Improved Lost Circulation Well Control Techniques
Introduction
Lost circulation is an important
well control problem which occurs during drilling and completion operations.
This happens when drilling fluids flow into highly permeable or fractured
formations instead of coming back to the surface. A poorly controlled lost
circulation can cause high-impact consequences in terms of well control,
formation damage, and even blowouts. 2Execution of effective lost circulation
well control techniques in the well is key to maintaining wellbore integrity
and maximizing achievable drilling performance. Here are the top five
strategies for effectively managing drilling fluid losses, maintaining wellbore
stability techniques and ensuring a high probability of drilling success.
Theory: Lost circulation well control
Lost circulation is when drilling
fluid is lost to subsurface formations rather than returning to the surface. It
is usually found in reservoirs with naturally broken formation, uncemented
sands, caverns and others with high permeability. Losses can be classified
into: depending on severity
–Seepage losses (10 bbl./hr.)
Partial losses (10 to 500 bbl./hr.)
–Significant losses (greater than
500 bbl./hr.)
Total losses (full blown loss of
returns)
Coherently formation pressure
management with early detection and proactive mitigation (for example, some
reconciliation with the solution of excessive fluid losses) are necessary for
effective well control strategies.
Major Considerations for Lost Circulation in Well Control
1. Simultaneously Converted into Flow in the Same Zone
Lost circulation is a significant
phenomenon associated with the oilfield where the drilling fluid does not
return to the surface due to permeable formations, fractures, or caverns; every
year during drilling operations, it is estimated that nearly 10% of the spent
fluid is lost in the reservoir. When lost circulation occurs in a reservoir and
the operation shifts to flow, a strict method of managing the well is applied
through a series of drifting techniques involving the use of lost circulation
materials (LCM) that can be used in the well.
–Pump in a lower density
control/weight (C/W) fluid to fill the drill pipe.
–Document and track _standpipe
pressure (SPP)_hits.
Set the density of the C/W fluid by
formation pressure management calculated from standpipe pressure.
Keep well control strategies in
check by maintaining the hydrostatic pressure balance within the safe margin to
prevent loss of capacity or blowouts
2. Inadequate Density of Completion Fluid Resulted in Lost Circulation in Other Hole Sections
Improper completion fluid density
can cause lost circulation, leading to wellbore instability techniques.
If hydrostatic pressure balance is
greater than reservoir pressure, lower the completion fluid density to balance
the reservoir pressure.
Check the mud weight and adjust the
weight as required in order to maintain a balanced wellbore stability,
Mitigate losses by utilizing
wellbore strengthening techniques.
3. Lost Circulation is Here to Stay for Other Subsurface Hole Sections
In cases where, for whatever reason,
drilling fluid losses have occurred (due to the use of an inappropriate
completion fluid density) but the wellbore hydrostatic pressure appears to be
balanced, you need to take certain steps.
Add lost circulation materials (LCM)
to the killing fluid in order to seal fractures and permeable zones.
Keep circulation rates relatively
high, consistent with placement of LCM.
Good LCM is made up of a mixture of
fibrous, granular, and flake material
4. Excessive Annulus Circulation Pressure causing Lost Circulation
Higher annulus circulation pressure results
in lost circulation well control complications.
Lower mud pump rate to lower the equivalent circulating density (ECD).
— Reduce the rate of penetration
(ROP) to reduce surge and swab pressures.
Fill lost circulation materials
(LCM) to C/W fluid to close the formation and restore wellbore stability
techniques;
Continuous or managed pressure
drilling (MPD) techniques for dynamic management of formation pressure.
5. Loss Zone under Reservoir with Blowout on Top
When there is a loss zone beneath
the reservoir, covered by a blowout above and fluid losses during drilling, the
situation becomes complicated.
Initial control losses with cement
plugging for lost circulation, bridge plugs or weighted pill fluids.
Run well killing operations at the same
time to balance off pressures.
Use a combination of wellbore strengthening methods and dynamic circulation methods to regain control.
Advanced techniques are routinely employed to improve lost circulation well control and minimize drilling fluid losses:
1. Techniques used for strengthening the wellbore
The 13 wellbore strengthening methods
are based on increasing the formation fracture resistance, reducing fluid loss.
Use toughened LCM blends to
reinforce fragile formations.
Use stress cage techniques to build
stress response around the wellbore.
Use deformable sealing materials for
crack arrest.
2. Managed Pressure Drilling Format: Managed Pressure Drilling (MPD)
Managed pressure drilling (MPD) is a
sophisticated drilling technique that assists in dynamic formation pressure
management.
Allows accurate control of
bottomhole pressure (BHP).
Minimizes risk associated with well control
strategies as the system maintains a near-balanced pressure condition.
Uses better pressure regulation with
automated choke systems
3. Cementing to Control Severe Losses
For total loss circulation cases,
lost circulation cement plugging is applied to barrier hostile formation.
—properly calculate cement volume to
avoid over placement.
If coverage is not attainable, apply
multiple staged cementing.
Give enough curing time so that it
is stable for operations.
4. Cross-linked Polymer Gels
Cross-linked polymer gels are
effectively used for blocking large fractures, including formations.
Provides high viscosity and rapid
expansion for formation plugging.
Wellbore stability approaches that
give long-term durability.
−Usually applied in
high-permeability and fractured zones.
Lost Circulation Prevention Best Practices
Generally speaking, preventing lost
circulation well control problems is better than reducing their effects. Follow
these best practices:
–Pre-drilling assessment: Prior to
drilling, perform extensive geological studies to anticipate the occurrence of
loss of drilling fluid.
Correct mud density choice: Apply
density within formation pressure control.
Prevention of Lost Circulation in
Drilling Pit With Details on Lost Circulation Materials (LCM) and Mud System
Treatment
Constant drilling parameters:
Control ROP, pump speed and ECD as they will help decrease pressure
fluctuations.
Monitoring and early detection: Make
use of real-time downhole monitoring tools to monitor early for well control strategies.
Conclusion
Lost circulation well control is a difficult
problem in well control but must be anticipated and executed properly.
Operators can treat and prevent drilling fluid losses by avoiding the root
causes and applying best practices, including the ability to adapt fluid
density, add materials to help with lost circulation to support the well, and
employing new advances like MPD and wellbore strengthening techniques. Wellbore
stability techniques and cement plugging for lost circulation operations are
maintained through proper planning, real time monitoring and adaptive formation
pressure management strategies.
Incorporating these insights and
techniques empowers oil and gas professionals to reduce lost circulation well
control risks and improve the effectiveness of well control strategies.
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