Gas/Water Production Model For Steep-dip And High-thickness Coal Reservoir

Steep-dip,high-thickness and low-strength(referred to as special coal reservoir in this dissertation)are the prominent characteristics of coal reservoirs in the southern margin of Junggar basin,China.Based on the physical simulation and on-site coalbed methane(CBM)production data of coal reservoir in Fukang west block,southern margin of Junggar basin,combined with numerical simulation,this dissertation analyzes the influence of gas / water production on the mechanical properties and permeability of coal with low-strength in CBM production,discusses the law of vertical distribution of gas content and permeability heterogeneity and mechanism in different buried depths of high-thickness coal reservoir,and studies the CBM production in steep-dip coal reservoir.The physical property evolution law in CBM production of steep-dip,high-thickness and low-strength is summarized.The results show that: 1)in the process of water / gas production,the Young's modulus of coal reservoir gradually increases,the Poisson's ratio gradually decreases,the permeability decreases rapidly in the early stage of production,the permeability rebound is obvious in the late stage of production,and the influence of low-strength reservoir on permeability is more obvious.2)the vertical permeability of shallow high-thickness coal reservoir gradually decreases,and the gas content increases,while that in the deep reservoir is opposite.3)the gravity effect of steep-dip coal reservoir causes the initial and peak desorption time of methane to be out of sync in the up-dip and down-dip directions,resulting in the gradual development of gas production profile from "single-peak" to "double-peak" with the increase of reservoir dip angle,and the difference of gas content and permeability caused by reservoir dip also promotes the formation of "double-peak" gas production profile;4)The CBM production of special reservoirs under the combination of steep-dip,high-thickness and low-strength is more complex.The larger the physical properties difference between the up-dip and down-dip direction of the coal reservoir,the more obvious the "double-peak" gas production profile is,among which the vertical gas content heterogeneity of the high-thickness coal reservoir has a greater impact on the gas production profile of the steep-dip reservoir,and the vertical permeability heterogeneity has a little influence on the gas production profiles of the steep-dip coal reservoir.Under lower coal strength,the change of Young's modulus and Poisson's ratio with gas / water production has a greater impact on gas production,while the change of Young's modulus and Poisson's ratio has a weaker impact on gas production under higher coal strength.The results of this dissertation reveal the gas / water flow law in the process of CBM production in steep-dip,high-thickness and low-strength coal reservoir,which has a guiding role for CBM production in special reservoirs.