CHAPTER ONE
INTRODUCTION
1.1 Background of Study
Drilling for oil and gas with a drilling mud began many years ago in the 18th century. The first reported use of a drilling fluid was noted in France in 1845, when water was pumped down a hollow boring rod, while drilling water wells to bring the cuttings from the bottom of the well to the surface. (Ikeh, 2014)
Through the 1920’s Iron oxide and Barium Sulphate (Barite) was used to increase the density of the drilling mud, thus preventing entry of the formation fluid into the borehole. The use of bentonite in 1930’s to suspend Barite formed the basis for today’s large commercial drilling mud industry. (Evabeta, 2004)
The term “drilling fluid” includes air, gas, water and mud or could either be a combination of two or all the above. The common type of fluid most often used in mud suspension of solid clay is a liquid and emulsion mud (suspension of solid and droplets of liquid). The drilling fluid is a term that comprises all the components of clay and additives suspensions used to effect the removal of rock cuttings from the subsurface (bottom hole) to the surface while drilling.
Thus, in other to enhance the drilling operation, the selected drilling mud must perform certain functions to avoid delay in operation and occurrence of associated drilling problems. Some of these functions are highlight below.
1.1.1 Functions of drilling fluids
Lubricate the drill bit, string, bearings, mud pump and drill pipe, particularly as it wears against the sides of the well when drilling deviated wells around corners.
Clean and cool the drill bit as it cuts into the rock.
Lift rock cuttings to the surface and allow cuttings to drop out in the mud pit or shakers to prevent them re-circulating.
IV. Suspend cuttings and weighting material when circulation is interrupted
Protect the formation from caving
Provide information to the drillers about what is happening down hole by monitoring the behavior, flow rate, pressure and composition of the drilling fluid.
Prevent well blow-out by including very heavy minerals such as barite (weighing agent) to counteract the pressure in the hole (reservoir pressure).
Drilling mud helps in suspension of drilling assemble and casing, delivery of hydraulic energy, being a suitable medium for logging and to being environmentally acceptable.