Research On Coal Bed Methane Seepage In Liaoning Mining Area

CBM is efficient and clean energy in place of natural gas,it has the broad development prospects. Some areas of our country have already formed the industrialization of coalbed methane resources, Liaoning CBM resources are abundant, although development started early, and achieved great success, but not yet formed a comprehensive industrialization. The main reason is that the majority of coal seams are low-permeability and contain water, gas output goes with water output in the process of drilling, while water affects the coalbed methane's output. From the retrieval, seepage rule system analyses of Liaoning mine CBM exploration is lesser. By combining laboratory test with the numerical simulation, further research in consideration of the slippage effect of water-gas two-phase percolation mechanism, influencing factors and mathematical model are made, found by the laboratory tests: the permeability of the same coal samples decrease with the increase of confining pressure, and in high confining pressure, coal sample can have certain permeability only getting enough pressure gradient,seepage curves are almost V shape. When the same confining pressure,permeability decrease with the increase of irreducible water saturation under different water content, the gas through the same coal sample start-up pressure increase gradually, that show up the same effect of the linear phase confining pressure increase.When considering slippage effect's influence, through the experiment fitting results can found that slippage effect and darcy seepage exist simultaneously, during the test, when pore pressure is lower, slippage effect is the main seepage mode. With the increase of pore pressure,effective stress reduces, darcy seepage approaches to grow, slippage effect begins to decrease, When pore pressure reach to the extreme value point, darcy seepage began to increase rapidly, slippage effect mode slow down.. Through the established mathematical model and the given basic assumptions,CBM permeability and reservoir pressure of considering slippage effect and without considering slippage effect are comparatively studied by FEPG software. The results show that the pressure near wells in consideration of slippage effect is higher than that without considering of slippage effect, distribution area of the effect pressure also bigger than that without considering of slippage effect. Regional stress of darcy flow and slippage effect near the production wells change acutely than that of distal area, the influence to pressure of Darcy flow is lower than slippage effect flow's,and pressure gradient is higher than slippage effect flow. Through contrastive analysis of the laboratory test sample parameters of coal reservoir pressure, concentration, moisture content, the relative permeability and drainage date and field data analysis can found that the simulation results and the field measured data are consistent. The result could provide scientific basis and productivity prediction for the exploitation of low permeability gas reservoirs.