Department of Chemical and Environmental Engineering, Yale University, 17 Hillhouse Avenue, New Haven, Connecticut 06520, USA.
Environ Sci Process Impacts. 2018 Feb 21;20(2):318-331. doi: 10.1039/c7em00470b.
Hydraulic fracturing coupled with horizontal drilling (HDHF) involves the deep-well injection of a fracturing fluid composed of diverse and numerous chemical additives designed to facilitate the release and collection of natural gas from shale plays. Analyses of flowback wastewaters have revealed organic contamination from both geogenic and anthropogenic sources. The additional detections of undisclosed halogenated chemicals suggest unintended in situ transformation of reactive additives, but the formation pathways for these are unclear in subsurface brines. To develop an efficient experimental framework for investigating the complex shale-well parameter space, we have reviewed and synthesized geospatial well data detailing temperature, pressure, pH, and halide ion values as well as industrial chemical disclosure and concentration data. Our findings showed subsurface conditions can reach pressures up to 4500 psi (310 bars) and temperatures up to 95 °C, while at least 588 unique chemicals have been disclosed by industry, including reactive oxidants and acids. Given the extreme conditions necessary to simulate the subsurface, we briefly highlighted existing geochemical reactor systems rated to the necessary pressures and temperatures, identifying throughput as a key limitation. In response, we designed and developed a custom reactor system capable of achieving 5000 psi (345 bars) and 90 °C at low cost with 15 individual reactors that are readily turned over. To demonstrate the system's throughput, we simultaneously tested 12 disclosed HDHF chemicals against a radical initiator compound in simulated subsurface conditions, ruling out a dozen potential transformation pathways in a single experiment. This review outlines the dynamic and diverse parameter range experienced by HDHF chemical additives and provides an optimized framework and novel reactor system for the methodical study of subsurface transformation pathways. Ultimately, enabling such studies will provide urgently needed clarity for water treatment downstream or releases to the environment.
水力压裂与水平钻井（HDHF）涉及深井注入由多种和大量化学添加剂组成的压裂液，旨在促进页岩层中天然气的释放和收集。对回流废水的分析表明，有机污染物既有地质成因的，也有人为成因的。额外检测到未披露的卤代化学品表明，反应性添加剂会在原地发生意想不到的转化，但这些物质在地下卤水中的形成途径尚不清楚。为了开发一个有效的实验框架来研究复杂的页岩井参数空间，我们回顾并综合了详细说明温度、压力、pH 值和卤化物离子值以及工业化学物质披露和浓度数据的地理空间井数据。我们的研究结果表明，地下条件的压力可达 4500 磅/平方英寸（310 巴），温度可达 95°C，而工业界至少披露了 588 种独特的化学物质，包括反应性氧化剂和酸。鉴于模拟地下环境所需的极端条件，我们简要介绍了现有的达到必要压力和温度的地球化学反应器系统，并确定了通量是一个关键限制。为此，我们设计并开发了一种定制的反应器系统，能够以低成本在低至 5000 磅/平方英寸（345 巴）和 90°C 的温度下实现通量，并且有 15 个单独的反应器可以随时更换。为了证明该系统的通量，我们在模拟地下条件下同时对 12 种披露的 HDHF 化学物质与自由基引发剂化合物进行了测试，在一次实验中排除了十几种潜在的转化途径。本综述概述了 HDHF 化学添加剂所经历的动态和多样化的参数范围，并提供了一个优化的框架和新型反应器系统，用于系统地研究地下转化途径。最终，开展此类研究将为下游水处理或向环境释放提供急需的明确性。
