Overpressure zones, with abnormally high pore-fluid pressure, can exist directly beneath the base of salt. Drilling into one of these is a common cause of a well blowout. Hence, the ability to predict overpressure zones prior to drilling is extremely valuable.
Accurate salt exit velocities help identify subsalt overpressure zones, which are typically characterized by a low velocity. Knowledge of salt exit velocities also enables the calculation of effective stress to aid well design.
The CGG Salt Exit Velocity Inversion (SEVI) method utilizes two-way wave-equation modeling and RTM 3D angle gathers to accurately predict salt exit velocities, through analysis of seismic amplitudes at the base of salt.
With conventional workflows it is difficult to estimate salt exit velocities due to limited angle illumination. Salt exit velocities can be used to constrain high-resolution tomography, leading to greatly enhanced subsalt images.
The benefits of more accurate salt exit velocities are demonstrated clearly on these Gulf of Mexico Green Canyon WAZ results. The computed salt exit velocity was measured to be within 4% of the actual velocity at the well location (black dotted line).
Retain the rich azimuth and reflection angle information carried in wide-azimuth data and bring the outstanding quality of RTM pre-stack.
Go beyond constant velocity assumptions using our range of tomography and inversion tools to derive internal velocity structure of salt structures.
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