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Drilling Engineering > Unit 11 - Directional Drilling > Flashcards

Unit 11 - Directional Drilling Flashcards

1
Q

What are some typical applications for directional controlled well drilling?

A
  • multi-well platform drilling
  • fault drilling
  • inacessible locations
  • sidetracking and straightening
  • salt dome drilling
  • relief wells
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2
Q

What is multi well platform drilling?

A
  • to drill a large number of wells (up to 40-60) from one location
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3
Q

What is fault drilling?

A
  • if well is drilled across a fault, casing can be damaged by fault slippage → potential for damaging the casing can be minimised by drilling parallel to a fault and then changing the direction of the well to cross the fault into the target
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4
Q

The three dimensional system that is generally used to define the position of a particular point along the wellpath is ?

A
  • The vertical depth of the point below a particular reference point
  • The horizontal distance traversed from the wellhead in a Northerly direction
  • The distance traversed from the wellhead in an Easterly direction
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5
Q

Which datum systems are most widely used?

A
  • Mean Sea Level, MSL
  • Rotary Table Elevation, RTE
  • 20” Wellhead Housing
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6
Q

What is the Along Hole Depth (AHD) or measured depth (MD)

A
  • the depth of a point from the surface reference point, measured along the trajectory of the borehole
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7
Q

All displacements while drilling are referenced to ?

A
  • to the wellhead position
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8
Q

What are the three types of deviated well profiles?

A
  • build and hold
  • S-shaped
  • Deep kick off
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9
Q

Which well profile is the most difficult one?

A
  • the deep kick-off since it is necessary to initiate the deviated trajectory in deeper, well compacted formations
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10
Q

What are the three specific parameters when planning a trajectory?

A
  • kick-off point
  • buildup and drop off rate
  • tangent angle off the well
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11
Q

What is the Kick-off Point ?

A
  • is the along hole measured depth (AHD) at which a change in inclination of the well is initiated and the well is oriented in a particular direction
  • the most distant targets have the shallowest KOPs in order to reduce the inclination of the tangent section of the well
  • kick off should be initiated in stable formations which are not likely to cause drilling problems
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12
Q

What is the Build up Rate and Drop Off Rate?

A
  • in degrees of inclination
  • rates at which the well deviates from the vertical
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13
Q

What is the tangent angle (or drift angle) ?

A
  • the inclination of the long straight section of the well after the build up section of the well
  • the tangent angle will generally be between 10 and 60 degrees → since it is difficult to control the trajectory of the well at angles below 10 degrees and it is difficult to run wireline tools into wells at angles of greater than 60 degrees
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14
Q

Which technical constraints and issues will have to be considered when planning a directional well?

A
  • Target location
  • Target size and shape
  • Surface location (rig location)
  • Subsurface obstacles (adjacent wells, faults etc.)
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15
Q

How do target size and shape have an influence on the deviated well?

A
  • the target area will be dictated by the shape of the geological structure and the presence of geological features such as faults

→ in general: the smaller the target area, the more directional control that is required and so the more expensive the well will be

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16
Q

What are the two basic principles that deflection tools work on?

A
  • bit tilt angle just above the bit
  • introduce sideforce to bit
17
Q

What are the major detection tools currently used?

A
  • Bent Sub and Positive Displacement Motor
  • Non-Rotating Steerable Drilling Systems
  • Rotary Steering System
  • Directional Bottom Hole Assemblies (BHA)
  • Whipstocks
18
Q

What is a bent sub?

A
  • short length of pipe with a diameter which is approximately the same as the drillcollars
  • manufactured in a way that the axis of the lower connection is slightly offset (less than 3 degrees) from the axis of the upper connection
  • when made up into the BHA, it introduces a “tilt angle” to the elements of the BHA below it and therefore to the axis of the drillbit

→ but you can’t rotate the drillstring then anymore from surface

19
Q

The bent sub must be used together with?

A
  • Positive Displacement Motor (PDM) or a Drilling Turbine
20
Q

Where is the mud motor installed?

A

Below bent sub → between bent sub and drill bit

21
Q

How does the mud motor work?

A
  • when the drilling fluid is circulated through the drillstring the inner shaft of the mudmotor, which is connected to the bit, rotates and therefore the bit rotates

→ therefore not necessary to entire drillstring from surface if a mud motor is included in BHA

22
Q

In which parts of the drilling operation will you use a bent sub and mud motor?

A
  • build up or drop off portion off the well → because bit will continue to drill in direction of tilt angle as long as bent sub is in assembly and mud motor is being used to rotate the bit → this is a major disadvantage of the use of a bent sub and mud motor
23
Q

What is the advantage of a steerable drilling system?

A
  • allows directional changes of the well to be performed without tripping to change the BHA
24
Q

A steerable drilling system consists of which parts?

A
  • drill bit
  • stabilized positive displacement steerable mud motor
  • a stabilizer
  • directional surveying system → monitors and transmits to surface the hole azimuth, inclination and toolface on a real time basis
25
Q

What is the task of the directional surveying system in the steerable drilling system?

A
  • it monitors and transmits the hole azimuth, inclination and toolface on a real time basis to the surface
26
Q

Why can you rotate the steerable drilling system also from the surface even though you can not do that with a bent sub?

A
  • because the tilt angle is much closer to the bit than a conventional bent sub assembly → therefore it produces a much lower bit offset and this means that the drill bit can also be rotated by rotating the entire string at surface
27
Q

When do you use the term “oriented or sliding” drilling?

A
  • when using the navigation sub and mud motor to drill a deviated section of hole (such as build up or drop off section of hole)
28
Q

When do we use the term “rotary” drilling?

A
  • when drilling in a straight line, by rotation of the assembly
29
Q

What are the five components in a steerable drilling system?

A
  • drill bit
  • mud motor
  • navigation sub
  • navigation stabilizers
  • survey system
30
Q

Rotary Steering System (Picture)?

A
31
Q

What is the huge advantage of a rotary steering system?

A
  • you can rotate the drillstring even when you are drilling directionally → you can rotate the drillstring at all times during the operation
32
Q

What is the biggest advantage of being able to rotate the drillstring of a rotary steering system at all times?

A
  • much easier to transport cuttings from wellbore when drillstring is rotating → when drillstring is not rotating, there is a tendency for cuttings to settle around the drillstring and it may become stuck
33
Q

What are the three bottom hole assemblies, that have been used in the past to control the hole deviation?

A
  • packed hole
  • pendulum
  • fulcrum
34
Q

Describe the Packed Hole Assembly!

A
  • very stiff assembly
  • drill collars and stabilizers positioned to reduce bending and keep the bit on course
  • often used in the tangential section of a directional hole
35
Q

Describe the Pendulum Assembly!

A
  • principle: unsupported weight of drill collars will force the bit against the low side of the hole
  • resulting decrease or drop off in angle depends on WOB, RPM, stabilization and the distance between the bit and the first reamer
36
Q

In a Pendulum Assembly, how can I increase the tendency to drop the angle?

A
  • Apply less WOB (lower penetration rate)
  • Apply more RPM and pump pressure in soft formations where jetting and

Reaming down is possible

  • Use bigger size Monel DC below the reamer, small DCs above.
37
Q

What is the principal behind a fulcrum assembly?

A
  • place a reamer near the bit and apply high WOB
  • When WOB is applied → DCs above reamer will tend to bend against the low side of hole

→ it makes the reamer act a fulcrum and forces the bit upwards

  • build up rate depends on WOB, size of collars, position of reamer and stabilization above the reamer
38
Q

How can you increase the build in a fulcrum assembly ?

A
  • Add more WOB
  • Use smaller size monel (increase buckling effect)
  • Reduce RPM and pump rates in soft formations
39
Q
A

Drilling Engineering (13 decks)

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