Research on Water Alternating Gas (WAG) Flooding Dynamic Adjustment of Water-Gas Ratio and Slug Sizes Method in Low Permeability Reservoir

CO2 flooding is being widely practiced in low permeability reservoirs for Enhanced Oil Recovery, which is of profound significance in reducing greenhouse gas emissions considerably. Water Alternating Gas (WAG) flooding is the primary method to restrict gas channeling. Still, the WAG flooding with the constant water-gas ratio and slug size of water cannot match the variety of interwell permeability. A method is developed to design dynamically varying water-gas ratios and slug sizes in WAG flooding, which is expected to improve the effectiveness of CO2 drive field applications significantly. Aiming at these problems, the phase behaviors of light oil–CO2 systems were firstly tested, and two types of CO2 injection experiments-constant and dynamic WAG flooding -were conducted in core plugs. Second, based on fluid phase fit-ting, history-matching studies on experimental results were completed. Third, a WAG scheme with varying water-gas ratios and slug sizes were simulated using the numerical model. A set of dynamic WAG drive design templates with different interwell permeability was developed using recovery and CO2 utilization as evaluation metrics. Finally, the vibrant WAG drive scheme is prepared and applied in the field block. The results of laboratory experiments show that compared with constant WAG drives. Dynamic WAG drives significantly reduce the gas-oil ratio in mid-late production and increase the ultimate recovery by five percentage points. The main control factor of the water-gas ratio and segment plug size of the dynamic WAG drive is internal gas saturation. The key parameters are the initial water-gas ratio and the adjustment range of the water-gas ratio. The larger the permeability differential, the more suitable dynamic WAG drive is. Timely adjusting the water-gas ratio and slug size can effectively control fluid mobility within the reservoir. This paper proposes analyzes the optimal water-gas ratio and slug size for dynamic WAG drive under different permeability differentials. Using laboratory experiments and numerical modeling, which can effectively improve CO2 development and facilitate the long-term efficient operation of CO2 drive projects.