Killing Method: Bull heading Method
Bull heading is a shut-in well
control technique to be used to pump fluids underground without returns. This
method is typically used in situations where circulation cannot be performed,
such as when a packer in the wellbore is set, or when an annular influx blocks
standard circulation. The bullhead is an operation focused on forcing
kill-weight fluid into the formation, displacing the influx and controlling the
well.
This article will describe the bull heading operation in details giving its general requirement, alternate
conditions, preparation steps and the operational procedure. Also discussed will
be important safety concerns and best practices for implementing them safely
and safely.
Bull heading Operation General Requirements
During a bull heading operation, various important parameters need to be assessed to ensure effective well control.
Assessment of Key Factors
Prior to undertaking a bull heading operation, the following parameters must be, established and assessed:
ESTIMATED MAXIMUM SURFACE PRESSURE –
It is important to know how high a pressure the well might see to avoid
equipment failure.
Type of influx – Knowing if the
influx gas, oil, or water, will help define the kill fluid and strategy.
Squeeze mud ahead of influx — If the
influx has migrated or has been circulated up, it is important to squeeze mud
ahead of the influx to correctly displace it.
Mud gas separator capacity –
Evaluation of separator capacity, vent line size and killing rate effect on
system
Formation fracture risk –
Establishing the risk of formation fracture during routine killing operations
to avoid unintentional losses.
Formations Data Training
As a result, contractors must estimate
the pressure required to fracture formation via its strength at the kicking
zone. So the applied pressure is guaranteed, never exceeds the safe limit, etc.
Pressure Data Recording
All pressure data should be
documented during well killing But when everything is at stake, and you need to
have that well under control as soon as possible, data acquisition might go to
the background because safety is your priority.
Proper Use of Killing Lines
When installed according to the
pre-processing program, both the inlet killing line and the outlet killing line
must use a hard line.
Fluids Killing Compatibility
Therefore, the kill fluid shall be
formation compatible to minimize formation damage and fulfill geological and
operational parameters.
Adequate Kill Fluid Volume
The kill operation and any
subsequent testing or fracturing will require sufficient well-killing fluid
available on location.
Pressure Assessment
Maximum allowable treating pressure
is to be determined by a complete review of working pressure for all components
(i.e., what the well head and respective equipment down hole can withstand.
Gas Invasion Monitoring
No gas is leaking into the well,
which must be verified. Gas shall be routed to the poor boy degasser and flare
line bled, with personnel at flare outlet.
Venting and Ignition Planning
A ventilation and ignition plan
should be developed that is based on the wind direction. If hazardous gases
such as H2S are present in the emitted gas, then they should be flared.
Hazardous Gas Monitoring
Monitoring for toxic gas (natural
gas, H2S, CO2) should be continuous and the data recorded. Make sure if this is
the case, proper signage and barricades are placed to mitigate risks.
Fire and Explosion Prevention
Open flames and hot work shall be
prohibited.
Ensuring correct protection of
electrical facilities.
Any other potential secondary
hazards should also be neutralized (i.e. relocating flammable items like fuel
tanks upwind of the explosion).
Conditions Under Which Bull heading is Used
Bull heading is employed throughout any situation where normal circulation is not feasible — for example: Tubing in the well with a packer set –The tubing is not communicated with annulus.
Tubing in well, influx in annulus –
Cannot circulate through tubing.
No tubing is present in the well.
Influx is already in the casing, which makes bullheading the simplest and most
rapid.
Depleted formations — With low
formation pressure circulation is challenging.
H2S Influx – Surface handling is
dangerous.
Surprisingly high surface pressures
– Results in device operating beyond stress levels.
Constrained casing pressure –
Bull heading may be required due to well pressure.
Minimize or mitigate risk to rig and
equipment due to high surface pressures – Standard killing methods may pose
significant danger
Training for Bull heading Operation
Preparation is the key to safe and
effective bull heading. You should do the following steps:
Pre-job Safety Meeting
Discuss its responsibilities,
operational risks and safety control measures.
Confirm that everyone involved
understands the steps to operate and the safety precautions.
Killing lines and valves inspection
Assurance Line Validate killing line
and valve system integrity and work before starting
The making of Kill Fluid and Spacer
High volumes of well-killing fluid
and spacer should be provide in accordance to the well-killing program.
Clearing High-Pressure Areas
Prior to operation, ensure
evacuation of non-essential personnel from high-pressure areas.
Procedure for Bullheading Operations
Systematic bullheading needs to be
followed to make bullheading a success. The key steps include:
Calculate pump rate and total volume
Loss of circulation occurs in the
geological environment when the pump rate surpasses the upward path taken by
the gas bubbles.
Pressure Testing
Balance systemby connecting the pump
line and performing a pressure test.
Control Bleed-Off Pressure
Bleed off pressure in stages prior
to kill in order to stabilize conditions.
Pump Spacer
As per program requirement, pump a spacer
fluid to ensure an effective kill operation.
Ongoing Pressure Assessment
Keep a check on the pressure during
the entire operation.
Keep pressure less than the minimum
working pressure of wellhead equipment, casing strength, and formation fracture
pressure.
Flow Check and Observation
To ensure the well is under control,
make sure the outlet is free of overflow.
Conclusion
Well killing is a vital operation
process when conventional circulation is impossible, and with bull heading
method be used extensively. Due to the adherence of strict safety procedures,
careful assessment of the critical parameters during the well control operation
ensures that this method provides a successful well control operation with
minimum harm to formation and operational hazards.
The Bull heading method is one of the important and mostly applied techniques on well killing, oil and gas well control,
kill-weight fluid, formation fracture pressure, how to handle H2S gas, and well
intervention for
well control operations guidance.
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