Experimental Research On Desorption Response Behavors And Mechanism Of Tectonically Deformed Coal Inducecd By Geostress Relief

The desorption response characteristics and mechanism of tectonically deformed coal inducecd by geostress relief are the theoretical basis for the exploration and development of coalbed methane in tectonic coal development area.This paper takes the coal seam No.11-2 of Liuzhuang mine field in Huainan coalfield as the research object,based on the geological conditions of coalbed methane in the minefield,the characteristics of the coal seam fissures and the structure and connectivity development characteristics of the coal seam.The self-developed"CO₂ injection and coalbed methane enhanced development experimental simulation system"was used to carry out the stress and strain experiments and adsorption-desorption experiments of the tectonic coal during the process of geostress release.Based on the experimental data,the surrounding rock pressure,coal structure,reservoir pressure,reservoir temperature,coal water content and other factors on the desorption of tectonic coal during the process of geostress release reveal the desorption response characteristics of tectonically deformed coal inducecd by geostress relief,and discuss the desorption mechanism of tectonic coal coalbed methane released by geostress.Research has made the following main conclusions:?1?The experimental results of low temperature liquid nitrogen adsorption and mercury intrusion show that the crushed coal sample has higher stage mercury intake,cumulative mercury intake and withdrawal,pore volume increment,pore specific surface area increment,cumulative pore specific surface area,cumulative pore volume and so on,mainly because the shredded coal structure is more broken than broken coal.The lag ring of broken coal sample is wider than that of broken coal sample,and its pore-fracture connectivity is worse,which is proved by the characteristics of coal adsorption loop.Because along with the coal body structure destruction degree aggravates,the pore-fracture of coal matrix is more developed and the coal particle is smaller,which is more conducive to the adsorption and desorption of coal.Through the observation of scanning electron microscope and stereo microscope,it can be seen that the structural cracks and endogenous cracks of fractured coal are well developed,the density and mesh of cracks are better,and the two or three cracks tend to show the characteristics of intersecting fracture development;the long and wide cracks of fragmented coal are more,and the cracks are linear and parallel,and partially filled with minerals.?2?Stress-strain experiments show that with the aggravation of the destruction degree of coal body structure,the axial pressure required for the deformation of the coal pillar becomes smaller,and the absolute value of the axial strain and the radial strain of the coal pillar becomes larger..The results of adsorption-desorption simulation experiments show that the instantaneous desorption and cumulative desorption of tectonic coal decrease with the increase of confining pressure,the instantaneous desorption and cumulative desorption of tectonic coal increase with the increase of the surrounding rock pressure,and the cumulative desorption of fractured coal pillars is about 1.5 times of that of primary structured coal in the first 100 s of desorption process,and the cumulative desorption of fractured coal briquettes is large.The cumulative desorption amount of fragmented briquette is about 4.5 times of that of primary structured coal;temperature has dual effect on coal desorption,and the influence of reservoir temperature rise on coal desorption is not obvious;the more water content,the less desorption amount of coal,and the cumulative desorption amount of dry coal is about the cumulative desorption amount of saturated coal.The cumulative desorption of coal with carbon dioxide as Adsorbate is about 3 times that of coal with nitrogen as Adsorbate.?3?According to the characteristics of the experimental data,the rate of decay of the suction is understood.The increase of the surrounding rock pressure and the decrease of the water content of the coal have a negative effect on the time required for the desorption rate of the desorption of the coal to be gentle.The pressure of the adsorption gas is increased and the coal body is increased.The degree of structural damage and carbon dioxide have a positive effect on the time required for the desorption rate of the decomposed coal to stabilize.The increase in reservoir temperature has little effect on the time required for the desorption rate of the decomposed coal to be flat.Because of the special coal structure of the coal,the coalbed methane desorption process of the coal under the ground stress release condition takes a short time,so the coalbed methane in the initial period of the desorption of the coalbed methane?0<t?3min?The desorption law has a better fitting relationship with the Venter model,and the analytical fitting of the experimental data also proves this.The paper contains 59 figures,9 tables and 146 references.