Patent ID: 8995224
Filing Date: 2015-03-31
Classification: G01V

Abstract:
1. A method for estimating pore pressure ahead of a drill bit comprising: disposing the drill bit into a borehole penetrating a subsurface formation, wherein the drill bit is coupled to a drill string of a drilling system and the subsurface formation includes a target reflector located at a depth ahead of the drill bit; generating seismic waves from at least one surface seismic source at at least one offset position within a maximum offset distance from an entrance of the borehole at the surface of the Earth, wherein the maximum offset distance is determined based upon the depth of the drill bit, the depth of the target reflector, and known velocity trends in the subsurface formation; using at least one seismic receiver disposed on the drill string to detect reflected seismic waves from the target reflector; determining the travel time of the reflected seismic waves; inverting the travel time of the reflected seismic waves to determine velocities ahead of the drill bit; and using the determined velocities ahead of the drill bit to determine pore pressures ahead of the drill bit.