A Preliminary Evaluation of the Impact of CO2 Injection in Deep Rock on Flow Behavior

摘要：深部岩石注入流体及其流动在石油、采矿、天然气和环境工程等领域具有重要意义。任何流体在岩石中的流动都非常依赖于岩体中的裂缝网络模式和有效应力，有效应力随岩石孔隙压力的变化而变化。注入流体后，有效原位应力降低，导致固体和孔隙/裂缝空间的几何和体积变化，从而显著提高渗透率。然而，当向深层碳质岩石注入二氧化碳时，渗透率降低了150倍。因此，注入二氧化碳后，其在裂缝中移动并进入固体基质并储存在微孔中，导致裂缝孔径减小。然而，在文献中没有证据表明这一现象已经被研究过，也没有一个合适的模型可以用来表示和有效地模拟岩石中二氧化碳的流动。本研究的基础是假设固体煤/碳质岩在高压CO2作用下体积增大，且体积应变对裂缝孔径的负作用大于有效应力减小的正作用。进一步假设这两种影响是耦合的。本研究旨在确定注入CO2与有效应力的变化对煤的固体体积/裂缝压缩性和渗透率的影响。将采用实验、理论和数值程序来达到下列目标：(a)确定由于注入而造成的固体和裂缝的体积应变；(b)进一步确定体积应变和有效应力的影响是否耦合；(c)确定注入对可注入二氧化碳量的影响。该研究的实验部分将包括首先测量煤暴露于越来越多的二氧化碳中的体积应变，以确定二氧化碳注入对固体和裂缝体积的影响。这将随后测量体积应变增加的二氧化碳量，而样品保持在三轴应力状态下。结果将显示外部应力是否禁止/抑制或诱导在CO2存在下固体体积的额外变化，以及变化的幅度。理论部分将包括使用测量的体积变化来确定相应的裂缝体积变化，从而使用标准流动方程确定两种情况下的裂缝孔隙度和渗透率。数值部分将包括利用计算出的渗透率/孔隙度变化来模拟体积应变对深部煤/碳质页岩中长期CO2流动的影响。在成功完成本研究后，将对应力和非应力试验结果进行比较，以确定应力对CO2引起的体积应变的影响，即两者是否耦合导致裂缝孔径整体减小。此外，压力与孔隙度/渗透率之间的关系也将变得可行。这将使二氧化碳注入情景的初步和改进的模拟成为可能。一名研究生将参与该项目，研究成果将发表在岩石力学和石油工程的期刊和/或会议论文集上。

CMS-0231593PI: Satya HarpalaniInstitution: Southern Illinois University at CarbondaleTitle: "A Preliminary Evaluation of the Impact of CO2 Injection in Deep Rock on Flow Behavior"Abstract:Injection of fluids in deep rock, and its flow, are important in the fields of petroleum, mining, natural gas and environmental engineering. Flow of any fluid through rock is very dependent on the fracture network pattern in the rock mass and the effective stresses which are altered as the pore pressure in the rock changes. With fluid injection, the effective stress in situ decreases causing geometric and volumetric changes in solid and pore/fracture space, and thus a significant increase in the permeability results. Yet, when CO2 is injected in deep carbonaceous rock, reduction in permeability of as much as 150 times has been observed. Injection of CO2, its movement in the fractures and entry in to the solid matrix where it gets stored in the micropores, therefore, results in a decrease in the fracture aperture. However, there is no evidence in the literature that this phenomenon has been studied, or that a proper model available to represent and effectively simulate the flow of CO2 in rock. The basis for this research is the hypothesis that the volume of solid coal/carbonaceous rock increases when exposed to high pressure CO2 and the negative effect of this volumetric strain on fracture aperture is more pronounced than the positive effect of decreased effective stress. It is further hypothesized that these two effects are coupled. This research deals with determining the effect of injecting CO2, coupled with changes in effective stress, on solid volume/fracture compressibility and permeability of coal. Experimental, theoretical and numerical procedures will be used to reach the following goals: (a) To determine the volumetric strain of solid and fractures as a result of inejction; (b) To further determine if the effects of volumetric strain and effective stress are coupled; and (c) To determine the impact of injection on the amount of CO2 that can be injected. The experimental component of the research will include first measuring the volumetric strain for coal exposed to increasing amounts of CO2 to determine the effect of CO2 injection on solid and fracture volumes. This will be followed by measuring the volumetric strain for increasing amounts of CO2 while the sample is held under triaxial state of stress. The results will show whether external stress prohibits/inhibits, or induces, an additional change in solid volume in the presence of CO2, and the magnitude of the change. The theoretical part will include using the measured volumetric changes to determine the corresponding changes in fracture volume, and hence, the fracture porosity and permeability for both cases using standard flow equations. The numerical part will include utilizing the calculated permeability/porosity changes to model the impact of volumetric strain on flow of CO2 in deep coal/carbonaceous shale over the long-term. Upon successful completion of the proposed research, the results for the stressed and unstressed tests will be compared to determine the impact of stress on volumetric strain induced by CO2, that is, whether the two effects are coupled resulting in an overall reduction in the fracture aperture. Also, a relationship between pressure and porosity/permeability will become available. This will enable a preliminary and improved simulation of the CO2 injection scenario. One graduate student will work on this project and research findings will be published in a journal and/or conference proceedings in rock mechanics and petroleum engineering.