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DRILLING-YEAR 2 > Module 14-Mud motors > Flashcards

Module 14-Mud motors Flashcards

1
Q

What kind of motor assembly to the majority of directional wells drilled in North America use?

A

Steerable Motor Assembly

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2
Q

Downhole motor benefits?

A
  • option of either drilling in traditional rotary mode or a sliding mode
  • permit control of the well bore direction thus creating a more effective deviation control than conventional rotary methods
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3
Q

Advantages of downhole motors over conventional rotary drilling?

A
  1. excellent rotation power to the bit
  2. Increase RPM
  3. Reduces need for weight on the bit
  4. Reduces drill pipe and casing wear
  5. Increases the rate of penetration
  6. Accurately drills deviated holes
  7. Provides long runs for extended interval drilling
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4
Q

How are down hole motors powered?

A

Mud flow

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5
Q

What are the 2 types of motors?

A

Turbine

PDM

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6
Q

All basic mud motors have 4 basic components, name them from the top down?

A
  1. Dump Valve Assembly
  2. Power Section (the PDM)
  3. A connecting Rod Assembly & Bent Housing
  4. Bearing and Drive Shaft Assembly
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7
Q

Dump Valve Assembly

A

When there is no drilling fluid circulation, a spring holds the piston in the “up” or “open port” position. This opens the external ports and allows fluid to bypass the motor assembly.

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8
Q

How much of the tool does the power section make up?

A

half the tool length

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9
Q

What 2 parts does the power section have?

A

a coated steel rotor and a rubber stator

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10
Q

Describe the function of the power section?

A

As fluid is pumped into the tool, it seems a path through these cavities. The force turns the rotor to turn within the stator creating a rotational force that is transmitted to the bit

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11
Q

How many more lobes will the stator have than the rotor?

A

1

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12
Q

As the number of lobes increases, speed is?

A

reduced

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13
Q

PDM have much better application with?

A

roller cone bit and core heads

PDC bits, especially those with the large, limited numbers of cutter heads which require the high torque levels

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14
Q

Define rotor/stator interference fit

A

is the difference between the size of the rotor mean diameter and the stator minor diameter

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15
Q

What is one stage considered in a PDM?

A

one complete spiral and 2 complete spirals of the rotor

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16
Q

Is the drive shaft constructed rigidly in a PDM?

A

YES!

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17
Q

Where is the bering supported within in the PDM?

A

within the housing by radial and axial thrust bearings

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18
Q

Where does the majority of the flow through in a PDM?

A

through the drive shaft but a portion is used to

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19
Q

All mud motors have what 4 basic components?

A
  1. Dump Valve Assembly
  2. A Power Section (the PDM)
  3. A connection rod Assembly and bent housing
  4. Bearing and Drive Shaft Assembly
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20
Q

What forms the outer body of the motor assembly?

A

The stator tube

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21
Q

What shape is the stator in the power section of a PDM?

A

Helix shape

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22
Q

What is the rotor in the power section in a PDM machined from?

A

solid allow steel bar and plated with hard chrome to reduce wear caused by abrasives in the drilling fluid.

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23
Q

As the number of lobes is increased in the power section of the PDM, speed __________ and torque _____________.

A

is reduces and torque increases

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24
Q

Multilobe motors have a much better application with what kind of bit?

A

Roller Cone bit and core heads.
They can also be used with PDC bits, especially those with the large, limited numbers of cutter heads, which require high torque.

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25
Q

The demential tolerances of the rotor OD and stator ID are designed to create what?

A

a slight interference fit, which controls motor power.

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26
Q

What is defined as the rotor/stator interference fit?

A

The difference between the size of the rotor mean diameter

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27
Q

What is the mean stator diameter?

A

valley to lobe peak measurement

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28
Q

What is the stator minor diameter?

A

Lobe peak to lobe peak measurement

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29
Q

define the rotor/stator interference fit

A

The difference between the size of the rotor mean diameter and the stator minor diameter

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30
Q

Rotors in the power section of the PDM are sized __________ than the stator internal bore under planned downhole conditions.

A

larger

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31
Q

Drilling torque is directionally proportional to the mud pressure drop across the______________?

A

mud motor

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32
Q

The tools hydraulic motor is directly proportional to ___________ through the motor.

A

Fluid flow rate

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33
Q

What percentage of reduction in speed in seen during no load to a maximum load (AKA- just before a stall/stall load)?

A

10%

34
Q

A motor has multiple stages. What is a stage?

A

one complete spiral of the stator and two complete spirals of the rotor

35
Q

What is reactive torque?

A

Reactive left hand (counter clockwise) torque in the motor housing vs right hand (clockwise) normal turning of the drill bit.

36
Q

Reactive torque increases as what increases and when does it reach the max?

A

As bit weight increases and reaches a max as the tool stalls.

37
Q

The connection rod assembly is attached to what?

A

The lower end of the rotor

38
Q

What does the connection rod assembly do?

A

transmits the torque and rotational speed from the motor to the drive shaft and the bit.

39
Q

How is flexibility in the connection rod assembly achieved?

A

through 2 opposing universal type-joints or through the use of a flex rod.

40
Q

When selecting a bit, the rule of thumb is:

A

The tooth structure at least 1 grade harder than if the rotary drilling were used in the same formation.

41
Q

What are conventional connections in a connecting rod assembly?

A

U joints and these are used in most PDM’s.

42
Q

Turbines is made up of 3 primary stages

A
  1. Drive stage or turbine
  2. The axel thrust bearing and radial bearing
  3. The bit drive sub
43
Q

What is the drive shaft?

A

is a rigidly constructed, hollow steel shaft.

44
Q

How is the drive shaft supported?

A

It is supported within the housing by radial and axial thrust bearings,

45
Q

Turbines, a continuous flow of fluid (aka mud) under pressure passes through a series of turbine stages and gives up some of the pressure to create what?

A

Rotational torque

46
Q

The majority of the drilling fluid flows through the ______ _______ but a portion is used to _______ and _________ the __________.

A

drilling fluid, cool and lubricate, bearings

47
Q

In the turbo drill, high rotational speed is proportional to what?

A

The flow

48
Q

Name 7 advantages of PDM’s?

A
  1. Low pressure
  2. Can handle high bit pressure drops
  3. Wide range of bits
  4. Can handle LCM
  5. Low thrust load
  6. Lower lost in hole cost
  7. Short tool
49
Q

Name 5 advantages of turbines?

A
  1. High power
  2. High speed
  3. Reliable as fuck, 250 +
  4. No universal joint
  5. No dump valve
50
Q

Name 2 disadvantages of PDM’s

A
  1. Lower temp rating

2. Connecting rod assembly

51
Q

3 Disadvantages of the turbines?

A
  1. High pressure requirement
  2. High maintenance costs
  3. Long tool
52
Q

What is the most common type of assembly used in drilling today?

A

Steerable motors

53
Q

Describe a bent sub or bent housing

A

used to achieve deviation by placing a bend in the pipe.

54
Q

What are the 3 main elements in a bearing assembly in a PDM?

A
  1. Off bottom thrust bearings
  2. Radial support bearings
  3. On-bottom thrust bearings
55
Q

What is a bent housing?

A

a bend at the connecting rod housing

56
Q

With a bent housing, the bend is located much _________ to the bit.

A

closer

57
Q

What are 4 benefits of a bent housing?

A

Less lateral displacement
The entire BHA may be rotated
assembly is easier to run in the hole
assembly will be easier to orient

58
Q

a PDM’s bearing assembly serves what purpose?

A

To support the tool weather it hanging freely or on the bottom

59
Q

Motors are available with the following bent housings?

A

0 degrees 45’, 1 degree 00’, 1 degree 15’, 1 degree 30’, 1 degree 40’, 1 degree 45’.

60
Q

A concentric stabilizer is placed on the bearing housing and should always be slightly ____________, generally about ___mm.

A

underage about 3 mm

61
Q

Advantages of adjustable bent housing?

A

Field adjustable, increments from 0 to 3 degrees, improve drilling efficiency and control.

62
Q

The bent housing allows the driller to change the __________ or the __________ when the rotary table is locked and the well is being drilled with the motor turning (sliding).

A

inclination and azimuth

63
Q

Generally, it is possible to increase ROP up to _______ times for rotary drilling vs sliding in a BHA.

A

three

64
Q

Why is it difficult to steerable BHA’s?

A

reactive torque

65
Q

The MWD or NMDC’s will in all probability be run ________ the motor.

A

above

66
Q

Stators are larger than the rotor? T or F

A

FALSE

If true, explain
if false, explain
ALSO, DRAW A DIAGRAM

67
Q

Describe and draw positive interference via compression of the stator vs. negative interference in a 5 lobe configuration

A

see power point

68
Q

How are the diameters of the rotor vs stator sized in inches via a difference? This difference helps produce what?

A

motor mean diameter is more than 0.022 inches greater than the stator minor diameter at downhole conditions. Capable of producing large pressure drops.

69
Q

What fluid is the downhole motor designed to operate effectively?

A

practically all types of drilling fluids, such as:

  • fresh or salt water
  • water or oil based clay
  • additives for viscosity control or lost circulation
  • even air!!
70
Q

What are PDM cavities?

A

Pockets capable of holding pressure

71
Q

As cavities increase, what increases?

A

PDM’s holding pressure

72
Q

With more cavities, comes what?

A

The total pressure drop over the power section increases.

73
Q

As the number of cavities increases, what happened to pressure drop and stall torque capability via theoretical inferences?

A

The total pressure drop and stall torque capability theoretically increase linearly with the number of stages.

74
Q

What the range for typical angle set on a steerable BHA?

A

0.25 to 1.25.

75
Q

Whats the purpose of a dump valve in a PDM?

A

To have a dry tool during rig out and a way of filling the motor during initial movement.

76
Q

On bottom thrust bearings, what do they do?

A

transmit drilling loads from the non rotating house assembly to the rotating drill.

77
Q

Radial support bearings- what do they do?

A

They support the drive shaft and regulate flow of drilling fluid through the bearing assembly.

78
Q

When pressure jumps several hundred PSI and does not vary as additional weight on bit is added, what does this mean?

A

STALL

79
Q

What is chunking and what is sign of it?

A

When a stall occurs, fluid passes across the seal face at a high velocity. This deforms the stator lobes and leads to chunking.

80
Q

How do you prevent chunking?

A

Take care to select appropriate rotor/stator interface relative to downhole mud temp.

81
Q

Differential pressure/pressure loss/pressure drop across the motor are proportional to what?

A

additional weight on bit or the drilling torque required.

DRILLING-YEAR 2 (4 decks)

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