The enrichment and high yield law of CBM in Yanjiao syncline in Zhijin Block, Guizhou Province

In view of the problems such as the large number of coal seams, the thin single layer, the complex structure, much mylonite coal and hard to evaluate favorable area in southern China, this paper makes use of the exploration achievements and tests data of Zhijin Block to study the reservoir-forming conditions of multiple coal seam CBM. The results show that the enrichment and high yield CBM in south China is characterized by “sedimentation storage-control, preservation gas-control, geostress coal structure control production”. The thickness, number and quality of coal are controlled by sedimentation, which determines the resource base of coal bed methane. The coalbed controlled by tidal flat marsh has stable distribution and good continuity. The ash content is less than 20% and the volume fraction of vitrinite is more than 80%. The structure and hydrogeology jointly control the gas content of coal seam, showing the characteristics of rich gas at the core of syncline and the wing part of Zhuzang sub-syncline develops towards the core. With the increase of burial depth, the mass concentration of chlorine root and the reservoir pressure gradually increase, and the gas content gradually increases from 8 m3/t to 28 m3/t. Tectonization affected coal structure, the magnitude and state of geostress, directly affects the productivity of coalbed methane wells by influencing the effect of fracturing and seepage conditions. NE trending structure and NW trending structure belong to different deformation areas. The Zhuzang, Agong and Santang subsyncline of NW trending structure formed later than Bide and Shuigonghe sub-syncline of NW trending structure, and the tectonic action is relatively weak. The present geostress is less than 20 MPa, and the coal body structure is mainly composed of primary structural coal or fractured coal, and the horizontal stress is bigger than the vertical stress, the fracture is mainly horizontal fracture, which is advantageous to the fracture extension in the coal reservoir, so the CBM development condition is more advantageous. Based on the study of the law of enrichment and high production, it is considered that the implementation of multiple coal seam resource base in south China and the effect of structure on geostress and coal body structure are the key factors for multiple coal seam selection evaluation, and it is clear that the Zhuzang, Agong, Santang sub-syncline in the Yanjiao syncline is a favorable area for CBM development. Regionally, the NE coal-bearing syncline, far from the Weining fault, is the key direction of multiple coal seam CBM exploration in southern China. © 2021 Meitiandizhi Yu Kantan/Coal Geology and Exploration. All rights reserved