Numerical Analysis of Hydraulic Fracture Propagation Characteristics in Fractured Coal Rock Based on Digital Image Technology
DOI:
https://doi.org/10.54097/2v855027Keywords:
Coalbed methane, hydraulic fracturing, fracture network, RFPA2D, digital image technologyAbstract
China is rich in coalbed methane resources. However, due to the strong heterogeneity of coal and rock and the complexity of natural fracture system, the fracture propagation mechanism of hydraulic fracturing is not clear, which restricts the accurate prediction of reservoir reconstruction effect. Traditional numerical simulation methods mostly use statistical distribution function to describe the heterogeneity of materials, which is difficult to reflect the real morphology of coal-rock fractures. Therefore, based on the real fracture process analysis software RFPA2D, this paper introduces digital image technology (DIT) to construct a numerical model that can reflect the real spatial distribution of natural fractures in coal and rock, and systematically studies the influence of in-situ stress difference coefficient and natural fracture density on the propagation characteristics of hydraulic fractures. The results show that the existence of natural fractures is the basic condition for the formation of complex fracture network. Under the condition of low in-situ stress difference (ks=0.2), there is a significant positive correlation between the complexity of hydraulic fractures and the density of natural fractures. High-density natural fractures can effectively induce the diversion and branching of hydraulic fractures, thus forming a more developed fracture network. The final form of hydraulic fractures is the result of the competition and synergy between the in-situ stress field and the natural fracture network. When the local stress difference is small, the natural fracture plays a major role in the fracture propagation. When the local stress difference increases, the in-situ stress field gradually becomes the dominant factor controlling the direction and shape of fracture propagation. It is concluded that the coupling effect of in-situ stress difference coefficient and natural fracture density is the key factor to control the complexity of coal-rock hydraulic fracture network. The relevant understanding can provide theoretical basis for the optimization of hydraulic fracturing parameters and the evaluation of permeability enhancement effect in coal seams.
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