Permeability Variation and Its Impact on Oil Recovery from Unconsolidated Sand Heavy-Oil Reservoirs during Steamflooding Process

Abstract

Summary In the steam-injection processing of unconsolidated heavy-oil reservoirs, the pore space may change because of the overburden pressure increase and wormhole generation. Meanwhile, injected high-temperature steam can result in mineral dissolution and alteration and consequent diameter change of sand particles and pore space. To obtain a better and more thorough understanding of permeability variation characteristics during the steamflooding process, a series of experiments with sand-packed tubes was designed and conducted. On the basis of quantified experimental data, a numerical model was built by taking various permeability variation mechanisms into consideration. Reservoir simulations were consequently carried out to study the permeability distribution variation on the field scale and its impact on oil recovery. The results showed that with increasing overburden pressure, the permeability and porosity of the sand tube were both decreased. Permeability decrease ranged from 35 to 54%, and porosity decrease was approximately 5%. The partial permeability was increased by more than four times when a wormhole was generated at the outlet. The permeability and porosity of sand-packed tubes were increased because of mineral dissolution in the steamflooding process. Particle migration and mineral dissolution resulted in permeability variation and formation of a high-permeability region in the reservoir, which enhanced the heterogeneity of the reservoir. The high-permeability region mainly formed at the upper layer of the reservoir in the vertical direction and on the line between steam injection and oil production wells in the horizontal direction. Permeability variation exacerbated the steam channeling, which resulted in more remaining oil and a lower oil recovery rate of the reservoir. When permeability variation was considered in a numerical simulation, the cumulative oil production for 4 years was decreased by approximately 7000 m3, and the oil recovery rate was decreased by 4.3%.