Impact of Rock Plasticity on Hydraulic Fracture Propagation and Closure

Dam, D.B. van; Papanastasiou, Panos; Pater, C.J. de

doi:10.2118/78812-pa

Cited by 54 publications

(26 citation statements)

References 18 publications

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“…The unconsolidated nature of the material means that if an opening is created, the tip of the opening cannot sustain large stress contrast, and plastic yielding is expected. Influence of plasticity in hydraulic fracturing has been examined for both cohesive and cohesionless materials [Papanastasiou and Thiercelin, 1993;van Dam et al, 2002;Abou-Sayed et al, 2004;Papanastasiou and Atkinson, 2006;Wu, 2006]. In general, one-dimensional leakoff model [Carter, 1957] is assumed for fluid flow from the fracture faces to the matrix in conventional LEFM-based models.…”

Section: Background and Experimental Motivationmentioning

confidence: 99%

Coupled discrete element modeling of fluid injection into dense granular media

2013

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[1] The coupled displacement process of fluid injection into a dense granular medium is investigated numerically using a discrete element method (DEM) code PFC2D r coupled with a pore network fluid flow scheme. How a dense granular medium behaves in response to fluid injection is a subject of fundamental and applied research interests to better understand subsurface processes such as fluid or gas migration and formation of intrusive features as well as engineering applications such as hydraulic fracturing and geological storage in unconsolidated formations. The numerical analysis is performed with DEM executing the mechanical calculation and the network model solving the Hagen-Poiseuille equation between the pore spaces enclosed by chains of particles and contacts. Hydromechanical coupling is realized by data exchanging at predetermined time steps. The numerical results show that increase in the injection rate and the invading fluid viscosity and decrease in the modulus and permeability of the medium result in fluid flow behaviors displaying a transition from infiltration-governed to infiltration-limited and the granular medium responses evolving from that of a rigid porous medium to localized failure leading to the development of preferential paths. The transition in the fluid flow and granular medium behaviors is governed by the ratio between the characteristic times associated with fluid injection and hydromechanical coupling. The peak pressures at large injection rates when fluid leakoff is limited compare well with those from the injection experiments in triaxial cells in the literature. The numerical analysis also reveals intriguing tip kinematics field for the growth of a fluid channel, which may shed light on the occurrence of the apical inverted-conical features in sandstone and magma intrusion in unconsolidated formations.Citation: Zhang, F., B. Damjanac, and H. Huang (2013), Coupled discrete element modeling of fluid injection into dense granular media,

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Section: Background and Experimental Motivationmentioning

confidence: 99%

Coupled discrete element modeling of fluid injection into dense granular media

2013

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“…The pressure at the moment a fracture closes is widely accepted as the minimum confining stress acting normal to the fracture [6]. Recent experiments have shown that in some cases fractures could close at pressures that differ from the confining stress, a finding that is at odds with some stress testing interpretations [76]. Recent analyses of the process of hydraulic fracture closure (e.g.…”

Section: Analysis Of a Deformable Fracturementioning

confidence: 99%

“…Recent analyses of the process of hydraulic fracture closure (e.g. References [76][77][78]) have assumed uniform pressure and effective stress in the fracture, and have used simplified analyses of leakoff. It seems reasonable to expect that flow within a hydraulic fracture during closure will affect the pressure log, so the approach described above could improve interpretations of stress tests and explanations of laboratory tests.…”

Section: Analysis Of a Deformable Fracturementioning

confidence: 99%

Analysis of a deformable fracture in permeable material

Murdoch

Germanovich

2006

Int. J. Numer. Anal. Meth. Geomech.

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SUMMARYThe response of deformable fractures to changes in fluid pressure controls phenomena ranging from the flow of fluids near wells to the propagation of hydraulic fractures. We developed an analysis designed to simulate fluid flows in the vicinity of asperity-supported fractures at rest, or fully open fractures that might be propagating. Transitions between at-rest and propagating fractures can also be simulated. This is accomplished by defining contact aperture as the aperture when asperities on a closing fracture first make contact. Locations on a fracture where the aperture is less than the contact aperture are loaded by both fluid pressure and effective stress, whereas locations where the aperture exceeds the contact aperture are loaded only by fluid pressure. Fluid pressure and effective stress on the fracture are determined as functions of time by solving equations of continuity in the fracture and matrix, and by matching the global displacements of the fracture walls to the local deformation of asperities.The resulting analysis is implemented in a numerical code that can simulate well tests or hydraulic fracturing operations. Aperture changes during hydraulic well tests can be measured in the field, and the results predicted using this analysis are similar to field observations. The hydraulic fracturing process can be simulated from the inflation of a pre-existing crack, to the propagation of a fracture, and the closure of the fracture to rest on asperities or proppant. Two-dimensional, multi-phase fluid flow in the matrix is included to provide details that are obscured by simplifications of the leakoff process (Carter-type assumptions) used in many hydraulic fracture models. Execution times are relatively short, so it is practical to implement this code with parameter estimation algorithms to facilitate interpretation of field data.

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“…The commonly used pseudo 3D fracture models that use stress intensity factor based criteria for the fracture propagation problem do not explicitly include pore pressure. Recent experimental work indicates that the LEFM approach for fracture propagation is not always valid and a cohesive zone description is necessary (Van Dam and de Pater, 2001;2002). Such cohesive zone models (CZM) would then use effective stress at the tip exceeding tensile strength as a propagation criterion which introduces the effect of pore pressure.…”

Section: Introductionmentioning

confidence: 99%

Pore pressure effects on fracture net pressure and hydraulic fracture containment: Insights from an empirical and simulation approach

Prabhakaran

Pater²,

Shaoul³

2017

Journal of Petroleum Science and Engineering

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A B S T R A C TPore pressure and its relationship with fracture net pressure has been reported qualitatively from both field and experimental observations. From a modeling perspective, the ubiquitously used pseudo 3D (P3D) models that are based on linear elastic fracture mechanics (LEFM) do not include the effect of reservoir depletion (or overpressure). Models that utilize effective stress as propagation criteria with a cohesive zone description, introduce the pore pressure directly into the simulation and hence can potentially capture the effect of pore pressure on fracture propagation. This work investigates the effect of pore pressure on hydraulic fracturing net pressure and geometry using empirical and numerical simulation approaches. We carried out an analysis of more than 400 datafrac injections spanning a wide range of geological ages and depositional environments in order to investigate the relationship between observed net pressure and reservoir pore pressure. The net fracture propagation pressure from the fracture treatment analysis was seen to be correlated with the effective stress in the reservoir. Fracture propagation simulations were performed using a coupled finite element -finite difference fracture simulator. The code uses a cohesive zone model (CZM) to describe fracture propagation. Four different effective stress scenarios were used to study the effect of effective stress on net pressure. The simulation results closely match the empirical relation between net pressure and effective stress as obtained from the analysis of actual frac treatment data. It is observed from the simulations that the magnitude of the effective stress also has an effect on the fracture geometry with a high effective stress leading to wider, shorter and more radial fractures. The derived empirical correlation is hence useful as a fracture design parameter. The datafrac net pressure diagnostics workflow in the pseudo 3D models can incorporate local tip pore pressure as a new pressure matching parameter. The pore pressure effect can thus explain high net pressures routinely observed in frac operations and also as a containment mechanism.

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Impact of Rock Plasticity on Hydraulic Fracture Propagation and Closure

Cited by 54 publications

References 18 publications

Coupled discrete element modeling of fluid injection into dense granular media

Coupled discrete element modeling of fluid injection into dense granular media

Analysis of a deformable fracture in permeable material

Pore pressure effects on fracture net pressure and hydraulic fracture containment: Insights from an empirical and simulation approach

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