Rheology is mainly to study the deformation and flow of fluids. Viscosity is used to measure the forces that prevent fluid from deforming, and shear forces control many aspects of viscosity associated with drilling operations. For this reason, the shear viscosity (or simply “viscosityâ€) of drilling fluids is most commonly used for testing and control as a drilling fluid. The retention of the drilling fluid on the surface of the drill cuttings is considered to be one of the basic functions of the drilling fluid viscosity and is due to the wetting properties of the drilling fluid.
The viscosity of the drilling fluid increases at high shear rates, and the drilling fluid tends to hold more drilling fluid on the surface of the cuttings. It also reduces the efficiency of high shear equipment such as drilling and oscillating vibrating screens. Conversely, drilling fluids with increased viscosity at low shear rates reduce the efficiency of low shear equipment such as centrifuges because the sedimentation rate and separation efficiency of the pellets are inversely proportional to the viscosity of the drilling fluid. Water or diluent can reduce the effect of high shear rate viscosity and low shear rate sag on separation efficiency. Also, in drilling operations that generate large amounts of cuttings (such as reaming), the key is to increase the speed of the drilling fluid or to reduce the drilling speed.
Other rheology may also affect the retention of drilling fluid on the cuttings surface and the interaction between drill cuttings. Some drilling fluids are not only elastic but also viscous. These viscoelastic fluids exhibit some solid-like properties (elasticity) and conventional liquids (sexuality), especially at low shear rates. For example, xanthan gum drilling fluids with shear thinning tend to be viscoelastic, and low shear rate separation equipment such as gauge separation tanks and centrifuges are less efficient.
The viscoelasticity discussed above is based on the shear flow of fluids. However, what is currently attracting attention is that another type of prison elasticity is tensile viscoelasticity. At high flow rates, tensile viscoelasticity can be important, including the performance of fluids as they pass through drill bits and potentially high throughput handling equipment. Polymeric surface-active polymers such as PHPA and 2-alenamide-1-2-propylpropionic acid (AMPS)-acryloyl complex. These polymers are used as mud shale coatings to produce high tensile viscosities. This type of drilling fluid, especially the new type of drilling fluid, tends to slowly move down like a “walking down†vibrating screen. Additives such as barite or bentonite , which are fine or ultrafine solid phase, are minimally affected.
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