Article featured in Oilfield Technology

For all plug and abandonment applications, either permanent or for slot recovery, the sealing performance of well system components needs to be assured, and remain intact. 

Well systems are complex and need to work perfectly to perform safely, cleanly, and productively. Understanding the condition and sealing performance of well system barriers can be challenging once the well has been brought onstream and access to these elements and components is restricted.  

Current mainstream technologies only provide partial answers, leading to an incomplete assessment. However, through-barrier diagnostics look at the well system in a far more holistic and uncompromising way. These technologies have the capability of seeing through multiple barriers to provide a more complete picture of the condition of the metal tubulars and the flow around them to see if the seals are holding, prior to plug and abandonment.  

In the case of permanent abandonment, natural barriers that prevent the movement or migration of downhole fluids, must be restored. And the performance of the well system barriers  must remain intact indefinitely.  

In the case of slot recovery, the well components must be in good enough condition to be used again for the upcoming production cycle.  

A comprehensive integrity assessment is required for either scenario. 

Planning and executing a flawless plug and abandonment requires prior knowledge of the integrity of the well barriers, and the precise position of all downhole completion elements. Operators armed with this information can determine the location of the permanent plugs and the best depths for the casing cuts for an optimised retrieval procedure.  

During the productive life of a well it may experience several operator changes, perhaps after concessions expire or following divestment decisions. This can often lead to historical data being lost which, when it comes to well decommissioning, can increase the potential for making decisions without knowing all the facts about the well system, particularly the position of the casing collars, fins, centralisers or other components that impede successful decommissioning.  

Using a simple multifinger caliper or an ultrasound survey, the location of the first-barrier casing collars can be determined, but the locations of the collars in the subsequent casing strings remain unknown. This approach contains an element of risk and may result in a cut planned directly in line with a thick section of metal, like a casing collar, or fin. Cutting across a collar or a fin, would mean an increase in the rig and intervention time of several hours, or potentially days. 

TGT’s Multi Tube Integrity product uses the Pulse electromagnetic sensing platform to provide accurate barrier-by barrier assessment of up to four concentric tubulars (up to 20” diameter) in one single through-tubing deployment. Pulse can also pinpoint to within 1ft the location of completion elements. 

The ‘electromagnetic signature’ of each tube or metal completion component, contains information about its wall thickness. The Pulse platform harnesses this information and through 3D modeling, can decipher metal loss as well as metal gain, in multiple casing strings throughout the entire well system.  

Pulse can identify the location of known completion elements, but also identify new ones, not expected including welded fins on the outer casing string, often inaccessible to other evaluation technologies.  

If Multi Tube Integrity is used prior to the P&A planning, the diagnostic results would remove the uncertainty allowing operators to confirm the optimum cutting window location in all casings, thus minimising the intervention time and reducing rig time and costs. 

Slot recovery offers operators a way of capitalising on existing assets, by providing a new means of extending a well’s productive life.  

It is a robust solution which utilises the existing surface and downhole infrastructure, to create a “new” offshoot well, which would reduce the costs associated with drilling. However, before this can become a reality, the inspection of downhole completion elements such as surface casing and its cemented annulus are a must.  

Limitations in current technologies have meant that barrier verification is performed while the rig is in place, and once the tubulars (production and intermediate casings) have been retrieved.  

Key input parameters, such as the cement condition and the integrity of the casing are obtained at the last stage of the planning. The late arrival of this critical information results in a complex well intervention plan, with several contingent scenarios based on a range of potential outcomes from the downhole integrity assessment.  

The industry is calling for a new solution. One which can determine the condition and sealing performance of the cement and the metal barriers, prior to planning the slot recovery. 

TGT’s Multi Tube Integrity product used together with the Multi Seal Integrity product is the answer. This powerful combination utilises TGT’s Pulse electromagnetic platform, the Chorus acoustic platform and the Indigo multisense platform, and it can be deployed in one through-tubing deployment.

Pulse is used to evaluate the metal thickness of multiple tubulars, including the surface casing. It also has the unique capability of being able to confirm the position of critical completion components, including collars, centralisers, and casing shoes.

Chorus is used to assess the hydraulic seal integrity of the cement barrier to determine where the cement is sealing and where it is not. Fluid flow in the well system creates a rich spectrum of acoustic energy that penetrates the surroundings. This acoustic wave is encoded with information that Chorus can convert into acoustic spectra that can locate leaks and flowpaths throughout the well system, from the wellbore to the outer annuli.

The Pulse, Chorus and Indigo platforms are part of TGT’s True Integrity System which provides a clear diagnosis of integrity dynamics throughout the well system.

It is critical that before slot recovery can be executed, there is an understanding of the collective integrity of the tubes, seals and barriers of the mother well. Only in doing this can there be a guarantee of the secure passage for pressurised fluids.

The key to success for any P&A or slot recovery operation is knowing all the facts about the integrity of the well system prior to planning and execution. This delivers the potential to reduce costs, minimise schedule overruns, and ensures the integrity of the final outcome.