Application of Horizon Control Method in Velocity Field Construction of Underlying Strata Under Salt Domes

In the eastern margin of the Caspian Basin, the Lower Permian sedimentary thick salt strata in the B oilfield in the eastern margin of the Caspian Basin, due to the buoyancy of the tectonic movement salt dome and the difference in formation compaction, resulting in the formation of many underground salt domes of different sizes. The velocity differential between the salt body and the neighboring rock matrix manifests as an upward shift in the seismic cross-section corresponding to the substrata beneath the salt dome, resulting in structural illusions, and the real structural form is difficult to implement,thereby limiting the characterization of potential structural traps.In view of the above problems, the application of seismic stacking velocity, VSP, acoustic wave (AC) and horizon control method to establish the spatial average velocity field and improve the reliability of the structural form of seismic interpretation is the key and difficult point in the study of subsalt structure in this area. It is realized in three steps: (1)Using Dix formula and seismic stacking velocity data, the layer velocity of salt rock section is calculated, corrected and replaced, and the appropriate layer velocity of salt rock section in this area is obtained.(2)The layer velocity of the overlying and underlying sedimentary layers of the salt rock layer is controlled by the superposition velocity trend and the well speed. (3)The reasonable layer velocity and time model of each layer after processing is applied to fill the velocity, and the three-dimensional average velocity body is established. The average velocity field established by the application layer position control method is used for variable-speed mapping. The error between the structural map and the actual drilling depth is less than 1%, which meets the accuracy requirements of the velocity field, providing a basis for identifying favorable structural traps and thereby advancing hydrocarbon exploration.