Experimental study on solid particle migration and production behaviors during marine natural gas hydrate dissociation by depressurization

Sand production is one of the main obstacles restricting gas extraction efficiency and safety from marine natural gas hydrate(NGH)reservoirs.Particle migration within the NGH reservoir dominates sand production behaviors,while their relationships were rarely reported,severely constrains quantitative evaluation of sand production risks.This paper reports the optical observations of solid particle migration and production from micrometer to mesoscopic scales conditioned to gravel packing during depressurization-induced NGH dissociation for the first time.Theoretical evolutionary modes of sand migration are established based on experimental observations,and its implications on field NGH are comprehensively discussed.Five particle migration regimes of local borehole failure,continuous collapse,wormhole expansion,extensive slow deformation,and pore-wall fluidization are proved to occur during depressurization.The types of particle migration regimes and their transmission modes during depressurization are predominantly determined by initial hydrate saturation.In contrast,the depressurization mainly dominates the transmission rate of the particle migration regimes.Furthermore,both the cumulative mass and the medium grain size of the produced sand decrease linearly with increasing initial methane hydrate(MH)saturation.Discontinuous gas bubble emission,expansion,and explosion during MH dissociation delay sand migration into the wellbore.At the same time,continuous water flow is a requirement for sand production during hydrate dissociation by depressurization.The experiments enlighten us that a constitutive model that can illustrate visible particle migration regimes and their transmission modes is urgently needed to bridge numerical simulation and field applications.Optimizing wellbore layout positions or special reservoir treatment shall be important for mitigating sand production tendency during NGH exploitation.

MXene:From synthesis to environment remediation

A new burgeoning family of two-dimensional(2D)transition metal carbides/nitrides,better known as MXenes,have received extensive attention because of their distinct properties,such as metallic conductivity,good hydrophilicity,large surface area,good mechanical stability,and biodegradability.About 40 different MXenes have been synthesized,and dozens more structures and properties have been theoretically predicted.However,the recent progress in MXenes development is not well covered in chronological order based on different applications.This review article focuses on emerging synthesis methods,the properties of MXenes,and mainly the applications of MXenes and MXene-based material family in environmental remediation,a comprehensive review of gaseous and aqueous pollutants treatment.

Constitutive model for monotonic and cyclic responses of loosely cemented sand formations

This paper presents a model to simulate the monotonic and cyclic behaviours of weakly cemented sands.An elastoplastic constitutive model within the framework of bounding surface plasticity theory is adopted to predict the mechanical behaviour of soft sandstone under monotonic and cyclic loadings. In this model, the loading surface always passes through the current stress state regardless of the type of loading. Destruction of the cementation bonds by plastic deformation in the model is considered as the primary mechanism responsible for the mechanical degradation of loosely cemented sands/weak rock.To model cyclic response, the unloading plastic and elastic moduli are formulated based on the loading/reloading plastic and elastic moduli. The proposed model was implemented in FLAC2D and evaluated against laboratory triaxial tests under monotonic and cyclic loadings, and the model results agreed well with the experimental observations. For cyclic tests, hysteresis loops are captured with reasonable accuracy.

Evaluation of numerical schemes for capturing shock waves in modeling proppant transport in fractures

In petroleum engineering, the transport phenomenon of proppants in a fracture caused by hydraulic fracturing is captured by hyperbolic partial differential equations(PDEs). The solution of this kind of PDEs may encounter smooth transitions, or there can be large gradients of the field variables. The numerical challenge posed in a shock situation is that high-order finite difference schemes lead to significant oscillations in the vicinity of shocks despite that such schemes result in higher accuracy in smooth regions. On the other hand, first-order methods provide monotonic solution convergences near the shocks,while giving poorer accuracy in the smooth regions.Accurate numerical simulation of such systems is a challenging task using conventional numerical methods. In this paper, we investigate several shock-capturing schemes.The competency of each scheme was tested against onedimensional benchmark problems as well as published numerical experiments. The numerical results have shown good performance of high-resolution finite volume methods in capturing shocks by resolving discontinuities while maintaining accuracy in the smooth regions. Thesemethods along with Godunov splitting are applied to model proppant transport in fractures. It is concluded that the proposed scheme produces non-oscillatory and accurate results in obtaining a solution for proppant transport problems.

Additive manufacturing of metallic and polymeric load-bearing biomaterials using laser powder bed fusion:A review

Surgical prostheses and implants used in hard-tissue engineering should satisfy all the clinical,mechanical,manufacturing,and economic requirements in order to be used for load-bearing applications.Metals,and to a lesser extent,polymers are promising materials that have long been used as load-bearing biomaterials.With the rapid development of additive manufacturing(AM)technology,metallic and polymeric implants with complex structures that were once impractical to manufacture using traditional processing methods can now easily be made by AM.This technology has emerged over the past four decades as a rapid and cost-effective fabrication method for geometrically complex implants with high levels of accuracy and precision.The ability to design and fabricate patient-specific,customized structural biomaterials has made AM a subject of great interest in both research and clinical settings.Among different AM methods,laser powder bed fusion(L-PBF)is emerging as the most popular and reliable AM method for producing load-bearing biomaterials.This layer-by-layer process uses a high-energy laser beam to sinter or melt powders into a part patterned by a computer-aided design(CAD)model.The most important load-bearing applications of L-PBF-manufactured biomaterials include orthopedic,traumatological,craniofacial,maxillofacial,and dental applications.The unequalled design freedom of AM technology,and L-PBF in particular,also allows fabrication of complex and customized metallic and polymeric scaffolds by altering the topology and controlling the macro-porosity of the implant.This article gives an overview of the L-PBF method for the fabrication of load-bearing metallic and polymeric biomaterials.

Numerical investigation of the hydraulic fracturing mechanisms in oil sands

This paper presents a numerical investigation of hydraulic fracturing in oil sands during cold water injection by considering the aspects of both geomechanics and reservoir fluid flow.According to previous studies,the low shear strengths of unconsolidated or weakly consolidated sandstone reservoirs significantly influence the hydraulic fracturing process.Therefore,classical hydraulic fracture models cannot simulate the fracturing process in weak sandstone reservoirs.In the current numerical models,the direction of a tensile fracture is predetermined based on in situ stress conditions.Additionally,the potential transformation of a shear fracture into a tensile fracture and the potential reorientation of a tensile fracture owing to shear banding at the fracture tip have not yet been addressed in the literature.In this study,a smeared fracture technique is employed to simulate tensile and shear fractures in oil sands.The model used combines many important fracture features,which include the matrix flow,poroelasticity and plasticity modeling,saturation-dependent permeability,gradual degradation of the oil sands as a result of dilative shear deformation,and the tensile fracturing and shear failure that occur with the simultaneous enhancement of permeability.Furthermore,sensitivity analyses are also performed with respect to the reservoir and geomechanical parameters,including the apparent tensile strength and cohesion of the oil sands,magnitude of the minimum and maximum principal stress,absolute permeability and elastic modulus of the oil sands and ramp-up time.All these analyses are performed to clarify the influences of these parameters on the fracturing response of the oil sands.

Relationship between rock macro-and micro-properties and wellbore breakout type

This study numerically investigates the effect of material micro-and macro-parameters on the failure mechanisms and geometry of a wellbore breakout.The analysis of the borehole breakout is essential in addressing wellbore stability,well completion,and sand production problems.The three-dimensional discrete element method(DEM)was used in the simulations.The numerical tool was used in numerical model simulations of drilling through sandstone in cubic samples at the laboratory scale subjected to pre-existing far-field stresses.Besides,a series of triaxial testing simulations were performed to relate the micromechanical parameters to the macromechanical material properties.The results showed that the geometry of the breakout is affected,among the material micro-parameters,by the particle contact modulus,bond normal and shear strengths,particle crushing strength,and particle size distribution.Further,it was found that the macro-parameters including Young’s modulus,friction and dilation angles,and uniaxial compression strength(UCS)also affect the type of breakout.