SIL Assessment & Verification For EPIC Produced Water & NGL Effluent Treatment Facilities Of Qatar Energy

iFluids Engineering and Consultancy WLL was awarded to perform SIL Assessment and verification for various facilities of Qatar Energy

• EPIC For Produced Water Utilization at Degassing Stations For PWI
• EPIC For New NGL Effluent Treatment Plant at Mesaieed

What is SIL Study?

In order to determine the specific level for defining the security integrity requirements of the security instrumented functions (SIF) to be assigned to the security instrumented systems, the Safety Integrity Level (SIL) Study is essential. The Layer of Protection Analysis (LOPA) methodology is used to account for the protective layers that prevent or lessen the effects of dangerous events by preventing their occurrence or by using design concepts that are inherently safe. To know more about SIL study click here.

Case study 1: SIL Verification EPIC For Produced Water Utilization at Degassing Stations For PWI

The state-owned company Qatar Energy is in charge of producing, refining, and exporting gas and oil from Qatar. The onshore and offshore oil and gas producing fields are located in Dukhan on Qatar’s eastern and western coasts, respectively. Dukhan Field is divided into six production and operating zones: Gas Recycling Plant-Arab D, Khatiyah, Dukhan Township, Fahahil, Jaleha, and Diyab. It has injection wells for gas, oil, and water. The primary facilities for processing and storing crude oil in the Dukhan region are Khatiyah Main Degassing Station (KMDS), Fahahil Main Degassing Station (FMDS), and Jaleha Degassing Station (JDS).

Before being pumped out to Mesaieed via a pipeline via Um Bab, stabilised crude oil from KMDS, FMDS, and JDS separators is dewatered, settled, and stored in crude oil storage tanks (COST). Currently, wells connected to the Umm-Er Dhuma aquifer receive produced water from the COST at the KM, FM, and Jaleha degassing stations into them. To preserve the groundwater ecosystem, Qatar Energy plans to recover produced water from these COSTs rather than pour it into the wells. After being collected in an underground tank, the recovered produced water from COST will be sent to a new Produced Water Secondary Treatment (PWST) unit, where it is intended to be used as injection water going forward.

Well fluids from the Arab C, Arab D, and Uwainat oil reservoirs are processed at KMDS.

FMDS, which has two stations, Fahahil North and Fahahil South, is situated in the middle of the Dukhan Fields. Well fluids from the Arab C and Arab D fields, which are situated in the Fahahil Main area, as well as partially degassed crude from Fahahil South and Fahahil North, are processed at the Fahahil Main degassing station.

About 10 km separate JDS from the Umm Bab cement works and about 35 km from Dukhan.  Well fluids are supplied to the Jaleha (JAL) Degassing Station for use in production wells located in the Arab C and Arab D reservoirs. The Diyab manifold is being used to pipe in some of the well fluids.

The well fluids undergo four stages of separation and separate into three phases:

• Degassed crude oil
• Rick-associated gas (RAG)
• Produced Water

Before being sent to Umm Bab Booster Station and then Mesaieed, the degassed crude oil is stabilised and kept in COSTs. Crude is settled, desalted, dewatered, and stored at this COST. After being dehydrated, the RAG is exported to the FSP for additional processing or for gas lift. Water produced during the separation process is fed to the PWI system via PW transfer pumps after passing through a water treatment unit (hydrocyclone and degasser).

In the unlikely event that the PWI system is unavailable, there is another way to dispose of the PW into disposal or dump wells.A new PWST is planned as part of the DPFU initiative. Just the proposed change to collect wastewater drained from the COSTs into a new collection tank and then route it to the PW secondary treatment section for degassing so that it can be used for PW injection—as opposed to the current practice of routing it to disposal wells into an aquifer—is included in the project scope.

The objective of SIL verification in this project is utilisation of produced water from crude oil storage tanks at degassing stations for PWI, Dukhan.

Case study 2: SIL Assessment EPIC For New NGL Effluent Treatment Plant at Mesaieed

Wastewater from the Natural Gas Liquid (NGL) Complex in Mesaieed Industrial City (MIC) is produced as surface run-off and process runoff. NGL Plants do not yet have any wastewater treatment facilities.

It is against the rules set forth by the Ministry of Municipality and Environment (MME) for industries to release treated industrial and process effluent into the maritime coastal environment from their current facilities. Rather, the wastewater will be subjected to additional treatment in order to fulfil the irrigation water quality requirements specified in the “Consent to operate” (CTO).

The resultant treated water will then be utilised for the landscaping and irrigation of NGL facilities.A New Effluent Water Treatment Plant, or “NEWTP,” has been suggested to treat the effluents generated from NGL Plants to meet the irrigation water quality criteria in order to meet MME requirements.

Front End Engineering Design (FEED) was completed by another contractor covering the following:

• Identification of the effluent sources.
• Provision of suitable collection and transfer systems at NGL areas.
• New effluent treatment facility to treat the effluents to meet irrigation water quality.

SIL Assessment

It is a defined process of hazard analysis of identified hazard(s) for the purpose of determining the SIL required of the SIF(s) which are required to protect against the hazard(s).

The intent of the SIL Assessment study is to assess the safety integrity requirements on the Safety Instrumented Functions (SIF) to be allocated to the Safety Instrumented Systems (SIS). The SIL assessment determines the risk reduction required of the SIF such that it provides sufficient protection layer or safeguard to meet the required risk reduction for a hazard.

Quantification of the risk reduction requirements is given in terms of a Safety Integrity Level (SIL) requirement. The risk reduction is calculated as the gap between the existing risk posed by the process or equipment and the risk target. Risk reduction is provided by process and mechanical integrity, independent protection layers and if so required SIS.

It also answers the following questions:

• What is the likelihood of an undesirable event?
• What is the risk associated with the event?
• Are there sufficient risk control measures (or “layers of protection”)?

The study on SIL classification has been carried out utilising the LOPA methodology in order to allocate SIL levels to the Safety Instrumented Systems. The SIL classification study is a methodology used to determine the appropriate design of safety measures, including instrumentation, that effectively mitigate process hazards in terms of safety, environmental consequences, and economic losses. It comprises a semi-quantitative assessment of the process equipment and systems to be protected by the Safety Instrumented system, to identify potential hazards and to assess the risk.

This assessment is developed on the basis that, initially, no protective systems are in place, so that a basic level of risk can be established for the equipment under control. The SIL derived rating is a quantification of the level of risk mitigation necessary for the Safety Instrumented System to ensure that the remaining risk is deemed acceptable or ALARP (As Low As Reasonably Practicable).

The SIL rating covers the complete loop and is used in the specification of the Safety Instrumented System, e.g., from initiating devices through the logic solvers and controllers to the final actuating elements, in order that the system will adequately meet the design intent. The SIL classification study has been conducted as a team based brainstorming workshop led by the chairman with proceedings recorded by a dedicated scribe.

The following documents/ drawings were referred during the SIL workshop.

• P&IDs used for HAZOP Workshop.
• Cause and Effect diagram.

The preparation work consists of four stages: training / briefing to team members, obtaining the necessary data; converting the data to a suitable form, planning the study sequence and arranging the meetings.

The LOPA methodology uses order of magnitude categories for initiating event frequency, consequence severity, and the likelihood of failure of IPLs to approximate a risk level for any hazardous scenario.

The steps used to conduct the LOPA are listed below:

• Step 1: Select Hazard Scenario from HAZOP based on its severity level.
• Step 2: Select Target Mitigated Event Frequency (TMEF).
• Step 3: Identify cause(s) from the HAZOP and quantify Initiating Event Frequency.
• Step 4: Determine Intermittent Hazard(s) credit if applicable.
• Step 5: Identify Independent Protection Layers (IPLs) from HAZOP safeguards.
• Step 6: Quantify the Probability of Failure on Demand (PA) for each IPL.
• Step 7: Identify and quantify Conditional Modifiers / Vulnerability Factors if applicable.
• Step 8: Calculate the LOPA Ratio for each Safety, Environment and Asset Consequence Category as applicable. Using the LOPA Ratio, determine Integrity Level requirements for the existing Safety Instrumented System (SIS) (if required), or identify requirements for additional IPL or SIS and evaluate SIS integrity level.

Where protection is provided by SIS, or a SIS is recommended, the LOPA determines the Safety Integrity Level (SIL).

The LOPA ratio for Safety, Environment, Asset and Reputation Integrity Levels were used to determine the required Integrity Level and PFD of each SIS. The highest of the four integrity levels were used as the design basis for that SIS. The IL of the SIS is the highest integrity level for which the SIS provides protection.

For example, different ILs may be calculated for each separate Cause- Consequence pair for which the SIS acts as protection. The PFD of the SIS is required to be less than or equal to the LOPA ratio for all Safety, Environment, Asset, Reputation Integrity Levels for which the SIS provides protection. The risk reduction requirement for each IL rating were derived from Qatar Energy Standard to conduct SIL study and is tabulated below. The PFD of the overall safety provisions must meet these values, regardless of the method used.

The SIL study team consisted of a multi-disciplinary team from Qatar Energy, Al Balagh and iFluids Engineering & Consultancy W.L.L. This includes personnel from Process, Piping, Instrumentation & Control, Electrical, HSE, Civil and Structural, System & Control, Project, Operations and Maintenance.

SIL Verification

The individual certification of the sub-components comprising the Safety Instrumented System (SIS) loop has been conducted to assess their compatibility with the Safety Integrity Level (SIL). The primary aim of the verification study is to determine the average Probability of Dangerous Failure (PFD_avg) and the architectural limitations that govern the attainable Safety Integrity Level (SIL) rating for the Safety Instrumented System (SIS) loop.

The SIL Verification study has been conducted for the specified configuration. Based on the Failure Rate Data provided for the individual components, the quantitative analysis of the sub-components for the identified SIF loops have been performed. This analysis has revealed the overall SIL Rating for the Safety Instrumented System.

This report focuses on the validation of SIF loops through the careful selection of components and configuration.

The calculations of the failure rate for the system took into account the following assumptions.

• Failure rates are assumed to be constant during the usable life of the sub-components (Break–in period failures or end of life scenarios are not taken into account).
• Proof Tests are assumed to detect all of the faults in the system
• The calculation of PFDavg involves utilising a minimum proof test period that exceeds 50% of the demand of the subsystem.
• All components have been identified to be operating under Low Demand mode
• The total number of operational hours in a single year is assumed as 8760 hours.
• The mean time to repair/ restoration (MTTR) for each component was assumed as 24 hours.
• Restoration is assumed to be 100% effective to restore each component to fault-less state.
• Non-interfering components, i.e. those components which do not impact the performance of the safety function of the system (Interaction-Free modules), are not included in the verification calculations.

The approach followed for the verification of the SIL rating of the identified SIF loops are given below:

• Estimation of the PFD_avg for the individual sub-systems (Initiating Device; Logic solver; Final Element).
• The allocation of SIL compatibility ratings to the assembly based on their respective configurations.
• Selection of proof test interval to obtain the least PFD_avg.

The values of Failure rate in Time (FIT) used in the calculations were collated either from the certificates issued or from the failure rate data shared by the client for the individual components. In compliance with applicable portion, the calculations were carried out for each design configuration within the specified assembly.

The current report contains the results of the verification of the SIL class of the identified SIF loops of KMDS as per IEC requirements for subsystem.Achieved SIL rating/ RRF is higher than Targeted SIL rating/ RRF, so the current SIL rated SIF loops have met the requirement.