Study On Microscopic Characteristics Of Sealing Material Of Gas Drainage Borehole In The Underground Coal Seam And Its Application

Oil and natural gas is a strategic energy related to the national economy and people’s livelihood.In order to ensure energy security and sustainable development,a complete and diverse energy structure is the only way for the development of national energy strategy.As an unconventional oil and gas energy,the development and utilization of coalbed methane is an important part of the country’s "clean,efficient,safe,and sustainable" modern energy system.At present,the extraction of coalbed methane(gas)through the implementation of drainage drilling by well workers is one of the main methods of coalbed methane recovery.Gas extraction in underground coal mines can not only provide the use of gas energy,but also help eliminate gas disasters during coal mining.The sealing performance of gas drainage boreholes directly affects the drainage effect.Due to the construction of the borehole,it is easy to form a fractured coal body,increasing the gas leakage channel,and realizing the efficient sealing of the drainage borehole is a key issue that must be solved.At present,although scholars have proposed numerous sealing materials and technologies,the sealing problem of gas drainage boreholes has not yet been fundamentally solved.In this paper,by analyzing the sealing mechanism of the drainage borehole,the distribution state of the fissures around the borehole and the leakage channels existing in the drainage process are studied and judged.The drilling sealing material needs to achieve effective plugging for three air leakage channels that exist in the roadway pressure relief zone,the air leakage channel in the broken hole and the sealing material itself during gas drainage.Therefore,the research and development of high-efficiency sealing materials must possess the properties of microscopic properties,compactness,compression resistance,deformation resistance and the ability to adhere to the hole wall.Since ordinary cement materials are prone to water infiltration,the micro-characteristics and application research of borehole sealing materials for underground coal seam gas drainage need to consider the tightness,fluidity,and adhesion between the material and the hole wall.After selecting appropriate raw materials and conducting comparative test studies of multiple combined materials,the appropriate material ratio is determined,and an efficient sealing material for gas drainage drilling has been developed.The main research conclusions are as follows:(1)In view of the microscopic properties,compactness,pressure resistance and bonding ability of the drilling sealing material,and according to the requirements for sealing the microcracks of the drilling,the cement-based modified composite sealing material has been developed.(2)Cement with silica can make up for the problem of shrinkage and development of cracks in the process of ordinary cement solidification.It can plug the cracks around the borehole and fill the entire borehole,and its own compactness is relatively greatly improved.However,there are still many pores in the material,and its own mechanical properties have also been improved;after adding the styrene-acrylic emulsion,the compactness and adhesion of the sealing material are greatly improved.(3)The effects of modified materials on the pore structure and physical strength of cementbased sealing materials were qualitatively and quantitatively analyzed through experiments such as nuclear magnetic resonance,uniaxial compression,and SEM.Through numerical simulation analysis,the appropriate position of the sealing section of the borehole is established,and the device and method for the pressure sealing of the full-length screen pipe in the soft coal seam are researched and designed,which can not only realize simple and effective sealing,but also ensure long-term high-efficiency gas drainage.(4)After adding silica and styrene-acrylic emulsion to the material,Dw and Ds further increase,indicating that silica and styrene-acrylic emulsion can improve the pore connectivity,enhance the sealing performance of boreholes,and improve the efficiency of natural gas drainage Good positive meaning.However,adding silica and sodium silicate to the material at the same time has a negative effect.The Dw and Ds values decrease compared with cement,the pore structure of the material becomes uniform,and the connectivity becomes stronger.