Reducing Well Deliverability Time and Drilling Costs using Casing While Drilling Operations, West Kuwait

Abstract

Casing while Drilling (CWD) is a method of drilling which has been proven to mitigate many of the drilling problems. In this technique, drilling, and casing of a well bore is carried out concurrently, which enhances the drilling efficiency by decreasing the non-productive time (NPT). It has shown to be advantageous in controlling loss circulation and improving wellbore stability by ‘Plastering’ effect, high quality cement job and increased rig floor safety. Casing while drilling techniques use a drillable drill bit. This bit is specially designed and manufactured with a material that can be drilled out with either conventional roller core or fixed cutter bits. A plastering process was used, which smears the cuttings generated by drilling against the borehole wall, seals the pores or fractures in the formation, and helps reduce fluid losses while maintaining well integrity. Several challenges have been monitored during casing while drilling such as severe mud loss, destabilized shale, and hole instability. These conditions can result in hole collapse, or the drill string lost in hole that requires sidetracking. The main aims of this paper are to present an engineering solution to drill through the difficult zones, reducing nonproductive time, and reduce the total well cost. Umm Gudair field in western Kuwait faces a lot of challenges while drilling, specially while drilling 16-in casing section. The successful implementation of 16 x 13.375-in. casing-while-drilling job in Umm Gudair field reduced well delivery time for the operator and saved 17 rig days with cost savings of 450,000 US Dollars considering rig rate only. The maximum drilling torque is 16,260 ft-lb at 6,962 ft, which represents 24% of the maximum torque for the 13.375-in 68 ppf, K-55. A 7 bladed and 16 mm cutter size was selected for drilling operation. The section was drilled successfully while encountering total mud losses through fractured dolomitic limestone and sandstone formations.