降压边界和水合物饱和度对含水合物沉积物分解特性影响

Effects of depressurization boundary and hydrate saturation on dissociation characteristics of hydrate-bearing sediments

水合物开采时的降压边界和水合物饱和度对研究储层分解和变形特性具有重要意义。基于浙江大学研制的水合物伺服降压开采实验装置,针对不同初始水合物饱和度的沉积物模型,通过竖井降压和上边界一维降压两种方式的开采实验研究含水合物沉积物分解特性,探索水合物饱和度和降压边界条件对水合物相变速率、液气渗流模式和骨架变形特性的影响规律。结果表明:随着水合物饱和度增大,含水合物沉积物固有渗透率显著下降,水合物的非均匀分布引起局部孔隙封闭现象。水合物沉积物中的赋存形式由胶结型逐渐转为孔隙填充型,水合物比表面积随之下降,降低水合物相变分解速率。竖井降压利于实验中模型排水、增大气相相对渗透系数从而出现较高产气速率峰值,开采井周土体沉降、远离井区域出现隆起变形。一维降压实验中模型产水量较小,液相热容高、传热快的特性促使模型传热效率和水合物相变速率提高,水合物分解后模型整体呈隆起变形。

Based on the apparatus developed for hydrate exploitation modelling by Zhejiang University,the dissociation characteristics of hydrate-bearing sediments were studied by model tests with different hydrate saturation through upper boundary depressurization and vertical well depressurization.The effects of hydrate saturation and depressurization boundary on hydrate dissociation rate,liquid-gas seepage and skeleton deformation characteristics were investigated.The results show that the intrinsic permeability of hydrate-bearing sediments decreases with the increase of hydrate saturation,and the non-uniform distribution of hydrate causes local pore blockage.With the increase of hydrate saturation,the hydrate morphology changes from cementing to pore filling,and the specific surface area of hydrate decreases,which is disadvantageous for phase transition.The vertical well depressurization is beneficial to the drainage of the model and increase the relative permeability of gas,resulting in the high gas production rate,soil settlement around the well and the uplift away from the well.In the one-dimensional depressurization experiment,small water production results the characteristics of heat capacity and fast heat transfer of liquid improve heat transfer efficiency and phase transition rate,and surface uplift of the model after test.