Abstract
In this paper, we present a detailed analysis of walkaway vertical seismic profiling (VSP) data, which can be used to obtain Thomsen parameters using P-wave-only inversion. Data acquisition took place in difficult field conditions, which influenced the quality of the data. Therefore, this paper also shows a seismic data processing scheme that allows the estimation of correct polarization angles despite poor input data quality. Moreover, we showed that it is possible to obtain reliable and detailed values of Thomsen’s anisotropy parameters for data that are challenging due to extremely difficult field conditions during acquisition and the presence of an overburden of salt and anhydrite (Zechstein formation). This complex is known for its strong seismic signal-attenuating properties. We designed a special processing workflow with a signal-matching procedure that allows reliable estimation of polarization angles for low-quality data. Additionally, we showed that P-wave-only inversion for the estimation of local anisotropy parameters can be used as valuable additional input for detailed interpretation of geological media, even if anisotropy is relatively low.
Highlights
Exploration of dwindling deposits of raw materials requires increasingly more accurate methods of geophysical imaging and accurate interpretation of the obtained results
The biggest challenge was related to the fact that we already know from the surface seismic survey that this geological medium has very low anisotropy strength, and estimated anisotropy parameters were very low; these parameters have a significant impact on seismic processing and migration
The theoretical isotropic vertical slowness line passes through the center of the predicted points. This is a very thin marl layer where δ and η are close to zero. These results clearly show that the presented P-wave-only vertical seismic profiling (VSP) data inversion methodology can be used for lithology studies
Summary
Exploration of dwindling deposits of raw materials requires increasingly more accurate methods of geophysical imaging and accurate interpretation of the obtained results. The biggest challenge was related to the fact that we already know from the surface seismic survey that this geological medium has very low anisotropy strength, and estimated anisotropy parameters were very low; these parameters have a significant impact on seismic processing and migration This accurate information about local anisotropy could improve reprocessing of seismic data in the future, especially model building for depth migration [6]. The obtained results showed that combining the advanced processing of challenging walkaway VSP data with detailed data analysis of P-wave-only inversion gives additional helpful reservoir information that can be used to make interpretation more accurate when other surveys produce poor quality results and even if anisotropy is relatively low. This allows for a thorough understanding of the presented case study
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