EXPERIMENTAL INVESTIGATION OF THE EFFECTS OF CONTAMINANTS ON THE RHEOLOGICAL PROPERTIES OF WATER-BASED MUD ABSTRACT: This project focuses on Investigation of effect of contaminants on the Rheological Properties of Water-based Drilling Mud. For any drilling operation to be termed successful, care must be taken during the selection and application of the drilling fluid which are key factors that should be considered. Any actions contrary to carefully selection and application of drilling fluids could have very dire consequences.Based on the experiment work done on water base mud system to ascertain the effect of contaminants (salt, silica sand, cement and carbonate) on the rheological properties and performance of the mud, it shows that the presence of a contaminant on the drilling mud either reduces or increases the rheological properties of the mud system and in turn affects the rate of penetration, it performance and also poses serious drilling problems.It was observed that the presence of Sodium salt in the mud system increased the fluid loss into the formation.It was further observed that while Apparent Viscosity, Gel Strength increases as the mass increase from 1g to 5g, the pH and Plastic Viscosity almost did not change. The Yield point increases little. With Cement as contaminant, it shows all rheological properties of the mud increased markedly, as the quantity of the cement used is increased from 1g to 5g and the pH does not change. Silica contaminationhas not showed any marked effect on the nature of the drilling mud. In fact, the more the amount of the contaminant (Silica) is added, the closer it properties are to the blank sample that do not have contaminants. The carbonate effect is largely on the Gel strength which decreases as the amount of added carbonate increases. The pH has no charges, which also means carbonate keeps the mud in it alkaline state, as it was the case with cement.Chapter One1.0 Introduction1.1 Background of StudyWhenever hydrocarbons are discovered in some subsurface formations, it sounds interesting to all parties involved but in reality, we cannot confirm the presence of the hydrocarbon without making a hole to the target zone. Thus, the drilling of oil and gas well is a high risk and challenging venture with some associated problems. Despite these challenges, wells are still being drilled globally and only experience a slow or no drilling operations in recent times due to the global drop in oil price. It is the aim of every field operator to get the oil or gas from the reservoir rock to the surface production facilities in a safe and cost effective way thereby maximize profit by reducing the cost of drilling the required number of wells to drain the reservoir fluid.In the cause of drilling a well to the target zone, there are some associated problems that might occur such as lost circulation, formation damage, kick and if not control can result to a blowout, pipe sticking, hole instability etc.which can be prevented by the use of adequate drilling mud.Also, a poor hole cleaning can lead to a reduced penetration rate, a loss circulation of fluid, and increase in rotary torque, break down in the formation and stuck pipe (Hussain et al, 2010). Therefore, to successfully drill a well to the pay zone of the reservoirrequires the formulation of appropriate drilling fluid which is a primary well control technique to overcome the formation pressure as the wellDeepings. Drilling mud is seen as the life blood of every drilling operation which implies thatdrilling mudneeds to possess some required properties (both physical and chemical) withstandvarious well conditions encountered with even greater variety. Every rotary drilling operation implies three systems that work simultaneously in boring a hole; a rotating system which rotates the drill bit, a hoisting system that raises and lowers the drill string into the hole, and a circulating system which performs the function of moving a fluid around from the drill stem, out of the drill bit and up again to the hole at the surface (Van Dyke & Baker 1998). This fluid otherwise called drilling fluid, in its liquid form, may be water or a mixture of water and oil, clay with some additives. This mixture in drilling parlance is termed drilling mud by drilling operators, henceforth, the terms “drilling fluid” and “drilling mud” would be used interchangeably.A circulating system on any drilling rig is a closed loop of activities consisting primarily of a drilling fluid which is the workhorse of the whole drilling operation and other equipment which aid in the circulation of the drilling fluid. It is quite interesting to know that this system functions in like manner as the circulatory system in the human body. The functions of this fluid can be likened to those of the liquids running or circulating in the blood vessels of the human body, the mud pump equivalent to the heart, and the drilled out cuttings represent the slag products (Skalle 2010). The mud cleaning system which is at the surface represents the kidney and the lungs. A schematic of a circulatory mud system is shown in figure 1..