The brittleness indices used in rock mechanics and their application in shale hydraulic fracturing: A review

Zhang, Decheng; Ranjith, P.G.; Perera, M.S.A.

doi:10.1016/j.petrol.2016.02.011

Cited by 351 publications

(111 citation statements)

References 40 publications

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“…The prospectivity of shales is often assumed to be linked to the so-called brittleness of rocks, where a number of different empirical definitions exist (Rybacki et al, 2016;Zhang et al, 2016a). As a first approximation, brittleness can be simply determined from composition if P-T effects are neglected.…”

Section: Effect Of Composition Orientation and Brittleness On Primarmentioning

confidence: 99%

“…The presence of water also accelerates the rate of fracture permeability reduction, in particular for clay-rich shales (Akrad et al, 2011;Alramahi and Sundberg, 2012;Guo and Liu, 2012;Kassis and Sondergeld, 2010;LaFollette and Carman, 2010;Liu and Sharma, 2005;Morales p [4] et Pedlow and Sharma, 2014;Reinicke et al, 2010;Stegent et al, 2010;Volk et al, 1981;Zhang et al, 2013;Zhang et al, 2015;Zhang et al, 2016b). The brittleness of shales, which correlates to some extent with their composition and elastic properties (Rybacki et al, 2016;Zhang et al, 2016a), may be also relevant for the long-term fracture healing rate. Fast healing is expected for more ductile shales by rapid proppant embedment or enhanced creep of contact areas in unpropped fractures.…”

Section: Introductionmentioning

confidence: 99%

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Creep of Posidonia Shale at Elevated Pressure and Temperature

et al. 2017

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The economic production of gas and oil from shales requires repeated hydraulic fracturing operations to stimulate these tight reservoir rocks. Besides simple depletion, the often observed decay of production rate with time may arise from creep-induced fracture closure.We examined experimentally the creep behavior of an immature carbonate-rich Posidonia shale, subjected to constant stress conditions at temperatures between 50° and 200°C and confining pressures of 50 to 200 MPa, simulating elevated in-situ depth conditions. Samples showed transient creep in the semibrittle regime with high deformation rates at high differential stress, high temperature, and low confinement. Strain was mainly accommodated by deformation of the weak organic matter and phyllosilicates and by pore space reduction.The primary decelerating creep phase observed at relatively low stress can be described by an empirical power law relation between strain and time, where the fitted parameters vary with temperature, pressure and stress. Our results suggest that healing of hydraulic fractures at low stresses by creep-induced proppant embedment is unlikely within a creep period of several years. At higher differential stress, as may be expected in situ at contact areas due to stress concentrations, the shale showed secondary creep, followed by tertiary creep until failure. In this regime, microcrack propagation and coalescence may be assisted by stress corrosion.Secondary creep rates were also described by a power law, predicting faster fracture closure rates than for primary creep, likely contributing to production rate decline. Comparison of our data with published primary creep data on other shales suggest that the long-term creepbehavior of shales can be correlated to their brittleness estimated from composition. Low creep strain is supported by a high fraction of strong minerals that can build up a load-bearing framework.

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Section: Effect Of Composition Orientation and Brittleness On Primarmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Creep of Posidonia Shale at Elevated Pressure and Temperature

et al. 2017

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“…Zhang et al (2016) quote many researchers, who pointed out, that approaches shown by Rickman et al (2008), Sun et al (2013) and Luan et al (2014) assume the same sensitivity of rock brittleness to E and ν. Determination of rock brittleness using only E and ν relations is not accurate, as rock brittleness depends on many other parameters such as bulk modulus and pore pressure.…”

Section: Methodsmentioning

confidence: 99%

Rock anisotropy and brittleness from laboratory ultrasonic measurements in the service of hydraulic fracturing

Moska¹

2018

Acta Geodynamica Et Geomaterialia

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Ultrasonic velocity anisotropy in the rock provides information of variability of the dynamic elastic moduli. Young's modulus and Poisson's ratio calculated from waves velocities can be used to determine brittleness index, which is usually used to predict rock susceptibility for hydraulic fracturing. This paper describes laboratory ultrasonic measurements carried out in order to improve hydraulic fracturing designing. The research was conducted over two types of rock: shale and limestone. The samples were cut out perpendicularly and parallel to the bedding planes. Next they were tested for effective porosity and mineral composition using XRD method. Directionally depended seismic velocities revealed noticeable anisotropy of laminated shale, caused by orientation of the bedding planes and weak anisotropy of limestone. Based on the velocities, dynamic elastic moduli and its anisotropy coefficients were determined. Calculations of brittleness index based on Young's modulus to Poisson's ratio relation and three types of mineral composition brittleness indexes, revealed strong variability in brittleness for both kind of tested formations. These results show, that different types of brittleness indexes should be used complementary, to better describe fracability of the rock. ARTICLE INFO

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“…The stress-strain-based calculation, which consists of a strain-based method, Young's modulus-based method, Poisson's ratio-based method, and energy-based method, is commonly used in brittleness evaluation [29]. As the compression process of a rock presents a balance between energy storage and consumption, the energy-based method is chosen for the brittleness evaluation in this study.…”

Section: Theoretical and Empirical Equations For Brittleness Index Camentioning

confidence: 99%

“…However, expressions to define rock brittleness are various [29,30]. Considering all the proposed definitions, brittleness can be calculated by three categories: (1) stress-strain curvebased approach.…”

Section: Introductionmentioning

confidence: 99%

A Damage Constitutive Model for the Effects of CO₂-Brine-Rock Interactions on the Brittleness of a Low-Clay Shale

et al. 2018

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CO 2 is a very promising fluid for drilling and nonaqueous fracturing, especially for CO 2 -enhanced shale gas recovery. Brittleness is a very important characteristic to evaluate the drillability and fracability. However, there is not much relevant research works on the influence of CO 2 and CO 2 -based fluids on shale's brittleness been carried out. Therefore, a series of strength tests were conducted to obtain the stress-strain characteristics of shale soaked in different phases of CO 2 including subcritical or supercritical CO 2 with formation of water for different time intervals (10 days, 20 days, and 30 days). Two damage constitutive equations based on the power function distribution and Weibull distribution were established to predict the threshold stress for both intact and soaked shale samples. Based on the results, physical and chemical reactions during the imbibition cause reductions of shales' peak axial strength (20.79%~61.52%) and Young's modulus (13.14%~62.44%). Weibull distribution-based constitutive model with a damage threshold value of 0.8 has better agreement with the experiments than that of the power function distribution-based constitutive model. The energy balance method together with the Weibull distribution-based constitutive model is applied to calculate the brittleness values of samples with or without soaking. The intact shale sample has the highest BI value of 0.9961, which is in accordance with the high percentage of brittleness minerals of the shale samples. The CO 2 -NaCl-shale interactions during the imbibition decrease the brittleness values. Among the three soaking durations, the minimum brittleness values occur on samples with 20 days' imbibition in subcritical and supercritical CO 2 + NaCl solutions and the reductions of which are 2.08% and 2.49%, respectively. Subcritical/supercritical CO 2 + NaCl imbibition has higher effect on shale's strength and Young's modulus than on the brittleness. The low-clay shale still keeps good fracture performance after imbibition.

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The brittleness indices used in rock mechanics and their application in shale hydraulic fracturing: A review

Cited by 351 publications

References 40 publications

Creep of Posidonia Shale at Elevated Pressure and Temperature

Creep of Posidonia Shale at Elevated Pressure and Temperature

Rock anisotropy and brittleness from laboratory ultrasonic measurements in the service of hydraulic fracturing

A Damage Constitutive Model for the Effects of CO₂-Brine-Rock Interactions on the Brittleness of a Low-Clay Shale

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The brittleness indices used in rock mechanics and their application in shale hydraulic fracturing: A review

Cited by 351 publications

References 40 publications

Creep of Posidonia Shale at Elevated Pressure and Temperature

Creep of Posidonia Shale at Elevated Pressure and Temperature

Rock anisotropy and brittleness from laboratory ultrasonic measurements in the service of hydraulic fracturing

A Damage Constitutive Model for the Effects of CO2-Brine-Rock Interactions on the Brittleness of a Low-Clay Shale

Contact Info

Product

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A Damage Constitutive Model for the Effects of CO₂-Brine-Rock Interactions on the Brittleness of a Low-Clay Shale