Journal of Natural Gas Science and Engineering

Article	Citations
A review on the role and impact of various additives as promoters/ inhibitors for gas hydrate formation	133
External corrosion of oil and gas pipelines: A review of failure mechanisms and predictive preventions	96
Review of CO2 injection techniques for enhanced shale gas recovery: Prospect and challenges	86
A new hybrid algorithm model for prediction of internal corrosion rate of multiphase pipeline	80
Superhydrophobic coatings for steel pipeline protection in oil and gas industries: A comprehensive review	77
Experimental study on the mechanical properties of bedding planes in shale	76
A comprehensive review of value-added CO2 sequestration in subsurface saline aquifers	74
A review of the features and applications of ZIF-8 and its derivatives for separating CO2 and isomers of C3- and C4- hydrocarbons	73
Feasibility evaluation of hydraulic fracturing in hydrate-bearing sediments based on analytic hierarchy process-entropy method (AHP-EM)	69
CO2 capturing, thermo-kinetic principles, synthesis and amine functionalization of covalent organic polymers for CO2 separation from natural gas: A review	68
Quantitative characterization of coal microstructure and visualization seepage of macropores using CT-based 3D reconstruction	66
Effect of surface morphology on fluid flow in rough fractures: A review	66
Pore characterization of shales: A review of small angle scattering technique	64
Use of existing steel pipeline infrastructure for gaseous hydrogen storage and transport: A review of factors affecting hydrogen induced degradation	62
Kinetic and thermodynamic evaluation of effective combined promoters for CO2 hydrate formation	61
Daily natural gas load forecasting based on the combination of long short term memory, local mean decomposition, and wavelet threshold denoising algorithm	59
Natural gas consumption forecasting: A discussion on forecasting history and future challenges	57
Quantitative visualization and characteristics of gas flow in 3D pore-fracture system of tight rock based on Lattice Boltzmann simulation	56
Experiences and lessons learned from China's shale gas development: 2005–2019	55
Liquid nitrogen fracturing efficiency as a function of coal rank: A multi-scale tomographic study	53
Machine learning-based production forecast for shale gas in unconventional reservoirs via integration of geological and operational factors	52
Estimation of adsorption capacity of CO2, CH4, and their binary mixtures in Quidam shale using LSSVM: Application in CO2 enhanced shale gas recovery and CO2 storage	51
Pore structure characteristics and fractal dimension analysis of low rank coal in the Lower Indus Basin, SE Pakistan	50
Numerical study of depressurization and hot water injection for gas hydrate production in China's first offshore test site	49
Robust optimization of CO2 sequestration through a water alternating gas process under geological uncertainties in Cuu Long Basin, Vietnam	49

Insights into the application of surfactants and nanomaterials as shale inhibitors for water-based drilling fluid: A review	47
A comprehensive review of proppant transport in fractured reservoirs: Experimental, numerical, and field aspects	46
Characteristics of methane adsorption/desorption heat and energy with respect to coal rank	46
Waterborne polymers as kinetic/anti-agglomerant methane hydrate and corrosion inhibitors: A new and promising strategy for flow assurance	46
Mechanisms of fracturing fluid spontaneous imbibition behavior in shale reservoir: A review	46
Experimental investigation on the effects of thermal treatment on the physical and mechanical properties of shale	46
Gas pipeline leak noise measurements using optical fibre distributed acoustic sensing	46
Accurate characterization of coal pore and fissure structure based on CT 3D reconstruction and NMR	46
Experimental investigation of the petrophysical properties, minerals, elements and pore structures in tight sandstones	46
The role of storage systems in hydrogen economy: A review	45
Prediction of the internal corrosion rate for oil and gas pipeline: Implementation of ensemble learning techniques	45
Study on the mechanical properties of man-made salt rock samples with impurities	44
Permeability and porosity prediction using logging data in a heterogeneous dolomite reservoir: An integrated approach	44
Aminoantipyrine derivatives as a novel eco-friendly corrosion inhibitors for P110 steel in simulating acidizing environment: Experimental and computational studies	43
Assessment of rock-hydrogen and rock-water interfacial tension in shale, evaporite and basaltic rocks	43
Experimental study of hydraulic fracture initiation and propagation in highly saturated methane-hydrate-bearing sands	43
Integrated sedimentological and petrophysical characterization for clastic reservoirs: A case study from New Zealand	42
The influence of key parameters on combustion of double gas hydrate	42
Neural network application to petrophysical and lithofacies analysis based on multi-scale data: An integrated study using conventional well log, core and borehole image data	42
Erosion simulation and improvement scheme of separator blowdown system ——A case study of Changning national shale gas demonstration area	42
Particle size effect on pore structure characteristics of lignite determined via low-temperature nitrogen adsorption	42
Discrete element numerical simulation of mechanical properties of methane hydrate-bearing specimen considering deposit angles	41
Experiment and numerical simulation of sand particle erosion under slug flow condition in a horizontal pipe bend	40
Enhancement of gas production from natural gas hydrate reservoir by reservoir stimulation with the stratification split grouting foam mortar method	40
Experimental study on the effect of fracture surface morphology on plugging efficiency during temporary plugging and diverting fracturing	40
CFD-DEM simulation of proppant transport by supercritical CO2 in a vertical planar fracture	40
Gas breakthrough pressure of tight rocks: A review of experimental methods and data	40
A review on non-aqueous fracturing techniques in unconventional reservoirs	40
Numerical analysis of sand production during natural gas extraction from unconsolidated hydrate-bearing sediments	40
3D investigation of the effects of multiple-well systems on methane hydrate production in a low-permeability reservoir	39
Evaluation of the gas production enhancement effect of hydraulic fracturing on combining depressurization with thermal stimulation from challenging ocean hydrate reservoirs	39
Pillared cloisite 15A as an enhancement filler in polysulfone mixed matrix membranes for CO2/N2 and O2/N2 gas separation	38
Fracture identification by semi-supervised learning using conventional logs in tight sandstones of Ordos Basin, China	38
Insights into NMR response characteristics of shales and its application in shale gas reservoir evaluation	38
A perspective on the potential application of bio-inhibitors for shale stabilization during drilling and hydraulic fracturing processes	38
Review on the accumulation behavior of natural gas hydrates in porous sediments	37
Laboratory-scale study on proppant behaviour in unconventional oil and gas reservoir formations	37
A proposed classification for the reservoir quality assessment of hydrocarbon-bearing sandstone and carbonate reservoirs: A correlative study based on different assessment petrophysical procedures	37
Flow modeling in shale gas reservoirs: A comprehensive review	36
A review of numerical research on gas production from natural gas hydrates in China	36
A comprehensive review of proppant embedment in shale reservoirs: Experimentation, modeling and future prospects	36
Organic matter pores structure and evolution in shales based on the he ion microscopy (HIM): A case study from the Triassic Yanchang, Lower Silurian Longmaxi and Lower Cambrian Niutitang shales in Chi	36
Hydrogen in pipeline steels: Recent advances in characterization and embrittlement mitigation	36
Casing deformation mechanisms of horizontal wells in Weirong shale gas field during multistage hydraulic fracturing	36
Comparison of the characteristics of corrosion scales covering 3Cr steel and X60 steel in CO2-H2S coexistence environment	36
A review on gas hydrates and kinetic hydrate inhibitors based on acrylamides	36
Differential enrichment mechanism of organic matters in the marine-continental transitional shale in northeastern Ordos Basin, China: Control of sedimentary environments	35
An Overview on the potential application of ionic liquids in shale stabilization processes	35
Chronic leak detection for single and multiphase flow: A critical review on onshore and offshore subsea and arctic conditions	35
Hydrocarbon source rock evaluation and quantification of organic richness from correlation of well logs and geochemical data: A case study from the sembar formation, Southern Indus Basin, Pakistan	35

Evolution of methane ad-/desorption and diffusion in coal under in the presence of oxygen and nitrogen after heat treatment	35
Gas hydrate formation in the presence of mixed surfactants and alumina nanoparticles	35
Comparison of the pore structures of Lower Silurian Longmaxi Formation shales with different lithofacies in the southern Sichuan Basin, China	35
Hydrogen-induced cracking and blistering in steels: A review	35
An updated study on CH4 isothermal adsorption and isosteric adsorption heat behaviors of variable rank coals	35
Proppant placement in complex fracture geometries: A computational fluid dynamics study	35
Mechanical study on the wellbore stability of horizontal wells in natural gas hydrate reservoirs	34
Dynamic failure behavior of buried cast iron gas pipeline with local external corrosion subjected to blasting vibration	34
Effects of L-glutamic acid, N, N-diacetic acid as chelating agent on acidification of carbonate reservoirs in acidic environments	34
A new approach modeling permeability of mining-disturbed coal based on a conceptual model of equivalent fractured coal	33
Advantages of supercritical CO2 compound fracturing in shale on fracture geometry, complexity and width	33
Study on the damage and control method of fracturing fluid to tight reservoir matrix	33
Effect of fracture roughness on the hydrodynamics of proppant transport in hydraulic fractures	33
Mechanical behavior of hydrate-bearing sands with fine particles under isotropic and triaxial compression	33
Failure pressure prediction by defect assessment and finite element modelling on natural gas pipelines under cyclic loading	33
Scale-span pore structure heterogeneity of high volatile bituminous coal and anthracite by FIB-SEM and X-ray μ-CT	33
Pressure-transient analysis in shale gas reservoirs: A review	33
Influence of pore structural properties on gas hydrate saturation and permeability: A coupled pore-scale modelling and X-ray computed tomography method	32
Comparison of permeability predictions on cemented sandstones with physics-based and machine learning approaches	32
A review on gas hydrate production feasibility for permafrost and marine hydrates	32
Analysis of the mechanical properties of methane hydrate-bearing sands with various pore pressures and confining pressures	32
Hydrodynamic characteristics and mass transfer performance of rotating packed bed for CO2 removal by chemical absorption: A review	32
Pore structure and diffusion characteristics of intact and tectonic coals: Implications for selection of CO2 geological sequestration site	32
CO2 adsorption and swelling of coal under constrained conditions and their stage-change relationship	32
Development of renewable energy system integrated with hydrogen and natural gas subsystems for cleaner combustion	32
Effect of supercritical-CO2 interaction time on the alterations in coal pore structure	32
Time-dependent coal permeability: Impact of gas transport from coal cleats to matrices	32
Pore formation and evolution of organic-rich shale during the entire hydrocarbon generation process: Examination of artificially and naturally matured samples	31
3D microfracture network and seepage characteristics of low-volatility bituminous coal based on nano-CT	31
Coal and gas outburst control using uniform hydraulic fracturing by destress blasting and water-driven gas release	31
Experimental and numerical analyses of electro-pulse rock-breaking drilling	31
Estimation of reservoir porosity based on seismic inversion results using deep learning methods	30
A comprehensive review of laboratory, field and modelling studies on drilling mud rheology in high temperature high pressure (HTHP) conditions	30
Modeling viscosity of CO2 at high temperature and pressure conditions	30
The impact of supercritical CO2 on the pore structure and storage capacity of shales	30
Study on the surface crack propagation mechanism of coal and sandstone subjected to cryogenic cooling with liquid nitrogen	30
Simultaneous measurement of water permeability and methane hydrate pore habit using a two-dimensional glass micromodel	30
Improving the shale stability with nano-silica grafted with hyperbranched polyethyleneimine in water-based drilling fluid	30
Shale lithofacies controls on porosity and pore structure: An example from Ordovician Goldwyer Formation, Canning Basin, Western Australia	30
Thermal methods in flow assurance: A review	30
Numerical study on the diffusion process of pinhole leakage of natural gas from underground pipelines to the soil	30
The effect of clay-swelling induced cracks on imbibition behavior of marine shale reservoirs	30
Quantitative calculated shale gas contents with different lithofacies: A case study of Fuling gas shale, Sichuan Basin, China	30
Experimental study on coal permeability and cracking characteristics under LN2 freeze-thaw cycles	30
Integration of discrete fracture reconstruction and dual porosity/dual permeability models for gas production analysis in a deformable fractured shale reservoir	29
Review of methods and applications for promoting gas hydrate formation process	29
Impact of zinc oxide nanoparticles on the rheological and fluid-loss properties, and the hydraulic performance of non-damaging drilling fluid	29
Development and application of three-dimensional discrete fracture network modeling approach for fluid flow in fractured rock masses	29
A review of foam-based fracturing fluids applications: From lab studies to field implementations	29
Damage effects on coal mechanical properties and micro-scale structures during liquid CO2-ECBM process	29
Modeling of local buckling of corroded X80 gas pipeline under axial compression loading	29
A review of laboratory studies and theoretical analysis for the interaction mode between induced hydraulic fractures and pre-existing fractures	29
A novel custom ensemble learning model for an improved reservoir permeability and water saturation prediction	29
Oxidative coupling of methane (OCM): An overview of the challenges and opportunities for developing new technologies	29
Water-soluble polymers for high-temperature resistant hydraulic fracturing: A review	29
Fracture initiation pressure and failure modes of tree-type hydraulic fracturing in gas-bearing coal seams	29
The effect of clay-swelling induced cracks on shale permeability during liquid imbibition and diffusion	29
Analysis of corrosion failure and materials selection for CO2–H2S gas well	28
Molecular insights into the kinetic hydrate inhibition performance of Poly(N-vinyl lactam) polymers	28
The characteristics and its implications of hydraulic fracturing in hydrate-bearing clayey silt	28
CH4 and CO2 sorption and diffusion carried out in various temperatures on hard coal samples of various degrees of coalification	28
Improving class G cement carbonation resistance for applications of geologic carbon sequestration using synthetic polypropylene fiber	28
Artificial neural network (ANN) approach to predict unconfined compressive strength (UCS) of oil and gas well cement reinforced with nanoparticles	28
Comprehensive review of geomechanical constitutive models of gas hydrate-bearing sediments	28
Experimental and numerical simulation of erosion-corrosion of 90° steel elbow in shale gas pipeline	28
The seepage properties and permeability enhancement mechanism in coal under temperature shocks during unloading confining pressures	28
Physical simulation of flow field and construction process of horizontal salt cavern for natural gas storage	28
A fractal model for gas-water relative permeability curve in shale rocks	28
The calculations of pore structure parameters from gas adsorption experiments of shales: Which models are better?	27
Modeling In-situ tectonic stress state and maximum horizontal stress azimuth in the Central Algerian Sahara – A geomechanical study from El Agreb, El Gassi and Hassi Messaoud fields	27
Exploration potential of different lithofacies of deep marine shale gas systems: Insight into organic matter accumulation and pore formation mechanisms	27
Mechanical characterization of continental shale in Sichuan Basin of China and its potential impact on reservoir stimulation	27
Analysis of natural gas leakage diffusion characteristics and prediction of invasion distance in utility tunnels	27
High pressure rheological studies of methane hydrate slurries formed from water-hexane, water-heptane, and water-decane multiphase systems	27
Temperature impact on linear and radial wormhole propagation in limestone, dolomite, and mixed mineralogy	27
Synthesis and performance evaluation of a novel polymeric fluid loss controller in water-based drilling fluids: High-temperature and high-salinity conditions	27
A comparative study of fracture surface roughness and flow characteristics between CO2 and water fracturing	27
A novel pore size classification method of coals: Investigation based on NMR relaxation	27
Characterization of refracture orientation in poorly propped fractured wells by pressure transient analysis: Model, pitfall, and application	27
Gas transport through coal particles: Matrix-flux controlled or fracture-flux controlled?	27

Multi-scale modelling of gas transport and production evaluation in shale reservoir considering crisscrossing fractures	27
Formation damage mitigation mechanism for coalbed methane wells via refracturing with fuzzy-ball fluid as temporary blocking agents	27
The effect of subcritical and supercritical CO2 on the pore structure of bituminous coals	27
Xenon recovery from natural gas by hybrid method based on gas hydrate crystallisation and membrane gas separation	26
Influence of tectonic evolution on pore structure and fractal characteristics of coal by low pressure gas adsorption	26
An adsorption model for evaluating methane adsorption capacity in shale under various pressures and moisture	26
Evaluation of methods for determining rock brittleness under compression	26
Pore structure typing and fractal characteristics of lacustrine shale from Kongdian Formation in East China	26
Developmental characteristics and controlling factors of natural fractures in the lower paleozoic marine shales of the upper Yangtze Platform, southern China	26
Semi-analytical modeling of transient rate behaviour of a horizontal well with multistage fractures in tight formations considering stress-sensitive effect	26
CO2 geological storage: Critical insights on plume dynamics and storage efficiency during long-term injection and post-injection periods	26
Gas in place and its controlling factors of the shallow Longmaxi shale in the Xishui area, Guizhou, China	26
A comparison of nano-scale pore attributes of Barakar Formation gas shales from Raniganj and Wardha Basin, India using low pressure sorption and FEG-SEM analysis	26
Analytical interpretation of hydraulic fracturing initiation pressure and breakdown pressure	26
Experimental quantification of the effect of oil based drilling fluid contamination on properties of wellbore cement	26
Early gas kick detection in vertical wells via transient multiphase flow modelling: A review	26
Machine learning-informed ensemble framework for evaluating shale gas production potential: Case study in the Marcellus Shale	26
Microcosmic retaining mechanism and behavior of screen media with highly argillaceous fine sand from natural gas hydrate reservoir	26
Critical factors controlling adsorption capacity of shale gas in Wufeng-Longmaxi formation, Sichuan Basin: Evidences from both experiments and molecular simulations	25
The shear-wave velocity prediction for sedimentary rocks	25
Leakage diffusion characteristics and harmful boundary analysis of buried natural gas pipeline under multiple working conditions	25
Gas permeability characteristics of marine sediments with and without methane hydrates in a core holder	25
Numerical simulation of proppant transport in liquid nitrogen fracturing	25
Machine-learning predictions of the shale wells’ performance	25
Mesoscopic structure characterization of plugging zone for lost circulation control in fractured reservoirs based on photoelastic experiment	25
Effect of microstructure and chemical composition of coal on methane adsorption	25
Safety, economics, environment and energy based criteria towards multi-objective optimization of natural gas sweetening process: An industrial case study	25
CFD numerical simulation of standalone sand screen erosion due to gas-sand flow	25
The geochemical characteristics, origin, migration and accumulation modes of deep coal-measure gas in the west of Linxing block at the eastern margin of Ordos Basin	25
Real-time determination of rheological properties of high over-balanced drilling fluid used for drilling ultra-deep gas wells using artificial neural network	25
The ungrind and grinded effects on the pore geometry and adsorption mechanism of the coal particles	25
Nanoconfined methane density over pressure and temperature: Wettability effect	25
Integrated wireline log and seismic attribute analysis for the reservoir evaluation: A case study of the Mount Messenger Formation in Kaimiro Field, Taranaki Basin, New Zealand	25
Gas hydrate nucleation and growth in the presence of water-soluble polymer, nonionic surfactants, and their mixtures	25
Characterization of pore structure of tight sandstone reservoirs based on fractal analysis of NMR echo data	25
Effects of different amin-based core-shell magnetic NPs on CO2 capture using NMP solution at high pressures	25
A detailed morphology investigation on the effects of mixed anionic and nonionic surfactants on methane hydrate formation and dissociation	25
Effect of water-based working fluid imbibition on static and dynamic compressive properties of anisotropic shale	24
Highly permeable innovative PDMS coated polyethersulfone membranes embedded with activated carbon for gas separation	24
Influence of cryogenic liquid nitrogen cooling and thermal shocks on petro-physical and morphological characteristics of Eagle Ford shale	24
Modified Peng-Robinson equation of state for CO2/hydrocarbon systems within nanopores	24
Experimental study on the anisotropy of the effective stress coefficient of sandstone under true triaxial stress	24
Nonlinear finite element analysis on the sealing performance of rubber packer for hydraulic fracturing	24
Fracture penetration and proppant transport in gas- and foam-fracturing	24
Pressure performance of multi-stage fractured horizontal well with stimulated reservoir volume and irregular fractures distribution in shale gas reservoirs	24
Numerical simulation of hydraulic fracturing based on two-dimensional surface fracture morphology reconstruction and combined finite-discrete element method	24
Self-healing hydrogels and their action mechanism in oil–gas drilling and development engineering: A systematic review and prospect	24
Local buckling failure analysis of high strength pipelines containing a plain dent under bending moment	24
Systematic sensitivity analysis of cuttings transport in drilling operation using computational fluid dynamics approach	24
ROP and TOB optimization using machine learning classification algorithms	24
An insight into pore-network models of high-temperature heat-treated sandstones using computed tomography	24
Numerical reactive flow transport simulation on core samples during acid fracturing in carbonaceous shale	24
Energy, exergy and economic (3E) evaluation of CO2 capture from natural gas using pyridinium functionalized ionic liquids: A simulation study	24
Hybrid machine learning algorithms to predict condensate viscosity in the near wellbore regions of gas condensate reservoirs	24
Numerical simulation of fracture initiation, propagation and fracture complexity in the presence of multiple perforations	24
Examining the relationship between Tmax and vitrinite reflectance: An empirical comparison between thermal maturity indicators	24
Influence of clay minerals and cementation on pore throat of tight sandstone gas reservoir in the eastern Ordos Basin, China	24
Microbiologically influenced corrosion of carbon steel pipeline in shale gas field produced water containing CO2 and polyacrylamide inhibitor	24
The Role of Time Lapse(4D) Seismic Technology as Reservoir Monitoring and Surveillance Tool: A Comprehensive Review	23
Hydraulic fracturing characteristics and evaluation of fracturing effectiveness under different anisotropic angles and injection rates: An experimental investigation in absence of confining pressure	23
Pore-scale influence of methane hydrate on permeability of porous media	23
Semi-analytical modeling of transient pressure behaviour for a fractured vertical well with hydraulic/natural fracture networks by considering stress-sensitive effect	23
Dissolution versus cementation and its role in determining tight sandstone quality: A case study from the Upper Paleozoic in northeastern Ordos Basin, China	23
Stress shadow effects and microseismic events during hydrofracturing of multiple vertical wells in tight reservoirs: A three-dimensional numerical model	23
Experimental research of the surfactant effect on seepage law in coal seam water injection	23
Microscopic distribution and dynamic variation of water under stress in middle and high rank coal samples	23
CO2 absorption/desorption in aqueous DEEA/MDEA and their hybrid solutions with sulfolane	23
Effects of waxes and asphaltenes on CO2 hydrate nucleation and decomposition in oil-dominated systems	23
Effects of testing method, lithology and fluid-rock interactions on shale permeability: A review of laboratory measurements	23
An integrated petrophysical and geomechanical characterization of Sembar Shale in the Lower Indus Basin, Pakistan, using well logs and seismic data	23
A brittleness index evaluation method for weak-brittle rock by acoustic emission technique	23
A review of recent advances and prospects on nanocellulose properties and its applications in oil and gas production	23
Population-balance modeling of CO2 foam for CCUS using nanoparticles	23
Experimental investigation and mathematical modelling of shale gas adsorption and desorption hysteresis	23
The development of leak detection model in subsea gas pipeline using machine learning	23
Quantitative analysis of pore structure and permeability characteristics of sandstone using SEM and CT images	23
CH4 recovery and CO2 sequestration from hydrate-bearing clayey sediments via CO2/N2 injection	23
Towards a fundamental understanding of biopolymers and their role in gas hydrates: A review	23
A three components thixotropic agent to enhance the thixotropic property of natural gas well cement at high temperatures	23
Numerical investigation of complex hydraulic fracture network in naturally fractured reservoirs based on the XFEM	22
A review on polymer-nanofiller composites in developing coated sand proppants for hydraulic fracturing	22
Evaluation of enhanced coalbed methane recovery and carbon dioxide sequestration potential in high volatile bituminous coal	22
Coupling rate of penetration and mechanical specific energy to Improve the efficiency of drilling gas wells	22
Pore structures of shale cores in different tectonic locations in the complex tectonic region: A case study of the Niutitang Formation in Northern Guizhou, Southwest China	22
Liquefied synthetic methane from ambient CO2 and renewable H2 - A technoeconomic study	22
Effects of permeability anisotropy on coal mine methane drainage performance	22
Effect of temperature on the electrochemical pitting corrosion behavior of 316L stainless steel in chloride-containing MDEA solution	22
Coupled wellbore–reservoir heat and mass transfer model for horizontal drilling through hydrate reservoir and application in wellbore stability analysis	22
Empirical methods of decline-curve analysis for shale gas reservoirs: Review, evaluation, and application	22
Experimental study of the influence of water-based fracturing fluids on the pore structure of coal	22
Effects of temperature on the corrosion behaviour of X70 steel in CO2-Containing formation water	22
Mechanical properties of remolded hydrate-bearing clayey-silty sediments	22
Glutamine functionalized iron oxide nanoparticles for high-performance carbon dioxide absorption	22
CH4, CO2, N2 diffusion in Bowen Basin (Australia) coal: relationship between sorption kinetics of coal core and crushed coal particles	22
Anisotropic characteristics of the energy index during the shale failure process under triaxial compression	21