Abstract: General fracturing techniques are extremely difficult to satisfy requirements of the development of shale gas, due to the highly low porosity and permeability and well developed natural fractures and horizontal beddings in shale reservoirs. Therefore, one of and key technologies is the multiple clusters staged hydraulic fracture of horizontal well, which can greatly increase the stimulation volume, the production rate of gas and final recovery efficiency. In order to locate the fracturing point and fracturing pressure of multiple clusters staged horizontal well of shale gas reservoir, a three-dimensional breaking model of multiple clusters staged horizontal well is established with finite element method, which considers cement mantle and casing. Comparing the simulation results with laboratory experiment of fracturing pressure, the good agreement indicates that the numerical model is reliable and validity. This paper further studies the effect of parameters on fracturing points and fracturing pressure of multiple perforation clusters within multi-stage hydraulic fracturing in shale gas horizontal well using the simulation model. The research results show that fracturing points are found near the roots of perforation clusters, when there is no influence of natural fractures and horizontal bedding plane around perforations. The smaller perforation cluster spacing is, the greater interference between perforation clusters is, which may induce that the perforations cluster in the middle is unable to fracture. Moreover, the fracturing pressure is reduced with the increase of perforation density and perforation length. The existence of natural fracture can reduce the fracturing pressure and change the fracturing initiation position under certain circumstance, mainly depending on the natural fracture distribution and orientation and horizontal principle stress difference. In addition, the bedding plane may reduce the fracturing pressure, but relating to the difference between vertical principal stress and minimum horizontal principal stress. The regularity of fracturing pressure can provide basis for further research on the fracture propagation in multiple clusters staged horizontal well of shale gas reservoir. This study also offer concrete advises on perforating parameters in hydraulic fracture design and hydraulic operation in shale gas reservoir.

Key words: shale gas, horizontal well, multiple clusters staged, perforation, fracturing pressure, finite element method, cased completion