John Fraser, Coretrax, discusses how wellbore clean-up and abandonment can be made more efficient for operators.
Oilfields around the world are ageing. As reservoirs near the end of their productive life the amount of wells that need to be plugged and abandoned is rising exponentially. Worldwide, companies are being encouraged to permanently take these wells offline to prevent any environmental impact.
As decommissioning and abandonment operations become increasingly more frequent for operators, it goes without saying that this has to be done in a safe, economic and environmentally responsible way despite the complexities and uncertainties of these operations. Operators, now more than ever, look to reduce costs and find tools and methods to improve efficiency.
Coretrax, a UK-based specialist in wellbore clean-up and abandonment, has been working since 2009 to streamline this process by improving the way bridge plugs are installed during wellbore abandonment programmes.
The company’s pioneering One Trip Abandonment system has significantly reduced rig time, costs and the risk associated with additional trips for a number of oil and gas operators, through the use of several innovative products.
The CX-2 bridge plug focuses on minimising gas migration and is activated by dropping a ball from surface, which is then set with the application of pressure and overpull. Disconnecting from the plug is achieved through rotation and leaves the setting mandrel slick with the pipe, with a substantial ID for cementing operation. With the slimline setting mandrel, the application allows for quick cement placement and minimal disturbance when the mandrel is pulled through the cement.
The system also utilises the CX-Drillable Brush to perform scraping to set the plug and cement in the same run, in a safe and efficient manner and ensures a clean area for plug setting. The integration of a drillable brush (or sacrificial scraper) with the bridge plug ensures clean casing to provide a solid base for cement bond, reducing any micro-annulus. Furthermore, it ensures a clean area for plug setting.
After the plug setting process, the CX-Ball is utilised. The product is a foam wiper ball wrapped in a soluble material that is shipped in a sealed transport tube. The transport tube is then placed over the drillpipe connection allowing the ball to be smoothly installed into the drillpipe. Once the ball makes contact with the well fluid, the soluble material covering the ball dissolves, allowing the ball to reform to its normal shape as it is pumped down the string to clean the ID of any residual cement.
Isolating and abandoning several sections of a well can result in multiple cement plugs and numerous trips in a costly and time consuming process, but the CX-2 bridge plug and CX-IST (Inflation Support Tool) work in tandem to optimise zonal isolation operations.
The CX-IST provides a 100% seal between the tool and the casing wall or formation and gives a positive indication to operators that the cement will be set in the correct place. The CX-IST reaches the bottom of the workstring and latches into a pre-installed landing sub. Once secure, pump pressure inflates the elastomer to seal the wellbore and the CX-IST is then released by simply picking up the workstring. The CX- IST landing sub can be pre-installed in the setting mandrel of the CX-2 bridge plug, without restricting cementing operations, therefore running the CX-IST and CX-2 bridge plug together allows operators to isolate multiple zones without having to make multiple trips.
Figure one shows an example of potential time and cost savings through utilising a one trip abandonment system.
An example of potential time and cost savings through utilising a one trip abandonment system.
Coretrax engineers with the Inflation Support Tool (IST).
Case study: Decommissioning in the UK North Sea
During a recent extensive decommissioning campaign in the UK North Sea, the capabilities of these products were demonstrated throughout a three year period involving 30 well abandonments using a semi-submersible rig.
The operator also recognised there was a requirement to remove large amounts of swarf from the ram cavities, to protect BOP equipment and components in the mud circulating system. Section milling of casing was required on most wells in order to set cement barriers which required Coretrax to run in excess of 45 bridge plugs and cement retainers, including some with a drillable brush.
Appreciating the volume of potential debris required to be recovered, Coretrax identified that magnets with a large surface area would offer the highest carrying capacity for swarf, and so utilised the SP Magnet to remove up to 56 kg of an average return per operation. The magnet technology was coupled with high pressure jets to achieve a high standard of BOP cleaning on every run.
Prior to having a BOP cleaning assembly on board, the BOP was pulled between every well to be cleaned by hand, resulting in several kilograms of debris having to be removed by deck crew. However, since the BOP jetting assembly has been available, the debris has almost been eliminated, therefore minimising time spent on these activities.
As well abandonment continues to be a costly and lengthy process, the utilisation of products that offer cost and time efficiency and vital safety benefits, will be imperative for efficient and effective decommissioning operations. Ultimately, technological developments must continue to evolveand accelerate in order to meet the demands of these challenging operational complexities.
The CX Drillable Brush can reduce rig time significantly by eliminating the need for a dedicated scraper trip.
The CX-2 Bridge Plug allows for quick cement placement with minimal disruption
Edited for web by Cecilia Rehn