Kilometer-scale upward migration of hydrocarbons in geopressured sediments by buoyancy-driven propagation of methane-filled fractures

Nunn, Jeffrey A.; Meulbroek, Peter

doi:10.1306/61eedbd4-173e-11d7-8645000102c1865d

Cited by 17 publications

(5 citation statements)

References 32 publications

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“…Fractures are very efficient paths for the migration of hydrocarbons in reservoirs (Mandl and Harkness, 1987;Aydin, 2000;Nunn and Meulbroek, 2002). A rock body with fractures that have significant effect on its fluid transport is a "fractured reservoir" (Nelson, 1985(Nelson, , 2001Aguilera, 1995).…”

Section: Reservoir Fractures and Fluid Transport Models Of Reservoir mentioning

confidence: 99%

Effects of mechanical layering on hydrofracture emplacement and fluid transport in reservoirs

2013

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Fractures generated by internal fluid pressure, for example, dykes, mineral veins, many joints and man-made hydraulic fractures, are referred to as hydrofractures. Together with shear fractures, they contribute significantly to the permeability of fluid reservoirs such as those of petroleum, geothermal water, and groundwater. Analytical and numerical models show that-in homogeneous host rocks-any significant overpressure in hydrofractures theoretically generates very high crack tip tensile stresses. Consequently, overpressured hydrofractures should propagate and help to form interconnected fracture systems that would then contribute to the permeability of fluid reservoirs. Field observations, however, show that in heterogeneous and anisotropic, e.g., layered, rocks many hydrofractures become arrested or offset at layer contacts and do not form vertically interconnected networks. The most important factors that contribute to hydrofracture arrest are discontinuities (including contacts), stiffness changes between layers, and stress barriers, where the local stress field is unfavorable to hydrofracture propagation. A necessary condition for a hydrofracture to propagate to the surface is that the stress field along its potential path is everywhere favorable to extension-fracture formation so that the probability of hydrofracture arrest is minimized. Mechanical layering and the resulting heterogeneous stress field largely control whether evolving hydrofractures become confined to single layers (stratabound fractures) or not (non-stratabound fractures) and, therefore, if a vertically interconnected fracture system forms. Non-stratabound hydrofractures may propagate through many layers and generate interconnected fracture systems. Such systems commonly reach the percolation threshold and largely control the overall permeability of the fluid reservoirs within which they develop.

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Section: Reservoir Fractures and Fluid Transport Models Of Reservoir mentioning

confidence: 99%

Effects of mechanical layering on hydrofracture emplacement and fluid transport in reservoirs

2013

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“…Hydrofracture propagation facilitates the development of permeable pathways, which significantly enhance flow rates. This behavior impacts on fluid migration in geological systems in a number of ways for instance reservoir quality [13][14][15], episodic expulsion and entrapment of ore-forming fluids [16] as well as the activation of geothermal circulation/venting with the induction of pressure and temperature anomalies [11,17]. Miller and Nur [18] describe the "toggle switch" behavior of hydrofractures leading to sudden permeability enhancement or reduction associated with a switch from high to low pressure and backwards.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of hydrofracturing and permeability evolution in layered reservoirs

Ghani¹,

Koehn

Toussaint

et al. 2015

Front. Phys.

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International audienceA coupled hydro-mechanical model is presented to model fluid driven fracturing in layered porous rocks. In the model the solid elastic continuum is described by a discrete element approach coupled with a fluid continuum grid that is used to solve Darcy based pressure diffusion. The model assumes poro-elasto-plastic effects and yields real time dynamic aspects of the fracturing and effective stress evolution under the influence of excess fluid pressure gradients. We show that the formation and propagation of hydrofractures are sensitive to mechanical and tectonic conditions of the system. In cases where elevated fluid pressure is the sole driving agent in a stable tectonic system, sealing layers induce permutations between the principal directions of the local stress tensor, which regulate the growth of vertical fractures and may result in irregular pattern formation or sub-horizontal failure below the seal. Stiffer layers tend to concentrate differential stresses and lead to vertical fracture growth, whereas the layer-contact tends to fracture if the strength of the neighboring rock is comparably high. If the system has remained under extension for a longer time period, the developed hydrofractures propagate by linking up confined tensile fractures in competent layers. This leads to the growth of large-scale normal faults in the layered systems, so that subsequently the effective permeability is highly variable over time and the faults drain the system. The simulation results are shown to be consistent with some of the field observations carried out in the Oman Mountains, where abnormal fluid pressure is reported to be a significant factor in the development of several generations of local and regional fracture and fault sets

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“…The crack will extend downward along the interface as hydrate continuously dissociates until the stress intensity factor at the upper crack tip reaches the sediment fracture toughness. At this moment, the crack begins to propagate upward unstably driven by the buoyancy force of water and gas much like the case of buoyancy-driven propagation of a crack filled by a single-phase fluid [Nunn and Meulbroek, 2002;Jin and Johnson, 2008]. We focus on the stability of the crack during hydrate dissociation.…”

Section: Fracture Mechanics Modelmentioning

confidence: 99%

“…Hence, our model is applicable to marine mud but not sand sediment that behaves more like a rheological material or fluid during bubble growth [Boudreau et al, 2005]. Moreover, almost all gas hydrate-filled fractures in nature are observed in marine muds [Cook et al, 2014], so using linear elastic fracture mechanics is a reasonable assumption.…”

Section: 1002/2015gl066060mentioning

confidence: 99%

Crack extension induced by dissociation of fracture-hosted methane gas hydrate

Jin

Johnson

Cook

2015

Geophys. Res. Lett.

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We investigate extension of a vertical crack filled by water and methane gas induced by dissociation of methane hydrate in low‐permeability muddy sediment. We model the sediment as an impermeable elastic medium and consider a thin sheet configuration of hydrate that initially occupies a vertical fracture. The crack development and the amount of dissociated hydrate are determined using sediment elasticity, fracture mechanics, kinetics of hydrate dissociation, and the equation of state for methane gas. Young's modulus and fracture toughness of the sediment greatly affect the mass of hydrate required for crack extension; lower Young's modulus and higher fracture toughness require greater hydrate mass to induce unstable, buoyancy‐driven crack propagation. Our numerical results suggest that propagation of gas/water‐filled cracks occurs quickly in a matter of seconds and may be an important mechanism for methane transport in low‐permeability sediments when hydrate‐filled fractures are under conditions of gas hydrate dissociation.

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Kilometer-scale upward migration of hydrocarbons in geopressured sediments by buoyancy-driven propagation of methane-filled fractures

Cited by 17 publications

References 32 publications

Effects of mechanical layering on hydrofracture emplacement and fluid transport in reservoirs

Effects of mechanical layering on hydrofracture emplacement and fluid transport in reservoirs

Dynamics of hydrofracturing and permeability evolution in layered reservoirs

Crack extension induced by dissociation of fracture-hosted methane gas hydrate

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