基于核磁共振信号标定法的致密油藏渗吸实验研究

Tight oil imbibition based on nuclear magnetic resonance signal calibration method

基于一种新的核磁共振信号标定法开展了致密砂岩岩样的油水渗吸实验,该方法可以根据回归模型将核磁信号总量换算为含油体积,相较常规方法计算更方便、更准确。研究发现渗吸过程可划分为过渡渗吸和稳定渗吸2个阶段,低黏度煤油渗吸样品最佳渗吸时间集中在68 h左右,高黏度致密油渗吸样品最佳渗吸时间集中在188 h左右。渗吸时间充足的情况下,煤油和致密油的最终换油率相差不大,但如果渗吸时间较短,则黏度越大换油率越低。同层位、同黏度的样品具有相似的渗吸动态特征;同层位、高黏油的样品达到稳定渗吸阶段无因次渗吸时间相较低黏油更短。以半径0.5µm作为大、小孔隙的分界线,煤油渗吸样品中半径小于0.5µm的孔隙渗吸换油贡献率平均为83.93%,占据主导地位,原油动用率平均为23.54%;半径大于0.5µm的孔隙渗吸换油贡献率平均为16.07%,相对较少,原油的动用率平均为8.50%,普遍较低,容易形成水锁。致密油渗吸样品在所有孔隙中的渗吸换油贡献率则相对均衡,半径小于0.5µm的孔隙原油动用率平均为14.82%,相对较低;而半径大于0.5µm的孔隙原油动用率平均为29.82%,在焖井过程中普遍会得到有效动用。

This study explores oil-water imbibition dynamics in rock samples of tight sandstone with similar physical properties using a novel NMR signal calibration method.This method can translate the total NMR signal output into oil volume via a regression model,offering enhanced convenience and accuracy compared to traditional approaches.The imbibition process is characterized by two distinct phases:a rapid imbibition stage and a stable imbibition stage.Optimal imbibition times were identified as approximately 68 hours for oil from coal samples and 188 hours for tight oil samples.When imbibition times are sufficient,the recovery ratios for oil from coal and tight oil are comparable.However,with insufficient imbibition time,the recovery ratio for oil from coal is lower than that for tight oil.Within the same stratigraphic layer,samples with identical viscosity exhibit similar imbibition dynamics,with tight oil samples reaching the stable stage more quickly than oil from coal samples.The pivotal radius distinguishing large and small pores is established at 0.5μm.In low-viscosity crude oil samples,small pores significantly dominate the imbibition process,contributing 83.93%to the recovery,while large pores contribute only 16.07%.The overall mobilization of crude oil is low at 8.50%,frequently resulting in the formation of water locks.In contrast,tight oil samples show a more balanced contribution across all pore sizes during the soaking period.The average utilization ratios of crude oil are 14.82%in small pores and 29.82%in large pores.