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A series of interactive experiments are conducted to analyze the drag reduction technology with a rotating disk apparatus that combines microgroove structure and drag‐reducing additives including polyethylene oxide (PEO), cetyltrimethyl ammonium chloride (CTAC), and sodium salicylate (NaSal). By varying the disk type, concentration of drag‐reducing additives, temperature, and Reynolds number (Re), the corresponding drag reduction rates are obtained effectively. The experimental results indicate that adding CTAC strengthens the heat degradation and shear resistance of PEO; while PEO can enhance the ability of CTAC to form micellar structures and balance energy distribution at low concentrations. Moreover, the synergistic effect of these two additives presents a better drag reduction performance with a maximum drag reduction rate of 24.1%; while the microgroove structure enhances the effect of active drag reduction. Therefore, the combination of active and passive drag reduction technology broadens the application of energy saving and consumption reduction in hydraulic rotating machinery. [ABSTRACT FROM AUTHOR]

In the practical application of hydraulic rotating machinery, it is essential to thoroughly explore drag reduction and rheological characteristics of drag-reducing additives to optimize machinery efficiency and reduce equipment consumption. This paper combines simulation and experimental approaches to investigate the drag-reduction performance and rheological properties of drag-reducing additives. Numerical simulations are initially conducted to investigate the shear-thinning properties of drag-reducing fluid and explore variations in drag-reduction rate. Turbulent phenomena characteristics are described by analyzing turbulent statistical quantities. Subsequently, the rheological behaviors of polyethylene oxide (PEO), cetyltrimethyl ammonium chloride (CTAC), and their mixed solutions under different conditions are scrutinized using a rotational rheometer. The findings indicate that the drag reduction effect amplifies as the rheological index n and characteristic time λ decrease. The numerical simulations show a maximum drag reduction rate of 20.18%. In rheological experiments, a three-stage viscosity variation is observed in single drag-reducing additives: shear thickening, shear thinning, and eventual stabilization. Composite drag-reducing additives significantly reduce the apparent viscosity at low shear rates, thereby strengthening the shear resistance of the system. [ABSTRACT FROM AUTHOR]

The primary purpose of the present study is to investigate the unsteady flow and heat transfer characteristics of non-Newtonian power-law fluid over an oscillating flat plate. The power-law fluid model is employed to distinguish the non-Newtonian fluid behavior, which has wide applications in nature and technology, such as crude oil exploitation, polymer processing and some bio applications. In this work, the governing equations are set up using the non-Newtonian fluid model. The radial basis function collocation method (RBFCM) and the finite element method (FEM) are used to solve the coupled equations. The numerical results of the fluid velocity and fluid temperature fields are analyzed in detail. For authentication of the proposed schemes, the results are compared with earlier research works. To further verify the validity of the FEM and the RBFCM results, the flow behavior of crude oil was studied and the obtained results were found to be consistent with each other using both methods. Our results provide further guidance for evaluation aspects dealing with crude oil in a pipe, which are basic tools in oil and gas explorations. [ABSTRACT FROM AUTHOR]

The primary purpose of the present study is to investigate the unsteady flow and heat transfer characteristics of non-Newtonian power-law fluid over an oscillating flat plate. The power-law fluid model is employed to characterize the non-Newtonian fluid behavior, which has wide applications in nature and technology, such as crude oil exploitation, polymer processing and some bio applications. In this study, the coupled governing equations are set up using the non-Newtonian fluid model. The radial basis function collocation method (RBFCM) and the finite element method (FEM) are used to solve the coupled equations. The simulation results on the fluid velocity and temperature distribution are analyzed in detail. For authentication of the proposed schemes, the numerical results are compared with earlier research works. To further verify the validity of the FEM and the RBFCM results, the flow behavior of crude oil was studied and the obtained results were found to be consistent with each other using both methods. Our results provide further guidance for evaluation aspects dealing with crude oil in a pipe, which are basic tools in oil and gas explorations. [ABSTRACT FROM AUTHOR]

AbstractThe efficient development of oil resources is significant for alleviating the increasingly serious contradiction between oil supply and demand and ensuring national oil security. Surfactant flooding technology is one of the essential methods to enhance oil recovery and has been widely used in oil and gas development. The screening and development of traditional surfactants for oil displacement are mainly focused on reducing interfacial tension based on the theory of capillary number while ignoring the emulsification effect of surfactants. For different types of residual oil/remaining oil, the main contradictions faced by the target reservoir should be thoroughly analyzed to clarify whether the performance of surfactants used for oil displacement is mainly to reduce interfacial tension or strong emulsification capacity, and then screen surfactants suitable for reservoir characteristics and crude oil properties. In this article, the principle and application of surfactant flooding technology are reviewed from two aspects of interfacial tension and emulsification performance, the interrelationship between interfacial tension and emulsification capacity is explored, and the evaluation indicators and existing problems of surfactant used for oil displacement are analyzed in detail. Most of the evaluation methods for emulsification in the past were based on water extraction rate. A method for evaluating the emulsification ability of surfactants to crude oil is introduced. It is expected to provide scientific guidance for the screening and development of surfactants for oil displacement. [ABSTRACT FROM AUTHOR]

Abstract Various formulas describing non-Darcy flow have been applied to quantify fluid flow in natural geological media, while there is no universal law or formula that can reliably describe the complex relationship between the flow rate and the pressure gradient for single-phase fluid flow in natural oil/gas reservoirs. This study aims at proposing and evaluating a spatial fractional Darcy's law model for the calculation of the flow rate of fluids in natural heterogeneous oil/gas reservoirs at any scale. Experiments documented in literature are revisited to identify the transport characteristics of fluid flow in natural media with complex heterogeneity and structures, including for example discontinuous and/or interconnected pores. The fitting exercises show that the spatial fractional Darcy's law can felicitously depict the flow properties and match well the experimental data shown in seepage curves. The model parameters can also be reasonably simplified, given the possible physical interpretation closely related to the medium structure. Highlights • A spatial fractional Darcy's law to calculate the flow rate in oil/gas reservoirs. • Fractional derivative model can well depict the experimental data. • Model parameters are simplified by employing the spatial fractional model. [ABSTRACT FROM AUTHOR]

Variable-order (VO) fractional differential equations (FDEs) with a time (t), space (x) or other variables dependent order have been successfully applied to investigate time and/or space dependent dynamics. This study aims to provide a survey of the recent relevant literature and findings in primary definitions, models, numerical methods and their applications. This review first offers an overview over the existing definitions proposed from different physical and application backgrounds, and then reviews several widely used numerical schemes in simulation. Moreover, as a powerful mathematical tool, the VO-FDE models have been remarkably acknowledged as an alternative and precise approach in effectively describing real-world phenomena. Hereby, we also make a brief summary on different physical models and typical applications. This review is expected to help the readers for the selection of appropriate definition, model and numerical method to solve specific physical and engineering problems. [ABSTRACT FROM AUTHOR]

Fractional-derivative models have been developed recently to interpret various hydrologic dynamics, such as dissolved contaminant transport in groundwater. However, they have not been applied to quantify other fluid dynamics, such as gas transport through complex geological media. This study reviewed previous gas transport experiments conducted in laboratory columns and real-world oil–gas reservoirs and found that gas dynamics exhibit typical sub-diffusive behavior characterized by heavy late-time tailing in the gas breakthrough curves (BTCs), which cannot be effectively captured by classical transport models. Numerical tests and field applications of the time fractional convection–diffusion equation (fCDE) have shown that the fCDE model can capture the observed gas BTCs including their apparent positive skewness. Sensitivity analysis further revealed that the three parameters used in the fCDE model, including the time index, the convection velocity, and the diffusion coefficient, play different roles in interpreting the delayed gas transport dynamics. In addition, the model comparison and analysis showed that the time fCDE model is efficient in application. Therefore, the time fractional-derivative models can be conveniently extended to quantify gas transport through natural geological media such as complex oil–gas reservoirs. [ABSTRACT FROM AUTHOR]

This study is mainly to explore gas transport process in heterogeneous media, which is to lay the foundation for oil-gas exploitation and development. Anomalous transport is observed to be ubiquitous in complex geological formations and has a paramount impact on petroleum engineering. Simultaneously, the random motion of particles usually exhibits obvious path- and history- dependent behaviors. This paper investigates the time-space fractional derivative models as a potential explanation for the time memory of long waiting time and the space non-locality of large regional-scale. A one-dimensional fractional advection-dispersion equation (FADE) based on fractional Fick’s law is firstly used to accurately describe the transport of Carbon dioxide (CO2) in complex media. The new fractional Darcy-advection-dispersion equation (FDADE) model has subsequently been proposed to make a comparison with FADE model and demonstrate its physical mechanism. Finally, the priori estimation of the parameters (fractional derivative index) in fractional derivative models and corresponding physical explanation are presented. Combined with experimental data, the numerical simulations show the fractional derivative models can well characterize the heavy-tailed and early breakthrough phenomenon of CO2 transport. [ABSTRACT FROM AUTHOR]

This paper aims to numerically investigate the thermodynamic effect on attached cavitation and cavitation-vortex interaction around a NACA0015 hydrofoil. Based on the isothermal cavitation model, the compressibility and thermodynamic effect are considered by adding the state equation and modifying the evaporation and condensation source term in the mass transport equation. The thermodynamic effect on the hydrodynamic performance and the cavity volume fluctuations, the temporal evolution of the unsteady cavitation, the temporal evolution of vortex structures in the hydrofoil wake, and the cavitation-vortex interaction are presented. The main features of the unsteady quasi-periodic cavitation behavior are illustrated for the isothermal and non-isothermal conditions. The new omega vortex identification method depicts the influence of the thermodynamic effect on the shedding structure around the wake of a hydrofoil. Furthermore, the cavitation-vortex interaction is examined to show the relationship. • The predicted lift coefficients and the cavity volume change quasi-periodically in both isothermal and non-isothermal conditions in the typical cycles. • The coupling mechanism of thermal effect, vorticity, and cavitation is examined. • The evolution of cavitation is closely related to the vortex structure. • The vortex stretching term, the dilatation term and the baroclinic torque term play a major role in the cavitation-vortex interactions. [ABSTRACT FROM AUTHOR]