Abstract:The formation of dense spacing fracture network is crucial to the hydraulic fracturing treatment of unconventional reservoir. However, one difficulty for fracturing treatment is the lack of clear understanding on the nature of fracture complexity created during the treatment. In this paper, fracture propagation is numerically investigated to find the conditions needed for the stable propagation of complex fracture network. Firstly, starting from a parallel fracture system, the stability of fracture propagation is analyzed and a dimensionless number M is obtained. Then, by developing a hydraulic fracturing simulation model based on displacement discontinuity method, the propagation of parallel fractures is simulated and a clear relation between M and the stability of parallel fractures is obtained. Finally, the investigation on parallel fractures is extended to complex fracture networks. The propagation of complex fracture networks is simulated and the results show that the effects of M on complex fracture networks is the same to that of parallel fractures. The clear relation between M and fracture propagation stability is important for the optimization of hydraulic fracturing operation.
Compression is one of the most important mechanical aspects of behaviour of municipal solid waste (MSW) which concerns stability, deformation and structural performance in a landfill. Previous studies have shown that compressible particles play a significant role in MSW compression. Definition of the void ratio in classical soil mechanics theory may no longer be applicable for MSW material since high non-linearity between void ratio changes and vertical stress changes have been identified in compression tests. A new phase relationship for MSW has been developed to include the volume loss of compressible particles and this has been evaluated using one-dimensional compression test data. The comparison between analytical and test results has demonstrated that the MSW phase relationship is capable of analysing the volume losses originated from inter- and intra-void ratio changes, in addition to the total volume loss of the MSW sample under different vertical stresses. Since it can isolate the volumetric change of compressible particles from the total volume loss, the MSW phase relationship is important when developing a constitutive model for MSW assuming elasto-plastic material behaviour, which couples the volumetric and shear behaviour.
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