Empty Hole Well Control
In drilling and well intervention, the operations involved in empty hole well control is one of the most critical, helping to maintain wellbore stability despite unpredicted gas invasions. Using the right methods helps prevent well kicks and blowouts, and damage to formations. This paper discusses categories of empty hole WHC, best practices, and techniques to control wellbore pressures.
1. Definition and Importance
The wellbore is Open (no
pipe in the hole), and gas invasion occurs, Empty hole well control is
required. This is done to ensure that formation pressure and wellbore
hydrostatic pressure are in equilibrium and thus avoid an uncontrolled influx
and a potential hazard.
1.1. Hydrostatic Pressure Greater Than the Formation Pressure
Invasive gas may migrate
through the borehole system and up to the surface, as the wellbore hydrostatic
pressure becomes greater than the formation pressure. Then, the subsequent steps
shall be taken:
• With the well shut in, venting gas through
the bleed choke valve.
• Section by section strip in pipe
to circulate and remove gas pockets.
1.2 Hydrostatic Pressure Drop and a Well Kick
An analysis of a well kick:- A well kick
happens whenever the gas invasion causes lower the fluid density such that the
hydrostatic pressure is less than the formation pressure. This can be achieved
by immediate empty hole well control measures which will guarantee wellbore
stability.
1.3 Wireline Logging Overflows Management
If overflow signs are observed during
wireline logging, the following actions are suggested:
• Bring the wireline back up to the
surface as fast as possible.
• If retrieval is not possible, shut
the well in by shearing the wireline using the shear ram blowout preventer
(BOP) and securing the well.
1.4 Well Kill Methods Selection
Various well kill methods can be
employed depending on downhole conditions:
Stripping-In Well Kill
To load an open-ended string and
strip it into the well.
o Affix a steering implement to the
low end of the string.
o Place a 1-way valve at the bottom
of the string to regulate the flow of fluid.
Volumetric Well Kill Method
o Use mainly of water-based mud
(WBM) systems.
o When the gas arrives at the
wellhead, saturated saltwater is the recommended displacing fluid.
o Overcome formation breakdown and
maintain wellhead pressure — especially in low-pressure high-permeability
sections or at casing shoes.
o Oil-based mud (OBM) systems are
not recommended for this method because gases can have a tendency to compress
and circulate inefficiently.
Bullhead Method
o The bullhead method can be
utilized if the conditions of the formation allow.
o Gas invasion is expelled back into
the formation as a plug flow.
o Intermittent gas squeezing based
on formation pressure and absorption capacity to prevent excessive formation
loss.
1.5 Finalization of Alpha Strike
Following the initial well kill
operation:
• Drill in hole (DIH) to the casing
shoe.
• Shut in the well to circulate out
residual gas.
• Keep drilling the hole section by
section until the gas pockets are all cleared.
Operational lessons in Empty Hole
Well Control
Preventing Gas Migration
• Pressure fluctuations are also
monitored for early signs of gas influx.
• Choke valves should be utilized to
safely vent gas.
• Use appropriate fluid management
to preserve hydrostatic balance.
Equipment Readiness
• Confirm BOPs and shear rams are functional.
• Thoroughly prepare stripping and bullhead
tools.
• Use the reliable one-way valves to
avoid reverse passage of fluid.
Mud System Selection
• Water-based muds (WBMs) shall be
made up with suitable salinity to the control gas (expansion).
• Disadvantage of oil-base muds
(OBMs) for volumetric methods with regard to gas compressibility
Operational Efficiency
• Train personnel to manage
emergency well control situations.
• Review rig crew and well control
specialist communication.
• Monitor pressure and fluid
movements with real-time data.
Conclusion
Empty hole well control is an
integral aspect of drilling and well intervention. Gas migration and formation
pressure imbalances can be ensured with proper well kill techniques such as
stripping-in, volumetric, and bullhead. Best practices in wellbore preparation and
keeping the mud system operationally ready are essential for the success of
operations.
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