A Collaborative Approach for the Planning and Execution of a North Sea Drilling with Liner Operation

Abstract

A mature field in the southern sector of 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, which leads to wellbore stability risks because of 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.

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 and land 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. 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.

The DwL process enables isolation of a hazard interval in a single trip, resulting in less risk and exposure than with the use of conventional drilling methods. Because DwL technology encompasses a multitude of engineering disciplines, they would be seamlessly integrated into the drilling plan so that the DwL objectives would be met.

The collaborative effort was established very early in the well design process and resulted in the formulation of a detailed well engineering analysis taking a holistic approach to the intended well objectives. The analysis included procedures and related simulation modeling for the running, drilling, and cementation of the 9 5/8-in. x 11 3/4-in. liner and as contingencies a 7 5/8-in. x 9 5/8-in. DwL liner design and a 6-in. expandable liner, ensuring the results aligned with the operator's well objectives.

During the planning phase, regular operator-service company communications along with project scheduling software gave the operator assurance that agreed upon deliverables would be completed in the allotted time frame and that the intended well objectives would be met. Potential concerns and drilling hazards were identified, which enabled reducing them to a manageable level. Ultimately, the 9 5/8-in. x 11 3/4-in. liner successfully drilled through the overpressured Scruff Shale and reached the required setting point in the Fan Carbonates, with the expected losses mitigated to manageable levels. Close collaboration with the same service company helped the operator to safely meet the well objectives when experiencing lost circulation events even after installation of the last planned contingency, the 6-in expandable liner. This paper will present the collaborative methods, associated well engineering analyses, DwL operation, and management of the subsequent lost circulation events.