| The thesis takes the 15 th coal seam of Qiyuan mining area as the research object,and aims at improving the recovery rate of coalbed methane by nitrogen injection,and carries out nitrogen injection experiments and numerical simulation research on the15 th coal seam of Qiyuan mining area.The thesis mainly analyzes the regional profile,stratum lithology and structural characteristics,analyzes the reservoir characteristics of the No.15 coal seam in the block,clarifies the composition,content,distribution law and influencing factors of the coalbed methane in the study area,and reveals the mechanism and damage of the coalbed methane reservoir The reasons for the low production were clarified the mechanism of the improvement of nitrogen injection to increase the recovery rate,and the nitrogen injection process was proposed to increase the efficiency of coalfield gas production.The field application effect of the improvement of nitrogen injection was analyzed based on the field receipt data.The main results are as follows:(1)The coal reservoir characteristics of the No.15 coal seam in the Qiyuan mining area of the Shouyang block are revealed.According to the analysis of reservoir characteristics,it can be seen that the No.15 coal seam in the Shouyang block has the characteristics of low porosity,low permeability,fracture development and adsorption,and strong stress sensitivity.Its damage mechanism is mainly water sensitivity and water blocking damage,polymer and solid particle transport.To remove damage to the pore throat and stress sensitivity caused by drilling pressure.Therefore,the clean water drilling fluid can be improved by introducing inorganic salts,surfactants,and inorganic flocculants.(2)Get the mechanical parameters of No.15 coal seam in Qiyuan mining area of Shouyang block.Through triaxial rock mechanics experiments,the average elastic modulus of the coal in the block is 3.5 GPa and the average Poisson's ratio is 0.35.The in-situ stress in Qiyuan mining area and adjacent blocks was inverted,revealing the distribution law of in-situ stress in the research block.The direction of the maximum horizontal in-situ stress is 45°?80° east by north and the direction of the minimum horizontal in-situ stress It is 135° ? 175° east by north;the average minimum horizontal principal stress in Qiyuan mining area is 10 MPa,and the average maximum horizontal principal stress is 14 MPa.(3)The gas adsorption-desorption capacity of No.15 coal seam in Qiyuan mining area is revealed.The adsorption-desorption experiment was carried out on coal samples and the situation of its single component was analyzed.The results showed that in the Langmuir adsorption of methane and nitrogen,the specific result was that the volume of methane adsorption was greater than that of nitrogen,that is,the adsorption capacity of methane in this coal seam was greater than that of nitrogen adsorption.In addition,the adsorption of the mixed components is determined by the adsorption capacity,and is also affected by the concentration ratio and partial pressure of the specific components in the gas mixture.The process of adsorption and desorption of coal mixture is not necessarily related to the sequence,but only depends on the adsorption concentration ratio or partial pressure ratio and equilibrium pressure.(4)In this paper,a new technology of nitrogen injection and stimulation for enhancing oil recovery is established.According to the field construction data analysis of coal seam nitrogen injection process,the productivity of well Y-03 increases by more than 20 times after nitrogen injection into coal seam,and the production is stable for 4-6 months.On this basis,the optimization suggestions and matters for attention of nitrogen injection construction are put forward,and a new technology of nitrogen injection stimulation for coal seam to improve oil recovery is established. |
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