摘要
利用不同频率的核磁共振仪器(23 MHz和2 MHz)测试不同粉碎程度页岩样品的孔隙度,评价页岩孔隙度的有效性,探究粉碎粒径对页岩样品孔隙度的影响。实验结果发现,与2 MHz仪器相比,23 MHz仪器在信噪比和回波间隔上有明显优势,更适合于评价页岩孔隙度;60~80目范围内页岩碎样的核磁共振T2谱、核磁共振孔隙度与完整柱状页岩测试结果一致;粉碎程度达到120目时,部分页岩样品的孔隙度出现一定程度减小,这与样品内部孔隙结构被破坏有关;当粉碎粒径超过230目时,页岩的主要粒度组分(即粉砂)被破坏,导致所有页岩样品核磁共振T2谱改变的同时孔隙度也明显减小,且页岩粉粹过程大孔隙的损失是影响T2谱变化的重要原因。在一定粒径范围内粉碎的页岩样品依然能够保持自身孔隙的完整性;当粉碎超过一定程度时,页岩的粒度组成与孔隙结构均会遭受破坏从而导致孔隙度明显降低。对页岩粉碎程度与粒度之间关系对比分析认为60目范围内的页岩碎样依然能准确表征页岩储层本身的孔隙度。
Researchers prefer to use crushed shales rather than plugs to derive the total porosity. However, there is no generally acceptable conclusion for the crushing level. Based on this, the different-frequency with low-field NMR apparatuses is used to measure the shale samples with different crushing sizes. Our aim is to evaluate the validity of shale porosity using NMR and the relationship between particle size and shale porosity. The higher frequency NMR instruments（23 MHz）have obvious advantages in signal-to-noise ratio and echo interval contrast to the 2 MHz apparatus, which makes it better in porosity measurement. The NMR（23 MHz）porosity for the aliquot within the range of 60 meshes consistent with the intact aliquot. As the particle is crushed to 120 meshes, the pore structure of the two samples will be destroyed and the porosity will also reduce to a certain extent. While crushing over 230 meshes, the main grain composition of silt will be altered, as a result, T2 spectrum of all samples will be changed, and the porosity decreases obviously. It indicates that crushing within a certain range can still maintain the integrity of the pores. However, once excess a certain mesh, the shale particle size composition and pore structure will be destroyed, resulting in a significant reduction in the porosity. The comparative analysis between the shale crushing degree and grain size shows that cuttings within 60 meshes can still accurately characterize the porosity of shale reservoir well.
出处
《测井技术》
CAS
CSCD
2017年第5期512-516,共5页
Well Logging Technology
基金
国家自然科学基金(41574122
41374124)
国家科技重大专项(2016ZX05006002-004)
作者简介
孙建孟,男,1964年生,博士生导师,从事测井资料数字处理与解释的教学与研究工作。E-mail：sunjm@upc.edu.cn
