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为给深部盐岩地层(≥1 500 m)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10-16 m2逐渐下降至10-21 m2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1 500~2 000 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 scientific guidance for the stability and confinement evaluation of natural gas reservoirs built in deep salt rock strata (≥1,500 m), salt rock samples with different impurity contents from Jintan, Jiangsu Province, University HPT laboratory carried out under the conditions of triaxial compression transient permeability tests to reveal the deformation characteristics of salt rock and permeability evolution. Experimental results show that the permeable rate of low-salt mudstone after damage decreases gradually from 10-16 m2 to below 10-21 m2 with the deviatoric stress increasing from 0-40 MPa at normal temperature of 20 MPa confining pressure, The permeability of high-salt mudstone after injury is on the order of 1-2 orders of magnitude higher than that of the former ones. It is presumed that the rock salt after the damage is closed and the porosity is reduced, the compression gradually compacts, and the permeability decreases rapidly , But also shows that the compression effect of external load on the salt rock crack compression closure, or even more significant damage repair role. Based on the experimental results and analysis of the stress state of the surrounding rock of the spherical cavity in the salt rock formation located in the depth of 1 500 ~ 2 000 m using the salt rock compression-expansion boundary line established by H. Alkan et al. [11], the surrounding rock Almost all of them are located in the safe area below the expansion boundary. Based on this, it can be inferred that the sealing performance of the cavity is excellent even if the expansion failure in the surrounding rock is difficult due to the low-pressure operation of the gas reservoir. This study provides favorable support for the feasibility and tightness evaluation of deep salt cavern gas reservoirs.