, pp Leismer (1993) A System Approach to Annular Control for Total Well Safety, paper SPE presented at the 25th Annual Offshore Technology Conference, Houston, 3-6 May Slettet:

10 10 Appendix 1 Minutes of meetings and presentations from industry meetings See separate link on the PSA website. Appendix 2 Lecture Well Safety in Gas Lift Wells, 17th Conference on Drilling and Well Technology, Kristiansand, September 2004, See separate link on the PSA website Appendix 3 Lecture Well Integrity in Gas lift Wells, presented at Well Regulators Meeting, Aberdeen November 17-18, 2004 See separate link on the PSA website