三塘湖盆地MZ区块致密油藏CO_(2)吞吐提高采收率

Enhanced Oil Recovery by CO_(2) Huff⁃n⁃Puff in Tight Oil Reservoirs in Mazhong Block,Santanghu Basin

三塘湖盆地MZ区块致密油藏具有中—高孔隙度、特低渗透率和高含油饱和度的特征。开发初期采用水平井体积压裂获得高产,但自然递减率大,后期通过注水吞吐使得储量得到有效动用,但经过多年开发后注水吞吐效果逐轮变差,目前采出程度仅5.6%。为进一步提高采收率,开展了5口水平井CO_(2)吞吐试验。结果表明:CO_(2)在致密油提高采收率中主要发挥溶胀、增能、降黏、萃取轻质组分、提高流体流动能力等作用;在注入、焖井及生产全过程,CO_(2)作用机理会发生变化,从而造成原油性质的变化;CO_(2)在提高原油采收率的同时还具有较高的埋存率,兼具经济效益和社会效益,在致密油藏开发中具有较好的适应性和推广应用前景。

The tight oil reservoirs in the MZ block of the Santanghu basin are characterized by medium⁃high porosity,ultra⁃low permeabili⁃ty,and high oil saturation.In the initial development stage,high production rate was achieved by virtue of volume fracturing in horizontal wells,but declined greatly.In the late stage,the reserves were effectively produced through water huff⁃n⁃puff.After years of development,the effect of water huff⁃n⁃puff became worse.The current recovery percent of reserves is only 5.6%.For further enhancing the oil recovery,CO_(2) huff⁃n⁃puff experiments were conducted in five horizontal wells.The results show that CO_(2) plays a pivotal role in enhancing recovery in tight oil reservoirs through the mechanisms such as swelling,energy augmentation,viscosity reduction,light component extraction,and fluid mobility improvement.The impact of CO_(2) varies throughout the injection,soaking,and production stages,leading to alteration in crude oil properties.CO_(2) can enhance oil recovery and also demonstrate a high storage rate,offering both economic and social benefits.CO_(2) huff⁃n⁃puff is adaptable and promising for tight oil reservoir development.