Study On The Adsorption Property And Deformation Model Of Methane Under Acidification

Gas is one of the important factors affecting coal mine dynamic disasters.Studying the occurrence of gas in coal seam is of great significance to the safety of production.Methane,the main component of gas,exists in the coal seam in an adsorbed state.Temperature,pressure,degree of metamorphism,degree of damage,water content,etc.are the relevant factors affecting the methane adsorption in the coal seam.Since coal is a porous medium and pore-fissure is the main storage place for methane,the study on the pore structure of coal seam can better understand the relevant mechanism of coal adsorption gas microscopically.Acidification is the main measure of oil and gas well stabilization.Acidification can lead to different coal sample adsorption gas capacity.The determination of mineral composition by X-ray diffractometer was carried out,and the acid system was determined by the experimental results,so as to provide guarantee for field application.Before and after the acidification of coal samples at low temperature liquid nitrogen experiment to explore the change of nitrogen adsorption amount before and after the acidification of coal samples,as well as the number of pores before and after acidification,the size of the pore size distribution changes,which can verify the acidification of the coal seam pore-The impact of phylogeny.Under the conditions of 25?,35?and 55?,the adsorption isotherms of coal sample before and after acidification were respectively studied.The results show that the development of coal pore-fracture system has an influence on the capability of coal adsorption.Based on the experiments of cryogenic liquid nitrogen and isothermal adsorption experiments,the maximum adsorption capacity of coal sample was discussed by using the adsorption potential theory.The experiment of coal reservoir deformation by the change of pore-fissure system after coal acidification was discussed by the adsorption-deformation formula analysis and research.Based on the above experiments,we can get the following research results:?1?By X-ray diffraction instrument for coal samples taken from the Yibin Baijiao coal mine to determine the mineral composition found that:except for the crystalline and kaolin clay minerals in the mine area are mainly carbonate minerals,carbonate minerals,Mainly calcite and dolomite.The total content of calcite and dolomite reaches26%.Many pores and fractures of the coal sample may be blocked by minerals such as calcite and dolomite and related impurities.And thus determine the acid system to hydrochloric acid-based.?2?SEM scanning of coal samples.The coal sample surface shows a few pores and micro-cracks clearly,the length of micro-size is about 1 m.Less coal crystal surface material,the rest of the formation of uniform.After image processing can be found in detail the large pores and micro-cracks more.?3?The industrial analysis of the coal samples before and after acidification showed that the fixed carbon did not change much,but the ash and volatile matter decreased compared with the acidified coal sample YB₂ without the experimental treatment.That acidification process,the blockage first react with the acid to form the relevant chloride,resulting in reduced ash.?4?It was found through the low-temperature nitrogen experiment that after the acidification treatment,the activation degree increased.Increase the number of micropores,pore size increases.The majority of occluded pores turn into open pores.The specific surface area,pore volume increase and pore volume increment increase,providing more area and place for gas adsorption.?5?The amount of methane adsorbed by YB₂ coal is much larger than that of YB₁.In the adsorption isotherm,the amount of gas adsorbed increases with the increase of adsorption pressure.As the adsorption proceeds further,the rate of increase of the amount of methane adsorbed by the coal slows down until the adsorption equilibrium is reached.Temperature is an important factor that affects methane adsorption.Increasing temperature will promote desorption.Adsorption potential theory fitting YB₁ and YB₂adsorption characteristic curve,YB₂ coal sample adsorption capacity than the YB₁ coal sample.It shows that the acidification technology changes the pore structure of coal,and the change of pore structure is an important factor that affects the adsorption performance of coal.?6?Based on the thermodynamics foundation,the coal rock adsorption deformation model under low pressure is obtained.And through this model calculation to explore the law before and after acidification coal sample adsorption and coal strain.The strain and adsorption capacity of methane adsorbed by YB₁ and YB2 coal samples showed a linear relationship within a certain range.The slope of acidified YB₂ coal sample in the relationship between adsorption strain and adsorption amount is much larger than that of YB₁ coal sample without acidification.It indicates that the increase of adsorption amount of coal sample after acidification leads to the increase of its adsorption strain.