致密砂岩储层黏土矿物特征及敏感性分析--以鄂尔多斯盆地吴起油田寨子河地区长6油层为例

Tight Sandstone Reservoir Clay Minerals Characteristics and Sensitivity Analysis——A Case Study of Chang 6 Formation in Zhaizihe Area,Wuqi Oilfield,Ordos Basin

致密砂岩储层孔喉结构复杂、比表面积大,岩石颗粒表面附着大量的黏土矿物,容易受到外来流体的影响,发生颗粒膨胀、迁移、离子沉淀等反应伤害储层,从而影响生产效率。本文以鄂尔多斯盆地吴起油田寨子河地区延长组6段油层为例,通过岩石薄片观察、扫描电镜、X射线衍射仪(X-RD)实验、压汞实验和储层敏感性实验等方法,对研究区储层物性、孔喉结构、黏土矿物特征和储层敏感性类型、伤害程度及敏感性影响因素进行分析。岩心分析实验表明,储层黏土矿物由绿泥石、高岭石、伊利石和伊蒙混层4种矿物组成,影响储层渗透性的敏感性伤害强弱依次为酸敏、水敏、碱敏、盐敏和速敏。并结合实际生产中存在的问题,提出绿泥石富集区域尽量避免储层酸化等改造措施;对伊利石及伊蒙混层含量高、易水敏的地区,压裂改造过程需要提高压裂液砂比,减小压裂液量,从而降低储层损害。

Tight sandstone reservoir has complex pore throat structure,large specific surface area,the surface of rock particles attached to a large number of clay minerals and easy to be affected by external fluid and causes damage to reservoir due to particle swelling,migration and ion precipitation,which will affect the production efficiency,thus affecting the yield increase.Taking Ordos Basin,Wuqi oilfield Zhaizihe area Chang 6 formation for example.Analyze the reservoir physical properties,pore-throat structure,clay mineral characteristics and reservoir sensitivity types,damage degree and sensitivity of study area by means of rock slices analysis,scanning electron microscopy,clay mineral X-ray diffraction analysis,Mercury intrusion experiment and sensitivity testing.The cores experimental results show that the clay minerals are mainly composed of four kinds of minerals,chlorite,kaolinite,illite and illite and smectite layer.Affect the sensitivity of the reservoir from strong to weak followed by acid sensitivity,water sensitivity,alkali sensitivity,salt sensitivity and speed sensitive.Combining with the problems existing in the actual production,the retrofit measures such as chlorite enrichment zone are put forward as far as possible to avoid reservoir acidification.For the region where easy water sensitive,with high content of illite and illite and smectite layer,it is necessary to improve the sand ratio when fracturing and decrease the fracturing fluid,so as to reduce the reservoir damage.