Enhancing CO2 Sweep Efficiency in Tight Reservoir Horizontal Wells: A Segmented Huff-and-Puff Strategy to Mitigate Heterogeneity Effects

CO2 huff-and-puff in horizontal wells is a key technique for enhancing oil production and improving recovery in tight oil reservoirs. It offers dual benefits: supplementing reservoir energy and promoting carbon sequestration, aligning with the green, low-carbon direction of energy development. However, the overall development performance of such reservoirs is often unsatisfactory. The fundamental reason lies in the strong heterogeneity of tight formations, which leads to uneven fluid intake along horizontal sections. CO2 tends to preferentially channel into high-permeability zones, severely limiting its sweep volume and resulting in the poor recovery of remaining oil in low-permeability areas. This study innovatively proposes a segmented CO2 huff-and-puff approach for horizontal wells. Using two real wells (H1 and H2), numerical simulations were conducted to compare the performance of conventional uniform injection and segmented injection. This study also examined how different segmental injection sequences (heel–middle–toe vs. toe–middle–heel) and injection rates affect CO2 huff-and-puff efficiency. Results show that, compared to uniform huff-and-puff, segmented huff-and-puff improved the oil recovery factor by an absolute value of more than 3.58% in both wells and reduced the average water cut by 4.67%. Among sequencing strategies, the toe–middle–heel injection sequence yielded the best performance, with oil production at the toe increasing by up to 53.64%. Additionally, high injection rates (6 m3/min) significantly expanded the CO2 diffusion range and enhanced its interaction with crude oil. This work proposes a new technique to expand the sweep range and improve production in long horizontal wells within highly heterogeneous tight reservoirs, contributing significantly to more uniform reservoir utilization and enhanced recovery.