Structural Features And Prediction Of Coal Reservoir Fissure Development In Laochang Area,eastern Yunnan

The shearing fracture of coal reservoir is the storage space and migration channel of coalbed methane.The shearing fracture is also a key factor affecting coalbed methane exploration and development.But the shearing fracture is buried in the ground,and the development is not uniform in the rock,the prediction of the shearing fracture has become a hot and difficult point in the development of coalbed methane.This paper takes the Laochang in eastern yunnan province as the research area and takes tectonic control as the main line.Based on the tectonic analysis of different scales such as geotectonics,regional tectonics and field tectonics,the tectonic assemblage and its formation mechanism in laochang area were explored.Furthermore,the shearing fracture prediction model based on lithology,thickness and stress is constructed.Finite element stress simulation method is used to predict the shearing fracture density and direction of coal reservoir.The main conclusions are as follows:(1)The structure of the Laochang area can be divided into four structural zones: Dehei-qinkou curved extrusion deformation zone,Laochang diamond dome deformation zone,Puqiao-Longtan brush-shaped compression and torsion structural zone,and Buyang-Xiaolaja curved extrusion structural zone.It is formed by the superposition of the Indochina,Yanshan and Himalayan tectonic movements,since the formation of the coal measures of the Longtan formation and the basement structures such as the Mile-Shizong,Baise-Longlin and Nanpanjiang faults.The closure of the Mayangjiang river and Qinzhou trough during the indo-Chinese period laid the foundation for the main tectonic pattern of the Laochang area(2)During the process of closure of Mayang river and the formation of Qinzhou orogenic belt,the study area was subjected to a north-south resultant force.It is applied to the triangular block surrounded by Nanpanjiang,Mile-Shizong and Baise-Longlin faults.Finally,Laochang anticline,F1,F2 towards NE and B401,S401 towards NEE were formed in the Laochang diamond dome deformation zone.Around the old factory dome,Tehei syncline and Qingkou syncline are formed in Tehei-Qingkou arc extrusion deformation zone.In the Puqiao-Longtan brush-shaped compression and torsion structural belt,the clockwise twisting brush-shaped structure and its associated NE and SW tensional structure are formed.In the south of the study area,an arcuate fracture protruding southward is formed in the Buyang-Xiaolaja arcuate compression tectonic belt.(3)The article improves the calculation model of shearing fracture density based on the Coulomb shear fracture criterion,which increases the influence of thickness on the shearing fracture density compared to the previous model.The effectiveness is verified based on field measurement data.The results show that the influence of thickness on shearing fracture density can be expressed by a normal function.(4)Using the calculation model of shearing fracture density,a prediction method of underground coal reservoir cracks based on surface rock outcrop shearing fracture measurement and finite element stress simulation software was established.This method applies the same boundary stress conditions based on structural analysis to the geological models of underground coal reservoirs and surface rock layers in the study area,to obtain the distribution density of coal and rock shearing fractures,and to reverse the coal reservoir through the measured shearing fracture density constraints of the surface rock Shearing fracture density distribution.(5)The shearing fracture density of coal reservoirs in the Laochang area is mostly 10-20 pieces / m.In the vicinity of F1-19 fault,F9 fault and B401 anticline,the development of shearing fracture is relatively dense,but in the vicinity of the Dehei-Qingkou syncline and Laochang anticline,which are closer to the Mile-Shizong and Baise-Longlin faults,The development of shearing fracture is relatively sparse.Judging from the stress direction,the shearing fracture in the area mainly develop two groups of shearing fracture,NNE and NEE.Combining with the development of the structure in the area,judging only from the development of shearing fracture,it can be considered that the sweet spot for coal seam development in the Laochang area should be located in the south of the Yuwang block.