Let’s start with a quick overview of subsea numbers and where we are headed in our industry. Subsea continues to grow and we are up to almost 5000 wells that are operating. Deepwater has grown from close to zero in the mid-1990s to almost 30% of the total wells in operation. The industry is pursuing more subsea intervention and there are more wells that will need plugging and abandonment (P&A) in the future.
Subsea well intervention is a topic that is receiving more and more attention for subsea wells, and specifically for P&A, but also for other services to reenter wells. When you look at P&A issues, there are subsea wells today that are over 40 years old and still on the seafloor. The equipment is still there, but the equipment has not been abandoned or may yet be producing. Intervention tooling and running tools can be very difficult to obtain for older wells. The equipment could have been made by a manufacturer that is no longer in business or may not be supported by the original manufacturer any more.
Information on the older wells, which was all pre-computer and pre-electronic, is very hard to obtain. It may be in a box in a warehouse somewhere or may have disappeared. So, when you go back to P&A the well, it can be hard to get the information.
For well intervention vessels, thinking primarily about P&A, operators want versatility of supply, a full market place of vessels, a lot of systems, and a lot of technical capability. From the service side, building on speculation is a risky venture. There have been a few vessels put into this kind of service, but most of them are struggling to find work and there is certainly not an ongoing steady need for intervention and P&A vessels.
Subsea decommissioning is a growing problem for the industry. It’s a problem in that there is no upside to it; there is no financial benefit to decommissioning. There are regulatory, environmental, cost, and public relation issues for the oil companies that have those wells. The average age of subsea wells is steadily increasing. Every day they become older and almost every well is in decline during that period. An increasing number of wells and wells of older age will result in more subsea decommissioning than in the past. There are more and more companies active in this space and more oil companies that have to do this work. Regulatory agencies are requiring decommissioning of fields as they become economically nonviable. There is a set period of time after a well has been shut-in when it has to be decommissioned, whether it is a platform or subsea well, meaning that there is a ticking clock on all these wells that has to be dealt with.
P&A of subsea wells is far and away the most expensive single element and fraught with the most risks for subsea decommissioning projects. There is other infrastructure: manifolds, flowlines, umbilicals, and other equipment to be dealt with in decommissioning a subsea field, but P&A is the hardest one to estimate and is usually the most difficult thing to do.
In the Gulf of Mexico, most operators plan to abandon seafloor components in place in water depths greater than 800 meters. The North Sea region follows the original guidelines to recover everything possible. Generally this is in shallower water and more subsea equipment is recovered. Places like Indonesia and Malaysia have not yet formalized their requirements. They tend toward returning the seabed to its original condition, although that is not always well defined.
One of the concerns is whether to leave equipment on the bottom or not. There are cost, future access and environmental concerns. This includes whether the equipment will be in the way of future projects or future activity in those areas. In the past, most companies have been required to recover the seafloor hardware which was above the mudline, and leave buried hardware such as pipelines in place. Common practice is for anything left on the seafloor to be flushed, all hydrocarbons removed, and the hardware shown to be clean.
The problem with recovery is that this activity can do more damage than leaving the equipment in place. When you start removing equipment, you may damage something else. The concept of subsea wellhead recovery after the tree is removed is being reconsidered for several reasons. A subsea wellhead may extend 5 to 20 feet above the seafloor. Do you leave it there or cut it off below the mudline? In the US, the rule has been that the wellhead is cut off 15 feet below the mudline. If the wellhead is removed, it is difficult to get back into the well if there is a problem. Recent experience indicates that it is better to leave wellheads in place in case a future problem occurs with the well bore, because it is much easier to intervene if the wellhead is still in place. The BOP stack can still be landed on the wellhead and other equipment can be attached to the well. If the wellhead and casing are cut off 15 feet below the mudline, there is a clean seafloor, but if bubbles or hydrocarbons are leaking in the future, it is much more difficult to access the well.
On the pipeline side, there is some discussion that pipelines should be recovered. However, wherever there is a pipeline or flowline or umbilical, there is almost always marine growth and other marine activity around or on top of that line. If you go in and tear all of that out of the seafloor, you have created more environmental damage in almost all cases than if you left it there. There was an example several years ago with the Exxon Zinc template. A very rare coral was found on the template before starting template recovery. Both the environmentalists and those who were responsible for the template recovery came to the conclusion that it was better to leave the template there, mainly for environmental reasons, rather than recover the template as had been originally planned.
We at Endeavor have done some work in this area of subsea decommissioning and have some key lessons learned. These include:
1.Planning cannot be overemphasized, which includes identifying possible problems which might be encountered and having predetermined solutions. You may need extra tooling on the beach or on the rig that you might need in a P&A situation. You want to plan for anything that you might run into.
2.You need to ensure that the equipment, including the vessel and personnel, are well qualified to undertake the tasks identified in the scope of work. For example, consider the use of a drilling rig to P&A a subsea well. This is probably not the most efficient way to do the work. A smaller intervention vessel with a trained P&A crew might be a better choice.
3.Ensure that the host facility remains in place until all decom work is complete. The facility may be needed for flushing and other tasks. If an existing platform or floating production facility is removed before all subsea decom is complete, it becomes much more difficult to flush lines and there may be other tasks for which the facility may be needed. It is best to deal with the well first and delay removal of the facility to the last.
4.An experienced decommissioning team, who has a thorough understanding of the field to be decommissioned, is essential to ensuring that the planning meets everyone’s expectations. Generally, those are the people who drilled/completed the wells and those who operated the field and know the wells. They can bring to bear the knowledge needed to plan and manage decommissioning.
5.Each P&A is unique. Do not underestimate the time required to compile and review the documentation. We performed an internet survey and found 30% of the respondents spent 6 to 12 months planning the decommissioning project and an additional 30 % spent more than a year on planning. However, over 60% completed the subsea decom work in less than 8 weeks. Finding the information, getting the services, and locating the right equipment can take much longer than doing the actual work.
In the current low price market, decommissioning is an area where collaboration is of real benefit. Most companies are forced to perform this work due to regulatory requirements. The cost and effort put into decommissioning is a drain on company resources, yet must be carried out fairly quickly after the field has ceased production. While the regulatory requirements are well defined in some geographical areas, there are still specific issues under discussion and many of these can result in saving costs.
Endeavor has commenced work on a new Subsea Decommissioning Joint Industry Project (JIP) with funding from a number of operators and service companies. These include ExxonMobil, Freeport- McMoRan, Marubeni, Shell, Stone Energy, Baker Hughes/Aker Solutions Subsea Alliance, GE Oil and Gas, Halliburton, Oceaneering and Petrolatina Assets. The value of working in JIP format is to include multiple companies in order to:
-Minimize the cost for each participant;
-Encourage collaboration with Operators and Service Companies;
-Carry out economic trade-offs on specific Issues;
-Gather information on industry technology for specific Issues.
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