| 摘要 |
<p>A method for predicting the formation pore-pressure ahead of the drill bit (24) while drilling is disclosed. During the drilling process, the drill bit impacting the earth generates a seismic signal. The seismic signal propagates away from the drill bit in a radial fashion with some rays paths propagating directly towards the surface (16), while others propagating downward are reflected back towards the surface. The direct and reflected seismic signals are received by seismic sensors at one or more locations. The signals produced by the sensors are recorded for later processing. From the recorded signals an interval velocity for each formation behind the drill bit is determined much in the same way a vertical seismic profile is made. From the reflected seismic signals, an acoustic impedance for each formation ahead of the drill bit is determined. The results of the interval velocity determination and the acoustic impedance information are combined to produce a log-like impedance estimation curve which reflects the pore-pressure present in the subsurface units ahead of the drill bit. This information is helpfull to the drilling engineer who can predict the appropriate weight of the drilling mud and thus prevent possible blow-outs and pressure kicks.</p> |
