2019 Vol. 40, No. 4

Display Method:
Pressure Transient Analysis of the Fractured Vuggy Reservoir Model Coupling Oil Flow and Wave Propagation
DU Xin, LU Zhiwei, LI Dongmei, XU Yandong, LI Peichao, LU Detang
2019, 40(4): 355-374. doi: 10.21656/1000-0887.390123
Abstract(795) HTML (98) PDF(659)
Fractured vuggy reservoirs consist of matrix, fractures and vugs. Researchers usually treat the matrix-fracture-vug interaction as inter-porosity flow due to their complex pore system and flow mechanism.In fact, vugs play an important role in fractured vuggy reservoirs and can’t be simplified to one homogeneous medium. The idea that pressure spreading in vugs is in form of wave, which is similar to pressure decline, was proposed. Based on that, an analytical well test model for fractured vuggy reservoirs combined with seepage equations for outer formation was presented. Then the log-log type curves of the wellbore pressure and its derivative were obtained through the Laplace transform and numerical inversion. The results show that, the pressure curve forms were influenced by dimensionless parameters related to flow and wave propagation, also by dimensionless parameters related to the outer formation. Sensitivity analysis of these parameters were done. Lastly, a field example was demonstrated to validate the accuracy of the proposed model, which matched the real geological data well.
A Mechanical Constitutive Model for Hydrate-Bearing Sediments and Calculation of Material Parameters With the Discrete Element Method
ZHOU Bo, WANG Hongqian, WANG Hui, XUE Shifeng
2019, 40(4): 375-385. doi: 10.21656/1000-0887.390284
Abstract(938) HTML (108) PDF(621)
To soundly describe the mechanical behaviors of hydrate-bearing sediments in the cases of different saturation levels of hydrate and various confining pressures, the stress-strain relation equations and elastic modulus weak-form equations for hydrate-bearing sediments were developed based on the generalized Hooke’s law. The softening coefficient and softening exponent of the hydrate-bearing sediments were determined according to the triaxial compression test results. A discrete element method (DEM) to calculate the initial elastic moduli of hydrate-bearing sediments was proposed based on the 3D particle flow code (PFC3D). The mechanical behaviors of hydrate-bearing sediments under 6 various conditions related to saturation levels of hydrate and confining pressures, were numerically simulated with the stress-strain relation equations, elastic modulus softening equations and the DEM together. Numerical results show that, the proposed stress-strain relation equations, elastic modulus softening equations and the DEM can effectively predict the mechanical behaviors of hydrate-bearing sediments under various saturation levels of hydrate and confining pressures. The work gives a theoretical basis and a computational method for the investigations on the mechanical behaviors of hydrate boreholes and the safe exploitation of hydrate.
Research on the Implicit AUSMV Algorithm for the 1D Gas-Liquid Two-Phase Drift Flux Model
XU Chaoyang, MENG Yingfeng, GUO Jinsong, LI Gao, QIU Quanfeng
2019, 40(4): 386-397. doi: 10.21656/1000-0887.390110
Abstract(1080) HTML (128) PDF(377)
The time step of the explicit AUSMV (advection upstream splitting method combined with flux vector splitting) algorithm is limited by the CFL (Courant-Friedrichs-Lewy) conditions. To improve computational efficiency, an implicit AUSMV algorithm was proposed for the gas-liquid two-phase drift flux model. The numerical flux of convective terms in the continuity equations and motion equations was set up with the AUSM scheme plus the FVS (flux vector splitting) scheme, while the numerical flux of pressure terms in the motion equations was built with the AUSM scheme. The nonlinear dynamical discrete governing equation system was solved numerically with the 6th-order Newtonian method and the numerical Jacobian matrix. The classical test examples were simulated, which involved the Zuber-Findlay shock tube problem and the variable mass flow problem with complex slip relation. The numerical results show that, the implicit AUSMV algorithm has small dispersion effects, no numerical oscillation and high computational accuracy. Under the condition of high pressure wave velocity, the algorithm has superior calculation efficiency with low dissipation effects.
Convection Patterns and Corresponding Critical Conditions in an Inclined Layer
NING Lizhong, WU Hao, NING Bibo, TIAN Weili, NING Jinghao
2019, 40(4): 398-407. doi: 10.21656/1000-0887.390102
Abstract(811) HTML (103) PDF(371)
Through numerical simulation of the basic equations for 2D fluid mechanics, the convection patterns and the critical conditions for pattern transition in an inclined rectangular cavity with Prandtl number Pr=6.99 were studied. According to the variations of inclination angle θ and relative Rayleigh number Rar, the convection patterns in the inclined layer can be divided into the convection single-roll pattern, the multi-roll pattern filling the cavity and the multi-roll pattern in the transitional stage. With constant inclination angle θ,the system transforms from the multi-roll pattern filling the cavity to the single-roll pattern with the decrease of relative Rayleigh number Rar, where the convection amplitude and Nusselt number Nu increase with Rar. For Rar=9,the system transforms from the multi-roll pattern filling the cavity to the single-roll pattern with the increase of inclination angle θ,where the convection amplitude decreases with θ,and the Nusselt number increases with θ.The simulation results of the transition from multi-roll to single-roll patterns in plane θc-Rar show that, for Rar=2,the multi-roll pattern is not found in the cavity. For Rar=2.5 or so, the transition from the multi-roll pattern to the single-roll pattern appears in the cavity. The critical θc value for the transition from the multi-roll to the single-roll patterns increases with the decrease of Rar for θc<10. The θc value increases with Rar for θc>10, where θc increases rapidly with Rar for Rar≤5,and increases slowly with Rar for Rar>5. The relation between θc and Ra is similar to θ.
Electrokinetic Flow and Heat Transfer in Soft Microtubes
XU Lina, JIAN Yongjun
2019, 40(4): 408-418. doi: 10.21656/1000-0887.390155
Abstract(587) HTML (55) PDF(650)
The electrokinetic flow and heat transfer characteristics of fluid in soft microtubes, of which the walls were covered by polyelectrolyte materials as the fixed charge layer, were studied based on previously obtained analytical solutions of electrical potentials and velocities, and numerical solutions of streaming potentials. Under the assumption of a constant wall heat flow, the energy equations including the effects of viscous dissipation and Joule heat were solved with the finite difference method and numerical solutions of the dimensionless temperature were obtained. Numerical calculations also gave the influences of related dimensionless parameters on the velocity, the temperature and the Nusselt number. The study shows that, when other parameters are fixed, the dimensionless velocity and temperature decrease with thickness d of the polyelectrolyte layer but increase with equivalent electric double layer to electric double layer thickness ratio Kλ; the Nusselt number decreases with Joule heat coefficient S and polyelectrolyte layer thickness d,but increases with Kλ.
Analysis on Free Deformation Characteristics of Packer Rubber Surface Under the Initial Sealing Load
ZHANG Fuying, LI Tiantian, ZHANG Yufei
2019, 40(4): 419-432. doi: 10.21656/1000-0887.390096
Abstract(632) HTML (65) PDF(455)
The displacement and deformation characteristics of the inner and outer surfaces of the packer rubber under the initial load in the free deformation stage were investigated. Based on the continuum mechanics, a finitedeformation mathematical model was established in the free deformation stage. The process of radial deformation of the inner and outer surfaces of the packer rubber under the initial axial load was given, and the analytical solution of the nonlinear deformation of the packer rubber was obtained. Through numerical calculation, based on the solution of analytical formulae for free deformation of the outer surface, the influences of the nonlinear deformation law and the relevant parameters on the sealing performance of the inner surface were further analyzed. The results of deformation characteristics can be applied to different types of packer rubbers, and provide an important theoretical basis for the sealing and reliability design of packer rubbers.
Solitary Wave Evolution and Non-Smooth Solitary Waves in Microstructured Solids
2019, 40(4): 433-442. doi: 10.21656/1000-0887.390069
Abstract(686) HTML (35) PDF(447)
A new free energy function was given with all quadratic terms of macro strain and micro deformation, as well as cubic terms of macro strain. A new model for description of the longitudinal wave propagation in microstructured solids was established by means of the new free energy function and Mindlin’s microstructure theory. Based on the dynamical system theory for singular traveling wave systems developed recently, all bifurcations of phase portraits of the traveling wave systems were analyzed, and the periodic wave solutions, the solitary wave solutions, the quasi peakon solutions, the peakon solutions and the compacton solutions were given. The obtained peakon and compacton solutions effectively prove that non-smooth solitary waves such as the peakon and the compacton can form and exist in microstructured solids under certain conditions. The results further exceed the conclusion that only smooth solitary waves can exist in microstructured solids.
Parameter Uncertainty in Statistical Energy Analysis
XIAO Yanping, SONG Haiyang, YE Xianhui
2019, 40(4): 443-451. doi: 10.21656/1000-0887.390216
Abstract(828) HTML (70) PDF(844)
The statistical energy analysis (SEA) is an effective method to calculate the vibration and noise, where the damping loss factor and the coupling loss factor have very small values and usually are difficult to accurately measure. Then large measurement errors result in significant deviation between the calculated value and the true value of the total energy. To tackle this problem, 4 kinds of different energy interval analysis methods: the interval matrix perturbation approach, the method based on the properties of interval variables, the affine arithmetic and the inverse affine matrix, were used to calculate the steadystate SEA subsystems, where the effects of measurement errors of the damping loss factor and the coupling loss factor on the calculation results were fully considered. Two numerical examples with different errors of loss factors were provided, and the total energy intervals based on different methods were compared. The work improves the existent SEA theory and proves the superiority of the inverse affine matrix over other methods.
Characterizations of HContinuity for Solution Mapping to Parametric Generalized Weak Vector QuasiEquilibrium Problems
SHAO Chongyang, PENG Zaiyun, WANG Jingjing, ZHOU Daqiong
2019, 40(4): 452-462. doi: 10.21656/1000-0887.390198
Abstract(859) HTML (60) PDF(355)
The stability of a class of parametric generalized weak vector quasi-equilibrium problems (PGWVQEP) in Hausdorff topological vector spaces, were studied. First, a parametric gap function for the problem was given, and the continuity property of the function was studied. Next, a key hypothesis related to the gap function for the considered problem was presented, the characterizations of this hypothesis were discussed, and an equivalence theorem for the key hypothesis was given. Finally, by means of the hypothesis, the sufficient and necessary conditions for the Hausdorff semicontinuity of the solution mapping to PGWVQEP were obtained. Examples were given to verify the obtained results.
The First Passage Failure Probabilities of Dynamical Systems Based on the Failure Domain Reconstruction and Important Sampling Method
REN Limei
2019, 40(4): 463-472. doi: 10.21656/1000-0887.390169
Abstract(758) HTML (82) PDF(425)
For linear dynamical systems, the system failure domain was reconstructed, an important sampling density function was built with the probability of the basic failure domain and the important sampling simulation method was employed. For the nonlinear dynamical system, the equivalent linear system was constructed according to the principle that they have the same mean high level crossing rate for the specified threshold. Two numerical examples were given to demonstrate the accuracy and efficiency of the proposed method.