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Ester-based drilling fluids have been accepted as an alternative tomineral oils in drilling applications and currently being utilized to drill oilor gas wells around the world. However, the ester-based fluids havedeficiencies that limit its ability to carry and transfer drilled solids, stabilizethe wellbore and drill the extended reach wells. Several approaches havebeen considered to overcome the ester limitations. Thus, the main aim of thisstudy is to overcome these limitations by developing the high performanceester-based green drilling fluids for deep and ultra-deep wells. The lowpressuretechnology was applied in the synthesis of the ester to minimizeester hydrolysis and thermal instability issues during the drilling operation.The rapid ester synthesis involved the 2-ethylhexanol and vegetable oilbasedmethyl esters C12 in the presence of sodium methoxide as thecatalyst. Performances of 2-EH ester-based drilling fluids behaviour wasassessed under different hot rolling temperatures (121, 149, 177, and200oC) for 16 hours. The rheological properties in terms of low shear rateof 6 and 3 rpm were superior which verified that these ester-based mudscould be used in deep and ultra-deep wellbores without sagging, pipesticking and unbalanced wellbore problems.

ester-based mud --- drilling fluid formulation --- high temperature --- thermal stability --- rheology