Experimental Investigation and Subsequent Modeling of the Cement Microstructure and Integrity of Cement/Casing and Cement/Formation Interfaces Under Downhole Stress Conditions

甲烷是一种强效温室气体（GHG），其威力是二氧化碳的25倍。在加拿大，甲烷排放量约占所有温室气体排放量的15%。上游石油和天然气设施是加拿大最大的甲烷工业排放者，释放的甲烷占该国甲烷总排放量的44%。在上游油气行业，甲烷排放的很大一部分是由地面套管排气流（SCVF）和气体运移（GM）引起的逸散性泄漏造成的。大块水泥，以及水泥/套管和套管/岩石界面，可能是油气井在泄漏和长期井完整性方面的薄弱环节。套管和/或地层上的水泥脱落，以及随后的层间隔离失效，是油气井中SCVF和GM挥发性甲烷排放的重要原因。了解泄漏通道形成的机制对于评估和改善油气井的水泥性能至关重要，无论这些井是在生产还是封堵并废弃。因此，提出了对水泥破坏和脱粘机制的综合实验和数值研究，以及这些机制如何影响流体在水泥微观结构中的运动。先进的井筒模拟器能够在实际的井下条件（即43 MPa和120°C）下研究水泥井段的流动情况，并在典型的井下应力条件（即循环压力和热应力条件）下研究水泥体的完整性以及水泥/套管界面。利用纳米ct对模拟水泥体和各种界面条件（如水泥-套管、水泥-岩石）的缩小样品进行数字图像处理，分析井下应力条件的影响。该技术将与地层流体通过样品的三维微观结构流动的计算流体动力学建模相结合。总之，这种新方法将评估胶结井段的渗透率，这代表了井中潜在的微尺度泄漏路径。本项目提出的实验调查和数值模型研究将有助于更好地理解流体泄漏背后的驱动因素（即沿水泥/套管、水泥/井眼界面和水泥体内微裂缝形成的应力）。研究结果将有助于设计和开发新的、更可靠的屏障技术，这些技术可用于更具成本效益地减少逸散性甲烷排放。作为《泛加拿大清洁增长和气候变化框架》的一部分，加拿大政府重申其到2025年将温室气体排放量在2012年的基础上减少40-45%的承诺。因此，拟议的研究与加拿大政府努力减少温室气体排放的战略方向完全一致。

Methane is a potent greenhouse gas (GHG) that is 25 times more powerful than carbon dioxide. In Canada, methane emissions make up about 15% of all GHG emissions. Upstream oil and gas facilities are Canada's largest industrial emitters of methane, releasing 44% of the country's total methane emissions. Within the upstream oil and gas industry, a significant fraction of methane emission results from fugitive leaks arising from surface casing vent flow (SCVF) and gas migration (GM). Bulk cement, as well as cement/casing and casing /rock interfaces, are likely to be the weak spots in oil and gas wells in terms of leakage and long term well integrity. Debonding of cement from casing and/or formation, and subsequent loss of zonal isolation, is a significant contributor to fugitive methane emissions from SCVF and GM in oil and gas wells. Understanding the mechanisms of leakage pathway formation is crucial for assessment and improvement of cement performance in oil and gas wells - whether the wells are producing or plugged and abandoned. Comprehensive experimental and numerical studies of the mechanisms of cement failure and debonding, and how these impact fluid movement through the cement microstructure, are therefore proposed. An Advanced Wellbore Simulator capable of investigating flow through cemented wellbore sections under realistic downhole conditions (i.e. 43 MPa and 120 °C) will be used to investigate the integrity of the cement body, as well as the cement/casing interfaces, under representative downhole stress conditions (i.e., cyclic pressure and thermal stress conditions). Nano-CT based digital image processing of downscaled samples simulating cement body and various interface conditions (e.g., cement-casing, cement-rock) will be used to analyze the effect of downhole stress conditions. This technique will be combined with a computational fluid dynamic modelling of formation fluid flow through the 3D microstructures of the samples. Together, this new methodology will assess the permeability of cemented wellbore sections, which represent potential microscale leakage pathways in a well. The experimental investigation and numerical model study proposed in this project will result in an improved understanding of the drivers behind fluid leakage (i.e. stresses creating microchannels along the cement/casing, cement/borehole interfaces and microfractures within the cement body). The results will allow for the design and development of new, more reliable barrier technologies that can be used for more cost-effective mitigation of fugitive methane emissions. As part of the Pan-Canadian Framework on Clean Growth and Climate Change, the Government of Canada reaffirmed its commitment to reduce GHG emissions 40-45% below 2012 levels by 2025. The proposed research is, therefore, well aligned with strategic direction of the Government of Canada's efforts to reduce GHG.