The Study And Application For Seismic Wave Attenuation Rules In Zhongyuan Oil Field

The study on seismic wave attenuation rules in layers have always been one of the most important research fields for Geophysicist. According to the attenuation rules in practical layers, we can offset the absorbed energy to enhance the seismic wave energy at different depths, and make events more consistent on seismic section, which can provide high-quality seismic data for succedent processing. The research on seismic wave energy attenuation mechanism and its influence factors affords the theoretical base for the research on absorption and attenuation rules in layers. We must find out the seismic wave attenuation mechanism in layers and summarize the quantitive absorption and attenuation rules before our study on arithmetic design of quality factor(Q) inversion and seismic energy balancing.According to the attenuation rules in viscoelastic medium, we firstly design the synthesis method for zero-offset VSP record in viscoelastic medium, and actualize the forward course of synthesizing VSP record of horizontal layered viscoelastic medium model; then we carry through the arithmetic design and experiment of spectral ratio method and centroid downshift method on the synthetic VSP record of horizontal layered viscoelastic medium model, and get the conclusion that the main factors influencing the calculation precision of spectral ratio method and centroid downshift method include interference, time window length and rounding error. The experiment result indicate that the inherent rounding error of designed arithmetic lead the inversed Q value greater than the real Q value. In order to overcome these inherent error, we have designed the iterative arithmetic of spectral ratio method and centroid downshift method to make the error converge gradually, which can greatly improve the precision of quality factor inversion; Finally, we have designed the energy balancing arithmetic of inverse Q filtering and the inner Hilbert transform arithmetic, then we have executed energy balancing on the synthetic VSP record, with the gained information of quality factor, and proved the validity of quality factor inversion arithmetic, which have provided reference for quality factor inversion of practical VSP record. The influence factors of seismic wave energy in practical VSP data include not only nonelastic medium absorption, but also geometric spreading, nonzero-offset, interference, reflection and refraction. In order to overcome these influence factors, we must execute geometric spreading compensation, wave field separation to the practical VSP data, and select the zero-offset VSP data for quality factor inversion. Moreover, we have compartmentalized the stratum at the location of VSP logging into several thick layers, according to the information of geologic formation and well logging tour report, and carried through equivalent quality factor inversion with iterative arithmetic separately, which have avoided the influence of short-path multiples in lamellas. Then we use inverse Q filtering method to compensate the seismic wave energy on the VSP data, and examine the validity of equivalent quality factor inversion.