Factor Analysis and Prediction on Recovery Efficiency in Offshore Sandstone Reservoirs with Thick–Thin Interbedding

Chinese oil companies have formulated an empirical recovery efficiency model derived from an analysis of over 140 water-flooded oilfields. Initially successful in thick sandstone reservoirs (TSR), the industry has shifted focus to thick–thin interbedded sandstone reservoirs (TTISR). The empirical formula, however, falls short of the desired accuracy (below 60%) in TTISR due to the unique challenges posed, including diverse sand body scales, strong heterogeneity, and easily developed faults. To address these challenges, a comprehensive prediction model (CPM) has been introduced. This model integrates key parameters and refines the predictive capabilities. Noteworthy relationships include the arctangent function correlation between water flooding control (Es) and well density, as well as the linear relationship between the fault interference coefficient (Ef) and fault block. Reservoir heterogeneity, assessed using Lorenz coefficient L, is intricately incorporated into the CPM. The resulting relationship with the heterogeneity interference coefficient (EL) follows a quadratic function. The presence of these typical features results in a lower recovery efficiency for TTISR compared to TSR. The CPM unfolds in a three-stage pattern, featuring a concave-ascending trend, followed by a period of linear increase, and concluding with a convex-ascending trend as well density grows. This implies that the incremental oil yield diminishes in later stages compared to earlier stages. The effectiveness of the CPM is substantiated by verifying recovery data from the A area of the PL oilfield, achieving an impressive accuracy rate of 91%. Furthermore, the CPM facilitates the swift prediction of well numbers in the B area, showcasing its practical utility. This method not only serves as a robust tool for predicting recovery efficiency but also offers valuable insights for optimizing well numbers in similar oilfield development schemes.