Objectives/Scope 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. Methods, Procedures, Process 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. Results, Observations, Conclusions 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. Novel/Additive Information 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.

The 12-1/4-in. directional application is one of the most challenging applications in North Kuwait. The section requires drilling from the Mutriba (Santonian) to Burgan (Albina) formations through highly interbedded, high-compressive-strength carbonates (limestone and dolomite), sandstones, and shales. In recent years, Kuwait Oil Company (KOC) has tested many different bit designs in an attempt to minimize stick/slip vibrations and maximize the rate of penetration (ROP). This paper presents the technology used to nearly eliminate stick/slip vibrations, leading to a field record (and a consistent performance) for this application, as well as the process used to develop the technology. The interval was drilled using a rotary steerable system (RSS) to maximize wellbore quality and to provide consistent build-up rates (BUR) required. Parameters run in this application are often limited because stick/slip becomes uncontrollable when transitioning through the many formation types. In addition, reactive and stressed caving shales are regularly observed in the Ahmadi and Wara formations drilled during the interval. Special care is needed to mitigate these drilling challenges and to successfully drill the interval with low stick/slip vibrations and high ROP. Using proprietary state-of-the-art design and analysis technologies, a new polycrystalline diamond compact (PDC) bit was designed for use specifically with RSS tools to minimize the vibrations. The solution required a thorough offset analysis before the interval that was presented using the design process. The design process enabled the presentation of a driller's roadmap to be used in conjunction with the new bit to enable a benchmark ROP to be achieved. The use of the newly designed PDC bit produced minimal torsional vibrations, enabling a 62% increase in ROP over the field average. This increased ROP resulted in a savings of USD 90,000, reducing the cost per foot by 33%, as compared to the field average. The bit also came out in excellent condition, enabling future use in similar applications for KOC.