Numerical Simulation on Gas Huff-n-Puff of Nanopores in Shale Oil Reservoirs

The huff-n-puff gas injection is more advantageous than water flooding in the development of shale oil reservoirs with micro-nano pores. In particular, the phase state of fluid components confined by nanopores cannot be ignored. In this paper, we built a single well mechanism model in the study area, it combined with the geological and fluid parameters of the Jimsar Sag shale oil reservoirs. In this model, we introduced a modified Peng-Robinson equation of state in nanopores. Through component numerical simulation, we studied the effects of some parameters on enhanced oil recovery by the huff-n-puff gas injection, including reservoir parameters (reservoir thickness, pore radius, matrix permeability), and hydraulic fracturing parameters (fracture number, fracture half length, fracture conductivity). And we carried out parameter sensitivity analysis. The results show that the crude oil phase diagram studied by the modified phase equation shows obvious shrinkage, which is due to the influence of nanopores. The corresponding minimum miscibility pressure of huff-n-puff gas injection is smaller, and it is easier to miscibility than huff-n-puff gas injection in conventional reservoirs. The sensitivity of recovery after huff-n-puff gas injection is analyzed by compositional numerical simulation. The results show that the sensitivity of fracture conductivity is strong. The second is reservoir thickness, matrix permeability, pore radius, fracture half length, and fracture number. The recovery is positively correlated with pore radius, matrix permeability, fracture number, and fracture half length. And it is negatively correlated with reservoir thickness.