Traditional MGS design shows small and short mid long mud seal (3-4 ft) and google search shows that many supplier sell equipment not knowing sizing requirement for the mud seal height. MGS Mud seal is used to maintain the internal pressure of Mud Gas Separator (MGS). The parameters used to estimate the internal pressure of MGS are simulated through the gas kick and Geometry of MGS. For example, if the MGS geometry is identical and it is except the gas diameter then the vent line will be increased by 5cm.
Well Control Incident Learning from IOGP (International Association of Oil and Gas producers) Alert #16-1, shows that while MPD operation high-pressure gas and condensate exploration well, drilling in the reservoir section below 16500, the mud seal of the MGS was lost while crew was bleeding off some of the gas through the choke and mud-gas separator (MGS). The reservoir pressure was only about 375 psi below the MPD set point. Small influxes occurred when the pumps were not circulating through the bit – the auto-choke that was supposed to apply pressure to the annulus was not in the optimum position to maintain control. Correct equipment sizing (correct mud seal height) and maintained (calibrated) equipment could have helped avoiding influx, influx could have circulated via choke using MPD operations and technology.
Kapwell calculates minimum mud seal height by using the vent line friction pressure. This pressure is used to identify the overall height. The drilling mud density is typically expected to see during the well operation. The overall capacity of the vent is managed, then it is controlled by the mud seal height of the liquid seal and the diameter of the mud gas vent. This can be reduced when the long pipe is installed as well as the vent capacity will also be reduced for a given seal height. It is recommended that seal should have a height starting from the 10 feet, but preferable is 20 feet depend on the drilling programme conditions. Kapwell has proven record of detailed calculation to ensure equipment comply with well bore conditions and regulator requirements.
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