A small-scale experimental study of CO_(2) enhanced injectivity methods of the high-rank coal  

作　　者：Qing-He Niu Li-Wen Cao Shu-Xun Sang Wei Wang Wei Yuan Jiang-Fang Chang Xiao-Jun Jia Wei-Min Zheng Zeng-Xue Zhang 

机构地区：[1]State Key Laboratory of Mechanical Behavior and System Safety of Traffic Engineering Structures,Shijiazhuang Tiedao University,Shijiazhuang,050043,China [2]Hebei Technology and Innovation Center on Safe and Efficient Mining of Metal Mines,Shijiazhuang,050043,China [3]School of Resource and Earth Science,China University of Mining and Technology,Xuzhou,221008,China [4]Jiangsu Key Laboratory of Coal-based Greenhouse Gas Control and Utilization,China University of Mining and Technology,Xuzhou,221008,China [5]Hebei Academy of Emergency Management,Shijiazhuang,050081,China [6]Hebei Iron and Steel Group Mining Co.,Ltd,Tangshan,063000,China [7]Minmetals Mining Holding Co.,Ltd,Hefei,241000,China

出　　处：《Petroleum Science》2021年第5期1427-1440,共14页石油科学（英文版）

基　　金：sponsored by the National Natural Science Foundation of China(Grant nos.41727801,41972281,51979170,11902208,U1967208 and 41330638);the National Key Research and Development Plan Project of China(2018YFB0605600);the Natural Science Foundation of Hebei Province(E2021210077);the Autonomous subject of State Key Laboratory of Mechanical Behavior and System Safety of Traffic Engineering Structures(ZZ2020-29);Science and Technology Research Project of Hebei Province Colleges and Universities(QN2021129)。

摘　　要：The attenuation of CO_(2)injectivity has become the biggest technical barrier for the application of CO_(2)enhanced coalbed methane recovery(CO_(2)-ECBM).Commonly,the intermittent CO_(2)injection,N2 displacing CO_(2)and pre-fracturing are the potential CO_(2)enhanced injectivity methods for coal reservoirs,but their mechanism and effectiveness remain to be clarified.This paper thus conducted small-scale experiments to simulate the working process of these engineering measures by an independently developed experimental device.Results show that the CO_(2)injectivity of coal is remarkably improved by the intermittent injection mode since the CO_(2)injection time is increased by folds and the loss of reservoir pressure can be complemented in time.The N_(2)displacing CO_(2)method promotes the desorption of CO_(2)and reduces the swelling strain,with the result that the permeability of coal is improved by 74.82%and 64.95%compared with the methods of the primary subcritical CO_(2)(Sub CO_(2))and supercritical CO_(2)(Sc CO_(2))injection.However,the permeability reduces again with the secondary CO_(2)injection.The permeability of the coal sample after pre-fracturing is averagely improved by 1-2 orders of magnitude,the irreversible permeability loss rate,average stress sensitivity coefficient and the permeability loss rate due to adsorption are averagely reduced by 95.885%,61.538%and 96.297%,respectively.This indicates that the permeability of coal after pre-fracturing is no longer sensitive to both the effective stress and Sc CO_(2)adsorption,the injectivity is thus improved and stable.The CO_(2)enhanced injectivity effects of the intermittent CO_(2)injection,the N_(2)displacing CO_(2)and the pre-fracturing are various,which thus can be selected individually or jointly to improve the CO_(2)injectivity according to the reservoir physical properties and geological conditions.This research deepens the understanding of the functional mechanism of CO_(2)enhanced injectivity methods and provides some guidance for their selection

关 键 词：Supercritical CO_(2) Permeability Intermittent injection N_(2)displacing CO_(2) PRE-FRACTURING 

分 类 号：TE377[石油与天然气工程—油气田开发工程]