Basic Research On In-seam Layout Of Multilateral Well By Imitating Leaf Veins In Shaqu No.1 Mine

In order to realize the efficient exploitation of coalbed methane resources and ensure the safe and efficient production of the mine,the bionics theory was applied to optimize the in-seam layout of multilateral wells along 3+4# coal seam in Shaqu No.1 Mine.By combining theoretical analysis,experimental study and numerical simulation,the similarities between 3+4# coal seam and laminae were clarified from two aspects of structure and fluid migration characteristics.The extraction efficiencies of different vein-shaped drillings were compared and analyzed.The high efficiency of vein-shaped drilling for gas extraction was clarified.It provide a theoretical support for the optimization of in-seam layout of multilateral well by imitating leaf veins.The main research results are as follows:Leaf samples of six plants,Fatsia japonica,Acer truncatum Bunge,Lagerstroemia subcostata Koehne?Photinia serrulata Lindl.,Aucuba japonica Thunb.,Cinnamomum bodinieri Lévl.,were selected for observation and statistics of macro structure characteristics.Among these,the densities of the primary and tertiary veins of Cinnamomum bodinieri Lévl.leaves were the lowest,and the density of the secondary veins was only higher than that of Aucuba japonica Thunb.leaves.The evaporative flux method was used to determine the hydraulic conductivity of different leaves,the water transport efficiency of Lagerstroemia subcostata Koehne leaves was the highest,followed by Cinnamomum bodinieri Lévl.leaves.The structure characteristics of mesophyll tissue and coal pore-fracture were characterized by X-ray ?CT scanning technology.The permeability anisotropies of the apoplast of different laminae and the percolation cluster of coal were analyzed by numerical simulation.It has been clarified that the distribution of geometrical morphological parameters of coal percolation cluster structure units was most similar to that of the apoplast of Lagerstroemia subcostata Koehne leaves,that the fractal dimension and the coordination number of the equivalent pore network model of coal percolation cluster were most similar to that of the apoplast of Cinnamomum bodinieri Lévl.leaves,that the permeability anisotropy of coal percolation cluster was most similar to that of Cinnamomum bodinieri Lévl.leaves.The principles of optimization by imitating leaf veins for in-seam layout of multilateral well were proposed.According to different leaf vein structures,18 kinds of multilateral well layout schemes were designed,and the hydro-mechanical-thermo coupled numerical model for gas extraction was established.The influence of permeability anisotropy on gas production and the extraction efficiency of different vein-shaped drillings were analyzed.By comparing the cumulative gas production per unit well length between vein-shaped drillings and SQN-0501-4 well group,the high efficiencies of gas extraction by vein-shaped drillings with the vein patterns of Cinnamomum bodinieri Lévl.leaf and Lagerstroemia subcostata Koehne leaf were verified.The high efficiency of vein-shaped drilling for gas extraction is illustrated from four aspects:The influence of vein-shaped drilling construction and drainage operation on coal seam permeability and pressure transmission was analyzed;By dividing the seepage field,conformal transformation and equivalent seepage resistance method were used to study the influence of structural parameters of vein-shaped drillings on gas flow resistance and skin effect;Taking 3+4#coal seam of Shaqu No.1 Mine as engineering background,the influence of vein-shaped drillings structure parameters on gas production under permeability anisotropy was analyzed by using numerical simulation method;According to the geometrical configuration of vein-shaped drillings arrangement,the risk of drilling section failure and the difficulty of screen completion of the veinshaped drillings with vein patterns of Cinnamomum bodinieri Lévl.leaf and Lagerstroemia subcostata Koehne leaf were compared and analyzed.The research results further improve the theoretical system of optimization by imitating leaf veins for in-seam layout of multilateral well,which has important theoretical and practical significance for improving the efficient and low-cost development of coalbed methane resources,as well as,the effect of gas disaster prevention and control.There are 99 figures,27 tables and 239 references in this paper.