基于力学平衡原理定量表征致密储层含油饱和度

In order to predict the sweet spot of tight oil, this study is based on mechanical balance, energy conservation principle and the pore structure characterization experiment of tight reservoirs, to quantitatively characterize the spatial distribution of the tight reservoir oil saturation. By analyzing the relationship among the pore structure, sedimentary micro-facies and diagenesis, the tight reservoir types can be divided according to the pore structure characterization, and carrying out the relative correction according to differences between experimental and geological conditions, the mean capillary pressure curve plate of different types of tight reservoir will be established. Through analyzing the variation of driving force for oil migration in fault and tight reservoirs based on mechanical balance and energy conservation principle, we will establish the overpressure attenuation equation within fracture system and tight reservoir. Based on the tight oil accumulation period and the results of reconstruction overpressure history, the oil initial expulsion force from source rocks will be determined. Using the overpressure attenuation equation and the mean capillary pressure curve, we can quantitatively characterize the oil migration driving force and the oil saturation in tight reservoir. The calculated oil saturation will be corrected by the measured oil saturation, and then the remaining overpressure- pore structure- oil saturation plate will be established. The research methodology was applied to the study target, to quantitatively characterize the spatial distribution of the tight reservoir oil saturation, thereby guiding the related work of tight oil exploration and development, such as the well disposition, resource assessment, et al..

为了预测致密储层的含油性“甜点”，本项研究基于力学平衡和能量守恒原理以及孔喉结构表征实验，定量表征致密储层含油饱和度的空间分布。通过分析致密储层孔喉结构与沉积微相、成岩作用的关系，依据孔喉结构特征划分致密储层类型，根据实验条件与地质条件的差异进行相关校正，从而建立不同类型致密储层平均毛管压力曲线图版；基于力学平衡和能量守恒原理分析原油运聚时驱动力在断裂系统和致密储层中的变化规律，建立断裂系统和致密储层内的超压衰减方程；依据致密油成藏期和烃源岩超压史恢复结果，厘定烃源岩初始排烃力，利用超压衰减方程定量表征致密储层中原油驱动力的大小，并结合平均毛管压力曲线计算致密储层的含油饱和度，在此基础上依据实测数据进行校正，建立剩余超压—孔喉结构—含油饱和度关系图版，并应用于研究靶区，从而定量表征致密储层含油饱和度的空间分布，以期指导我国致密油的井位部署、储量评价等相关勘探开发工作。

致密油“甜点”的预测和评价无论在各大油田还是研究机构均备受关注，也成为致密油气勘探所面临的关键问题，相关研究在致密油勘探开发中对于井位部署、储层评价、储量计算等方面意义更为重大。本项研究以松辽盆地南部扶余致密油层为研究对象，开展致密油源岩的生排烃、致密油驱动力的定量模拟；基于油气运聚的力学特征和储层的微观结构表征，划分致密储层等级，评价致密储层的成岩演化特征及致密化机制；在致密油气充注模拟实验基础上，分析致密油运聚成藏的地质因素、动力学特征，建立致密油含油饱和度评价地质模型，并开展了研究区致密油含油饱和度的平面预测。. 研究表明，当致密油源岩的源内超压大于7MPa、排烃量大于8mg/g岩石时，不仅具备较大的油气驱动力，还具备充足的油气来源，是致密油的聚集和甜点形成的先决条件。此外，由于成岩作用类型和强度的不同，致使储层孔喉结构及尺寸的差异化，也造成了致密储层内含油饱和度分布的非均质性。孔隙度介于9~12%、渗透率介于0.1~1.0mD的I类致密储层为致密油气富集提供了有利场所，是致密油甜点的潜在发育区。通过分析致密油运聚成藏的力学特征和影响力学特征的相关地质因素，松辽盆地南部扶余油层的Ⅰ砂组含油饱和度与古超压、储层质量、下排深度以及源岩排烃强度均存在一定的关系，但与距断层的横向距离无关；II~IV砂组含油饱和度随下排深度、距断层横向距离呈负相关，与古超压、储层质量、以及源岩排烃强度呈正相关。根据含油饱和度地质评价模型的预测结果，四套砂组含油饱和度高值区均分布在长岭凹陷北部查24-查34区域和乾140-乾215-乾深3-乾深6-乾深12区域以及两井地区，且从Ⅰ砂组到Ⅳ砂组，含油饱和度整体上逐渐降低。基于地质模型建立的含油饱和度预测模型不仅可以评价单井垂向上的含油饱和度演变，还可表征井间致密储层的含油性变化，为致密油气开发部署以及水平井井轨迹设计提供参考。