WELLBORE STABILITY FOR CARBON SEQUESTRATION IN GEOLOGICAL FORMATION

1. 随着对二氧化碳对气候变化影响的认识的增加，科学家和工程师们开始研究通过减少二氧化碳排放到大气中来控制全球变暖的机制。一种很有前景的方法是碳捕获与封存（CCS）。在CCS计划中，二氧化碳从大规模的工业排放者那里被捕获，并被运输到被利用（例如藻类种植）或永久储存在地质地点，在那里它被注入岩石地质构造中。由于注入二氧化碳过程中不同的应力、裂缝和压力会影响储存地点的储存能力，因此对如何在地质岩层中储存二氧化碳进行了研究。2. 该项目的主要目的是建立一个二氧化碳注入模型，该模型将考虑间歇性注入二氧化碳对井筒稳定性造成的热-水-机械耦合效应。本研究的主要目标如下：*将提出一个鲁棒弹塑性损伤本构模型。所建立的模型将考虑井筒内CO2压力和温度的不规律性。*该模型将应用于有限单元法（FEM），并根据现有的实验室测试结果进行校正。校正后的数值方法将用于对各种井眼设计进行更多的分析，以寻求地质地层中CO2注入的最佳设计。在不同载荷和温度变化的影响下，井筒周围的破坏程度会产生不同的曲线。这些曲线可以提供给行业，以改善未来的井眼设计。3. 研究将分为以下四个部分：*前两年建立复杂加载条件下双孔隙度岩石的本构模型。所创建的模型将描述二氧化碳从船上一直到井筒的流动情况。它还能预测二氧化碳的近场膨胀。经过6个月的文献研究，并发表了一篇“ARMA纽约研讨会”总评会议论文，本构模型与监督团队一致，决定对Ma and Zhao（2018）和Khalili and Valliappan（1996）的研究进行跟进和升级。到目前为止，对Ma和Zhao（2018）使用的模型的控制方程进行了仔细的研究，以便能够创建适当的编码来复制他们的结果。采用MATLAB软件对THM进行本构建模。本文选择Bai（2016）的博士论文和Khalili等人（2010）的研究作为修改Ma和Zhao（2018）本构方程的指导，以便在模型中包含热效应。这将为裂缝性多孔介质/岩石提供一个稳健的THM本构模型。*博士项目的最后阶段是进一步完善数值模型。该模型将使用文献中现有实验室结果的结果进行校准。将采用有限元法（FEM）。校正后的模型将应用于更多的场景和工作条件。然后可以在各种工作条件下提出更可靠的井眼设计。参考文献白旸。2016。双孔隙率可变形多孔介质中多相流动的热-水-力耦合模型。博士学位论文。Khalili-Naghadeh， N.和S. Valliappan, 1991。流动通过裂隙多孔介质与可变形的矩阵：隐式公式。水利学报，27(7),pp.1703-1709。Khalili， N.， A. Uchaipichat和A. Javadi, 2010。饱和均匀多孔介质的骨架热膨胀系数及热-水-力本构关系。材料力学，42(6),pp.593-598。马军，赵广峰。2018。Ela裂缝性多孔介质井眼稳定性分析

1. INTRODUCTIONThe increase of knowledge of the effect of CO2 on climate change has led scientists and engineers to investigate mechanisms to control global warming by decreasing the emissions of CO2 into the atmosphere. One promising approach is Carbon Capture and Storage (CCS). In CCS schemes, CO2 is captured from large-scale industrial emitters and transported to either be used (e.g. algae cultivation) or stored permanently in geological sites, where it is injected into rock geological formation. Research studies were undertaken on how to store CO2 in geological rock formations as different stresses, fractures and pressures during CO2 injection can compromise the storage capacity of the storage site. 2. AIM AND OBJECTIVES OF THE PROJECTThe main aim of the project is to develop a CO2 injection model which will consider the thermo-hydro-mechanical coupling effect on the wellbore stability caused by intermittent injection of CO2. The main objectives of this study will be as follows:* A robust elastic-plastic damage constitutive model will be proposed. The created model will consider the irregularity of CO2 pressure and temperature inside the wellbore.* The model will be implemented into the Finite Element Method (FEM) and calibrated by existing laboratory testing results from literature. The calibrated numerical method will be used to do more analysis for various wellbore design to seek the optimised design for intermediate CO2 injection to geological formations.* Different curves will be created relating the degree of damage around the wellbore to the effects of different loadings and temperature changes. These curves can be provided to the industry in order to improve future wellbore designs. 3. METHODOLOGYThe research would be accordingly comprised of four parts as follows: * During the first two years, a constitutive model of double porosity rock under complex loading conditions will be created. The created model will describe the flow of CO2 from the ship all the way down to the wellbore. It would be also capable to predict the near-field expansion of CO2. After a 6 month literature research and publishing a general review conference paper for "ARMA symposium in New York", the constitutive model in agreement with the supervisory team was decided to follow and upgrade the study of Ma and Zhao (2018) and Khalili and Valliappan (1996). So far, the governing equations of the model used by Ma and Zhao (2018) were studied carefully in order to be able to create the appropriate coding that can reproduce their results. MATLAB software will be used for the THM constitutive modelling. Bai's (2016) PhD dissertation and Khalili's et al. (2010) research were selected as a guideline for modifications on the constitutive equations of Ma and Zhao (2018) in order to include thermal effects in the model. This will give a robust THM constitutive model for fractured porous media/rock. * The final stages of the PhD project are to further improve the numerical model. The model will be calibrated using the results of existing laboratory results in literature. Finite Element Method [FEM] will be adopted. The calibrated model will be applied to further scenarios and working conditions. A more reliable wellbore design can then be proposed under various working conditions. ReferencesBai, Y. 2016. Coupled thermos-hydro-mechanical (THM) model for multiphase flow through deformable porous media with double porosity. PhD dissertation. Khalili-Naghadeh, N. and S. Valliappan. 1991. Flow through fissured porous media with deformable matrix: Implicit formulation. Water Resources Research, 27(7), pp.1703-1709.Khalili, N., A. Uchaipichat, and A. Javadi. 2010. Skeletal thermal expansion coefficient and thermo-hydro-mechanical constitutive relations for saturated homogeneous porous media. Mechanics of Materials, 42(6), pp.593-598.Ma, J., and G.F. Zhao. 2018. Borehole Stability Analysis in Fractured Porous Media Associated with Ela