Drilling horizontal wells in the Oriente Basin of Ecuador presents specific challenges due the presence of the troublesome Napo shale. The presence of an intrusive formation overlaying the reservoir in a development field vastly increases the potential for wellbore instability problems and the array of associated drilling problems. In a joint initiative to address this problem, the operator and drilling fluids supplier have undertaken an extensive evaluation of offset data and potential fluids solutions as well as implementing more efficient drilling fluid designs and drilling practices. This paper discusses the development and deployment of a water based drilling fluid incorporating aluminum chemistry coupled with an organo-amine salt complex, an ROP enhancer, sealing agents and an extreme pressure lubricant, which demonstrates excellent wellbore stability attributes when implemented in conjunction with improved drilling practices. This paper also presents field data and performance indicators from over forty five (45) wells drilled in the area over the last four years. The data collected demonstrates that a properly designed water base drilling fluid stabilizes troublesome formations in an area where in the past, oil base drilling fluids had been the only feasible technical option. An additional benefit is a reduction in environmental impact in an area surrounded by indigent cultures

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