Study On The Mechanism And Effect Evaluation Of CO₂ Gas Flooding Development

Low-permeability reservoirs account for more than half of the total oil and gas reserves,and as the demand for oil and gas continues to increase,the focus of domestic oil and gas extraction is gradually shifting to low-permeability reservoirs.Taking the low-permeability reservoirs in the YY1 block of Daqing Oilfield as an example,this study investigated the CO₂displacement mechanism and conducted field experiments to obtain significant results that provide guidance for gas-driven development of low-permeability reservoirs.Firstly,starting from the geological overview of the block and analyzing the development key points,the basic conditions for conducting CO₂flooding field tests in the FY oil formation of the YY1 block were established.Secondly,various laboratory experiments were conducted on underground oil samples and core samples in the research area to gain insights into the relevant laws of CO₂displacement development.By comparing and analyzing the high-pressure physical properties of underground oil samples,it was found that CO₂extraction reduced the interfacial tension,lowered the phase mixing pressure,changed the crude oil density and viscosity,and increased the oil recovery.Interface tension tests using the pendant drop method were conducted to monitor the interfacial tension relationship between CO₂and reservoir crude oil,indicating a gradual decrease in interfacial tension under the same pressure.Oil samples were collected during different displacement stages of the experimental wells in the study area to study the variation patterns of crude oil components and propose key points for experimental design.Thirdly,the injection and production processes used during CO₂displacement in the research area were explored.By analyzing the corrosion patterns,protection strategies were proposed to address corrosion issues during CO₂flooding,as well as control measures for freeze plugging and gas leakage during the displacement process.Fourthly,based on the design principles of the gas injection plan in the research area,the displacement mechanisms of different CO₂injection methods were summarized,and the inter-well displacement conditions in the research area were analyzed and classified.Typical cases,such as wells with marginal structure response,gas-water alternate displacement response,and the formation of high-permeability channels in the reservoir,were presented based on the gas-driven development data in the research area.Additionally,a summary analysis of gas channeling issues during CO2 displacement in the research area was provided,identifying conditions such as high structural positions,high-permeability zones,proximity to faults,and micro-fractures that are prone to gas channeling,along with corresponding gas channeling control strategies.This study systematically investigated the economically effective gas injection and development strategies for CO₂flooding in low-permeability reservoirs,providing an effective approach to further enhance the development level of such reservoirs.