Real-Time Pore Pressure Detection: Indicators and Improved Methods

Table 1

Real-time indicators of abnormal pore pressures.

Indicators	General behaviors
Total gas	Total gas should increase when an underbalanced drilling occurs in a gas-bearing formation.
Background gas	Background gas should increase with ROP. For a constant ROP, background gas is expected to increase as the pore pressure increases.
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.
Gas cut mud	Gas cut mud is a sign of abnormal pore pressure and underbalanced drilling.
ROP	ROP increase may indicate the pore pressure gradient increasing.
Dxc	Gradual decrease in Dxc compared to its NCT may indicate the pore pressure gradient increasing (Figure 11).
Resistivity	Gradual decrease in resistivity compared to its NCT may indicate the pore pressure gradient increasing (Figure 11).
DT	Gradual increase in sonic transit time (DT) compared to its NCT may indicate pore pressure gradient increasing (Figure 11).
PWD and temperature	Sudden increase in PWD with increase of MWD temperature may indicate an influx or kick.
Mud volume	Mud pit volume increasing may indicate a kick.
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.
Hole fill	Hole fills (i.e., cavings falling in) after connections indicate wellbore instability and it may need to increase the mud weight.
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.