Incorporating Scale-Dependent Fracture Stiffness for Improved Reservoir Performance Prediction

Crawford, Brian; Tsenn, Michael C.; Homburg, J. M.; Stehle, R. C.; Freysteinson, J. A.; Reese, W. C.

doi:10.1007/s00603-017-1314-z

Cited by 14 publications

(13 citation statements)

References 28 publications

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“…Most laboratory shear flow tests on fractures have focused on force-driven fracture slip using direct shear design (Esaki et al, 1999;Gutierrez et al, 2000;Li et al, 2008;Olsson & Barton, 2001;Olsson & Brown, 1993;Park et al, 2013;Samuelson et al, 2009;Yeo et al, 1998) or have manually displaced the fractured specimen to represent fracture slip (Chen et al, 2000;Crawford et al, 2017;Durham & Bonner, 1994;Fang et al, 2017;Hofmann et al, 2016;Ishibashi et al, 2016;Vogler et al, 2016;Zhang et al, 2013). The observations in most of these tests have been used to prove that fracture self-propping and associated permeability increase can be obtained by fracture shearing.…”

Section: Introductionmentioning

confidence: 99%

Injection‐Induced Shear Slip and Permeability Enhancement in Granite Fractures

2018

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Shear stimulation, so‐called hydroshearing, is believed to reactivate critical or near‐critical preexisting fractures by pressurized fluid injection, causing them to slip and dilate for economic production from geothermal and unconventional petroleum reservoirs. However, little or no experiments have been conducted to directly probe the coupled hydromechanical responses and permeability evolution during fracture shearing. In this paper, we present the results of novel injection‐induced shear tests on cylindrical granite samples each containing a single tensile or saw cut fracture. The shear test on rough fractures demonstrates that retainable permeability enhancement can be achieved through dilatant shear slip. The characteristic stick‐slip behavior of the fracture during shearing is also observed. Fracture aperture controlled by effective normal stress dominates the fluid flow in stick state, while in slip state, the major contributor to production increase is the irreversible normal dilation caused by fracture shear slip. The experimental data show that depending on the fracture roughness, the fracture slip process includes two quasi‐static slip intervals with a slip velocity of ~10−9 to ~10−6 m/s and a dynamic slip interval with a slip velocity of ~10−7 to ~10−5 m/s. The fracture slip correlates well with the associated stress relaxation: a faster fracture slip induces a quicker stress relaxation, and vice versa. The influence of surface roughness on the hydromechanical responses during fracture shearing and the shear‐induced asperity degradation are also studied. The various experimental observations on rough and smooth fractures clearly indicate that the key component to shear stimulation is fracture self‐propping by asperities.

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Section: Introductionmentioning

confidence: 99%

Injection‐Induced Shear Slip and Permeability Enhancement in Granite Fractures

2018

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“…Moreover, fractures in granite and granodiorite are hard to completely close, either mechanically or hydraulically, under purely normal stresses (Hofmann et al 2016;Vogler et al 2016) unless the fracture surfaces are mated and/or subjected to extremely high loads (Kranzz et al 1979;Durham and Bonner 1994). In addition, studies on fractures in other rock types, such as slate, sandstone, dolerite, and limestone, essentially yielded similar results (Bandis et al 1983;Crawford et al 2017), which permit to conclude that the permeability of mismatched fractures is more sustainable in comparison to aligned fractures at the same normal stress conditions.…”

Section: Introductionmentioning

confidence: 86%

“…This scale-dependence issue commonly exists in laboratory studies due to the limitations of the sample size (Hofmann et al 2016;Vogler et al 2016;Crawford et al 2017). However, for hydraulic fracturing induced fractures, which are in the scope of this study, and unlike faults, these are commonly not displaced by large amounts.…”

Section: Fracture Roughness and Displacement-relatedmentioning

confidence: 99%

“…Numerous experimental studies on the hydromechanical properties of single fractures have previously been performed, generally considering a lithostatic load equivalent to 1-3 km crustal depth (23 MPa/km) (Bandis et al 1983;Hofmann et al 2016;Milsch et al 2016;Vogler et al 2016;Crawford et al 2017) but in some cases down to 7 km depth (Kranzz et al 1979;Durham and Bonner 1994). Experimentally it showed, that a mismatched joint in granitic rocks remains hydraulically conductive under normal stresses up to 160 MPa (Durham and Bonner 1994).…”

Section: Introductionmentioning

confidence: 99%

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Hydromechanical Investigations on the Self-propping Potential of Fractures in Tight Sandstones

Cheng

Milsch

2021

Rock Mech Rock Eng

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The hydromechanical properties of single self-propping fractures under stress are of fundamental interest for fractured-rock hydrology and a large number of geotechnical applications. This experimental study investigates fracture closure and hydraulic aperture changes of displaced tensile fractures, aligned tensile fractures, and saw-cut fractures for two types of sandstone (i.e., Flechtinger and Fontainebleau) with contrasting mechanical properties, cycling confining pressure between 5 and 30 MPa. Emphasis is placed on how surface roughness, fracture wall offset, and the mechanical properties of the contact asperities affect the self-propping potential of these fractures under normal stress. A relative fracture wall displacement can significantly increase fracture aperture and hydraulic conductivity, but the degree of increase strongly depends on the fracture surface roughness. For smooth fractures, surface roughness remains scale-independent as long as the fracture area is larger than a roll-off wavelength and thus any further displacement does not affect fracture aperture. For rough tensile fractures, these are self-affine over a larger scale so that an incremental fracture wall offset likely leads to an increase in fracture aperture. X-ray microtomography of the fractures indicates that the contact area ratio of the tensile fractures after the confining pressure cycle inversely correlates with the fracture wall offset yielding values in the range of about 3–25%, depending, first, on the respective surface roughness and, second, on the strength of the asperities in contact. Moreover, the contact asperities mainly occur isolated and tend to be preferentially oriented in the direction perpendicular to the fracture wall displacement which, in turn, may induce flow anisotropy. This, overall, implies that relatively harder sedimentary rocks have a higher self-propping potential for sustainable fluid flow through fractures in comparison to relatively soft rocks when specific conditions regarding surface roughness and fracture wall offset are met.

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“…During shear stimulation, a small reduction of effective normal stress by direct injection or by leak‐off from a hydraulic fracture can be sufficient to induce the dilatant shearing of optimally oriented preexisting fractures. A number of injection experiments on rock fractures have been conducted to explore permeability enhancement resulting from this process (Crawford et al, ; Fang et al, ; Gutierrez et al, ; Li et al, ; Park et al, ; Samuelson et al, ; Vogler et al, ; Wu et al, ; Zhang et al, ). In our companion paper (Ye & Ghassemi, ), we described injection‐induced shear tests on granite fractures using a more realistic boundary control, allowing us to capture the permeability evolution, slip characteristics, and stress relaxation during fracture shearing.…”

Section: Introductionmentioning

confidence: 99%

Injection‐Induced Propagation and Coalescence of Preexisting Fractures in Granite Under Triaxial Stress

Yan

Ghassemi

2019

JGR Solid Earth

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The dilatant shear slip of preexisting fractures/faults by injection at pressures below the minimum in situ stress has been recognized as an important permeability creation mechanism during reservoir stimulation. However, interconnected fracture network generation through the propagation and coalescence of preexisting fractures during shear stimulation has been rarely studied through laboratory experiments. To examine permeability enhancement through the propagation and coalescence of preexisting fractures, we conducted novel triaxial‐injection experiments under representative crustal stress conditions on cylindrical granite samples containing single or double preexisting fracture(s)/flaw(s). In the sample with a single fracture, SW‐1, new cracks propagated from the preexisting fracture due to injection. In the sample with two fractures, SW‐2, a highly conductive fracture network was created by the coalescence of newly formed cracks with preexisting fractures. As a result, the equivalent permeability of the sample was enhanced by 17 to 35 times. Both tensile wing cracks and shear and/or mixed‐mode secondary cracks were detected from the scanning electron microscope images of the tested samples. Our results suggest that in addition to dilatant shear slip, propagation and coalescence of preexisting fractures significantly contribute to reservoir permeability creation during low injection pressure stimulation in fractured rocks. Although the experiments focused on reservoir stimulation, the results have relevance to crustal permeability evolution and induced seismicity.

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Incorporating Scale-Dependent Fracture Stiffness for Improved Reservoir Performance Prediction

Cited by 14 publications

References 28 publications

Injection‐Induced Shear Slip and Permeability Enhancement in Granite Fractures

Injection‐Induced Shear Slip and Permeability Enhancement in Granite Fractures

Hydromechanical Investigations on the Self-propping Potential of Fractures in Tight Sandstones

Injection‐Induced Propagation and Coalescence of Preexisting Fractures in Granite Under Triaxial Stress

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