Evaluation method and application of fracturing effect based on dynamic permeability change of coal reservoir hydraulic fracturing

The fracturing construction curve is considered to be an important basis for reflecting the fracturing effect, while the dynamic change of reservoir permeability in the fracturing stage can more intuitively reflect the effect of fracture formation. In this paper, a quantitative evaluation method for reservoir dynamic permeability in fracturing stage was established based on the principle of well testing. Then, the method was applied to evaluate the fracturing effect of two coalbed methane (CBM) wells in a block in southern Junggar Basin, and the dynamic permeability curve of reservoir during fracturing stage is obtained. Meanwhile, the G-function method was used to further evaluate the fracturing effect. The results show that the fracturing effect reflected by the dynamic permeability curve is consistent with the G-function analysis and the evaluation results based on the relationship between displacement and bottom hole pressure, which can reflect the opening and extension effects of fractures in the reservoir. Large-scale fracture network transformation of coal reservoirs and surrounding rocks was implemented in Well CMG-01, and the reservoir permeability in the fracturing stage was up to 2.5 μm², showing a good fracturing effect. While the reservoir permeability of CBM-02 Well was kept below 1.8 μm² after conventional hydraulic fracturing was performed in the coal reservoir. There are significant differences between conventional hydraulic fracturing of coal reservoirs and large-scale fracture network reconstruction of coal reservoirs and surrounding rocks. The formation of the quantitative evaluation method for reservoir dynamic permeability in fracturing stage can make up for the lack of quantitative evaluation of the fracturing effect, which provides a basis for optimizing hydraulic fracturing technologies of CBM or coal measure gas wells.