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 are 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 corresponding concept model was built and numerical experiments were carried out to quantify the gas sweeping efficiency of physical simulation experiments.

The simulation experiments show that the sweeping effect decreases with the increase in the distance from the aquifer when CO₂ is injected from one horizontal well. Furthermore, when two optimized horizontal wells huff the same amount of CO₂, gas sweeping efficiency becomes more significant. For a higher drop in overall water cut (57.7% to 52.10%), more oil recovery increase (18.62% to 16.93%), more efficient gas utility ratio (1.27g/g to 1.18g/g) and a lager gas sweeping volume (33.56% to 24.66%) are observed in the simulation experiments. It is concluded that CO₂ sweeping efficiency could be improved within the same gas volume during the CO₂ huff and puff by multiple horizontal wells.

Both physical and numerical conceptional model of fault-block reservoir is devised. And the improved CO₂ sweeping efficiency by multiple horizontal wells CO₂ huff and puff offers theoretical reference for field application.