湖相页岩油储层油水岩相互作用的实验研究

The lacustrine shales in China, containing abundant hydrocarbon resources, are important and potential targets for hydrocarbon exploration and development. The fluidity of shale oil prohibits the effectiveness of oil development, while the occurrence pattern is one of the most important controlling factors on the fluidity of shale oil. However, there has not been thoroughgoing studies yet, although it has been recognized that the interaction between oil, water and rock, associated with the properties of wettability and absorption, play important impacts on the occurrence pattern and fluidity in the process of shale oil generation and occurrence. The lacustrine shales of the Shahejie Formation in Jiyang Depression (Bohai Bay Basin) are sampled to characterize the interactions between oil, water and rocks. Firstly, the overall wettability can be characterized by utilizing liquid-liquid extraction, spontaneous imbibition, contact angle measurement, NMR, Zeta potential measurements, etc. The wettability properties of reservoirs with different maturity and lithofacies, together with the primary controlling factors of shale wettability are also revealed by analyzing the above experimental results. Secondly, the oil-rock absorption capacity, stability of adsorbed layer can be investigated by absorption-desorption experiments, in order to reveal the absorption-desorption mechanism between oil and rocks. Thirdly, on the basis of the above two aspects of studies, the effects of wettability and absorption-desorption on the occurrence properties of fluids in shale reservoirs will then be investigated by oil-water saturation experiments within shales with different original wettability. The outcomes of this research may provide significant hints for evaluating the occurrence pattern and fluidity of shale oil.

我国湖相页岩沉积中含有丰富的油气资源，是重要的潜在勘探开发目标。可流动性制约着页岩油的有效开发，而赋存方式是影响可流动性的重要因素之一。页岩油生成和赋存过程中油、水、岩相互作用与岩石表面的润湿性和吸附性有关，对页岩油赋存方式、可流动性评价具有重要影响。然而，油水岩相互作用的研究还较为薄弱。本项目以济阳坳陷沙河街组为研究对象，以油水岩相互作用为出发点展开研究。首先，利用液液萃取法、自吸速率法、接触角测量、核磁共振、Zeta电位法等手段实现对页岩油储层整体润湿性的表征，分析不同成熟度、岩相页岩油储层的润湿性，并探讨润湿性的主要影响因素。其次，通过油-岩相互作用模拟实验分析油-岩吸附量和吸附层的稳定性，阐明油-岩的吸附解吸特征。在此基础上，通过对不同原始润湿性的页岩开展油水饱和模拟实验，探讨润湿性、吸附解吸对页岩储层流体赋存特征的影响。研究结果对页岩油的赋存方式及可流动性评价具有重要的理论意义。

我国东部湖相页岩层系中含有丰富的页岩油气资源，其有效开发受到可流动性的制约。鉴于页岩油生成和赋存过程中的油水岩相互作用对页岩油赋存特征、可流动性评价具有重要影响，本项目选择渤海湾盆地济阳坳陷沙河街组湖相泥页岩为研究对象，围绕油水岩相互作用表征展开研究。结果表明：（1）气液固体系中，泥页岩样品表面既为水湿也为油湿，表现为斑状润湿；相同总有机质范围内，硅质-富硅质泥页岩相对亲水，钙质-富钙质泥页岩相对亲油，富泥质泥页岩则为混合润湿；提出了常温常压条件下硅质-富硅质泥页岩水-岩-气接触角的回归方程。（2）有机质含量、有机质成熟度、地层水类型及矿化度、矿物组成、油组分、温度、压力等因素对泥页岩润湿性具有不同的影响作用；含硅质矿物（石英、钠长石、钾长石）、碳酸盐矿物（方解石、白云石）和黄铁矿的亲水性依次降低；水接触角与有机质含量、石英含量呈较好的正相关关系，与方解石含量呈一定的负相关关系；油润湿强度还与油润湿路径连通性有关，高孔渗、层理发育的样品油润湿性更强；随着温度增高，岩石表面更加亲水，油水岩体系中，压力对油水流体密度影响较弱，因而对润湿性影响不大，在气水岩体系中，压力增大，泥页岩表面可由亲水逐渐向亲气转变。（3）原油中极性组分的吸附作用可极大改变矿物表面的润湿性，在特定的水型及矿化度条件下，强极性的N,N-二甲基十二胺可以破坏含硅质矿物表面水膜并吸附在矿物表面，使得矿物表面由亲水向弱亲水或亲油性转变，而弱极性或无极性的油组分对改变矿物的润湿特征作用不大。（4）页岩油的吸附量与孔体积、比表面积具有较好的正相关关系，与有机质、粘土矿物含量具有一定的正相关关系，与钙质矿物含量呈负相关关系。（5）强极性烃类在矿物表面的吸附量相对更大、更稳定；储层物性、润湿性及矿物组成影响流体可动性。上述研究结果可为页岩油的赋存方式及可流动性评价研究提供科学依据。