| The pores and fissures in the structural coal are extremely developed.The coal is soft and easy to be broken,and its compressive strength and tensile strength are far less than that of the original structural coal.The poor coal strength is bound to affect the drilling efficiency and even cause accidents.Therefore,it is of great significance for the development of structural coal-bed methane to study the deformation of surrounding rock of structural coal shaft wall during drilling.Based on the national major scientific research instrument development project of the National Natural Science Foundation,"simulation test system for in-situ CBM horizontal well cave pressure relief development of structural coal"(no.41727801),this thesis studies the basic mechanical properties,resistivity characteristics and acoustic emission characteristics of remolded structural coal by means of indoor tests,theoretical analysis and other research methods,and explores the relationship between multi-stage hole enlargement and the deformation of surrounding rock of structural coal hole wall,The action mode and deformation zoning of multi-stage reaming drilling technology and surrounding rock deformation of structural coal hole wall are determined.The main research results of this thesis are as follows:(1)The basic properties of remolded structural coal such as water loss rate,compressive strength,resistivity and acoustic emission response were obtained.By analyzing the water loss curve and the change law of mechanical properties of remolded structural coal standard sample,it is concluded that the remolded structural coal with more than 96 h curing time and three layers of pressing is the closest to the original structural coal.The resistivity and acoustic emission characteristics of remolded structural coal under uniaxial compression are further studied.The initial resistivity of the specimen increases with the increase of curing time and the number of pressing layers.During uniaxial compression,the resistivity of the specimen first decreases sharply,then slows down,and then increases gradually after the specimen is damaged.With the increase of curing time and the number of pressing layers,the acoustic emission energy of the sample increases,and the slope of the cumulative energy curve is the largest before and after the failure of the sample.(2)The surrounding rock model of multi-stage reaming structural coal is established.The model can basically complete multi-stage reaming drilling by changing the drill bit in the horizontal direction.At the same time,it can change the WOB and rotating speed during drilling,and dynamically collect and analyze parameters such as torque and surrounding rock strain of structural coal hole wall.In this thesis,nine groups of multi-stage reaming structural coal surrounding rock drilling tests with WOB of 5N,10 N,15N and rotational speed of 80 rpm,120rpm and 160 rpm are carried out through this model.(3)The strain characteristics of surrounding rock of structural coal hole wall under multi-stage reaming with drilling parameters are tested and analyzed.The increase of WOB and rotating speed makes the strain of the surrounding rock of the hole wall of remolded structure coal in the initial drilling stage,the first stage of reaming and the second stage of reaming gradually increase.With the gradual increase of WOB and rotating speed,the variation range of the strain curve of the surrounding rock of the reconstructed structural coal hole wall increases in the initial drilling stage and the first stage of reaming,while in the second stage of reaming,the overall variation range of the surrounding rock strain of the structural coal hole wall is low.The torque has a strong response to the drilling stage,in which the average torque in the first stage reaming stage is 228.8% higher than that in the initial drilling stage,and the average torque in the second stage reaming stage is 219% higher than that in the first stage reaming stage.(4)The action mode of multi-stage reaming drilling technology and surrounding rock deformation of structural coal hole wall is expounded.In the initial drilling stage,the WOB compresses the coal and rock mass to produce elastic-plastic deformation and micro cracks,and then the structural coal is finally broken under the action of the bit speed,which is an action mode in which the WOB fracture mode and the speed fracture mode occur alternately;In the first stage of reaming,WOB exerts a squeezing effect on the side wall of the structural coal,while the surrounding rock of the structural coal hole wall is plastic deformed,resulting in a squeezing effect towards the center of the borehole,which is the action mode of WOB plastic deformation;In the second stage of hole enlargement,the plastic deformation of the surrounding rock of the hole wall of the structural coal is further enhanced,and then the structural coal is broken under the rotary cutting action of rotating speed,which is the action mode of rotational speed plastic deformation.(5)The deformation zoning of surrounding rock of structural coal hole wall under multi-stage reaming drilling technology is divided.According to the multi-stage reaming structural coal surrounding rock drilling test,the deformation area of structural coal hole wall surrounding rock can be divided into drilling fracture area and plastic area.According to the total stress-strain curve of structural coal,the deformation area of structural coal surrounding rock should also include elastic area and original rock stress area.Therefore,the range of each group of plastic areas divided according to the experiment is expanded,Finally,the deformation of the surrounding rock of the structural coal hole wall under the multi-stage reaming drilling process is divided into four areas: drilling fracture area,plastic area,elastic area and original rock stress area.With the progress of the reaming stage and the increase of WOB and rotating speed,the range of each deformation area increases to varying degrees.(6)The mathematical models of stress field,range displacement,WOB and rotating speed in the elastoplastic deformation zone of surrounding rock of structural coal hole wall under multi-stage reaming drilling technology are derived.The radial stress and circumferential stress in the plastic zone decrease with the increase of WOB and with the increase of rotating speed;The theoretical model of the radius of plastic zone,WOB and rotating speed.The radius of plastic zone increases with the increase of WOB,rotating speed and drilling radius;The radial stress in the elastic zone decreases with the increase of WOB,decreases with the increase of rotating speed,and the circumferential stress increases with the increase of WOB,and increases with the increase of rotating speed;The displacement of elastic zone increases with the increase of WOB speed.The thesis has 150 figures,14 tables,and 127 references. |
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