Research On Instability Mechanism For Sealing Segment Of Boreholes And Reinforcing Dynamic Sealing Techniques

Borehole extraction is widely used to control mash gas in coal mine. In somecases, coal seam destroyed by geological processes so that the physical property ofcoal is instability. If the gas pressure of coal seam is large enough, the coal seam canbe called high gassy and soft coal seam. The boreholes in these coal seam are easy toproduce distortion. It’s hard to seal borehole and pose a great difficult to dischargemash gas from the high gassy and soft coal seam. On the basis of the stability ofboreholes, the effect of sealing has an impact on the gas concentration and negativepressure, and even the effect of drainage in the whole boreholes field. Therefore,performing the research relating to dynamic sealing techniques for boreholes witheasy-failure sealing segment is one of important practical significance to improve theefficiency of drainage and reduce the number of boreholes, and to prevent and controloutburst of gas and explosion.This paper firstly analyzed the characters of failure for boreholes in high gassyand soft coal seam, and studied the reasons for it. Then it was got that the efficiencyof sealing was influenced since the failure of sealing segment resulted to thedevelopment of fractures around the boreholes. Theoretical analysis suggested thenovel sealing techniques and materials could meet the need from borehole sealing andrealizing the high-efficiency drainage.Secondly, this paper studied the mechanism of grouting reinforcement for sealingsegment and the law of flowing for seriflux, which suggested that the groutingtechniques could inject the seriflux into the fractures existing in coal and rocks andmade the coal and rocks form novel structures with high intention and stability,and improving the properties and stability of coal and rock. A reasonable depth forsealing was determined to14m finally for coal seam in test field. Internal conditionsof boreholes were got through the infrared borehole imaging tool. According to thelaw between the amount of cuttings and depth of boreholes, sealing segment wasdivided into fractures and inflation developing area, fractures and inflation stable area,fractures and inflation severe area, fractures and inflations decreasing area and nonefractures and inflation area.Thirdly, in allusion to the problem in sealing for easy-failure boreholes in highgassy and soft coal seam, this paper came up with a novel approach for sealing byreinforcing dynamic sealing techniques. Based on the“solid seal liquid, liquid sealgas” Mechanism and the requirements of matched materials, cement solidification drilling materials was developed by adding swelling agent and water reducing agent.Incorporation and infiltrate in borehole walls for polyurethane material and curedmaterial were compared through environmental scanning electron microscope FEIQuantaTM250. According to the mechanism of reinforcing dynamic sealingtechniques and the requirements of matched materials, seriflux with certain cohesionwas got, which could meet the need of reinforcing dynamic sealing techniques. On thebasis of generalized Darcy’s law, spherical and cylindrical theoretical model fordiffusion, mechanism of diffusion for power law was got. The distribution of serifluxinjected in coal and rock was simulated through FLUENT, which optimized the lengthof every stage.Finally, in order to evaluate the effect of reinforcing dynamic sealing techniques,field tests were performed in NO.53panel of Chang Cun coal mine belonging to LuAn Company, as well as tests and analysis of relating parameters for gas drainage.Through above research, this paper theoretically expounded the mechanism ofreinforcing dynamic sealing techniques, then developed novel techniques of dynamicsealing with pressure which is appropriate to nearly horizontal boreholes in high gassyand soft coal seam and matched materials. In terms of equipment, pneumatic thickseriflux grouting pump and matched pneumatic mixer. Field applications indicted thesystem has great advantages comparing with traditional materials and techniques.During the research, the authors published10papers, in which five has been indexedby EI, obtain or apply for the processing of9patents,4of which are invention patents,and won the first award for Scientific Advencement of provincial, ranking tenth.