Research On Novel Sealing Material For Gas Extraction Borehole Based On Microcapsule

Coal,a kind of important industrial raw material in China's modernization,provides a powerful guarantee to industrial and economic development.Gas explosion and other potential hazards are constantly impacting China's coal mine safety production due to a gradual decrease in shallow coal reservoirs.Borehole gas extraction,a fundamental and effective approach,can eliminate the hidden danger gas brought.Meanwhile,the use of gas borehole sealing material with high performance for borehole sealing is one of the important means of improving gas extraction efficiency.Given the ineffective expansion and low strength caused by premature expansion of borehole sealing materials,this paper proposed a method to delay expansion by increasing the encapsulation rate of the expansion components with microcapsule technology through theoretical research and physical experiment.The main contributions and achievements of the thesis are as follows:(1)Based on a large amount of literature research and laboratory physical experiments,microcapsule technology was proposed to encapsulate the expansion agent in the borehole-sealing material to delay expansion.Ethylcellulose was selected as the wall,sodium bentonite as the core,and phase separation as the process of developing microcapsules after materials selecting.(2)The effects of core-wall ratio,PE dosage,and stirring rate on the encapsulation rate of microcapsules were analyzed by single-factor experiments,the interaction among the key parameters was obtained by the response surface method(RSM),and the influence degree of each influencing factor on the encapsulation rate was obtained.And with the help of Design-Expert software,the best parameters for microcapsule preparation are as follows:core-wall ratio is 0.8,the amount of PE is 1.5%,and the stirring rate is 400r/min.(3)The microcapsules with different proportions were added into cement-based sealing materials to make pure cement samples,ordinary expansive cement samples and new sealing materials samples,respectively.The influence of different proportions of expansive agents on the mechanical properties of cement samples was explored.It is concluded that the mechanical strength of the new sealing material can be increased by more than 20%compared with ordinary sealing materials,and the optimal content of microcapsules is 3%.(4)The expansion characteristics of ordinary cement,ordinary expansive cement and new sealing materials are studied respectively,and the expansion development curves of three different materials are obtained.The new sealing materials are divided into slow release period,rapid expansion period and stable period,verifying that the new sealing material has Certain delayed expansion characteristics.(5)Nuclear magnetic resonance(NMR)analysis was carried out on the ordinary expansive material and the new sealing material,and the T2 of the samples were obtained.The changes of moisture and pore structure in the hydration process of the two materials were analyzed and compared,which verified the excellent performance of the new sealing material in the microscopic perspective.Field industrial tests were carried out in Changcun Coal Mine of Luan Group to verify the laboratory tests and theoretical research.The new sealing material and ordinary expansion material were used to seal the bedding borehole.The real-time monitoring of gas extraction concentration and flow proves that the new material can effectively improve the borehole sealing effect and field borehole-sealing technology.