Pre-amble: Understanding Subsea Blowout Control
The health and safety of offshore workers and environmental protection are paramount. Prevention of accidents and incidents is key in offshore operations and operators are required to reduce risks to as low as is reasonably practicable. Thousands of offshore wells have been drilled worldwide without a major incident, but the recent experience in the Gulf of Mexico (2010) reveals the seriousness of these events when they do occur.
Offshore regulators and oil and natural gas production companies have been working to implement lessons learned from past events and improve best practices in well control, blowout prevention and emergency response. Emphasis remains on incident prevention, but emergency response preparedness is also a priority.
Prevention of blowouts while drilling occurs is achieved by maintaining two regularly tested barriers (or safeguards), the primary one being the drilling fluid within the well, and the secondary barrier being the well envelope which includes the blowout preventer (BOP), wellhead, casing and cement. Testing occurs on an ongoing basis during all drilling operations and is a key aspect of the regulatory requirements, and a key aspect of the CNSOPB’s regulatory oversight of offshore drilling programs.
Operators are also required to have in place contingency plans, which have been reviewed and found acceptable by the CNSOPB, for emergency situations and events including the possibility of a blowout and/or oil spill. The overall goal of such contingency plans is to ensure that the appropriate response measures necessary to re-gain well control are implemented as soon as possible so as to minimize the environmental impact. The full complement of response measures described in the contingency plans is evaluated by the CNSOPB to determine if collectively they provide an appropriate response to a blowout, which would include the potential deployment of a capping stack.
The most important safeguard in any blowout incident is the blowout preventer. A blowout preventer is a large mechanical device weighing in excess of 200 tons which has multiple sealing devices that can be used to control, monitor and seal oil and gas wells. Blowout preventers are designed to cope with extreme pressures and uncontrolled flow (also known as a “kick”) coming from a well during drilling. Blowout preventers are critical to the safety of crew and the environment, and to the monitoring and maintenance of well integrity.
Blowout preventer systems are used to regulate and monitor the wellbore pressure (i.e. the pressure within the hole being drilled); and to shut in the well. BOP’s have been used in the industry for nearly 100 years to control, monitor and seal a well when required. Several improvements to their reliability have been introduced since the Gulf of Mexico incident. For example, regulators’ now require that BOP’s have multiple cutting and sealing devices to provide redundancy in case of failure of one of the devices.
The BOPs importance for the safety of the crew and environment is why regulations require that BOPs be regularly inspected, tested and maintained.
Questions and Answers about the Environmental Assessment for the Project
1. What was the decision of the Minister of the Environment respecting environmental effects of the proposed Shelburne Basin Venture Exploration Drilling Project in relation to the environmental assessment conducted under CEAA 2012?
After considering the report of the Canadian Environmental Assessment Agency on the Shelburne Basin Venture Exploration Drilling Project and the implementation of mitigation measures that she considers appropriate, the Minister of the Environment determined that the Designated Project (the Shelburne Basin Venture Exploration Drilling Project) is unlikely to cause significant adverse environmental effects
2. What does the Environmental Assessment report prepared by the Canadian Environmental Assessment Agency conclude with respect to the effects of accidents and malfunctions?
Section 7.1.7 of the Environmental Assessment Report states:
The Agency considers that the effects of a major accident or malfunction from the Project on marine birds, current use, and fisheries would likely be significant; however, the probability of occurrence for a major event is very low and thus significant effects are unlikely to occur. As a result, the Agency concludes that the Project is not likely to cause significant adverse environmental effects as a result of accidents and malfunctions.
The Agency is satisfied with the proponent's approach to risk management and that the proponent will take all reasonable measures to minimize the probability of malfunctions and accidents. The Agency is satisfied that the proponent's response plans that will be developed to meet the CNSOPB’s regulatory standards will be appropriate for the scenarios that could occur. This includes the proponent's commitment, in the event of a blowout, to begin the immediate mobilization of primary* and back-up capping stacks and associated equipment to the project area.
* Note: the Environmental Impact Statement prepared by Shell Canada and submitted to the Agency identifies the location of the primary capping stack as Stavanger, Norway.
Questions and Answers about Subsea Well Control, Blowout Preventers, and Capping Stacks
3. What are the chances of a blowout occurring in the Shell program?
The chance of a blowout with a large spill of hydrocarbons occurring is extremely rare.
The Environmental Impact Statement addresses the rarity of this possibility – the chance of a blowout is one release in every 1,287 years. Furthermore, the chance of a large volume spill (release of 49,150 barrels per day for 30 days) during a blowout is one in every 18,392 years.
Of the approximately 50,000 exploratory wells drilled worldwide, there have been 2 large blowouts, one in 1979 offshore Mexico, and the Macondo blowout. Analysis of international data was taken into consideration in the Environmental Impact Statement. The results indicate that if a blowout does occur, there is a 56% chance that it will last only two days or less, meaning there would be no requirement for a capping stack.
Regardless, at the first sign of a blow out, preparations for intervention including potential use of a capping stack would begin.
4. What are the primary means of preventing subsea blowouts?
The CNSOPB holds operators accountable to ensure that the control of a well is maintained at all times by way of the following measures:
- Maintaining two tested well barrier envelopes (safeguards) at all times to prevent loss of well control, verified on an ongoing basis;
- Testing of primary and back-up BOP control systems on an ongoing basis;
- Ensuring at all times a comprehensive means of wellbore monitoring, kick prevention, kick detection, well control and blowout prevention; and
- Ensuring the ability to activate the BOP stack in a timely and effective manner at all times using either of the two redundant primary BOP control systems; the back-up acoustic control system; the auto-mode function, the dead-man system or the remote operating vehicle intervention package, with the readiness and reliability of these systems verified on an ongoing basis through testing.
In the event that the measures described above fail to prevent a blowout, it will be necessary to implement the pre-approved contingency plans and take whatever steps are necessary to regain well control in the safest, most effective and most expedient way possible.
5. What is a blowout preventer?
A blow-out preventer (BOP) is a sophisticated piece of well control equipment placed on the sea floor, directly on the wellhead. It has multiple sealing and cutting faces (i.e. redundancy is designed in such that there are back-up seals and cutting faces in case of failure of the primary features) that can be used to regain well control, or to completely shut in a well to stop the flow of oil or gas in the case of a loss of well control event. Additionally, BOP’s have many secondary features that would allow them to function even in situations where the drilling rig is no longer connected to the well (via a remote operated vehicle (ROV) or acoustic signal), and other automatic features which activate the cutting and sealing devices if all communication is lost. Verification is required to show that pipe in the well can be cut if needed by the BOP shear rams. Regular testing of the BOP functions is required throughout the drilling program.
6. What is a capping stack?
A capping stack is similar to a blowout preventer (BOP) stack. It is kept in readiness at an onshore location for deployment if well control is lost and in the unlikely event that the BOP stack fails to function and a blowout occurs.
The BOP stack provides well containment in the event of an unintended influx of hydrocarbons into the wellbore (i.e. drilled hole). If the BOP stack fails, a capping stack may be installed on top of the BOP stack to either shut-in the well or to otherwise contain the flow of hydrocarbons until steps are taken to re-gain well control and permanently seal the well.
7. What steps must an operator take in responding to a subsea blowout?
In the event that the primary and secondary well barrier envelopes (safeguards) are breached and the primary and back-up BOP systems are not activated in a timely manner and loss of well control occurs, a number of contingency plans (that would need to have been reviewed and found acceptable in advance by the CNSOPB) will be implemented immediately and concurrently by the operator. These include:
- Implementing the oil spill contingency plan, which focuses on containment and clean-up of hydrocarbons on the surface;
- Direct well intervention to re-gain well control – this would include, among other possible intervention methods, the manual activation of the BOP systems subsea using a remote operating vehicle to close the shear rams on the BOP stack to stop the flow of hydrocarbons;
- Commencing a relief well with the primary drilling installation;
- Mobilizing the designated back-up drilling installation to either assist with, or perform, relief well drilling or to assist with deployment of a capping stack;
- Mobilization of a capping stack; and
- Preparation of the BOP (or wellhead) to allow a capping stack to be installed, including clearance of debris.
The response to a subsea blowout is a multi-tiered approach that prioritizes direct well intervention as the most expedient means to re-establish well control. However, as an additional precaution, relief well drilling arrangements, the mobilization of the back-up drilling installation and the mobilization of a capping stack are other means that would be pursued concurrently.
8. If the BOP can seal a well and stop the flow of oil, then when is a capping stack used?
A capping stack may be used if there is a blowout from a subsea well due to multiple failures of primary and back-up well control systems, procedures and equipment.
A capping stack would be deployed if all of the following circumstances occur:
- The implementation of secondary well control procedures fail in relation to shutting-in the well, circulating out the influx and restoring well control with heavy fluid that resolves pressure issues;
- There are failures of the primary and secondary BOP control systems, including the auto-shear system (auto-mode function), the deadman system, the acoustic system and/or the deployment of a remote operating vehicle (for which there are two available) to the ocean floor to directly activate the BOP;
- There is concurrent failure of a critical element of both the primary and secondary sealing devices within the BOP , including the shear ram(s);
- Other direct well intervention methods fail; and
- There is a determination based on the unique circumstances leading to the loss of well control, that a capping stack is a means of re-gaining primary well control or containing hydrocarbons from the blowout.
9. What are the regulatory requirements with respect to contingency plans for a loss of well control event?
The CNSOPB and Canada-Newfoundland and Labrador Offshore Petroleum Board (C-NLOPB) have jointly published Drilling and Production Guidelines that describe the Boards’ expectations of operators in complying with the Drilling and Production Regulations promulgated by both the federal and provincial governments. Section 6.5.11 of these guidelines contains a comprehensive set of expectations surrounding contingency planning for emergency situations and events including the possibility of a blowout and/or oil spill. For matters pertaining to relief well drilling, and subsea blowout capping and containing systems, the guidelines state.
The operator is expected to have a contingency plan for the identification and sourcing of an alternate drilling installation(s) that is capable of drilling a relief well. The plan should provide a description of the installation’s required operating capability, ancillary equipment, availability, and the schedule for mobilization to the wellsite. The source of supply for a backup wellhead system and all consumables required to set conductor and surface casing for the relief well should also be identified.
The operator should also describe its plans for intervention at, or around, subsea equipment to mitigate an uncontrolled flow of petroleum from this equipment, including the location and readiness of the equipment that would be required to support this effort.
For critical wells, which the CNSOPB defines as any well drilled in deep water, and / or any well that may encounter high pressure or high temperature, the operator is required to verify to the CNSOPB, prior to starting the drilling (spudding) of each critical well, that:
- The operator has confirmed its ability to drill a relief well, including plans to access an alternate drilling installation;
- The operator has access to all materials and consumables necessary to drill a relief well;
- The contingency plan for the relief well has been established, including the potential surface location (and alternate locations) of the relief well;
- Arrangements have been confirmed to access well containment systems including a capping stack; and
- Oil spill countermeasures plans are appropriate.
10. Is a capping stack required for a natural gas blowout or only an oil spill?
Yes, it can be used to cap a natural gas blow-out as well.
Questions and Answers about Spill Response
11. Could oil wash ashore?
The Environmental Impact Statement filed with the Canadian Environmental Assessment Agency indicates that the probability of shoreline oiling is very low. Only 13 scenarios out of 960 modelled resulted in any shoreline oiling. The reason for this is because of the distance from shore, the wind direction and the currents. And under these scenarios, oil would need to remain on the surface for one month or more to be transported to shore.
12. In the case of a major spill of oil, what spill response methods would be employed?
The type of response that may be used depends on a number of factors. For more information, please visit the Spill Prevention, Preparedness and Response web page.
13. Does the authorization of a drilling program or an approval to drill a well enable an operator to use dispersants at their own discretion?
No. Operators cannot use dispersants without prior approval from the CNSOPB’s Chief Conservation Officer.
If a major incident was to occur, and an Operator was to consider the use of a dispersant, legislation requires that a specific request for approval be made at that time to the CNSOPB’s Chief Conservation Officer (CCO). Such a request would have to be accompanied by an incident specific Net Environmental Benefit Analysis. (NEBA). The use of dispersants would only be considered in cases where this analysis concludes that it is better for the environment to do so.