Viscoelastic Mixtures Research Articles

RESEARCH AND IMPROVEMENT OF THE QUALITY OF OIL AND GAS WELL KILLING TECHNOLOGY THROUGH THE USE OF VISCOELASTIC COMPOSITIONS

Currently, many enterprises of the oil and gas industry are faced with such a problem as a significant decrease in the productivity coefficient of the well after repair work. As a result of such a complication, the process of normalization of the bottom of absorbing wells becomes more difficult, and the period of underground repair increases. The most developing direction in well jamming technology is the use of viscoelastic compositions, since this method eliminates the risk of penetration of the jamming fluid into the collector. Viscoelastic compositions are solutions of crosslinked polymers in the form of elastic gels with high viscosity and high shear stress. The compositions injected into the well limit the penetration of the jamming fluid into the bottom-hole zone of the formation and preserve its reservoir properties. The prepared formulations should take the form of a filling volume and gradually harden over a given time, but not turn into a solid composition.But, despite the high efficiency of using viscoelastic mixtures, this method of jamming has negative sides: premature structuring of the mixture, failure of downhole pumping equipment. The reason for this is the heterogeneous composition of the viscoelastic mixture. The choice of formulations for conducting a complex of laboratory studies implies work to determine the effective type of blocking composition and the choice of reagent brands.To clarify the conditions for the effective use of viscoelastic formulations and cooking technologies, an analysis of domestic and foreign experience in their application was carried out.During the research, optimal formulations of viscoelastic mixtures were selected that meet the requirements of well jamming technology at the «X» field. These samples are capable of forming strong cross-linked plugs that do not change the strength characteristics of the structure over time. To remove the composition of the silencing fluid from the borehole, the technology of dispersing viscoelastic mixtures using a hydroperite destructor was tested. After the introduction of the destructor, the ionic bonds of the composition are destroyed, which leads to a decrease in viscosity to minimum values and the possibility of its complete removal from the formation.

Impacts of wheat bran on the structure of the gluten network as studied through the production of dough and factors affecting gluten network

Wheat flour with high protein quality is utilized for a wide scope of heated items particularly bread because of the viscoelastic property of the wheat flour that exhibits both viscous and elastic characteristics when undergoing deformation. Wheat contains the gluten framing proteins that structure a viscoelastic. D-glucans is considered as one of the best hydrocolloids for their gelling capacity and ability to impart the viscosity of aqueous solutions. By framing this viscoelastic mixture, permits the air cell to join and opposes its blend. The blending procedure includes the blending of flour and different fixings with water and which is also affects the last item surface. The target of blending is to shape and form the gluten organizes into a viscoelastic, with the capacity to hold joined air. The acid and basic value of pH is important for every sector such as; food and chemical industries, some important bakery products, and pH (Biscuits; 7.0-7.2, Baker’s yeast bread; 5.3-5.8 and Sourdough bread; 3.8-4.6, etc.). Gluten makes them flexible enough to expand as a little inflatable without damaging the air pocket dividers before the bread is proven. The flavor and crunchy texture of wheat pieces of bread sharpen our appetite and satisfy our basic human cravings for comfort as well as nutrition. At the point, when flour produced using pounding these grains are blended in with water, the two proteins join and structure gluten and without water, gluten isn't shaped. According to its summary article, it tries to clarify how the chemical compatible properties of dough work to make and preserve gluten framing proteins. Wheat bran increased dough stability by raising the farinograph property, enhanced dough elasticity by raising elastic modulus and decreased tan of the dough at all gluten contents, according to viscoelastic profiles. The findings help to understand the mode of action of the modification on wheat bran and the formation of the gluten network.

Evaluation of the cracking and aging susceptibility of asphalt mixtures using viscoelastic properties and master curve parameters

Aging can significantly affect the performance of asphalt mixtures, causing increase in stiffness, reduction in relaxation capability and increase in cracking susceptibility. It is also well known that fundamental viscoelastic properties are used for design and modelling of asphalt mixtures and pavement structures to addressing rutting, fatigue and thermal cracking concerns. The objective of this paper is to study how the viscoelastic properties of asphalt mixture change over time, and evaluate and identify the cracking and aging susceptibility of asphalt mixtures with different mix variables during material selection and mixture design. Ten mixtures are evaluated using different laboratory conditioning protocols to simulate a range of aging levels in the field. The complex modulus test is then conducted on the lab aged mixtures to measure the viscoelastic properties in order to construct the dynamic modulus and phase angle master curves. The mixture Glover-Rowe (G-Rm) parameter and the shape parameters of the dynamic modulus and phase angle master curves, including inflection point frequency (−β/γ), difference between the glassy modulus and the inflection point modulus (γ), peak value of phase angle (a) and the horizontal position (frequency) of the peak phase angle value (c), are determined and evaluated for the mixtures with different aging conditions and mix variables. The study indicates the ability of the G-Rm parameter and all the master curve shape parameters to capture the effect of different aging conditions on linear viscoelastic mixture properties, as well as the cracking and aging susceptibility of asphalt mixtures.

Potential method in the linear theory of viscoelastic porous mixtures

In the present paper, the linear theory of viscoelasticity for binary porous mixtures is considered. The fundamental solution of the system of steady vibration equations is constructed, and its basic properties are established. Green’s identities of this theory are obtained. The uniqueness theorems for classical solutions of the internal and external basic boundary value problems (BVPs) of steady vibrations are proved. The surface and volume potentials are introduced, and their basic properties are established. The determinants of symbolic matrices of the singular integral operators are calculated explicitly, and the BVPs are reduced to the always solvable singular integral equations for which Fredholm’s theorems are valid. Finally, the existence theorems for classical solutions of the internal and external BVPs of steady vibrations are proved by means of the potential method and the theory of singular integral equations.

A problem with viscoelastic mixtures: numerical analysis and computational experiments

ABSTRACT In this paper, we study, from the numerical point of view, a dynamic problem involving a mixture of two viscoelastic solids. The mechanical problem is written as a system of two coupled partial differential equations. Its variational formulation is derived and an existence and uniqueness result, and an energy decay property, are recalled. Then, fully discrete approximations are introduced by using the classical finite element method and the implicit Euler scheme. A discrete stability property and a priori error estimates are shown, from which we deduce the linear convergence of the algorithm. Finally, some numerical simulations, including examples in one and two dimensions, are presented to show the accuracy of the approximation and the behaviour of the solution.

Effect of surfactant chemistry on drilling mud performance

Drilling muds used in deepwater operations experience large variations in temperature, as well as pressure, when flowing through the different geometric conduits that are; the drill string, openhole (casing) - riser annuli present when drilling offshore. They behave as viscoelastic mixtures due to the suspension- and emulsion-dispersions used in their preparation. As a consequence, they display liquid-like and solid-like flow properties depending on the time scale of deformation they are subjected to. In addition to rate of deformation, environmental conditions such as temperature, and to a lesser extent pressure, are known to affect their rheological behavior.Nonionic surfactants are commonly used upstream in the stabilization of emulsions in drilling fluids, and in some instances as wetting agents. Inversion of pure emulsions systems stabilized by nonionic surfactants, from one type to another, as a result of temperature changes has been investigated and finds great application in the food and chemical industries.In this study, assessment of phase inversion occurrence in drilling muds, as well as resulting changes in their rheology was experimentally investigated at temperatures ranging from 0 to 90. Water- (WBM) and oil-based muds (OBM) samples were prepared using nonionic and ionic surfactants. Effect of surfactant nature and dispersed phase volume fraction on fluid loss properties of the different mud samples was equally carried at room temperature.Phase inversion of WBM samples stabilized by nonionic polyoxyethylene oleyl ether surfactants was observed for the range of conditions covered in the experimental investigation. Differences in flow behavior and apparent viscosity of the sample, as a result of inversion from one mud type to another, was equally noted.On one hand, the results underscored the importance of assessing potential application of nonionic surfactants to induce phase inversion in drilling fluids used for offshore operations. On the other hand, setbacks observed in the use of complex fluids for offshore drilling could possibly be accounted by the unknown occurrence of this phenomenon.

Well-posedness and exponential stability in binary mixtures theory for thermoviscoelastic diffusion materials

A nonlinear theory is derived for a thermoviscoelastic diffusion composite which is modeled as a binary mixture consisting of two Kelvin–Voigt viscoelastic materials. First, the basic equations of the nonlinear theory of heat and diffusion conducting viscoelastic mixtures are derived in Lagrangian description. Then, the theory is linearized and field equations are given for both anisotropic and isotropic centrosymmetric materials. We establish the necessary and sufficient conditions to get a dissipation inequality for isotropic centrosymmetric materials. With the help of the semigroup theory of linear operators, we establish the suitable framework where the linear problem is well posed. Finally, we prove that generically the solution decreases exponentially thanks to the viscous dissipation effects of the constituents.

Optimal bounds for attenuation of elastic waves in porous fluid-saturated media.

Explicit expressions for bounds on the effective bulk and shear moduli of mixture of an elastic solid and Newtonian fluid are derived. Since in frequency domain the shear modulus of the Newtonian fluid is complex valued, the effective mixture moduli are, in general, also complex valued and, hence, the bounds are curves in the complex plane. From the general expressions for bounds of effective moduli of viscoelastic mixtures, it is shown that effective bulk and shear moduli of such mixtures must lie between the real axis and a semicircle in the upper half-plane connecting formal lower and upper Hashin-Shtrikman bounds of the mixture of the solid and inviscid fluid of the same compressibility as the Newtonian fluid. Furthermore, it is shown that the bounds on the effective complex bulk and shear moduli of the mixture are optimal; that is, the moduli corresponding to any point on the bounding curves can be attained by the Hashin sphere assemblage penetrated by a random distribution of thin cracks. The results are applicable to a variety of solid/fluid mixtures such as fluid-saturated porous materials and particle suspensions.

On the Viscoelastic Mixtures of Solids

In this paper we analyze an homogeneous and isotropic mixture of viscoelastic solids. We propose conditions to guarantee the coercivity of the internal energy and also of the dissipation, first in dimension two and later in dimension three. We obtain an uniqueness result for the solutions when the dissipation is positive and without any hypothesis over the internal energy. When the internal energy and the dissipation are both positive, we prove the existence of solutions as well as their analyticity. Exponential stability and impossibility of localization of the solutions are immediate consequences.

Plane waves and uniqueness theorems in the theory of viscoelastic mixtures

In the present paper, the linear theory of binary viscoelastic mixtures is considered. The basic properties of plane harmonic waves are established. Green’s first identity for 3D bounded and unbounded domains is obtained. On the basis of this identity the uniqueness theorems of regular (classical) solutions of the boundary value problems (BVPs) of steady vibrations are proved. Then these theorems are established in the quasi-static case. Finally, the uniqueness theorems for the first internal and external BVPs of steady vibrations in general and quasi-static cases are proved under weak condition on the viscoelastic constants.

Анализ и обоснование выбора составов для ограничения водопритоков при заканчивании скважин

The aim of the work is to increase efficiency of well completion under conditions of water inflow by use of viscoelastic gas-liquid mixtures to shut-off permeable formations. At present, there is an increase in rates of drilling of wells in abnormal conditions, such as abnormal formation pressure (both low and high), unstable rocks, rocks of high hardness, permafrost etc. The quality of well construction in such conditions influences subsequent development and operation of the field greatly. Aquifer isolation is an extremely important issue due to the fact that from them water breaks through in production wells which has a significant impact on quality of fluid produced. The main solution for water breakthrough challenge is formation isolation, which is performed by use of various plugging material. At present, there are many mixtures that limit water inflows such as fast-setting plugging materials, gel-cement mixtures, polymeric swelling nets, latexes, synthetic resins, viscoelastic mixtures, materials for selective isolation etc. Under conditions of abnormally low reservoir pressures, it is important to consider density when selecting drilling fluids and plugging materials. Therefore, it is recommended to use screens based on viscoelastic three-phase stabilized gas-liquid mixtures for temporary blockage of permeable aquifer. With use of such mixtures liquid penetration flow rate is significantly reduced compared to other viscoelastic systems, which makes it possible to increase reliability of temporary isolation of aquifers. The paper presents an analysis of domestic and foreign experience of blocking permeable formations by different mixtures. Three-phase blocking mixtures are studied and requirements for them are generalized.

Numerical analysis of a viscoelastic mixture problem

In this paper, we study, from the numerical point of view, a mixture problem involving a viscoelastic material and an elastic one. The mechanical problem is written as a linear system of two coupled hyperbolic partial differential equations. An existence and uniqueness result and an energy decay property are recalled. Then, fully discrete approximations are introduced by using the finite element method to approximate the spatial variable and the backward Euler scheme to discretize the time derivatives. A priori error estimates are proved from which, under suitable regularity conditions, the linear convergence of the algorithm is derived. Finally, some numerical simulations are presented to demonstrate the accuracy of the approximations and the behaviour of the solutions.

Primary and secondary instabilities of viscoelastic mixtures saturating a porous medium: Application to separation of species

By exploiting the coupling between convection and thermodiffusion, we examine in this study the possibility to perform separation of species in viscoelastic solutions saturating a porous cavity heated from below. We analyze the thermal convection thresholds and linear characteristics of the primary and secondary instabilities for binary mixtures with viscoelastic properties taking into account the Soret effect and the lateral confinement of the medium. We focus on viscoelastic mixtures with positive separation ratio ψ, a dimensionless parameter which represents the mass contribution divided by the temperature contribution to buoyancy forces and is proportional to the strength of the Soret effect. In that case, the lighter component of the viscoelastic solution is driven into the direction of the bottom of the cavity, thus further enhancing the density gradient. We find that for sufficiently elastic mixtures, oscillatory instability may be sustained for small positive ψ contrary to the case of Newtonian mixtures, where oscillatory convection occurs only for ψ<0. For ψ>ψmono>0 a stationary bifurcation leads to a monocellular flow at the onset of convection, with a horizontal stratification of the concentration, allowing separation of species between the two ends of the cell. The optimum of separation is obtained for a particular value Raopt of the Rayleigh number. The linear stability analysis of the monocellular flow is performed, and the critical conditions above which the flow becomes unstable are determined. The combined influence of the viscoelastic parameters and the lateral confinement on the characteristics of the secondary instability is quantified as a function of ψ. It is found that, depending on the lateral confinement, the monocellular flow may lose its stability via a Hopf bifurcation giving rise to transversal travelling rolls or via a stationary bifurcation to fixed longitudinal rolls. When the secondary bifurcation is a Hopf one, two regimes of convection are identified. While the viscoelastic mechanism plays a key role in one regime, the other regime is dominated by the Soret effect. Independently of the nature of the secondary instability pattern, it is shown that the monocellular flow remains stable beyond Raopt indicating that optimal separation of species is possible for viscoelastic solutions.

On uniqueness and continuous dependence of solutions in viscoelastic mixtures

This note deals with the isothermal linear theory of porous viscoelastic mixtures. Questions of uniqueness and continuous dependence for solutions of various classes of initial boundary value problems in mixtures consisting of two constituents: a porous elastic solid and a porous Kelvin–Voigt material are studied. The Lagrange identity and Logarithmic convexity methods are used to establish uniqueness and continuous dependence results, with no definiteness assumptions upon the internal energy.

Fundamental solution in the theory of viscoelastic mixtures

Fundamental solution in the theory of viscoelastic mixtures

Micromechanical finite element framework for predicting viscoelastic properties of asphalt mixtures

A micromechanical finite element (FE) framework was developed to predict the viscoelastic properties (complex modulus and creep stiffness) of the asphalt mixtures. The two-dimensional (2D) microstructure of an asphalt mixture was obtained from the scanned image. In the mixture microstructure, irregular aggregates and sand mastic were divided into different subdomains. The FE mesh was generated within each aggregate and mastic subdomain. The aggregate and mastic elements share nodes on the aggregate boundaries for deformation connectivity. Then the viscoelastic mastic with specified properties was incorporated with elastic aggregates to predict the viscoelastic properties of asphalt mixtures. The viscoelastic sand mastic and elastic aggregate properties were inputted into micromechanical FE models. The FE simulation was conducted on a computational sample to predict complex (dynamic) modulus and creep stiffness. The complex modulus predictions have good correlations with laboratory uniaxial compression test under a range of loading frequencies. The creep stiffness prediction over a period of reduced time yields favorable comparison with specimen test data. These comparison results indicate that this micromechanical model is capable of predicting the viscoelastic mixture behavior based on ingredient properties.

On the Theory of Viscoelastic Mixtures and Stability

A theory is developed for binary mixtures of viscoelastic materials. The basic equations of a nonlinear theory of heat conducting viscoelastic mixtures are derived in Lagrangian description. The individual components of the mixture are modeled as Kelvin—Voigt viscoelastic materials. A nonlinear constitutive relation which generalizes Darcy's law is derived. The linearized version of the theory is established. In the present theory the diffusive force depends on relative displacement and relative velocity. Stability results are presented in the context of materials which are non-conductor of heat.

A Theory of Porous Thermoviscoelastic Mixtures

In this article we derive a theory for binary mixtures of viscoelastic bodies. The individual components of the mixture are modelled as porous Kelvin-Voigt viscoelastic materials. First, the basic equations of the nonlinear theory of heat conducting viscoelastic mixtures are derived in lagrangian description. A frame independent nonlinear constitutive relation which generalizes the Darcy's law is derived. Then, the theory is linearized and a uniqueness result is presented. Finally, an exponential decay estimate of the solutions is established.

Some Results in the Dynamics of Viscoelastic Mixtures

The present article studies some qualitative properties of solutions in the dynamics of viscoelastic mixtures made by two constituents: a porous elastic solid and a viscous fluid. In this sense, some results concerning the theory of semigroups of linear operators are used to establish the existence and uniqueness of the weak solutions of the initial boundary value problems associated with the linear theory. The continuous dependence problem upon initial data and supply terms is also investigated. Then, the temporal behavior is studied in terms of the Cesáro means of various parts of the total energy. The relations that describe the asymptotic behavior of mean energies are established by using some Lagrange—Brun identities.

A New Algorithm for Determination of Crack Growth Path in HMA Materials

ABSTRACT In this paper, a new algorithm is presented for determination of the crack growth path in hot mix asphalt (HMA) materials. In a newly developed fracture simulator, the pavement structure is modeled with a viscoelastic boundary element method, which provides an attractive alternative to finite element-based methods for modeling crack initiation and growth. According to the HMA fracture mechanics, a fundamental energy-based threshold is used to determine crack growth and the direction of crack growth, and viscoelastic mixture properties are used to determine the rate of crack growth. To determine where a crack propagates, a grid in the critical zone is defined to cover a range of possible crack growth directions and locate the direction of the maximum dissipated creep strain energy (DCSE). The crack will propagate in the direction of the maximum DCSE when the DCSE in this direction reaches the damage threshold. The fracture simulator is shown to predict top-down crack growth patterns in hot mix asphalt pavements observed in the field.