盐岩渗透特性的试验研究及其在深部储气库中的应用

EXPERIMENTAL STUDY OF PERMEABILITY OF SALT ROCK AND ITS APPLICATION TO DEEP UNDERGROUND GAS STORAGE

为给深部盐岩地层（≥1500m）中所建天然气储库的稳定性和密闭性评价提供科学指导,针对取自江苏金坛的不同杂质含量盐岩试样,在荷兰乌德勒支大学HPT实验室开展了在三轴压缩条件下的瞬态法渗透率测试研究,揭示盐岩的变形特征与渗透率演化规律。试验研究表明：在围压20 MPa的常温测试条件下,随着偏应力从0~40MPa递增,损伤后的低含泥盐岩的渗透率从10-16m2逐渐下降至10-21m2以下,而损伤后的高含泥盐岩的渗透率则平均高出前者1~2个量级,推测表明损伤后的盐岩在加载下裂纹闭合、孔隙减小、逐渐压缩密实,进而渗透率快速降低,同时也表明外载压密作用对纯盐岩的裂纹压缩闭合、甚至损伤修复作用更显著。根据试验成果,并利用H.Alkan等[11]建立的盐岩压缩–扩容边界线对位于1500~2000 m深部的盐岩地层中的球形腔体的围岩应力状态分析显示,围岩几乎都位于扩容边界以下的安全区域,由此推知：即使在储气库低压运行条件下,围岩中较难发生扩容而导致密闭性失效事件发生,腔体的密闭性能极好。该研究为深部盐穴储气库的可行性和密闭性评价提供有利支撑。

In order to provide reliable data for evaluating the integrity of gas storage caverns constructed in deep salt formations（≥ 1 500 m）, experiments have been conducted to assess the effect of deformation on the permeability of the impure salt rock samples from Jiangsu province, China. The transient method of step-decay of Argon gas was used in conjunction with the conventional triaxial compression tests with the samples incrementally deformed and the permeability measured at the same time. The tests were performed at room temperature and at the effective confining pressures of 20 MPa in Utrecht University, Netherlands. It was found that the permeability of relatively pure salt samples decreased from 10-16 m2 to below 10-21 m2 with the increasing of differential stress（0 - 40 MPa）, presumably due to the crack closure and the porosity reduction. Thepermeability of the samples with high impurity content was 1 - 2 orders higher than that of the pure salt rock, which was interpreted to be due to the more effective compaction occurred in the pure salt. Using the concept of dilatancy boundary, the stress state around the spherical storage caverns in the deep subsurface is analyzed; and it is found that the stress state in the rock wall remained completely in the non-dilatant field（region of compression）. It could be deduced that even under low-pressure conditions of cavern operation, dilatancy would not easily occur in the cavern walls, implying the high sealing integrity of deep storage cavern in salt rock.