In-situ stress field of deep coal reservoir in Linxing area and its control on fracturing crack

In-situ stress is the key controlling factor for fracturing stimulation of coal reservoirs. Based on the data of electro imaging logging and hydraulic fracturing,combined with Abaqus software simulation,the spatial distribution characteristics of in-situ stress of deep coal reservoir in the study area was identified,and its effect on crack extension was discussed. The results indicate that the maximum horizontal principal stress direction is approximately EW in Linxing area. The vertical distribution of in-situ stress has obvious zonal distribution. There are two critical conversion depths of 1 200 m and 2 000 m,respectively. When the buried depth is less than 1 200 m,the in-situ stress is characterized by vertical principal stress;when the buried depth is between 1 200-2 000 m,the horizontal principal stress dominates;when the buried depth exceeds 2 000 m,the in-situ stress is characterized by vertical principal stress again. The in-situ stress of deep coal reservoir in study area is characterized by σhmax>σV>σhmin. The plane distribution of the in-situ stress is controlled by both the buried depth and the structure. The burial depth causes the in-situ stress to be high in the south and low in the north,and high in the west and low in the east. The horizontal in-situ stress in the part is relatively large,and the horizontal in-situ stress in the syncline core and the fault development area is relatively small. The characteristics of in-situ stress combination in the study area determine that the fracture is dominated by vertical cracks,and some complex cracks are easily formed locally. In the presence of natural fractures,when the horizontal principal stress difference is less than 3 MPa,the fracturing cracks expand along the natural fractures;when the horizontal principal stress difference exceeds 6 MPa,the fracturing cracks expand along the maximum horizontal principal stress direction;when the horizontal principal stress difference exceeds 10 MPa,the fracturing cracks is basically a single crack along the maximum principal stress direction. The analysis of fracturing examples shows that the extension direction and propagation characteristics of cracks are obviously controlled by in-situ stress. The research results provide theoretical guidance for fracturing transformation of deep coal reservoirs.