Multiphase flow modeling of a crude‐oil spill site with a bimodal permeability distribution

Abstract

Abstract. Fluid saturation, particle-size distribution, and porosity measurements were obtained from 269 core samples collected from six boreholes along a 90-m transect at a subregion of a crude-oil spill site, the north pool, near Bemidji, Minnesota. The oil saturation data, collected 11 years after the spill, showed an irregularly shaped oil body that appeared to be affected by sediment spatial variability. The particle-size distribution data were used to estimate the permeability (k) and retention curves for each sample. An additional 344 k estimates were obtained from samples previously collected at the north pool. The 613 k estimates were distributed bimodal lognormally with the two population distributions corresponding to the two predominant lithologies: a coarse glacial outwash deposit and fine-grained interbedded lenses. A two-step geostatistical approach was used to generate a conditioned realization of k representing the bimodal heterogeneity. A cross-sectional multiphase flow model was used to simulate the flow of oil and water in the presence of air along the north pool transect for an l 1-year period. The inclusion of a representation of the bimodal aquifer heterogeneity was crucial for reproduction of general features of the observed oil body. If the bimodal heterogeneity was characterized, hysteresis did not have to be incorporated into the model because a hysteretic effect was produced by the sediment spatial variability. By revising the relative permeability functional relation, an improved reproduction of the observed oil saturation distribution was achieved. The inclusion of water table fluctuations in the model did not significantly affect the simulated oil saturation distribution.

Inverse modeling of BTEX dissolution and biodegradation at the Bemidji, MN crude-oil spill site

“…The estimated hydraulic conductivity was 7.02 Â 10 À 5 m/s, about an order of magnitude higher than the geometric mean conductivity of 5.6 Â 10 À 6 m/s obtained from particle-size-distribution estimates (Dillard et al, 1997). This suggests that the plume concentration distribution is a reflection of flow in the high conductivity channels within the heterogeneous porous medium, and/or that conductivities estimated from particle size distributions may underestimate large-scale aquifer hydraulic conductivity.…”

“…An average value of n of 3.98 was estimated using observed particle-size distributions and the methods of Essaid et al (1993) and Dillard et al (1997). Water relative permeabilities ranged from 0.02 in the highest oil saturation core of the oil body to close to 1.0 in the low oil saturation edges of the oil body.…”

Reactive transport modeling of geochemical controls on secondary water quality impacts at a crude oil spill site near Bemidji, MN

“…Heterogeneous permeability values based on geostatistical interpolation of grain size data are available from Dillard et al [1997] down to an elevation of 421 m and over a 120 m horizontal interval of our domain. Permeability values were replicated to cover our computational domain and converted to saturated hydraulic conductivity.…”

“…The domain was discretized into 4.3 m (horizontal) by 0.47 m (vertical) grid cells allowing efficient computation of multicomponent kinetic simulations. The homogeneous porosity is assigned to be 0.38, which is the mean value determined for the north pool area [Dillard et al, 1997]. Longitudinal and transverse dispersivity were set to 1 and 0.04 m, respectively.…”

Computational Flow Dynamic Simulation of Micro Flow Field Characteristics Drainage Device Used in the Process of Oil-Water Separation

“…And unstructured grids are used too; the EquiSize Skew and EquiAngle Skew in detection are 0.52 and 0.43, respectively. It is indicated that the grids generated are simple, of high quality, and suitable [12].…”