Experimental investigation into the enhancement of oil recovery and analysis of influencing factors for hydrocarbon gas flooding in high-water-cut ultra-deep oil reservoirs

Deep oil reservoirs, characterized by high temperature and high pressure, are conducive for enhancing the miscibility between gas and crude oil, thereby improving oil recovery. This paper focuses on a high-water-cut deep oilfield in Xinjiang and experimentally investigates the potential and influencing factors of gas flooding for enhancing oil recovery. These factors include permeability, type of injection gas, injection rate, injection pressure, and injection method. Based on geological characteristics, three types of experimental long-core samples: high permeability, medium permeability, and low permeability, were selected. Hydrocarbon gas injection experiments were conducted after water flooding at conditions of 112 °C and 55 MPa to evaluate displacement effects. Results indicated that high permeability cores exhibited the best displacement, with gas flooding recovery rates 39.53% higher than those from water flooding. Low permeability cores demonstrated a 35.46% increase in oil recovery, significantly surpassing the 29.31% increase observed in medium permeability layers. Among the four flooding media tested, CO2 was found to have the best displacement effect, increasing oil recovery by 33.22%, followed by hydrocarbon gas and associated gas, while N2 was the least effective (7.27%). Higher injection pressures (55 MPa) notably improved the final recovery degree, resulting in a 41.40% increase. Additionally, alternating injections of water and gas enhanced recovery by 13.02% compared to continuous gas injection. A lower injection rate of 0.5 ml/min improved recovery by 7% over 1 ml/min. Therefore, for medium permeability layers under high-water-cut conditions, the optimal gas injection scheme consists of using hydrocarbon gas as the injection medium, with an injection flow of 0.5 ml/min and a pressure of 55 MPa, employing a water–gas alternating injection mode. This study provides valuable experimental and theoretical support for enhancing oil recovery through gas flooding in high-water-cut deep reservoirs.