页岩带压渗吸核磁共振响应特征实验研究

An Experimental Study on NMR Response Characteristics of Imbibition Subjected to Pressure in Shale

为进一步认识页岩气储层岩石中压裂液等外来流体的影响,选择四川某页岩气藏岩样完成了不带压和带压下渗吸核磁共振响应特征实验。结果表明,不带压自发渗吸过程中,岩样的T2谱曲线峰值增加、两翼扩展,从单峰特征变成了双峰特征,表明页岩岩样中的渗吸量随时间的增加不断地增加,并形成了新的孔缝系统,这与扫描电镜实验观察的渗吸前后孔隙结构变化结果一致。带压渗吸过程中,岩样的T2谱曲线表现为单峰特征,且基本上不发生变化;当卸载应力后完成不带压自发渗吸实验时,岩样的T2曲线表现出了与之前不带压自发渗吸实验观察一致的结果,这说明岩样上作用的应力影响页岩的渗吸特征。因此,在页岩渗吸实验评价及应用中应考虑应力敏感性的影响。

The imbibition of shale samples from the Sichuan Basin are studied under different pressure cycles using the technology of NMR in order to have some insight into the influence of invading fluids in shale gas reservoirs.The results show that the T2 curve of sample S1(confining pressure 0)gradually expands during the process of spontaneous imbibition and changes from a single peak to bimodal ones,indicating that the amount of imbibition continuously increases and a new pore-fracture system is formed,which is observed in microstructure experiments.Meanwhile,the T2 curve of sample S2(confining pressure 8 MPa)has single peak and almost remain unchanged;when the confining pressure on sample S2 is unloaded,the T2 curve turns into the bimodal ones,which is consistent with the results of sample S1,illustrating that the stress on the shale sample has an effect on the imbibition of shale.Therefore,it is suggested that the effect of stress sensitivity on shale imbibition should be considered in future study and application.