Gravity stability mechanism and prediction model for natural gas injection flooding in multi-layered, heterogeneous reservoirs with high dip angles

The mechanism of gravity-stable flooding with top gas injection differs significantly from that of thick-layer homogeneous reservoirs owing to the strong intra- and interlayer heterogeneity in high-dip reservoirs. This study analyzes the geological characteristics of the LBIV oil group, assesses the basic displacement mechanism through the minimum miscibility pressure test of crude oil in reservoirs, and evaluates the displacement efficiency from water flooding to gas flooding using long-core analysis. The stability mechanism of secondary gas top injection is thoroughly examined by combining two-dimensional profile physical and numerical simulations. Using the dynamics of the gas injection test group as a reference, a relationship equation for a comprehensive prediction model of gravity-stable flooding of top gas injection, based on the Dietz model, is proposed along with a method for predicting gas–liquid interface. This prediction method considers various factors, including injection-production patterns, well spacing, elevation differences between injection and production wells, reservoir rhythm, and injection–production ratio. The results show that the comprehensive relationship effectively reflects the influence of stable flooding engineering and geological parameters of artificial gas caps, accurately predicts the displacement dynamics of artificial gas caps under different parameter combinations, and precisely analyzes the dynamics of gas storage construction.