INTERLINKING HAZOP AND SIL FOR WELL INTERVENTION AND WORKOVER SYSTEMSAN INTRODUCTION TO A PROPOSED METHODOLOGY

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• Hazard and Operability (HAZOP) is process hazard analysis method where hazards and operability issues are identified through a multi-discipline workshop by use of parameters and guidewords. Based on the output, actions for risk mitigating are recommended where applicable

• A standard methodology for application of process or operability related parameters and guidewords may not cover all aspects for well intervention or workover. Hence, a method utilizing a combination of accidental scenarios based on historical data and process/operability related parameters/guidewords is applied

• During well intervention, the SIL classified and validated Safety Instrumented Function (SIF) in the subsea XMTs (OLF 070, Isolation of subsea well) is bypassed

• On the Norwegian Continental Shelf (NCS), there is no specific SIL requirements for well intervention and workover SIFs

• ORS has developed an approach for interlinking a customized HAZOP with LOPA, SIL classification and verification of workover/well intervention systems

INTRODUCTION

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1. Identification of risks

2. Classification of SIFs

3. Validation of SIFs

4. Monitoring of SIF performance during operation

STEP-BY-STEP APPROACH

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• Apply a HAZOP methodology customized for well intervention/workover systems. Focus on:

– Barrier status and shutdown sequences for various operational modes

– Identification of the minimum list of main components needed to prevent applicable accidental scenarios

– Semi-quantitative approach to demand rate (Combine experience and specific well data)

– Interfaces to auxilliary systems (due to use of fail-as-is SIFs)

– Consideration of contingencies as Independent Protection Layers (IPL)

STEP 1: IDENTIFICATION OF RISKChoose an

accidental scenario or apply a process/operability related

parameter

Identify deviations

Examine cause for deviation

Identify existing safeguards

Evaluate consequences (take

safeguards into account)

Specify recommendations if

applicable

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• Based on information from the customized HAZOP, perform a LOPA for the SIF (s) in question

• The LOPA is based on the SIFs in the various operational modes. For each operational mode, evaluate the demand rate, barrier status and contingencies (from the HAZOP)

• Quantify risk reduction from contingencies and applicable barriers that can be justified as IPLs, with a special focus on operator intervention

• Operator intervention is assessed by including TESEO tables for operator responses to various hazardous events

• Utilize available data to estimate the required PFD level for each operational mode

STEP 2: PFD REQUIREMENTS FOR WELL INTERVENTION SIFS

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• By combining detailed knowledge of the system and the identified minimum list of safeguards from the HAZOP, a Reliability Block Diagram (RBD) is developed for each SIF

• Special attention should be given to the following:

– Definition of operating envelope for SIF (Limitations for SIF applicability)

– Common components between protection layers, including the SIF in question

– Components in auxilliary systems needed to achieve safe state, e.g. hydraulic system, close assist system, etc.

– Contingencies not already listed as IPLs may provide redundancy

• Based on the RBDs, a Fault Tree (FT) analysis can be performed to demonstrate SIL compliance with regards to PFD requirements

– Special attention should be given to common cause failures

• A separate assessment of hierarchical and software requirements should be performed as part of the SIL validation process

STEP 3: VALIDATION OF SIFS

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• Test and maintenance procedures for well intervention systems ensures typically loop testing of the SIFs, i.e. end-to-end tests

• Normally, function tests are performed prior to operations, excluding the cutting capability. This needs to be reflected in the SIL verification process

• As the SIL verification is dependent on the actual oil/gas well, the SIF performance monitoring is also to be updated accordingly. This is because the demand rate for the SIF may vary depending on the location for the well intervention or workover operation.

• Include a sufficient margin between the required and achieved PFD to prevent SIF redesign or excessive testing on high demand wells.

STEP 4: MONITORING OF SIF PERFORMANCE DURING OPERATION

Morten Nilstad Pettersen

mnp@orsconsulting.no

+47 97 73 17 80

Johan Tengelin

jte@orsconsulting.no

+46 72 300 90 70

For more information, please contact:

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