A major Operator in Kuwait have used historically Non-Aqueous Fluid (NAF) to drill the buildup section through the challenging shale formations, mainly due to wellbore stability issues and lubricity requirements. As part of the operator's environmental improvement strategy, the operator and fluids provider team identified potentially fit for purpose High Performance Water Base Mud (HPWBM) as the most suitable, environmentally acceptable alternative to NAF’s.
A HPWBM system was designed and proposed based on extensive laboratory testing to overcome drilling challenges. Inhibition characteristics and formation sealing capabilities of conventional KCL polymer mud with sulphonated asphalt were enhanced by using a liquid polyamine based clay hydration suppressant and a co-polymeric nano-sized shale-sealing additive. A customized bridging package based on the pore size distribution was also introduced, using calcium carbonate and resilient graphite particles. The combination of effective bridging and sealing polymer helped in sustaining high overbalance to avoid differential sticking tendency, designed in laboratory conditions during the planning stage.
The field trial was a great success compared to the use of conventional fluid systems and methodologies. Using High Performance Water Base Mud, the operator successfully drilled and cased 12.25" and 8.5" sections as per plan with stable wellbore indicated by the smooth trips and no string stalling or sticking tendency. Drilled 1077 feet of 12.25-in hole section crossing Ahmadi shale and 683 ft. of 8.5" section crossing troublesome Wara shale without any well-bore instability issues even at high inclination. Also, while drilling across depleted Mauddud limestone with 1800-psi overbalance, no differential sticking tendency observed. Both sections were completed in record 11 days, fastest comparing to offset wells drilled with NAF.
In this paper, the authors will detail this novel approach of using an environmentally acceptable HPWBM system in the North Kuwait Basin, from planning to execution, which can be implemented further on the field and offers significant cost saving and reduces the risk of HSE issues related to Diesel based NAF systems.