A simple and reproducible analog experiment was used to simulate fracture formation in a low-permeability elastic solid during internal fluid/gas production, with the objective of developing a better understanding of the mechanisms that control the dynamics of fracturing, fracture opening and closing, and fluid transport. In the experiment, nucleation, propagation, and coalescence of fractures within an elastic gelatin matrix, confined in a Hele-Shaw cell, occurred due to CO_{2} production via fermentation of sugar, and it was monitored by optical means. We first quantified how a fracture network develops, and then how intermittent fluid transport is controlled by the dynamics of opening and closing of fractures. The gas escape dynamics exhibited three characteristic behaviors: (1) Quasiperiodic release of gas with a characteristic frequency that depends on the gas production rate but not on the system size. (2) A 1/f power spectrum for the fluctuations in the total open fracture area over an intermediate range of frequencies (f), which we attribute to collective effects caused by interaction between fractures in the drainage network. (3) A 1/f^{2} power spectrum was observed at high frequencies, which can be explained by the characteristic behavior of single fractures.

Numerous geological observations evidence that inelastic deformation occurs during sills and laccoliths emplacement. However, most models of sill and laccolith emplacement neglect inelastic processes by assuming purely elastic deformation of the host rock. This assumption has never been tested so that the role of inelastic deformation on the growth dynamics of magma intrusions remains poorly understood. In this paper, we introduce the first analytical model of shallow sill and laccolith emplacement that accounts for elastoplastic deformation of the host rock. It considers the intrusion's overburden as a thin elastic bending plate attached to an elastic‐perfectly plastic foundation. We find that, for geologically realistic values of the model parameters, the horizontal extent of the plastic zone lp is much smaller than the radius of the intrusion a. By modeling the quasi‐static growth of a sill, we find that the ratio lp/a decreases during propagation, as 1/a4ΔP, with ΔP the magma overpressure. The model also shows that the extent of the plastic zone decreases with the intrusion's depth, while it increases if the host rock is weaker. Comparison between our elastoplastic model and existing purely elastic models shows that plasticity can have a significant effect on intrusion propagation dynamics, with, e.g., up to a doubling of the overpressure necessary for the sill to grow. Our results suggest that plasticity effects might be small for large sills but conversely that they might be substantial for early sill propagation.

Experiments in which CO2 gas was generated by the yeast fermentation of sugar in an elastic layer of gelatine gel confined between two glass plates are described and analyzed theoretically. The CO2 gas pressure causes the gel layer to fracture. The gas produced is drained on short length scales by diffusion and on long length scales by flow in a fracture network, which has topological properties that are intermediate between river networks and hierarchical-fracture networks. A simple model for the experimental system with two parameters that characterize the disorder and the intermediate (river-fracture) topology of the network was developed and the results of the model were compared with the experimental results.

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h i g h l i g h t s• A novel discrete element model (DEM) for fracturing in elastic solids is proposed. • By splitting nodes, contrary to breaking bonds, lattice artefacts are reduced.• Fracture volumes and surfaces are naturally represented for all fracture apertures. • The fracture representation simplifies coupling of fracturing to fluid transport. • Applications include fracturing driven by fluid generation in geological systems. a b s t r a c tA new discrete element model (DEM) has been developed for the purpose of simulating dynamic fracturing driven by the internal generation of fluids in low permeability elastic solid bodies. The elastic material is represented by a network of nodes connected by springs, and fracture nucleation and propagation is implemented by splitting nodes and reconnecting the spring network. This produces realistic fracture shapes, and reduces lattice artefacts compared with DEM models in which fracturing is implemented by breaking/removal of springs. Fracture volumes and surfaces are explicitly represented in terms of the voids in the reconnected spring network, simplifying the coupling between mechanical deformation and fluid pressure in the fractures, and facilitating the modelling of fluid transport. The model is illustrated by applying it to fracturing driven by internal fluid generation in an impermeable quasi two-dimensional system. This is relevant for many geological processes, including primary migration of oil and gas in low-permeability source rock. The model may also be adapted to hydraulic fracturing processes, which are of industrial interest in connection with unconventional oil and gas production.