Drilling fluid rheology plays an important role on deepwater well drilling. Major challenges concerning rheological design include: hole cleaning and friction loss minimization at highly inclined sections, loss circulation zones, fluid gelification at the low seafloor temperatures, reservoir invasion, etc. Due to the different nature of the operations, several natures of drilling fluids are considered, including both water (polymer based, drill in) and organic based (n-paraffines, esters) systems. Due to their diverse chemical nature, such systems present different rheological behavior. The purpose of this paper is to present an extensive rheological characterization task for these systems, including conventional oilfield besides additional measurements which add information for the fluid behavior through the circulation system. The final purpose is to establish rheological design parameters for different oil well cementing operations. Rheological tests performed include, low shear viscosity, viscoelastic parameters and creep and recovery besides conventional oilfield rheological analysis. A detailed comparison of results for all the systems allows a definition of advantages and disadvantages of each one regarding gelification tendency, hole clean capacity and invasion tendency. A case study of abnormal events regarding this issue is also presented

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