Analysis of Seismic Response Characteristics of Coal-Bearing Strata in Pinghu Formation of Xihu Depression

Objectives: Pinghu formation is the main target layers for oil and gas exploration in the western slope of Xihu Depression as well as a coal bearing transition between land and sea. The main characteristics of its coal seams are thin single layer and multiple layers, which make seismic waves susceptible to interference during propagation. Methods: Based on these characteristics in the research area, 4 theoretical geological models have been established for the Pinghu Formation of the Paleogene in the Xihu Depression, and forward simulation of these models was carried out using the wave equation. The influence of the thickness of coal seams in sandstone and the relative position between coal seams and sandstone on seismic reflection characteristics was studied, providing a theoretical basis for reservoir prediction. Results and Conclusions: The following three points of understanding have been achieved: 1) In the combination form of “sand coal sand”, when the thickness of the coal seam increases within the range of 0 - 5 m, the reflection characteristics of the coal seam to the top and bottom interface of sand and mud are reflected as amplitude enhancement, and the polarity reversal of the reflection amplitude does not occur. 2) In the combination form of “sand coal interbed”, when the thickness of the coal seam increases within the range of 0 - 5 m, the influence of the coal seam on the reflection characteristics of the sand and mud roof and bottom increases with the increase of the thickness of the coal seam, and the polarity reversal of multiple reflection amplitude occurs. 3) When the thickness of the coal seam is constant, the influence of the coal seam on sandstone decreases with the increase of its relative distance. When the relative distance is within 10 - 20 m, the polarity reversal of the sand and mud interface occurs.