STOCHASTIC FEM FOR INVESTIGATING H-M COUPLING BEHAVIOR IN UNDERGROUND FRACTURES

摘要

Fluid flow in fractures is widely involved in different fields because of high permeability of fracture paths.For instance,water or gas rapid flow through fractures can probably lead to an unhappy accident of water inrush or gas outburst in coal mines.Similarly, hydraulic fracturing is usually employed to increase reservoir permeability in methane exploitation.However,geometry, direction and connection of fractures are totally indefinite,or stochastic, due to difficulty in exploration.To better investigate the impact of random fractures on permeability and solid stress,we put forward a stochastic finite element method based on hydraulic-mechanical coupling and parameter perturbation.In analysis, stochastic properties of elastic coefficient and permeability come from sample experiments.Coupling calculation is realized by pressure transfer iteration between fluid and solid, until occurrence of a sufficiently small output difference for two series steps.As an example,we calculated an underground tunnel under a fractured aquifer.The results show that, 1) stochastic analysis exhibits H-M coupling behavior in statistical fractures more actually; 2) solid stress plays an unimportant role in distribution of fluid pressure, but remarkably disturbs flow rate; 3)fluid action on fractures can cut down surrounding wall stress; 4) permeability variability determines flow rate variability; 5) while the relative skewness for our example approaches 50, the variability for pressure or stress reaches a maximum value.