致密砂岩储层多尺度裂缝分级建模方法——以红河油田92井区长8储层为例

Hierarchical modeling of multi-scale fractures in tight sandstones: A case study of the eighth member of the Yanchang formation in wellblock 92 of the Honghe oilfield

天然裂缝是致密砂岩储层的重要储集空间和渗流通道,具有明显的多尺度特征,建立多尺度裂缝三维地质模型对提高该类油藏开发效率具有重要的实际意义。但是,目前多尺度裂缝建模方法缺少系统深入的研究,尤其是小尺度裂缝建模约束条件单一,随机性强,可靠性低。因此,本文以红河油田92井区长8储层为例,首先利用野外露头、岩心、测井、地震等资料,将天然裂缝主要分为3种规模类型:大尺度裂缝、中尺度裂缝、小尺度裂缝。在此基础上,提出了多尺度裂缝分级建模思路:(1)用人工地震解释的确定性方法建立大尺度裂缝模型;(2)用蚂蚁体追踪的确定性方法建立中尺度裂缝模型;(3)在建立三维脆性指数模型和地震属性融合体的基础上,利用多元线性回归方法融合岩石脆性指数模型、到断层距离属性体、地震属性融合体建立井间裂缝发育概率体,并以此为软数据约束建立裂缝密度模型,然后在裂缝几何形态和裂缝密度模型的约束下,用基于目标的示性点过程模拟方法建立小尺度裂缝模型。最后,将大尺度裂缝、中尺度裂缝和小尺度裂缝离散网络模型融合成综合离散裂缝网络模型,并通过粗化得到裂缝属性模型。经验证,建立的裂缝模型与地质认识和生产动态数据均吻合较好,为油藏数值模拟提供了地质依据。

Natural fractures are an important storage space and major flow channels in tight sandstones, and have obvious multi-scale features. Thus the establishment of three-dimensional multi-scale fracture geological models has important practical significance for improving the development efficiency of this kind of reservoir. However, multi-scale fracture modeling methods lack systematic and detailed research. Especially the small scale fracture model generally has strong randomness and low reliability due to a single constraint condition. Therefore, taking the eighth member of the Yanchang Formation in wellblock 92 of the Honghe oilfield as an example, based on outcrop, core, logging and seismic data, this paper divides natural fractures into three types, namely large scale fractures, mesoscale fractures and small scale fractures. On this basis, a hierarchical modeling approach to multi-scale fractures is proposed:(1)The large scale fracture model is built by using the deterministic method of manual seismic interpretation;(2) the mesoscale fracture model is set up by using the deterministic method of ant tracking;(3) on the basis of establishing a 3 D brittle index model and a seismic attribute fusion body, the multiple linear regression method is used to combine the rock brittleness index model, the fault distance property body and the seismic attribute fusion body to obtain the inter-well fracture development probability body, which is used as secondary data to establish the fracture density model. Next, under the constraint of fracture geometry and the fracture density model, the small fracture model is constructed by an object-based marked point processes simulation. Finally, a comprehensive discrete fracture network model is built by integrating the large scale, mesoscale and small scale fracture models and fracture properties models are established by upscaling. It is proved that fracture models established are in good agreement with the geological understanding and production data, which provide the geological foundation for the numerical reservoir simulation.