Rapid And Accurate Determination Method And Equipment Development Of Coalbed Methane Content

Coalbed methane content is the key basic parameter for coal mine methane disaster prevention and control,and the accuracy of its measurement results restricts the reliability of methane disaster prediction and the effectiveness of methane management measures.However,existing coalbed methane content determining methods and equipment cannot meet the requirements of frequent,rapid,and accurate determination in mines,and are not conducive to the supervision of the security department.Therefore,how to achieve accurate,rapid,and efficient determination of coalbed methane content parameters is currently an urgent problem to be solved.In this article,we studied the characteristics of frictional heat generation during drilling sampling,analyzed the mechanism of methane anomalous diffusion under the effect of frictional heat,explored the dynamic evolution of the amount of gas lost in advance during the drilling stage,developed a complete set of equipment for the downhole automatic rapid determination of coalbed methane content and carried out engineering tests by means of data research,theoretical modeling,numerical simulation and experimental verification.The main conclusions are as follows: 1)During the drilling process,the temperature of the drill bit rose rapidly at the beginning,and then the rate of temperature increase slowed down until the end of drilling when the temperature reached its peak,with an instantaneous maximum temperature of 460 K.The heating rate of the drill bit and the peak temperature of the coal cuttings are both proportional to the drilling speed and feed rate.The temperature variation law of heated coal cuttings under natural desorption conditions is following the negative exponential function.2)A new method of "fivestage" determination of coalbed methane content including gas dissipation during the borehole drilling stage is proposed.By establishing a coupled model of gas flow and coal deformation with dual pore-fracture,it is found that the gas dissipated during the borehole drilling stage is mainly the free gas in the fractures.The amount of advanced lost gas is 9.8% of the original coalbed methane content,indicating that the traditional model underestimated the original coalbed methane content by about 10%.The decrease of permeability resistance,the change of local stress state of coal around the borehole,the increase of permeability pressure difference,and the effect of frictional heating jointly led to the acceleration of advanced lost gas when the drill bit approached the sampling location.The advanced lost coefficient method can be used to quickly correct the results of traditional methods and thus improve the accuracy of coalbed methane determination.3)A non-isothermal fractional-order gas diffusion model was developed,which improves the accuracy of extrapolation of the lost gas volume by 17.7%compared to the isothermal model.If the exposure time of the coal sample does not exceed 20 min,the error of using the non-isothermal fractional order model to estimate the lost gas quantity is within 10%,and the error of determining the gas content does not exceed 5%.In contrast,the errors of the t model and the power function model are above 60%,and the average determination error of gas content is above 18%.It proves that the non-isothermal fractional order model is more adaptable to various underground conditions and the results of coalbed methane content determination are more accurate.4)In response to the shortcomings of traditional aboveground and underground phased determination methods,an on-site automated measurement technology for coalbed methane content was proposed and a complete set of equipment was developed.By crushing the coal sample underground,measuring the gas desorption flow intelligently,calculating the lost gas amount automatically,processing the data automatically and sending it wirelessly,the whole process of gas content determination can be completed underground and the determination time can be shortened to less than60 min.The application of the equipment in the Huainan-Huaibei mines shows that:the determination results of the CWH12 coalbed methane content underground automatic rapid determination instrument are 20.79% higher than the traditional coalbed methane content determination device on average,and the measured amount of desorbable methane is 17.15% higher on average.The research results of this article have achieved rapid,accurate,and automatic measurement of coalbed methane content,promoting the further development of mine methane disaster prevention and control technology.There are 94 figures,22 tables,and 206 references in this dissertation.