Identification of Interlayer Blocking Ability in Delta Facies Reservoirs of Z Oilfield in Bohai Bay Basin

The interlayers within deltaic sand bodies are thin, complexly distributed, and have varying blocking capabilities, which are crucial to the fluid flow and remaining oil distribution in water-flooding developed reservoirs. Taking the Z oilfield in the Bohai Sea's double-high stage as an example, and combining with the data from the cored wells, this paper selects the natural gamma and density logging curves to classify and identify two types of interlayers: high-mud-content impermeable interlayers and low-mud-content low-permeability interlayers. The interlayers are mainly formed by the lateral migration of channels and the superposition of multiple sand bodies. They present a horizontal arch shape against the direction of the source and a prograding cross-bedding in the direction of the source. Based on the differences in the water-flooding degree of the sand bodies caused by the interlayers overcoming gravity in the vertical direction, their blocking capabilities can be classified into three types: strong, medium, and weak blocking. Combining the logging response characteristics, a recognition chart for the blocking capabilities of interlayers within deltaic sand bodies is established. From the sedimentary center to the sedimentary margin, the blocking capabilities of the interlayers gradually increase. Due to the long-term water injection development of the oilfield, the medium and strong blocking interlayers within the reservoir block the fluid displacement, resulting in local accumulation of remaining oil. The research results provide geological basis for the in-depth exploration of remaining oil within the layers in the middle and late stages of oilfield development.