Downward hydrocarbon migration predicted from numerical modeling of fluid overpressure in the Paleozoic Anticosti Basin, eastern Canada

Abstract

The Anticosti Basin is a large Paleozoic basin in eastern Canada where potential source and reservoir rocks have been identified but no economic hydrocarbon reservoirs have been found. Potential source rocks of the Upper Ordovician Macasty Formation overlie carbonates of the Middle Ordovician Mingan Formation, which are underlain by dolostones of the Lower Ordovician Romaine Formation. These carbonates have been subjected to dissolution and dolomitization and are potential hydrocarbon reservoirs. Numerical simulations of fluid-overpressure development related to sediment compaction and hydrocarbon generation were carried out to investigate whether hydrocarbons generated in the Macasty Formation could migrate downward into the underlying Mingan and Romaine formations. The modeling results indicate that, in the central part of the basin, maximum fluid overpressures developed above the Macasty Formation due to rapid sedimentation. This overpressured core dissipated gradually with time, but the overpressure pattern (i.e. maximum overpressure above source rock) was maintained during the generation of oil and gas. The downward impelling force associated with fluid-overpressure gradients in the central part of the basin was stronger than the buoyancy force for oil, whereas the buoyancy force for gas and for oil generated in the later stage of the basin is stronger than the overpressure-related force. Based on these results, it is proposed that oil generated from the Macasty Formation in the central part of the basin first moved downward into the Mingan and Romaine formations, and then migrated laterally up-dip toward the basin margin, whereas gas throughout the basin and oil generated in the northern part of the basin generally moved upward. Consequently, gas reservoirs are predicted to occur in the upper part of the basin, whereas oil reservoirs are more likely to be found in the strata below the source rocks.

Effects of hydrocarbon generation on fluid flow in the Ordos Basin and its relationship to uranium mineralization

“…(2000), Speight (2006), Pepper and Corvi (1995) and Pepper and Dodd (1995) as summarized in Chi et al (2010).…”

“…Because Basin2 does not have a module of hydrocarbon generation we used the program BsnMod in the present study. It was initially developed by Chi and Savard (1998) and Chi (2001) based on the mathematical model of Bethke (1985), with a module of hydrocarbon generation being added by Chi et al (2010). Detailed derivation and description of the governing equations (medium continuity, mass balance, energy conservation, and hydrocarbon generation) can be found in Bethke (1985) and Chi et al (2010), and are not repeated here.…”

“…A heat flux of 59.55 mW/ m 2 is supplied from the bottom based on an estimation of geothermal gradient of 3.1 C/100 m (Ren et al, 2006), and a fixed temperature of 20 C is set on the surface. The fluid properties (thermal expansion coefficient, compressibility coefficient, heat capacity, and heat conductivity), solid matrix properties (density, heat capacity, and heat conductivity), and parameters related to porosity as a function of depth and permeability as a function of porosity, are generic and are adopted from Bethke (1985) and Garven (1985), as summarized by Chi and Savard (1998) and Chi et al (2010). Hydrocarbon properties and kinematic parameters (including kerogen-to-oil conversion and oil-togas conversion) used in the modeling are based on type-II kerogens as the dominant hydrocarbon generator (Yang and Pei, 1996;He, 2003;Li et al, 2005), and are adopted from Lee and Williams Fig.…”

An overview of hydrodynamic studies of mineralization

“…Basin2 is mainly used for modeling fluid flow during the evolution history of sedimentary basins, including those related to fluid overpressures and topographic relief (e.g., Bethke, 1986;Chi et al, 2006b;Xue et al, 2010). A home-made program similar to Basin2 but with additional capacity taking into consideration the effect of hydrocarbon generation on fluid overpressure development has been developed and used in the study of various sedimentary basin-related mineralization systems (Chi and Savard, 1998;Chi, 2001;Chi et al, 2010;Xue et al, 2011). TOUGH2 and TOUGHREACT have been used in various hydrothermal systems, especially those involving multiple phases and watererock interactions (e.g., Todesco et al, 2003;Mannington et al, 2004), FEFLOW for modeling various fluid convection systems (e.g., Cui et al, 2010;Ju et al, 2011), and FLAC2D and FLAC3D mainly for modeling coupled deformation and fluid flow (Zhang et al, 2006(Zhang et al, , 2011Ju and Yang, in press).…”

Revisiting the Appalachian structural front and offshore Anticosti Basin (northern Gulf of St. Lawrence, Canada) by integrating old and new geophysical datasets

“…However, several lines of indirect evidence or interpretations provide supportive arguments for the hydrocarbon prospectivity of the offshore segment of this Paleozoic platform Chi et al, 2010;Dietrich et al, 2011).…”