Study On Injecting Heat And Seepage Law In Coalbed Gas Of Low Permeability Coal Seam

Coal bed gas is a new clean energy raised in recent years which mostlyreserved in coal bed. Coal bed gas resource is abundant but the industry isrestricted in our country because of its high storage and low permeabilitycharacteristic. To raise the permeability of low permeability coal bed in order toraise the economic benefits of extracting coal bed gas is hot and difficult in theresearch. The traditional method of hydraulic fracturing in coal seam gas hasalready taken a concrete shape. Also, the gas injection method has begun to rise.But the coal bed gas production and economic benefit has not yet reached thedesired for the above two methods. In a relatively short period of time thetraditional method of hydraulic fracturing is effective. Along with the increaseof time, the pore closes and permeability reduces. As a result, the productionfallen sharply and coal bed gas is not fully extracted. Hydraulic fracturing hasbeen insufficient to meet the industrial demand. The transformation of themining technology of coal bed gas is imminent and the coal seam gas injection production technology is put forward accordingly. After the injection, the coalparticles expand with the increase of temperature. The internal mutualconstraints which produce thermal stress. When the thermal stress is greaterthan the ultimate strength of coal, thermal cracking happens. At the same time,thermal cracking will change the mechanical properties of the solid skeleton andthe permeability of coal. Whether the heat injection can increase the productionof coal bed gas and the temperature has much impact on the reservoirpermeability is in urgent need of researching. This article conducts research onheat injection and the improvement of permeability of coal reservoir.Conclusions are drawn based on the research on the mechanism of gas transportin coal bed and seepage characteristics of low permeability coal and rock massas well as numerical simulation of thermal transformation of coal reservoirpermeability.(1) According to the characteristics of the percolation feature of lowpermeability coal seam and its dual medium structure, considering theinteraction between the pores and fractures in coal, the double permeabilitymodel with temperature effect is established. Dynamic change model that issuitable for their characteristics of matrix porosity and fracture porosity is builtand the relationship between the two can be obtained.(2) For the low permeability coal seam infusion of thermal hydrologicmechanical of basic assumptions, the numerical model and numerical solutionformulas are derived for the establishment of low permeability of coal and rock mass.(3) According to the mathematical model of the heat injection exploitationof low permeability coal seam gas, numerical simulation of high temperaturesteam fracturing injection is conducted combined with engineering background.The fracturing process of low permeability coal is simulated under hightemperature steam and the given the initial conditions and boundary conditions.The results have shown that after1hr of high temperature steam fracturing, thepermeability of coal bed increased10times of the original. After7hrs of hightemperature steam fracturing, the permeability Increased about30%of that after1hr fracturing.(4) Based on the simulation results, the permeability increasing mechanismof low permeability coal and rock mass under heat fluid solid coupling isanalyzed.