This paper details the challenges associated with performing a coiled tubing (CT) intervention on a long-reach interventionless well in the Dutch sector of the North Sea.
The well was originally drilled in 2009 as a gas producer. However, in 2012, it was shut in because of excessive liquid loading and salt deposition. Re-assessing the situation, the operator decided to reperforate a 3-m interval and use hydraulic reservoir stimulation (HRS) to help increase production. A 60° deviation of the well design made it essential to seal the bottom 95 m of the 5-in. completion, which proved to be a challenging operation. Additional well parameters, such as a 2.82-in. ID restriction within the 3 1/2-in. tail-end and a bottomhole static temperature (BHST) of 160°C, limited the methodologies that could be used to successfully seal this zone.
The anticipated well conditions required the use of high-yield-strength Grade 130-kpsi CT steel, which at the time was a novelty for most North Sea operating companies. Using this specialist component dictated the handling equipment, such as injector heads, pressure control equipment (PCE), and connectors, be carefully selected and fully tested before mobilization. These downhole conditions were not the only restricting factor within the operational design. The platform had limited deck space, and the well position required the use of a jackup boat on location and manufacture of a specialist CT tower substructure. Despite the additional deck space provided by the jackup boat, equipment selection and layout were carefully considered to incorporate a full well test package throughout the CT spread. This paper also discusses the results and lessons learned from the 16 CT runs performed during the operation. The main issues discussed include the difficulties handling (spotting and cleaning out) sand within the highly deviated tubular completion and ensuring the accuracy of bottomhole assembly (BHA) depth correlation.
The operational results allowed for the review of simulation- and onshore-based testing and trials to be analyzed and reviewed for future CT deployments.