Method for detecting formation pore pressure by detecting pumps-off gas downhole

摘要

A method for the detection of gas invading a wellbore during drilling by the influx of fluids which contain gas from the formations penetrated by a wellbore.

主权项

1. A method for sensing an amount of gas in drilling fluid in a wellbore during drilling from an earth surface and penetrating a plurality of subterranean formations, the method comprising:
a) pumping drilling fluid through a drill pipe extending into a wellbore to provide pressure on the drilling fluid in the drill pipe and discharging drilling fluid from a bottom end of the drill pipe into a drill bit and an annulus between an outside of the drill pipe and an inside of the wellbore to drill the wellbore to a greater depth; b) supporting at least one gas sensor by the drill pipe near the bottom of the drill pipe and positioned and adapted to sense the amount of gas in the drilling fluid in the annulus at a depth of the at least one sensor c) sensing information indicating the amount of gas in the drilling fluid in the annulus at the level of the at least one sensor during a period when pumping has been stopped while in one or more relatively low permeation formations; and, d) comparing the amount of gas in the drilling fluid in the annulus at the level of the at least one sensor during said period to a previous amount of gas sensed during a previous period when pumping had been stopped in order to avoid drilling into a relatively high permeability formation before adjustments can be made to prevent a kick or blow out.