【作者】 刘爱华；

【导师】 傅雪海；

【作者基本信息】 中国矿业大学 ， 地质资源与地质工程， 2013， 博士

【摘要】 为了揭示沁南煤储层排采水地球化学动态变化规律及煤层气解吸-扩散-渗流特征，本文提出了排采水离子浓度动态变化的表征参数——“变化率”和“变化速率”来划分煤储层水系统类型；通过大块煤样带压解吸、煤岩气、水单相、气水两相渗透率以及煤基质扩散系数物理模拟来研究煤储层三级流动特征及煤储层各排采阶段的气、水解吸、流动规律。利用排采水离子浓度动态变化表征参数将煤储层水系统划分为“开放型”和“封闭型”两种类型，“封闭型”煤储层水系统的煤层气井各离子浓度“变化率”较“开放型”煤储层水系统大2倍左右，“封闭型”煤储层水系统的“变化速率”比“开放型”煤储层水系统高2³个数量级。基于高煤级大块煤样的逐级降压解吸模拟，发现了高煤级储层内部过渡孔、微孔吸附气的“解吸滞后”导致了每一压降阶段解吸气量呈现出波动变化、平稳升高、衰减下降的三阶段特征、累计解吸率与废弃压力呈指数关系、废弃压力0.7MPa下，高煤级储层的累计解吸率为53.46%、逐级降压解吸量是常压解吸量的1.46倍。基于不同尺度空间结构渗透率、扩散系数的静态实验，结合有效应力效应、煤基质收缩效应及滑脱效应综合作用下的煤岩渗透率动态模拟，认为煤岩宏观裂隙渗透率为高效渗透率，显微裂隙渗透率为低效渗透率，煤层气的扩散以过渡型扩散为主；指出煤储层三级流动是在煤层气高效渗流场、低效渗流场、煤层气扩散场之间的连续流动。根据煤储层排采的流体响应特征，从煤储层解吸的角度将煤层气井排采划分为水流阶段（I阶段）、不稳定解吸阶段（Ⅱ₁+Ⅱ₂阶段）、稳定解吸阶段（Ⅲ阶段）和衰减解吸阶段（Ⅳ阶段）。I阶段：压裂液及储层动水孔隙中重力水产出，煤层气无解吸；Ⅱ₁阶段：随压力降低，游离气与水溶气产量逐渐增加，出现第一个短期产气高峰；Ⅱ₂阶段：孔隙气解吸滞后及有效应力作用下裂隙渗透率降低，产能出现低谷；Ⅲ阶段：微孔内吸附气平稳解吸，煤基质收缩效应作用下裂隙渗透率增大，产量渐增，形成连续产气的第二个高峰；Ⅳ阶段：煤基块内压差与浓度差小，解吸缓慢，气产量逐渐减少。空间上煤层气解吸由井筒向外递进推进，时间上煤储层各处经历了前述四个阶段的解吸、流动过程，时空上煤储层排采呈现出“接力供气”的特征。更多还原

【Abstract】 In order to investigate the dynamic change regularities of underground waterduring coal reservoir drainage in southern Qinshui basin and the determination offollow-up CBM desorption, diffusion and flow process to CBM production,“changerate” and “variation velocity”, characterization parameters of dynamic change of ionsconcentration, were put forward to differentiate coal reservoir water systems. Throughdesorption experiments of bulk coal sample at fixed pressures, coal gas and liquidsingle phase permeability, gas-liquid two phases permeability and coal matrixdiffusion coefficient simulation, the three-level flow laws of coal reservoir werediscussed, as well as gas-water desorption and flow features in different drainagestages were revealed.In this paper, coal reservoir water systems were classified into two types, i.e.“connected” and “unconnected”, based on the characterization parameters of dynamicchange characteristics of ion concentration. In a short time, the ionic concentration“change rate” of CBM well water of the “unconnected” type was about two timeslarger than that of the “connected” one. In addition, the difference in the magnitude of“variation velocity” of ion concentration between the two water systems was2-3orders. On the basis of desorption experiments of bulk high-rank coal at step-downpressures,“desorption hysteresis” in micro-pore and transitional pore in high-rankcoal reservoir was considered to result in the fluctuations, rise and decline of threedesorption stages in each pressure-drop stage. What’s more, there exists anexponential relationship between the accumulative desorption rate and abandonmentpressure. Under an abandonment pressure0.7MPa, the accumulative desorption ofhigh-rank coal reservoir, and total desorption amount of step-down-pressuredesorption was1.46higher than that of desorption under normal pressure. Based onstatic simulation of permeability and diffusion coefficient on coal structure ofdifferent space scales, combining with dynamic simulation of coal permeability underthe comprehensive function of effective stress effect, coal matrix shrinkage effect andslippage effect, the coal macro-fracture permeability was defined as high-efficiencypermeability while the coal micro-fracture permeability was defined as low-efficiencypermeability and transitional diffusion mode dominated in all the CBM diffusionmodels. The three-level flow was pointed out to be a continuous flow in the CBMhigh-efficiency flow space, low-efficiency flow space and CBM diffusion space.Based on response characteristics of fluid in the coal reservoir drainage process, in terms of desorption in coal reservoir the drainage process was divided into four stagesi.e.（I） liquid flow,（Ⅱ₁+Ⅱ₂） unstable desorption,（Ⅲ） stable desorption, and （Ⅳ）attenuation desorption. Stage I: fracturing fluid and gravity water in reservoir poresoutput without CBM desorption. Stage Ⅱ₁: the first short peak of gas generationoccurred with the increase of free gas and water soluble gas due to the decrease ofpressure. Stage Ⅱ₂: the production reached a low point because of a desorption lag ofadsorbed methane and the reduction of fracture permeability under the function ofeffective stress. Stage Ⅲ: the adsorbed gas desorbed in the micro-pore steadily andthe production gradually increased due to the increase of fracture permeability underthe function of coal matrix shrinkage effect and there went up to the second peak ofgas-generating. Stage Ⅳ: the CBM production gradually reduced due to the differenceof pressure and reduction of concentration difference in the coal matrix, at lastdesorption dried up. The CBM desorption is proceeding from the wellboreprogressive outward in space. Coal reservoir has experienced the four stages ofdesorption and flow process in time and coal reservoir shows the characteristics of therelay gas supply in time and space.更多还原