Laboratory Investigation of Sweeping Efficiency by Multiple Horizontal Wells CO₂ Huff and Puff in Fault-Block Reservoirs with an Edge Aquifer

Water coning constrains the effective development of fault-block reservoirs by horizontal wells. CO₂ huff and puff from field cases prove to be effective in water control and oil stimulation. However, gas sweeping efficiency varies due to geological complexity and unclear oil-water interaction. Therefore, CO₂ huff and puff by multiple horizon wells needs to be optimized for a better sweep efficiency. A physical model similar to a fault-block reservoir with edge aquifer and reservoir dip was devised. Three horizontal wells were deployed according to the distance from the aquifer. CO₂ huff and puff experiments were conducted to investigate sweeping results of the selection of injecting well, combination of injection wells within the model. In addition, one numerical model corresponding to the physical one was built and numerical experiments were carried out to quantify the gas sweeping efficiency. The simulation results show that the sweeping effect decreased with the increase in the distance from the aquifer as CO₂ was injected from one horizontal well. Furthermore, when two optimized horizontal wells huffed the similar amount of CO₂, gas sweeping efficiency improved: A higher drop in water cut (34.26% to 33.53%), more oil recovery increase (15.38% to 17.59%), and a lager gas sweeping volume (33.56% to 24.66%) were obtained in the simulation experiments. It was concluded that CO₂ sweeping efficiency could be further improved within the same gas volume by horizontal wells optimization. Both physical and numerical conceptional model of fault-block reservoir was devised. And the improved CO₂ sweeping efficiency by multiple horizontal wells CO₂ huff and puff offers theoretical reference for field application.