致密砂岩微米-纳米孔喉系统石油充注的有效性及其成藏效应

Currently,the study on tight sandstone reservoir has been mainly focused on geological conditions of hydrocarbon accumulation, pore throat structures of reservoirs and mechanism of oil charging, while few on the effectiveness of micro-nano pore throat system to oil charging and its control on oil accumulation. Taking the tight sandstone reservoirs of Lucaogou Formation in Jimusaer Depression and Yanchang Formation in Ordos Basin as examples, three main aspects will be studied in this project. First, mico-nano pore system heterogeneity will be studied by means of nano CT and mercury injection to establish the relationship between pore throat distribution and geological factors such as grain size, mineralogical components, diagenesis and porosity of sandstone for the prediction of tight reservoir heterogeneity. Secondly, the oil occurrence in micro-nano pore system of tight sandstone reservoirs and the minimum pore throat system that filled with oil will be analyzed by CT scanning and Nuclear Magnetic Resonance (NMR).Physical simulation experiments of oil charging will be applied to establish the relationship between charging power and pore throat threshold which oil can break through, and the relationship among charing power,pore throat structures and effective oil accumulation space. Finally, the relationships and models will be applied to the cases in Jimusaer Depression and Ordos Basin to couple with the geological conditions,such as the asemblage of and the evolution of pressure difference between source and reservoir, and reservoir densification history, to study the process of tight oil charging and accumulation, and then predict the tight oil favourable area.

目前致密油研究重点集中在成藏宏观地质条件、储层孔喉结构及充注机理方面，但对致密储层微米-纳米孔喉系统对石油充注和聚集的有效性研究很少。本项目以吉木萨尔凹陷芦草沟组和鄂尔多斯盆地延长组致密砂岩油为研究对象，利用纳米CT、压汞等方法研究致密储层微米-纳米孔喉系统的非均质性，建立致密储层孔喉分布与粒度、成分、成岩程度、物性及其它地质因素的关系和致密储层孔喉分布非均质性的预测模型；利用CT扫描、核磁共振分析含油致密砂岩储层样品微米-纳米孔喉系统中石油的分布状态，研究不同地质条件下石油在致密储层中赋存的孔喉下限；开展致密砂岩储层石油充注的物理模拟实验，建立充注动力与所能突破的致密储层孔喉下限关系模型和充注动力、孔喉结构与有效聚集空间的关系图版；最后，将上述关系模型或图版与典型研究区地质条件（源储配置、源储剩余压差演化、储层致密史）进行耦合分析，研究其致密油的充注和成藏过程，预测致密油富集区。

目前致密油研究重点集中在成藏宏观地质条件、储层孔喉结构及充注机理方面，但对致密储层微米-纳米孔喉系统对石油充注和聚集的有效性研究很少。本项目以吉木萨尔凹陷芦草沟组和鄂尔多斯盆地延长组致密砂岩油为研究对象，利用氮气吸附、压汞、核磁共振等方法研究了致密储层微米-纳米孔喉系统的非均质性，明确了储层孔喉分布非均质性的地质控制因素，建立了致密砂岩储层孔喉大小与粒度、成分、物性的关系模型。研究表明，致密砂岩储层以纳米级孔喉为主；孔喉中值半径与碎屑颗粒粒度、石英和长石含量及孔隙度与呈现正相关关系，而与黏土矿物、碳酸盐矿物含量呈现负相关关系。利用岩石热解、抽提方法研究了致密储层含油性，并讨论物性、孔隙结构、生烃作用及充注动力等地质因素对致密储层含油性的影响作用，表明储集空间是致密储层含油的先决条件，孔隙结构和充注动力耦合控制着含油饱和度，而生烃作用是决定芦草沟组自生自储式致密油形成的关键因素。致密砂岩储层石油充注的物理模拟实验研究结果表明，充注动力与所能突破的致密储层孔喉下限存在着幂函数关系，即充注动力能够在一定程度上弥补孔隙结构致密导致的成藏难度。最后，将上述关系模型与典型研究区地质条件（源储配置、源储剩余压差演化、储层致密史）进行耦合，着重分析了不同致密储层的成藏效应。以上研究结果不仅对理解致密油的充注机理和成藏过程具有重要意义，而且能为预测致密油富集区提供理论指导。