In the Peregrino field, located in the Campos Basin offshore Brazil, the operator adopted the use of water-based drilling fluids for drilling development wells due to rig limitations. In the 12 ¼-in. sections of several wells drilled in this field, high dispersion of shale minerals suffered by the drilling fluid caused increments of viscosity, which subsequently affected the drilling process through higher-than-expected circulation pressures, dilution rates, and costs. Although the wells have been drilled within the estimated times and budgets, an improvement in the fluid inhibition capability was initiated.

A detailed laboratory effort was conducted to obtain a combination of inhibitors capable of controlling excessive clay dispersion, minimizing fluid rock interaction, and reducing dilution requirements while helping to ensure an adequate rheological profile throughout the interval.

Laboratory validation of the interaction between the fluid and rock samples provided a better understanding of the inhibition mechanisms and helped ensure that stability of the reactive minerals drilled could be maintained. Various additives were tested against samples of commercial-reactive and field-reactive clays. Product concentrations were adjusted to reduce the interaction between the drilling fluid and the formation while helping to ensure that fluid capabilities, such as cuttings suspension, filtration control, and bridging, were maintained. An adequate environmental profile to enable safe disposal of fluid in compliance with local environmental regulations was also obtained.

After identifying an adequate solution, a detailed utilization plan was developed and put in place. To aid proper deployment while drilling, specific mixing procedures at the support liquid mud plant, transportation vessels, and at the rig site were determined. The next step was to assign a candidate well for the application – an Extended Reach Well (ERW) with step-out ratio of 2.9. While drilling the 12-¼-in. section of the pilot well with the proposed fluid technology, a significant improvement was observed on cuttings integrity, which led to a reduction in the required volume of dilution and a subsequent drilling fluids cost reduction Also, better hole quality and reduced operational risks were obtained. The well was safely drilled with a 76° sail inclination, 7938 meters of Measured Depth (MD) and 2368 meters of True Vertical Depth (TVD), and lessons learned from the first utilization of the described fluid system were implemented on subsequent wells to continue obtaining the benefits of the new fluid formulation.

High Performance Water Based Drilling Fluids (HPWBDF) are not new and are thought by most to be a mature technology. However, advancements in water-based drilling fluid additives have enabled these systems to mimic the performance of non-aqueous systems more closely. This paper discusses how understanding the chemistry of the formations to be drilled and customizing chemical additive blends for those formations can help to improve operational efficiency and minimize costs.

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