FORMULATION OF THE PROBLEM
Hydraulics system plays an important role during rotary drilling operations. Proper design and maintenance of this system increases drilling efficiency (high rate of penetration) and lowers the overall drilling cost. The hydraulic system is the drilling fluid system in the wellbore when the fluid is in static or dynamic state. The dynamic state deals with the fluid movement, pipe movement, and cutting transport. Drilling is the art and science of making boreholes for hydrocarbon production, in a manner that is safe, economic, and environmentally responsible. An efficient hydraulics system is a prerequisite to the success of any drilling and completions operation. It affects mud circulation, hole-cleaning efficiency, cementing, rate of penetration (ROP), and hence total drilling time and cost. Rotary drilling hydraulics is concerned with proper utilization of the drilling fluid pump horsepower. It is affected by the drilling fluid properties and geometry (configuration) of the circulating system.
Rotary drilling involves the circulation of formulated drilling fluids (called mud), to perform certain functions. The functions of the drilling fluid include:
1. To maintain well control by counteracting and suppressing the formation pressure
2. To clean the surface of the bit and transport cuttings to the surface
3. To lubricate and cool the drill bits.
4. To hold the cuttings in suspension when fluid circulation is stopped
5. To transmit hydraulic force from the surface through the drill string to the bottom hole assembly (BHA)
6. To enhance wellbore stability
7. To serve as a means of logging and formation evaluation