208 / 2019-06-20 09:56:32

Analysis of Parautochthonous Sedimentary Facies and Its Significance to Reservoir Research

Parutochthonous Sediments,BZ19-6 large condensate gas field,Shahejie Fm,Glutenite reservoir,Weathering Crust

Deposited near the provenance area but not completely above the provenance area are often referred to as parautochthonous sediments. The concept of " parautochthonous " has been mentioned more frequently in the study of bauxite deposits and the analysis of the genesis of glauconite, but the reservoir characteristics of this genesis were rarely discussed separately. In outcrops, parautochthonous sediments are often deposited in low-lying areas of the weathering crust, mainly gravel, and their composition was similar to that of parent rocks. The transport distance of sediment was short, the separation and grinding roundness were medium, and the thickness of sediment was small. Due to the different weathering degree, the vertical particles became finer upward and had poor stratification. BZ19-6 large condensate gas field, located in the southwest of Bozhong Sag, Bohai Bay Basin, China, is the largest gas field discovered so far in Bohai Bay Basin. Previous studies have suggested that the Paleogene Shahejie Fm was previously considered as source rock and local caprock. However, with the deepening of exploration and development, there was a new understanding of reservoir development characteristics — the glutenite at the bottom of Shahejie Fm in the North block of BZ19-6 structure also has reservoir properties. Research on core data shows that it has typical characteristics of parautochthonous deposition. The source of the glutenite in Shahejie Fm was mainly the underlying Archaean metamorphic rocks. Including incompletely weathered gneiss blocks and strongly weathered cuttings and clay. The main reservoir space was the fracture and dissolution pore formed by weathering and leaching. In this study, the BZ19-6 structure Shahejie Fm was taken as the research object. The single well, section and plane facies of Shahejie Fm in BZ19-6 structure were analyzed by combining core, well logging and seismic data. The predominant reservoir development position could be predicted by the characteristics of sedimentary distribution, which provides guidance for the next well location deployment plan.