含夹层盐岩渗透特性及其细观结构特征

 由于盐岩具有极低渗透率，因此很多国家将盐岩作为能源和高放废物储存库的首选储库介质。选取湖北云应盐矿层状盐岩，对20个标准试样(f 25 mm×50 mm)进行渗透特性测试以及CT扫描试验。试验结果表明，盐岩的孔隙度普遍低于0.25%；且渗透率极低，为10－16～10－18 m2，从总体趋势上看，渗透率随着围压的增大而减小。进一步通过工业CT试验，揭示了盐岩极低渗透率在细观结构方面的原因。发现层状盐岩的细观结构极其致密，其中纯盐岩仅含少量微孔洞和微裂隙，而夹层几乎不存在缺陷，因此对气体渗透具有明显的屏蔽作用；且在围压和渗流作用下，盐岩因细观结构演化致使渗透性能发生较大改变，渗透率随围压的变化趋势与孔隙度变化趋势一致。

PERMEABILITY AND MESO-STRUCTURE CHARACTERISTICS OF BEDDED SALT ROCK

Salt rock，as a medium with extremely low permeability，has been widely used for oil and gas underground storages and high-level radioactive waste disposals in many countries. Twenty standard salt rock samples with dimensions of 25 mm in diameter and 50 mm in height，taken from the Yunying salt mine in Hubei Province，are tested by the automated core measurement system and the X-ray industrial CT to obtain their permeability characteristics and meso-scale structures. The test results indicate that the porosity of salt rock samples is less than 0.25% and the permeability is as low as 10－16–10－18 m2，and all decrease gradually with the increase of confining pressure in general. The mechanism of very low permeability subjected to meso-structure of salt rock is revealed by the X-ray industrial CT tests. It is shown that the salt rock is very compact at the meso-scale，and there are very few micropores and microfissures in pure salt rocks；and interlayer in salt rock is even more compact than that of pure salt rock，resulting in a shielding effect on permeability of bedded salt rock. Moreover，the effects of confining pressure and seepage lead to an obvious decrease in permeability. And the decrease of permeability agrees well with the decrease of porosity along with confining pressure.