# A dimensionless group model of the gas–oil interface stability for CO2 gas cap flooding and storage in fault block reservoirs

## TL;DR

This paper introduces a new model to assess the stability of gas-oil interfaces during CO2 gas cap flooding, which can improve oil recovery and enable large-scale CO2 storage.

## Contribution

The study proposes a novel dimensionless group model (N_GOI) to evaluate the stability of gas-oil interfaces during CO2 gas cap flooding.

## Key findings

- The N_GOI model can assess the feasibility of artificial CO2 gas cap flooding for enhanced oil recovery and CO2 storage.
- Reservoirs with specific properties are more suitable for stable gas-oil displacement using this method.
- The model is validated through theoretical deductions, experiments, and field data.

## Abstract

The stability of the gas displacing oil front (i.e., gas–oil interface) is of the utmost importance for the success of the immiscible gas flooding project under crestal gas injection. However, the preceding gas flooding assessment models are deficient in their description of the gas flooding mechanism, and they do not take into account the critical influencing factors in a comprehensive manner. Utilizing theoretical derivation, oilfield justifications, criterion and experiment validation, and dimensional analysis on crestal gas injection for stable flooding, this study presents an innovative theory and technique for artificial CO2 gas cap immiscible rigid stable gas flooding under CO2 injection, which could not only greatly improve crude oil recovery but also realize CO2 geological storage on a large scale, and new insights into displacement mechanism on the gas–oil interface through artificial CO2 gas cap immiscible rigid stable gas flooding process. Based on the multiphase filtrate theory, considering the influencing factors such as crude oil density, crude oil viscosity, density of injected gas, gas injection rate, strata dip, liquid phase relative permeability, air permeability in formation direction, viscosity of injected gas, gas phase relative permeability and the acting forces such as buoyancy, gravity, driving pressure, capillary pressure, viscous force and additional resistance in multiphase flow during the artificial CO2 gas cap immiscible rigid stable gas flooding process under CO2 injection, A simple quantified artificial CO2 gas cap immiscible rigid stable gas flooding assessment model (\documentclass[12pt]{minimal}
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\begin{document}$${N_{{\text{GOI}}}}$$\end{document}) was established. The results indicate the artificial CO2 gas cap immiscible rigid stable gas flooding process has the theory and field feasibility of greatly enhancing crude oil recovery and realizing CO2 geological storage on a large scale. And the oil reservoirs with strata dip, which have large oil and gas density difference, small oil and gas viscosity ratio, large oil and gas relative permeability ratio, large strata dip, and large air permeability in the direction are easy to exert gravity and buoyancy, reduce the influence of capillary pressure, viscosity and additional resistance, benefit to maintain the stability of gas displacing oil front and improve microscopic oil displacement efficiency, and facilitate the implementation of artificial CO2 gas cap immiscible rigid stable gas flooding development. In addition, the theoretical deduction, field and experimental validation indicate that artificial CO2 gas cap immiscible rigid stable gas flooding under CO2 injection can be realized when \documentclass[12pt]{minimal}
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\begin{document}$${N_{{\text{GOI}}}}$$\end{document} is greater than 1. The proposed \documentclass[12pt]{minimal}
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\begin{document}$${N_{{\text{GOI}}}}$$\end{document} model can be used as a creterion to assess the stablity and efficiency of the crestal gas injection for stable flooding such as artificial CO2 gas cap immiscible rigid stable gas flooding, artificial CO2 gas cap immiscible stable gas flooding, GAGD, gravity assisted gas injection, and crestal gas injection for stable gravity flooding for theoretical investigation, numerical simulation, laboratory test and field trial project design or operation.