Customized High Performance Water Based Mud Substituting Oil Based Mud to Drill Nahr Umr Shale and High Over Balance Reservoirs in Onshore Abu Dhabi

Abstract In alignment with Abu Dhabi onshore operation's sustainability pillar to reduce carbon emission in the operation and identified significant waste management cost saving of oil-based mud cuttings, operator and fluids provider team collaborated to customize and conduct trial for using a high-performance water-based mud to drill Nahr Umr shales, substituting normal practice with oil-based mud. Extensive laboratory work was carried out i.e., cation exchange capacity, capillary suction time, XRF/XRD analysis, linear swelling test, accretion and erosion test using Nahr Umr shales’ cuttings to customize the fit for purpose high-performance water-based mud. Both parties successfully used a high-performance water-based mud system to drill challenged wells. Trials evaluated the fluid performance for different well designs – where the subjected section size varies between 8½ in and 12¼ in. Trials-as well-included wells with expected severe to complete loss of circulation scenarios therefore, expanding the evaluation of fluid ability for stabilizing the shale under such tough operational conditions. The operation's success in achieving well objectives depended on appropriate mud formulation and maintaining the right concentration of shale inhibitors. This paper describes the development and field trial of fit for purpose solution of high-performance water-based mud that enhances shale stabilization properties much like oil-based mud but without the associated waste management cost and it is an environmentally friendly system. Furthermore, other benefit is to overcome the logistic challenges of handling oil-based mud in the event of total losses that quite often happened across the high over balance formations below Nahr Umr shales as the rigs are remotely located in the desert.