According to the requirements of scientific drilling, drilling fluid system should have performances of low viscosity, low gel, low solid content, low filter loss, and with good lubrication property.
Besides satisfying the basic requirements of scientific drilling construction, drilling fluid should satisfy the requirements of scientific test, well logging and borehole log, etc. Detailed requirements can be found as follows:
Mud rheology refers to the mud of deformation and flow behavior of all forms of matter. Certain rheologic measurements made on fluids, such as viscosity, gel strength, etc. help determine how this fluid will flow under a variety of different conditions. This information is important in the design of circulating systems required to accomplish certain desired objectives in drilling operations.
Viscosity is defined as the resistance of a fluid to flow and is measured as the ratio of the shearing stress to the rate of shearing strain.
Adverse effects caused by drilled solids account for a major portion of drilling fluid maintenance expenditures. Drilled solids are the number one contaminant of all drilling fluids. Considering that a 12¼ in. gauge hole drilled to 10,000 ft would result in 1,327,000 lb or more of drilled solids, the above statement is not surprising.