不同孔隙类型火山岩储层渗透率应力敏感特征

针对火山岩气藏储层岩石孔隙结构复杂、矿物组成及成岩机制与沉积砂岩不同等特点，选取尺寸较大的不同孔隙结构全直径岩芯进行渗透率应力敏感试验研究。试验结果表明，低渗火山岩气藏岩芯具有较强的应力敏感特征，岩芯渗透率的减小主要发生在有效应力小于20 MPa的范围内，但当有效应力大于30 MPa后，渗透率仍然具有一定程度的减小，这与低渗沉积砂岩具有明显的差别。岩性差异所引起的矿物组成、颗粒胶结等因素对火山岩渗透率应力敏感特征影响较小，孔隙结构差异是导致岩石渗透率应力敏感强弱差异的主要原因，其中裂缝型岩石应力敏感性最强，致密型和孔隙型岩石应力敏感性相对较弱。反复加载试验表明，钻井取芯所引起的应力释放是导致岩芯渗透率应力滞后效应的根本原因，2次加载和卸载过程中岩石孔隙发生的主要是弹性变形。岩芯高围压下的地层渗透率平均仅约为地面渗透率的50%。

Characterization of stress-dependent permeability of volcanic gas reservoir of different types of pore structure

Stress-dependent permeability of volcanic gas reservoir rock has been studied using the larger size rock samples because the volcanic gas reservoir has some special features including complex pore structure, mineral composition and different diagenetic mechanism compared with the conventional sandstone reservoir. The experimental results indicate that the low permeability volcanic rock has strong permeability stress-dependent. The permeability of rock decreases with the increase of effective stress but most of the permeability reduction happens when the effective stress is less than 20 MPa. The rock permeability continuously decreases when the effective stress is larger than 30 MPa. It has been also found that difference in rock pore structure is the main factor affecting the feature of stress-dependent permeability. Rock samples containing fractures demonstrate the strongest stress-dependent permeability. Repeated loading and unloading experiments suggest that stress release caused by drilling is the key factor leading the hysteresis phenomenon. The rock samples occurs mainly elastic deformation when loading and unloading in the second cycle. Rock permeability under high effective stress is only fifty percent of that under low effectiveness.