李曜轩 张艳 王兴义

摘      要：基于减少开采页岩气对地层损害的目的，研究超临界二氧化碳压裂作用下页岩的宏观力学特性和孔隙度十分必要。通过室内物理模拟超临界二氧化碳压裂页岩过程，分析了超临界二氧化碳注入页岩后岩石力学特征与孔隙度的变化规律。研究结果表明：当页岩所受围压一定的条件下，随着超临界二氧化碳注入压力的增加，页岩的抗压强度、弹性模量随之减小，泊松比增加，页岩的力学参数抗压强度、弹性模量、泊松比分别与实验过程中注入超临界二氧化碳压力大小成二次多项式关系。超临界二氧化碳注入页岩岩芯后，样品的质量减小，孔隙度显著提高且最高增幅将近四倍，经分析发现页岩的弹性模量、抗压强度和泊松比与岩石孔隙度呈二次多项式关系，这表明超临界二氧化碳可以很好地改善页岩的物性特征。

关  键  词：超临界二氧化碳;压裂液;页岩;力学参数;孔隙度

中图分类号：TE357.7       文献标识码： A       文章编号： 1671-0460（2020）04-0572-05

Abstract： In order to reduce the damage of shale formation， it is necessary to study the macroscopic mechanical properties and porosity of shale under supercritical carbon dioxide fracturing.In this paper， the physical simulation of supercritical carbon dioxide fracturing shale process was carried out in the room to analyze the rock mechanical characteristics and porosity changes after injecting supercritical carbon dioxide into the shale.The results showed that when the shale was under constant confining pressure， with the increase of supercritical carbon dioxide injection pressure， the compressive strength and elastic modulus of the shale decreased， Poisson's ratio increased， the mechanics parameters of the shale including compressive strength， elastic modulus and Poisson's ratio had respectively quadratic polynomial relation with the injection pressure of supercritical carbon dioxide in the process of experiment. After supercritical carbon dioxide was injected into the shale core， the quality of the sample decreased， and the porosity significantly increased， and the highest growth almost reached four times. The results proved the supercritical carbon dioxide fracturing is a good way to improve the physical characteristics of the shale.

Key words： Supercritical carbon dioxide; Fracturing fluid; Shale; mechanical parameters; Porosity

1  引 言

隨着我国页岩气开发的突破，页岩气技术的相关研究逐渐兴起，但传统开采油气技术存在着环境污染和生态破坏等问题[1]，而采用超临界二氧化碳作为压裂液则可以完全避免地层污染。El Hajj等[2]发现超临界二氧化碳注入开采后的碳酸盐岩储层可以通过其与碳酸盐等的相互作用将储层压力升至露点压力以上，并且可以通过二氧化碳与碳酸盐的溶蚀作用和沉淀作用实现固碳的目标，从而加快油气的再生。……