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[ Original Paper ] | |
Journal of the Korean Society of Marine Engineering - Vol. 43, No. 2, pp. 120-131 | |
Abbreviation: J. Korean Soc. of Marine Engineering (JKOSME) | |
ISSN: 2234-7925 (Print) 2234-8352 (Online) | |
Print publication date 28 Feb 2019 | |
Received 01 Nov 2018 Revised 07 Jan 2019 Accepted 09 Jan 2019 | |
DOI: https://doi.org/10.5916/jkosme.2019.43.2.120 | |
Safety design principles and best engineering practices for well stimulation vessels | |
Duo Ok†
| |
Correspondence to : †Principal Engineer, Reginal Approval Center, DNV GL, 1400 Ravello, Katy, Texas, USA, TX77449, E-mail: happysomer@gmail.com, Tel: +1-713-894-8559 | |
Copyright © The Korean Society of Marine Engineering This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. | |
Many offshore supply vessels are actively involved in well stimulation and well intervention operations in the Gulf of Mexico and other parts of the world. The potential risks associated with these operations are significantly high when the operation profile includes the exposure of hydrocarbon returns, carriage of low-flash point liquids, and handling and transport of liquefied nitrogen and other hazardous chemicals. Identification of the hazards, operational limitations, and risks that may be faced during these operations is important for preventing accidents which can damage property, the environment and endanger lives. Many of these vessels are not purpose-built but are mobilized for temporary assignments, i.e., specific stimulation and intervention jobs. This type of vessel is chartered with a very short notice within a short time frame. Preparing the vessel to safely perform the required tasks within the framework of the required rules and regulations is challenging for designers, operators, shipyards, and classification societies. Because each operation and vessel is unique, no universal rules or guidelines currently exist to cover the wide range of operational profiles. In this study, various existing rules, references, standards, and guidelines that are relevant to well stimulation operations were reviewed. Various operational risks of different well stimulation operations, safety arrangements, design considerations, and best engineering practices were discussed and recommended in order to satisfy the relevant safety objectives and functional requirements. The proposed key design recommendations may be considered at the early design stage of newbuilding or temporary mobilization projects to enhance the overall safety and prevent undesirable incidents in well stimulation vessels.
Keywords: Safety design, Well stimulation, Offshore supply vessel, Risk, Hydrocarbon |
The aging installed base of subsea wells is forecasted to surpass 7,000 by 2019, and operators are exhibiting a growing interest in improving the recovery rates of existing and future subsea wells [1]. Well stimulation is a well intervention method performed on an oil or gas well to increase production by improving the flow of hydrocarbons from the drainage area into the well bore [2]. It is a type of light well intervention that involves high-pressure pumping of fluids into the wells to break or fracture reservoirs. The potential risks associated with temporary mobilization for well operations in offshore supply vessels (OSVs) are significantly high due to the nature of handling hydrocarbons, chemicals, and hazardous liquids or gases during the operations. Some publications indicate the recent statistics of offshore incidents, which include loss of well controls [3][4].
Safe, effective, and cost-efficient well stimulation and well intervention operations are beneficial for all stakeholders, including regulators, vessel owners, and oil and gas producers. Owing to the unique nature of each temporary mobilization job, there are no universal rules or guidelines addressing the wide range of well stimulation operations and the various chemical additives and equipment used in these activities.
In this study, various safety aspects of the design and operations in typical well stimulation vessels were investigated that utilize chemical injection and hydraulic fracturing as the main methods of well stimulation, with consideration of the possible fire and explosion risks, environmental pollution, and personal safety during operations. Various key parameters which are to be considered in the design, construction, and operational procedures were addressed to limit accidental events and enhance the overall safety of well stimulation vessels. Proper and inherent safety barriers implemented within the design and operational procedures are essential for enhancing the overall safety and reducing risks. The topics considered include the general arrangement and layout, fire protection and detection, ventilation, hazardous-area control, emergency shutdown (ESD) and disconnection system, emergency response and personal protection. The findings and recommendations presented herein are intended to enhance the overall safety level regarding designs and safety procedures. The major recommendations highlighted in the paper may be considered (to the extent that they are practical) for existing well stimulation vessels, temporary mobilization, and newbuilding projects.
There are numerous international codes, standards, rules, and guidelines that can be referred and implemented in well stimulation safety design, arrangement and procedures. Each classification society has its own rule sets to guide and specify requirements for different projects and vessels. The objectives of the rules and guidelines are to provide an internationally acceptable standard of safety by defining the requirements for the design loads, arrangements, area classification, shutdown logic, alarms, escape ways, and communication; to provide a contractual reference document between suppliers and purchasers; to provide guidelines for designers, suppliers, purchasers, and regulators; and to specify procedures and requirements for units and installations [5].
This section addresses various requirements from existing codes, standards, rules, and guidelines. Additionally, comparisons and gap analyses between relevant rules and guidelines are performed. These references were collected, reviewed, and summarized to identify the essential requirements to be considered in the design and operations of well stimulation vessels.
IMO A.673(16) was developed for the design, construction, and operation of offshore support vessels that transport limited amounts of hazardous and noxious liquid substances in bulk for servicing and resupplying offshore platforms, mobile offshore drilling units, and other offshore installations, including those employed in the search for and recovery of hydrocarbons from the seabed [6]. The guideline is used for various offshore activities related to well stimulation and well intervention. Generally, this guideline together with the International Bulk Code (IBC) [7] and SOLAS [8] are baseline requirements of most of flag states and classification societies. The guidelines cover damage stabilities, various ship designs and arrangements, various safety aspects, pollution prevention, personal protection, and operational requirements. The IBC [7] contains the IMO regulations that govern the design, construction, and safety requirements for various chemicals and liquids used for well stimulation operations.
The FSS Code [9], FTP Code [10] and SOLAS Ch. II-2 describe the mandatory requirements for active and passive firefighting systems, detection, personnel protection, and safe escape. The LSA Code [11] and SOLAS Chapter III describe lifesaving appliances and arrangements as a part of the safety barrier. USCG has a CG-ENG Policy Letter No.03-12 [12] regarding the implementation of IMO Resolutions A.673(16) and provides the United States’ interpretations for the design, construction, and operation of new and existing U.S. flagged OSVs.
The DNV GL [13] and ABS [14] rules specifically address the safety design requirements for tank systems and equipment, piping systems, and control and monitoring systems, personnel protective equipment, intact and damage stability applicable to well stimulation vessels. The principle of safety design for both the rules are the same, but each classification society has slightly different rule details and descriptions.
MARPOL [15] regulates the control of pollution by noxious liquid substances in bulk in Annex II and the prevention of pollution by harmful substances in Annex III, which are used as chemicals and additives during well stimulation activities.
API RP 505 [16] and IEC 60092 [17] specify the hazardous area classification and selection of electrical equipment in vessels carrying liquids that are flammable—either inherently or because of their reaction with other substances—or flammable liquefied gases. Area classification is a method for analyzing and classifying the areas that may contain explosive gas atmospheres. The objective of the area classification is to limit the potential ignition sources and allow the selection of electrical apparatus that can be operated safely in these areas.
IMO Circ. 1321 [18] specifies the control of flammable material and ignition sources, the lighting within the cargo pump room space, the temperature monitoring system and gas detection system for cargo pumps, and the ventilation control in the cargo pump room space. Cargo pump rooms should be mechanically ventilated, and the capacity of the fan should be at least 20 air changes per hour of the total volume of the cargo pump room as per this circular.
IMO MSC/Circ. 1165 [19] provides principal requirements for the water-based fire-extinguishing system used in the cargo pump room.
IMO Circ. 672 [20] addresses measures for preventing explosions in the cargo pump room, including pump shaft temperature-sensing devices, alarms, lighting interlock with ventilation, a gas detection system in the pump room, and a bilge level monitoring system in the pump room.
The MODU Code [21] covers all the safety barriers, such as prevention and detection mitigation and emergency response, which includes machinery and electrical installation fire safety and lifesaving equipment and procedures.
The OCIMF “An Information Paper on P/R Safety” [22] specifies recommendations for various design aspects for pump room safety. These aspects include monitoring, detection, entry procedures, inspection and maintenance.
NORSOK S-001 [23] specifies a risk reduction principle. The objectives of the risk reduction principle and the inherent safety design are to reduce potential hazards, reduce the probability of unwanted events, reduce the inventory and damage potential, strive for simplicity and reliability, and prevent escalation. The layout, safety design, detection, ignition source control, communication, passive and active fire-fighting system, escape and evacuation, etc. are addressed.
An inherently safe design for well stimulation operations should use a combination of rules, standards, guidelines, and industrial best engineering practices to address all the safety barriers for avoiding undesirable incidents. The mandatory regulatory requirements (such as SOLAS and the rules of classification societies) pertain to only the baseline mandatory requirements, which should be strengthened according to the technical and safety standards, procedures and best engineering practices of the operators and designers.
In this section, various design features and design requirements are reviewed, with a focus on the main safety barriers that must be considered in the design and operations of a vessel, such as prevention, detection and control, mitigation and egress, and emergency response. The following key design considerations for ensuring the safe operations of well stimulation vessels are discussed.
The design features and recommendations presented in this section are high-level and key items that are addressed in the SOLAS [8], IMO A.673(16) [6], and Classification Society’s rules [13][14]. Various rules and guidelines are employed to make useful recommendations for enhancing the safety of the well stimulation vessel design. Additionally, the experience of the author from many temporary well stimulation mobilization projects and newbuilding projects is used to identify key issues in design and installation.
Well stimulation vessels are equipped with various additional equipment and items compared with general offshore supply or support vessels, such as acid tanks, well stimulation equipment and tools, fuel tanks, control cabins, hydraulic power units (HPUs), generators, cryogenic tanks and piping, additive chemicals, mixers and blenders and associated piping for uninhibited acid, chemical pumps and high-pressure injection pumps, filters, dry chemical storage spaces, hose reels, injection manifolds, and liquid additive skids. Well stimulation vessels are also equipped with a dynamic positioning system in order to maintain their position safely during well stimulation operations. The arrangement of the system and equipment must consider various safety barriers, such as prevention, detection and control, mitigation and egress, and emergency response. The important design principle of “General Arrangement and Layout” is to ensure segregation and separation between high-risk hazardous spaces and low-risk nonhazardous spaces, as well as spaces containing important safety and control functions, machinery spaces, and accommodation and service spaces. In offshore units, the arrangement and layout undergo a formal safety assessment (e.g., hazard identification: HAZID hazard and operability study: HAZOP) to identify various potential hazards and risks. This additional assessment is not mandatory for SOLAS vessels, but it is recommended that equivalent risk assessments should be considered during the design phase.
Figure 1 shows the one of the aft deck arrangement of the well stimulation vessel that is equipped with various well stimulation equipment, chemical and addictive tanks, a control cabin, a fixed foam firefighting system, etc. The arrangement indicates the complexity of the well stimulation area due to the size restriction of OSVs. Well stimulation equipment should be properly secured and attached to the hull structure of the vessel using a suitable means of fastening as per the approved cargo securing manual for the vessel, and the securing arrangements should not adversely affect the equipment operation, emergency response, or escape of personnel [14].
IMO A.673(16) [6], DNV GL [13], and ABS [14] have the following common arrangement requirements for well stimulation vessels.
In many cases, well stimulation vessels have other additional functions, such as fire-fighting vessels, offshore supply vessels, and crane vessels. Some well stimulation vessels have a complicated arrangement with a double-deck well stimulation area configuration, which is similar to the topside of the FPSO. These configurations require extra design consideration with regard to ventilation, fire and gas detection, the effective fixed firefighting system, and safe escape and evacuation.
The following are additional design considerations that should be implemented and considered and that are not clearly addressed in IMO A.673(16) [6] and the Classification Society’s rule requirements [13][14].
The basis of the fire protection system in well stimulation vessels is presented in Chapter II-2 of the 1974 SOLAS Convention, as amended [8] IMO A.673(16) [6] the Classification Society’s rules [13][14] and the Flag Administration requirements. Passive fire protection should also be arranged according to the rules and regulations, e.g., SOLAS Ch. II-2 [8], the FSS Code [9], and MODU 2009 [21], to prevent or mitigate the serious consequences of a fire.
The following provisions apply for the carriage of flammable liquids, which is addressed in IMO A.673(16) [6].
DNV GL has the following additional requirements under the classification notation LFL [24].
In addition to the foregoing, the following principles should be considered in design.
IMO A.673(16) [6], DNV GL [13][24], and ABS [14] specify the following requirements for fire and gas detection system and control actions.
For LFL cargo handling, the following design aspects should be considered [24].
In addition, the followings are recommended to improve the safety and efficiency of the fire and gas detection design and arrangement which are not addressed in IMO A.673(16) [6] or Classification Society’s rules [13][14].
Electrical installations should satisfy the requirements of Chapter 10 of the International Bulk Chemical Code. [7]. The electrical equipment and components shall be a certified and an approved type for their intended service and hazardous-area location. API RP 505 [25] and IEC 60092-502 [17] provide relevant hazardous-area criteria for the installation of electrical equipment. Separation between hazardous well stimulation areas and nonhazardous areas, such as the engine room and accommodation space, is important for eliminating sources of ignition and accidental events.
The following are recommendations for hazardous-area control in well stimulation areas.
The ventilation arrangement is important for ensuring a hydrocarbon- and flammable gas-free environment in the cargo handling space. The ventilation system should eliminate areas of stagnant gases within the space to provide a non-flammable environment.
IMO A.673(16) [6], DNV GL [13][24], and ABS [14] specify the following key requirements for pump-room ventilation and the cargo-tank ventilation system.
In addition, the following are recommended as best engineering practices.
Although the design follows the applicable Classification Society requirements and IMO A.673(16) [6], there are areas in which the cargo handling design can be improved to enhance the safety of the well stimulation vessel. Among others, the followings are some of the key requirements of the Classification Society [13][14][24] and IMO A.673(16):
In addition, the following are recommended to ensure the safety of the well stimulation cargo piping and safety system.
The purpose of the emergency shutdown (ESD) systems in the event of abnormal conditions is to minimize the escalation of events and to minimize the extent and duration of such events. This is achieved by a combination of actions, including stopping of hydrocarbon flow and shutdown of equipment and systems to bring them to a predefined safe state [5]. Shutdown systems shall be so designed that the risk of unintentional stoppages caused by malfunction in a shutdown system and the risk of inadvertent operation of a shutdown are minimized [21].
IMO A.673(16) [6], DNV GL [13][24], and ABS [14] specify the following requirements for the ESD system.
The following should be considered in ESD philosophy and design.
Chemical or cryogenic liquid spillage can damage the hull and environment and endanger humans. For preventing such spillage, there are many design considerations, including material selection, leakage control using a shield, spill coaming or drip trays, and safe drainage. IMO A.673(16) [6] and Classification Society rules [13][14] specify as follows.
In many cases, well stimulation vessels carry chemicals and additives that are not listed in the International Bulk Code [7]. Chemicals to be carried in bulk that are not classified by the IBC require tripartite agreements among the owner of the vessel the governments of the country of manufacturing or shipping and the country of receiving and the Flag Administration. This is to be assessed by the Administration and IMO as per MEPC.1/Circ. 512 Section 3 and Section 7 with the tripartite agreement. The process, along with the applicable forms are described in MEPC.1 Circ. 512. The assessment shall include IBC designations in accordance with the table in Chapter 17 of the IBC. Additives that fall outside the scope of products in IMO A.673(16) Sec. 1.2.2 may be carried in limited amounts in accordance with requirements acceptable to the Administration. The aggregate amount of such additives that may be transported should not exceed 10 % of the vessel’s maximum authorized quantity of products subject to these guidelines. An individual tank should contain not more than 10 m3 of these additives. However, each additive still needs operator’s assessment for each of the chemicals, although it does not need to be subject to tripartite agreement.
The design of the well stimulation vessel should include a safe and controlled emergency response to accidental events. The escape way shall be marked so that personnel can identify the routes of escape and easily find the escape exits. Safe, direct, and unobstructed exits, access, and escape routes should be provided from the well stimulation area to the safe area, muster areas, and embarkation or evacuation points. It is important to ensure that the escape routes are not blocked by equipment, such as piping and fittings. The surfaces of decks, walkways, platforms, stairs, ladder rungs, etc. should be non-slip and designed for drainage and easy removal of contaminants such as mud and oil. Communication and alarm systems should be provided to alert all personnel on board at any location of an emergency. The systems should be suitable to provide instructions for an emergency response. The alarms shall be clearly audible and easily distinguishable at all locations. In locations where machinery noise prevents the alarm from being heard, additional a visible means of alarm (e.g., rotating light) shall be provided.
The following should be considered as per IMO A.673(16) [6], DNV GL [13], and ABS [14].
Well stimulation vessels shall have an approved operation manual readily available on board. The manual shall give instructions and information on safety aspects related to well stimulation processing. Each ship certified to carry noxious liquid substances should be provided with a Cargo Record Book, a Procedure and Arrangements Manual, and a Shipboard Marine Emergency Plan developed for the ship in accordance with Annex II of MARPOL 73/78 [15] and approved by the Administration [6][13].
Considering the nature of the operation profiles of well stimulation vessels, the potential risks associated with operations of well stimulation vessels are significantly high. The industry practice is to design the vessel in accordance with the project specifications and relevant mandatory rules and regulatory requirements, while minimizing the cost.
However, the rules and regulations defined by the project specifications may only provide a minimum safety level for well stimulation vessels therefore, additional design, safety, and company procedures should be considered to ensure safe operation of well stimulation vessels.
In this paper, numerous documents, rules, and guidelines were reviewed, and various design considerations, best engineering practices, and guidelines that are essential for reducing the risks of different well stimulation operations, including temporary assignments for non-purpose-built vessels, were addressed. These references and recommendations should be considered to the extent that they are practical and applicable to the existing and the for newbuilding design. The implementation of the items discussed herein is left to the operators, designers, builders, and corresponding authorities, based on principle of the sound engineering practice.
The opinions expressed herein are solely those of the author and do not represent the views or opinions of the author’s employer or any other parties.
The following statements should be used “Conceptualization, Duo Ok; Methodology, Duo Ok; Software, N/A ; Validation, N/A; Formal Analysis, N/A; Investigation, Duo Ok; Resources, Duo Ok; Data Curation, N/A; Writing—Original Draft Preparation, Duo Ok; Writing—Review & Editing, Duo Ok; Visualization, Duo Ok; Supervision, Duo Ok; Project Administration, Duo Ok; Funding Acquisition, N/A.
1. | Infield Systems Ltd, Subsea Well Intervention Market Report to 2019, https://www.infield.com/market-forecast-reports/subsea-well-intervention-market-report, Accessed February 26, 2019. |
2. | WIKIPEDIA, https://en.wikipedia.org/wiki/Well_stimulation., Accessed July 22, 2018. |
3. | BSEE, Loss of Well Control Occurrence and Size Estimators, Phase I and II, Report no. ES201471/2, (2017). |
4. | BSEE, https://www.bsee.gov/stats-facts/offshore-incident-statistics., Accessed July 22, 2018. |
5. | DNV GL, (DNVGL-OS-A101), “Safety principles and arrangements”, (2018). |
6. | IMO, Res A.673(16), (1989), “Guidelines for the Transport and Handling of Limited Amounts of Hazardous”, amended in 2006. |
7. | IMO, “International Code for the Construction and Equipment of Ships carrying Dangerous Chemicals in Bulk”, 2016 edition. |
8. | IMO, SOLAS, “International Convention for the Safety of Life at Sea”, consolidated edition in 2014. |
9. | IMO, FSS Code, “International Code for Fire Safety Systems”, 2015 edition. |
10. | IMO, FTP Code, “International Code for the Application of Fire Test Procedure”, 2012 edition. |
11. | IMO, “International Life-Saving Appliance (LSA) Code”, 2017 edition. |
12. | CG-ENG Policy Letter, No.03-12, Policy on the implementation of IMO Resolutions A.673(16), Guidelines for the Transport and Handling of Limited amounts of Hazardous and Noxious Liquid Substances in Bulk on Offshore Support Vessels, USCG, (2012). |
13. | DNV GL, DNVGL-RU-SHIP Pt.5 Ch.10, Sec.8 “Well Stimulation Vessels,” , July, 2018. |
14. | ABS, Guide for Building and Classing Offshore Support Vessels, Part 5, Ch.11 Well Stimulation, July, 2018. |
15. | IMO, MARPOL, “The International Convention for the Prevention of Pollution from Ships”, consolidated edition 2017. |
16. | API, (RP 505), Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Division 1 and Division 2, (1997). |
17. | IEC, 60092, Electrical Installations in Ships - Part 502: Tankers-Special features, edition 1999. |
18. | IMO, MSC.1/Circ.1321, Guidelines for Measures to Prevent Fires in Engine-Rooms and Cargo Pump Rooms, IMO, June, 2009. |
19. | IMO, MSC/Circ.1165, Revised Guidelines for The Approval of Equivalent Water-Based Fire Extinguishing Systems for Machinery Spaces and Cargo Pump Rooms, IMO, June, 2005. |
20. | IMO, Circ. 672, Measures to Prevent Explosions in Cargo Pump Rooms on New and Existing Oil Tankers, IMO, December, 1994. |
21. | MODU, Code for The Construction and Equipment of Mobile Offshore Drilling Units, December, 2009. |
22. | OCIMF, Oil Companies International Marine Forum Information Paper, “An Information Paper on P/R Safety”, (1995). |
23. | Standards Norway, “NORSOK Standard S-001, Technical Safety”, 4th Edition, February, 2008. |
24. | DNV GL, (DNV GL-RU-SHIP Pt.6 Ch.5 Sec.9), Offshore Service Vessels for Transportaion of Low Flashpoint Liquid, July, 2018. |
25. | API, API RECOMMENDED PRACTICE 505: Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Division 1 and Division 2, API, August, 2013. |
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