Unit 10 - Hydraulics

Question 1

How do you call the necessary amount of pressure in a system that is required to overcome the resistance to flow of a fluid in a system?

Answer 1

circulating pressure

Question 2

Hydraulic power needed to circulate the fluid is a direct function of ?

Answer 2

pressure losses and flowrate through the system?

Question 3

does the flowrate change during different parts of the system?

Answer 3

no

Question 4

what are sacrifical pressure losses?

Answer 4

pressure required to circulate the fluid through the drillstring and annulus → because they do not contribute anything to the drilling process

Question 5

why is it desirable to optimise the pressure losses through the nozzles?

Answer 5

• because it helps to clean the drilled cuttings from the face of the bit

Question 6

What are the principial factors, which influence the magnitude of the pressure losses in the system?

Answer 6

• The geometry of circulating system (e.g. I.D. of drillpipe, length of drillpipe)
• The flowrate through the system
• The flow regime in which the fluid is flowing (laminar/turbulent)
• The rheological properties of the circulating fluid

Question 7

What are the two types of flow pattern?

Answer 7

• laminar flow
• turbulent flow

Question 8

If you circulate a newtonian fluid through a pipe, the onset of turbulence is dependent on which parameters?

Answer 8

• Pipe diameter, d,
• Density of fluid, r
• Viscosity of fluid, µ
• Average flow velocity, v

and if the combination of these values exceeds a value of 2100

Question 9

What are the different rheological models used by drilling engineers to describe drilling fluids?

Answer 9

• newtonian model
• non-newtonian model
• bingham plastic model
• power-law model

Question 10

What are examples of newtonian fluids?

Answer 10

• water
• gases
• high gravity oil

Question 11

How will a model according to the bingham plastic model behave?

Answer 11

• will not flow until applied shear stress, exceeds a certain minimum shear stress value known as the yield point
• but after yield point has been exceeded, changes in shear stress are directly proportional to changes in shear rate, with the constant of proportionality being called the plastic viscosity, µp.

Question 12

What does the gel strength represent?

Answer 12

the shear stress to shear rate behaviour of the fluid at near zero shear rate conditions

Question 13

• the power law can be used to represent what kind of fluids?

Answer 13

• pseudoplastic fluids ( n<1)
• newtonian fluids (n=1)
• dilatant fluids (n>1)

Question 14

the deviation of the non-newtonian exponent from 1 describes what?

Answer 14

• the degree to which the fluid behaviour is non-newtonian

Question 15

What is the apparent viscosity?

Answer 15

the shear stress to shear rate relationship measured at a given shear rate in a non - newtonian fluid

Question 16

When do you call a non - newtonian fluid pseudoplastic?

Answer 16

if the apparent viscosity decreases with an increasing shear rate

Question 17

When do you call a non-newtonian fluid dilatant?

Answer 17

• when the apparent viscosity increases with increasing shear rate

Question 18

which fluids are generally pseudo-plastic?

Answer 18

• drilling fluids
• cement slurries

Question 19

When will you get a turbulent flow?

Answer 19

• when fluid is pumped at a high rate the fluid laminae become unstable and break into a chaotic, diffused flow pattern

Question 20

The frictional pressure loss associated with the turbulent flow of a Bingham plastic fluid is affected primarily by ?

Answer 20

density and plastic viscosity.

Question 21

What are the two major aims for an optimum hydraulics programme?

Answer 21

• clean hole effectively
• make best use of power available to drill the hole

Question 22

what are the two different approaches to optimum hydraulics design?

Answer 22

• maximise hydraulic horsepower at bit → assumes that best method of cleaning the hole is to concentrate as much fluid energy as possible at the bit.
• maximise hydraulic impact at bit → assumes that most effective method is to maximise the force with which the fluid hits the bottom of the hole.

Question 23

What is the real purpose of the jet nozzles?

Answer 23

• improve cleaning action of drilling fluid at the bottom of the hole

Question 24

What is the pressure of the returning mud at the flowline?

Answer 24

• atmospheric pressure

Question 25

Where do you have the biggest pressure drop in the system?

Question 26

What kind of flow do you generally have in the annulus?

Answer 26

• laminar flow

Question 27

What kind of flow do you generally have in the drillstring?

Answer 27

• turbulent flow

Question 28

Why do you usually try to avoid turbulent flow in the annulus?

Answer 28

• it may cause washouts in the formation by erosion