Study On Low Velocity Seepage Of Low Permeability Rocks With Electric Drive

Slow velocity flow of low permeability rock is a hot research field, will be of great significance to the development of oil and gas migration, pollution, hazartdous waste landfill. In the course of the study, it is found that the solw velocity seepage of low permeability rock is obviously deviated from Darcy law. However, because of the experimental methods and conditions, it is difficult to obtain the seepage experimental data at slow velocity, especially at the stage of the start-up. Slow velocity seepage mechanism and related theoretical research has not yet formed a unified view. The method fot direct measurement of low permeability rock mass starting pressure gradient and solw seepage state is the emphasis and difficulty in the study of slow seepage at present. It has gread theoretical and practical significance in the research of slow non-Darcy flow.With the theoretical analysis and laboratory experiments, this paper deeply studies the problems of the seepage state measurment method for slow velocity, the experimental method for slow seepage, the measurement method for stating pressure gradient and the for slow non-Darcy flow. The main work is as follows:1. By means of kinetic analysis, the electrolytic polariztion process is analyzed. The electrolytic polarization tracing method for measuring slow seepage state is proposed. The slow seepage sensor, measurement and control system is designed. The sensor performance test results show that the method can measure the slow seepage state at the μL·min-1 levels velocity.2. From the principle of electrokinetic phenomena, the principle of the electroosmotic pump is analyzed. An electroosmotic pump for the slow seepage experiment is designed. Through the perfomance test for this pump, the maximum output pressure is 1.179MPa, the resolution flow is 73.48nL·min-1 · V-1. This pump for slow seepage experiment can provide steady flow at the range of μL · min-1.3. Form the principle of the electroosmotic pump, an electric drive method for slow seepage experiment is proposed. The measuring method of start-up pressure gradient and the base steps for the electric drive method is introduced. The experimental device and control systme are designed. By using the equal diameter capillary tube bundle and the core of the real low permeability standstone, a slow seepage experiment is carried out with the electric drive. The resluts show that the electric drive method can directly measure the starting pressure gradient. The method can get more experimental data of seepage state at the range of μL·min-1. The seepage curve for the equal diameter capillary tube bundle is the straight line which dose not pass through the origin. For the capollary and the low permeability standstone, the start-up pressure gradient is existence. The slow seepage for the low permeability standstone is non-Darcy flow.4. Based on the previous research results, the theoretical model of non-equal diameter capillary tube bundle with low velocity non-Darcy flow is proposed. The relationship between pore throat structure characteristics and pore throat distribution is given. The slow seepage state with different pore throat distribution is analyzed. The relationship between flow rate and pressure gradient is derived from the theoretical model. The results show that the difference bewteen the pore throat distribution is the main cause of low velocity non-Darcy flow.The electric drive method provides a new method for low permeability rock seepage experiment. The method can derectly measure start-up pressure gradient. The details of slow seepage state at the range of μL·min-1 can be observed better. With the relation between the characteristics of pore structure and seepage law, the theoretical model of non-equal diameter capillary tube bundle can be used to characterize the low velocity percolation characteristics of different pore throat characteristics, which provides a theoretical basis and direction for the study of the law of slow seepage. The model explains the different seepage characteristics in rock mass flow at low velocity, has a certain theoretical value and application prospect.