Physical modeling of seismic response for the coal seams of Yan'an Formation in loess tableland of North China

A seismic physical simulation is carried out for the complex seismic response of the coal seam of Yan'an Formation in the loess tableland. First, the physical model materials for the dry layer near the surface of the loess tableland and the coal seam are developed. After several tests, a mixture of silicone rubber with silicon aerogel powder is selected to simulate the surface of the loess tableland, and the mixture with ultra-fine carbon powder added to silicone rubber is used to simulate the low-speed and low-density coal seam. Through the methods of molds control layer, layer by layer pouring, three-dimensional carving of undulating strata, a three-dimensional seismic physical model of the typical geological structure in the loess tableland is constructed, and seismic physical simulation and seismic imaging analysis are carried out. The results show that there is a strong reflection amplitude because of the great difference in impedance between the coal seam and surrounding rock of Yan'an Formation. Therefore, it has a strong shielding effect on the imaging of the lower strata. There are internal multiple waves in the multiple sets of coal seams, affecting the imaging of the underlying layer. The calculation time window greater than 40 ms is more favorable to coal seam identification when the coal seam is described by the seismic amplitude attribute. But there are some traps in predicting coal seam thickness by seismic attributes because of the coal seams tuning effect.