Wilke Franziska D H, Schettler Georg, Vieth-Hillebrand Andrea, Kühn Michael, Rothe Heike
GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany.
GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany.
J Environ Radioact. 2018 Oct;190-191:122-129. doi: 10.1016/j.jenvrad.2018.05.005.
The production of gas from unconventional resources became an important position in the world energy economics. In 2012, the European Commission's Joint Research Centre estimate 16 trillion cubic meters (Tcm) of technically recoverable shale gas in Europe. Taking into account that the exploitation of unconventional gas can be accompanied by serious health risks due to the release of toxic chemical components and natural occurring radionuclides into the return flow water and their near-surface accumulation in secondary precipitates, we investigated the release of U, Th and Ra from black shales by interaction with drilling fluids containing additives that are commonly employed for shale gas exploitation. We performed leaching tests at elevated temperatures and pressures with an Alum black shale from Bornholm, Denmark and a Posidonia black shale from Lower Saxony, Germany. The Alum shale is a carbonate free black shale with pyrite and barite, containing 74.4 μg/g U. The Posidonia shales is a calcareous shale with pyrite but without detectable amounts of barite containing 3.6 μg/g U. Pyrite oxidized during the tests forming sulfuric acid which lowered the pH on values between 2 and 3 of the extraction fluid from the Alum shale favoring a release of U from the Alum shale to the fluid during the short-term and in the beginning of the long-term experiments. The activity concentration of U is as high as 23.9 mBq/ml in the fluid for those experiments. The release of U and Th into the fluid is almost independent of pressure. The amount of uranium in the European shales is similar to that of the Marcellus Shale in the United States but the daughter product of U, the Ra activity concentrations in the experimentally derived leachates from the European shales are quite low in comparison to that found in industrially derived flowback fluids from the Marcellus shale. This difference could mainly be due to missing Cl in the reaction fluid used in our experiments and a lower fluid to solid ratio in the industrial plays than in the experiments due to subsequent fracking and minute cracks from which Ra can easily be released.
非常规资源的天然气生产在世界能源经济中占据了重要地位。2012年，欧盟委员会联合研究中心估计欧洲技术可采页岩气储量为16万亿立方米。考虑到非常规天然气开采可能伴随着严重的健康风险，因为有毒化学成分和天然存在的放射性核素会释放到回流水体中，并在二次沉淀物中近地表积累，我们研究了丹麦博恩霍尔姆岛的明矾黑页岩和德国下萨克森州的波西多尼亚黑页岩与含页岩气开采常用添加剂的钻井液相互作用时铀、钍和镭的释放情况。我们在高温高压下对来自丹麦博恩霍尔姆岛的明矾黑页岩和德国下萨克森州的波西多尼亚黑页岩进行了浸出试验。明矾页岩是一种不含碳酸盐的黑页岩，含有黄铁矿和重晶石，铀含量为74.4μg/g。波西多尼亚页岩是一种含黄铁矿的钙质页岩，但不含可检测量的重晶石，铀含量为3.6μg/g。试验过程中黄铁矿氧化形成硫酸，使明矾页岩提取液的pH值降至2至3之间，有利于在短期和长期试验开始时铀从明矾页岩释放到提取液中。在这些试验中，提取液中铀的活度浓度高达23.9mBq/ml。铀和钍向提取液中的释放几乎与压力无关。欧洲页岩中的铀含量与美国马塞勒斯页岩中的铀含量相似，但与马塞勒斯页岩工业回流水体中发现的镭活度浓度相比，欧洲页岩试验浸出液中铀的子产物镭活度浓度相当低。这种差异主要可能是由于我们实验中使用的反应液中缺少氯离子，以及与实验相比，工业开采中由于后续水力压裂和微小裂缝导致的液固比更低，镭更容易从中释放出来。
