Good knowledge of formation pore pressure is required for the safe and economic drilling of wells. At present, Eaton and Bowers methods are widely used in pore pressure prediction, and the prediction accuracy of these methods is dependent on the accuracy of the underlying formation velocity prediction. However, the accuracy of the velocity field created by conventional velocity modeling struggles to meet the requirements for accurate pore pressure prediction. To solve this problem, a new velocity modeling method is proposed that in depth domain is based on grid tomographic inversion with structural constraints. The new method allows to build a high-precision velocity model, which can help improve the accuracy of pore pressure prediction.
The research results based on physical model data show that this method can improve the modeling accuracy of the velocity field significantly, and the position and size of even small-scale geological bodies with anomalous velocities can be clearly described. This method is applied to identify a subtle velocity anomaly in the sub lacustrine fan area of the Bohai Q oilfield. In the process of velocity modeling, interpreted seismic horizons are used to constrain the velocity changes, and a seismic amplitude attribute is mapped to delineate the fan body to establish an accurate velocity field for regional pore pressure prediction. After the study, an exploratory well was drilled in this area, and its measured pressure data was found to be consistent with the predicted prespud pressure, which proved that the high-precision velocity field established by this method can improve the accuracy of pressure prediction and ensure the safety of drilling construction.