Despite the associated waste management cost to comply with the international standards, Oil Base Mud (OBM) remains the drilling fluid of choice to drill trouble prone formations in PDO LLC, Oman drilling operations mainly through the formations of Fiqa Sharji, Nahr Umr, Khuf and Gharif in different fields of Oman. Low Toxicity Oil Base Mud (LTOBM) is exhibiting excellent well bore stability due to oil wet property, however, its high cost resulting from low aromatic base oil and associated waste management to comply with the international standards and local environmental regulations provided the impetus to conduct a feasibility study to identify an environmentally friendly and cost effective drilling fluid without impairing drilling performance. The evolvement of High Performance Water Base Mud (HPWBM) technology helped to identify a fit for purpose drilling fluid capable to deliver near OBM drilling performance with cost effective environmental compliance with local regulations. The following tests were carried out on different cuttings samples collected from the aforementioned formations when exposed to different drilling fluids formulations: Cation Exchange Capacity (CEC). Linear Swelling. Shale recovery. Accretion. As a result of the intensive laboratory work, an appropriate HPWBM system was selected for each formation and each field. The first fields' trials concluded promising results with 100 % success rate on vertical wells and 50 % success rate on horizontal wells. HPWBM drilling performance was competing with OBM with significant cost reduction of 33-70 %. Further benefits, such as better zonal isolation achieved through better cement bonding to both formation and casing is worth considering. More importantly, two wells drilled by this HPWBM were initially planned to be water injector wells and ended by being converted to oil producers after positive logging results. This is an important field proven feature for a reservoir friendly system. This paper details the engineering works performed at PDO laboratory on testing the shaly cuttings behavior against different drilling fluids and at the field trials describing the best practices.
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