致密砂岩储层微观孔喉非均质性及对石油分布的控制作用

Tight oil is a new hotspot of unconventional hydrocarbon exploration and development in the world. There is a low understanding on heterogeneity of microcosmic pore-throat systems and their controlling on oil distribution in tight sandstone reservoir. Revealing the change rules of heterogeneity of microcosmic pore-throat systems and their controlling on oil distribution in tight sandstone reservoir has the significance for comprehending the oil-bearing difference between the tight sandstones under the same geological conditions and improving the success of exploration, taking the typical tight sandstone oil-bearing area of Chang 6 and Chang7 Member of Yanchang Formation in the Ordos basin as an example. The key research content includes that the multiscale detailed description and characterization test on micrometre and nanometer pore-throats in tight sandstones are researched using the high precision testing means such as environmental scanning electron microscope and energy spectrum, focused ion beam scanning electron microscopy and so on combining the casting thin sections. Heterogeneity of microcosmic pore-throats are quantitatively characterized and then their distribution features are summarized. The oilness of different scales microcosmic pore-throat are researched using the scanning electron microscopy and energy spectrum combining core and fluorescence chip observation. The controlling of heterogeneity of microcosmic pore-throat systems on oil distribution in tight sandstone reservoirs are revealed after the research on the relationship of development degree of heterogeneity of microcosmic pore-throats and oilness of microcosmic pore-throats .

致密油是世界非常规油气勘探开发的一个新热点，目前对于致密砂岩储层微观孔喉非均质性变化及对石油分布的控制作用的关键科学问题的研究较为薄弱。以鄂尔多斯盆地典型区块延长组长6-长7致密砂岩油为例，揭示致密砂岩储层微观孔喉非均质性变化规律及其控油作用，对理解致密砂岩含油性差异、提高勘探成效具有重要意义。重点研究内容包括：①利用环境扫描电镜、聚焦离子束扫描电镜等高精度测试手段结合常规铸体薄片，进行致密砂岩储层微米－纳米孔喉多尺度精细描述与表征测试研究；量化表征其孔喉非均质性，进而分析总结致密砂岩储层孔喉非均质性分布特征；②利用环境扫描电镜配合能谱等高精度测试手段结合岩心观察、荧光薄片等，观察、检测并分析不同尺度微观孔喉的含油性，探讨微观非均质发育程度与微观孔喉含油性的关系，进而揭示微观孔喉体系非均质性对石油分布的控制作用。

致密砂岩储层微观孔喉非均质性变化及对石油分布的控制作用的关键科学问题的研究较为薄弱。为此，选取了资源丰富、勘探程度较高且代表性较强的鄂尔多斯盆地典型地区延长组长6—长8致密砂岩油，开展了储层孔喉类型、组合特征、孔径分布、孔喉非均质性表征、含油性等方面研究，探讨微观非均质发育程度与储层含油性的关系，揭示微观孔喉体系非均质性对石油分布的控制作用。.研究结果显示：①孔喉的主要分布区间为10-10000nm，主要是微米级和纳米级孔；纳米孔所占比例主要为57.3%-99.1%，平均为83.4%。微米级的孔隙主要分布在1-5μm，占微米级孔喉的83%-95%。②致密砂岩含油饱和度测试值为16.79%-31.56%，校正计算后得到的储层初始含油饱和度为47.92%-62.75%，含油率主要分布在2.48%-6.32%。③反映致密砂岩孔喉非均质性的参数分选系数越大，其分均质性越大，这时致密砂岩的含油性越小，而且含油率与大于50nm和大于100nm的孔喉占比呈现较好的正比关系，反映了致密砂岩50-100nm的孔喉对油气含油性贡献极大。同样，可动流体率与大于50nm的孔喉及大于100nm的孔喉呈正比关系。致密砂岩的孔喉非均质性较强，孔喉直径分布范围是影响含油饱和度的一项重要因素，分布越集中，大于50nm的孔喉数量越多，含油性越好。这些结论性认识对了解致密砂岩含油性及富集规律具有重要的科学和实际意义。.