Drilling fluids annular flow

A mud rotary rig cuts a borehole by rotating a bit into the formation materials and removing the cuttings by continuous circulation of a drilling fluid. In a conventional rotary system, mud is pumped down through the drill pipe and out through nozzles in the bit. The mud flows upward in the annular space around the drill pipe to the surface, where it is channeled into a settling pit and a... 

The return flow of the drilling fluid in the wellbore is considerably more complex than in the drill pipe as the flow is annular and the drilling fluid is rotated by the rotating drill pipe. In addition, the flow is fre-... 

Marken et al. (110) have given a detailed account of the factors affecting annular pressure losses, including the effects of rotational flow in the annulus. It might be expected that rotational flow in the annulus would decrease the frictional pressure losses as the increased shear rate would lower the viscosity. However, Marken et al. observed an increase in frictional pressure due to the formation of Taylor vortices. McCann et al. (J07) have observed increases in the frictional pressures in slimhole annuli due to annular rotation of the drilling fluid. 

A drilling fluid consisting of a china clay suspension of density 1090 kg/m flows at 0.001 m /s through the annular cross-section between two concentric cylinders of radii 50 mm and 25 mm, respectively. Estimate the pressure gradient if the suspension behaves as ... 

Silva, M.G.P., Evalution of the Flow Regime of Drilling Fluids in Annular Sections. (In Portuguese), 2 Drilling Fluids Seminar, Salvador, BA, pp. 1 - 10, (1989). 

Dynamic filtration in Newtonian fluids. While borehole annular flows are rarely Newtonian (e.g., fluids such as water or air, where viscous stress is linearly proportional to the rate of strain), many drilling fluids are thin and briny, and at times, simply water. Thus, for analysis purposes, the study of Newtonian flows is more than academic. Furthermore, the mathematical simplicity that it offers sheds some insight into the parameters that influence the value of equilibrium cake thickness in the presence of erosive annular flow. Whether our annular flow is Newtonian or power law, concentric or eccentric, it is important to consider two underlying asymptotic fluid-dynamical models. The first applies during small times when borehole fluid enters the formation radially as filtrate, decelerating with time, while the second deals with large times, when invasion rates are so slow that we essentially have classical no-slip velocity boundary conditions. We will first eonsider the small time limit, assuming that the drill pipe does not rotate. 

Where conditions are such that it is impractical to measure static pressure at the wall, a combined pitot-static tube may be used. This is actually two tubes, one inside the other. The outer tube is plugged off at the end facing the flowing fluid, but small holes are drilled through it to receive the fluid pressure. These holes open into the annular space between the tubes. The static pressure is measured through two or more of these holes, and it is assumed that the flow follows along the outside of the tube in such a way that the true static pressure is obtained. 

An aqueous bentonite suspension of density 1300kg/m, used to model an oil drilling mud, is to be pumped through the annular passage between the two concentric cylinders of radii 101.6 mm and 152.4 mm, respectively. The suspension, which behaves as a Bingham plastic fluid with /xg = 20 mPa s and r = 7.2 Pa, is to be pumped at the rate of 0.13m /s over a distance of 300 m. Estimate the pressure drop. Over what fraction of the area of the annulus, the material is in plug flow ... 

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