摘要
探讨吞吐过程中CO2与吸附气作用机理对提高页岩气采收率的意义。基于低场核磁共振T2谱测试原理,对鄂尔多斯盆地苏里格东区长7段页岩开展了注CO2吞吐实验,通过对T2谱分布中的吸附态、游离态和自由态CH4的识别与标定,从微观孔隙尺度研究了CO2注入后焖井阶段和衰竭降压过程中吸附气的解吸机理,定量表征了多态CH4间的转化特征和采出程度。实验结果显示,随着页岩体系饱和压力的升高,3种形态CH4的赋存量也在不断增加。在CO2注入后的焖井阶段,吸附态CH4的解吸效率随焖井时间的增加先快速增加后趋于稳定,而解吸速率则呈现先增大后降低的趋势,解吸后的吸附态CH4会向游离态发生转换,但并不能直接转换为自由态。在衰竭降压过程中,随着吸附态CH4含量的减少,多态CH4间的动态转换平衡被破坏,当吸附态向游离态再向自由态转换的速率小于产气速率时,自由态CH4对应的波峰将消失。衰竭降压可以提高游离态和自由态CH4的采出程度,但很难增大吸附态CH4的采出程度,且衰竭降压开发时存在一定的压力下限(5.8 MPa),当压力低于此下限时,继续降压对多态CH4采出程度的影响很小。
It is very important to clarify the contact mechanism between CO2 and adsorbed gas for improving shale gas recovery in the process of CO2 huff and puff.Based on the principle of low field nuclear magnetic resonance(NMR)T2 spectrum test,the Chang 7 shale samples in the east Sulige gas field,Ordos Basin,are selected for CO2 huff and puff experiments.Through the identification and calibration of adsorbed,free and bulk CH4 in T2 spectrum distribution,the desorption mechanism of adsorbed gas in the process of soaking and depletion is studied from the micro pore scale,and the transformation characteristics and recovery degree of polymorphic CH4 are quantitatively characterized.The experimental results show that with the increase of shale saturation pressure,the stock of three forms of CH4 is also increasing.In the soaking stage after CO2 injection,the desorption efficiency of CH4 in the adsorption state increases rapidly with the increase of the soaking time and then tends to be stable,while the desorption rate increases first and then decreases.After desorption,the adsorption state CH4 transforms to the Free State,but it cannot be directly converted to the Free State.In the process of depletion,the quantity of bulk CH4 decreases and the transition between polymorphic CH4 is destroyed.When the conversion speed is less than the production speed,the corresponding peak of bulk CH4 disappears.Depressurization can improve the recovery of free and bulk CH4,but it is difficult to improve the recovery of adsorbed CH4.There is a certain lower pressure limit(5.8 MPa)in the development of depletion and depressurization.When the pressure is lower than this lower limit,continuous depressurization has little effect on the recovery of polymorphic CH4.
作者
黄丹
余浩杰
李武科
冯敏
邓宝康
于占海
吴小宁
郭愿刚
HUANG Dan;YU Haojie;LI Wuke;FENG Min;DENG Baokang;YU Zhanhai;WU Xiaoning;GUO Yuangang(Exploration and Development Research Institute of PetroChina, Changqing Oilfield Company, Xi'an 710018, China;National Engineering Laboratory for Exploration and Development of Low-Permeability Oil & Gasfield, Xi'an 710018, China;Sichuan OGT Technology Development of Oilfield Co., Ltd., Chengdu 610059, China)
出处
《成都理工大学学报（自然科学版）》
CAS
CSCD
北大核心
2020年第4期472-480,共9页
Journal of Chengdu University of Technology: Science & Technology Edition
基金
国家科技重大专项(2016ZX05050)。
