吉木萨尔页岩储层孔隙结构表征及空气可注入性实验研究

Experimental study on pore structure characterization and air injectability of Jimsar shale reservoir

利用X射线衍射(XRD)、扫描电镜矿物定量评价(QEMSCAN)、微米CT扫描技术及AVIZO可视化软件先进的数学算法,构建了新疆吉木萨尔凹陷芦草沟组页岩储层的三维数字岩心,开展了不同类别页岩储层的微观孔隙结构表征研究。在此基础上,辅以高温高压物理模拟驱替系统进行了不同类别页岩储层的空气可注入性实验研究,并探讨了裂缝对于空气注入能力的影响。结果表明,研究区页岩储层的矿物分布及孔隙结构特征差异显著,层理分布呈现明暗交互的纹层状排布,孔隙结构主要以连续带状或孤立状分布,孔隙结构连通性差,非均质性较强。向页岩储层注入空气可与原油接触发生低温氧化反应(LTO),具有较好的膨胀降粘,增强流动性作用,空气注入能力的变化过程可划分为注入指数降低、注入指数上升、注入指数稳定3个阶段,升高注采压差能有效改善空气注入效果,缩短注采周期。裂缝可有效降低注采压差,减小基质内油气渗流阻力,提高页岩储层的空气注入指数,但突破时间相对变快,在合理生产压差下,结合空气泡沫等调剖体系进行适当的压裂改造有助于提高空气注入效果。该研究成果可为页岩储层注空气的高效开发提供借鉴。

The three-dimensional digital core of the Lucaogou Formation shale reservoir in the Jimsar Sag,Xinjiang was constructed by using X-ray diffraction(XRD),scanning electron microscopy mineral quantitative evaluation(QEMSCAN),micro-CT scanning technology,and advanced mathematical algorithms of AVIZO visualization software,and microscopic pore structure characterization of different types of shale reservoirs was carried out.On this basis,the experimental study on air injectability of different types of shale reservoirs was investigated through the high-temperature and high-pressure physical simulation displacement system,and the influence of fractures on air injection capacity was discussed.The results show that the mineral distribution and pore structure characteristics of shale reservoirs in the study area are significantly different,and the bedding distribution shows a layered arrangement of light and dark interaction.The pore structure is mainly distributed in a continuous band or isolated shape,and the pore structure has poor connectivity and strong heterogeneity.The low-temperature oxidation reaction(LTO)can occur by injecting air into the shale reservoir to contact the crude oil,which has a good effect on expansion,viscosity reduction,and fluidity enhancement.The variation process of air injection capacity can be divided into three stages:injection index decreased,injection index increased,and injection index stability.Meanwhile,increasing the injection-production pressure difference can effectively improve the air injection effect and shorten the injection-production cycle.Fractures can effectively reduce the injection-production pressure difference,decrease the seepage resistance of oil and gas in the matrix,and improve the air injection index of shale reservoirs,but the breakthrough time is relatively fast.Under the reasonable production pressure difference,combined with the profile control system such as air foam,appropriate fracturing is beneficial to improve the air injection effect.The research results can provide a reference for the efficient development of air injection in shale reservoirs.