External casing patches are as well known in the industry as a method of repair and recovery as they are for their weaknesses with their tensile and compression loads and longevity of the elastomer seals.
As a result, their use is only a temporary solution for reconnection of casing downhole.
However, READ has developed an Hydraulically Expandable Tubular System (HETS) external patch that provides a method of reconnecting two pieces of casing downhole and offers a permanent gas-tight “life of well” solution.
The ability to successfully connect casing downhole enables the replacement of damaged casing or the retrieval of a stuck casing string, or when the outer conductors/casings are badly corroded, it allows for well-slot slot recovery.
“When READ submitted their proposal to ITF, HETS external patches were being individually designed to meet specific client requirements and, once fabricated, the qualification was unique to meet the particular client well specification,” said Poxon.
“This approach added significantly to the lead time, as well as the cost of supply. Likewise, the test specification had been limited, and in no case had the HETS-EP system been tested to its limits.
“The individual qualification process had become a barrier to the implementation of this new technology.
“READ approached ITF to discuss a project that could circumvent these issues and take the technology into commercial implementation.”
The proposal that READ submitted detailed a programme of work that would experimentally qualify a range of full-size HETS external patch connections in accordance with an agreed set of ISO-equivalent test procedures.
READ wanted to test the HETS system under a variety of well conditions, so the project included the building of computer-simulated models of the connection (FEA).
The analytical data from the computer simulations can be correlated with the empirical data from the experimental qualification and used to accurately predict the performance of connections made in alternative pipe materials and sizes.
According to ITF, this will effectively extend the qualification envelope both for pipe size and material, increasing the value of the test data.
“The project will eliminate the need to individually qualify HETS-EP on a well-by-well basis, thus permanently reducing the cost and perceived risk of deploying this new technology in the field and improving availability,” added Poxon.
The project was launched in January, 2007, with the support of three operating companies, and work is expected to continue until spring 2009.
During 2008, the ISO-qualified HETS external casing patch has been successfully run in the North Sea for two major operators, solving two serious casing problems and reducing operator time and cost.