基于低场核磁共振技术的岩心内流体 “可视化”评价方法研究

Visual Evaluation Method for Fluids in Cores Based on Low Field Nuclear Magnetic Resonance Technology

丁 彬 罗健辉 耿向飞 贾 辰 贺丽鹏 王平美 彭宝亮

DING Bin LUO Jianhui GENG Xiangfei JIA Chen HE Lipeng WANG Pingmei PENG Baoliang

岩心等多孔介质中流体的流动状态在线监测与 “可视化” 评价已成为驱油与扩大波及体积微观机理研究的重要方法。本文将低场核磁共振与岩心驱替装置联用， 基于核磁共振原理， 得到了岩心横向驰豫时间 （T2） 分布，结合压汞孔隙半径分布测试结果， 采用插值与最小二乘法， 建立了饱和水后的岩心核磁共振 T2谱与孔隙分布关系。以中高渗和低渗透两种岩心为例， 结合不同流体的岩心驱替实验， 利用转化的核磁孔喉分布得到了岩心孔隙结构与可动流体及剩余油分布的关系， 解析了水驱、 聚合物驱对不同孔隙的原油动用率。研究结果表明， 中高渗（256×10-3μm2）岩心平均孔隙直径为 72 μm， 主要集中在 1～500 μm之间， 微米级孔隙较发育； 低渗（7.51×10-3μm2）岩心平均孔隙直径为 86 nm， 主要集中在 10 nm～1 μm之间， 纳米-亚微米级孔隙发育。中高渗岩心与低渗岩心的束缚水主要集中在直径小于 1 μm和直径小于 0.5 μm的孔隙空间内。岩心驱替实验结果表明， 水驱主要动用孔隙直径大于 10 μm的储油空间， 聚合物驱原油动用区域与水驱基本一致， 提高驱替效果有限， 残余油 80%以上富集在孔隙直径小于 1 μm孔隙内。改善低渗透区域水驱效果将是提高采收率技术的关键。图5表 2参 19

The online monitoring of fluids flowing status in cores and visual evaluation had become important experiment method for oil displacing and enlarge sweep volume mechanism. In this paper， low field nuclear magnetic resonance and core flooding equipment were combined， and the distribution of transverse relaxtion time（T2）was obtained based on nuclear magnetic resonance theory. Combined with mercury injection pore radius analysis results， the relationship between nuclear magnetic resonance T2 spectrogram and pore radius of core was established using interpolation and least square method. Taking two kinds of cores with medium-high permeability（256 × 10-3 μm2）and low permeability（7.51 × 10-3 μm2）as an example，binding with core flooding experiments of different fluids，and using conversed nuclear magnetic pore throat distribution，the relationship between pore structure of core and the distribution of movable fluids and residual oil was obtained. The oil exploiting rate in different pore by water flooding and polymer flooding was also analyzed. The results showed that the average pore diameter of medium-high permeability core was 72 μm， the pore diameter was mainly 1—500 μm， indicating good micro-level pore development. The average pore diameter of low permeability core was 86 nm，the pore diameter was mainly 10 nm—1 μm，indicating good nano and sub-micro-level pore development. The bound water of medium-high permeability core and low permeability core was mainly concentrated in the pore space with the diameter less than 1 μm and 0.5 μm respectively. The core flooding experiments results showed that oil in pores larger than 10 μm was displaced by water， and polymer flooding showed the same tendency and oil flooding efficiency was limited. More than 80% of the residual oil was in the pores smaller than 1 μm. Improving the water flooding efficiency of low permeability zone was the key point for EOR in the future.

10.19346/j.cnki.1000-4092.2018.01.032