Research on the Four-Property Relationships of Carbonate-Filled Cavern Reservoirs

Carbonate-filled cave reservoirs represent a special and important type of hydrocarbon accumulation in oil and gas exploration and development. Their complex filling characteristics and pore structures pose significant challenges to well-log interpretation. The filled cave reservoirs in N Oilfield exhibit a typical triple porosity structure: internal pores within the fillings are influenced by the type of filling material and diagenesis, the pores between the fillings and cave walls are mostly chemically cemented, and residual cavern spaces exist in cases of incomplete filling. This study investigates the relationships among lithology, physical properties, fluid properties, and electrical properties (four-property relationships) of filled cavern reservoirs using core data, well logs, laboratory analyses, and production test data. The results show that the PE value is sensitive to the lithology of carbonate cavern fillings in N Oilfield, and five lithologies were identified using the PE-RT crossplot. The density curve exhibits the best correlation with porosity, enabling the establishment of a porosity interpretation model based on density. Finally, the Archie formula was applied in combination with production test data to determine the oil-water layer identification criteria for the study area. This research clarifies the four-property relationship characteristics of carbonate-filled cavern reservoirs, providing a basis for the efficient development of N Oilfield and serving as a reference for similar reservoirs in future studies.