Study on sediment environment and rock mechanics characteristics of the delta plain of Jurassic coalfield in northern Shaanxi

Delta plain sedimentary environment is one of the coal-forming environments of the coal resources of Jurassic coalfield in northern Shaanxi. In order to get the rock mechanics parameters and characteristics of coal seam roof in different environments and to further investigate the relationship between the sedimentary environments and the rock mechanics characteristics, firstly from the analysis of the regional sedimentary environments, then by using techniques such as accurate core description, sedimentary structural analysis, facies analysis of geophysical logging, the microfacies were recognized, the sedimentary microfacies types of roof and their combination characteristics were classified. Later, rock samples of different lithology at different position were collected by layer, tested and analyzed. Finally, the rock mechanics characteristics of different microfacies of seam roof were analyzes comprehensively. The results show that sedimentary environment not only controlled coal seam roof lithologic distribution but also controlled the rock mechanics parameters and the distribution of water yield properties of aquifer. Direct roof of coal seam in the study area dominated by mudstone and silty mudstone, was formed in the delta plain sub-facies of swamps, locally siltstone and fine-grained sandstone were formed in shunt rivers and natural embankment microfacies. The basic roof lithology is dominated by medium and fine-grained sandstone formed in the branch river and onshore natural levee sedimentary microfacies, coal seam roof stability is medium, the main roof sandstone aquifer is the major risk for mine production in the future, among them, lake and swamp mudstone roof area is the key part of roof support, multi-stage distributary channel sandstone overlapping top plate area is the key area for mine water prevention and drainage in the future.