Abstract Analysis of 87Sr/86Sr ratios and modelling of formation water, injection water and produced water compositions from the CO2CRC Otway Research Facility in Victoria, Australia are used to test tracer behaviour and response in push-pull experiments. Such experiments are an essential pre-requisite to understanding the controls imposed by reservoir heterogeneities on CO2 dissolution rates which may be an important stabilising mechanism for geological carbon storage. The experiments (Otway stage 2B extension in 2014) comprised two sequential tests in which ~100 t of CO2-saturated water was injected with combinations of Sr and Br or Li and Fluorescein tracers, each injection being followed by two staged extractions of ~10 t and a final extraction of ~50 t all spaced at ~10 day intervals. Analysis of the 87Sr/86Sr ratios of the produced fluids from the first injection, spiked with SrCl2 and NaBr, is consistent with Sr behaving conservatively. This contrasts with previous interpretations in which Br was argued to have behaved conservatively while Sr, which dilutes ~three times as fast as Br, was thought to be lost to a mineral phase. Such Sr-loss cannot explain the evolution of 87Sr/86Sr ratios. The analysis of 87Sr/86Sr ratios in the waters produced after the second injection episode, spiked with LiCl and Fluorescein tracers, allows calculation of the fractions of the formation waters and the injection waters from both tests 1 and 2. The Sr, Li and SO4 tracers (the later formed by oxidation of formation sulphide) all indicate similar rates of dilution that is consistent with conservative behaviour. The results of the two injection episodes with spaced extractions are compared with two subsequent push-pull injections in which the produced waters, spiked with methanol, were extracted continuously. These continuous extraction experiments exhibited significantly less dilution over the same range of produced to injected water volumes (up to only ~0.6) than the earlier experiments with spaced extractions. This implies that some process related to the pauses in extraction enhances mixing of injected and formation waters. Achieving the objective of using push-pull experiments to assess reservoir heterogeneities and CO2 dissolution rates will require better assessment of the various tracers to establish which behave conservatively followed a proper understanding of the causes of the variations in mixing as fluids are extracted from the formations.

中文翻译：

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澳大利亚 CO2CRC Otway 研究机构的 CO2 推拉注入实验中 Sr 同位素比的痕量混合和分散

摘要 澳大利亚维多利亚州的 CO2CRC Otway 研究设施的 87Sr/86Sr 比率分析和地层水、注入水和采出水组成的建模用于测试推拉实验中的示踪剂行为和响应。这些实验是了解储层非均质性对 CO2 溶解速率的控制的必要先决条件，这可能是地质碳储存的重要稳定机制。实验（2014 年的 Otway 阶段 2B 扩展）包括两个连续的测试，其中向约 100 吨的 CO2 饱和水注入 Sr 和 Br 或 Li 和荧光素示踪剂的组合，每次注入之后是约 10 吨的两个阶段提取最终提取约 50 吨，间隔约 10 天。对第一次注入（添加 SrCl2 和 NaBr）的产出流体的 87Sr/86Sr 比率的分析与 Sr 的保守行为一致。这与之前的解释形成对比，其中 Br 被认为表现得保守，而 Sr 的稀释速度是 Br 的三倍，被认为丢失到矿物相中。这种 Sr 损失无法解释 87Sr/86Sr 比率的演变。分析第二次注入后产出的水中的 87Sr/86Sr 比率，添加 LiCl 和荧光示踪剂，可以计算测试 1 和 2 中地层水和注入水的分数。 Sr、Li 和 SO4示踪剂（后者由地层硫化物氧化形成）都表明稀释率相似，这与保守行为一致。将间隔提取的两次注入事件的结果与连续提取加有甲醇的采出水的两次后续推拉式注入进行比较。与早期的间隔萃取实验相比，这些连续萃取实验显示出在相同范围内的生产与注入水体积（仅约 0.6）内的稀释程度显着降低。这意味着与提取暂停相关的某些过程增强了注入水和地层水的混合。实现使用推拉实验来评估储层非均质性和 CO2 溶解速率的目标将需要更好地评估各种示踪剂，以确定哪些表现保守，并正确理解从地层中提取流体时混合变化的原因。