【作者】 杨新乐；

【导师】 张永利；

【作者基本信息】 辽宁工程技术大学 ， 工程力学， 2009， 博士

【摘要】 我国煤层气储量丰富,煤层气的抽采不仅可以缓解我国能源紧缺的局面,同时可以保护环境和防治瓦斯灾害,目前,煤层气的“高储低渗”的特点一直制约我国煤层气工业的发展。当前如何提高低渗透煤层的渗透率是煤层气开采解决的难点,其理论未形成突破。注热开采煤层气是学术界普遍认同的很有可能成为未来煤层气资源的实际开采方法,但是注热开采煤层气增产机理还存在较大争议。本文基于传热学、热力学、岩石力学、弹性力学、渗流力学等多学科理论,通过实验室实验、数值模拟等方法和手段,对温度影响下煤层气赋存运移变化规律、注热开采煤层气的热力学评价理论及热采煤层气热-固-流耦合机制及规律进行了系统的研究。本文主要研究成果如下:(1)通过改装已有自主知识产权的三轴渗透仪,在实验室进行了考虑不同温度、应力条件下,两种煤样的煤层气解吸渗流实验。实验结果显示,升高温度后,煤层气分子吸收热量后,活性增强,内能增加,从煤基质表面的脱附能力提高,煤层瓦斯渗透率随温度的增加呈指数递增趋势,同时在低温吸附,升高温度后解吸,煤层气渗流量较低温吸附解吸时增加;在低应力时,由于煤体的膨胀影响较小,增量更为明显。(2)实验结果揭示了注热开采煤层气的增产机理:煤层气吸热后,气体分子动能增加,活性增强,大量从煤基质表面解吸出来,煤层气浓度增加,在浓度梯度作用下,更多的煤层气体通过基岩和孔隙向外扩散至裂隙,在裂隙中由于气体密度增加,压力梯度增加,最终导致气体渗流量的增加。(3)根据传热学,认为向煤层注热后,煤层气解吸区域按照温度不同分为加热区、加热前沿和未加热区,建立了这三个区温度场的一维数学模型,并利用相似变换法和积分方程近似解法求解了加热区、未加热区的温度场及加热前沿位置随时间变化的解析解。在此基础上,得出注热开采煤层气开采热效率和开采能量效率,为评价热采煤层气的经济性提供理论依据。(4)利用传热学和弹性力学理论,引入热弹性虎克定律,建立了煤层热-固耦合数学模型,并利用有限元软件进行了工程实例数值模拟。模拟结果表明,由于水蒸气的相变释放潜热作用,热扩散半径较为理想,同时由于注热时具有一定的压力,煤层气产出压差增加,煤层气解吸能力得到进一步增强。(5)利用传热学、热力学、弹性力学、渗流力学和岩石力学理论建立了注热时煤层气热-固-流耦合扩散渗流数学模型,给出了各场有限元弱解方程,利用有限元软件进行了煤层气注热单井开采的数值模拟。模拟结果表明,在注热开采条件下,煤层气渗流压力较未注热开采降低更为明显,渗流产量提高。模拟结果与实验相吻合,由此证明了数学模型的正确性及进一步说明注热开采煤层气是合理的。(6)在单井开采的基础上,为改善单井生产的局限性,进一步研究了井间干扰对煤层气渗流规律的影响。通过简化数学模型,编制了计算程序,对多生产井条件下煤层气渗流规律进行了数值模拟。模拟结果表明,在井间干扰的条件下,多生产井开采将增大煤层气解吸能力,增大煤层气产量。由数值模拟结果可以得出,在单井注热开采基础上,若采用多井整体吞吐技术,将增强注热开采煤层气效果。本文的研究为低渗透煤层注热开采煤层气的研究提供了可靠的理论研究和技术支持,同时对环境保护、煤矿安全生产也具有实用价值。更多还原

【Abstract】 The reserve of coal-bed gas is rich in china and the exploration of coal-bed gas can relax the short state of energy and protect the environment and prevent the gas disaster at the same time. At present, the characteristic, high reserve and low permeability restrict the development of coal-bed gas industry. The difficulty of coal-bed gas exploration is how to improve the permeability of coal-bed, and the theory breach is not formed. The technology of heat injection to exploit coal-bed gas that the scholar identified commonly maybe becomes a practical way, but there is a big disputed to the mechanism of the technology. Based on the theory of heat transfer, thermodynamics, rock mechanics, elastic mechanics, seepage mechanics, through the method of experiment and numerical simulation, the change rule of deposit and flow of coal-bed gas under the conditions of different temperature, the theory of thermodynamic evaluation and the coupling mechanism and rule of heat-solid-fluid is studied by the numbers.The main result of this paper is list as follows:(1) Through modified tri-axial seepage instrument of our own property rights, the two coal samples of coal-bed gas desorption and seepage experiment were carried in laboratory considered at different temperatures, stress conditions. The experimental results showed that the coal-bed gas molecules absorbed heat after elevated temperatures, the activity and inner energy increased, and desorption capacity increased from the surface of coal unite, coal bed gas permeability increases with temperature exponentially increasing. coal-bed gas seepage increases than lower temperature; at low stress, due to the expansion of coal was less affected, this increment is more evident.(2) The experimental result show the increase production mechanism of heat injection to exploit coal-bed gas: After the coal-bed gas absorbed heat, the kinetic energy and nature of molecules enhanced and escaped from coal mass surface greatly, and the consistency of gas enhanced. More coal-bed gas diffuses to crane from bedrock and pore under the condition of consistency gradient. In crane, the density of coal-bed gas induced to the increase of pressure gradient, and it’s a main reason that results in the increase of the seepage flux.(3) Based on heat transfer, after heat injection to coal-bed, desorption area of gas is divided to three according to different temperature: heated area, heated boundary and non-heated area. The one-dimensional mathematical model is set up to three area and resolve result is gained using similarity transform and integral equation approximated solution. On the basis of this solution, the exploitation thermal efficiency and energy efficiency is obtained and the theory to appraise the economy is supplied.(4) Utilize the heat transfer theory and elasticity theory, introduce heat elasticity Huke law, set up a hot - solid coupling mathematical model of coal seam and make use of FEPG. to set up examples of numerical simulation. The simulation results show that, in spite of smaller thermal conductivity of coal seam, because of the latent heat of water vapor phase change is released, the radius of thermal diffusivity is desirable, and the pressure difference is increased because of the pressure of heat injection, so desorption capacity of coal-bed gas is further increased.(5) The theory of heat transfer, thermodynamics, elasticity mechanics, seepage mechanics, rock mechanics is applied to set up the hot - solid - fluid coupling mathematical model of coal-bed methane with diffusivity seepage, and the finite element software is used to simulate a single well when exploited with heat rejection. The simulation results show that, the seepage pressure dropped more obvious and the production increase more than general exploitation under the condition of heat injection. The simulation results are accorded with experiment, therefore confirm the correctness of the mathematical model and the reasonability of heat injection is reasonable further.(6) On the basis of the exploitation of a single well, in order to improve the limitations of single well production, the impact on seepage rule of coal-bed gas of inter-well interference is further studied. By simplifying the mathematical model, the calculation procedures are writing and the seepage rule of coal-bed gas is stimulated under the conditions of multi-producing wells. The simulation results show that multi-production wells will increase desorption capacity and production of coal-bed gas. By the numerical simulation results can be drawn that on the base of single well exploitation with heat injection, the effect of heat injection exploitation is enhanced if the technology of multi-production well heat injection is adopted.Through the above research, the heat rejection exploitation of coal-bed gas is reasonable and feasible and a well-established channel is provided.更多还原