During the development phase of a gas field, the abnormal pressure in a dolomitic limestone formation demanded an extremely high mud weight to control the well. The casing design of this case-study field has entailed the installation of a 7″ × 9-5/8″ liner hanger in combination with a liner top packer followed by a tieback to surface. Due to this hole section being directly above the pay zone, it is crucial that the liner installation and the wellbore integrity are not compromised for the subsequent well completion.
The downhole pressure conditions require a drilling mud weight up to 157 pcf (~ 21 ppg), where solids content could reach as high as 49% using conventional weighing materials. For a liner deployment, this means that the high concentration of solids can cause plugging in the setting ports of conventional hydraulic liner hanger and running tool system. Additionally, the thin balance between ECDs and the formation fracture pressures in this field generated events of severe fluid loss during the liner deployment or while cementing. A liner not fully supported by cement — due to severe fluid loss during cementation — can experience ballooning, and be unable to withstand piston forces acting against the liner top packer during well completion operations. These forces can, in some cases, exceed the ratings of the liner top packer's hold-down slips, therefore allowing the packing element of the liner top packer to not set properly.
For these reasons, an optimized deployment strategy was planned and implemented to address these challenges. It included improvements to the hydraulic liner hanger and running tool system, calculations to simulate an optimal running speed of the liner, enhanced procedures for liner deployment and cementation, including revised setting procedures for the liner hanger slips, and modifications to drill pipe wiper plug design.
The objective of this paper is to detail the benefits of implementation, detailed pre-job planning, improvements for optimal drilling mud properties and modifications to the liner hanger system, and procedures that resulted in successful deployments of liners in this field. In addition, a case study will be shared as a way to institute lessons learned and best practices.