二氧化碳深含水层隔离的二相渗流模拟与岩石物理学研究

【作者】 刘小燕；

【导师】 席道瑛；

【作者基本信息】 中国科学技术大学 ， 固体地球物理学， 2005， 博士

【摘要】 近百年来气候的急剧变化引起人们对温室气体排放问题的注意，为了遏制全球增暖趋势，收集人类集中排放的CO₂并进行地下隔离成为减排对策之一。目前CO₂深部隔离储存的地点和方式可有以下几种选择：已废弃、无商业开采价值的油气田、深部煤层、深海隔离、深含水层隔离等。其中CO₂深部地下含水层储存，因其具有隔离储存空间大、封闭隔离时间长、分布广易于在排放点位置就近选择的优点，成为目前最受瞩目及最具潜力的隔离方法之一。 位于挪威北海中部Sleipner地区的Utsira砂层是世界上第一个以商业为目的大型超临界CO₂深含水层隔离的项目，从1996年开始每年向地下注入约100万吨CO₂，项目开展起来的6年时间里进行过3次时延地震，其监测资料对科学研究而言具有十分重要的意义。基于发表的数据和资料，本文拟对此进行更深入的研究工作，继续修改流动模型机制和提出适应于二相渗流分布的岩石物理学模型，为Sleipner地区CO₂深含水层隔离的时延地震某些流体异常提供新的机制解释。 针对超临界CO₂地中隔离的多组分多相渗流特点，构建了考虑局部非热均衡效应的非等温两相渗流THM耦合框架，开发了有限元模拟程序，以SACS计划设立的用于各国模拟程序对比的概化模型为BMT（Bench Mark Test）进行程序验证和核准，得到了考虑毛细管力和相对渗透率的两相非混溶渗流CO₂饱和度分布时间演化规律。由于模拟框架考虑了固液三相非等温的热传递过程，这为将来模型应用考虑相变情况的预留了拓展空间。 考虑超临界CO₂与地下水的粘度差异，CO₂深含水层隔离二相渗流可能产生粘性指进现象。对超临界CO₂在含水层中运移的两相流界面非稳定粘性指进现象进行了渗流力学机制分析，在二相流THM耦合模型中引入流度比判断条件下渗透率概率扰动项，将其引入非等温两相渗流的有限元模拟中，得到了CO₂在运移过程中的细部发育特征，特别的是CO₂中间饱和度区域将出现粘性指进引起的两相密集交错带；基于对由介质孔隙结构（如渗透率分层和毛管力作用）导致的优势流（或称沟槽流）指进形态的模拟，本文对三种指进的差异及其共同作用下CO₂在深含水层中驱替运移特征进行了比较分析。 针对裂隙性多孔介质，率先提出了含裂隙非均匀介质的地震波传播中波致流体弛豫的尺度效应概念。就不同的裂隙空间分布进行符合波传播特点的渗透率尺度效更多还原

【Abstract】 It seems certain that the change in CO₂ concentration in the atmosphere is due to human energy production from fossil fuels. The global warming issue has sparked public interest on all levels. To reduce CO₂ emissions, one must either reduce CO₂ production, or find alternative disposal schemes. Several different sequestration schemes — injection into deep oceans, un-minable coal seams, depleted oil reservoirs and saline aquifers, have been proposed to reduce atmospheric emissions. Sequestration of CO₂ by injection into deep geological aquifers appears to be the best choice in terms of resident storage time, storage capacity and proximity to emission cites.The Norwegian oil company, Statoil, is injecting approximately one million tonnes per year of recovered CO₂ into the Utsira Sand, a saline formation under the sea associated with the Sleipner West Heimdel gas reservoir. The large contrast in seismic impedence between water and supercritical CO₂ in Utsira sand has been successfully monitored with repeated surface seismic measurements in 1999,2001 and 2002. Based on these published time-lapse data, this thesis focuses on the developement of two-phase flow model and rock physics model in order to further characterize the CO₂ plume e.g. with respect to the distribution of CO₂ saturation in seismic section, the geophysical abnormity signature caused by immiscible pore fluids, and to find or analyse some new machanisms.Fluid flow simulation is performed using FEM （finite element methord） modeling for considering the THM couling effect on the two phase flow process. A coupled thermoporoelastic model of non-isothermal flow and deformation in elastic porous media with two immiscible porous fluids （CO₂ and groundwater） is presented, accounting for porosity change, compressibility and thermal expansion of convective heat flow. The govening equations are based on the equations of equilibrium, Darcy’s law, Fourier’s law and the conservation equations of mass and energy. Three phases and constituents （solid rock skeleton, liquid water and liquid or supercritical CO₂） are identified with no consideration of the supercritical CO₂ phase change in short time about saveral years after CO₂ injection. Thermal non-equilibrium between the phases is assumed throughout with a advantage in the convenience in model modifying to get the CO₂ phase changing effect. The simulating results can provide fluid pressures, relative saturation, and distribution of the fluids in the reservoir. The simulating code is validated on two BMT case with different codes from GEO-SEQ participate research teams.However, when CO₂ is injected underground, it forms fingers extending into the rock pores saturated with water, brine or petroleum. This flow instability phenomenon, known as viscous fingering, is significant for CO₂ sequestration because it will govern the available volume for CO₂ storage in the deep formation and the most important, from更多还原