1.0 INTRODUCTION
A typical drilling fluid mixture is constituent of various additives each of which plays their specific role in the drilling fluid. Drilling fluid rheology, which is practically the most important of these characteristics, is highly dependent on the constituents of the mixture. The rheology must be accurate in order to achieve basic goals such as cuttings removal, well stability and cleaning operations. Drilling mud rheology is highly affected by temperature, pressure and aging [1] and additives such as Versaclean and pH modifiers in this case. Standard rheological models such as the Bingham model (1925), the power law model (1925) and the Herschel Bulkley model (1926) are used in order to gain full knowledge of drilling fluid rheology. The drilling fluid being considered in this paper is a type of oil-based mud, Invert emulsion mud and in order to understand and fully analyse its rheology, research for this paper will correlate data collected from an experiment carried out, a drill bench simulation and the standard rheological models. The rheology and properties of drilling mud, its formulation and how they affect well construction and stability will then be noted.