CO<sub>2</sub> Huff and Puff Rates Optimization of Multi-Stage Fracturing Horizontal Wells Based on Proximal Policy Optimization Algorithm

CO2吞吐是致密油藏多段压裂水平井衰竭弹性开发后续提高采收率重要接替手段，吞吐注采优化具有成本低、易实现和效果明显的优点。目前吞吐注采优化方法存在不足，未充分考虑不同吞吐轮次和吞闷吐不同阶段间的干扰，本文建立了基于近端策略优化算法多段压裂水平井CO2吞吐注采优化新方法，以净现值为优化目标，吞吐注采参数为优化变量，新方法实现了不同吞吐轮次变注采速度和变注采时长的动态注采优化，充分考虑了吞吐各阶段之间的干扰。实例Y区块CO2吞吐注采优化结果表明：最优方案通过降低返排速度延长返排时间，充分提高返排阶段动用程度，提高了注入CO2吞吐效率，减少吞吐轮次大幅降低注气成本，能够获得最优经济效益，为现场实际注采优化提供指导。CO2 huff and puff is an important replacement method for the subsequent improvement of oil recovery in 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 is not fully considered. A novel CO2 huff and puff injection and production rates optimization method for multi-stage fractured horizontal wells based on the proximal policy optimization algorithm has been proposed. With the net present value as the optimization goal and huff and puff injection and production rates parameters as the optimization variables, the new method realizes 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 considers the interference between various stages. The injection and production rates optimization results of Y block CO2 huff and puff indicate that the optimal project extends the backflow time by reducing the backflow speed, 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 can 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.