致密砂岩储层与常规砂岩储层成藏动力学特征的差异性:以松辽盆地北部三肇地区扶余油层砂岩储层为例

摘要

为了研究三肇地区扶余油层砂岩储层特征,采用三维CT扫描技术和恒速压汞技术,对储层微观孔喉结构特征进行表征.结果表明,常规砂岩储层的孔喉大量发育,连通性好,为微米级孔喉.致密砂岩储层孔喉非均质性强,孤立零散分布,连通性差,以纳米级孔喉为主.微观孔喉特征的差异决定了油气充注、运移、聚集及渗流机理等成藏动力学特征具有差异性.通过对该区扶余油层砂岩储层的高压压汞实验、浮力与毛细管阻力公式计算及岩芯流动实验进行分析,认为油气在常规砂岩储层中初次运移动力是超压,二次运移及聚集的主要动力是浮力,油气以侧向运移为主,断层和砂体的匹配是主要的运移通道,流体流动状态呈达西渗流规律;油气在致密砂岩储层中运移动力为超压,油气以垂向运移为主,流体呈低速非达西渗流现象,以活塞--推挤的方式聚集.由于常规和致密油藏成藏动力学特征的差异,决定了油藏地质特征及分布的差异.三肇地区常规油藏主要是远距离、构造高部位聚集,上油下水规律明显,受构造控制;致密油藏主要是近距离、源下聚集,"甜点区"富集,圈闭边界不明显.%In order to investigate the characteristics of Fuyu oil sandstone reservoir, three-dimensional CT scanning technology and rate-controlled mercury penetration technique are used to describe the micro pore throats structure.Results show that the widely developed pore throats of conventional sandstone reservoirs are micro scale pore throats with good connectivity.The scattered developed pore throats of tight sandstone reservoirs are nano scale pore throats with poor connectivity.The differences of micro pore throats determine the differences of oil and gas filling,migration, accumulation and percolation mechanism.By means of high pressure mercury injection test, buoyancy and capillary resistance formula and core flow test in Fuyu reservoir,it is concluded that the driving force for primary migration of oil and gas is overpressure and the main driving force for the second migration and accumu-lation is buoyancy in the conventional sandstone reservoir.Oil and gas mainly migrate laterally,and the association of faults and sand bodies provides the main migration pathway.Fluid flow state follows Darcy flow law in the con-ventional sandstone reservoir.Whereas in tight sandstone reservoir,the driving force of oil and gas is overpressure. Oil and gas mainly migrate vertically,and the fluid presents low velocity non-Darcy flow phenomenon.The differ-ence of reservoir-forming dynamics determines the difference of reservoir geological characteristics and distribution. The analysis shows that the conventional reservoir in Sanzhao area is mainly in the long distance and high structure area with obvious oil-water contact,i.e.the water is under the oil,which is subjected to structural control,while the tight reservoir is mainly located near and below the source,and oil and gas are accumulate in"sweet spot"are-a.Trap boundary is not obviously.