页岩储层纳微米孔隙CO2/CH4吸附及驱替特性研究进展

利用CO₂开采页岩气不仅能够提高页岩气采收率, 还能够节省水资源并且对CO₂进行地质封存, 有助于实现页岩气开采过程的碳中和. 富有机质页岩储层纳微米孔隙中气体运移机制不同于常规储层, CO₂在储层中具有超临界特性, 致使开采机理复杂, 无法得到CO₂开采页岩气微观机理的准确认识, 所以研究CH₄, CO₂及其二元混合物在页岩储层纳微米孔隙中的吸附及驱替特性对准确评估和高效开采页岩气至关重要. 本文从实验、理论以及模拟方面对页岩储层纳微米孔隙中CH₄的吸附特性、CO₂/CH₄二元混合物竞争吸附特性以及驱替特性进行了综合分析, 对气体在纳微米孔隙中吸附及驱替特性的基础研究及关键问题进行讨论分析并提出了展望. 研究表明CH₄在页岩储层中表现为物理吸附, 有机质特征(丰度、成熟度、类型)、孔隙结构、无机矿物组成、温度和压力、含水率对页岩的CH₄吸附能力均有一定程度的影响. 在相同条件下, CO₂比CH₄更易被页岩储层吸附, 在页岩储层中注入CO₂可以促进CH₄的解吸, 并有利于CO₂的地质埋存. 开采方案的部署可采用井网形式的注采方式, 可以通过调整注入井的位置、数量以及CO₂注入速率对开采方案进行优化.      

CO2微气泡溶解动力学及提高采收率机理研究

CO₂微气泡是一种具有潜力的提高采收率与碳埋存方法,本文在自主设计的CO₂微气泡发泡装置的基础上,表征了高温高压条件下微气泡形态,进一步研究了微气泡的溶解特征,研究结果表明:10 MPa下制备出的微气泡直径10～70μm,平均直径34.43μm; 15 MPa下制备的微气泡直径更小,平均直径25.03μm;地层水高矿化度条件下,平均气泡直径277.17μm,且气泡稳定性降低.微气泡的溶解实验结果表明CO₂微气泡的溶解速率较高,但是未溶解的CO₂仍以气泡的形式在地层中运移,微气泡注入地层后将形成“碳化水+微气泡”的运移模式.采用可视化微流控平台,首次研究了高温高压条件下无化学剂辅助CO₂微气泡的提高采收率机理:(1)提高微观洗油效率;(2)通过体积膨胀、溶解携带作用将油滴带出盲端,采出盲端中的剩余油;(3)打破油滴的毛管压力平衡状态,采出柱状残余油;(4)在流动中产生“贾敏效应”,封堵大孔隙、提高波及效率.本文研究可为CO₂微气泡提高油藏采收率与碳封存提供指...     

惰性气体N2/CO2抑制瓦斯爆炸实验研究

为探究惰性气体(N₂和CO₂)对瓦斯气体爆炸影响,采用中型尺寸瓦斯爆炸实验装置,在N₂及CO₂体积分数为0%、9%、14%工况下开展了瓦斯爆炸实验研究,获取了N₂和CO₂对矿井瓦斯抑爆特性的影响规律,并针对瓦斯爆炸过程中惰性气体N₂和CO₂对爆炸超压变化的影响及爆炸抑制效果进行了对比分析。结果表明:随着初始混合气体中惰性气体N₂或CO₂含量的升高,瓦斯爆炸超压均明显降低,CO₂的抑爆效果优于N₂;N₂和CO₂对较高浓度瓦斯气的抑爆效果更为显著。     

超临界CO2直旋混合射流破岩特性的实验研究

超临界二氧化碳(CO₂)射流破岩既能降低岩石门限压力又能有效保护储层,直旋混合射流兼具直射流和旋转射流特点可提高破岩效率,基于此提出了超临界CO₂直旋混合射流的破岩方法。为了揭示超临界CO₂直旋混合射流破岩特性,设计加工出叶轮式直旋混合射流喷嘴,通过岩石定点冲击破碎实验对比了该射流与常规水射流的破岩效果,并研究了叶轮长度、叶轮中心孔直径、混合腔长度、喷射距离、射流压力等重要参数对超临界CO₂直旋混合射流破岩效果的影响。结果表明:相同实验条件下,该射流方法的平均破岩能力比常规水射流提高了42.9%;超临界CO₂直旋混合射流破岩易出现较大体积岩屑崩落现象;随着叶轮长度、混合腔长度、喷射距离的增大破岩效果均先增强后减弱,实验条件下上述参数存在最优范围值;叶轮中心孔直径的增大会导致岩石破碎孔深度增加、直径减小;随着射流压力的升高,超临界CO₂直旋混合射流破岩效果有着较为明显的提升。研究结果可为超临界CO₂直旋混合射流破岩方法的进一步研究提供实验依据。     

中国海域盆地CO2地质封存选址方案与构造力学分析

本文围绕“碳达峰、碳中和”国家战略目标,从断裂活动、盆地压力、构造沉降特征、地震活动性和地温梯度等角度综合分析中国海域盆地适宜大规模CO₂地质封存的条件与目标,在宏观上认为东海陆架盆地、珠江口盆地、琼东南盆地东部以及南海中央海盆是最佳CO₂地质封存区域,但这并不排除其他盆地内部存在适宜的CO₂地质封存点,因为具体某个地质封存工程目标的范围相对较小.东海陆架盆地、珠江口盆地和琼东南盆地内适用于CO₂地质封存的地层包括盆地晚期快速沉降期沉积层的底部咸水层和热沉降沉积层内的含油气单元,在适宜的海底之下800～4000 m深度范围内,孔隙度大于10%,静水压力约在8～40 MPa之间、静岩压力约在13～83 MPa之间变化.在此压力范围和合适的地温梯度范围内, CO₂以超临界状态存在,其密度随温压变化相对稳定,有利于CO₂的流动和渗透.另外,盆地内的基性岩浆岩建造的规模和数量也为CO₂地质封存和永久矿化提供了很好的条件.虽然工程难度大和代价高...     

初始温度对CO2抑爆作用的影响

将CO₂充入的液化石油气中并进行点火,研究不同初始温度下CO₂对多元混合气液化石油气爆炸的抑制作用。实验显示:初始温度15℃时CO₂体积分数达到36%时,混合气体退出可爆范围,临界氧浓度为12.8%;初始温度50℃时CO₂体积分数达到39%时,混合气体退出可爆范围,临界氧浓度为12.2%。结果表明:CO₂对液化石油气爆炸的抑制效果在一定程度上要受环境温度的影响。     

惰性气体对C3H8可燃下极限的影响

为探究CO₂、N₂和Ar对C₃H₈可燃下极限的影响,在5 L爆炸容器中测定了C₃H₈在O₂/CO₂、O₂/Ar、O₂/N₂三种气氛下的可燃下极限。首先分析了稀释气浓度、稀释气种类和氧气浓度对C₃H₈的可燃下极限的影响。结果表明,在O₂/CO₂气氛下,稀释气浓度变化对C₃H₈的可燃下极限影响最大,对O₂/Ar的影响次之,对O₂/N₂的影响最小。在相同稀释气浓度条件下,CO₂对C₃H₈可燃下极限的影响最大,N₂的影响次之,Ar的影响最小。随着O₂浓度的上升,O₂/CO₂气氛的可燃下极限出现较为明显的下降,O₂/N₂和O₂/Ar的氛围的可燃下极限平缓上升。通过建立能量平衡方程分析了稀释气的比热和辐射效应对可燃下极限的影响。结果表明,混合气比热的改变是C₃H₈可燃下极限改变的主要原因,辐射热损失是影响可燃下极限的重要因素。     

超临界CO2气爆煤体致裂机理实验研究

为提高超临界CO₂气爆低渗透煤层增透技术的应用水平,进一步研究超临界CO₂气爆煤体致裂机理,利用自主研发的超临界CO₂气爆装置,在多通道电液伺服相似材料试验台上,对原煤和混凝土大试件(1 m×1 m×0.5 m)进行了超临界CO₂气爆实验,用动态应变仪采集试件内部监测点处的变形和破坏信息,并用工业窥镜对爆破孔内裂隙分布进行了观测。分析气爆应力波的变化规律和气爆后试件的破坏形貌特征可知,距离气爆孔由近及远依次分为粉碎区、裂隙区和震动区,其形成机理为:超临界CO₂冲击气爆孔周围介质并形成远超介质抗压强度的球面纵波,介质在径向压应力作用下发生粉碎性破坏,形成粉碎区;应力波传播能量逐步衰减,不足以使介质产生压缩破坏,然而脆性材料抗压不抗拉,其产生的环向应力仍然使介质产生径向裂隙,应力波之后具有准静态加载作用的高压CO₂气体进入裂隙形成气楔,促使裂隙进一步发育和扩展,形成裂隙区;裂隙区以外的介质在低能量应力波的作用下只发生震动,未发生明显破坏,即震动区。裂隙的扩展速度与其到气爆孔距离符合“S”形曲线衰减,裂隙的高速扩展发生在粉碎区,低速扩展发生在裂隙区;距离气爆孔越远,测点的峰值应变越小,相同距离内节理裂隙等结构面越复杂,峰值应变减小的幅度越大且应变波形差别越大。     

磁场效应对甲烷爆炸影响的机理

为了揭示磁场对甲烷爆炸特征的影响机理,开展了磁场对甲烷爆炸影响实验,得出了磁场对甲烷爆炸压力、火焰传播速度、爆炸产物组分及体积分数的影响规律。利用Chemkin-Pro软件模拟甲烷爆炸链式反应过程,得到了甲烷爆炸过程中的关键自由基和基元反应。通过理论计算,对不同自由基在磁场作用下的受力进行分析,揭示了磁场对甲烷爆炸的影响机理。研究结果表明,磁场能够降低甲烷爆炸压力和火焰传播速度,降低CO和CO₂的生成量,增加甲烷的残余量;·H、·O、·OH、·CH₃、·CH₂O是甲烷爆炸的关键自由基,由于·O的磁化率较高,被吸引到磁感线密集的区域,·O与其他自由基的碰撞几率减少,从而降低·HCO→CO→CO₂的链式反应速率,导致CO和CO₂生成量降低,且甲烷爆炸强度降低。     

CH4/N2、CH4/CO2二元和CH4/N2/CO2三元混合气体爆炸极限的实验与估算

为了获取甲烷与不可燃组分组成的混合物的爆炸极限,采用一种基于绝热火焰温度的混合物爆炸极限估算方法,对CH₄/N₂和CH₄/CO₂这2种二元混合气体及3种不同阻燃剂体积分数的CH₄/N₂/CO₂三元混合气体的爆炸极限进行实验研究,并将实验结果与估算值进行比较。CH₄/N₂与CH₄/CO₂二元混合物实验值与估算值在爆炸上限处的平均绝对偏差为0.34%,在爆炸下限处的平均绝对偏差为0.15%。3种不同比例的三元混合物实验值与估算值在爆炸上限处的平均绝对偏差为0.43%,在爆炸下限处的平均绝对偏差为0.20%。结果表明,估算方法对甲烷与不可燃组分的二元混合物与三元混合物爆炸极限的估算均具有较高的准确度。     

钻井式煤炭地下气化技术的发展及关键力学问题

煤炭地下气化技术是有希望解决我国能源危机的重要手段之一,是煤炭资源高效清洁利用的有效手段之一,是拓展天然气资源实现战略资源接替的有效方法之一.本文通过调研国内外煤炭地下气化技术,将煤炭地下气化技术分为两类,即钻井式技术和巷道式技术,并重点叙述了钻井式煤炭地下气化技术开发模式.钻井式煤炭地下气化技术的发展可分为4个阶段:...     

CT Imaging of Low-Permeability, Dual-Porosity Systems Using High X-ray Contrast Gas

Low-permeability, dual-porosity media such as coal and gas shale (i.e., mudstone) exhibit structural and chemical features across a range of scales spanning from tens of meters to nanometers. Characterization methods and efforts for these porous media are needed to understand gas in place, gas flow behavior, and storage capacity for potential CO $_{2}$ sequestration. Characterizing the structure and heterogeneity of representative samples helps determine how the physical and chemical processes associated with CO $_{2}$ transport in coal and gas shale affect injectivity and storage capacity (over long periods of time), and the ability of these media to sequester CO $_{2}$ (as both a free and adsorbed phase) for thousands of years. In this study, an imaging technique focused on the submillimeter scale is applied to shale and coal samples of interest. In particular, porosity, component matrix distribution, and evidence of gas transport through these tight media were studied.     

煤炭地下气化关键力学问题的数值研究进展

煤炭资源的清洁高效利用已成为“双碳”背景下科学研究的重要方向和新课题.在众多相关技术中,煤炭地下气化技术近年来得到快速发展并展现出巨大潜力.然而,由于室内实验和现场试验的实施成本非常高,气化机理认识和控制运行工艺优化方面的研究均受到很大限制.近年来,运行成本低、操作简单、实施周期短的数值模拟方法成为重要的研究工具,得到越来越多的关注.由于煤炭地下气化过程极其复杂,数值模拟方法在数学建模和数值求解方面均面临巨大挑战.对此,本文开展了以下工作:对煤炭地下气化过程进行了详细分析,阐明各个运行空间的物质和关键问题,厘清煤炭地下气化的本质;归纳出流体动力学问题、热力学问题、材料应力问题以及化学反应动力学问题等4类关键力学问题;详细介绍每个关键力学问题数值研究的最新成果和发展历程;介绍煤炭地下气化数值研究的工程应用,并指出其发展趋势.本文工作对推动煤炭地下气化数值方法的发展以及指导我国煤炭地下气化先导试验设计和现场实施有积极的理论意义.     

南海潜在地质灾害因素研究

南海是我国海洋开发的重点海区之一, 调查潜在地质灾害因素, 科学地评价海洋工程地质条件至关重要。本文根据20多年的调查资料, 研究了南海可能产生的地质灾害类型、规模、分布特征、形成机制和诱发因素, 分析了南海地质灾害因素主要特征, 提出今后研究方向, 为科学开发海洋资源提供依据。     

New Trapping Mechanism in Carbon Sequestration

The modes of geologic storage of CO₂ are usually categorized as structural, dissolution, residual, and mineral trapping. Here we argue that the heterogeneity intrinsic to sedimentary rocks gives rise to a fifth category of storage, which we call local capillary trapping. Local capillary trapping occurs during buoyancy-driven migration of bulk phase CO₂ within a saline aquifer. When the rising CO₂ plume encounters a region (10⁻² to 10⁺¹m) where capillary entry pressure is locally larger than average, CO₂ accumulates beneath the region. This form of storage differs from structural trapping in that much of the accumulated saturation will not escape, should the integrity of the seal overlying the aquifer be compromised. Local capillary trapping differs from residual trapping in that the accumulated saturation can be much larger than the residual saturation for the rock. We examine local capillary trapping in a series of numerical simulations. The essential feature is that the drainage curves (capillary pressure versus saturation for CO₂ displacing brine) are required to be consistent with permeabilities in a heterogeneous domain. In this work, we accomplish this with the Leverett J-function, so that each grid block has its own drainage curve, scaled from a reference curve to the permeability and porosity in that block. We find that capillary heterogeneity controls the path taken by rising CO₂. The displacement front is much more ramified than in a homogeneous domain, or in a heterogeneous domain with a single drainage curve. Consequently, residual trapping is overestimated in simulations that ignore capillary heterogeneity. In the cases studied here, the reduction in residual trapping is compensated by local capillary trapping, which yields larger saturations held in a smaller volume of pore space. Moreover, the amount of CO₂ phase remaining mobile after a leak develops in the caprock is smaller. Therefore, the extent of immobilization in a heterogeneous formation exceeds that reported in previous studies of buoyancy-driven plume movement.     

松辽盆地咸含水层埋存CO2储存容量初步估算

沉积盆地深部存在体积巨大的咸含水层,是很好的埋存CO2的地质储体。可靠合理的估计CO2储存容量是选择场址的重要前提。目前国际上较为通用的评价CO2储存容量是金字塔评价方法。松辽盆地咸含水层岩性以白垩系的嫩江组砂岩和青山口组砂岩为主,空隙发育较好,盖层连续完整且封闭良好,决定了其可以作为储存CO2的地质储体。以松辽盆地为实例,估算了咸含水层CO2理论储存容量大约为6916Gt。     

涡流检波器特性测量与参数识别

新型涡流检波器已在地质、石油、煤炭人工地震勘探中采用。本文将最新的振动试验方法、数据处理技术及模态参数识别应用到检波器特性参数的确定中。论述它的有效优化方法,并首次将它应用到传感器的标定技术中,做到快速准确测定它的参数值,为检波器的生产、使用提供技术保证,亦为涡流检波器参数综合测试仪研制提供理论基础。     

Characteristics of Salt-Precipitation and the Associated Pressure Build-Up during CO<Subscript>2</Subscript> Storage in Saline Aquifers

Mitigation and control of borehole pressure at the bottom of an injection well is directly related to the effective management of well injectivity during geologic carbon sequestration activity. Researchers have generally accepted the idea that high rates of CO₂ injection into low permeability strata results in increased bottom-hole pressure in a well. However, the results of this study suggested that this is not always the case, due to the occurrence of localized salt precipitation adjacent to the injection well. A series of numerical simulations indicated that in some cases, a low rate of CO₂ injection into high permeability formation induced greater pressure build-up. This occurred because of the different types of salt precipitation pattern controlled by buoyancy-driven CO₂ plume migration. The first type is non-localized salt precipitation, which is characterized by uniform salt precipitation within the dry-out zone. The second type, localized salt precipitation, is characterized by an abnormally high level of salt precipitation at the dry-out front. This localized salt precipitation acts as a barrier that hampers the propagation of both CO₂ and pressure to the far field as well as counter-flowing brine migration toward the injection well. These dynamic processes caused a drastic pressure build-up in the well, which decreased injectivity. By modeling a series of test cases, it was found that low-rate CO₂ injection into high permeability formation was likely to cause localized salt precipitation. Sensitivity studies revealed that brine salinity linearly affected the level of salt precipitation, and that vertical permeability enhanced the buoyancy effect which increased the growth of the salt barrier. The porosity also affected both the level of localized salt precipitation and dry-out zone extension depending on injection rates. High temperature injected CO₂ promoted the vertical movement of the CO₂ plume, which accelerated localized salt precipitation, but at the same time caused a decrease in the density of the injected CO₂. The combination of these two effects eventually decreased bottomhole pressure. Considering the injectivity degradation, a method is proposed for decreasing the pressure build-up and increasing injectivity by assigning a ‘skin zone’ that represents a local region with a transmissivity different from that of the surrounding aquifer.     

A Study of Microscale Gas Trapping Using Etched Silicon Micromodels

Immobilization and trapping of carbon dioxide (CO₂) enhances the security of geological storage. Trapping mechanisms have been characterized in four groups: structural, residual, dissolution, and mineralization. While structural trapping acts immediately when injection starts and is well investigated, the contribution of residual and dissolution trapping increases over storage time and these contributions need to be better understood for better predictions. This paper focuses on an experimental pore-scale investigation of residual and capillary trapping. CO₂?Cwater imbibition experiments were conducted in micromodels whose homogenous pore space is geometrically and topologically similar to Berea sandstone. Microvisual data, photographs and video footage, describes the trapping mechanism and, especially, the disconnection and shrinkage of the CO₂ phase. Results show that depending on the flow rate of the imbibing water different trapping mechanisms are observed. Lower flow rates, comparable to the trailing edge of a CO₂ plume, lead to more snap-off events and greater trapped residual saturation, whereas rates comparable to the near wellbore area during enhanced sequestration showed displacement of gas bubbles and greater dissolution that ultimately leads to very low or zero gas saturations. Furthermore, complete dissolution events showed that homogenous as well as heterogeneous dissolution occurs. Whereas the latter is subdivided into microbubble formation and dissolution on crevices or pore roughness, the former occurs without the influence of pore walls. Based on the observations we suggest that the type of rock and its roughness as well as the fines present at the CO₂ brine interface are important factors determining the dissolution mechanism.