Multivariate Constraints Time-Depth Conversion Method Based On Velocity Tomography and Application in Bohai K Oilfield

Bohai K Oilfield is located in the southern Bohai Sea of China. At the same time, part of the Guantao Formation in the oilfield developed igneous rocks with large thickness changes, resulting in laterally rapid variation of velocity. In the case of less drilling, the conventional time-depth conversion method can not meet the accuracy requirements for the interpretation of the structure and reservoir in the reserves evaluation. According to the complex geological conditions in the this oilfield, a multivariate constraints time-depth conversion method based on velocity tomography is proposed. First, velocity tomography inversion is carried out under the constraint of logging velocity and igneous rock amplitude to obtain high-precision seismic velocity. Then, the seismic velocity is trend-corrected with the well-calibrated average velocity under the constraint of the structure to obtain the final 3D velocity volume for time-to-depth conversion. The result shows that this method combines the advantages of logging velocity and seismic velocity. The structure map is more consistent with the geological structure, effectively ensuring the accuracy of the time-depth conversion, and provides a strong support for the reserves evaluation of the oil field.