Pore pressure influence on tensile fracture propagation in sedimentary rock

Bruno, Michael S.; Nakagawa, Frank

doi:10.1016/0148-9062(91)90593-b

Cited by 170 publications

(82 citation statements)

References 20 publications

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“…However for rock tensile failure, the experimental work by Schmitt and Zoback. (1989), Bruno and Nakagawa (1991) and Visser (1998) indicate that the failure criterion is based on Terzaghi effective stress. The Frac3D code uses single component elasticity and in the propagation criterion effective stress is used.…”

Section: Frac3d Coupled Simulationmentioning

confidence: 99%

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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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Section: Frac3d Coupled Simulationmentioning

confidence: 99%

“…Schmitt and Zoback (1989) conducted laboratory tests on the effect of pore pressure on tensile failure. Bruno and Nakagawa (1991) presented theoretical analysis based on Griffith strain energy release criteria that suggested that tensile fracture is controlled by general effective stress.…”

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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“…Many well-controlled, small-scale laboratory experiments on hydro-fracture are documented in the literature (Jaeger, 1963;Zoback et al, 1977;Warpinski et al, 1982;Bruno and Nakagawa 1991;Johnson and Cleary 1991;Song et al, 2001;Jeffrey and Bunger, 2007;Bunger et al, 2011). For such experiments, samples of various shapes (e.g., hollow cylinders and perforated prisms) are loaded along their boundaries and the internal fluid pressure is increased until a hydraulic fracture initiates and propagates.…”

Section: Laboratory-scale Hydraulic Fracturing Experimentsmentioning

confidence: 99%

The seismo-hydromechanical behavior during deep geothermal reservoir stimulations: open questions tackled in a decameter-scale in situ stimulation experiment

et al. 2018

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Abstract. In this contribution, we present a review of scientific research results that address seismo-hydromechanically coupled processes relevant for the development of a sustainable heat exchanger in low-permeability crystalline rock and introduce the design of the In situ Stimulation and Circulation (ISC) experiment at the Grimsel Test Site dedicated to studying such processes under controlled conditions. The review shows that research on reservoir stimulation for deep geothermal energy exploitation has been largely based on laboratory observations, large-scale projects and numerical models. Observations of full-scale reservoir stimulations have yielded important results. However, the limited access to the reservoir and limitations in the control on the experimental conditions during deep reservoir stimulations is insufficient to resolve the details of the hydromechanical processes that would enhance process understanding in a way that aids future stimulation design. Small-scale laboratory experiments provide fundamental insights into various processes relevant for enhanced geothermal energy, but suffer from (1) difficulties and uncertainties in upscaling the results to the field scale and (2) relatively homogeneous material and stress conditions that lead to an oversimplistic fracture flow and/or hydraulic fracture propagation behavior that is not representative of a heterogeneous reservoir. Thus, there is a need for intermediate-scale hydraulic stimulation experiments with high experimental control that bridge the various scales and for which access to the target rock mass with a comprehensive monitoring system is possible. The ISC experiment is designed to address open research questions in a naturally fractured and faulted crystalline rock mass at the Grimsel Test Site (Switzerland). Two hydraulic injection phases were executed to enhance the permeability of the rock mass. During the injection phases the rock mass deformation across fractures and within intact rock, the pore pressure distribution and propagation, and the microseismic response were monitored at a high spatial and temporal resolution.

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“…Bruno and Nakagawa [1991] demonstrated that induced hydraulic fractures will propagate toward regions of higher local pore pressure, or lower effective stress. The stress concentrations at crack tips are locally influenced by matrix pore pressure magnitude.…”

Section: Introductionmentioning

confidence: 99%

Role of permeability and storage in the initiation and propagation of natural hydraulic fractures

Boutt

Goodwin

McPherson

2009

Water Resources Research

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[1] Joint sets within sedimentary basins are commonly interpreted to have formed by tensile failure in conditions where pore fluid pressure was elevated. Such tensile fractures are inferred to be a part of the process that relieves high fluid pressure by locally increasing rock permeability. In spite of the importance of this feedback mechanism, the detailed mechanics of hydraulic fracture genesis remain poorly understood. We describe the results of both experimental and numerical studies of hydraulic fracture genesis on the basis of an experimental protocol that combines rock extension with elevated pore fluid pressure such that the hydraulic fracture criterion is met in the sample interior. This is achieved by simultaneously dropping both minimum stress and external pore fluid pressure, inducing a large fluid pressure drop between the sample interior and its ends. Poroelastic modeling suggests that the pore fluid pressure is highest close to, but not at, the sample ends and is locally maintained at levels that meet the hydraulic fracture criterion for up to 50 s. Application of this experimental protocol to an impure sample of sandstone resulted in the generation of several hydraulic fractures subparallel to the maximum principal stress. Fracturing did not occur in a drained test on the same sample, demonstrating that the elevated pore fluid pressure was critical to fracture formation. To better understand the experimental results, we explore the role of rock permeability and storage on fracture processes using a numerical model that directly couples a lattice-Boltzmann model for fluid mechanics with a discrete element model for solid mechanics. Like the experiment, the numerical simulations produced opening mode fractures when operated to replicate the conditions of the experiment. Fractures preferentially occur in portions of the model inferred to be mechanically weak. Local fluid pressure gradients strongly influence the state of stress in the solids and thereby fracture growth. Increasing the model permeability increases fracture propagation rate, decreases sample deformation, and increases fracture spacing. Sample deformation increases, and fracture spacing decreases, with increasing overpressure. It appears that bulk forcing of the solid via fluid seepage forces is important in fracture genesis, explaining the key roles of permeability and diffusivity in the hydrofracture process.

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Pore pressure influence on tensile fracture propagation in sedimentary rock

Cited by 170 publications

References 20 publications

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

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

The seismo-hydromechanical behavior during deep geothermal reservoir stimulations: open questions tackled in a decameter-scale in situ stimulation experiment

Role of permeability and storage in the initiation and propagation of natural hydraulic fractures

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