Quantitative Evaluation of CO2 Swept Range and Iterative Huff and Puff Technology for Complex Fault-Block Reservoirs

Complex fault-block reservoirs are characterized by fragmented geological structures, strong reservoir heterogeneity, and significant fault shielding effects. After years of high-cycle CO2 huff and puff, the displacement efficiency gradually decreases, and the swept range is limited. To improve the utilization degree and development effect of CO2 in complex fault-block reservoirs, a quantitative evaluation method for CO2 swept range based on dynamic geological modeling and multi-source data fusion was carried out. Through high-precision 3D geological modeling and numerical simulation, the influence of fault combination, reservoir physical property heterogeneity, and fracture network on CO2 migration path was quantified, and a swept efficiency evaluation model based on dynamic monitoring data was established. A series of iterative huff and puff technologies were innovatively proposed, including low initial viscosity gel-assisted deep huff and puff, horizontal well precise huff and puff, and imbibition agent atomization-promoted washing huff and puff. Through the optimization of the “gas injection-soaking-production” cycle, combined with big data to dynamically adjust the injection pressure, cycle duration, and slug size, the effective swept volume of CO2 was gradually expanded, and gas channeling was suppressed. Field tests have shown that the CO2 swept range is funnel-shaped, with the largest swept radius at the top and the smallest at the bottom, diffusing to the formation in the range of the swept radius. At the same time, the swept radius of directional wells is much larger than that of horizontal wells. The application of iterative huff and puff technology has increased the vertical swept efficiency of CO2 by 18% to 25% in the target block, improved the single-well recovery factor by 7.3% to 12.6%, and achieved CO2 storage. The research results provide theoretical support and technical paths for the collaborative optimization of efficient development and carbon storage in complex fault-block reservoirs.