Construction And Application Technology Research Of Elastic Wave ADCIG

Elastic wave reverse time migration （RTM）, imaging both longitudinal wave （P-wave） and shear wave （S-wave） at the same time, could simultaneously utilize both P-wave and S-wave information of the subsurface medium. It is of great significance to the exploration of unconventional hydrocarbon reservoirs such as coal bed gas reservoirs, shale gas reservoirs and so on. There are two main objectives of Elastic wave RTM, first achieving migration imaging of P-wave and S-wave of subsurface medium, and second providing high-fidelity input gathers for the following prestack inversion.First of all, the paper introduces the key technologies of elastic wave RTM. Based on the first-order velocity-stress elastic wave equation, derived the high-order finite difference scheme of the forward continuation and the reverse continuation in the staggered grids, and study the hybrid boundary condition to absorb boundary reflections generated from artificial boundary, then achieve decoupling P-wave and S-wave during the continuation of the source wavefield and the receiver wavefield. Next, use the appropriate imaging condition to imaging independently on P-wave and S-wave. The migration noises generated form conventional RTM will serious reduce the quality of the imaging profile, and the Laplace filter is used to reduce the migration noises and to improve the imaging accuracy. There exists enormous hard disk storage requirements and I/O time requirements on conventional RTM. The paper uses the effective boundary storage strategy boundary to reconstruction the source wavefield. By exchanging calculation for storage, it could greatly reduce the amount of storage and save I/O time of RTM based on a small increase in the amount of calculation. To verify the absorbing affection of the hybrid boundary condition, the paper uses the equal model as a trial calculation, and the results show the absorbing affection of the hybrid boundary is better than conventional PML absorbing boundary and the computational efficiency is higher as well. A two-double horizontally layered model is used as the migration noises reduction trial calculation, and the results show the Laplace filter can effectively suppress low-frequency migration noises and improve imaging quality.Angle domain common image gathers （ADCIG） is the prestack gathers with higher precision, so it is widely recognized as the prestack gathers with highest accuracy. In the paper, the wavefront vector method is studied as the construction technology of P-wave ADCIG and S-wave ADCIG based on the elastic wave RTM. Firstly, analyze the geometry relationship and the mathematical relationship between the propagation angle of the source of P-wave, the local formation dip and the incidence angle of P-wave and S-wave. Then obtain the propagation angle of the source of P-wave by calculating the wavefront vector of the decoupled source P-wave on the maximum energy moment of the down-going wavefield. And obtain the local formation dip by calculating the complex wavenumber of the P-wave migration stack section. Then the incidence angle of P-wave and S-wave is the difference between the two. Finally, get P-wave ADCIG and S-wave ADCIG by rearranging the shot domain gathers according to the incidence angle.While the elastic wave ADCIG is gathers with higher precision, it has an important role to true amplitude imaging, AVO\AVA and interval velocity modeling in depth domain. Since RTM requires extremely high for velocity field using to migration, so interval velocity modeling in depth domain is even more urgent compared with the previous two. The paper briefly describes the application of the elastic wave ADCIG in preserving amplitude, AVO\AVA and polarity correction of the migration results of the S-wave. The paper mainly research on the application in interval velocity modeling in depth domain of RTM. Firstly, introduce the criterion of the elastic wave interval velocity in depth domain. Based on this, derived the migration depth equation of P-wave ADCIG and S-wave ADCIG. Meanwhile, give the basic flows of interval velocity modeling in depth domain of P-wave and S-wave.The paper respectively use horizontally layered model, tilt model, Marmousi₂ model and actual data to verify the extraction algorithm and the application technology of the elastic wave ADCIG The results show that:using the ADCIG extraction algorithm can effectively extract P-wave ADCIG and S-wave ADCIG. The extracted P-wave ADCIG and S-wave ADCIG can meet the precision of AVO\AVA and can be used for polarity correction of S-wave migration results. The method of interval velocity modeling in depth domain can construct the interval velocity model in depth domain of P-wave and S-wave meeting the accuracy requirements of elastic wave RTM. Based on this, the substance medium can achieve P-wave imaging and S-wave imaging accurately.