Study On Hydraulic Fracture Network Propagation Rule Of Shale Reservoir

Shale gas is one of the most realistic resources of conventional oil and gas resources, at present, the irregular and asymmetric complex fracture network that generated by fracturing is one of the core technologies of unconventional natural gas exploitation. Because of the low porosity and low permeability of reservoir, in addition, the characteristics of the layered structure and the natural fractures in the reservoir are different, which affect the crack extension rule and the formation of the network fracture is an important influence, the spatial distribution of fracturing fracture is difficult to predict. Therefore, the research on the influence factors and the extension law of the fracture extension direction of the shale hydraulic fracturing, and get the judgment criterion of the hydraulic fracture network of shale reservoir, which are very important to the reservoir fracturing drilling layout and the recovery efficiency improvement.In order to further understand the crack extension law of shale reservoir hydraulic fracturing and the formation condition of fracture network, a two dimensional model of hydraulic fracturing fracture in shale gas reservoir is established. This paper analysis the hydraulic fracture extension direction of the stress difference coefficient, natural fracture and bedding surface combined with the theory and numerical simulation. And then the mechanism and conditions of the formation of the hydraulic fracture network in the rock stratum are obtained.The main conclusions of the paper are showed as following:①The main factors influencing the fracture network of the hydraulic fracturing of shale reservoir are analyzed. Critical hydraulic pressure of crack in bedding planes and natural crack tip are obtained based on the theory of elasticity and fracture mechanics, and the analysis shows that the stress difference coefficient, bedding planes and natural fracture feature of shale reservoir hydraulic fracturing crack extension law plays a decisive role.②Revealed the effect of extended characteristics on fracture of shale bedding. When shale matrix mechanics are the same, when the hydraulic fractures and bedding planes intersect, Fracture trend is from the fracture through bedding extension required critical water pressure and fracture along the bedding produced open shear and extension of the required size relationship between critical hydraulic pressure, with the increase of the strength of the stress difference coefficient and bedding, cracks tend to through bedding face is formed along the maximum principal stress direction of extension of a single crack.③The crack extension of shale hydraulic fracturing under the effect of interlayer shielding is revealed. When the shale layer matrix between intensity differences and shale layer is no longer uniform, hydraulic fracture in the process of extending due to the shielding effect of the existence of, cause the crack deflection, which influences the formation of fracture network; Cracks on both sides of the matrix strength increases abruptly. When the crack initiation and extends to the interface between layers, the hydraulic fracture by high strength rock matrix block, cracks appear short passivation crack arrest, to be sewn inside the pressure reaches a certain value, crack along the interface layer extension, conversely, crack directly through the bedding planes into the other side of the rock matrix and crack extension scope increases.④The criteria for the formation of the hydraulic fracture network of shale reservoir are established. Hydraulic fracture on bedding planes between bifurcation and communication of main and natural fractures is the key to the formation of fracture network. Stress difference coefficient, bedding planes and natural fractures approaching angle shall be under the condition of a certain critical combinations, deviate from the conditions will have a single crack; when the interface strength is moderate, the formation of fracture network is related to the combination of ground stress and the characteristics of natural fractures. It is more advantageous to the formation of the fracture network when the approaching angle is high.