Indicators of Formation Pressure Changes During Drilling Operations

Identifying signs of formation pressure changes is crucial for drilling operations, ensuring the safety and efficiency of the process. Drilling team on the rig plays a vital role in recognizing and communicating these indicators to supervisors. The following key signs should be closely monitored, acknowledging that some may have alternative interpretations.

1. Change in Rate of Penetration:
   • An alteration in drilling speed is a prominent indicator of potential formation pressure changes.
   • Increase or decrease in drilling rate may suggest drilling into higher-pressure zones.
   • Abrupt changes, known as drilling breaks or reverse breaks, can signal transitions into abnormal pressure areas.
2. Cuttings Changes: Shape, Size, Amount, Type:
   • The characteristics of rock cuttings provide valuable insights into formation conditions.
   • Size, shape, and amount alterations may signify changes in pressure differentials, bit conditions, or formation types.
3. Torque/Drag Increase:
   • Gradual increases in rotary torque and drag may indicate larger amounts of cuttings entering the wellbore.
   • These changes can result from the bit encountering softer formations or increased formation pressure.
4. Sloughing Shale/Hole Fill:
   • As formation pressure surpasses mud column pressure, shale may slough off the wellbore walls.
   • Sloughing shale can lead to complications such as tight holes and equipment becoming stuck.
5. Gas Content Increase:
   • Elevated gas content in drilling fluid is a reliable indicator of abnormally pressured zones.
   • Differentiate between drill gas, connection gas, and background gas to interpret pressure changes accurately.
6. Variations from “d” Exponent:
   • The “d” exponent method offers a simple means to detect abnormal pressures.
   • Changes in the slope of the “d” exponent line on a plot can indicate pressured zones, aiding in mud weight predictions.
7. MWD and LWD:
   • Measurement while drilling and logging while drilling tools provide real-time information on drilling conditions.
   • Parameters such as resistivity, torque, and pressure can help identify changes in drilling conditions and influx detection.
8. Shale Density Decrease:
   • Deviations from the predicted increase in shale density can suggest higher pore pressure zones.
   • Challenges in measuring shale density should be considered when interpreting results.
9. Flowline Temperature Increase:
   • An abnormal increase in flowline temperature can indicate a transition zone or higher pressure.
   • Temperature curves offer additional insights, considering factors like circulation rate and mud properties.
10. Change in Chloride Content:
    • Alterations in chloride ion content within drilling fluids serve as a valid pressure indicator.
    • Monitoring chloride content changes requires meticulous control of mud checks for accurate interpretation.

Rig personnel must be vigilant in recognizing these indicators, as prompt communication and appropriate responses are essential to managing the challenges posed by formation pressure changes during drilling operations.

References 

Cormack, D. (2007). An introduction to well control calculations for drilling operations. 1st ed. Texas: Springer.

Crumpton, H. (2010). Well Control for Completions and Interventions. 1st ed. Texas: Gulf Publishing.

Grace, R. (2003). Blowout and well control handbook [recurso electrónico]. 1st ed. Paises Bajos: Gulf Professional Pub.

Grace, R. and Cudd, B. (1994). Advanced blowout & well control. 1st ed. Houston: Gulf Publishing Company.

Watson, D., Brittenham, T. and Moore, P. (2003). Advanced well control. 1st ed. Richardson, Tex.: Society of Petroleum Engineers.

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