Advancing well abandonment

Valerio Orsini, Antonio Sardo, Weatherford and Les Johnstone, Eljay Well Services, highlight a well abandonment operation in offshore Tunisia that was performed through an integrated process.

Well abandonment is the inevitable endgame of any oil or gas well, as dwindling production turns it from profitable asset to liability. However, unlike other intervention operations designed to revitalise the well (such as performing a workover, repairing/replacing downhole equipment or bringing previously bypassed parts of the reservoir into production), abandonment represents a pure cost to the operator, with no promise of boosted profits.


Graphic representation of the Tunisian wells prior to the abandonment operation (above), and what a fully plugged and abandoned wellbore would look like following the integrated abandonment operation (below).

As a result, while operators accept that well abandonment is a necessary stage of the asset lifestyle, they also need to ensure that this operation is executed as quickly, cost effectively and safely as possible. Challenges to efficient well abandonment continue to mount in the form of more stringent environmental regulations, rising insurance premiums and a growing number of wells being stockpiled for abandonment. The number of idle wells awaiting abandonment is growing globally at a rate of 8 to 10% per year, many in major producing regions including the US, North Sea, Asia-Pacific and sub-Saharan Africa.

Seamless service for late-life wells

To help navigate these challenges and ensure that a well is abandoned efficiently and reliably the first time, operators increasingly rely on service providers to develop new abandonment solutions. To that end, Weatherford has developed a full suite of plug-and-abandonment (P&A) equipment and services to safely and efficiently abandon ageing wells. While P&A activities were traditionally carried out from conventional drilling rigs or hydraulic workover units, the integrated well abandonment offering is flexible and modular enough to be deployed from a range of service vessels, including lower cost commercial vessels.

The integrated service was initially deployed in 2006 to assist with abandonment activities in the US Gulf of Mexico in the wake of Hurricane Katrina. Since then, it has continued to expand to include a full range of late stage, intervention and well-abandonment equipment and operational expertise.

By leveraging a global and cross-organisational approach to well abandonment, an operator can be assured of a service solution that is customised for their particular needs, rather than having to accept a ‘one size fits all’ offering. For each abandonment project, Weatherford’s well abandonment and intervention group – led by an expert advisor in well abandonment – provides pre-job planning, risk and cost analysis, compliance, engineering, scheduling, execution and contingency planning to ensure that the job is executed correctly the first time. A ‘first time right’ mindset assures that the right combination of intervention technologies is deployed to dismantle a well’s infrastructure, while protecting personnel and mitigating environmental hazards. This helps the operator avoid leaks, pollution risks and associated cleanup costs, even years after the abandonment operation.


Weatherford’s single-source approach to well abandonment includes the use of a dedicated project manager couple.

This integrated group is also organised to help operators decide whether to extend a mature well’s productive life with a workover or abandon the well altogether. Regardless of the decision, intervention services are readily available to maximise resources and minimise costs and safety risks for both operations.

For example, the group’s integrated operational planning and execution service is backed by engineering support from reservoir analysis and petroleum consulting to determine the remaining reserves and the best intervention processes to economically recover them. The service offers synergies in the form of the same personnel, application expertise and equipment to help operators extend production to maximise late-life recovery, and then seamlessly transition to decommissioning and abandonment operations.

Trial in Tunisia

In 2012, an operator working off the coast of Tunisia required such a full-service offering to P&A two wells, an oil producer and a water injector, located at a seabed depth of approximately 935 ft (285 m). The objectives of the job were to properly abandon the wells to the requirements set forth by the Tunisian government, with all isolation tests recorded and verified before moving on from the site. Abandonment operations were to be conducted from a multi-service vessel and included cutting and pulling tubulars and clearing the seabed.

The operator would normally hire a semisubmersible rig or drillship to carry out the abandonment operations, but these vessels were in short supply in the region and carried high daily rental rates. In addition, the operator did not possess local abandonment expertise and lacked sufficient knowledge of local service companies, regulatory procedures and laws.

Eljay Well Services AS was contracted by the help to plan and support the overall well abandonment operation, and Weatherford was selected to deliver onshore facilities and provide a full suite of offshore equipment. By delivering the majority of abandonment equipment as a single-source provider, Weatherford alleviated the operator’s concerns of having to co-ordinate separate abandonment services from multiple providers. If a question arose or if a change to the process was required during the abandonment job, the operator could simply go through a single service provider. This was considered a more efficient option compared to having to track down answers from different service providers who would likely be working in a siloed, rather than coordinated, fashion.

A Weatherford project co-ordinator was assigned to the P&A campaign. The coordinator was a specialist in well abandonment operations charged with providing expertise, advice and oversight of all of Weatherford’s well abandonment services and activities, which included managing the onshore preparation and the offshore field job. Preparation services provided out of the onshore base included facilities for storage, collection and testing areas for third-party equipment, as well as offices with Internet and conferencing capabilities for personnel to integrate and plan the offshore operations in detail. Additional onshore support included logistics, loading and transportation of equipment to the site and travel and accommodations for the offshore abandonment crews.

The offshore scope of work called for a systematic process of re-entry, retrieval and isolation, which included:

  • Tying into the subsea wellhead with re-entry and retrieval tools and 7 in. casing string used as a riser.
  • Punching and cutting 5½ in. and 7 in. tubing strings.
  • Pumping/testing reservoir, and intermediate well isolation cement plugs.
  • Retrieving the riser and tubing with the assistance of a remotely operated vehicle (ROV).
  • Cutting the flow line with the ROV.
  • Retrieving the subsea wellhead.
  • Running and setting a bridge plug via wireline.
  • Pumping/testing the upper environmental cement plug.
  • Installing a fishing net overtrawl structure.

The offshore job mobilised personnel and integrated equipment and services from multiple product lines. The modularity of these products allowed Weatherford to load all necessary equipment onto the multi-service vessel, which was equipped with a crane, compensator and heavy-duty and observation ROVs.

Weatherford’s project co-ordinator also ensured that all services and equipment were available when required offshore. The services mobilised for the Tunisian job included:

  • Fishing and re-entry services, which deployed fishing, milling and cleaning tools for the tubing and casing strings. A customised milling system was developed for the application, using the historical milling data gathered in Weatherford’s performance tracking system as a basis. With a better idea of the milling requirements for this job, the service provider’s mill engineering and certified welders developed mills that would ensure a consistent and durable cutting surface specially configured for the wells.
  • Cased-hole completions services provided bridge plugs for casing and tubing isolation, crossover seals and wireline adapters.
  • Tubular running services employed a four-man crew to pull out the tubing strings. This included onshore handling of tools and loading via crane onto the vessel. Once on the job site, the crew used power tongs and handling equipment to retrieve the tubing.
  • Wireline services provided a wireline skid unit and deployed and set the bridge plugs. The six-man wireline crew also deployed non-explosive, chemical-based wireline cutting tools and punching tools to sever the tubing. The use of a chemical cutting package was particularly important, given the challenges with importing and transporting explosives into the region.

This integrated P&A service offering was a key component of the successful execution of the two-well abandonment operation from a single commercial vessel. The operation was completed in full accordance with Tunisian government regulations, and without any personnel injuries or pollution to the environment. The single-source provider model reduced the costs associated with managing resources from multiple service providers, and the dedicated project coordinator eliminated the need for a separate procurement and operations manager.

The operator valued the role of the expert advisor as a single point of contact throughout the abandonment operation. The advisor was observed as being continually engaged in all aspects of the operation; fully informed on equipment inventories, logistics and activities; and keen to offer suggestions and provide input in solving any problems that arose. These observations extended to the overall abandonment crew in the field as well.

The integrated service offering played a key role in completing the abandonment operation ahead of schedule. The abandonment was completed in 23 days, versus the planned schedule of 25 days, despite 9.5 days of weather-related downtime and a further 8 hours of equipment downtime (which was attributed to another subcontractor provided with the vessel). No failures were observed from any of the equipment provided by Weatherford.

The operator estimated that without the weather and equipment-related downtime, the entire operation would have been successfully completed in just 13 days and 8 hours, or an average of six days and 16 hours per well. This was in line with Eljay’s previous abandonment work in the same region for another operator, a five-well abandonment project conducted in 1998. That project was completed in 35 days, or an average of seven days per well.

Conclusion

The single-source approach to well abandonment has provided efficiency and safety gains for offshore operators on the global stage. In addition to the operation in Tunisia, the integrated combination of equipment and cross-disciplinary expertise has contributed to the successful recovery of more than 1500 subsea wellheads using semisubmersibles, jackup rigs and monohull vessels. As more mature wells make the inevitable transition from asset to liability, this project management approach stands ready to produce a customised, safe and long-term abandonment solution.


Adapted by David Bizleyfrom an article published in the March 2015 issue of Oilfield Technology.

Published on 31/03/2015


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