The Modes And Mechanisms Of Natural Earthquakes Affect The Migration Of Underground Fluid

The research on the natural earthquake affects underground fluid migration is interdisciplinary.Over the years,most of the theoretical descriptions on this problem are based on the qualitative analysis.There's an urgent need to introduce new techniques and methods to deal with the problems such as the dynamical mechanism,fluid anomaly and so on.Based on the idea,we use the seepage mechanics,linear elastic theory of porous media,fractal statistics and nonlinear elastic theory to analyze the dynamical mechanism on the interaction of underground fluid with natural earthquakes.In this paper,the problem has been investigated theoretically and numerically.Some important outcomes and knowledge are listed below:1.Many models and hypotheses have been discussed based on the post-earthquake underground fluid anomaly.Combing the dynamics and seepage mechanics,the mode of the natural earthquakes influence on the underground fluid migration are divided into two typical types:?1?Natural earthquakes change the energy state of underground fluid.Natural earthquake may transfer the energy to the underground fluid through the propagation of seismic wave,and result in the migration of the underground fluid.?2?Natural earthquakes change the seepage characteristic of the underground fluid-bearing layer.After the natural earthquakes,many new micro-cracks are formed,which can provide new channels for underground fluid migration.2.On the research of the underground fluid energy state changing after the natural earthquakes,the former oil blob-porous throat model has been improved by considering the viscous resistance.The whole process of oil blob traversing the porous throat promoted by the pulse seismic wave has been simulated numerically.Based on the numerical simulation,the relationship between the structural parameters and the acceleration threshold for oil blobs traversing the porous throats have been found out.3.On the research of the seepage characteristic changing of the fluid-bearing layer after the natural earthquake,fractal permeability model,and the physical mechanics for the post-earthquake permeability increasing have been deeply analyzed.The relation mechanism between natural earthquake and the permeability of underground layer have been founded.By using the production data of the oil wells in 2008,the maximum crack width on the wall of the oil wells are estimated,the order of magnitude is about 10^-4?10^-3m.4.In this paper,we introduce the stress relaxation effect of viscoelasticity into the fractal crack permeability model,and found the time-evolution theory of fractal crack system permeability.Using the time-evolution theory we calculate the variation curve of permeability of rock sample after the vibration,which is agree with test results qualitatively.5.Based on the theoretical analysis,we point out that the phenomenon of permeability increasing sharply and then dropping slowly should be regard as an ubiquitous post earthquake effect instead of the abnormal occurrence.The new post-earthquake permeability change phenomenon is named as the effect of fractal crack permeability stress relaxation.