TY - JOUR
T1 - Numerical Investigation of Fracture-Rock Matrix Ensemble Saturation Functions and their Dependence on Wettability
AU - Sedaghat, Mohammadhossein
AU - Azizmohammadi, Siroos
AU - MatthÃ¤i, Stephan K.
PY - 2017/11
Y1 - 2017/11
N2 - Quantification of multiphase flow in fractured permeable rocks is vital for hydrocarbon recovery, gas storage, and water resource management. Where fractures provide the permeability and the rock matrix provides the storage for oil and gas, fracture-matrix transfer has a decisive impact on recovery and capillary-driven transfer. However, while most modeling efforts assume a constant fracture aperture and fracture capillary pressure, in reality, fracture aperture and capillary pressure, pcf vary among fractures. Here we contrast and compare relative permeability curves obtained from constant aperture or constant capillary pressure, discrete fracture and matrix (DFM) models with more realistic ones taking variations into account. These models are constructed from line drawings of pervasively fractured layered rock mapped in meter- to kilometer-scale outcrops. Fracture aperture is obtained by mechanical modeling. Capillary pressure is computed from fracture aperture taking into account the wettability of the rock matrix.An unsteady state approach is applied to the analysis of fracture-matrix ensemble relative permeability and ultimate recovery. Imbibition simulations are performed with the Finite Element-Centered Finite Volume Method (FECFVM). Globally flow-based upscaling is used to establish ensemble relative permeability curves between capillary and viscous limits.The obtained fracture-matrix ensemble relative permeability curves show that ultimate recovery is 2-3 times higher in the water-wet than in the oil-wet case. With increasing wetting angle, counter-current-imbibition (CCI) rate decreases because the capillary pressure difference between small fractures that contribute the most to the fracture-matrix transfer area is very small. As the rock becomes oil wet, ensemble relative permeability curves steepen and matrix imbibition proceeds only over a very narrow saturation range.
AB - Quantification of multiphase flow in fractured permeable rocks is vital for hydrocarbon recovery, gas storage, and water resource management. Where fractures provide the permeability and the rock matrix provides the storage for oil and gas, fracture-matrix transfer has a decisive impact on recovery and capillary-driven transfer. However, while most modeling efforts assume a constant fracture aperture and fracture capillary pressure, in reality, fracture aperture and capillary pressure, pcf vary among fractures. Here we contrast and compare relative permeability curves obtained from constant aperture or constant capillary pressure, discrete fracture and matrix (DFM) models with more realistic ones taking variations into account. These models are constructed from line drawings of pervasively fractured layered rock mapped in meter- to kilometer-scale outcrops. Fracture aperture is obtained by mechanical modeling. Capillary pressure is computed from fracture aperture taking into account the wettability of the rock matrix.An unsteady state approach is applied to the analysis of fracture-matrix ensemble relative permeability and ultimate recovery. Imbibition simulations are performed with the Finite Element-Centered Finite Volume Method (FECFVM). Globally flow-based upscaling is used to establish ensemble relative permeability curves between capillary and viscous limits.The obtained fracture-matrix ensemble relative permeability curves show that ultimate recovery is 2-3 times higher in the water-wet than in the oil-wet case. With increasing wetting angle, counter-current-imbibition (CCI) rate decreases because the capillary pressure difference between small fractures that contribute the most to the fracture-matrix transfer area is very small. As the rock becomes oil wet, ensemble relative permeability curves steepen and matrix imbibition proceeds only over a very narrow saturation range.
KW - relative permeability
KW - wettability
KW - Naturally Fractured Reservoir
KW - upscaling
KW - viscous-capillary coupling
KW - fracture-matrix transfer
U2 - 10.1016/j.petrol.2017.10.013
DO - 10.1016/j.petrol.2017.10.013
M3 - Article
VL - 159
SP - 869
EP - 888
JO - Journal of Petroleum Science and Engineering
JF - Journal of Petroleum Science and Engineering
ER -