# A New Method of Geological Modeling for the Hydrocarbon Secondary Migration Research
## 5 Discussion
During the process of deep burial, the structural heterogeneity of clastic rock reservoirs influences rock formation, and the variations in diagenesis further contribute to reservoir heterogeneity [86; 88]. Consequently, the migration and accumulation of oil and gas in structurally heterogeneous reservoirsdiffer from traditional understandings, emphasizing the importance of considering such heterogeneity in the transport layer. The traditional reservoir geological modeling methods fall short in providing a detailed description of heterogeneity in deep to ultra-deep reservoirs. In this study, we propose a unit sand body filling modeling method, guided by sedimentary geology (Figure 15), to establish a comprehensive three-dimensional geological model of structurally heterogeneous reservoirs. This model enables the characterization and evaluation of the spatial distribution of effective reservoir sandstones and their inter-relationships. Incorporating the concept of artificial intelligence, we construct various types of cellular sand body models and combine them to create a library of cellular sand body models. By considering reservoir sedimentary characteristics, diagenetic processes, and oil and gas migration and charging in the study area, we select the appropriate unit sand body model from the library and directly incorporate it into the reservoir geological model. Drawing on previous sedimentological knowledge, we establish independent unit sand body models that account for different sedimentary environments, sedimentary characteristics, sand body types, and diagenetic features. These models encompass effective reservoir rocks as well as potential interlayers of mudstone and tight sandstone. It is important to note that the same type of unit sand body exhibits varying structural characteristics under different sedimentary conditions, which necessitates the construction of different unit sand body models. For instance, the unit sand body of the fluvial facies is defined based on the fourth-order configuration interface. In the case of meandering rivers, the point bar system is considered as a complete unit, encompassing the point bar sand body, the abandoned channel, and mud drapes during falling flood stages. This unit allows for the description of lateral deposits within the point bar sand body as well, as the presence of mudstone or plastic granular sandstone interlayers between them. On the other hand, the unit sand body of a braided river consists of a multi-stage interbedding of the braided bars within the small channel, separated by the fourth-order configuration interface. This unit includes the rich plastic sandstone interlayer positioned between the single-braided bars and the overlying floodplain deposits. In the unit sand body filling modeling method constrained by sedimentary geology, the appropriate variation function difference is carefully selected, taking into account the sequential, event-based, and sedimentary microfacies constrained sand body superposition mode. The Sequential Indicator Algorithm is then employed to effectively fill the unit sand  
Figure 15: Schematic diagram of construction process for an element sand body model of braided river. (**A**) Distribution of core beach sand bodies in different sedimentary periods. (**B**) The braided river unit sand body model composed of interlocking core beach bodies; the internal secondary structure shown on the section of the cell sand body model. (**C**) The internal secondary structure shown on the section of the cell sand body model. bodies. Drawing from our understanding of the inheritance and transformation of effective rock facies within the reservoir, the porosity and permeability characteristics within each unit sand body are determined based on the specific conditions observed in the study area. This enables the assessment of reservoir availability during different oil-gas accumulation periods and facilitates quantitative characterization of the reservoir properties.