Empirical strength prediction for preserved shales

Dewhurst, David N.; Sarout, Joël; Piane, Claudio Delle; Siggins, Anthony F.; Raven, Mark

doi:10.1016/j.marpetgeo.2015.06.004

Cited by 49 publications

(26 citation statements)

References 49 publications

(81 reference statements)

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“…In consequence, shales exhibit a strong anisotropy in both physical and mechanical properties, which has been observed both at the field scale [ Alkhalifah and Rampton , ; Le Gonidec et al , ] and the laboratory scale [ Ibanez and Kronenberg , ; Masri et al , ; Ikari et al , ]. In particular, several experimental studies investigated the anisotropic strength of shales [ Niandou et al , ; Dewhurst et al , ; Shea and Kronenberg , ]. Including studies performed on other anisotropic rocks such as slates, mica schists, and gneiss [ Shea and Kronenberg , , ; Rawling et al , ], models of anisotropic failure criterions, either semiempirical [ Kronenberg et al , ; Cazacu and Cristescu , ; Tien and Kuo , ] or micromechanical [ Rawling et al , ], have been developed.…”

Section: Introductionmentioning

confidence: 99%

Strength anisotropy of shales deformed under uppermost crustal conditions

et al. 2017

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Conventional triaxial tests were performed on three sets of samples of Tournemire shale along different orientations relative to bedding (0°, 45°, and 90°). Experiments were carried out up to failure at increasing confining pressures ranging from 2.5 to 160 MPa, at strain rates ranging between 3 × 10−7s−1 and 3 × 10−5s−1. This allowed us to determine the entire anisotropic elastic compliance matrix as a function of confining pressure. Results show that the orientation of principal stress relative to bedding plays an important role on the brittle strength, with 45° orientation being the weakest. We fit our results with a wing crack micromechanical model and an anisotropic fracture toughness. We found low values of internal friction coefficient and apparent friction coefficient in agreement with friction coefficient of clay minerals (between 0.2 and 0.3) and values of KIc comparable to that already published in the literature. We also showed that strain rate has a strong impact on peak stress and that dilatancy appears right before failure and hence highlighting the importance of plasticity mechanisms. Although brittle failure was systematically observed, stress drops and associated slips were slow and deformation always remained aseismic (no acoustic emission were detected). This confirms that shales are good lithological candidates for shallow crust aseismic creep and slow slip events.

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Section: Introductionmentioning

confidence: 99%

Strength anisotropy of shales deformed under uppermost crustal conditions

et al. 2017

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“…The increasing significance of shale gas plays has led to the need for deeper understanding of shale behavior (Dewhurst et al 2015). In both exploration and production of shale gas, brittleness and ductility of shale are important evaluation parameters as they are closely related to natural shale fracture (Ding et al 2012), artificial hydraulic fracturing , drilling (Eshkalak et al 2015;Zeng et al 2015), permeability (Ghanizadeh et al 2013) and gas preservation (Yarali and Kahraman 2011;Gale et al 2014;Hu et al 2015;Liu and Sun 2015;Zeng et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production

et al. 2017

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Brittleness and ductility of shale are closely related to shale gas exploration and production. How to predict brittleness and ductility of shale is one of the key issues in the study of shale gas preservation and hydraulic fracturing treatments. The magnitude of shale brittleness was often determined by brittle mineral content (for example, quartz and feldspars) in shale gas exploration. However, the shale brittleness is also controlled by burial depth. Shale brittle/ductile properties such as brittle, semibrittle and ductile can mutually transform with burial depth variation. We established a work flow of determining the burial depth interval of brittle-ductile transition zone for a given shale. Two boundaries were employed to divide the burial depth interval of shale brittle/ductile properties. One is the bottom boundary of the brittle zone (BZ), and the other is the top boundary of the ductile zone (DZ). The brittle-ductile transition zone (BDTZ) is between them. The bottom boundary of BZ was determined by the overconsolidation ratio (OCR) threshold value combined with pre-consolidation stress which the shale experienced over geological time. The top boundary of DZ was determined based on the critical confining pressure of brittle-ductile transition. The OCR threshold value and the critical confining pressure were obtained from uniaxial strain and triaxial compression tests. The BZ, DZ and BDTZ of the Lower Silurian Longmaxi shale in some representative shale gas exploration wells in eastern Sichuan and western Hubei areas were determined according to the above work flow. The results show that the BZ varies with the maximum burial depth and the DZ varies with the density of the overlying rocks except for the critical confining pressure. Moreover, the BDTZ determined by the above work flow is probably the best burial depth interval for marine shale gas exploration and production in Southern China. Shale located in the BDTZ is semi-brittle and is not prone to be severely naturally fractured but likely to respond well to hydraulic fracturing. The depth interval of BDTZ determined by our work flow could be a valuable parameter of shale gas estimation in geology and engineering.

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“…The first category focuses on the empirical formulations to evaluate the properties of shale rock [3][4][5][6][7][8]. For examples, Dewhurst et al presented the empirical strength prediction for preserved shales [3]; Farrokhrouz et al proposed the empirical estimation of uniaxial compressive strength of shale formations [4]; Sayers used the clay-particle orientation distribution function to characterize shale elastic-anisotropy in dynamic measurements [5]. These formulations are obtained by means of laboratory or site tests, which is the phenomenological way to formulate the behavior of shale rock.…”

Section: Introductionmentioning

confidence: 99%

Multi-scale approach for modeling the transversely isotropic elastic properties of shale considering multi-inclusions and interfacial transition zone

Chen

Nezhad

Fisher

et al. 2016

International Journal of Rock Mechanics and Mining Sciences

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Empirical strength prediction for preserved shales

Cited by 49 publications

References 49 publications

Strength anisotropy of shales deformed under uppermost crustal conditions

Strength anisotropy of shales deformed under uppermost crustal conditions

Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production

Multi-scale approach for modeling the transversely isotropic elastic properties of shale considering multi-inclusions and interfacial transition zone

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