QRA, 2D F&G Mapping, Firewater line Hydraulic study, Flare network analysis, De-pressuring & Blow down report for FGGS Project of OIL at Baghjan

With the objective to enhance the natural gas production facility at the Baghjan field in Upper Assam, India, Ms. Oil India Ltd., a Navaratna firm under the Ministry of Petroleum and Natural Gas, desires to build a Modular Field Gas Gathering Station (FGGS).

The Baghjan oilfield, which was discovered in 2000, is situated about 25 kilometers to the northwest of the Makum oilfield. With a large reserve of crude oil and natural gas, the field’s production is reasonable. Currently, an EPS (Early Production Setup) is utilized to manage production from 6 numbers of wells.

The complete scope of the Creation of FGGS at Baghjan was divided into 6 (six) big packages in order to make the process feasible. M/s HAL offshore Ltd., an LSTK contractor, engaged Tilda Systems Engineering Pvt Ltd to deliver the detailed engineering design for the installation of packages 3,5, and 6.

TILDA Systems Engineering Pvt Ltd awarded iFluids Engineering to carry out Fire and Gas Mapping Study for FGGS-Baghjan. This document describes the methodology and study results of the Fire and Gas Mapping Study conducted for Oil India Limited Field Gas Gathering Station, Bhagjan.

Oil India Limited Field Gas Gathering Station, Bhajan consists of the following facility to receive, treat and export the gas from producing wells,

  1. Heaters area
    1. Electrical heaters
    1. Water bath
  2. Separators section
    1. HP Separator
    1. Production Separator
  3. Gas Dehydration Unit
  4. Methanol Injection skid
  5. Fuel Gas system
  6. Drain system
  7. Flare

The scope of work for the Fire and Gas Mapping study for FGGS-Baghjan includes the following activities.

  • Hydrocarbon handling areas in the FGGS-Baghjan is covered for the Fire and Gas Mapping Study.
  • The F&G Study suggests the location, type, and number of detectors that need to be installed across various areas.

The objectives of F & G Mapping study for FGGS-Baghjan are:

  • Leaving no stone unturned in analyzing every possible risk that could cause the release or ignition of flammable gas.
  • Conducting extensive simulations to determine the potential impact of any gas leakage and assessing the severity of any hazardous situation that may arise within the project premises.
  • Our rigorous F&G methodology will lead us to propose revised protocols for fire and gas detection to guarantee the utmost safety and security of the project.

The facility in question deals with handling hydrocarbon gases, which inherently carry the risk of fire and explosion. As part of a thorough hazard identification process, the facility’s team recognized that fire and explosion hazards were primary concerns, while toxic hazards were not identified.

The main challenges revolved around the potential consequences of hydrocarbon leaks leading to fires and explosions. To address these risks, the facility required a robust system capable of both detecting hydrocarbon leaks and providing early fire detection.

The facility opted for a multi-pronged approach to address the identified hazards:

The installation of both point-type and line-of-site (open path) flammable hydrocarbon gas detectors were chosen. These detectors operate on infrared technology, enabling them to identify the presence of hydrocarbon gases by measuring the absorption of infrared light. Point-type detectors were placed strategically to cover specific areas, while open path detectors were used for broader coverage.

The facility also incorporated flame detectors that utilize three wavelengths of infrared (3IR) technology. These detectors are highly sensitive to the unique signature of flames, enabling rapid and reliable fire detection. The combination of multiple wavelengths enhances the detectors’ ability to distinguish between flames and other sources of infrared radiation.

To ensure the optimal deployment of detectors and achieve the required coverage, the facility conducted a Fire and Gas (F&G) Mapping study using an advanced software. This study enabled the team to analyse the Facility’s layout, potential hazard sources, and environmental conditions to determine the optimal locations for detectors. By leveraging this technology, the Facility could make informed decisions about the types and placements of detectors to ensure comprehensive coverage.

By implementing a comprehensive detection strategy, the facility achieved several significant benefits:

  1. The advanced detection system significantly reduced the risk of undetected hydrocarbon leaks and fires, safeguarding personnel and assets from potential harm.
  2. The combination of flammable hydrocarbon gas detectors and 3IR flame detectors ensured early detection, enabling prompt response and mitigation actions.
  3. The F&G Mapping study conducted using an advance software ensured that detectors were placed optimally, minimizing coverage gaps and maximizing efficiency.
  4. With the ability to detect hydrocarbon leaks and fires swiftly, the Facility mitigated the potential for major incidents, minimizing downtime, environmental damage, and safety hazards.

Through the strategic implementation of flammable hydrocarbon gas detectors and 3IR flame detectors, coupled with a meticulous F&G Mapping study using Detect 3D, the Facility successfully addressed the challenges posed by handling of hydrocarbon gases. Based on the F&G mapping study, it was recommended to place 21 Nos of Flammable Gas detectors and 20 Nos of Flame Detectors in FGGS-Baghjan for covering the critical areas. This comprehensive approach to hazard detection and mitigation serves as a model to other Facilities facing similar risks, highlighting the importance of advanced detection technologies in ensuring safety and operational continuity.

As a part of this, TILDA Systems Engineering Pvt Ltd has awarded iFluids Engineering to carry out Depressurization and Flare Network Hydraulic Study for FGGS-Baghjan.

Field Gas Gathering Station (FGGS) comprising of natural gas production facility including Heaters, test and production manifolds, and separators, gas dehydration unit, and required auxiliary, safety and utility units like Flare system, Fuel Gas system, Captive Power plant, Effluent Treatment Plant, formation water and effluent treated water storage system, Water treatment plant, Instrument air system, Chemical dosing system, Firefighting system, Control and Emergency shutdown systems, Telecommunication system etc.

Following are the facilities proposed to be constructed at FGGS Baghjan:

  1. Captive Power Plant
  2. Two trains for gas processing comprising of,
  3. Wells Tie-in, Electric Heaters & Water Bath Heaters
  4. Production separators
  5. HP separator for gas lifts
  6. MPFM for well testing
  7. All interconnecting piping, valves, instrumentation etc.
  8. Gas Dehydration Unit (GDU)
  9. The auxiliaries and utilities for the entire plant.
  10. ETP & Formation water storage tanks for storing Produced Water
  11. Treated water storage tanks for storing Treated Water
  12. Non-luminous, enclosed ground flare system with Flare Stack (separate for HP and LP) common for both FGGS and EPS.
  13. Firefighting system and its network
  14. Utilities and Other accessories

Huge Non-Associated Gas (NAG) potential exists in the Baghjan field, and 7.5 MMSCMD of continuous gas production is anticipated from this region. One modular Field Gas Gathering Station (FGGS) with natural gas production facilities must be built in order to explore these resources.. The facility shall include Production and Test Manifolds, Gas /Condensate/Water Separators, Fuel gas system, Flare system and formation water and effluent treated water storage system along with all the required utilities and auxiliary systems. The facility will have additional space set aside so that one more 2.5 MMSCMD train can be installed in the future to increase capacity..

The objectives of the BDV Depressurization and Flare Network Hydraulic Study are as follows:

  • To determine and calculate BDV relief loads for the FGGS facility.
  • To perform the HP and LP Flare network hydraulic analysis.
  • To determine the outlet line size of PSV, BDV as well as the flare main header and sub header of HP and LP flare system.

Blow-down is the process of depressurizing a given process unit or section of a plant after shut down. In this instance, a blow down valve (BDV) is utilized. In the event of emergency (e.g. fire, gas leaks etc.) the Emergency Blowdown Valves are open after plant shut down. This serves as a safety measure against escalation of the fire into a full blown explosion.

In an oil and gas/gas processing plant, the flare system is the single largest pipe network. It functions as a relief system for depressurizing various production and process units in the event of shutdown or unanticipated hazardous process events by collecting surplus fluid through relief devices.

The Flare network study includes the analysis of various scenarios such individual relief conditions, continuous/intermittent relief, least relief load and highest relief load cases.

Flare system in FGGS consists of different relief units that handle depressurization for the different processes taking place on the plant, to ensure safety of life and property on it.


The Depressuring study was carried out for Three Production Separators and One HP Separator in FGGS facility, to determine Blow Down Valve Restriction orifice (RO) Area/Diameter, Peak relieving flowrate, Final Pressure as well as to predict the Minimum temperature of piping/vessel during Depressuring event.

Depressurisation and BDV calculation study includes isolation of the vessel from its inlet and outlet stream shutdown valve (SDV) and evaluation of a hypothetical vessel volume including the volume in the vessel and pipes. Aspen HYSYS Depressuring tool was used to carry out the study. Depressuring event for both Fire and Adiabatic cases were considered.

 As per API STD 521, If vapor depressuring is required for both fire and process reasons, the larger requirement should govern the size of the depressuring facilities. This generally involves reducing the equipment pressure from initial conditions to a level equivalent to 50% of the vessels design pressure within approximately 15 min or depressuring to a gauge pressure of 690 kPa (100 psi) is commonly considered when the depressuring system is designed to reduce the consequences from a vessel leak.


The flare system shall receive PSV discharges and blow down from equipment and inlet manifolds. Condensate in the flare gas collected in the LP and HP flare KODs which is pumped using the respective KOD pumps to an underground Closed Blow down (CBD) vessel and the gas is routed to the non-luminous enclosed ground flare system.

The enclosed ground flare system shall also receive LP and HP flare gases from existing EPS facility at Baghjan. Baghjan EPS flare gas headers of suitable sizes with input points to hook up flare lines from existing HP Flare and from the existing LP and VLP Flare and PSV discharge shall be provided.

The flare system for the FGGS facility is a non-luminous enclosed ground flare system which comprises of the following:

  • HP Flare System
  • LP Flare System

The HP and LP Flare System together consists of approximately 46 relief sources respectively which includes PSV, PV, XV and BDV.

The study includes Flare network model development in the required software and evaluation of Backpressure, Mach number, Rho v2, Noise, Relieving Temperature, etc. which indeed used in determining the outlet line size of PSV, BDV as well as the Flare main header and sub header of HP and LP Flare system.


The study outcome includes evaluation of the parameters such as Back pressure, Mach number, Rho v2, Noise, etc. for consistencies as per the standard practice. Based on the observation from the study, the Tail pipe sizes of the Relief Sources were proposed in order to meet the Backpressure, Mach number and Rho v2 requirement criteria.