Varying Drilling-Fluids Properties Overcomes Drag in Offshore ERD Well

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 227986, “Overcoming Drag While Running Casing in an Extended-Reach Well by Varying Drilling-Fluids Properties, ” by Richard Walker, SPE, K&M Technology Group. The paper has not been peer-reviewed. _ Running casing from a floating offshore vessel bears increased risk because of the requirement for a subsea stack and the influence of vessel heave. The complete paper presents a solution involving using drilling fluids with varying properties to overcome drag to allow the casing to reach the planned depth. This approach to overcoming drag forces by using drilling-fluid weight and rheological properties enables large casings to be run to deeper depths in extended-reach wells where fully evacuated flotation or rotation are not feasible. Introduction The North Sea has historically been, and continues to be, a tremendously challenging environment for drilling and casing offshore wells. The well discussed in this paper is in a field in the East Shetland Basin of the North Sea with a water depth of 451 ft from the sea floor to the surface. The field has been in production since 2017 but still has untapped potential reserves now being targeted. Sea states in this area usually are moderate to high, with wave heights of 3. 4–5 m and wave periods of 5–7 seconds. Long lateral lengths and large casing sizes are used offshore to maximize production and return on investment. However, larger casings and longer-reach wells dramatically increase torque and drag, making running casing much more technically challenging. The longer measured depth (MD) compared with the total vertical depth (TVD) creates issues for maintaining adequate downhole pressure with the drilling fluids for wellbore stability without fracturing the formation or losing fluids to the formation. The most common methods of overcoming torque-and-drag issues while running casing on land are “floating” the casing, either empty or with mud over air, or rotating the casing while running in the hole. Neither of these methods were feasible for this casing run in a deepwater well. Because of rough seas and subsequent vessel heave, full or partially evacuated flotation is an undesirable option. Casing rotation is not possible because of the large casing size and subsequent heavy weight while full of fluid, generating extremely high torque that exceeds connection or top-drive limitations. Case Study Well The offshore well (NS Well) was planned from a high-specification semisubmersible drilling rig with a subsea wellhead. The wellhead was on the seabed with a water depth of 451 ft. The running and circulation of the casing were the primary focus of this study. The well path is a high-angle well (greater than 65°), making running large casing extremely difficult. The objective was to run the casing to total depth (TD) of 10, 300 ft for openhole slack-off friction factors (SOFF) of up to 0. 50, and to circulate and displace the wellbore and casing fluids before cementing.