Study Of Adsorption/desorption Characteristics In Coal Reservoirs And Scale-invariant Adsorption Mechanism On Pore-solid Surface

Coal reservoir is natural porous media with complex internal structures,and many of the physical properties and physicochemical phenomena involved are affected by this particular structure.Therefore,how to accurately describe the complex structure of coal reservoir,and use the physical parameters of coal reservoirs to summarize the internal physicochemical phenomena,have always been the study direction of experts and scholars.The fractal discipline,founded in the mid-1970 s,provided the theoretical basis for the resolution of this problem.A large number of studies have shown that coal reservoirs have fractal features.After nearly 60 years of development,fractal theory has very mature theories in the description of coal reservoir structure.However,most of these descriptions briefly introduced the fractal structure of coal reservoir and the acquisition of fractal dimension values,and fail to describe them accurately.This paper proposes that there are two fractal topologies in the coal reservoir,namely the number-diameter fractal topology and the length-pore size fractal topology.The fractal structure of the natural reservoir should be the coupling of these two fractal topologies.Based on this,an effective formula for calculating the porosity of coal reservoir using the new fractal topology theory is derived.Coalbed methane is an auxiliary product of coal reservoir and is widely used as a green clean energy source worldwide.CBM resource reserves account for 13% of the world in China,ranking third in the world.However,it is limited by mining conditions and technologies thus CBM has not been effectively utilized in China.Therefore,the relevant theories of coalbed methane mining still require further research.Coalbed methane is an unconventional energy resource that is often stored in natural reservoirs in an adsorbed state.In order to understand this adsorption mechanism and characterize the adsorption state,antecessors proposed many adsorption models,such as Langmuir model,BET model,and FHH model.However,due to the influence of measurement scale,experimental technology,environmental factors,etc.,these models have more or less certain defects,and cannot accurately describe the adsorption mode of coalbed methane.Therefore,based on the fractalstructure of coal reservoirs,a capillary monolayer adsorption model is established and has been verified by data that it can be consistent with the coalbed methane adsorption curve.In addition,generalize the adsorption to the general situation,the equivalent reservoir capillaries model with fractal characteristics is simulated.Based on the Polanyi adsorption potential and micro-pore filling theory,a fractal capillaries adsorption model is established.Combined with the heterogeneity of natural reservoirs,the fractal surface adsorption mode on the pore-solid surface is proposed.The data shows that the model can be consistent with the trend of the five-type isotherm adsorption curves classified by BDDT,which provides a new idea for the exploration of adsorption mechanism.