Development Characteristics of Interbeds and Interlayers and Their Influence on the Distribution of Remaining Oil—A Case Study of L Oilfield in the Bohai Bay Basin

The In the Dongying Formation of L Oilfield in the Bohai Bay Basin, delta-front sediments are well-developed. The distributary mouth bars in each main reservoir layer exhibit a lobate distribution pattern, while the distributary channels are in the form of narrow and elongated strips embedded within the distributary mouth bars. The sand bodies are thick, and the distribution of interlayers is intricate, which severely impacts the water-flooding development effectiveness and the distribution of remaining oil in the oilfield. To address this, by relying on core data, logging information, water-flooding data from adjustment wells, and reservoir production performance data, and taking the second member of the Dongying Formation (Ed2) as the research target, a detailed dissection of the genesis, types, and distribution characteristics of interlayers between and within layers has been carried out to clarify their influence on the distribution of remaining oil. The results reveal that two distinct types of interlayers, namely mudstone-type and physical-property-type, are predominantly developed in the study area. Integrating the sedimentary model of the delta-front sub-facies and under the constraint of sedimentary sequences, according to the differences in vertical thickness and lateral continuity of interlayers, the interlayers in Ed2 are vertically classified into three types: inter-oil-group interlayers, inter-layer interbeds, and interlayers within thick layers; and horizontally divided into three types: stable type, sub-stable type, and unstable type. The presence of interlayers affects the vertical seepage of fluids, leading to varying degrees of vertical water-flooding. Remaining oil is concentrated at the top of thick sand bodies and beneath stable interbeds and interlayers. The research findings offer a robust geological foundation for subsequent potential tapping and enhanced oil recovery in the oilfield.