CO_2微观驱油实验研究

Experimental Study on Micro-displacement Oil for Different CO_2 Displacement Mechanism

针对不同CO2驱油方式下提高采收率机理认识仍不完全清楚等问题,利用与地层孔隙结构相似的高压可视化微模型进行了水驱、CO2非混相驱、CO2近混相驱和CO2混相驱四组驱替实验,并采用微观驱油动态彩色图像分析和二值化处理相结合的研究方法,对比研究了不同驱替方式中驱替前缘形状、油气界面、油气分布特征、含油面积大小和模拟油颜色变化。结果表明:水驱油时,水大部分以非活塞形式驱油、油水界面呈凹凸弧线形;CO2非混相驱中,CO2与原油存在明显的两相流,界面形状比较锐利,窜流和混流比较严重,气体突破较早;CO2近混相驱替过程中,油气界面模糊、两相区不明显、没有形成明显的混相带;而混相驱过程中形成了清晰可见的混相带,油气界面明显圆滑和模糊,在相同条件下混相驱持续的时间最长,采收率最高。该研究对CO2有效驱油和驱油机理认识具有重要的理论意义。

For more direct observation and comparison of the enhanced oil recovery mechanism with different displacement ways by CO2,the high-pressure visualization micro model is adopted,which is similar to stratigraphic pore structure to perform four groups of experiment of water flooding,miscible displacement,nearly immiscible displacement and immiscible displacement by CO2 in this paper.Based on the color image processing technology and binary image two-value method,the different displacement front,oil-gas interface,oil-gas distribution characteristics,oil area in model and oil color change of the different displacement way are studied and contrasted.The research shows that most water displaces oil with unpistol-like flow during water displacement and oil-gas interface is of convex curve;in CO2 immiscible displacement,there are obvious gas-liquid two-phase flow between them,the shape of the gas-liquid interface is sharp and the streaming and mixed phase flow of gas-liquid is more serious and the gas breaks through early;In CO2 nearly immiscible displacement,the oil-gas interface is dim,gas-liquid diphase region is not obvious and no obvious gas-liquid transition zone is formed.While in the process of CO2 miscible displacement,a distinct gas-liquid transition zone is formed and oil-gas interface is obviously sleek and fuzzy.And, under the same condition,the CO2 miscible displacement lasts longer than others during the whole displacement process.This study is of great significance for understanding oil displacement with CO2 and its mechanism.