Study Of Failure Mechanism In Poorly Consolidated Sandstone Considering Shear Dilation And Compaction

The characteristics of poorly consolidated sandstone are high porosity,high permeability and different from well consolidated sandstone which has low strength and considerable plasticity.When hydraulic fracturing is conducted in this reservoir,there lacks a proper model to predict fracture propagation and corresponding rock failure.In a result,valuable suggestions are unavailable for field works like Frac&pack.In this work,first,we conducted physical tests and contrasted with field results to find a suitable constitutive model;Then numerical core tests are simulated under different stress paths to verify the model;Hydraulic fracture tests are also conducted to determine the main failure mechanism,and a fully coupled poroelastoplastic finite element model is established to simulate micro-fracture evolution,compaction failure and tensile fracture propagation during fluid injection into poorly consolidated sandstone reservoirThe model includes tensile failure,shear dilation,strain hardening and inelastic deformation.The effects of geomechanics(stress anisotropy and preconsolidated conditions)and fluid injection(fluid rheology and pore fluid diffusion)are investigated on rock deformation and fracture behavior.Results indicate that fluid rheology dominates the rock failure.High-efficiency and low-efficiency fracturing fluid can cause two kinds of shear dilation which are prior to tensile failure.The effect of compaction on permeability is slight,but significant on tensile fracture geometries These facture geometries differ from those under elastic and poroelastic conditions Preconsolidation affects the rock strength and shear band may not be generated under overconsolidated condition.