Essential Well Control Knowledge for Drilling Supervisors
Ⅰ.The "Three Early Actions" in Well Control
1. Early Detection: The earlier a kick is detected, the more favorable it is for shut-in control, resulting in lower wellhead pressure and reduced risks of borehole instability and fluid loss, enhancing safety.
2. Early Shut-In: Upon detecting a kick or suspecting its possibility (even with unclear signs), all operations must cease immediately, and the well should be shut in according to procedures for verification.
3. Early Handling: Accurately record kick data (shut-in drillpipe pressure, shut-in casing pressure, and mud volume increase), develop a kill plan, and prepare weighted mud for throttling operations.
Ⅱ.Implementing the Sitting Post System to Detect Kicks Early
Kicks exhibit visible signs that can be predicted and identified through diligent observation and accurate judgment via a rigorous sitting post system.
Requirements: From 100 meters before penetrating the oil/gas layer to completion, dedicated personnel from both the drilling and logging teams must monitor the wellhead and mud pit levels every 15 minutes. Indicators of a kick include:
During Drilling:
(1) Increased flow rate at the drill bit;
(2) Mud overflow after pump shutdown;
(3) Rising mud pit level;
(4) Increased mechanical drilling speed or "air drilling";
(5) Decreased pump pressure with increased pump rate;
(6) Changes in mud properties (density, viscosity);
(7) Variations in drillstring weight;
(8) Abnormal gas logging values;
(9) Oil bubbles or odors in the mud tank.
During Tripping Out:
(1) Mud overflow;
(2) Inability to fill the mud tank;
(3) Pumped volume less than the volume of the tripped-out drillstring.
During Tripping In:
(1) Mud overflow upon stopping downward movement;
(2) Returned mud volume exceeding the volume of the lowered drillstring.
When the Hole is Empty:
(1) Mud overflow;
(2) Rising mud pit level.
Ⅲ.Correct Handling of Detected or Suspected Kicks
Immediate Shut-In: If a kick is confirmed, shut down the well immediately.
Suspected Kicks: Shut down the well for observation. Timely shut-in prevents further invasion of formation fluids, avoids mud contamination, and maintains operational control.
Ⅳ.Post-Shut-In Handling
Prolonged shut-in without action is prohibited. Monitor standpipe and casing pressures and respond accordingly:
1. Both pressures zero: Resume circulation and closely observe mud flow.
2. Standpipe pressure zero, casing pressure non-zero: Throttle circulation to displace contaminated mud until casing pressure drops to zero.
3. Both pressures non-zero: Perform throttling kill. Do not open the blowout preventer until pressure conditions are met.
V.Correct Shut-In Procedures
Hard Shut-In:
Procedure: Detect kick → Immediately close the blowout preventer.
Characteristics: Fast action, minimal fluid entry, but strong water hammer impact on equipment.
Soft Shut-In:
Procedure: Detect kick → Open throttle channel → Close blowout preventer → Close throttle valve.
Characteristics: More actions, longer duration, weaker water hammer impact.
Ⅵ.Determining Maximum Allowable Casing Pressure
The maximum allowable casing pressure is the minimum of:
1. Blowout preventer rated pressure;
2 80% of the minimum casing collapse strength;
3 Formation breakdown (leak-off) pressure.
Ⅶ.Formation Breakdown (Leak-Off) Pressure Determination
Conduct a leak-off test using a cement truck or drilling pump:
Steps:
1. Test below the first sandstone layer after the casing shoe.
2. Predict test layer pressure based on adjacent well data or experience.
3. Verify pressure gauge accuracy and pipeline integrity.
4. Fill the well with mud, close the blowout preventer, and pump mud at low pulse rates.
5. Record pump pressure vs. volume until the pressure deviation point is identified (leak-off pressure, Pl).
6. Calculate formation breakdown pressure and determine maximum allowable mud density.
Ⅷ.Principles of Well Killing
Based on the "U-tube principle," balance bottomhole pressure by controlling annulus and drillpipe pressures via throttling.
Ⅸ.Well Killing Methods
Driller's Method (Two-Cycle Kill):
1. First cycle: Circulate original mud to displace contaminated fluid.
2. Second cycle: Pump weighted mud to restore pressure balance.
Engineer's Method (Single-Cycle Kill):
Directly pump weighted mud in one cycle while controlling backpressure.
Parallel Weighting:
Caution: High risk of formation damage due to unknown pressures. Use only in emergencies or without blowout preventers.
Ⅹ.Common Causes of Shut-In Failure
Insufficient surface casing depth or poor cementation.
Blowout preventer failure or inadequate pressure rating.
Incorrect shut-in procedures (e.g., using hard shut-in for gas kicks).
Delayed shut-in leading to severe mud contamination.
Improper installation or fixation of well control equipment.
Ⅺ.Core Requirements for Blowout Preventer Installation
Install tested, pressure-rated blowout systems.
Attach throttling and kill manifolds of matching pressure ratings.
Route mud recovery and vent lines to the mud pit and field edge, respectively.
Ⅻ.Remote Control Panel Standby Conditions
Fluid level above minimum marker.
Accumulator nitrogen pressure: 7±0.7 MPa.
Accumulator pressure: 18.5–21 MPa.
Manifold and annulus pressure: 10.5 MPa.
XIII.Preventive Measures for Leaky Formations
Add lost circulation material (LCM) to mud before drilling.
Enhance sitting post monitoring before reaching leaky zones.
Use small-volume circulation tanks for better liquid level observation.
XIV.Common Mistakes in Well Control Operations
Failing to shut down promptly upon kick detection.
Forcing tripping to preserve the drillstring, worsening the kick.
Delaying shut-in to complete drilling.
Ignoring prolonged gas kick risks.
Using parallel weighting without sufficient pressure data.