Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Drilling Engineering > Unit 6 - Well Control > Flashcards

Unit 6 - Well Control Flashcards

1
Q

What is well- control?

A

Control of formation pressure (primary- and secondary control)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What could be the consequences of a blowout?

A
  • loss of human life
  • loss of rig and equipment
  • loss of reservoir fluids
  • damage to the environment
  • huge cost of bringing well under control again
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

On what depends the severity of a kick (fluid amount, which enters the wellbore)?

A
  • type of formation → (porosity/permeability)
  • pressure → the greater the negative pressure differential, the easier for formation fluids to enter wellbore
  • nature of influx
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is primary well control?

A
  • maintenance of positive differential pressure or overblance on formation pressure
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

When is secondary control necessary?

A
  • necessary, when primary control has failed → formation fluids are flowing into well bore
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the goal of secondary control ?

A
  • stop flow of fluids into wellbore
  • allow influx to be circulated to surface and safely discharged, while preventing further influx downhole
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How come, that you loose primary control even if you calculated it before?

A
  1. formation pressure in penetrated zone is higher than predicted → because of that , mud weight is too low → bottom hole pressure is less than formation pressure
  2. Pressure due to column of mud decreases for some reason → bottom hole pressure drops below formation pressure
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are reasons, why the mudweight would reduce?

A
  • solids removal
  • excessive dilution of mud ( due to watering back)
  • gas cutting of mud
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How can the mudweight fall due to solids removal?

A
  • cuttings are removed and if equipment is not properly designed, big amount of weighting solids (Barite) may also be removed → if barite is removed, you have to replace it, before circulating it down again
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How can the mudweight fall due to dilution?

A
  • To improve viscosity of mud , it is usually diluted with water (called water-back)
  • or water is added for very deep drilling operations, where evaporation might be significant
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is gas cutting?

A

gas seeps from formation into mud → reduces density of mud

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are reason to why the mud column height may be reduced?

A
  • tripping
  • swabbing
  • lost circulation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What will happen to the mud column while tripping?

A
  • top of mud column will fall as drillpipe is pulled from borehole

→ therefore any point in wellbore has now less mud above itself → therefore bottom hole pressure will be reduced → hole must be filled up during tripping with mud

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is swabbing?

A
  • process by which fluids are sucked into borehole from formation, when drillstring is pulled out of hole
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How can swabbing happen?

A
  • When bit has become covered in drilled material and drillstring acts like a giant piston when moving upwards → creates low pressure region below bit → formation fluids are sucked into borehole
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How do you call the opposite effect of swabbing?

A

surging

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

The amount of swabbing will increase with ?

A
  • adhesion of mud to drillpipe
  • speed at which pipe is pulled
  • use of muds with high gel strength and viscosity
  • thick mud cake
  • inefficient cleaning of bit to remove cutting
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

When does lost circulation occur?

A
  • when a fractured, or very high permeability, formation is drilled → mud is lost to formation → reduction of column height in borehole
  • another option: mudweight is too choosen too high and formation fracture gradient is exceeded
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How can you minimise fluid losses to formation?

A
  • use lowest practicable mud weight
  • avoid pressure surges when running pipe in hole
  • avoid small annular clearances between drillstring and hole
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is a possum belly tank/

A
  • A trip tank, whit a small diameter to height ratio → it is therefore used to measure the amount of mud that is used to fill , or is returned from the hole, when the pipe is pulled from, or run intothe hole respectively
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What are primary indicators of a kick?

A
  • Increase of flow rate
  • pit volume increase
  • flowing well with pumps shut off
  • inproper hole fillup during trip
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what can be the reasons, that the well is flowing, when pumps are shut off?

A
  • fluid is pushed out of annulus by some force → could be formation pressure, which is higher than hydrostatic pressure due to column of mud and therefore that an influx of fluid is taking place
  • mud in borehole expands as it heats up → expansion results in small amount of flow when pumps are shut off
  • if small amount of heavy mud has accidentally been pumped in and therefore mud in annulus is being displaced
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What are secondary indicators for a kick?

A
  • drilling break
  • gascut mud
  • changes in pump pressure
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is a drilling break ? (kick indicator)

A

-abrupt increase in rate of penetration → may indicate that higher pressure formation has been entered → therefore the chip hold down effect has been reduched and/or a higher porosity formation (for example due to under-compaction and therefore indicative of high pressures) has been entered

→ but an increase in drilling rate could also be simply due to a change from one formation type to another

25
Q

What is gas cut mud?

A

when gas enters mud from formations being drilled → then the mud is said to be gas cut

26
Q

what are reasons, why you receive a gas influx ?

A
  • drilling into gas bearing formation
  • swabbing when making a connection during trips
  • influx due to negative pressure differential
27
Q

What is the first thing you do if you see indicators of an influx into the wellbore?

A
  • carry out a flow check
    1. pick up kelly until a tooljoint appears above rotary table
    2. shut down the mud pumps
    3. set slips to support the drillstring
    4. observe the flowline and check for flow from annulus
    5. - If the well is flowing → close the BOP
  • If well is not flowing, resume drilling and check for further indications of a kick
28
Q

What is the first step you need to do if primary control of a well is lost?

A
  • close the BOP valves and seal off drillstring to wellhead annulus at surface
29
Q

Why is it not necessary to close off the valves inside the drillpipe when primary control is lost?

A

Because since it is connected to the mudpumps, the drillpipe pressure can be controlled

30
Q

What is the shut in procedure step by step?

A
  1. raise kelly above rotary table until a tooljoint appears
  2. stop the mud pumps
  3. close the annular preventer
  4. read the shut in drill pipe pressure, annulus pressure and pit gain
31
Q

Why do you have to fully open the choke line before closing in the annular preventer while experiencing a kick?

A
  • to prevent surging effects on the openhole formations
32
Q

What do you have to do if you detect a kick while tripping?

A
  1. set top tool joint on slips
  2. install a safety valve (open) on top of the string
  3. close safety valve and annular preventer
  4. make up the kelly
  5. open safety valve
  6. read shut in pressures and the pit gain
33
Q

We do we assume in a calculation, that the influx goes into the annulus?

A
  • because you would expect it to follow the flow of fluids through the system when they enter the wellbore
34
Q

Pressure gradient ranges of gas, oil and seawater?

A
  • Gas: 0.075-0.150 psi/ft.
  • Oil: 0.3-0.4 psi/ft.
  • Seawater: 0.470-0.520 psi/ft.
35
Q

What are the factors, that affect the annulus pressure?

A
  • Size of the influx
  • gas buoyancy effect
36
Q

What can happen if you detect the influx late and have therefore a big volume of influx in the annulus?

A
  • You have a higher pressure on the annulus (PAnn) and in general the whole pressure along the entire wellbore will increase → two things can happen:
    1. At some point fracture pressure of one of the formations in open hole section may be exceeded → may lead to an underground blowout → formation fluid can enter the wellbore → leaving wellbore at some shallower depth
37
Q

Explain the gas buoyancy effect! Why does it affect the annulus pressure?

A
  • because of large density difference between gas and mud → gas bubble will be subjected to a large buoyancy effect → it will rise to the annulus and while it rises, it will expand and if the well is open it will displace mud from annulus

BUT: if well is not open→ mud cannot be displaced→gas can’t expand→gas influx will rise but will maintain its high pressure since it can’t expand

Result: PAnn will increase and higher pressures will be exerted all down to the well bore

38
Q

How can you identify the fact, that gas is rising in the annulus with a very high pressure?

A

-by a simultaneous rise in drillpipe and annulus pressure → in this case the pressure must be bled off from annulus by opening the choke in very small doses

39
Q

What is the MAASP?

A
  • maximum allowable annular surface pressure → the maximum pressure, which can be allowed at surface before the fracture pressure of the formation just below the casing shoe is exceeded
40
Q

Where is normally the weakest point in a drilled well?

A
  • the highest point in the open hole section → that is at the previous casing shoe
41
Q

Describe the volumetric method to circulate out an influx when there is no drillstring in the hole!

A
  • uses expansion from gas to maintain bottomhole pressure greater than formation pressure
  • pressures are adjusted by bleeding off at choke in small amounts
  • once gas reaches surface, it is gradually bled off, whilst heavier mud must be circulated → can be done with a snubbing unit (equipment, which allows a small diameter pipe to get into hole through closed BOPs
42
Q

What is stripping?

A

process, where pipe moves through closed BOPs under its own weight

43
Q

What is snubbing?

A
  • process, where pipe is forced through BOP mechanically
44
Q

What are the two methods to kill a well with the drillstring inside the well?

A
  • one circulation method
  • drillers method
45
Q

Describe quickly the one circulation method + the advantages of this method?

A
  • circulate influx out and circulate in the heavier mud simultaneously
  • influx is first of all removed with original mud
  • then well is displaced to heavier mud during a second circulation
  • safer, simpler and quicker than drillers method
46
Q

Main disadvantage of the one circulation method?

A
  • time taken to mix heavier mud which may allow a gas bubble to migrate
47
Q

What kind of ram type preventers are there?

A
  • Blind rams - completely close off the wellbore when there is no pipe in hole
  • pipe rams - seal off around a specific size of pipe thus sealing off the annulus

there are also variable rams - close and seal off on a range off drillpipe sizes

  • shear rams - same as blind rams but can cut through drillpipe for emergency shut in → only used as last resort
48
Q

Where do you use a casing spool?

A
  • wellhead, from which casing strings are suspended are made up of casing spools

→ casing spool will be installed after each casing string has been set → BOP stack is placed on top of casing spool and connected to it

49
Q

What is a diverter system and when do you use it?

A
  • diverter is a large, low pressure, annular preventer, equipped with large bore discharge flowlines → this type of BOP is usually used when drilling at shallow depths below the conductor
50
Q

Why do you usually use a diverter system in shallow depths?

A
  • because if the well was to kick at a shallow depth and you would try to close it in and attempt to contain the downhole pressure, it would probably result in fracturing the formations belwo the conductor →purpose of a diverter is it to allow the well to flow to surface safely →there it can be expelled safely through a pipeline leading away from the rig
51
Q

What is the task of the choke line?

A
  • to carry mud and influx from the BOP stack to the choke manifold
52
Q

What is a kill line and what is the task of a kill line?

A
  • a high pressure pipeline between side outlet, opposite of the choke line outlet on the BOP stack, and the mud pumps
  • provides the option of pumping fluids downhole when normal method of circulating down the drillstring is not possible
53
Q

What is a choke manifold?

A
  • arrangement of valves, pipelines and chokes, designed to control the flow from the annulus of the well during a well killing operation
54
Q

choke manifold must be capable of?

A
  • controlling pressures by using manually operated chokes or chokes operated from a remote location
  • diverting flow to a burning pit, flare or mud pits
  • have enough back up lines if any part of the manifold would fail
  • a working pressure equal to the BOP stack
55
Q

What is a choke devicee?

A
56
Q

Example of an internal blowout preventer?

A
  • float valve: will prevent upward flow but allow normal circulation to continue → often used to reduce backflow during connections
57
Q

What is a disadvantage of a float valve?

A
  • you can not read the drillpipe pressure at the surface
58
Q

What is ram to ram stripping?

A
  • When the hydril fails and the pipe is stripped into the well using the pipe rams
  • when the tooljoint reaches the upper pipe ram, the upper pipe ram is opened and then the tooljoint is allowed to pass → then upper pipe ram is closed and the lower opened to allow tooljoint to pass
59
Q
A

Drilling Engineering (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions