Salt usually seals, but sometimes leaks: Implications for mine and cavern stabilities in the short and long term

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• 作者：John Keith Warren
• 关键词：Salt anomaly ; Salt seal ; Salt leakage ; Salt texture ; Salt cavity ; Salt mining ; Water inflows in mines ; Storage cavity ; Waste storage
• 刊名：Earth-Science Reviews
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：165
• 期：Complete
• 页码：302-341
• 全文大小：10679 K
• 卷排序：165

文摘

Thick evaporite masses (bedded and halokinetic) dominated by the mineral halite, are currently mined using conventional solution mining techniques. After excavation, the resulting salt cavities are sometimes used as subsurface storage vessels for hydrocarbons or various types of waste, including low-level nuclear waste. There are plans being discussed to use purposed-designed solution cavities in thick salt masses for the long term storage of high-level nuclear waste. If high-level nuclear waste is ever to be safely stored in salt, it will involve a need for the encasing salt not to leak over time frames measured in tens of thousands of years. Understanding how, where and why accessible salt masses leak is the rationale for this review. It is the first step in assessing it a particular site's salt geology is suitable for storage.We know salt can act as an excellent longterm seal over hundreds of thousands of years, as evidenced by its ability to hold back significant columns of highly overpressured fluids, even in structurally complex settings. But we also know that locally salt bodies do occasionally leak large volumes of fluid, as evidenced by the loss of a number of salt mines to uncontrolled floods, the rapid creation of solution dolines atop subcropping salt masses and to black salt haloes around highly pressurized hydrocarbon reservoirs. These types of leakage are usually tied to the edges of a salt body being exposed to longterm crossflows of undersaturated pore waters or to the build-up of internal pressure to levels that exceed lithostatic.In fact, most zones where a salt body is liable to leak, or has leaked, are indicated by anomalous textural or mineralogical features when compared to the regional character of the salt. The time of leakage can be early (eogenetic), related to burial (mesogenetic) or related to uplift (telogenetic). If the salt mass is not entirely dissolved in the fluid crossflow, then the remaining salt tends to re-seal, especially in zones of ongoing salt flow. However, if non-salt sediment remains in the re-annealed salt mass, it will tend to retain permeability, and when intersected in a salt mine or by a well bore it will flow fluid. More problematic in terms of significant leakage are zones in contact with an aquifer external to the salt mass. These anomalous areas can transfer large volumes of fluid. For this reason, active telogenetic anomalies in a salt mass are the most problematic in terms of both mine safety and waste storage.Identifying the type of salt anomaly, the time in diagenesis when leakage occurred and proximity and volume of intersected fluids in the zone of leaking salt is fundamental to mine safety and reliable waste storage.