Abstract
A model is constructed for the underground natural gas storages reconstructed from the depleted fractured oil reservoirs, in which the diffusion of molecules and the deformation of medium are taken into consideration. The model is solved by finite difference method and applied to the reconstruction from a depleted bottom water fractured oil reservoir into gas storages. The effect of molecular diffusion and medium deformation on the dynamic of the storage is analyzed and the optimal scheme for the reconstruction is selected from 12 given schemes. After the numerical simulation, we conclude that the diffusion of molecules and the deformation of medium have significant influence over the dynamic performances of the gas storages altered from the fractured oil reservoirs.
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Abbreviations
- Φ lf :
-
The potential of the fluid in the fractures,Φ = pf − γlf ⋅ DD, l = o, g, w, DDstands for the depth.
- Φ lm :
-
The potential of the fluid in the bedrocks, Φ = pm − γlm ⋅ DD, l = o, g, w.
- p f :
-
Fluid pressure in the fractures, MPa.
- p m :
-
Fluid pressure in the bedrocks, MPa.
- γ lf :
-
Gravity of the fluid in different phases in the fractures,γlf = ρlfg, MPa.
- γ lm :
-
Gravity of the fluid in different phases in the bedrocks,γlm = ρlmg, MPa.
- ρ l :
-
Density of free gas in the factures, kg/m3.
- ρ m :
-
Density of free gas in the bedrocks, kg/m3.
- K f :
-
Absolute permeability of the fractures, μm2.
- K m :
-
Absolute permeability of the bedrocks, μm2.
- K fo :
-
Original absolute permeability of the fractures, μm2.
- K mo :
-
Original absolute permeability of the bedrocks, μm2.
- K rlf :
-
Relative permeability of different phases in the factures.
- K rlm :
-
Relative permeability of different phases in the bedrocks.
- μ lf :
-
Viscosity of different phases in the factures, mPa.
- μ lm :
-
Viscosity of different phases in the bedrocks, mPa.
- B lf :
-
Formation volume factor of different phases in the factures, m3/m3 .
- B lm :
-
Formation volume factor of different phases in the bedrocks, m3/m3.
- R sf :
-
Dissolved gas/oil ratio in the fractures, m3/m3.
- R sm :
-
Dissolved gas/oil ratio in the bedrocks, m3/m3.
- ϕ f :
-
Porosity of the fractures.
- ϕ m :
-
Porosity of the bedrocks.
- ϕ fo :
-
Original porosity of the fractures.
- ϕ mo :
-
Original porosity of the bedrocks.
- S lf :
-
Saturation of different phases in the fractures.
- S lm :
-
Saturation of different phases in the bedrocks.
- q o :
-
The volume of the oil recovered from the unit reservoir volume in unit time under standard conditions, i.e., volume of the stock tank oil.
- q g :
-
The volume of the gas injected or produced from the unit reservoir volume in unit time under standard conditions, the value is positive when injecting, negative when producing. Here, qg = qfg + qoRs, which means the gas production is composed of the free gas and the dissolved gas.
- q m :
-
The volume of the water injected or produced from the unit reservoir volume in unit time under standard conditions, the value is positive when injecting, negative when producing.
- L x,L y,L z :
-
the measure of the bedrocks in x, y, z directions, m.
- J I :
-
The volume of component I passing through the area A in unit time, which comes from the concentration difference in a binary fluid system composed of I andJ, m3/m2.
- C I :
-
The mass concentration of component I.
- D IJ :
-
Diffusion coefficient in J of component I.
- D goe :
-
Effective diffusion coefficient of gas in oil, m2/d.
- R sf∗ :
-
Dissolved gas/oil ratio corresponding to the pressure in fractures, m3/m3.
- S c :
-
Contact saturation between the fractures and the rocks.
- ρ gsurface :
-
Density of the gas under standard conditions, kg/m3.
- ρ osurface :
-
Density of the oil under standard conditions, kg/m3.
- MW g :
-
Molecular weight of gas.
- MW o :
-
Molecular weight of oil.
- Subscript u :
-
Stands for the arrangement of the values, that is, if the flow is from the rock to the fractures, we take the parameters of the rocks, and vice versa.
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Acknowledgments
This work was supported by the special fund of China’s central government for the development of local colleges and universities – the project of national first-level discipline in Oil and Gas Engineering.
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This article is part of the Topical Collection on Geological Modeling and Geospatial Data Analysis
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Fu, Y. Reconstructing depleted fractured oil reservoirs into underground natural gas storages with the consideration of the effect of molecular diffusion and medium deformation on the dynamic performances. Arab J Geosci 13, 122 (2020). https://doi.org/10.1007/s12517-020-5053-1
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DOI: https://doi.org/10.1007/s12517-020-5053-1