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Indicators | General behaviors |
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Total gas | Total gas should increase when an underbalanced drilling occurs in a gas-bearing formation. |
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Background gas | Background gas should increase with ROP. For a constant ROP, background gas is expected to increase as the pore pressure increases. |
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Connection gas and pump-off gas | Connection gas, swab gas, or pumps-off gas occurring may indicate that the pore pressure is higher than the ESD. |
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Gas cut mud | Gas cut mud is a sign of abnormal pore pressure and underbalanced drilling. |
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ROP | ROP increase may indicate the pore pressure gradient increasing. |
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Dxc | Gradual decrease in Dxc compared to its NCT may indicate the pore pressure gradient increasing (Figure 11). |
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Resistivity | Gradual decrease in resistivity compared to its NCT may indicate the pore pressure gradient increasing (Figure 11). |
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DT | Gradual increase in sonic transit time (DT) compared to its NCT may indicate pore pressure gradient increasing (Figure 11). |
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PWD and temperature | Sudden increase in PWD with increase of MWD temperature may indicate an influx or kick. |
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Mud volume | Mud pit volume increasing may indicate a kick. |
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Cuttings | Increase in percentage of cuttings may indicate wellbore instability or abnormal pore pressure. Splintery cavings may indicate underbalanced drilling, and large amounts of splintery and angular cavings indicate a wellbore collapse. |
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Hole fill | Hole fills (i.e., cavings falling in) after connections indicate wellbore instability and it may need to increase the mud weight. |
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High torque, overpull, tight hole, pack-off | Hole pack-off, overpull, tight hole, and increasing torque and drag are likely to be caused by a higher collapse pressure or higher pore pressure than the mud weight. It needs to increase the mud weight. |
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