Research On Drilling Force And Failure Mechanism In Soft Interlayer Overlying Stope

Gas is one of the important factors threatening the safety of coal mine production.Surface drilling and extraction is an efficient coal mine gas development model.However,in the process of coal seam mining,the overlying strata move violently,which causes significant shear,extrusion,stretching and other destructive effects on the drilling shaft,and even causes the drilling to break.When there is a weak interlayer in the local bed,drilling damage is more serious and more frequent,and drilling easily broken failure has become one of the key problems restricting the popularization and application of this technology.In this paper,by using the basic theory and case analysis,basic experimental research and numerical simulation experiment,the method of combining the mining area in the strata under the conditions of weak intercalated motion rule and characteristics of drilling was studied.1)By analyzing the caving characteristics of overburden under mining conditions and the actual engineering cases of huainan mining area and jincheng mining area,the following conclusions can be obtained:(1)In the process of rock strata movement,there is a dynamic response relationship between the limit of movement and the limit of inflection point and casing failure.The position of the lower part of bending internal test in casing deformation is determined to be a dangerous area which is easily destroyed.(2)The drilling failure of guqiao mine,xieqiao mine,panyi mine,zhangji mine and jincheng chengzhuang mine in huainan is statistically analyzed.It is concluded that the probability of casing failure in the soft rock layer is up to 82.8%.In addition,the damage of oil drilling in fuyu oilfield and xinli oilfield is analyzed.2)A targeted study was conducted on the soft rock interlayer area in the stratum,and the movement rule of HSH(hard-soft-hard)special structure specimen under uniaxial load was explored through laboratory experiments.The experimental results showed that:(1)The stress-strain curve of the test specimen is similar to the stressstrain curve of the soft rock,and the trend before the peak is basically similar,which verifies the feasibility and correctness of the simulation experiment.(2)After the uniaxial compression test,all the failures occurred from the weak interlayer in the middle,indicating that the dislocation of adjacent strata of soft rock was caused by the failure of soft rock itself.With the increase of the strength of the soft interlayer,the relative slip of the upper and lower sandstone blocks decreases linearly.3)Using the numerical simulation analysis software FLAC3 D to simulate the actual formation movement and drilling force:(1)When the working face is pushed over 140 m,that is,the disturbance effect reaches the position of soft rock,the overall stress characteristics of the drilling casing show that the shear force in the soft rock area increases rapidly.In addition,the maximum shear force in the position of soft rock is compared with and without soft rock.It is found that the maximum shear force on the casing in the soft rock area increases significantly.(2)The relative amount of slip between the rock interface and the soft rock in the soft rock area is analyzed to explore the root cause of drilling failure caused by the rock movement.(3)By means of sensitivity coefficient analysis,it is determined that mechanical parameters should be the first factor to consider the intensity of the movement of soft rock strata.