Lost Circulation Well Control Techniques

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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