BOP Basic Safety Functions. Katrine Harsem Lund Principal Engineer, Department Manager Scandpower AS

Transcription

1 BOP Basic Safety Functions Katrine Harsem Lund Principal Engineer, Department Manager Scandpower AS

2 Deepwater Horizon

3 Deepwater Horizon

4 Agenda What is a BOP/BOP Stack Safety Functions for a BOP Stack and Safety Integrity Levels (SIL) Critical components in BOP control systems and their reliability

5 What is a BOP? Annulus Drill pipe A blowout preventer (BOP) is a large, specialized valve used to seal, and control oil and gas wells. A BOP Stack (Well control package) is the assembly of well-control equipment including preventers, spools, valves, and nipples connected to the top of the wellhead. Topside/Subsea BOP stacks Fig: A typical BOP Stack

6 A BOP Stack consists of multiple components According to NORSOK D-001 "Drilling Facilities", paragraph , a BOP shall as a minimum consist of the following: One (1) annular preventer One (1) shear ram preventer Two (2) pipe ram preventers Minimum one (1) Choke Line outlet Minimum one (1) Kill Line outlet One (1) Wellhead coupling or connector Minimum two manual gate valves Minimum two remote operated gate valves.

7 BOP Stacks

8 Preventer valves Annular Preventer Pipe Ram Shear Ram

9 How does a Ram valve work?

10 Safety functions of a BOP Stack Prevention of blowouts and well leaks OLF Guideline 070, defines the following functions for the BOP: 1. Seal around drill pipe 2. Seal an open hole 3. Shear drill pipe and seal off well. Thus the guideline differentiates between two main functionalities and set SIL levels for: The annular preventer/pipe ram function (function 1) The shear ram function (function 2 & 3 combined).

11 No valves closed

12 Seal around Drill pipe

13 Shear drill pipe and seal off well

14 Setting A SIL Level for the BOP Safety Functions The BOP s are used for a number of drilling related safety functions Well intervention Drilling A SIL level is only set for the drilling BOP Based on data from a Scandpower report Blowout and Well Release Frequencies, it is estimated that the industry is operating with a blowout prevention reliability somewhere close to SIL 3 on average.

15 Setting a SIL Level for the BOP Safety Functions The OLF- guideline discussion concludes with the following: Setting a SIL 3 level to either function would lead to a significant increase in the standard for drilling BOPs. The challenge lies mainly in the need for documentation of the system reliability, Setting a SIL 3 level would most certainly also result in the need for changing the existing control system. It would also be necessary to include additional RAMs in standard BOP assemblies. The required PFD/SIL for the BOP function for each specific well should be calculated and a tolerable risk level set as part of the process applying for consent of exploration and development of the wells. As a minimum the SIL for isolation using the annulus function should be SIL 2 and the minimum SIL for closing the blind/shear RAM should be SIL 2.

16 There are MANY components in the BOP control system! Shuttle valves Hydraulic Reservoir Filter Check valves Accumulator bottles Bleed valves Flow Totalisers Push-to-hold button Indicator lights Hydraulic pumps Pipe Ram valves Hydraulic Block valves Pressure gauges Drillers Panel Pressure transmitter Wedge locks Gate valves Kill & Choke valves Shear Ram valve Flow transmitter Pilot valve Pneumatic Block valve Pressure regulator Hydraulic booster pump Pushbuttons SEM PCL Analogue input/output SCM Acoustic Transmitter Isolation valves Flow transmitter Solenoids Umbilical Tool pushers panel SPM valves Pressure Indicators Etc. Etc.

17 Components in BOP & control system How to decide which components are critical, and which are for information only, or not critical? FMECA with client, including operators/drillers SIL Workshops with client, including operators/drillers Accumulator bottles shall store hydraulic pressure to necessary volume and pressure to enable closing-opening-closing operation of all rams +25% of volume for one closing operation of each ram - function independent of many failures in the hydraulic system

18 Build Reliability Block Diagrams OLF Guideline 070 used to determine which functions of the BOP that shall be SIL rated SIL 2 = 100 % A Initiator(s) Logic Final Element(s) B 35 % PFD < % PFD < % PFD <

19 Reliability Block Diagram example topside BOP

20 Reliability Block Diagram example subsea BOP

21 Challenges All the SIFs for the BOP are manually initiated - Human Factors?? Difficult to find relevant reliability data Generic data Data from vendors Redundancy? Not always possible to use pipe rams or shear the drill pipe!

22 Not possible to Shear/close pipe ram

23 Remaining issues/questions When is it possible to move the drillpipe up/down if pipe ram/shear ram cannot close? Everything is manually initiated - Impact of Human Factor? The testing of the Shear ram does not include actual cutting of the pipe. I.e the main function is not really tested Test independent failures Should other BOP functions have a SIL rating? Is all critical components identified and included in the SIL function?

24 Should other BOP functions have a SIL rating?

25 References OLF Guideline 070 NORSOK D-001 NORSOK D-010 Sintef Memo: Barriers to prevent and Limit Pollutants to sea Sintef Memo: Drill, not Spill Transocean Deepwater Horizon Investigation report chp. 3.4 BP Deepwater Horizon Investigation report Sintef Report Reliability of Subsea BOP systems for Deepwater application, Phase IIDW

26 For more information, please contact: Katrine Harsem Lund Principal Engineer, Department Manager at Kjeller Office Scandpower AS T E khl@scandpower.com W w