Mechanism And Effect Analysis Of Resonance Improving Shale Reservoir Physical Properties

In recent years,unconventional oil and gas exploration and development in China has made rapid progress.Unconventional oil and gas resources such as shale gas,coalbed methane and tight sandstone gas have great potential.However,due to their tight reservoir,poor porosity and permeability and low natural productivity,it is necessary to make fractures and increase permeability through reservoir reconstruction,so as to realize effective exploitation.Resonance is common in nature,and it is an important research direction of unconventional reservoir reconstruction to use resonance to improve reservoir properties.Taking shale as the research object,this thesis studies the mechanism and effect of resonance improving shale reservoir physical properties by combining theoretical research,resonance experiment,observation of pores and fractures before and after resonance and testing of porosity and permeability parameters.The main achievements are as follows:The key to using resonance to improve shale reservoir properties is to induce fractures in the process of resonance,so as to improve shale permeability.There are two mechanisms of shale resonance fractures,namely,the expansion of original fractures and the generation of new fractures.There are four modes of resonance induced cracking in shale,i.e.micro fracture mode based on boundary cracking of mineral particles,micro fracture mode based on pore,one-way extension and expansion mode of primary fracture,and two-way extension,connection and combination mode of primary fracture.Resonance plays an important role in improving shale reservoir properties.After shale resonance,new pores and fractures can appear at the same time,the connectivity of pores and fractures is enhanced,and the pore fracture structure is improved.Shale fracture porosity increases after resonance,and shale with larger initial fracture porosity has larger increase after resonance.After resonance,the permeability of shale increases in both parallel and vertical bedding directions,but the increase of permeability in parallel bedding direction is greater than that in vertical bedding direction.The natural frequency of shale indirectly affects the effect of resonance improvement by affecting the resonance response.The factors that affect the natural frequency of shale include shale quality,density,mechanical properties and resonance excitation conditions such as resonance time and mode.The natural frequency of shale is directly proportional to density,and inversely proportional to quality and time;The higher the compressive strength of shale is,the more stable the natural frequency is;The measured natural frequency of shale placed horizontally is higher than that of shale placed vertically.Anisotropy,pore fracture structure,porosity and resonance times of shale directly affect the effect of resonance improvement by affecting permeability.The anisotropy of shale leads to different permeability improvement in different directions after resonance;The more developed the primary pores and fractures,the stronger the connectivity of pores and fractures after resonance,and the more obvious the permeability improvement effect;The permeability improvement effect of the second resonance is not as good as that of the first resonance.The application conditions of resonance improving reservoir technology are coal or shale reservoir,reservoir with poor compressibility and reservoir with poor microfracture development.The results of this study are helpful to the theoretical understanding and practical application of this technology.