Zhenjiang You

Particle mobilization in porous media: temperature effects on competing electrostatic and drag forces

The fluid flow in natural reservoirs mobilizes fine particles. Subsequent migration and straining of the mobilized particles in rocks greatly reduce reservoir permeability and well productivity. This chain of events typically occurs over the temperature ranges of 20-40 degrees C for aquifers and 120-300 degrees C for geothermal reservoirs. However, the present study might be the first to present a quantitative analysis of temperature effects on the forces exerted on particles and of the resultant fines migration. Based on torque balance between electrostatic and drag forces acting on attached fine particles, we derived a model for the maximum retention concentration and used it to characterize the detachment of multisized particles from rock surfaces. Results showed that electrostatic force is far more affected than water viscosity by temperature variation. An analytical model for flow toward wellbore that is subject to fines migration was derived. The experiment-based predictive modeling of the well impedance for a field case showed high agreement with field historical data (coefficient of determination R-2=0.99). It was found that the geothermal reservoirs are more susceptible to fine particle migration than are conventional oilfields and aquifers.

Size-Exclusion Colloidal Transport in Porous Media--Stochastic Modeling and Experimental Study

Suspension, colloidal, and emulsion flow in rocks with particle size-exclusion may have a strong effect on the reservoir and on the well behavior during fines migration and production, drilling-fluid invasion into oil- or gas-bearing formations, or injection of seawater or produced water. The stochastic microscale equations for size-exclusion colloidal transport in porous media (PM) are derived. The proposed model includes the following new features: It accounts for the accessible flux in the expression for capture rate, it accounts for the increase of inlet concentration caused by the injected particles entering only the accessible area, and it accounts for the dilution of effluent accessible flux in the overall flux of the produced suspension.

Size exclusion deep bed filtration: Experimental and modelling uncertainties

A detailed uncertainty analysis associated with carboxyl-modified latex particle capture in glass bead-formed porous media enabled verification of the two theoretical stochastic models for prediction of particle retention due to size exclusion. At the beginning of this analysis it is established that size exclusion is a dominant particle capture mechanism in the present study: calculated significant repulsive Derjaguin-Landau-Verwey-Overbeek potential between latex particles and glass beads is an indication of their mutual repulsion, thus, fulfilling the necessary condition for size exclusion. Applying linear uncertainty propagation method in the form of truncated Taylors series expansion, combined standard uncertainties (CSUs) in normalised suspended particle concentrations are calculated using CSUs in experimentally determined parameters such as: an inlet volumetric flowrate of suspension, particle number in suspensions, particle concentrations in inlet and outlet streams, particle and pore throat size distributions. Weathering of glass beads in high alkaline solutions does not appreciably change particle size distribution, and, therefore, is not considered as an additional contributor to the weighted mean particle radius and corresponded weighted mean standard deviation. Weighted mean particle radius and LogNormal mean pore throat radius are characterised by the highest CSUs among all experimental parameters translating to high CSU in the jamming ratio factor (dimensionless particle size). Normalised suspended particle concentrations calculated via two theoretical models are characterised by higher CSUs than those for experimental data. The model accounting the fraction of inaccessible flow as a function of latex particle radius excellently predicts normalised suspended particle concentrations for the whole range of jamming ratios. The presented uncertainty analysis can be also used for comparison of intra- and inter-laboratory particle size exclusion data.

Method of Taylor Expansion Moment Incorporating Fractal Theories for Brownian Coagulation of Fine Particles

Abstract Fine particles aggregating into larger units or flocculation body is a random combination process. Increasing the size and density of flocculation body is the main approach to rapid particle removal or sedimentation in water. Aiming at the Brownian coagulation of fine particles, a new method of Taylor expansion moment construction of fractal flocs has been developed in this paper, incorporating the Taylor expansion approach based on the moment method and the fractal dimension of the floc structure originated from fractal theories. This method successfully overcomes the limit of previous moment methods that require pre-assumed particle size distribution. Results of the zero and second order moments of Brownian flocs from the proposed method are compared with those from the Laguerre method, integral moment method and finite element method. It is found that the higher accuracy and efficiency of computation have been achieved by the new method, compared to the previous ones. Effects of the fractal dimension on the zero and second order moments, geometric average volume and standard deviation are also analyzed using this method. The self-conservation characteristics of particle distribution is observed without presumption of initial distributions.

Lost-Circulation Control for Formation-Damage Prevention in Naturally Fractured Reservoir: Mathematical Model and Experimental Study

Drill-in fluid loss is the most important cause of formation damage during the drill-in process in fractured tight reservoirs. The addition of lost-circulation material (LCM) into drill-in fluid is the most popular technique for loss control. However, traditional LCM selection is mainly performed by use of the trial-and-error method because of the lack of mathematical models. The present work aims at filling this gap by developing a new mathematical model to characterize the performance of drill-in fluid-loss control by use of LCM during the drill-in process of fractured tight reservoirs. Plugging-zone strength and fracture-propagation pressure are the two main factors affecting drill-in fluid-loss control. The developed mathematical model consists of two submodels: the plugging-zone-strength model and the fracture-propagation-pressure model. Explicit formulae are obtained for LCM selection dependent on the proposed model to control drill-in fluid loss and prevent formation damage. Effects of LCMmechanical and geometrical properties on loss-control performance are analyzed for optimal fracture plugging and propagation control. Laboratory tests on loss-control effect by use of different types and concentrations of LCMs are performed. Different combinations of acid-soluble rigid particles, fibers, and elastic particles are tested to generate a synergy effect for drill-in fluidloss control. The derived model is validated by laboratory data and successfully applied to the field case study in Sichuan Basin, China.

Exact Solution for Long-Term Size Exclusion Suspension-Colloidal Transport in Porous Media

Long-term deep bed filtration in porous media with size exclusion particle capture mechanism is studied. For monodispersed suspension and transport in porous media with distributed pore sizes, the microstochastic model allows for upscaling and the exact solution is derived for the obtained macroscale equation system. Results show that transient pore size distribution and nonlinear relation between the filtration coefficient and captured particle concentration during suspension filtration and retention are the main features of long-term deep bed filtration, which generalises the classical deep bed filtration model and its latter modifications. Furthermore, the exact solution demonstrates earlier breakthrough and lower breakthrough concentration for larger particles. Among all the pores with different sizes, the ones with intermediate sizes (between the minimum pore size and the particle size) vanish first. Total concentration of all the pores smaller than the particles turns to zero asymptotically when time tends to infinity, which corresponds to complete plugging of smaller pores.

The effects of closure model of fiber orientation tensor on the instability of fiber suspensions in the Taylor-Couette flow.

An analysis for the linear stability of fiber suspensions in the Taylor–Couette flow is conducted. The orientation state of fibers is determined using the linear, quadratic and composite HL-I closure model and the model of the fiber contribution to the total stress is established based on the slender-body theory. The linear stability equation is derived and solved with the Chebyshev spectral method. The results show that the suppression effect is most predominant for the composite HL-I model, while least predominant for the linear closure model. The longer fibers and suspensions with high volume fraction have a more predominant influence on suppressing the instability. The contribution of the suspending fluid to the change rate of the disturbance energy dominates the energy dissipation. While the contribution of the fiber shear stress increases monotonously with increasing fiber aspect ratio for the three closure models, the contribution based on the composite HL-I closure model is the largest, and that based on the linear closure model is the smallest. The effect of fiber aspect ratio on the change rate of the disturbance energy caused by the fiber shear stress is more predominant than that of the fiber volume fraction. The positive energy caused by the fiber shear stress consumes the gross energy of the fluid system and leads to a suppression of the flow instability.

Fines Migration in Fractured Wells: Integrating Modeling With Field and Laboratory Data

Production and drawdown data from 10 subsea deepwater fractured wells have been modeled with an analytical model for unsteady-state flow with fines migration. The simulation results and the field data indicated a good match, within 5%. A sensitivity study conducted on initial concentration of fines, flow rate, maximum fines-mobilization velocity, fines distribution, formation damage, and filtration coefficients confirmed that the model-matching parameters are within values reported commonly in the literature. This paper describes the methodology used to integrate the modeling predictions with field and laboratory data to identify probable causes for increasing skins and declining productivity-index values observed in some of the wells under investigation. It discusses the results of an experiment designed to simultaneously assess the effects of pressure depletion and compaction on fines production and permeability with a triaxial-stress apparatus. This is, to the best of our knowledge, the first time an experiment of this nature is reported in the literature. The good match between the modeling and the field data, further validated with laboratory experiments, allows for discussion of long-term predictions on well productivity impacting current reservoir-management strategies and field-development plans.

Non-axisymmetric instability in the Taylor-Couette flow of fiber suspension

An analysis of the instability in the Taylor-Couette flow of fiber suspensions with respect to the non-axisymmetric disturbances was performed. The constitutive model proposed by Ericksen was used to represent the role of fiber additives on the stress tensor. The generalized eigenvalue equation governing the hydrodynamic stability of the system was solved using a direct numerical procedure. The results showed that the fiber additives can suppress the instability of the flow. At the same time, the non-axisymmetric disturbance is the preferred mode that makes the fiber suspensions unstable when the ratio of the angular velocity of the outer cylinder to that of the inner cylinder is a large negative number.

Large eddy simulation of sediment-laden turbulent flow in an open channel

Sediment transport in fully developed turbulent open channel flow has been investigated using large eddy simulation (LES) of the incompressible Navier–Stokes equations. The scalar transport equation of the sediments concentration, which is based on the continuous-phase approach, is adopted. The settling process is taken into account with a modified settling velocity appearing in the sediment concentration equation. A Smagorinsky model allowing for the interaction between the fluid flow and the suspended sediment is used to simulate the unresolved, subgrid scale terms. The LES results are compared with the experimental data, and good general agreement is achieved.