Gum and asphaltene precipitation pattern in CO2 miscible flooding:A case study of Donghe 6 reservoir
During the CO2 injection process,it's essential to understand whether miscibility significantly impacts oil displacement efficiency and how asphaltene precipitation behaves in oil layers under CO2 injection.This paper outlines the design of a high-temperature and high-pressure mixing and precipitation experimental apparatus and details experimental studies on the precipitation pattern of asphaltenes and resins during CO2 miscible flooding.The research simulates the injection and production processes of the Donghe 6 reservoir,assessing the miscibility of the injected gas with the formation fluid and monitoring the precipitation pattern in asphaltene and resin content within the reservoir.The experimental results indicate that the CO2 flooding mechanism in the Donghe 6 reservoir is primarily of the contact miscible type.The relative precipitation of asphaltenes initially surges and then tapers off with increasing amounts of injected CO2,whereas the precipitation of resins first diminishes and then rises.After the CO2 injection,employing depressurization and depletion techniques preferentially extracts saturated hydrocarbons,resulting in a marked increase in asphaltene concentration in the reservoir's crude oil.To enhance displacement efficiency and mitigate resin and asphaltene precipitation during extraction,maintaining a minimum miscibility pressure of 45.4 MPa or higher for CO2 flooding in the Donghe 6 reservoir is recommended,which also contributes to an elevated crude oil recovery rate.The research results provide a method for measuring miscibility pressure and asphaltene precipitation in reservoirs undergoing CO2 injection,thereby supporting the development strategies for such reservoirs.
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