Multi-Scale Optimization of Three-Million-Ton-Class CCUS Project in the Largest Oilfield in China: Zone Control Technology of Large PV CO2 Flooding

Abstract

Abstract Large-PV (>1 PV) CO2 flooding is a technology that significantly improves oil recovery for ultra-low-permeability reservoirs. However, connected water-flooded channels formed by high-pressure water injection can lead to serious gas channeling, reducing the performance of large-PV CO2 injection. This article innovatively proposes a zoning control technology based on engineering geological characteristics of implementing million-ton CCUS in Changqing (China's largest oilfield). Multi-scale optimization is performed to achieve efficient and safe storage while maximizing oil recovery. Taking HX block of Changqing Oilfield as an example, through production performance analysis, the entire area is divided into different levels based on the lifecycle of the well network. Conduct sensitivity analysis and ranking of oil recovery and storage efficiency. Parameter optimization of typical well patterns through CMOST-AI. Based on the comprehensive economic indicators, the collaborative optimization of oil recovery and CO2 storage efficiency is completed, and the channeling control method is further explored through gel plugging and shut-in timing simulation. According to statistics, over 60% of the well patterns have entered the medium to high water cut. Through multi-scale classification and control, both types of well patterns CO2 flooding increased oil recovery by over 25%, and the ultimate CO2 storage capacity could reach over 3 million tons. The low water cut model was more effective in storing CO2 under the same injection conditions. Through sensitivity analysis, we found that the impact of injection-production parameters on recovery and storage efficiency varied. Gas injection pressure had the greatest impact on recovery and storage efficiency in the medium- to high-water-cut well patterns. While in the low-water-cut well pattern, it was the water slug volume. In addition, the water-to-gas ratio was the main influencing factor. Therefore, precise and case-specific optimization of injection parameters was necessary. In the later stage of the low-water-cut well pattern, gas channeling was severe, and the gradual alternation of water-gas-ratio can suppress this phenomenon. Consequently, appreciable oil recovery can be maintained in the later stages of development to ensure economic benefits. This article proposes for the first time a multi-scale collaborative, hierarchical classification-controlled large-PV CO2 injection technology that can simultaneously consider recovery efficiency and achieve CO2 million-ton level storage. In short, it is simple and fast to predict the development and storage effects of CO2 flooding in the entire region and provide guidance for the development of ultra-low permeability reservoirs and CCUS engineering.