The Fracturing Effect And Damage Behaviors For Microstructure In Shale Under Microwave Irradiation

There are abundant shale gas reserves in China,which is in the forefront of the world and has great prospects for development and utilization.However,the development and utilization of shale gas has not been carried out on a large scale due to the problems of low reservoir permeability,large investment in early development and insufficient existing fracturing technology in most shale gas wells.At present,it is urgent to develop new shale gas stimulation technology for its great development prospects and for the necessity of alleviating the contradiction between energy supply and demand and ensuring the long-term sustainable operation of energy system in China.Aiming at this point,the feasibility of improving shale gas reservoir permeability by microwave fracturing technology is discussed.Using the microwave irradiation device,we studied the heating effect and P-wave velocity variation of shale under microwave radiation,for analyzing the damage behaviors of microstructures and fracturing characteristics in shale.The results show that the temperature of shale under microwave irradiation increases rapidly and presents non-uniform distribution,and the higher the power,the stronger the non-uniformity.The damage degree of shale microstructure under microwave radiation is related to the microwave power,the irradiation times,the order of energy applying and the water saturation of shale.Under the same microwave energy,the number of microstructures of fully saturated shale increases more than that of dry shale.There are microwave energy threshold phenomena in the microstructure evolution and the macroscopic cracks development of shale samples.Under the same microwave energy,with the increase of radiation times,the number of shale microstructures shows a trend of significant increase,slight increase and smaller increase.Under the same irradiation time condition,the number of shale microstructures shows a trend of slight increase,significant increase and smaller increase,and it increases linearly with the decrease of microwave power.When the total microwave energy is less than 120 kJ,the order of applying microwave energy from small to large is more favorable to the microstructure development of shale.When the total microwave energy reaches 180 kJ,the microstructure development of shale is not sensitive to the order of microwave energy application.Microwave irradiation can cause the rigid particles in shale to produce fractures,the cracks appear at the particle interface and the water-bearing mineral chip break,showing a significant fracturing effect.This is conducive to improving the permeability of shale gas reservoirs.Then the application based on the experimental results of microwave fracturing technology to shale is proposed.