Numerical Simulation Of Influence Of Shale Minerals On Hydraulic Fracturing Crack Propagation

With the rapid development of industry,the world's energy demand has surged.Shale gas has received extensive attention as a clean energy source.Hydraulic fracturing has become an important means of shale gas mining.The shale has a complex microstructure and contains a variety of different minerals that cause shale heterogeneity.This heterogeneity affects the expansion of cracks during hydraulic fracturing and affects the gas production of hydraulic fracturing.The heterogeneity of shale is mostly based on the understanding of microscopic level.It is difficult to observe the shale microstructure in hydraulic fracturing experiments.There are few related studies on the heterogeneity of shale by numerical simulation.Therefore,for the complex microstructure of shale to summarize its heterogeneity characteristics,the analysis of the influence of shale minerals on hydraulic fractures by numerical simulation is of great significance for the selection of shale reservoirs.By reviewing the domestic and foreign literatures,the author summarized the previous understanding of shale microstructure,and used SEM and rock thin section to analyze the mineral morphology and mineral distribution in the shale microstructure.Most of the clay is scaly,and the quartz is widely distributed.The pyrite is brighter in the scanning electron microscope,showing a strawberry shape,and different minerals are randomly distributed.Using the differential effective medium theory to establish a petrophysical model with different minerals when the clay content is greater than 30%.Numerical simulation analysis of shale models with different mineral compositions,mineral particle sizes and mineral contents was carried out by extended finite element method.The results show that pyrite has the strongest barrier to crack propagation,followed by quartz and calcite,and clay is the weakest.For quartz,calcite and pyrite,when the mineral particle size is 50?m,60?m,40?m,respectively,the fracturing effect is best;when the mineral content is 33.912%,the crack opening and propogation is best.