有控放气措施下含浅层气地层的一维变形分析

人为控制性放气是杭州地铁工程施工前防治浅层气地质灾害的必要措施。通过对浅层气藏形成中的水气运移过程分析可知,气藏原始包气带内的水压力和吸力沿厚度呈线性分布,孔隙水压力的大小与其相同位置处的静水压力相当;借助储层土体的室内土-水特征曲线并结合现场勘探资料,能够获得气藏初始饱和度分布。在分析有控放气措施下气藏内部水气运移基础上,利用GDS非饱和应力路径三轴系统地研究了气体释放过程中储气砂土的湿化变形,并给出了气体释放引起的含气地层沉降变形的预测方法。结果表明,在经历了形成过程中的自然脱湿后,储集层砂土被进一步压密,而工程放气措施引起的水浸或再吸湿过程中,单由饱和度或吸力减小所引起的砂土湿化变形量很小,可忽略其工程影响;有控放气措施下,由气体释放引起的浅层含气地层沉降沿气藏厚度自上而下依次递减,总沉降量约为气藏总厚度的1‰～5‰。

Analysis of one-dimensional deformation of shallow gassy stratum caused by controlling gas release

The artificial control of pre-exhausting shallow gas is a necessary measure for preventing geological disasters before the construction of Hangzhou Metro. By analyzing the gas-water migration process during the formation of shallow gas reservoirs, it can be found that original pore water pressure and matric suction in aeration zone of reservoirs present linear distribution along the thickness; and the pore water pressure is equal to hydrostatic pressure of the same position. The original saturation distribution of reservoirs can be obtained through experimental research on soil-water characteristic curve of reservoir sample and in-situ survey data. Based on analysis of the gas-water migration inside of reservoirs during gas release, deformation studies of gassy sand in wetting process were carried out by GDS unsaturated stress path triaxial system; and a method to predict settlements of the aerated stratum induced by gas release was proposed. Results show that the shallow gassy sand going through natural dewetting during the formation of reservoirs is further compacted; the wetting deformation of sand caused by decrease of saturation degree or matric suction is very small during water immersion or re-wetting induced by the engineering measure of gas release; and the effect can be ignored; settlements of the shallow gassy soil caused by controlled gas release decrease gradually from top to bottom along the thickness of reservoirs; and the total settlement is about 1‰-5‰ of the total thickness of gas reservoirs.