53rd U.S. Rock Mechanics/Geomechanics Symposium,
New York City, New York
2019. American Rock Mechanics Association
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ABSTRACT: Two 0.3 m × 0.3 m × 0.3 m shale blocks, one representing a homogeneous sample while the other representing a naturally fractured sample, are modelled using the lattice based DEM code, XSite. The synthetic rock mass approach (SRM), which assigns the smooth joint contacts (SJM) to the weakness planes, is used to represent the natural fractures in shale block-2. Firstly, the developed models are compared with the findings of previously conducted true-triaxial hydraulic fracturing experiments with acoustic measurements, and their subsequent computed tomography (CT) and seismic velocity tomography results. The 3D model results confirmed the curved shape hydraulic fractures, which propagated perpendicular to the minimum stress directions in both shale blocks. Model results also captured the natural fracture (NF) and hydraulic fracture (HF) interaction, particularly the arrest, the dilation of major NFs, followed by crossing with offset mechanism, in shale block-2. Secondly, the parametric studies are carried out to investigate the role of fluid flow rate (q), and fluid viscosity (μ) on different NF/HF interaction mechanisms. The effects of q and μ are discussed based on the total stimulated area including the tensile and shear microcracks, the pipe apertures, and the pressure evolutions within NFs.
Presence of natural fractures (NF) is critical in defining a prospective shale gas play. The well-known gas shale plays which have contributed significantly to natural gas production in the United States are usually the naturally fractured reservoirs, in which the opening-mode of fractures enhance the production by increasing the treatment zone. The positive roles of natural fractures are explained as enhancing the reservoir permeability and the productivity in the case of open NFs, and increasing the fracture network complexity and the stimulated reservoir volume regardless of whether they are open or closed prior to fracture treatment (Li, 2014). On the other hand, a few researchers have indicated that the presence of NFs might be detrimental in gas production from shale plays (Walton and McLennan, 2013). To this end, a detailed analysis of NF and hydraulic fracture (HF) interaction mechanisms should be considered in the evaluation of naturally fractured unconventional reservoirs’ productivity.
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