基于核磁共振测量的页岩气游离吸附比例关系确定--以涪陵页岩气储层为例

Determination of Proportion of Shale Free Gas and Absorbed Based on NMR Measurements——Taking Fuling Shale Formation as An Example

对页岩岩心开展了不同条件下饱和油水的核磁共振观测对比研究,并基于饱和油的核磁T_2谱,确定了页岩有机孔中游离空间与吸附空间大小及比例。研究表明:(1)有机孔隙和无机孔隙的润湿性通过饱和油水的核磁响应得到体现,与自吸油状态下的核磁信号相比,干燥抽真空饱和油页岩的核磁T_2谱在大孔段信号明显增大,反映出干燥后黏土孔喉能够允许更多的油分子进入有机孔中,此时核磁T_2谱主要反映有机孔信号。(2)通过对地层条件下有机孔的模拟计算,确定了游离气和吸附气含量相等时对应的有机孔孔径大小,根据有机孔的核磁连续孔径分布,确定出储层游离气和吸附气所占比例。总体上,优质页岩气储层具有更大的核磁孔径响应分布及游离吸附比,对应着更好的资源潜力和产气能力。

This paper compared the nuclear magnetic resonance(NMR)measurements of oil and water saturated shale cores under different conditions,and determined the pore size and ratio of free gas and adsorption gas in shale organic pores based on the NMR T2spectrums of oil saturated shales.The results show that:①The wettability of organic pores and inorganic pores are reflected in the NMR T2spectrums of oil and water saturated shales.Compared the NMR signals of oil saturated shales that generated after self-priming and dry-vacuum,the large pore signal of latter in T2spectrum was enhanced.The result indicates that clay pore allow more of oil molecules entre the organic pore after dried.At this time,the T2spectrum mainly presents the signals of organic pores.②Determined the size of organic pore that was filled with equal volumes of free gas and adsorbed gas by simulating the organic pore under the formation condition.And determined the free gas to adsorbed gas ratio by continuous pore size distribution of organic pores.In general,high-quality shale gas reservoirs have stronger NMR response and larger free gas to adsorption gas ratio,which corresponding to better resource potential and gas production capacity.