Managing long-term barrier integrity in plugging and abandonment (P&A) activity is vital, as any failure in the wellbore can be catastrophic.
An abandonment plug – which can be either mechanical or cement-based - is placed as part of the permanent barrier system to isolate permeable formations, maintain well integrity, and allow the safe removal of subsea equipment. Placement of the plugs is usually performed by removing the tubular, then placing the cement plug in the wellbore. An alternative method is to seal off the outside of the tubular using cement or expanding formations, and place the plug on the inside without removing the casing.
“Operators are now realising that the technical challenges associated with P&A need to be addressed quickly to ensure it can be carried out safely and cost-effectively,” said Ben Foreman, Senior Technology Analyst with the Industry Technology Facilitator (ITF). “Though this type of work is not considered by many to be financially attractive, it is now a necessity to curtail the consequences of unprofitable assets and wells.
“Cement is the conventional material used to create a permanent barrier in the oil and gas industry today. However, despite the knowledge gained from operational experience and research to overcome its limitations, it continues to demonstrate a number of complex and costly challenges, particularly around the hydration and placement process. An alternative or revised solution is now needed as P&A activity becomes a reality.”
The problem with cement
The challenges in placing a successful cement plug in deepwater environments are accentuated by factors such as low temperatures associated with the water depth, setting long plugs in a single attempt, inability to use mechanical separators, and a variety of local regulations and stringent industry guidelines.
Problems include insufficient time to allow cement to cure and become a solid, tight material, which can cause premature hardening as well as other significant issues with its placement and long-term stability. Whilst in its liquid form, contamination can occur by an influx of gas or liquids, potentially changing the originally desired properties. In open hole situations, volume loss is another risk if the equivalent circulating density exceeds the formation strength. This can result in the plug not being the required length to pass Oil and Gas UK guidelines, NORSOK D10 Standard or NOGEPA guideline requirements.
As a brittle material, cement can potentially fracture if exposed to stress or geological changes. Poor mud removal prior to cementing is the number one cause of failures. This may also lead to mud remaining in the annulus, creating leak paths. Liquids, namely water, may also leak through the mud channels and encounter the cement causing shrinkage or cracking.
Different well environments can also cause problems. In HPHT wells, dramatic variations in temperature can affect both the formation and the casing. The Arctic environment can generate ‘permafrost’, where the mixture of water and cement freezes before it sets, resulting in cracking and the added risk of potentially dangerous quantities of methane being released. In corrosive conditions, the cement may have to withstand attacks from injection fluids such as those used in CO2 flooding for enhanced oil recovery or aggressive formations.
Call for proposals: alternatives to cement plugs
Decommissioning in the North Sea is an important issue for the international and influential members of ITF. The company has instigated a series of six Calls for Proposals to examine and support viable technical solutions to tackle the most pertinent P&A problems. Two calls have so far closed - through tubing logging and removal of casing and tubing. ITF, in conjunction with a group of operators, is now considering a number of solutions from technology developers within and outside the oil and gas industry.
“We’ve had an interesting variety of proposals and we’re now at the point of getting to a decision on sponsorship,” explained Foreman. “Though the industry is understandably reticent about investment in R&D in the current climate, our members are very encouraged by the quality of the submissions and the need for this new technology. The timeline is difficult to estimate but hopefully by the end of the year there will be a decision made and a joint industry project (JIP) kicked-off.”
The third invitation seeking alternatives to cement plugs is now open to qualified organisations. Whilst there are already a small number of potential solutions to the issues posed by the composition, installation and placement of cement plug material, ITF’s preferred solution will adhere to best practice guidelines and will have:
- Very low permeability to prevent flow of hydrocarbons or over-pressured fluids through the barrier
- Long-term integrity assurances and strong, long lasting isolation characteristics which will not deteriorate over time
- Non-shrinking features to prevent flow between the barrier plug/casing annulus
- Ductile, non-brittle material to accommodate mechanical loads and changes in the pressure and temperature regime whilst maintaining its strength
- Resistance to downhole fluids and any corrosive chemicals found in the oilfield
- Ability to bond to the casing or formation in which it is positioned
- Flexibility to be placed and set where required, for example, on a mechanical plug or self-supporting base
Successful applicants will have the opportunity to lead their own JIP with support, funding and participation provided by ITF members.
Throughout the initiative, the developer will receive technical guidance from ITF’s membership of global oil and gas operators and service companies to develop the technology further to best meet industry needs. This will profile the capabilities of the technology to a wider network of potential clients.
The deadline for submissions is Friday 22 July.
Dr Patrick O’Brien, CEO of ITF, added: “There is now a clear impetus from energy leaders to address decommissioning challenges from the outset before significant activity begins. We are looking for solutions that will safely improve operability, increase reliability and cut the cost of conventional technologies.
“Collaboration in technology development and delivery provides risk and cost reduction for the industry. We welcome submissions from all sectors, such as aerospace, medical and automotive, as often the answer can be transferred from outside our own field of expertise.”
For more information on ITF’s call for proposals visit: www.itfenergy.com
Adapted by David Bizley
Read the article online at: https://www.oilfieldtechnology.com/drilling-and-production/04072016/cement-alternatives-sought-for-safer-and-more-cost-effective-pa-operations/
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The well was drilled by the ‘Deepsea Stavanger’ drilling rig, about 25 km southwest of the Oseberg field in the North Sea and 150 km west of Bergen.