摘要
页岩基质赋水性是影响页岩气富集和运移的重要地质因素之一,但针对基质孔隙内不同状态(吸附与游离)水的定量表征理论和方法尚不成熟、微观赋存机制还不够清楚。基于孔隙内吸附水和游离水两相共存特征,提出了吸附比例方程和液体状态方程两个理论模型,前者可计算饱和页岩基质孔隙内吸附水所占质量比,后者可用于描述饱和页岩中孔隙水赋存状态及评估吸附参数(吸附水的密度和厚度)。进一步结合核磁共振技术,建立了基于核磁共振T2谱的(非)饱和页岩基质孔隙水定量评价方法,并以四川盆地东南部五峰组—龙马溪组海相页岩为例进行了应用。研究结果显示:①在实验室条件(20℃、常压)下,饱和蒸馏水页岩基质孔隙内吸附水质量比(即吸附比例)为26.8%~62.9%、平均为45.5%;吸附水饱和度为19.19%~52.36%,平均为35.71%;吸附水平均密度和平均厚度分别约为1.54 g/cm^3和0.65 nm。②在核磁共振T2谱上,吸附水主要分布于较小的T2值区间,游离水则反之,两者之间有交叉重叠。③存在一个临界孔径,小于该孔径的孔隙内完全被吸附水充填;大于该孔径的孔隙内吸附水和游离水两相共存,且随孔径增大,吸附水饱和度逐渐减小、游离水饱和度逐渐增加;总体上,吸附水主要分布于<50 nm的孔隙内,游离水分布于>50 nm的孔隙内。④同一页岩岩心在不同含水率情况下吸附水含量及分布总体上变化较小;随着含水率减小,游离水含量及分布变化较大,含量逐渐减小、幅度逐渐降低。
The water-bearing capability of shale matrix is one of the important geological factors affecting the enrichment and migration of shale gas.However,there is no mature theory and method of quantitative characterization for the water of different states(adsorption state and free state)in the matrix pores and the mechanism of microscopic occurrence is not clearly understood.Based on the fact that adsorbed water and free water coexist in the pores,this paper proposes two theoretical models of adsorption ratio equation and liquid state equation.The former can calculate the mass ratio of adsorbed water in the pores of saturated shale matrix,and the latter can be used to describe the occurrence state of pore water in saturated shale and evaluate adsorption parameters(density and thickness of adsorbed water).Furthermore,using nuclear magnetic resonance technology(NMR),this paper establishes a quantitative evaluation method for pore water in(un)saturated shale matrix based on NMR T2 spectrum,and applies it to the marine shale in Wufeng-Longmaxi Formation in the southeastern Sichuan Basin.The research results show:(1)under laboratory conditions(20℃,atmospheric pressure),the mass ratio of adsorbed water in matrix pores of the shale saturated with distilled water(i.e.,adsorption ratio)is 26.8%-62.9%,with an average of 45.5%;the saturation of adsorbed water is 19.19%-52.36%,with an average of 35.71%;the average density and average thickness of adsorption water are about 1.54 g/cm^3 and 0.65 nm,respectively.(2)In the NMR T2 spectrum,the adsorbed water is mainly distributed in the interval of small T2 values,and it is the opposite for the free water,and there is an overlap between the two.(3)There is a critical size for pores;with the pore size smaller than the critical value,the pores will be completely filled with adsorbed water;with the pore size greater than the critical value,the pores have both adsorbed water and free water.As the pore size increases,the saturation of adsorbed water gradually decreases and the saturation of free water gradually increases.In general,the absorbed water is mainly distributed in pores with the diameter<50 nm,and the free water is distributed in pores with the diameter>50 nm.(4)In the same shale core,under different water content,the content and distribution of adsorbed water change slightly;as the water content decreases,the content and distribution of free water changes greatly;the content and amplitude gradually decreases.
作者
李俊乾
卢双舫
张鹏飞
李文镖
荆铁亚
冯文俊
Li Junqian;Lu Shuangfang;Zhang Pengfei;Li Wenbiao;Jing Tieya;Feng Wenjun(School of Geosciences,China University of Petroleum,Shandong Qingdao 266580,China;College of Earth Science and Engineering,Shandong University of Science and Technology,Shandong Qingdao 266590,China;Huaneng Clean Energy Research Institute,Beijing 102209,China)
出处
《石油学报》
EI
CAS
CSCD
北大核心
2020年第8期979-990,共12页
Acta Petrolei Sinica
基金
国家自然科学基金项目(No.41972123,No.41672125)
国家科技重大专项(2016ZX05061)资助。
关键词
孔隙水
页岩基质
含量分布
页岩气
评价理论
评价方法
pore water
shale matrix
content distribution
shale gas
evaluation theory
evaluation method