What is Rheology?
“Rheology is the study of deformation and flow
•Rheological properties are very important in drilling fluids
•By making certain measurements on a drilling fluid it is possible to determine how that fluid will flow under a variety of conditions, including temperature, pressure and shear rate.
Rheological measurements.
•In the field, a rotational viscometer having an industry standardized bob and sleeve is used
.
•Shear stress, viscosity, or gel strength is determined from the degree of rotation of the bob under the influence of the shear rate created in the mud by the action of the outer, rotating sleeve.
.•Because most drilling muds are non-Newtonian in behavior (pseudoplasticand thixotropic), stress, viscosity and gel strength measurements must be performed at prescribed shear rates (rotational speeds).
•The industry standard rotational speeds are 600 and 300 rpm for any steady state of rheological parameter and 3 rpm for gel strength (an indication of thixotropy) measurements.
Procedures for rheological measurements.
•Place a recently agitated sample in a suitable container and lower the instrument head until the sleeve is immersed in the drilling mud sample exactly at the scribed line of the sleeve.
•With the instrument set at 600 rpm, rotate the sleeve until a steady dial reading is obtained, (for highly thixotropic muds, this may take some time).
•The 600 rpm dial reading is taken at the point for which the change in dial reading is less than 1 degree (one dial division over a stirring time of one minute).
•When the dial reading has reached this steady value, record this as the 600 rpm dial reading, D600.
•Lower the speed to 300 rpm, and stir the sample at this speed until a steady reading is obtained using the same criteria for the steady state point. Record this value at the 300 rpm dial reading, D300.
Calculations:Apparent viscosity (cP) = D6002Plastic viscosity (cP) = D600–D300Yield point (pa) = D300-PV2Yield point (lb/ft2) = D300-PV
”“Rheology is the study of deformation and flow
•Rheological properties are very important in drilling fluids
•By making certain measurements on a drilling fluid it is possible to determine how that fluid will flow under a variety of conditions, including temperature, pressure and shear rate.
Rheological measurements.
•In the field, a rotational viscometer having an industry standardized bob and sleeve is used
.
•Shear stress, viscosity, or gel strength is determined from the degree of rotation of the bob under the influence of the shear rate created in the mud by the action of the outer, rotating sleeve..•Because most drilling muds are non-Newtonian in behavior (pseudoplasticand thixotropic), stress, viscosity and gel strength measurements must be performed at prescribed shear rates (rotational speeds).
•The industry standard rotational speeds are 600 and 300 rpm for any steady state of rheological parameter and 3 rpm for gel strength (an indication of thixotropy) measurements.
Procedures for rheological measurements.
•Place a recently agitated sample in a suitable container and lower the instrument head until the sleeve is immersed in the drilling mud sample exactly at the scribed line of the sleeve.
•With the instrument set at 600 rpm, rotate the sleeve until a steady dial reading is obtained, (for highly thixotropic muds, this may take some time).
•The 600 rpm dial reading is taken at the point for which the change in dial reading is less than 1 degree (one dial division over a stirring time of one minute).
•When the dial reading has reached this steady value, record this as the 600 rpm dial reading, D600.
•Lower the speed to 300 rpm, and stir the sample at this speed until a steady reading is obtained using the same criteria for the steady state point. Record this value at the 300 rpm dial reading, D300.
Calculations:Apparent viscosity (cP) = D6002Plastic viscosity (cP) = D600–D300Yield point (pa) = D300-PV2Yield point (lb/ft2) = D300-PV