Elastic Anisotropy Reversal During Brittle Creep in Shale

Geng, Zhi; Bonnelye, Audrey; Chen, Mian; Jin, Yan; Dick, Pierre; David, Christian; Fang, Xin; Schubnel, Alexandre

doi:10.1002/2017gl074555

Cited by 46 publications

(21 citation statements)

References 52 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…At 75 °C, anisotropy reversal was reached at a strain of ~0.006 only. Geng et al () already extensively discussed anisotropy reversal and its implications, so in this paper, we discuss it only briefly.…”

Section: Resultsmentioning

confidence: 99%

Time and Temperature Dependent Creep in Tournemire Shale

et al. 2018

Self Cite

View full text Add to dashboard Cite

We conducted a series of triaxial creep experiments on shale specimens coming from Tournemire, France, using the stress‐stepping method up to failure, at a confining pressure of 80 MPa, on two orientations (parallel and perpendicular to bedding), and at temperatures of 26 and 75 °C. In these week‐long experiments, stress, strains, and P wave ultrasonic velocities were recorded (quasi‐) continuously. The strength at creep failure of Tournemire shale was ~70% higher than the peak strength measured during constant strain rate (~10−7/s) experiments, and failure was reached at larger strains. An overall transition from P wave velocity increase at moderate differential stress to P wave velocity decrease closer to brittle failure was also observed. At a smaller timescale, P wave velocities initially decreased and then increased gradually during each step of creep deformation. The magnitude of these variations showed important (i) stress, (ii) orientation, and (iii) temperature dependences: larger increase was observed for P wave propagating along the main compressive stress orientation, larger decrease for P wave propagating perpendicular to it, and a changing behavior enhanced at a higher temperature. Scanning electron microscopy performed postmortem revealed evidence of time‐dependent pressure solution, localized compaction, crack growth, and sealing/healing. Our data reveal that shale deformation is highly stress sensitive only in a narrow stress domain where stress corrosion cracking‐induced brittle dilatant creep deformation is dominant. At stresses below, pressure solution compaction creep dominates the deformation and shales compact, consolidate, and heal. This has important implications for the mechanics of shallow fault zones and accretionary prisms.

show abstract

Section: Resultsmentioning

confidence: 99%

Time and Temperature Dependent Creep in Tournemire Shale

et al. 2018

Self Cite

View full text Add to dashboard Cite

show abstract

“…Unlike stiff, well-indurated rocks, shales show measurable creep strains, even at low fractions of the FS (Parsons & Hedley, 1966). Among the parameters influencing creep response in shales are confining pressure (Rybacki et al, 2017), differential stress (Ghassemi & Suarez-Rivera, 2012;Li & Ghassemi, 2012;Sone & Zoback, 2013b), temperature (Geng et al, 2017(Geng et al, , 2018, rock anisotropy (Sone & Zoback, 2013b), and shale composition (Sone & Zoback, 2013b). Transient creep under triaxial loading may involve compaction (Villamor Lora & Ghazanfari, 2015), but, in some cases, high differential stresses can also activate dilational processes (Heap et al, 2015), which may lead to tertiary creep (Geng et al, 2017;Ghassemi & Suarez-Rivera, 2012;Nicolas et al, 2017;Rybacki et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Creep Deformation in Vaca Muerta Shale From Nanoindentation to Triaxial Experiments

et al. 2019

View full text Add to dashboard Cite

We tested samples cored from the Vaca Muerta shale reservoir using nanoindentation (2 min) and triaxial (12 hr) creep experiments in which confining pressure and differential stresses were <40 MPa. In all cases, we observed transient creep wherein strain increased as the logarithm of time. Creep was always compactional, led to increased moduli, was triggered by changes in either hydrostatic or deviatoric stress, and occurred under loads well below the failure stress. Our results are consistent with yield cap models proposed to describe shear‐enhanced compaction of sandstones and carbonates, assuming that the yield surface depends on strain rate. We compared our results to earlier studies that observed the transition from transient creep to approximately constant strain rate behavior. If short‐term creep can be quantified by a creep modulus, C, and long‐term creep, after a transition time, tc, by a linear viscosity, η, then η = Ctc. Owing to heterogeneity, the local values of Young's and creep moduli, E and C, measured during nanoindentation, varied by several orders of magnitude. Simple averaging of the indentation results overestimated E and C, as compared to their triaxial counterparts. The kinetics of log time creep, which is seen in various materials and loading circumstances, has been represented by a simple conceptual model incorporating the interplay of viscoelastic elements with widely distributed characteristic times. Thus, we argue that log time creep is an emerging phenomenon, independent of the identities of the underlying physical mechanisms.

show abstract

“…Rocks are well known to have cracks and defects at all scales [42][43][44][45][46][47][48]. In some case rocks are even elastic-anisotropic [49,50]. Another problem regarding performing the actual field-scale experiment is that the pore pressure was not considered in this study.…”

Section: Discussionmentioning

confidence: 99%

Experimental and Theoretical Study on Dynamic Hydraulic Fracture

Dong

Chen

et al. 2019

Energies

Self Cite

View full text Add to dashboard Cite

Hydraulic fracturing is vital in the stimulation of oil and gas reservoirs, whereas the dynamic process during hydraulic fracturing is still unclear due to the difficulty in capturing the behavior of both fluid and fracture in the transient process. For the first time, the direct observations and theoretical analyses of the relationship between the crack tip and the fluid front in a dynamic hydraulic fracture are presented. A laboratory-scale hydraulic fracturing device is built. The momentum-balance equation of the fracturing fluid is established and numerically solved. The theoretical predictions conform well to the directly observed relationship between the crack tip and the fluid front. The kinetic energy of the fluid occupies over half of the total input energy. Using dimensionless analyses, the existence of equilibrium state of the driving fluid in this dynamic system is theoretically established and experimentally verified. The dimensionless separation criterion of the crack tip and the fluid front in the dynamic situation is established and conforms well to the experimental data. The dynamic analyses show that the separation of crack tip and fluid front is dominated by the crack profile and the equilibrium fluid velocity. This study provides a better understanding of the dynamic hydraulic fracture.

show abstract

Elastic Anisotropy Reversal During Brittle Creep in Shale

Cited by 46 publications

References 52 publications

Time and Temperature Dependent Creep in Tournemire Shale

Time and Temperature Dependent Creep in Tournemire Shale

Creep Deformation in Vaca Muerta Shale From Nanoindentation to Triaxial Experiments

Experimental and Theoretical Study on Dynamic Hydraulic Fracture

Contact Info

Product

Resources

About