WELLBORE STABILITY FOR CARBON SEQUESTRATION IN GEOLOGICAL FORMATION

随着人们对二氧化碳对气候变化影响认识的增加，科学家和工程师开始研究通过减少向大气中排放二氧化碳来控制全球变暖的机制。一种很有前途的方法是碳捕获和封存(CCS)。在CCS计划中，从大型工业排放器捕获二氧化碳，并将其运输到使用(例如藻类培养)或永久储存在地质地点，在那里将其注入岩石地质构造。对如何在地质岩层中储存二氧化碳进行了研究，因为在注入二氧化碳时不同的应力、裂缝和压力可能会损害储存点的储存能力。2.项目的目的和目标本项目的主要目标是开发一种考虑间歇注入CO2对井壁稳定性的热-水-力耦合影响的CO2注入模型。本研究的主要目标如下：*提出一种稳健的弹塑性损伤本构模型。建立的模型将考虑井筒内二氧化碳压力和温度的不规则性。*该模型将被实施到有限元方法(FEM)中，并通过文献中现有的实验室测试结果进行校准。校准后的数值方法将用于对各种井筒设计进行更多分析，以寻求向地质地层注入中间二氧化碳的最佳设计。*将创建不同的曲线，将井筒周围的损害程度与不同载荷和温度变化的影响联系起来。这些曲线可以提供给业界，以改进未来的井筒设计。3.方法本研究将由以下四个部分组成：*在头两年内，将建立复杂加载条件下双重孔隙岩石的本构模型。创建的模型将描述二氧化碳从船上一直流向井筒的情况。它还将能够预测二氧化碳的近场扩张。经过6个月的文献研究和为《纽约ARMA研讨会》发表的综述会议论文，与监管团队达成一致的本构模型被决定遵循和提升Ma和赵(2018)以及Khalili和Valliappan(1996)的研究。到目前为止，对Ma和赵(2018)使用的模型的控制方程进行了仔细的研究，以便能够创建能够重现其结果的适当编码。采用MatLab软件对THM进行本构建模。白(2016)的博士论文和Khalili等人的。(2010)的研究被选为修正Ma和赵(2018)本构方程的指南，以便在模型中考虑热效应。这将给出裂隙多孔介质/岩石的稳健的THM本构模型。*博士项目的最后阶段是进一步完善数值模式。该模型将使用文献中现有实验室结果进行校准。将采用有限元方法。校准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筒设计。参考文献：白云，2016。双孔变形多孔介质多相渗流的热-水-力耦合模型。博士论文。Khalili-Naghadeh，N.和S.Valliappan。1991年。含变形基质裂隙多孔介质渗流：隐式公式。水资源研究，27(7)，第1703-1709页。2010年。饱和均质多孔介质骨架热膨胀系数与热-水-力本构关系。材料力学，42(6)，第593-598页。2018年。与Ela相关的裂缝性多孔介质井壁稳定性分析

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