Pore Structure Model And Gas-liquid Flow Law Of Low Rank Coal In Huolinhe Coalfield,Erlian Basin

Based on systematical summary of geological settings of low rank coal in Huolinhe coalfield of Erlian basin,combined with basic characteristics of low rank coal reservoirs,using mercury intrusion,low temperature nitrogen adsorption,low temperature carbon dioxide adsorption,isothermal adsorption and gas-water relative permeability measurement,pore structure characteristics of low rank coal were analyzed.In addition,full-range pore structure model for the studied coals was established and controlling effect on pore structure of each factor were analyzed,and characteristics and their controlling factors of adsorption/desorption,diffusion and gas-water two-phase relative flow were investigated as well.The results showed that the volumes of micropore,mesopore,macropore,and transitional pore are arrayed in descending order,and that the specific surface area is mainly contributed by micropore and full-range pore structure model is quantitatively characterized by piecewise function based on Gaussian peak accumulation model and power function model.Langmuir volume and Langmuir pressure are mainly controlled by micropore and transitional pore,followed by humic substance and median particle diameter.The diffusion amounts of methane and helium increase with time and tend to be constant at last,and the diffusion amount and initial diffusion velocities of both gas grow greater with higher pressure.The diffusion of helium levels off or approaches to equilibrium soon,while there is a clearly changing process during the diffusion-equilibrium of methane,indicating that the diffusion velocity of methane is slow and the desorption of methane needs some time.The diffusion type of low rank coal transformes from transitional diffusion to Fick diffusion as the equilibrium pressure increasing.Character parameters of gas-water relative permeability curves varies regularly with growth of effective stress,and the gas-water relative permeability curves of coal samples with good pore connectivity and high permeability shift to the left by comparison with coal samples with lower permeability,and the relative permeability curves also are featured with wide range of two-phase seepage,low irreducible water saturation,high residual gas saturation,low gas-phase relative permeability in irreducible water saturation,low water-phase relative permeability in residual gas.An integrated corresponding model of gas-water liquid changing with liquid saturation and effective stress for low rank coal reservoirs is established preliminarily,and the predicted results are consistent with measured value.