低渗透油藏CO_2气驱渗流机理核磁共振研究

NMR study on porous flow mechanisms in low permeability reservoirs with CO_2 flooding

对超低渗透油藏和特低渗透油藏注入CO2开采,已成为提高原油采收率的重要技术手段之一.利用吉林油田超低渗透和特低渗透砂岩岩样,设计混相气驱、非混相气驱、高压水驱和低压水驱4种岩心注入工艺实验,采用核磁共振技术,从微观孔隙角度分析CO2混相气驱、非混相气驱和水驱渗流机理.研究表明:气驱驱走了岩心大部分大孔隙中的可动流体,并有一部分原油进入小孔隙成为不可动流体;相对非混相气驱,混相气驱可动流体的采出程度高是混相气驱提高采收率的根本原因;注采压差的提高,增加小孔隙中不可动流体的采出程度是基于混相气驱提高采收率的有效方法.气驱优于水驱,混相气驱优于非混相气驱.

For the reservoirs with uhra-low permeability and extra-low permeability, gas flooding is one of the important ways to improve oil recovery. Using sandsome core samples of Jinlin low permeability reservoirs and extra-low permeability reservoirs, core tests including miscible displacement, immiscible displacement, low pressure water displacement and high pressure water displacement were designed. Porous flow mechanisms based on CO2 miscible displacement, CO2 immiscible displacement and water displacement were analyzed by microcosmic angle of NMR. It shows that gas displacement results from most of movable fluid located in macro pores and small portion of crude oil enter small pores to become unmovable fluid ; high recovery percents of movable fluid located in macro pores is a key reason for CO2 miscible displacement to enhance oil recovery. A effective way for enhancing oil recovery is based on CO2 miscible displacement to increase injection/production pressure difference and to improve recovery percentage of unmovable fluid located in small pores. Gas displacement is more effective than water displacement and miscible gas displacement is superior to immiscible gas displacement.