The North Sea presents major challenges to drilling and casing installation operations. Drilling a well through the overpressured Scruff Shale and Fan Carbonates in a single hole interval is extremely challenging because the Fan Carbonates have been depleted through production leading to wellbore stability risks due to severe fluid losses. After three unsuccessful attempts using conventional drilling methods resulted in two sidetracks and a well suspension, the North Sea operator looked for alternative means to satisfy the intended well construction objectives.
Drilling with Liner (DwL) technology was identified as the most appropriate technique for installation of the planned 9-5/8 in. x 11-3/4 in. liner because:
Documented lost circulation problems have been minimized or eliminated through prior use of liner drilling technology. The hazard interval can be isolated with a single trip using a PDC-drillable casing bit without sacrificing hole size.
Liner systems deployed for DwL provide for high torsional capability as well as resistance to projected cyclic fatigue stresses over the projected DwL interval. DwL BHA stabilization design has been proven to maintain established inclination and azimuth while drilling in liners over hundreds of feet.
This paper illustrates the collaborative approach a North Sea operator and international oilfield services company used for the planning and successful execution of a 9-5/8 in. x 11-3/4 in. drilling with liner (DwL) operation to drill through the over pressured Scruff Shale, landing the liner in the depleted Fan Carbonates in a single hole section. Early partnering with the service company led the operator to implement DwL technology to meet established well construction objectives. Since DwL technology encompasses a multitude of engineering disciplines, these would be integrated into the drilling plan in a seamless manner, ensuring the DwL objectives would be met. Also made evident is how the newly formed operator-service company team was able to react on short notice, facilitating installation of an unplanned solid expandable liner as well as additional liners to address subsequent lost circulation events.
