Many offshore oil fields throughout the world are reaching the end of their productive lives. Consequently, the operators are poised to plug and abandon a substantial number of wells in the next few years.
This proliferation of current and future needs however present unique challenges for the operators and for the offshore service companies. The challenges requiring the most deliberation include:
Partial plug & abandonment: A permanent abandonment of the bottom of the well and drilling new well from the upper section to access more productive targets allowing continued use of the existing platform infrastructure. The practice is known as slot recovery program.
Requirements of local regulatory agencies: The steps required to qualify the offshore wells as permanently abandoned vary widely with the local regulatory jurisdiction. The governing bodies of the North Sea and Gulf of Mexico are good examples of slightly varying requirements for well abandonment.
Combining safety and economics in meeting above two challenges.
To meet these challenges, the offshore service companies have worked with the operators in developing innovative technical solutions that are economically viable and safety compliant.
For Norwegian sector of the North Sea, a single trip casing cutting and pulling system has been developed and tested which provides multiple cuts capability and selective activation of heavy duty spear to overcome frictional resistance between casing and the cement or barite. A casing jack capable of pulling a million pounds of casing has been developed in case a need arises. Also a system designed to mill 150 meters of casing section is currently under field tests.
For the Gulf of Mexico, a hydraulically activated tool to cut up to 72 inch casing has been developed. Also a single trip cut and pull system has been in operation for wells in deep waters. The system eliminates the need to strip the workstring/BHA equipment once the cut casing is at the surface.
The authors will discuss these technical solutions in terms of new tools and procedures. Also discussed will be field data, lesson learned, planned improvements.
The decision to plug and abandon (P & A) a well is strictly based on the economics. Once the production rate has fallen off to a level where operating expenses are higher than operating income, the well becomes a prime candidate for permanent abandonment. In other instances, only the bottom of the well is permanently abandoned and a sidetracked well is planned from the upper portion of the well to access a new target. This way the top infrastructure can be used again which makes this approach an economically attractive proposition particularly for offshore platforms where multiple wells are drilled and/or producing from a single platform structure. This methodology is known as slot recovery procedure. Only the lower section of the well is permanently abandoned. The upper section is used in accessing a new target by sidetracking the well.