[Solved]In oilfield units, the laminar frictional pressure loss for a Bingham plastic fluid in a pipe and an annulus may be approx

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[Solved]In oilfield units, the laminar frictional pressure loss for a Bingham plastic fluid in a pipe and an annulus may be approximated by Note that d is measured in inches and yiled stress is measured in lbf/100 ft2.

Questions

1. In oilfield units, the laminar frictional pressure loss for a Bingham plastic fluid in a pipe and an annulus may be approximated by

Note that d is measured in inches and yiled stress is measured in lbf/100 ft2. (See equations (5.95d) and (5.91b) In the Drilling Text Book)

A Bingham plastic fluid has a plastic viscosity of 50 cP and a YP or 12 lbf/100 ft2.  Assuming that the flow pattern is laminar, compute the frictional pressure gradient resulting from (a) a flow rate of 50 gal/min through a drillstring with a 3.826-in ID and (b) a flow rate of 90 gal/min through a 10 x 7-inch annulus.

2. Outline the potential consequences of poor hole cleaning, i.e. failure to remove drilled cuttings efficiently from the well.

A hole of 8 3/4 in diameter is being drilled at an ROP of 20 ft/hr into a formation with 15% porosity. The drill collar OD is 6 ½ in and the mud circulation rate is 100 gpm.

Calculate the initial (or “feed”) volumetric concentration of cuttings at bottom hole from the formula

Here  is the volumetric mud flow rate in the annulus and  is the rate at which drilled solids are generated at the bit.

Calculate the mud velocity, U,  in the annulus

In the annulus the in situ volumetric concentration of drilled cuttings is denoted by Cand is related to the in situ mud velocity, U, and particle settling velocity by

Calculate C if the settling velocity is 0.17 ft/sec.

Is C higher than the feed concentration? Why?

An industry recommendation is that C should be less than 5%. Are we within this guideline? Could we safely increase ROP?