关键词: 超低渗油藏, 弹性开发, 减氧空气, 纳米驱油剂, 复合吞吐, 驱替, 现场试验

Abstract:

CO₂ huff-and-puff is considered as the most promising and effective enhanced oil recovery technique for depletion-drive development of ultra-low permeability reservoirs. Nonetheless, due to the limitations such as injection modes, gas costs, and safety/environmental concerns, it is urgent to find new huff-and-puff strategies for horizontal well depletion-drive development of these reservoirs. The alternating injection of nano-sized oil displacement agent and oxygen-reduced air not only leverages the oil displacement mechanisms of nanoparticles and gas, but also generates a distinctive synergistic effect. In this study, laboratory experiments were conducted to evaluate the oil displacement mechanisms of oxygen-reduced air and nano-sized oil displacement agent, and molecular simulation was employed at the microscopic level to investigate the synergistic effect of the combined huff-and-puff with oxygen-reduced air and nano-sized oil displacement agent. Then, reservoir engineering methods and numerical simulations were adopted to optimize key parameters including huff-and-puff timing, injection volume, injection rate, and soaking time. Finally, field tests were performed at horizontal wells C-H1 and D-H2 in the Z area. The tests revealed a cumulative incremental oil production of 4,526.7 tons and an input-output ratio exceeding 1∶2.5, demonstrating satisfactory huff-and-puff and displacement performance. The proposed combined huff-and-puff with oxygen-reduced air and nano-sized oil displacement agent provides a practical guidance for late-stage energy replenishment in horizontal well depletion-drive development of ultra-low permeability reservoirs.

Key words: ultra-low permeability reservoir, depletion-drive development, oxygen-reduced air, nano-sized oil displacement agent, combined huff-and-puff, displacement, field test