Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session A1: Porous Media Flows: Fracturing |
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Chair: Arshad Kudrolli, Clark University Room: Auditorium |
Sunday, November 22, 2015 8:00AM - 8:13AM |
A1.00001: Channelization and avalanche dynamics of sediments in a fracture driven by fluid flow Arshad Kudrolli, Xavier Clotet We investigate the evolution of porosity in a sediment bed induced by fluid flow which is important to understanding the structure of aquifers, dam-breaks, and extraction and sequestration of hydrocarbons in the subsurface. We demonstrate that a porous medium composed of granular matter in a thin model fracture becomes heterogeneous and develops channels due to growth of fluid flow coupled with increase in porosity. Erosion is observed to progress through stick-slip events with larger avalanches following longer wait times. Self-clogging is also observed where eroded particles collectively redeposit and jam within the channels, which are then stable to higher fluid fluxes. We model the spatial distribution of the flow within the medium using measured maps of the porosity and Darcy's law, and show that the channels grow on average at points where the perpendicular component of the fluid flux at the interface is the greatest. Adding a stochastic component to the model for the local erosion and deposition thresholds, we find the statistical features of the spatial development of heterogeneity to be consistent with those observed in the experiments. [Preview Abstract] |
(Author Not Attending)
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A1.00002: Impact of ductility on hydraulic fracturing in shales Lucy Auton, Chris MacMinn Hydraulic fracturing is a method for extracting natural gas and oil from low-permeability rocks such as shale via the injection of fluid at high pressure. This creates fractures in the rock, providing hydraulic access deeper into the reservoir and enabling gas to be collected from a larger region of the rock. Fracture is the tensile failure of a brittle material upon reaching a threshold tensile stress, but some shales have a high clay content and may yield plastically before fracturing. Plastic deformation is the shear failure of a ductile material, during which stress relaxes through irreversible rearrangements of the particles of the material. Here, we investigate the impact of the ductility of shales on hydraulic fracturing. We consider a simple, axisymmetric model for radially outward fluid injection from a wellbore into a ductile porous rock. We solve the model semi-analytically at steady state, and numerically in general. We find that plastic deformation greatly reduces the maximum tensile stress, and that this maximum stress does not always occur at the wellbore. These results imply that hydraulic fracturing may fail in ductile rocks, or that the required injection rate for fracking may be much larger than the rate predicted from purely elastic models. [Preview Abstract] |
Sunday, November 22, 2015 8:26AM - 8:39AM |
A1.00003: Fluid-driven fractures in brittle hydrogels Niall O'Keeffe, Paul Linden We study the physical mechanisms of fluid-driven fracture in low permeability reservoirs. This is done through the use of laboratory scale experiments on brittle heavily cross-linked hydrogels. These hydrogels have been shown to fracture similarly to ``standard'' brittle materials, such as PMMA and glass, which have been widely used to model geological mechanics. Crucially, the hydrogels are transparent, and permit fracturing at lower pressures and slower timescales. Their rheological properties can also be altered easily by varying the overall percentage of monomers and cross-linking molecules. Fracture dynamics are usually extremely hard to capture due to the fact that crack tips can approach material sound speeds. The sound speeds in these brittle hydrogels are 2-3 orders of magnitude less than in standard brittle materials. This allows us observe the complex fracture dynamics through the use of high speed camera techniques. [Preview Abstract] |
Sunday, November 22, 2015 8:39AM - 8:52AM |
A1.00004: High Speed Strain Measurements Surrounding Hydraulic Fracture in Brittle Hydrogel Will Steinhardt, Shmuel Rubinstein Hydraulic fractures of oil and gas shales occur miles underground, below complex, layered rocks, making measurements of their dynamics, extent, or structure difficult to impossible. Rocks are heterogeneous at a wide range of length scales, and investigating how these non-uniformities affect the propagation and extent of fractures is vital to improving both the safety and efficiency of hydraulic fracturing operations. To study these effects we have developed a model system using brittle, heavily cross-linked hydrogels that we can fracture with fluids and observe with a fast camera. By embedding tracer particles within the gel and using laser sheet microscopy, we obtain three dimensional stress and strain maps of the zone surrounding a hydraulic fracture tip. Gels can also be set in layers or interfaces with tunable strengths or with designed heterogeneities, allowing us to understand the fundamental science of hydraulic fractures and investigate the dynamics of controllably complex materials. [Preview Abstract] |
Sunday, November 22, 2015 8:52AM - 9:05AM |
A1.00005: Visualizing 3D fracture morphology in granular media Marie-Julie Dalbe, Ruben Juanes Multiphase flow in porous media plays a fundamental role in many natural and engineered subsurface processes. The interplay between fluid flow, medium deformation and fracture is essential in geoscience problems as disparate as fracking for unconventional hydrocarbon production, conduit formation and methane venting from lake and ocean sediments, and desiccation cracks in soil. Recent work has pointed to the importance of capillary forces in some relevant regimes of fracturing of granular materials (Sandnes et al., Nat. Comm. 2011), leading to the term hydro-capillary fracturing (Holtzman et al., PRL 2012). Most of these experimental and computational investigations have focused, however, on 2D or quasi-2D systems. Here, we develop an experimental set-up that allows us to observe two-phase flow in a 3D granular bed, and control the level of confining stress. We use an index matching technique to directly visualize the injection of a liquid in a granular media saturated with another, immiscible liquid. We determine the key dimensionless groups that control the behavior of the system, and elucidate different regimes of the invasion pattern. We present result for the 3D morphology of the invasion, with particular emphasis on the fracturing regime. [Preview Abstract] |
Sunday, November 22, 2015 9:05AM - 9:18AM |
A1.00006: Wettability and its impact on hydro-capillary fracturing in granular media Mathias Trojer, Pietro deAnna, Ruben Juanes Two-phase flow in geologic porous media is important in many natural and industrial processes. While it is well known that wetting properties of porous media can vary drastically depending on the type of media and the pore fluids, the effect of wettability on capillary-driven fracturing continues to challenge our microscopic and macroscopic descriptions. Here we study this problem experimentally, starting with the classic experiment of two-phase flow in a horizontal Hele-Shaw cell filled with a granular medium. We inject a low-viscosity fluid into a thin bed of glass beads initially saturated with a fluid 350 times more viscous. The control parameters are the injection rate, the confining stress and the contact angle of the liquid-liquid-solid interface; carefully chosen fluid pairs allow us to cover the entire range from drainage to imbibition. We demonstrate that wettability exerts a powerful influence on the invasion/fracturing morphology of unfavorable mobility displacements. High time resolution imaging techniques allow us to quantify matrix displacement and fracture opening dynamics. Our results provide insights on fracture propagation and fracture length distribution, parameters which are critically important to better understand long-term hydrocarbon production from shale [Preview Abstract] |
Sunday, November 22, 2015 9:18AM - 9:31AM |
A1.00007: Wetting and roughness: pattern formation in a rough fracture Amir Pahlavan, Luis Cueto-Felgueroso, Gareth McKinley, Ruben Juanes Wetting phenomena are inherently multiscale; owing to the complex nature of porous and fractured media, immiscible flows in this setting continue to challenge our microscopic and macroscopic descriptions. To gain some insight into the interplay between wettability and roughness of the medium, here we study experimentally the immiscible displacement of one fluid by another in a Hele-Shaw cell (two glass plates separated by a thin gap) with rough surfaces. We use a radial Hele-Shaw cell and saturate it with highly viscous silicone oil; we then inject a less viscous liquid at the center of the cell. Displacement of a more viscous liquid by a less viscous one leads to a hydrodynamic instability, known as viscous fingering. Wettability of the medium, however, has a profound influence on the displacement pattern and can lead to a complete suppression of the instability. Roughness, on the other hand, amplifies the wettability of the medium, and can also lead to contact-line pinning and intermittent avalanche-like behavior in the flow. We study the interplay between roughness and wettability of the medium by isolating each effect. We then propose a phase diagram that classifies the different displacement patterns, elucidating the underlying physics at play across scales. [Preview Abstract] |
Sunday, November 22, 2015 9:31AM - 9:44AM |
A1.00008: Modeling the Effect of Fluid Flow on a Growing Network of Fractures in a Porous Medium Mohammed Alhashim, Donald Koch The injection of a viscous fluid at high pressure in a geological formation induces the fracturing of pre-existing joints. Assuming a constant solid-matrix stress field, a weak joint saturated with fluid is fractured when the fluid pressure exceeds a critical value that depends on the joint's orientation. In this work, the formation of a network of fractures in a porous medium is modeled. When the average length of the fractures is much smaller than the radius of a cluster of fractured joints, the fluid flow within the network can be described as Darcy flow in a permeable medium consisting of the fracture network. The permeability and porosity of the medium are functions of the number density of activated joints and consequently depend on the fluid pressure. We demonstrate conditions under which these relationships can be derived from percolation theory. Fluid may also be lost from the fracture network by flowing into the permeable rock matrix. The solution of the model shows that the cluster radius grows as a power law with time in two regimes: (1) an intermediate time regime when the network contains many fractures but fluid loss is negligible; and (2) a long time regime when fluid loss dominates. In both regimes, the power law exponent depends on the Euclidean dimension and the injection rate dependence on time. [Preview Abstract] |
Sunday, November 22, 2015 9:44AM - 9:57AM |
A1.00009: On the Study of Lifting Mechanism of a Soft Porous Media under Fast Compression Qianhong Wu, S. Santhanam, R. Nathan Fluid flow in a soft porous media under fast compressions is widely observed in biological systems and industrial applications. Despite of much progress, it remains unclear for the lifting mechanisms of the porous media due to the lack of complete experimental verifications of theoretical models. We report herein a unique approach to treat the limitation. The permeability of a synthetic fibrous porous media as a function of its compression was first measured. The material was then employed in a dynamic compression experiment using a porous-walled cylinder piston apparatus. The obtained transient compression of the porous media and the aforementioned permeability data were applied in different theoretical models for the pore pressure generation, which conclusively proved the validity of the consolidation theory developed by Wu et al. (JFM, 542, 281, 2005). Furthermore, the solid phase lifting force was separated from the total reaction force and was characterized by a new viscoelastic model, containing a nonlinear spring in conjunction with a linear viscoelastic Generalized Maxwell mechanical module. Excellent agreement was obtained between the experiment and the theory. Thus, the lifting forces from both the fluid and the solid were determined. [Preview Abstract] |
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