Rates Optimization of CO₂ Huff and Puff in Multi-stage Fracturing Horizontal Wells Based on Proximal Policy Optimization Algorithm

CO₂ huff and puff is an important replacement method for the subsequent improvement of oil recovery after the elastic development of multi-stage fracturing horizontal wells in tight reservoirs. The rates optimization of huff and puff injection and production has the advantages of low cost, easy implementation, and obvious effects. At present, the rates optimization method of huff and puff injection and production is insufficient, and the interference between different huff and puff cycles and different stages were not fully considered. This paper established a CO₂ huff and puff injection and production rates optimization method for multi-stage fractured horizontal wells based on the proximal policy optimization algorithm. We took the net present value as the optimization objective and huff and puff injection and production rates parameters as the optimization variables. The new method realized dynamic injection and production rates optimization with different huff and puff cycles and variable injection and production speed and variable injection and production duration, and considered the interference between various stages. The rates optimization results of CO₂ huff and puff in multi-stage fracturing horizontal wells indicate that the optimal project extends the backflow time by reducing the backflow rate, fully improving the utilization degree of the backflow stage. At the same time, improving the efficiency of CO₂ injection and reducing the number of cycles significantly reduce gas injection costs, achieving optimal economic benefits and providing guidance for on-site actual CO₂ huff and puff injection and production rates optimization.