| The contradiction between the exploitation of two kinds of resources in the overlapping area of coal,oil and gas resources in Ordos Basin has become increasingly prominent,which provides new opportunities and challenges for the collaborative development of coal and oil and gas resources the goal of carbon peak and carbon neutrality.To realize the safe and efficient cooperative development of coal,oil and gas resources,the paper systematically studies the stability of oil and gas wellbore and the diffusion law of natural gas leakage caused by wellbore failure in the coordinated mining of coal and oil and gas based on oil and gas extraction corridors.The research results provide a theoretical basis for the safe and efficient collaborative development of coal,oil and gas in the overlapping area.The main conclusions are as follows:(1)The movement of overlying strata caused by coal seam mining has led to damage and deformation of oil and gas wells located in the oil and gas corridor area.The failure modes of oil and gas wellbore in the oil and gas corridor area can be divided into shear,tensile,compression,and torsion failure.Among them,shear failure is the main mode of wellbore.The stability evaluation models for casing under compression and shear failure were established using theoretical analysis methods,and the effects of load uniformity,casing wall thickness,outer diameter,and rock shear slip on the stability of oil and gas wells were analyzed.(2)On the basis of ensuring the functionality and integrity of the wellbore structure of oil and gas wells,the problem of retaining the width of protective coal pillars in the oil and gas corridor area of the Daniudi gas field in the Ordos Basin was analyzed.The horizontal deformation and shear stress of oil and gas well shafts in the corridor area are positively related to the burial depth and mining height of coal seams,while negatively related to the thickness of single rock layer in the overlying strata an d the magnitude of water pressure in the aquifer.The stage characteristics of the dynamic response of mining action to the stability of oil and gas wells in the oil and gas corridor area were obtained.Overall,with the successive recovery of working faces on both sides of the protective coal pillar,the horizontal deformation of oil and gas wells presents a stage evolution characteristic,while the dynamic response of the shear stress it is subjected to presents a cumulative response characteristic.(3)The mechanical deformation characteristics and permeability evolution laws of sandstone and sandy mudstone were explored by mechanical seepage coupling experiments.Under the mining stress path,the axial strain,radial strain,and volumetric strain of sandstone exhibit linear,exponential,and "V" shaped growth,respectively.As the initial confining pressure increases,the failure mode gradually transforms from shear failure to shear tensile failure.The mechanism of brittle ductile transformation of sandy mudstone were revealed,and the failure mode of brittle ductile transformation of sandy mudstone at macro and micro scales were mastered.With the increase of pore pressure,the permeability of brittle sandy mudstone increases 2.89%to 4.63% in the post peak stage.The exponential permeability prediction models for sandstone under mining stress state and improved exponential permeability prediction models for sandy mudstone considering gas slippage effect were established.(4)The numerical simulation method was used to reveal the distribution characteristics of the flow field inside the natural gas well leakage well,leakage outlet,and rock layer in the oil and gas corridor area.We studied the effects of leakage aperture,operating pressure,and rock resistance coefficient on the leakage rate of natural gas wells in the corridor area and constructed a prediction and calculation model for the leakage rate of natural gas wells in the oil and gas corridor area.Hazardous areas within natural gas leakage production sites within the oil and gas corridor area have been designated.The distribution characteristics of natural gas leakage concentration in the mining site were analyzed.As the leakage rate increases(leakage rate greater than 5 kg/s),when natural gas leakage occurs in the caving zone,the distribution of natural gas in the oil and gas corridor gradually changes from a point shaped to a horn shaped distribution.However,when natural gas leakage occurs in the fracture zone layer,it presents a "point shaped-horn shaped-feather shaped" distribution feature.The impact of different leakage rates and leakage layer conditions on the distribution of hazardous areas of leaked natural gas concentration in the oil and gas corridor area was clarified.Figure: [100];Table: [19];Reference: [175]. |
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