Research On Storage-Transportation Mechanism And Disaster Identification Technology Of H₂s In Coal Seam Influenced By Abandoned Oil Well

Hydrogen sulfide（H₂S）is the main toxic and harmful gas in the exploitation of oil and gas field,as well as in coal field.Due to oil and gas exploitation earlier than coal recovery in the areas with overlapping oil,gas and coal resources,while mining coal there have been a large number of abandoned oil-gas wells which could cause more serious H₂S hazard for safe and efficient production in coal mines.Taking Shuangma Coal Mine of Ningxia Coal Industry Group as a practical case,the dissertation studies on the sources,adsorption performance,storage-transportation mechanism of H₂S in coal seam influenced by abandoned oil wells,through experimental research,theoretical analysis,numerical modeling,on-site inspection.The permeation,diffusion,emission and migration laws of H₂S under the influence of mining have been studied as well in the coal mining area around abandoned oil wells.H₂S hazard forecast and treatment measures in the process of coal mining have been put forward.Following are the main results and conclusions thorough the researches above.First,according to the history of Shuangma Coal Mine,the paper studies the causes of H₂S formation in the area affected with abandoned oil wells,by revealing the condition of oil wells,such as wellbore structures and destructional forms,analyzing the source of H₂S emitting from coal mining face,and testing gas parameters.It is concluded that H₂S in coal measure strata in the affected area mainly comes from abandoned oil wells sealed incompletely,such as open wells or destructional wells with broken casing pipes.Under pressure,H₂S in abandoned oil wells permeates gradually into coal measure strata along fractures.Coal seams are the main enrichment layers of H₂S in the area affected with abandoned oil wells.Second,isothermal adsorption experiments were conducted with binary mixture gas composed of H₂S/He or H₂S/CH₄.It is illustrated that the curve features of coal absorbing H₂S gas is similar to that of coal absorbing CH₄.This result complies with the characteristics of Langmuir equation which represents monomolecular adsorption model.With the increase of pressure in absorbing equilibrium gas,the adsorption capacity grows gradually.The higher the gas boiling point is,the more the coal absorbs its corresponding gas.Coal has a stronger adsorption ability to H₂S than CH₄,H₂S in coal exists mainly in the state of adsorption and is only desorbed and released into mining space under the influence of mining action.It is the disturbed coal mass under mining that serves as the main source for H₂S that emits from the mining faces in the affected area of abandoned wells.Third,the distribution law of H₂S in original coal seams in the affected area of abandoned oil wells is studied by using a research method of simulating permeation-diffusion law of H₂S in different pressure,concentration,and burial depth and combining with on-site data measurement.It proves that,in the same coal seam,the concentration of H₂S is inversely proportional to distance from oil wells,the closer the distance,the higher the concentration.In addition,the increase of pressure leads to the migration speed increase of H₂S in coal and the increase of migration areas as well.The deeper burial and the greater pressure,the wider ranges in coal seam will be influenced by H₂S under same concentration condition.With steady pressure,migration range of H₂S has a limit value in coal seam in the affected area of abandoned oil wells.The concentration of H₂S has a tendency of gradual decline within the radial range centered on the oil well.Fourth,based on the variation of H₂S concentration measured during drilling,the position of emission,theoretical and experimental analysis,the paper explains distribution features of H₂S emission during mining and reveals the law of a leaking circle with a radius of 300 meters in the affected area of abandoned oil wells.Furthermore,it is predicted that harmful gas like H₂S with over-limited concentration would appear while mining the coal seam located in the affected area with a radius of about 300 meters around abandoned wells.Fifth,in order to identify H₂S hazard potential and to solve the over-limited problem of H₂S concentration during mining in Shuangma Coal Mine,classification indicators of abandoned wells are set up according to major influencing factors on mining around the abandoned wells.Abandoned wells can be classified into three categories:safe well,gas excessive well and seriously influential well,and corresponding controlling measures are put forward.The key comprehensive treatment and control technology system of H₂S for different categories of abandoned wells have been constructed with ground and underground supplemented treatment measures,including blocking,injecting,spraying,drainage,rising,lowering,monitoring,protective clothing and evacuating.The gas emission concentration of H₂S in mining face is taken as the indicator evaluating H₂S treatment effect in the affected area of abandoned oil wells.The research provides an important basis for optimizing design of protecting and controlling projects for harmful gas like H₂S in the affected area of abandoned oil wells,and has been put into use successfully in Shuangma Coal Mine.There are 73 figures,24 tables and 126 references in this thesis.