Higher than predicted pore pressure during completion operations lead to an influx after gravel pack operation
After finishing running lower completion with gravel pack, service tool was changed to reverse position, in order to place a lighter completion fluid on the annular. Despite the density of the lighter fluid being planned based on maintain overbalance to the highest anticipated pore pressure, when finishing displacing the lighter fluid, a gain was observed during flow check. This alert shows how important is to perform risk assessment of potential for having pressure higher than virgin sand pressure.
The lower completion was run and openhole gravel pack completed with 1.35sg CaBr2 brine. With the service tool in the reverse position the well above the gravel pack packer was displaced from 1.35sg CaBr2 brine to 1.20sg CaCl2 brine.
The density of this fluid was planned based on maintaining overbalance to the highest anticipated pore pressure in the open hole section. The next operation was to "dump" the seals and disengage the service tool from gravel pack packer.
After disengaging the service tool a flow check was performed before pulling out of hole with service tool. Positive flow was confirmed and the well was shut-in on the annular BOP. Total 4.5bbl volume gain was reported. Pressure monitoring was established. Pressure stabilized at SIDPP = 220psi and SICP = 237psi.
The well was killed by circulating to 1.35sg CaBr2 brine in two circulations with the driller's method.
What Went Wrong?:
- Higher than predicted pore pressure due to influence of mud volcanoes, offset injection or isolated sand at shale pressure higher than virgin sand pressure.
- Failure to communicate full uncertainty range of PPFG prediction.
Corrective Actions and Recommendations:
- Increase emphasis of risk of over-pressure due to offset well injection and/or proximity to mud volcanoes.
- Perform risk assessment of potential for having pressures higher than measured virgin sand pressure.
- Review pore pressure prediction with a multi-function team. Discussion should include range of uncertainty in the prediction.
safety alert number: 344
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