OFFSHORE MEDITERRANEAN SEA
Drilling wells in the one region of the Mediterranean Sea requires operators to drill directionally through highly reactive shale. While drilling through this formation with a conventional KCl-Polymer drilling fluid, an operator encountered hole stability issues, including sloughing shale, stuck pipe, lost bottom hole assemblies and difficulty running casing. The higher the angle of the hole, the more unstable it became due to the formation bedding plane. The KCl-Polymer fluid could not drill these holes efficiently because of increased instability and high torque and drag. A shale core was taken and for laboratory testing. The shale was highly laminated and heavily fractured. CEC tests indicated high reactivity and sensitivity to water. The laboratory findings noted a section with almost no fracture gradient window followed by a section with a narrow but manageable fracture gradient window.
After the laboratory testing, the operator considered switching to a low-toxicity oil-based fluid. Newpark proposed the DeepDrill® high-performance water-based system as an alternative. With a proven history of inhibiting and protecting even the most reactive shales, the DeepDrill system provided benefits over oil-based fluids of being environmentally friendly, cost effective, less hazardous and reusable. Newpark sent DeepDrill system components, formulations and mixing instructions to the operator’s laboratory for testing on shale samples. After the lab testing, the operator approved the DeepDrill system for trial run.
While drilling the trial well, the DeepDrill system provided wellbore stability throughout the problematic interval, even with several unexpected trips for downhole tools. The operator requested and used the DeepDrill system for the rest of the wells in the drilling program. The fluid was conditioned and reused well after well. While using DeepDrill, the operator reported no further issues of stuck pipe and a decrease in nonproductive time as it relates to drilling performance and hole conditions.