Experimental study of permeability characteristics for the cemented natural fractures of the shale gas formation

• Effect of filling minerals, morphology of the fracture surface was studied.
• Factors controlling fracture permeability were concluded from experiments.
• Residual fracture porosity increases while the stress sensitivity diminishes.
• Fracture-conductivity can be enhanced by forming unconformity surface.

It is critical to understand the permeability characteristics of the cemented natural fractures before and after the opening in shale gas reservoirs. In this study, the effect of filling minerals, morphology of the fracture surface, and acidizing treatment on the permeability of natural fractures with different fracture patterns are studied. Results showed that the fracture permeability is mainly determined by several factors including the shear displacement, integral roughness of the fracture planes, and the local roughness. For larger particles and higher hardness of cemented minerals, the residual fracture porosity increases while the stress sensitivity diminishes. The fracture-conductivity can be substantially enhanced with the acids by dissolving the cements and forming unconformity surface. The shale matrix and cementing mineral compositions must also be considered to avoid the reduction of shale hardness and the migration of particles.