Abstract The potential leakage of hydrocarbon fluids or carbon dioxide from subsurface formations is a primary concern in wellbore integrity, oil and gas production, and CO2 storage. Leaky wells with fractured cement or debonded microannuli are common sources of subsurface fluid leakage. The hydrocarbon fluid or CO2 can migrate through such pathways to shallower formations and ultimately to surface. Cement fractures may have apertures on the order of microns, which are difficult to seal with typical workover techniques. A material that provides low viscosity during the injection but much higher viscosity after injection, with a minimum pressure gradient to yield flow at the target zone, is a potentially effective approach to seal the leakage pathways through cement fractures. pH-triggered polymers are such a material: aqueous solutions with low viscosity at low pH, containing pH-sensitive microgels which viscosify upon neutralization to become highly swollen gels with substantial yield stress that can block fluid flow. For the wellbore leakage application, the large alkalinity of wellbore cement provides the required neutralization. Our coreflood and rheological experiments show that pH-triggered polymer sealants such as polyacrylic acid polymer provide a robust seal if the process is properly designed; however, its long-term applicability depends on the dynamic geochemical environment of the wellbore. The process comprises three stages: (1) injection of a chelating agent as the preflush to ensure a favorable environment for the polymer gel, (2) injection of polymer solution, and (3) shut-in for the polymer gelation. A systematic study was done to understand the conditions under which the polymer gel remains stable and effectively seals the leakage pathways. A numerical model, based on polymer rheological properties and governing mechanisms observed in the laboratory experiments, was developed to simulate the reactive flow and transport of pH-triggered polymers in narrow fractures. Comparison with experiments shows a generally good agreement, despite the relative simplicity of the model. The numerical model was used to investigate further the underlying mechanisms of the process. The results can be used to design effectively the remediation process for a known fracture aperture size of the target zone.

中文翻译：

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使用 pH 触发聚合物胶凝剂缓解井筒泄漏的实验和数值研究

摘要 地下地层中碳氢化合物流体或二氧化碳的潜在泄漏是井筒完整性、石油和天然气生产以及二氧化碳储存的主要问题。具有裂缝水泥或脱粘微环空的泄漏井是地下流体泄漏的常见来源。碳氢化合物流体或 CO2 可以通过这些路径迁移到较浅的地层并最终迁移到地表。水泥裂缝可能有微米量级的孔，这很难用典型的修井技术密封。在注入期间提供低粘度但在注入后提供高得多的粘度的材料，具有最小压力梯度以在目标区域产生流动，是密封通过水泥裂缝的泄漏路径的潜在有效方法。pH 触发聚合物是这样一种材料：在低 pH 值下具有低粘度的水溶液，含有 pH 敏感微凝胶，这些微凝胶在中和后会变粘，变成高度溶胀的凝胶，具有可阻止流体流动的显着屈服应力。对于井筒渗漏应用，井筒水泥的大碱度提供了所需的中和作用。我们的岩心溢流和流变实验表明，如果工艺设计得当，pH 值触发的聚合物密封剂（如聚丙烯酸聚合物）可提供牢固的密封；然而，其长期适用性取决于井筒的动态地球化学环境。该过程包括三个阶段：（1）注入螯合剂作为预冲洗剂以确保聚合物凝胶的有利环境，（2）注入聚合物溶液，以及（3）关闭聚合物凝胶化。进行了系统研究以了解聚合物凝胶保持稳定并有效密封泄漏路径的条件。基于在实验室实验中观察到的聚合物流变特性和控制机制，开发了一个数值模型来模拟窄裂缝中 pH 触发的聚合物的反应流动和传输。尽管模型相对简单，但与实验的比较显示出总体上良好的一致性。数值模型用于进一步研究该过程的潜在机制。结果可用于有效设计目标区域已知裂缝孔径的修复过程。基于在实验室实验中观察到的聚合物流变特性和控制机制，开发了模拟 pH 触发聚合物在狭窄裂缝中的反应流动和传输。尽管模型相对简单，但与实验的比较显示出总体上良好的一致性。数值模型用于进一步研究该过程的潜在机制。结果可用于有效设计目标区域已知裂缝孔径的修复过程。基于在实验室实验中观察到的聚合物流变特性和控制机制，开发了模拟 pH 触发聚合物在狭窄裂缝中的反应流动和传输。尽管模型相对简单，但与实验的比较显示出总体上良好的一致性。数值模型用于进一步研究该过程的潜在机制。结果可用于有效设计目标区域已知裂缝孔径的修复过程。数值模型用于进一步研究该过程的潜在机制。结果可用于有效设计目标区域已知裂缝孔径的修复过程。数值模型用于进一步研究该过程的潜在机制。结果可用于有效设计目标区域已知裂缝孔径的修复过程。