Multi-fracture interactions during two-phase flow of oil and water in deformable tight sandstone oil reservoirs

Tight oil reservoirs are complex geological materials composed of solid matrix,pore structure,and mixed multiple phases of fluids,particularly for oil reservoirs suffering from high content of in situ pressurized water found in China.In this regard,a coupled model considering two-phase flow of oil and water,as well as deformation and damage evolution of porous media,is proposed and validated using associated results,including the oil depletion process,analytical solution of stress shadow effect,and physical experiments on multi-fracture interactions and fracture propagation in unsaturated seepage fields.Then,the proposed model is used to study the behavior of multi-fracture interactions in an unsaturated reservoir in presence of water and oil.The results show that conspicuous interactions exist among multiple induced fractures.Interaction behavior varies from extracted geological profiles of the reservoir due to in situ stress anisotropy.The differential pressures of water and that of oil in different regions of reservoir affect interactions and trajectories of multi-fractures to a considerable degree.The absolute value of reservoir average pressure is a dominant factor affecting fracture interactions and in favor of enhancing fracture network complexity.In addition,difference of reservoir average pressures in different regions of reservoir would promote the fracturing effectiveness.Factors affecting fracture interactions and reservoir treatment effectiveness are quantitatively estimated through stimulated reservoir area.This study confirms the significance of incorporating the two-phase flow process in analyses of multifracture interactions and fracture trajectory predictions during tight sandstone oil reservoir developments.

Drying characteristics of biological porous media during convective drying

Experiments with potatoes were carried out in order to analyze the variation of the temperature and the mean dry basis moisture content over time,the effect of the drying conditions on the drying rate,and the relationship between deformation and dry basis moisture content.A two-way sequentially coupled thermo-hydro-mechanical math model was developed on the basis of Fickian diffusion theory,Fourier’s law of heat conduction and thermoelasticity mechanics in order to analyze the spatio-temporal distributions of moisture,temperature and drying stresses in the potatoes.The transient mathematical model,composed of a system of partial differential equations,was solved by finite difference methods.The numerical results obtained by using the mathematical model were in good agreement with the experimental data.The variations in temperature and moisture distributions,drying curves and stresses within potatoes over time were simulated,and the ways in which these are affected by the drying conditions were discussed.This work could help in developing an understanding of the relationship between mass and heat transfer,shrinkage,stress,and physical degradation of biological materials.