以鄂尔多斯盆地三叠系延长组长8段样品为例,对低渗透复杂润湿性储集层核磁共振T2（横向驰豫时间）谱进行了研究。选取异常高电阻率和正常电阻率岩心样品,设计并测量了不同润湿性和含水饱和度下样品的T2谱、接触角以及Amott润湿指数。实验结果表明,正常电阻率岩心100%含水T2谱反映水的表面弛豫;异常高电阻率岩心洗油后对应的T2谱为单峰宽谱,由水的表面弛豫和体积弛豫组成,表明其洗油后也并未完全亲水。油驱水至束缚水后,正常电阻率岩心的T2谱表现为常见的双峰特征;异常高电阻率岩心的T2谱（未老化和老化后）均与其在100%含水状态下T2谱基本一致。这反映出油驱水至束缚水过程中,该部分岩心的润湿性向亲油方向的转变已基本完成,老化过程对其改变很小。水驱油至残余油后,异常高电阻率岩心的T2谱均表现为3峰特征,其中,短弛豫时间峰为束缚水的表面弛豫,中等弛豫时间峰基本反映残余油的表面弛豫和体积弛豫,长弛豫时间峰基本反映大孔隙中水的表面弛豫和体积弛豫。图5表2参16
冯程
,
石玉江
,
郝建飞
,
王振林
,
毛志强
,
李高仁
,
姜志豪
. 低渗透复杂润湿性储集层核磁共振特征[J]. 石油勘探与开发, 2017
, 44(2)
: 252
-257
.
DOI: 10.11698/PED.2017.02.09
The nuclear magnetic resonance T2 spectra of low-permeability reservoirs with complex wettability were studied using the samples from the Chang 8 Member, Upper Triassic Yanchang Formation, Ordos Basin, China. Abnormal high resistivity and normal resistivity core samples were selected. T2 spectra under different wettability and water saturation conditions, contact angles and Amott wettability indexes were designed and tested. The test results show that under fully brine-saturated condition, the T2 spectra of normal resistivity core samples reflect surface relaxation of water, while the samples with abnormal high resistivity exhibit wide unimodal T2 spectrum, consisting of both surface and volume relaxation of water, which indicates that these cores are not fully water-wet after oil washing. In the process of oil displacing water, the T2 spectra of normal resistivity core samples present bimodal feature, and those of abnormal high resistivity core samples (both un-aged and aged) mainly show the same unimodal feature as those measured under fully brine-saturated condition. Based on these results, it can be inferred that the wettability change of abnormal high resistivity core samples to oil-wet has basically completed during oil displacing water process, and the ageing process has little effect on the wettability of abnormal high resistivity core samples. In the process of water displacing oil to residual oil, the T2 spectra of abnormal high resistivity core samples generally show trimodal feature, among which, the shortest relaxation time spectrum peaks coincide with that under irreducible water saturation condition, the moderate ones reflect surface and volume relaxation of residual oil, and the longest ones reflect surface and volume relaxation of water in large pores.
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