① static shear strength (τs)
Start drilling fluid flow required minimum shear stress , which is a continuous measure of the strength of the space frame structure of the drilling fluid formed in the stationary unit area . Continuous space grid structure called gel structure, also known as static shear gel strength . Closely related to the static shear size and drill cuttings and drilling fluid suspension heavier material 's ability to stop the cycle . However, static shear force can not be too large, otherwise the pump difficult and sometimes choke drain formation . Adjust the drilling fluid and the dispersion of clay content , plus inorganic electrolyte membrane adjust the electrostatic repulsion and hydration repulsion between the particles of clay , plus measures to adjust the viscosity fluids like static shear stress .
② ultimate static shear force
Various drilling fluid system clay particles due to the irregular surface charge and hydrophilic uneven shape at rest is easy to form a network structure. The minimum static shear stress damage drilling unit volume mesh structure on the need, the drilling fluid called "extreme static shear force ."
③ dynamic shear force (τ0)
Line segment extended flow curve intersects the axis of a shear stress τ0, which is a hypothetical value , a measure of the strength of the mesh structure of the drilling fluid when drilling fluid is reflected in a laminar flow state . Factors that affect the value and size of the adjustment method is basically the same as the static shear .
④ plastic viscosity (μPV)
Bingham formula derived from that plastic viscosity plastic fluid rheology curve segment is the reciprocal of the slope , it does not change with shear force . Description is the viscosity of the system architecture to break speed equal to the speed of recovery time . It is a fluid phase between the particles in a laminar flow system the solid state , between the solid particles and the surrounding liquid phase intermolecular friction formed . Plastic viscosity of the drilling fluid solid content , shape and degree of dispersion of solid particles , the surface lubricity and viscosity of the liquid itself, and other factors . It is directly related to the drilling fluid suspension capabilities, its value should be moderate. If the viscosity is too high the plastic system , reducing the time needed , the solids control equipment is generally used to reduce the solid phase solid phase content , increase inhibitory system, reduce the activity of the solid phase dispersion ; if urgent need to reduce the dilution water can be added . If you want to increase the viscosity of the system can be added to the plastic polymer organic polymer thickener or clay.
