Identification Characteristics of Interlayers and Interbeds in Shoreface Reservoirs and Their Influence on Remaining Oil Distribution—A Case Study of the Donghe Sandstone in the Hudson Oilfield

The Donghe Sandstone in the Tarim Basin represents marine littoral deposits. Cyclical variations in hydrodynamic conditions during sedimentary evolution led to the widespread development of intercalations/interbeds within the reservoir, which directly impact hydrocarbon development. It is imperative to elucidate the genesis, types, and distribution of these intercalations, and to reveal their controlling effect on residual oil. Based on detailed core observations, the genesis and classification of interbeds in the study area were determined. A three-dimensional cross-plot method was employed to establish interbed identification criteria, and architectural element analysis was used to predict their spatial distribution. Results indicate that interbeds in the study area can be classified into muddy interbeds, calcareous interbeds, and calcareous-muddy interbeds. The heterogeneity of interlayer and intralayer interbeds and sand body connectivity were systematically characterized. This enabled the prediction of distribution patterns and styles of different interbeds within the coastal-plain reservoir, as well as the relationship between residual oil and interbeds. Production practice shows that residual oil is mainly distributed in high-position well areas. This solves the problem of declining reservoir production in the Hadson Oilfield caused by interbed distribution and provides a reference for predicting residual oil distribution in marine coastal sedimentary oilfields.