Shut In Drill Pipe & Casing Pressure
After taking an influx, closing the BOP stack & shutting in the well, pressure will build up on the standpipe and casing gauges because of the hydrostatic under balance (drilling fluid weight too low to balance formation pressure). The pressure shown on the standpipe manifold is called "Shut In Drill pipe Pressure" SIDPP, and that shown on the casing gauges is called "Shut In Casing Pressure" SICP.
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