Experimental investigation of shale breakdown pressure under liquid nitrogen pre-conditioning before nitrogen fracturing  

作　　者：Yu Wu Jing Tao Jiehao Wang Yan Zhang Shuhua Peng 

机构地区：[1]State Key Laboratory for Geomechanics and Deep Underground Engineering,China University of Mining and Technology,Xuzhou 221116,China [2]School of Mechanical Engineering,Sichuan University of Science and Engineering,Zigong 643000,China [3]School of Mechanics and Civil Engineering,China University of Mining and Technology,Xuzhou 221116,China [4]Chevron Technical Center,Houston 77002,USA

出　　处：《International Journal of Mining Science and Technology》2021年第4期611-620,共10页矿业科学技术学报（英文版）

基　　金：This work was supported by the National Natural Science Foundation of China(No.51674247);the project for Fundamental Research Funds for the Central Universities(China University of Mining and Technology)under No.2015XKZD06.

摘　　要：Cryogenic fracturing with liquid nitrogen(LN_(2))offers the benefits of reducing the water consumption and adverse environmental impacts induced by water-based fracturing,as well as potentially enhancing the fracture complexity.We performed a series of laboratory experiments to explore the key mechanisms governing the breakdown pressures of shale during cryogenic fracturing.In this study,cylindrical shale samples were pre-conditioned by exposing a borehole to low-temperature LN_(2) for a certain time period,and then,the samples were fractured using gaseous N_(2) under triaxial stress and a high reservoir temperature.The effects of various key parameters on the breakdown pressure were investigated,including the duration of the low-temperature LN_(2) treatment,the confining pressure,the reservoir temperature,and the direction of the shale bedding relative to the borehole axis.The results demonstrate that the injection of low-temperature LN_(2) as a pre-fracturing fluid into a borehole can significantly reduce the breakdown pressure of the shale during subsequent nitrogen fracturing.This reduction in breakdown pressure can be further intensified by increasing the duration of the LN_(2) pre-conditioning.Without LN_(2) pre-conditioning,the breakdown pressure initially increases and then decreases with increasing reservoir temperature.When LN_(2) pre-conditioning is applied,the breakdown pressure keeps decreasing with increasing reservoir temperature.As the confining pressure increased,the breakdown pressure increased linearly in the tests with and without LN_(2) pre-conditioning.The experimental results demonstrate that LN_(2) preconditioning before N_(2) fracturing is a promising waterless fracturing technique that reduces the breakdown pressure and enhances the fracture complexity.

关 键 词：Breakdown pressure Liquid nitrogen(LN_(2))pre-conditioning Nitrogen(N2)fracturing Thermal shock 

分 类 号：TE37[石油与天然气工程—油气田开发工程]