Malcolm Pitman - Tendeka
With a cautious rise in drilling activity across the world, operators have to manage projects efficiently and effectively to maximize the potential return. In addition, operators are revisiting mature fields to extract marginal reserves in order to meet production quotas, and this comes with its own challenges.
Despite planning and preparation, drilling fluid losses occur during drilling construction and production, which in turn leads to cost overruns, particularly in mature fields with depleted reservoirs. Operators need solutions that can be implemented quickly in both the planning and construction process to address thief zones and to cement integrity, secure the well and prevent further losses, while simultaneously ensuring that drilling can continue safely.
The operator also must consider cost, efficiency, and permanency of the solution relative to the specific conditions of the well.
A major North Sea operator approached Tendeka with a troubled well. During drilling, a significant thief zone severely affected progress and the decision was made to suspend activity and cement before drilling ahead.
When drilling stopped, the loss rate had peaked at 1,600 bbl/hr, with 600 m (1,968 ft) still to be drilled. Successive remedial cement squeezes reduced the losses to 800 bbl/hr but no further. It became apparent that alternative solutions would need to be considered, as the well continued to drain seawater at a rate of 700 – 800 bbl/hr.
Following an assessment of the well, it was determined that a swelling packer that straddled the thief zone incorporated in the 7-in. liner would provide the ideal solution. Moreover, the high volumes of seawater passing the packer element would, in fact, assist the rate of swell. Another factor in favor of the swelling packers was the high loss rate, which suggested the hole was relatively clean, thus ensuring running in would not be a problem.
Packers can provide an efficient, cost-effective, and safe solution to well integrity issues in the harshest environments.
Analysis of the problem and dialog between Tendeka and the operator concluded that a bespoke packer would be the most effective solution. A packer was developed to run on the outside of the 7-in. liner that would not only swell quickly to halt losses, but could act as a permanent fix, retaining the ability to swell further over time as the geothermal gradient warmed on sustention of the losses and thus complement the cement.
The packer was developed and shipped to the site within seven days, which included engineering, testing, and manufacture of the design. The final product used many short elements on the same packer assembly, and this ultimately would play an important role in the success of the solution.
The multi-element design combined firstly oil swelling and secondly, two different temperature-water swelling elastomers within the same packer. This provided a high-performance packer capable of meeting the geothermal conditions pre- and post-loss scenarios and the 3,000 psi sealing requirement in only four days, while retaining the potential for a much higher pressure capability over the longer term.
At the time of the packer’s interception, a total of 14 remedial cementing operations had been performed and losses reduced to a little over 400 bbl/hr.
The shoe assembly and the 7-in. liner were made up with the swelling packer and run into the hole. The run was flawless, as the packer was successfully placed – without incident – within 16 hours, causing minimal disruption to the operator’s work schedule.
As expected, losses continued during the run in, and this optimized the performance of the water-swelling element. However, in a bid to prevent further losses, the decision was taken to place cement above and around the packer as it set. This belt-and-braces approach was deemed prudent given the losses suffered in this well with 14 cementations.
As the packer began swelling outwards to formation, the elements further up the hole acted as a restriction against the cement being placed. This slowed it down sufficiently for it to accumulate between and around the elements and the formation. Moreover, the lower elements would seal against the formation themselves if cement were unable to reach them.
The packer allowed for the well to be saved and for drilling to recommence within four days, impacting positively on the operator’s production schedule. Following the deployment of the swelling packer, there has been no evidence of any further losses.
Tendeka applied similar swellable solutions to solve problems in Russia in the variable quality of cement, where the wells also suffered from poor zonal isolation and premature water breakthrough. The company designed a packer that addressed zonal cement integrity issues to optimize performance. The operator now installs cement integrity packers in all wells with a cross flow potential.
Packers can provide an efficient, cost-effective, and safe solution to well integrity issues in the harshest environments. Technologies can be combined to optimize the performance of the well, while simultaneously providing a permanent fix and preventing against further problems.
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