Research On Multi-stage Pulse Fracturing Mechanism And Composite Technology Of Low Permeability Coal Seam

As a kind of unconventional natural gas resource,the development mode of coalbed methane is paid more and more attention by the oil and gas field.At present,the difficulty of coalbed methane development in China is that the geological characteristics of the reservoir are complex.The conventional fracturing reconstruction measures have been difficult to meet the requirements of stable production,and the exploration and research of new deep reservoir reconstruction technology are urgently needed.Therefore,this paper makes full use of the difference and complementarity of multi-stage pulse fracturing and hydraulic fracturing technology to explore the application of multi-stage pulse composite fracturing in the development of low-permeability coal seam.The simulation experiment of coal target is carried out to study its mechanism.The feasibility of multi-stage pulse fracturing for low-permeability coal seam is analyzed from the aspects of physical properties of coal reservoir,mechanical properties of coal,multiple desorption of coalbed methane and compositeness.In the process of multi-stage pulse fracturing,the model of propellant combustion fracture making,energy utilization and fracture dynamic extension are established.The model of propellant combustion fracture making is based on the equation of burning rate,mass conservation and energy conservation.The model of energy utilization considers the effect of kill fluid kinetic energy to analyze the fracture propagation.The model of fracture extension is based on the theory of elasticity,which leads to the multi-fracture propagation method is formed by adding weighting function,and the fracture propagation law is analyzed by software simulation.Through the simulation experiment,the dynamic test method of multi-stage pulse fracturing simulation experiment is improved,the mechanism of multi-stage pulse fracturing relaxation ground stress is revealed,the experimental data and P-T software processing system are established,and the multi-stage pulse fracturing simulation device is optimized.Furthermore,the theoretical design and method of multi-stage pulse composite process optimization are studied,and the multi-stage pulse fracturing device suitable for shallow coal layer is designed,which better solves the optimization of multi-stage charge and delay initiation structure.Finally,combined with thediscussion of specific parameters of well cases and the optimization design of active hydraulic fracturing composite process,especially the study of proppant settlement characteristics,the proppant settlement in fractures is analyzed as the main control factor.The results show that the multi-stage pulse fracturing fracture model,energy utilization model and coal target experiment established in this paper provide theoretical guidance for the composite process.It is suggested that further field application tests should be carried out to improve the multi-stage pulse compound fracturing technology of coalbed methane,which will have a bright future for the development of coalbed methane.