| Surface drilling gas extraction technology is an efficient gas extraction control method,but by the influence of coal seam mining,drilling is easy to be destroyed.At present,rigid casing is used in the production casing of gas pumping production in surface drilling.Due to limited local deformation ability,rigid casing is easily broken after being squeezed by rock and shear force,resulting in scrapping of pumping drilling.In this paper,the variation of the flow field in the deformation zone of rigid casing is studied by means of laboratory test and numerical simulation,and the factors that affect the shear deformation of flexible casing in the process of shear deformation are analyzed.The main conclusions are as follows:Through the use of Fluent numerical simulation software,the flow field distribution and local drag coefficient of the casing in three typical deformation regions are simulated.The distribution of flow field and the variation of local resistance coefficient in the deformation zone of casing are grasped:(1)The comparison of local resistance coefficient of different deformation forms shows that the local resistance coefficient of shear deformation casing is the largest,the extrusion deformation is the second,and the tensile deformation is the smallest.Compared with shear deformation,the local resistance of extrusion deformation and tensile deformation region of casing is small and can be ignored.(2)During the process of gas flow in the zone of casing tensile deformation,the direction of gas velocity near the pipe wall changes.In addition to the change of gas velocity direction,eddy current is formed during the process of gas flow in the casing extrusion and shear deformation region.In the process of shear deformation,the change of the over-flow channel in the shear deformation area of casing and the influence of different forms,external diameters and shear distance of casing on the shear deformation of casing are studied.The conclusions are as follows:(1)The wall of corrugated pipe is still intact after shear denaturation,which can keep the pumping channel running normally.(2)The shear load of double buckle pipe is the largest.However,the integrity of the pipe wall can not be guaranteed because of the failure of the pipe wall under the small shear displacement.The corrugated tube can bear the least shear load,but its local deformation capacity is very large.The reason is that when shear deformation occurs,the corrugated pipe wall extends along the axial direction to increase the length of the deformation area.(3)The outer diameter of the casing increases.The maximum shear load of double-buckle pipe decreases because the wall structure of double-buckle pipe is spiral structure.When the width of spiral bond is the same,the larger the diameter of pipe is,the smaller the stability of the structure is,and the more easily it will be destroyed.The shear displacement corresponding to the maximum shear load of the three types of casing increases with the increase of the shear distance,which indicates that the existence of the shear distance will increase the deformation capacity of the casing.By using the finite element program of LS-DYNA explicit dynamic analysis,the stress distribution law of different types of casing during shear deformation,different corrugated forms of bellows and the influence of material properties on casing deformation are studied.The conclusions are as follows:(1)The corrugated height of the bellows increases the deformation capacity of the bellows and the corrugated width T increases the deformation ability of the casing.(2)In engineering application,the material of bellows can select a smaller elastic modulus,which can increase the shear deformation resistance of casing.The ultimate strength can be selected as casing material in the range of 300~2000MPa. |
PDF Full Text Request