Hidden Killers in Drilling Operations: A Guide to Common Fault Diagnosis and Prevention

Hidden Killers in Drilling Operations: A Guide to Common Fault Diagnosis and Prevention

I. In-Borehole Accidents

These problems occur inside the borehole, are difficult to observe directly, and are time-consuming and labor-intensive to handle, representing the greatest source of risk.

1. Sticking Pipe

Symptom: The drill string cannot move up or down or rotate; it is "locked" by the borehole wall.

Diagnosis:

* **Mud Skin Adhesion Sticking:** Occurs in formations such as mudstone and shale that are prone to water absorption and expansion. Pump pressure is normal or increases, and the drill string can circulate but cannot move. It usually occurs after the drill string has come to a standstill.

* **Keyway Sticking:** Occurs in well sections with large doglegs (sharp bends in the wellbore). It usually occurs after normal drilling, when the drill string is pulled up and gets stuck at a specific point; lowering it is normal.

* **Falling Object Sticking/Wellwall Collapse Sticking:** Sudden sticking occurs; pump pressure may increase (due to collapse material clogging the annulus) or remain normal.

Prevention:** Use high-quality drilling fluid to reduce water loss and form a thin, tough mud skin.

Optimize wellbore trajectory and control dogleg degree.

Maintain stable drilling fluid density and balance formation pressure.

During tripping, repeatedly ream the well in sections prone to narrowing or complex formations.

Keep the borehole clean and avoid cuttings bed accumulation.

2. Drill String Breakage

Symptoms: Sudden drop in torque and drill pressure, possible drop in pump pressure, and "jumping" of the jib or power head.

Diagnosis:

Fatigue Fracture: Drill string breaks under long-term alternating stress, starting from scratches or corrosion points.

Overload Torsional Fracture: The drill bit stalls in hard rock, and the torque momentarily exceeds the drill pipe's limit.

Wear and Piercing: The drill pipe is thinned by the formation and pierced, eventually breaking.

Prevention: Strictly implement drill string inspection procedures and regularly inspect and replace old drill strings.

Avoid rough operations such as sudden drilling or sudden pressure increases.

In highly abrasive formations, control the rotation speed and use drill pipe clamps.

3. Loss of Fluid in the Well

Symptoms: A sudden and rapid drop in the drilling fluid level in the wellbore, with reduced or no return.

Diagnosis:

* **Permeability Loss:** Slow, continuous drop in fluid level, commonly seen in loose sandstone.

* **Fracturation Loss:** Moderate drop in fluid level, commonly seen in formations with well-developed natural fractures.

* **Cavitation Loss:** Fluid level instantly "cannot be filled," with drilling fluid disappearing without return; this is the most severe type.

Prevention:** Conduct geological forecasting before drilling and prepare plugging materials in advance for potential loss-of-fluid zones.

* **Before entering a prone-to-loss zone, appropriately reduce the drilling fluid density and pump flow rate.

* **Use "bridging plugging" materials for plugging while drilling.**

4. Well Kick/Blowout

Symptoms:** The outflow rate of drilling fluid exceeds the inflow rate, the fluid level in the mud pit rises, and fluid overflows from the wellhead after pump shutdown. Diagnosis: Formation pressure exceeds wellbore fluid column pressure, causing formation fluids (oil, gas, water) to flow into the well.

Prevention: Precisely design drilling fluid density to always maintain bottomhole pressure slightly higher than formation pressure.

Strengthen on-site observation and promptly detect overflow indicators (this is the most critical early warning!).

Strictly adhere to well control procedures; immediately and correctly shut in the well upon detecting an overflow.

II. Equipment Failure-Related "Killers" Sudden equipment failure can directly lead to wellbore accidents and even personal injury.

1. Hydraulic System Failure

Symptoms: Slow and weak actuator movement, severe system overheating, and abnormal noise.

Diagnosis:

Main pump wear: Insufficient flow and pressure.

Hydraulic oil contamination: Causes valve sticking and oil circuit blockage.

Damaged seals: Internal and external leakage, preventing pressure build-up.

Prevention: Regularly filter or replace hydraulic oil to maintain oil cleanliness.

Regularly check hydraulic oil level and temperature.

Promptly identify and address leaks.

2. Braking System Failure

Symptom: The main winch or feed system fails to brake, resulting in "drill slippage" or "drill blockage."

Diagnosis: Excessive brake pad wear, air ingress into the hydraulic braking system, or seal failure.

Prevention: Check brake pad wear daily and replace promptly.

Regularly bleed air from the braking system.

Routinely test brake performance before hoisting and during descent.

3. Power System Failure

Symptom: The engine or motor suddenly stops, causing a complete power loss on board.

Diagnosis: Fuel system malfunction, electrical problems, overload protection, etc.

Prevention: Perform routine maintenance to ensure clean and adequate fuel, engine oil, and coolant.

Regularly check batteries, cables, and connectors.

Avoid prolonged overload operation of equipment.

III. Human and Technological "Killers"

1. Drill Hole Deviation

Symptom: The actual wellbore trajectory deviates significantly from the design.

Diagnosis: Excessive drilling pressure, improper drill string assembly, or improper operation in formations with alternating soft and hard surfaces.

Prevention: Use full-hole drill string assemblies or pendulum drill string assemblies for anti-deviation.

Follow the "lifting" (light pressure, quick rotation) principle, especially at formation interfaces.

Perform single-point or multi-point deviation measurements regularly to monitor the wellbore trajectory in a timely manner.

2. Deterioration of Mud Performance

Symptoms: Uncontrolled adhesion and shearing, excessive water loss, excessively high solids content.

Diagnosis: Formation contamination, incorrect or ineffective treatment agents, improper use of solids control equipment.

Prevention: Regularly test mud performance and adjust it promptly according to formation changes.

Effectively use solids control equipment such as vibrating screens, desanders, and desilters.

Scientifically proportion mud chemicals and avoid blindly adding them.

Core Safety Culture: Building a "Prevention-First" Defense Line

Strictly implement the inspection system: Operators, foremen, and engineers should conduct pre-shift, during-shift, and post-shift inspections to resolve minor problems at an early stage.

Strengthen personnel training: Ensure every team member understands drilling principles, equipment performance, and malfunction symptoms, avoiding becoming "operators who only press buttons."

Establish operational standards: Develop standard operating procedures for critical operations (such as tripping in and out of the well, connecting single sections, and well control) and strictly adhere to them.

Respect downhole conditions: Any abnormal parameter changes (pump pressure, torque, sand return) are "signals" from downhole and must be investigated immediately; there should be no room for complacency.

Conclusion: Conquering the "invisible killers" in drilling operations relies not on luck, but on a rigorous system engineering approach: excellent equipment, scientific processes, meticulous management, and a high degree of responsibility. Only by implementing preventative measures effectively can safety, efficiency, and effectiveness be maximized.