AN EXPERIMENTAL STUDY OF THE EFFECT OF CONTAMINANTS ON THE FLOW PROPERTIES OF OIL BASED DRILLING MUD

This work presents an investigation of the Effect of Drill Cuttings on laboratory prepared oil base mud recommended to be used in drilling formation. The properties measured are plastic viscosity, yield point, apparent viscosity, mud weight, fluid loss, gel strength and electrical (emulsion) stability. The results show that cuttings increase drilling fluid viscosity, fluid loss and density as the adverse effects of it can lead to increase in thickness of filter cake, loss circulation, stuck pipe, increase in operational cost etc. It also shows the mud condition at which percentage of cuttings become catastrophic and the extent at which cuttings should be allowed in the mud. In geotechnical engineering, drilling fluid is a fluid used to drill boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs. Drilling fluids are also used for much simpler boreholes, such as water wells. The three main categories of drilling fluids are Water-Base Muds (which can be dispersed and non- dispersed), Non-Aqueous muds, usually called oil-based mud, and gaseous drilling fluid, in which a wide range of gases can be used. The Non-Aqueous fluids itself is Synthetic (water emulsified in oil), not a hundred percent oil. The main functions of drilling fluids include providing hydrostatic pressure to prevent formation fluids from entering into the well bore (controlling formation pressure), remove cuttings from the well, suspend and release cuttings, seal permeable formation, maintain wellbore stability, minimize reservoir damage, cool, lubricate and support the bit and drilling assembly, transmit hydraulic energy to tools and bit, ensure adequate formation evaluation, corrosion control, facilitate cementing and completion and minimize impact on the environment. Mud composition is affected by geographic location, well depth and rock type and is altered as rock depth formulations and other condition change. Drilling fluid maintenance costs can decrease greatly when proper solids control techniques are utilized. Adverse effects caused by drilled cuttings account for a major portion of drilling fluid maintenance expenditures. Considering that a 12 1/4 in gauge hole drilled to 10,000ft would result in 1,327,000lb or more of drilled cutting (1) . Drill cuttings contain, in addition to formation solids, small amounts of liquid and solid drilling mud components. The amounts of drilling fluid solids that remain attached to cutting vary, depending on the grain size of the crushed rock from the strata being drilled