| Carbon capture,utilization and storage（CCUS）is one of the key technologies to combat global climate change.Accelerating the development of key CCUS technologies will help achieve our country’s"peak carbon dioxide emissions and carbon neutrality"strategic goals.Supercritical carbon dioxide（SC-CO2）drilling fluid has its irreplaceable advantages in the process of coalbed methane development.While enhancing the stability of the wellbore,it can improve the recovery rate of coalbed methane.At the same time,carbon dioxide recovery and utilization are realized,and the storage is completed finally.However,the high threshold pressure of coal breakage and high energy consumption limit the development and application of SC-CO2jet drilling and storage technology.It is still necessary to further reduce the energy consumption of the system and improve the coal breakage efficiency of SC-CO2jet.The current research on SC-CO2jets is based on continuous jets.Compared with continuous jets,pulsed jets have higher impact pressure and weaker water cushion effect,and have higher coal and rock breakage efficiency.Self-excited oscillation pulsed jet is the most realistic form of pulsed jet combined with engineering.Moreover,the peak pressure of the self-excited oscillation pulsed water jet is 2.5 times that of the continuous water jet.And it has more efficient impact performance and coal-rock breakage efficiency than the continuous jet.Therefore,in this paper,a new type of jet is proposed,which is the self-excited oscillation pulsed SC-CO2jet.To carry out the experimental research on the structure design and performance of the self-excited oscillation pulsed SC-CO2jet nozzle.Its purpose is to further improve the coal breakage efficiency of SC-CO2jet and accelerate the popularization and application of SC-CO2jet drilling and storage technology.It also provides basic support for the industrialization of CCUS and promotes the early realization of the"peak carbon dioxide emissions and carbon neutrality"goal.Since the pulse mechanism of the self-excited oscillation pulsed SC-CO2jet is essentially different from that of the self-excited oscillation pulsed water jet,this paper studies and analyzes the nozzle structure parameters that affect the self-excited oscillation pulsed SC-CO2jet based on the compressible turbulence theory.Self-excited oscillation pulsed SC-CO2jet nozzle design was carried out in Helmholtz resonant cavity.Reynolds average simulation was used to optimize the structure and size parameters of the self-excited oscillatory nozzle,and a design method of the self-excited oscillation pulsed SC-CO2jet nozzle was proposed.The generation mechanism of the self-excited oscillation pulsed SC-CO2jet was studied by large eddy simulation,and the pulse characteristics such as the pulse speed and pulse frequency of the self-excited oscillation nozzle were analyzed.The pulse pressure and system pulse frequency of the self-excited oscillation nozzle are measured by the experimental,so as to confirm the correctness of the nozzle design method.At the same time,the coal-breakage experiment of the self-excited oscillation pulsed SC-CO2jet was carried out,which verified the coal breakage efficiency of the self-excited oscillation pulsed SC-CO2jet.It provides guidance for further optimization of self-excited oscillation nozzles.The main research results of this paper are as follows:（1）The self-excited oscillation nozzle structure suitable for water jet is not suitable for SC-CO2through Reynolds average simulation results.According to the compressible fluid turbulence theory,the conditions for realizing SC-CO2self-excited oscillation are obtained,and the key design parameters of the self-excited oscillation pulsed SC-CO2jet nozzle are determined.（2）Based on the Reynolds average simulation,the parameter ranges of the diameter of the oscillation cavity,the angle of the collision wall,the length of the downstream nozzle and the diameter of the downstream nozzle are optimized.And the coupling relationship between the structure of the upstream nozzle and the cavity diameter ratio is determined.The range of suitable cavity diameter ratio corresponding to different upstream nozzles is different,and the suitable cavity diameter ratio can enhance the peak velocity and pulse amplitude.While the cavity diameter ratio outside the range will suppress the jet pulse,resulting in a large amount of energy loss.According to the relationship between the numerical simulation results and structural parameters,a design method of self-excited oscillation pulsed SC-CO2jet nozzle is proposed.（3）The generation mechanism of self-excited oscillation pulsed SC-CO2jet was studied by large eddy simulation,and the pulse characteristics and laws of self-excited oscillation pulsed SC-CO2jet were analyzed.Compared with the continuous jet,the self-excited oscillation pulsed SC-CO2jet has a better velocity pulse effect.The pulse pressure and nozzle system frequency of the self-excited oscillation pulsed SC-CO2jet were tested using the I-Scan pressure test system and vibration sensor.The results show that the pulse amplitude of the self-excited oscillation nozzle is larger than that of the continuous jet nozzle,and its average pressure is about 1.5 times that of the Laval nozzle.The experiment verifies that the self-excited oscillation nozzle designed in this paper is suitable for SC-CO2,which can generate pulsed SC-CO2jet and improve the utilization rate of jet energy.The matching degree of the upstream nozzle structure and the cavity diameter ratio determines the coal breakage efficiency of the self-excited oscillation pulsed SC-CO2jet.The higher the matching degree,the higher the coal breakage efficiency of the nozzle.This point further optimizes the design of the self-excited oscillation pulsed SC-CO2jet nozzle.Among them,the broken coal samples with a size of less than or equal to 20 mm produced via the coal breakage of nozzle L1-baccounted for 97.14%of the total sample mass,and the nozzle L2-caccounted for 98.6%.The number of figures is 137,tables is 34 and references is 99 in this paper. |
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