Weiyao Zhu

Unstable seepage modeling and pressure propagation of shale gas reservoirs

Abstract Pressure disturbance propagation was investigated using the steady state replacement method, the relationship between moving boundary and time was obtained. An unstable seepage model in shale gas reservoirs was established considering the effects of desorption, diffusion, slip and moving boundary. Using Laplace transform, the pressure characteristics equation was solved for the condition of internal boundary being constant production and outer boundary being the moving boundary. Subsequently, combining the parameters of shale gas in southern China, unstable seepage pressure characteristics and its influence factors of shale gas reservoir were analyzed using MATLAB software. The results indicate that the pressure propagation is characterized by moving boundary effect during shale gas exploitation, which means that moving boundary is propagated outwards with the propagation velocity decreasing gradually. Under the effect of moving boundary or shale gas desorption, the pressure propagation velocity decreases and the reservoir pressure drop slows down. With the increasing of the diffusion coefficient, the reservoir pressure drop slows down and the effect of diffusion coefficient decreases gradually. In the process of gas reservoir exploitation, diffusion and slip contribute more and more to gas production, acting as the dominant factors, while the contribution of flow and desorption level off after decreasing.

Study on distribution of reservoir endogenous microbe and oil displacement mechanism

In order to research oil displacement mechanism by indigenous microbial communities under reservoir conditions, indigenous microbial flooding experiments using the endogenous mixed bacterium from Shengli Oilfield were carried out. Through microscopic simulation visual model, observation and analysis of distribution and flow of the remaining oil in the process of water flooding and microbial oil displacement were conducted under high temperature and high pressure conditions. Research has shown that compared with atmospheric conditions, the growth of the microorganism metabolism and attenuation is slowly under high pressure conditions, and the existence of the porous medium for microbial provides good adhesion, also makes its growth cycle extension. The microbial activities can effectively launch all kinds of residual oil, and can together with metabolites, enter the blind holes off which water flooding, polymer flooding and gas flooding can’t sweep, then swap out remaining oil, increase liquidity of the crude oil and remarkably improve oil displacement effect.

Flow characteristics and a permeability model in nanoporous media with solid-liquid interfacial effects

AbstractMolecular dynamics simulations of water flow through nanotubes have demonstrated higher flow rates than the flow rates predicted using classical models and a significant change in flow patterns due to the thin film that forms on the solid wall of the tubes. We have developed a two-region analytical model that described the flow characteristics and permeability of fluid flow through nanoporous media and considered the solid-liquid interfacial effects. Our model considers the influence of various interfacial effects, including long-range van der Waals forces, double-layer repulsive forces, and short-range structure repulsive forces, and it establishes relationships between the permeability and the average pore diameter, porosity, surface diffusion, and contact angle by numerical calculations. Our results indicate that the permeability calculated using the present model (with interfacial effects) is more than 30 times the results that were calculated using the Kozeny-Carman equation (without interfac...

Rheological Modeling of Dispersion System of Nano/Microsized Polymer Particles Considering Swelling Behavior

Rheological behavior of dispersion system containing nano/microsized cross-linked polymer particle was studied considering particle hydration and swelling. Viscosity of the dispersion system depends on swelling kinetics of polymer particles. Under shear flow, dispersion of swollen polymer particles is shear thinning. According to experimental results, kinetics of particle swelling and hydration was described well by second-order kinetic equation. Relational expression between equilibrium particle size and influencing factors of swelling such as salt concentration and temperature was presented. Assume that swollen polymer particles are uniform and have a simple core-shell structure, interacting through a repulsive steric potential. The rheological modeling of such dispersion system at low shear rate was presented using the concept of effective volume fraction, which depends on swelling kinetics and interparticle potential. Cross model was introduced to describe shear-thinning behavior. The viscosity equation allows correlation of experimental data of relative viscosity versus shear rate or hydration time; accounting for effect of temperature and salt concentration on viscosity. Predictions of the model have a good agreement with experimental results. GRAPHICAL ABSTRACT

Experiment and Capillary Bundle Network Model of Micro Polymer Particles Propagation in Porous Media

In this paper, a microscopic visualization experiment is conducted to explore the heterogeneous flow pattern of micro polymer particles in micron pore. A capillary bundle network model for micro polymer particles in porous media is established. The migration and retention mechanism of polymer particles can be clearly observed in the experiment and simulated with this numerical model. The result demonstrates that the block of large particles is one of the main factors by which micro polymer particles increase the flow resistance. The simulation results are consistent with the experimental results.

Compressible liquid flow in nano- or micro-sized circular tubes considering wall–liquid Lifshitz–van der Waals interaction

Although nano- and micro-scale phenomena for fluid flows are ubiquitous in tight oil reservoirs or in nano- or micro-sized channels, the mechanisms behind them remain unclear. In this study, we consider the wall–liquid interaction to investigate the flow mechanisms behind a compressible liquid flow in nano- or micro-sized circular tubes. We assume that the liquid is attracted by the wall surface primarily by the Lifshitz–van der Waals (LW) force, whereas electrostatic forces are negligible. The long-range LW force is thus introduced into the Navier–Stokes equations. The nonlinear equations of motion are decoupled by using the hydrodynamic vorticity-stream functions, from which an approximate analytical perturbation solution is obtained. The proposed model considers the LW force and liquid compressibility to obtain the velocity and pressure fields, which are consistent with experimentally observed micro-size effects. A smaller tube radius implies smaller dimensionless velocity, and when the tube radius decreases to a certain radius Rm, a fluid no longer flows, where Rm is the lower limit of the movable-fluid radius. The radius Rm is calculated, and the results are consistent with previous experimental results. These results reveal that micro-size effects are caused by liquid compressibility and wall–liquid interactions, such as the LW force, for a liquid flowing in nano- or micro-sized channels or pores. The attractive LW force enhances the flow’s radial resistance, and the liquid compressibility transmits the radial resistance to the streaming direction via volume deformation, thereby decreasing the streaming velocity.Although nano- and micro-scale phenomena for fluid flows are ubiquitous in tight oil reservoirs or in nano- or micro-sized channels, the mechanisms behind them remain unclear. In this study, we consider the wall–liquid interaction to investigate the flow mechanisms behind a compressible liquid flow in nano- or micro-sized circular tubes. We assume that the liquid is attracted by the wall surface primarily by the Lifshitz–van der Waals (LW) force, whereas electrostatic forces are negligible. The long-range LW force is thus introduced into the Navier–Stokes equations. The nonlinear equations of motion are decoupled by using the hydrodynamic vorticity-stream functions, from which an approximate analytical perturbation solution is obtained. The proposed model considers the LW force and liquid compressibility to obtain the velocity and pressure fields, which are consistent with experimentally observed micro-size effects. A smaller tube radius implies smaller dimensionless velocity, and when the tube radius dec...