kick_causes

Kick Causes

n Definition of Kick.n Definition of Blowout. n Kick Condition. n Kick Causes.

– No keeping the hole full. – Low density drilling fluids. – Overpressure.– Lost Circulation. – Swabbing.– ECD.– Gas / oil / water cut.– Loss of riser.

Kick Causes

At the end of this section you should be able to:

n Explain the concepts of: kick and blowout. n Describe various causes of a kick.

Well Kicks and BlowoutsWell Kicks and Blowouts

Kick:Kick: is an influx of formation fluids into the wellbore.

Well Kick

Blowout: Blowout: a surface uncontrolled flow of gas, oil or water from the wellbore, generally due to mechanical failure and / or human error. Underground Blowout: Underground Blowout: an uncontrolled flow of formation fluids in the wellbore from a higher pressure zone into a lower pressure zone.

Blowout

Underground Blowout

Kick CausesKick CausesKick Condition:Kick Condition: there is only one conditioncondition that allows a kick to occur.

The pressure in the wellbore The pressure in the wellbore becomes less than the pressure in the formationbecomes less than the pressure in the formation

Kick Causes:Kick Causes: the following are situations which can cause the wellbore pressure to be less than formation pressure, leading to a kick. These include:

n No keeping the hole full. n Low density drilling fluids.n Overpressure.n Lost Circulation.

n Swabbing.n ECD.n Gas / oil / water cut.n Loss of riser.

Kick CausesKick Causes

n No keeping the hole full. During tripping operations, as the drill string comes out of the well, the level of drilling fluid in the annulus drops by a volume equal to the volume of drill string removed. If the fluid level is allowed to drop too far, the hydrostatic pressure on the formation is reduced below formation pressure, which allows formation fluids to enter the wellbore.


n Low mud weight. Accidental dilution of drilling fluids with make-up water in surface pits, addition of drilled-up low density formation fluids into the mud column or weighting material settling out can cause the density of the drilling fluid to drop below the formation pressure.

n Overpressure.In some cases, abnormal pressure reservoirs are encountered while drilling with low-density drilling fluid. – Permeability barrier or rapid deposition prevents the formation water from

escaping causing above normal pressure.– Faulting, a normally pressured zone is uplifted to a higher depth creating

abnormal pressure at that depth.– Depth and structure changes within a reservoir.– Charged up zone due to channeling along a poorly cemented casing on a

near by well.


n Lost Circulation. Loss of drilling fluid to the formation can be caused by: – Formation Type: unconsolidated or

highly permeable low pressure formations, natural fractures or cavernous formations.

– High mud weight.– Surge pressures: running in hole

too fast with high gel strengths (possibly worse when running casing).

– High ECD.


n Swabbing.Occurs when the drill string is pulled from the well, producing a temporary bottomhole pressure reduction. This can lead to an underbalanced condition, allowing formation fluids to enter the wellbore below the drill string. Swabbing mainly caused by: – Balled-up bottom hole assembly. – Pulling pipe too fast.– Poor mud properties or high gel strength.– Heaving or swelling formations.– Large OD tools (small annular clearance).


n ECD. In some cases the drilling fluid density acting over the borehole in dynamic conditions is enough to contain the formation fluid from enter the wellbore, however when the ECD is removed the density of thedrilling fluid drops below the formation pressure causing a kick.

n Gas / oil / water cut.When the bit penetrates a porous formation, the fluids contained in the formation (gas, oil, or water) escape and mix with the drilling fluid. – Gas cutting: the presence of large volumes of gas in the returns can

cause a drop in the average density and hydrostatic pressure of the drilling fluid.

– Oil or saltwater cutting: oil and/or saltwater can also invade the wellbore from cuttings and/or swabbing, reduce the average mud column density and cause a drop in mud hydrostatic.


n Loss of Riser.

On floating unit operations, the loss of the drilling fluid column in the riser results in a reduction of hydrostatic pressure in the wellbore and may cause the loss of primary well control if an adequate riser margin is not maintained. This loss of riser hydrostatic column could be due to: – Accidental disconnect.– Riser damage.– Displacement of the riser with seawater.

kick_causes

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