Biots theory of poroelasticity describes seismic waves propagating through fluid-saturated porous media, so-called two-phase media. The classic Biots theory of poroelasticity considers the wave dissipation mechanism being the friction of relative motion between the fluid in the pores and the solid rock skeleton. However, within the seismic frequency band, the friction has a major influence only on the slow P-wave and has an insignificant influence on the fast P-wave. In order to represent the intrinsic viscoelasticity of the solid skeleton, we incorporate a generalized viscoelastic wave equation into Biots theory for the fluid-saturated porous media. The generalized equation which unifies the pure elastic and viscoelastic cases is constituted by a single viscoelastic parameter, presented as the fractional order of the wavefield derivative in the compact form of the wave equation. The generalized equation that includes the viscoelasticity appropriately describes the dissipation characteristics of the fast P-wave. Plane-wave analysis and numerical solutions of the proposed wave equation reveal that (1) the viscoelasticity in the solid skeleton causes the energy attenuation on the fast P-wave and the slow P-wave at the same order of magnitude, and (2) the generalized viscoelastic wave equation effectively describes the dissipation effect of the waves propagating through the fluid-saturated porous media.
The cathodic protection method is the most commonly used method for pipeline anticorrosion. A current is applied to the protected structure, and the potential is negatively shifted to the protective potential range by cathodic polarization, thereby the electrochemical corrosion of the structure is suppressed. In the cathodic protection system, small distance between the anode and the structure, high resistivity of the environment medium , and high requirement for the protection current, may result in uneven potential distribution on the structure. Aiming at this problem, the parameter optimization of the system is studied by boundary element method (BEM), radial integration method (RIM) and particle swarm optimization (PSO) based on the cathodic protection potential distribution model. Then, establish a cathodic protection optimization model that meets the cathodic protection requirements and has a uniform potential distribution by optimizing the anode position and the current density. Keywords-long-distance pipeline; cathodic protection(CP); boundary element method(BEM); radial integration method(RIM); anode position; particle swarm algorithm(PSO)I.
The kinetics of ordering in a (001) deposition monolayer in fcc alloy system is investigated by means of the micromaster equation method in the pair approximation. The time evolutions of the long-range order (LRO) and short-range order (SRO) parameters are calculated. There are transient ordered states during the relaxation from the disordered state to the equilibrium state. The transient ordered states have various features are due to different characteristic times for the atomic migration, the different first- and second-nearest- neighbors interactions, the different influence of short-range correlation and long-range correlation on relaxation.
The effect of bottom-hole pressure and formation pressure due to a partially penetrating well (PPW) is different from that for an open hole well. In order to analyze the effect of imperfection on pressure response type curves, this paper presents a 3D symmetry porous flow model for circularly partially penetrating wells. Laplace transform and Fourier transform and Bessel functions are applied to obtain the analytical solution of the model. The pressure response and pressure distribution are obtained and the influence on flow regime surrounding the well and pressure response caused by partial penetration are analyzed. Research results show that when the imperfect area tends to zero, the solution of the model can be reduced to the traditional model of the perfect wells presented by Theis, demonstrating the correctness of the solution. The early-time pressure is significantly lower than the case of complete well. The pressure difference between a partially penetrating well and a completely penetrating well decreases with time increasing. Without considering the variation of spatial distribution of flow field due to imperfect well it may bring about errors of formation parameters calculated by perfect well model. Those conclusions improve the seepage model and provide theoretical guidance for the transient pressure data interpretation, formation parameters calculation and productivity prediction of partially penetrating wells. The presented research content furthers the theory of well test analysis, and builds theoretical foundation for the technologies of well testing interpretation and reservoir numerical simulation.
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