Abstract. This paper gives out seismic information interpreting methods for deep steep structure in Sichuan, including connecting seismic data, processing and interpreting, marking stratigraphic, appreciating velocity information, making structure pattern, interpreting with seismic and geology, backing well information and so on.
INTRODUCTION The east Sichuan Basin consists of deformed, comb-shaped, asymmetrical high-steep structural area with complex geological framework. The subsurface structures are complex and the quality of the seismic data is poor. The Carboniferous carbonates are the most important gas reservoirs, but they form a thin interval having rapid lateral changes in physical properties. Therefore, an accurate description of the structural shape, lateral distribution and physical properties of the reservoir is crucial in increasing the success rate of exploratory drilling.
This paper summarizes the methods utilized to accurately interpret the structural shape and to increase the accuracy of prediction of the lateral extent of the reservoirs using the DTC structural zone example which is typical of the highly steep structures in eastern Sichuan Basin.
Accurately interpreting the structural shape The seismic processor and interpreter work closely with each other integrating the analysis of stacking velocity, building of the migration model and time to depth conversion. Thus, the resolution, S/N ratio and imaging quality of seismic sections have increased significantly.
The target formations have been accurately identified using the VSP log and synthetic seismograms.
The reliability and consistency of identifying the target formations were verified by checking the seismic line ties.
3. The structural model is being built by a combination of the drilling data with wave field features of the seismic sections, and through forward modeling. Once the model is established, it is modified till a final model is reached, which is then used to guide the interpretation of the sections.
4. Important geologic features and structural details are accurately interpreted in the seismic lines. In the eastern Sichuan Basin the small folds, reverse thrusts, and small-scale faults are developed.
Denudation and pinchout events are seen throughout the lines. There are rapid changes of the secondary thickness of the Triassic anhydrite formation. For this reason, the processor and the interpreter must understand the character of the reflection waves carefully, resolve and interpret complex wave fields to increase the interpretation accuracy.
5. Velocity data is analyzed and correctly applied.
The important factor that affects the accuracy of the structural results is