Feasibility study of CO2 geological storage in China

It has been proved to be one effective means to reduce emissions of CO2 to mitigate the worsening global climate change through lots of projects and tests about CO2 geological storage. The sites that are suitable for CO2 geological storage include coal seams that can not be mined, deep saline aquifers, oil fields, and depleted gas fields. The emission of CO2 from fuel combustion is about 3.54 Gt in China in 2003, which is the second biggest in the world. Because the energy consumption in China mainly depends on fossil fuels for a long time in the future, China will become a country with the biggest emission of CO2 in the world, which will make China have to reduce the emissions of CO2 by some methods including geological storage. Based on lots of information about the reserves of coal seam methane and the rank of coal in the 68 coal basins in China, the total CO2 storage capacity in these coal basins was estimated according to the recovery coefficient and exchange ratio of CO2 to CHa.The total storage capacity in deep saline aquifers can be regarded as the total quantity of CO2 that can be dissolved in the saline aquifers at the depth from 1000m to 3000m under ground. The quantity can be estimated by multiplying the solubility of CO2 in the saline water and the volume of the appropriate aquifers. According to the reserve and quality of crude oil in 46 main oil basins in China, the CO2 storage capacity and the quantity of enhanced oil were calculated. The storage capacity of depleted gas fields can be derived from the reserve and depth of the gas fields. The total CO2 geological storage capacity is about 196.2 Gt CO2 that is as against 55.4 times the CO2 emission from fuel combustion in China in 2003. According to the results of the finished projects and tests about CO2-EOR and CO2-ECBM, the CO2 geological storage capacities in coal seams, deep saline aquifers, oil fields and depleted gas fields will be estimated.     

渗透率的非均质性对CO_2地质封存的影响

CO2地质封存可以减少化石燃料燃烧排放的CO2量,有效减缓温室效应。储层渗透率可以决定CO2通道的形成,进而改变其在储层中的运移规律,因而是影响CO2地质封存的重要因素。根据研究区基本地质数据、三维地震勘探结果和统计规律确定了渗透率的分布情况,运用储层多相流模拟软件TOUGH2-MP分析了渗透率的非均质性对CO2地质封存的影响。结果表明:(1)渗透率的分布情况对CO2储存量和注入压力的影响很大,相比于均值模型,CO2的注入总量明显减少,到达最大允许压力积聚所需的时间要比均质模型短;(2)在保证注入速率和压力积聚不超过允许最大值的双重要求下,定压和定量两种注入方案都有待改进,建议考虑如人工压裂等工程措施;(3)渗透率的非均质性使得CO2晕呈现出不规则扩散,经过20年的注入,其最大扩散距离约800m,比均质情况下小150m,须做好相应的监测工作。     

On the risk of hydraulic fracturing in CO2 geological storage

We present a contribution on the risk of hydraulic fracturing in CO₂ geological storage using an analytical model of hydraulic fracturing in weak formations. The work is based on a Mohr–Coulomb dislocation model that is extended to account for material with fracture toughness. The complete slip process that is distributed around the crack tip is replaced by superdislocations that are placed in the effective centers. The analytical model enables the identification of a dominant parameter, which defines the regimes of brittle to ductile propagation and the limit at which a mode‐1 fracture cannot advance. We examine also how the corrosive effect of CO₂ on rock strength may affect hydraulic fracture propagation. We found that a hydraulically induced vertical fracture from CO₂ injection is more likely to propagate horizontally than vertically, remaining contained in the storage zone. The horizontal fracture propagation will have a positive effect on the injectivity and storage capacity of the formation. The containment in the vertical direction will mitigate the risk of fracturing and migration of CO₂ to upper layers and back to the atmosphere. Although the corrosive effect of CO₂ is expected to decrease the rock toughness and the resistance to fracturing, the overall decrease of rock strength promotes ductile behavior with the energy dissipated in plastic deformation and hence mitigates the mode‐1 fracture propagation. Copyright © 2016 John Wiley & Sons, Ltd.     

A pressure-monitoring method to warn CO2 leakage in geological storage sites

This paper proposes a pressure-monitoring method to warn any possible CO₂ leakage by monitoring pressure change at the upper layer of storage reservoirs within injection wells. The monitoring method is tested with two problems under various scenarios. With a current pressure detection limit, the proposed pressure-monitoring technique can be widely applicable wherever a permeable upper formation exists above the CO₂ storage reservoir and is effective even in offshore storage sites wherever conventional monitoring methods for onshore sites cannot be applied. Meanwhile, the method is limited to apply during injection and is subject to any possible pressure dampening.     

中国CO2地质埋存关联技术的现状

CO2地质埋存是减少CO2净排放量的有效措施之一。CO2地质埋存技术在发达国家已有十几年的研究历史。目前,我国这方面的研究工作刚刚起步,因此,很有必要对我国CO2地质埋存的技术现状进行调查。CO2地质埋存过程主要包括3个要素：从发电厂或者工业生产过程中回收CO2;将CO2运送到埋存场地;CO2注入与埋存。其中的很多技术在现有工业以及石油、天然气开采等行业中已经存在。对我国现有工业以及石油、天然气开采等行业中涉及到的CO2回收、运输以及注入与埋存等技术的现状进行了初步调查,并与国外进行对比。结果表明,我国CO2地质埋存技术现状与国外存在一定的差距,但还是有一定的技术基础,尤其是在CO2回收与注入方面有一定的实践经验。     

我国吉林油田大情字井区块CO2地下埋存试验区地质埋存格架

目前,我国在CO2地质埋存的试验研究才刚刚开始,其研究方法与研究思路需要不断探索。本文立足于吉林油田大情字井区块,从储层埋存潜力、埋存体稳定性及水文地质条件三个方面对试验区实施CO2地质埋存工程进行评价。通过对注CO2层段的储层砂体有效厚度、空间展布范围、储层物性及储层微观结构,以及在此基础上,对各砂体横向和垂向上的连续性、砂体间的连通性等等方面的分析和评价,试验区具备一定的埋存潜力,其有效储层厚度平均为273m;同时对试验区盖层的封盖性、断裂的稳定性及井筒的密封性三方面的评价,建立试验区埋存体稳定性评价体系。研究表明,试验区具备厚层泥岩封盖层、盖层内断裂不发育且比较单一以及储层内广泛发育隔夹层,可以有效地对CO2的运移或渗漏实施封盖和遮挡;另外,结合试验区矿化度、水化学成分的研究表明,试验区与邻近区域存在明显的矿化度分带特点、水化学成分也相对较单一以及含水层和隔水层均较发育。在一定程度上说明,试验区目的层段具有相对独立的地下水水体环境,比较有利于适合注入CO2,并进行地质埋存。通过这三方面的研究,建立大情字井区块适合CO2地质埋存的埋存格架,为该区实现CO2长期有效安全埋存奠定基础。     

Establishment of an assessment method for site-scale suitability of CO2 geological storage

Geological storage of CO2 (known as geological sequestration) is increasingly seen as a viable strategy to reduce the release of greenhouse gases into the atmosphere. China has become one of the largest emitters of CO2 in the world. Therefore, alongside other emissions reductions measures, the deployment of geological storage projects to capture CO2 in China is essential. This paper focuses on the establishment of qualitative and quantitative assessment methods for site-scale suitability of CO2 geological storage in deep saline formation systems. This is based on numerical modelling prior to the development a specific geological storage project, providing a more accurate selection of preferential sites from a list of potential storage locations. However, the detailed design of specific geological storage projects was not con?sidered.     

深部咸水层CO2地质储存地质安全性评价方法研究

CO2地质储存工程属于环保型工程项目,地质安全性是影响CO2长期封存的首要因素。深部咸水层CO2地质储存地质安全性影响因素主要包括盖层适宜性、场地地震安全性、水文地质条件、地面场地地质条件四个方面,其中盖层适宜性是CO2安全储存的最关键因素,场地地震安全性和水文地质条件次之,而地面场地地质条件也是影响工程施工的重要因素。本文基于CO2地质储存的地质安全性影响因素分析,建立了层次分析结构的地质安全性评价指标体系,并初步计算了评价指标的权重;提出可以利用模糊综合评价方法进行深部咸水层CO2地质储存地质安全性综合评价,为中国深部咸水层CO2地质储存的地质安全性评价方法和安全选址指明了方向。     

Numerical computations of rock dissolution and geomechanical effects for CO2 geological storage

The paper is motivated by the long‐term safety analysis of the CO₂ geological storage. We present a methodology for the assessment of the geomechanical impact of progressive rock dissolution. The method is based on the use of X‐ray tomography and the numerical dissolution technique. The influence of evolution of the microstructure on the macroscopic properties of the rock is analysed by using periodic homogenization method. The numerical computations show progressive degradation of all components of the stiffness (orthotropic) tensor. Moreover, the evolution of associated mass transfer properties (as tortuosity and conductivity tensors), by using the periodic homogenization method, is also calculated. The correlation between the mechanical parameters and the transfer properties during the dissolution process is presented. The results show that the highest increase of the hydraulic conductivity (in direction Y) is not associated with the highest decrease of Young modulus in this direction. Moreover, the highest decrease of Young modulus (in the direction X) is not associated with percolation in this direction. Finally, an incremental law to calculate settlement, in case of a rock with evolving microstructure, is proposed. The solution of the macroscopic settlement problem under constant stress and drained conditions showed that the geomechanical effects of the rock dissolution are rather limited. Copyright © 2014 John Wiley & Sons, Ltd.     

安徽省沉积盆地CO2地质储存适宜性评价

CO2的地质储存已成为减缓温室效应的一条有效的途径。区域的CO2地质储存适宜性评价是选址建设CO2地质储存工程的基础,而建立适当的评价指标体系与选择合理的评价方法对于CO2地质储存适宜性评价起到至关重要的作用。本次研究以安徽省内CO2减排需要为目的,根据研究区实际的地质条件,从CO2的地质储存所关联的多重因素出发,建立起包括安全性、技术性、经济性与社会环境性4个方面的评价指标体系,并引入变异系数法对评价指标确定权重与TOPSIS模型对研究区的CO2地质储存盆地适宜性进行排序。研究结果表明:阜阳盆地与合肥盆地为优先选择的CO2地质储存盆地。评价结果为安徽省初步选址CO2地质储存工程建设提供了科学依据。     

OpenMP在CO2地质储存数值模拟并行计算中的应用

为减少CO2地质储存数值模拟计算时间和增强计算规模,文章提出基于OpenMP和动态内存分配的方式,重构TOUGH2-ECO2N数值模拟器。通过耗时评估可知,模拟器的主要耗时部分为状态方程计算、组建矩阵方程和方程求解。基于此,在遵循OpenMP并行化原则下,采用动态内存分配、处理跳转语句和算法内部的相关性,以及函数内部参数优化等措施,完成了多相流模拟器的并行化。计算试验结果表明,并行化模拟器算法正确、执行效率高,且具有加速效果良好的特点。针对中小规模的模型对比试验,4核的加速比可以达到2.28倍。     

CO2地质封存中储层流体压力演化规律的解析模型

为使解析模型可以更加科学准确地描述储层中多相流体的迁移机制与压力演化规律,提高解析计算与分析的精度。首先将储层中的流场划分为3个区域,然后根据渗流体积守恒方程反演储层中两相流体混合渗流区的各相流体饱和度,进而将总流度直接引入到达西公式中得到了一个适用于两相流的广义达西公式,据此推导出了一个更为精确的表征储层流体压力演化规律的解析模型。最后,通过案例分析,将该解析模型的计算结果与既有文献的显式积分解及TOUGH2/ECO2N的数值解进行对比,验证了该模型的可靠性及相比于既有文献的显式积分解在计算精度方面的优越性。此外,计算结果也表明,该解析模型虽然是在稳态流的假定条件下得到的,但对于实际储层流体压力演化的全过程均具有很强的表征能力,这主要归因于该模型可科学准确地确定饱和度,因此,可以在工程中推广应用。     

我国海洋地质碳封存研究进展与展望

我国海洋地质碳封存潜力巨大,主要碳封存目标区与主要CO2排放源匹配性良好,可以为碳中和目标的实现提供重要助力。论文分析了我国开展海洋地质碳封存的必要性,介绍了国内外海洋地质碳封存工作的研究进展; 指出海洋地质碳封存区划研究、海洋地质碳封存与资源协同性研究、海洋地质碳封存数据库建设以及海洋地质碳封存示范工程的实施是当前工作的重点。研究可为我国碳中和目标的实现提供数据支撑和技术储备。     

规模化深部咸水含水层CO2地质储存选址方法研究

本文依据中国沉积盆地CO2地质储存潜力评价结果,认为深部咸水含水层是实现规模化CO2地质储存的主体,进而对适宜CO2地质储存的深部咸水含水层属性进行了界定。提出了深部咸水含水层CO2地质储存选址原则,合理划分了选址工作阶段。建立了选址技术指标、安全性评价指标、经济适宜性和地面地质-社会环境选址指标4个指标层,60余个指标的选址指标体系,提出了基于层次分析(AHP)的多因子排序选址评价方法。本文的研究成果对中国深部咸水含水层CO2地质储存场地选址具有一定的指导意义。     

CO2地质封存室内实验中盐水种类对残余水形成的影响

在咸水含水层中进行CO2地质封存是通过向含水层中注入CO2驱走咸水实现的。在大部分地下水被驱走之后,仍会有部分地下水残留在原来的岩石孔隙中形成残余水。残余水的形成过程及残余水饱和度的大小对CO2地质封存潜力及地质封存安全性等都具有重要影响。本研究通过超临界CO2排驱饱水岩心实验,研究了盐水种类对残余水的形成过程及残余水饱和度大小的控制作用。实验结果表明,在盐水浓度相同（35 g/L）的情况下,超临界CO2排驱盐水的最终稳定不可再降的残余水饱和度是去离子水＜NaCl盐水＜CaCl2盐水。从实验结果看,超临界CO2排驱咸水的过程可划分为3个阶段,本文分别称他们为活塞式排驱阶段、携带式排驱阶段和溶解式排驱阶段。论文提出了一个毛细管模型,利用这一模型对这3个阶段中CO2排驱水的机理进行了分析。     

水环境同位素技术在二氧化碳地质储存中的应用之探讨

通过分析二氧化碳地质储存的地下空间和时间特征,并结合水环境同位素技术的特点,提出将其应用于碳储存方面可以从以下三方面入手:(1)利用水环境同位素技术判断二氧化碳规模化封存场地的水文地质条件的方法,评价典型二氧化碳规模化封存咸水层的安全持久性及储存二氧化碳的适宜性;（2）确定判断泄露二氧化碳“碳源”的同位素方法,研究泄露的“碳”源;（3）通过水环境同位素技术,研究二氧化碳地质封存与地下水循环、径流之间的关系,评价规模化封存二氧化碳潜在泄露对浅层含水层的影响。     

鄂尔多斯深部咸水层CO_2地质封存效果评价

中国首个陆上咸水层CO_2地质封存全流程示范项目于2010年正式实施。为更加清晰、准确地了解注入场地储层的注入性能和注入封存过程中可能遇到的潜在问题,基于场地储层结构和注入监测数据,采用储层多相流模拟软件TOUGH2-MP/ECO_2N对鄂尔多斯105 t/a CO_2注入1 620 m以深的特低渗砂岩咸水含水层进行数值模拟,对储层的压力积聚和CO_2羽体扩散的动态演化以及储层封存量进行评估。结果表明,所建立的模型比较准确地反映了实际注入过程和注入效果。3a注入引起的最大压力抬升小于15 MPa,CO_2在含水层中总体呈均匀扩散,CO_2注入地下3a和53a后,羽体在刘家沟储层中的横向迁移距离分别为550 m和700 m左右。在目前的统注方案下,CO_2主要封存层位在储层上部的刘家沟组(埋深为1 690~1 699 m),其吸气量占整个储层封存量的80%以上,储层吸气能力具有由浅到深变差的特征。53a模拟期内,进入泥岩盖层的CO_2总量不及注入总量的0.05%。     

地质封存CO2水岩作用对页岩有机碳的萃取效应研究

CO₂ 水岩相互作用实验研究对于CO₂地质封存以及页岩气开发都具有重要意义。近年来多数研究主要侧重于岩石中矿物成分的反应过程,对于岩石中有机质成分的研究比较有限。本文选取盖层页岩,重点研究CO₂对于页岩中有机碳的萃取效应作用。实验使用高压反应釜在95 ℃和15 MPa条件下进行CO₂ 水页岩反应,同时考查不同的水岩接触方式对反应的影响,实验中分别测试了反应后水体中的溶解性有机碳(DOC)和反应前后岩石表面形态变化(SEM表征)。DOC的测试结果表明,相对于空白对照组高压N₂作用,超临界CO₂体系对于岩石有机碳具有明显的萃取效果,其中在不含水和仅含少量水的体系中,CO₂体系对DOC的萃取量能达到N₂体系的3倍以上,显示超临界CO₂极强的萃取能力。对比不同含水量的实验体系,发现含有少量水的情况下,CO₂对于有机碳的萃取量达到最大,比不含水的体系高出了87%,而这种能力的提高是由于少量极性分子H₂O的加入,能够增强超临界CO₂流体的溶剂化性能导致的。SEM结果也说明了不同的水岩气接触方式对岩石表面形貌具有不同的改造效果。本文实验结果有助于更好认识CO₂地质封存水岩作用及其潜在环境风险。     

A numerical study of mineral alteration and self-sealing efficiency of a caprock for CO2 geological storage

Geochemical interactions of brine–rock–gas have a significant impact on the stability and integrity of the caprock for long-term CO₂ geological storage. Invasion of CO₂ into the caprock from the storage reservoir by (1) molecular diffusion of dissolved CO₂, (2) CO₂-water two-phase flow after capillary breakthrough, and (3) CO₂ flow through existing open fractures may alter the mineralogy, porosity, and mechanical strength of the caprock due to the mineral dissolution or precipitation. This determines the self-enhancement or self-sealing efficiency of the caprock. In this paper, two types of caprock, a clay-rich shale and a mudstone, are considered for the modeling analyses of the self-sealing and self-enhancement phenomena. The clay-rich shale taken from the Jianghan Basin of China is used as the base-case model. The results are compared with a mudstone caprock which is compositionally very different than the clay-rich shale. We focus on mineral alterations induced by the invasion of CO₂, feedback on medium properties such as porosity, and the self-sealing efficiency of the caprock. A number of sensitivity simulations are performed using the multiphase reactive transport code TOUGHREACT to identify the major minerals that have an impact on the caprock’s self-sealing efficiency. Our model results indicate that under the same hydrogeological conditions, the mudstone is more suitable to be used as a caprock. The sealing distances are barely different in the two types of caprock, both being about 0.6 m far from the interface between the reservoir and caprock. However, the times of occurrence of sealing are considerably different. For the mudstone model, the self-sealing occurs at the beginning of simulation, while for the clay-rich shale model, the porosity begins to decline only after 100 years. At the bottom of the clay-rich shale column, the porosity declines to 0.034, while that of mudstone declines to 0.02. The sensitive minerals in the clay-rich shale model are calcite, magnesite, and smectite-Ca. Anhydrite and illite provide Ca²⁺ and Mg²⁺ to the sensitive minerals for their precipitation. The mudstone model simulation is divided into three stages. There are different governing minerals in different stages, and the effect of the reservoir formation water on the alteration of sensitive minerals is significant.