孔洞型碳酸盐岩应力敏感下孔隙结构CT研究

目前储层应力敏感性研究在微观孔隙结构层面研究不足,本文选取川中地区震旦系灯影组四段气藏孔洞型碳酸盐岩心,进行原位CT的应力敏感试验研究。试验表明:孔洞型碳酸盐岩的渗透率随地层有效应力的增加明显下降;有效应力的增加造成岩心的孔隙体积、孔喉直径、喉道长度均变小;岩心的孔喉直径分布曲线和喉道的概率分布曲线向橫坐标轴负方向偏移,形状因子的概率分布曲线向橫坐标轴正方向偏移,在不同的压力阶段对不同尺寸、形态的孔隙影响不同,对于微小孔隙和喉道伤害明显,孔喉连通性变差;压力变化造成岩心微观孔隙结构变化导致岩心渗透率下降,且随着有效应力降低岩心渗透率不能完全恢复,表明应力敏感造成不可逆伤害。

Study on Pressure Sensitive Pore Structure of the Hole-Type Carbonate Based on Situ CT

There are few studies on the stress sensitivity of reservoirs at the micropore structure level. A porous carbonate core of the fourth member of the Sinian Dengying formation gas reservoir in Central Sichuan is selected to conduct an in-situ submicron CT permeability stress sensitivity test. The experimental results show that the permeability of porous carbonate rock decreases obviously with the increase of effective stress. Increasing effective stress decreases the pore volume, pore throat diameter, and throat length. The probability distribution of the shape factor curve shifts to the right, while the diameter of the pore throat distribution curve and the throat probability distribution curve of the core shift to the left. In different pressure stages, it has different effects on different sizes and shapes of pores. For micro pores and throats, the damage is obvious, and the connectivity of the pore throat becomes poor. The change in pressure causes a change in the core micropore structure, which leads to the decline of core permeability. With the decrease of effective stress, the core permeability cannot be restored, which indicates that the damage caused by stress sensitivity is irreversible.