Architecture Characteristics of Lake-Bottom Fan Sedimentary Reservoir: A Case Study of the PG2 Oil Reservoir

The PG2 sandstone volatile oil reservoir, located in the Es1 formation of the Nanpu Depression is a lake-bottom fan sedimentary reservoir with significant internal heterogeneity. This heterogeneity is characterized by the development of interlayers and barrier layers, which result in complex seepage characteristics during the process of converting oil reservoirs into gas storage. The transportation and distribution patterns of the reservoir fluid are not well understood. Therefore, it is crucial to study the sedimentary architectural pattern and the distribution characteristics of architectural units to clarify the heterogeneity of the reservoir and the fluid transportation and distribution rules. This would provide theoretical support for the subsequent construction of the gas storage and help identify the favorable reservoir areas. To address these issues, this paper systematically quantifies and characterizes the architectural interfaces and units in a hierarchical order, guided by the sedimentary genetic model. On this basis, a multi-level architectural method is developed for quantitatively characterizing the internal structure of the reservoir. The specific steps are as follows: (1)After establishing that the seventh order consists of composite genetic units formed by multiple single-phase sandy debris flow events, while the eighth order is a single genetic unit formed by a single-phase sandy debris flow event, the architectural interface between the seventh and eighth orders of the reservoir is quantitatively characterized. As there are no horizontal well in the study area at the target interval, empirical formulas for single watercourses and beds in lake-bottom fans, developed by previous scholars, are applied. The structural unit boundaries in areas without wells are determined through a combination of empirical formulas, inter-well comparisons, and data from the geological knowledge base. This process is used to define the scale of the architecture units, and the relevant parameters are then statistical counted. (2)Based on the identification of architectural interfaces, the study focuses on the classification, recognition, and distribution of the seventh and eighth order architectural units. The distribution characteristics of these different architectural orders are depicted in detail, and a developmental model for the eighth-order architectural units is established. Finally, the results of the reservoir architectural characterization are verified using dynamic production data, which confirms that the method accurately characterizes the internal structure of the reservoir and quantitatively describes its internal heterogeneity and fluid transport and distribution patterns. This provides theoretical support for identifying favorable reservoir areas for converting oil reservoirs into gas storage.