In this paper, we introduce approaches for forward modeling and model constructing, and model a real complex structure. The selection of offset and datum affects the imaging quality of the synthetic data. Comparison of field data and synthetic data confirms the geologic interpretation.
Today, as we continue to use seismic surveying, more challenges occur, such as complex conditions in the work area, poor surface conditions, more faults, larger fault displacement, and deep reservoirs. These challenges create difficulty in acquisition, processing, and interpretation. In mountainous regions and piedmont zones, it is necessary to do further research in seismic theory and methods, so as to clarify the complex structures and to adjust the acquisition work, processing, and interpretation. Acting as a bridge between a geologic model and seismic section, wave-equation modeling can do much to determine the characteristics of seismic wave propagation and reflection.
We can do modeling based on a geophysical model and geologic interpretation, and compare the synthetic data with the field data. The error between the two data setsis used to evaluate the interpretation result. The further use of modeling is to verify the acquisition and processing parameters according to different data taken from different geometries.
Here, a model is established based on real geologic features and a geometry is put on it to produce a record. We discuss the effect of offset and datum selection on imaging quality. Complex structural imaging is discussed in this paper.Since the target is deep and the weathered layer is allowed, the pressure wave dominates the synthetic data, so we will only consider the acoustic wave equation in this paper.
The forward modeling requires interval velocities,which are calculated from the stack velocities. The velocities are not precise, however, they express the model on the whole. Vertical seismic profile (VSP) interpretation results can correctly indicate the local interval velocities, thus they can be used along with some adjustment to set up a precise velocity model. A surface model including information about the weathered layer should be added directly above the velocity model to form an integrated model. Such a model is shown in fig. 1.
In order to check the effect of overburdenlayer velocities onimaging,the geometry is a split spread, the source is 30 meters deep, the receivers are on the surface, the maximum offset is 8000 meters, and the receiver interval is 20 meters. An absorbing boundary condition is applied. Figure 2 shows two shot records.
Figure 3 shows that the medium offset section has higher signal-to-noise (s/n) ratio. It shows the reflection wave imaging, where the large offset benefits the overthrust imaging and the deep construct imaging. However, if the offset is too large, events maybe distorted due to anisotropy.
The post-stack time migration of the synthetic data is compared with the post-stack time migration of the field data to verify the velocity model. Figure 4 shows the consistency between the post-stack time migration results of the field data and synthetic data which illustrate that the construct and velocity from the interpretation is correct.
