A method for the esimation of pore pressure within a subterranean formation

摘要

A method for the estimation of pore pressure within a subterranean formation containing fluid during the drilling of a bore hole 6. The bore hole is drilled using a drill string 4 consisting of a drill bit 5 fitted to its lower end, and using drilling mud pumped from the surface through the drill string and finally evacuated. The method is characterised by, whilst the drill bit is level with the formation and whilst the drill string is being raised to the surface for a distance at least equalling the drill pipe length, a) the monitoring of the change in value of an initial parameter such as mud level in a mud tank to detect the influx of the fluid from the formation into the bore hole; b) the monitoring of the change in value of a second parameter such as the apparent drill string weight whereby the second parameter characterises the force applied at the surface to retrieve the drill string; c) the correlation of the values of the first and second parameters in order to detect an increase in one of the parameters, which would correspond to an increase of the other parameter, and then the determination of the increase in value of the second parameter; and d) the estimation of the pore pressure of the formation from the increase in value of the second parameter as determined in step c). IMAGE