Kick Warning Signs: What Drillers Need to Watch For
Kick warning signs are crucial indicators that help a driller recognize when the well is at risk of going underbalanced, which could lead to a kick (influx of formation fluids into the well). These warning signs fall into three categories, as defined by the API:
- Offset Well Information
- Physical Response Indicators
- Chemical and Technical Indicators
1. Offset Well Information
Offset wells refer to wells drilled in the same area before, providing valuable data on the formation and pressures. Information from offset wells can give advance warning of potential kick risks. Key data includes:- Formation pressure gradients: Information on pressure zones and their depths can indicate areas that may be capable of flowing.
- Fracture gradients: Data on the fracture pressure of the formations can warn of potential loss zones.
- Permeability: Permeability data shows how easily fluids can enter the wellbore, indicating potential kick risks if the formation is highly permeable.
2. Well Physical Indicators
Physical indicators are warning signs that can be observed directly during the drilling process. These indicators are often picked up through close monitoring of drilling parameters, mud monitoring systems, and flow line data. Physical warning signs include:- Drilling break: A sudden change in the rate of penetration can signal that you’re drilling into an under-compacted shale or a high-pressure zone.
- Lost circulation: If mud returns are lost to the formation, it indicates that hydrostatic pressure is being reduced, putting the well at risk of going underbalanced.
- Pump pressure/speed variations: If the pump pressure or speed fluctuates, it could suggest that a kick has occurred or that the well is drilling sloughing formations.
- Temperature gradient increase: Higher temperatures can indicate you are drilling into high-pressure or gas-bearing formations, or under-compacted shale.
- Reduction in mud density: A decrease in mud density might suggest an influx of less dense formation fluids, increasing the risk of a kick.
- Gas levels increase: Rising levels of gas after connections (connection gas) can indicate increasing formation pressures. Similarly, trip gas after circulating can signal that hydrostatic pressure is decreasing.
- Tight hole/sloughing: When the hole becomes tight or sloughing, it can suggest that you’re encountering high-pressure formations.
- Changes in cuttings: Significant changes in the size, shape, or quantity of the drill cuttings can indicate that you’re drilling into high-pressure formations.
3. Chemical and Technical Indicators
Chemical and technical indicators are usually monitored by specialized personnel such as mud engineers and mud loggers. These indicators help detect any subtle changes that might indicate a kick. They include:
- Chloride changes: Variations in chloride levels in the mud can point to a potential water kick.
- Oil shows and staining: If oil is observed on the cuttings or shaker screens, this can indicate an influx of formation fluids.
- Gas shows: Increased gas readings on the gas chromatograph are a common sign of formation fluids entering the wellbore.
- Formation fluid in mud: An influx of formation fluid into the mud can cause a decrease in mud density, possibly affecting its viscosity and gel strength.
- Shale density reduction: A decrease in shale density observed on logging while drilling (LWD) tools may signal under-compacted shale, which could be under pressure.
- Resistivity changes: Changes in resistivity on LWD logs can indicate changes in formation fluid properties.
- Decrease in the “d” exponent: This occurs when drilling through consistent shale beds and can indicate under-compacted shale, increasing the likelihood of a kick.