1. Sudden Increase in Pit Volume: During drilling operations, the drilling fluid (mud) is circulated through the wellbore to remove cuttings and maintain wellbore stability. If there is a sudden and significant increase in the volume of drilling fluid returning to the surface, it could indicate the influx of gas from the formation into the wellbore. This increased pit volume is often the first indication of a gas kick.
2. Drop in Mud Weight: The presence of gas in the drilling fluid reduces its density, resulting in a decrease in mud weight. This drop in mud weight can be monitored using mud logging equipment or by simply measuring the mud weight in the mud pits. A rapid and unexpected reduction in mud weight can be a sign of a gas kick.
3. Change in Flow Rate: The influx of gas can alter the flow rate of the drilling fluid returning to the surface. An increase in flow rate, known as "flowline surge," may occur as gas expands and pushes the drilling fluid up the wellbore. Conversely, a sudden drop in flow rate might indicate that gas is blocking the flow of drilling fluid and creating a partial obstruction in the wellbore.
4. Gas Readings: Real-time gas monitoring systems are used at the wellsite to detect the presence of hydrocarbons, including gas. These systems continuously analyze the drilling fluid and air near the rig floor for the presence of combustible gases. An increase in gas readings or alarms triggered by the gas detectors can indicate a gas kick.
5. Mud Properties Changes: The presence of gas in the drilling fluid can affect its rheological properties, such as viscosity and gel strength. These changes can be detected by monitoring the drilling fluid's properties at the surface and comparing them to baseline values. Deviations from the expected mud properties could indicate gas contamination.
6. Well Control Indicators: In the event of a significant gas influx, specific indicators related to well control may become evident. These include difficulty in maintaining wellbore pressure, inability to circulate drilling fluid, or even uncontrolled flow of gas and drilling fluid from the well. Prompt recognition and management of these indicators are critical to prevent a full-blown blowout situation.
When any of these indications are observed, the drilling crew must take immediate action to control the well, ensure crew safety, and prevent environmental damage. Procedures typically involve shutting in the well, increasing mud weight, and implementing appropriate well control techniques to regain control of the situation.
