Abstract:
Pore pressures of formations are one of the big problems facing the drillers in exploration areas. The pore pressure, together with fracture gradient, determines the amount of mud weight that is needed. Too much mud weight fractures the rock; too little mud weight allows formation fluids to come into the well and can cause blow-outs if not controlled.
This work examine a feasibility of a new approach to estimate the pore pressures of formations prior to drilling operation . Knowing the pressures ahead of time will allow the drillers to adjust mud weight or take other measures to avoid problems. The required data is surface seismic data, in the vicinity of the well, and real-time logs as the wells are being drilled. This method consists of predicting the seismic velocities by simultaneous use of the surface seismic and real-time check-shot information. Then, the predicted velocities are mapped to the pore pressures using an equation or empirical relation appropriate for the area. Surface seismic data has been used in the industry to predict formation pore pressures before any well has been drilled. This is done by estimating the subsurface velocities from seismic and then using a number of velocity-pressure relations appropriate for a given region. The combination of surface seismic data with a set of real-time well logs, acquired as the well is being drilled so, as to make a more reliable estimate of velocities ahead of the bit. In particular we make use of the real-time check-shot measurement (Seismic While Drilling) that was not available to be accurately determined. To combine these two pieces of information, the surface seismic data are inverted for seismic velocities ahead of the bit while the inversion is constrained with the real-time well log and check-shot measurements.
