Study On Non-Darcy Flow Experiment Of Low Permeability Rocks

Slow velocity flow of low permeability rock matrix has very wide application background in oilfield development and hydro-engineering. Currently, the low permeability oilfield in Changqing is in the status of low natural output capacity and difficulty to see injection-water effect of oil extraction well, therefore it is necessary to study non-Darcy flow characteristic and mechanism of low permeability rocks. The study was also supported by National Natural Science Foundation of China.Nowadays many researchers have drawn different conclusions from flow experiments on low permeability rocks with different flow experimental methods and instruments. The phenomenon suggests non-Darcy flow characteristic is affected by many factors. The different theories on the microcosmic mechanism of the existence of non-Darcy flow were comment on from the aspects of the pore structure of rock, the interaction between fluid and rock,as well as the property of fluid. It was discussed how the magnitude of the porosity and the throat affect threshold gradient and how surface tension,boundary layer,coupling flow and non-Newton fluid behave in the appearance of non-Darcy flow. In order to study non-Darcy flow characteristic and mechanism of low permeability rocks, the steady flow experiments on saturated sandstone and conglomerate specimens with low permeability were performed with precise FDES-641 triaxial system. Firstly, the basic physical parameters of all the specimens were measured. Then flow experiment of single-phase water and oil and confining-pressure coupling flow experiment. were conducted with constant flow-speed and differential-pressure method. In the steady flow experiments, the vacuumized and saturated rock specimens were horizontally mounted in the coreholder of FDES-641 system. The multispeed flow-pumps maintained a constant flow rate of liquid flowing through confined samples, while the pressure transducers measured the pressure-difference induced thereby. The flow characteristics of brine and distilled water respectively through sandstones and conglomerates were measured in the water flow experiments. And the flow characteristics of kerosene and simulated oil through sandstones were measured in the oil flow experiments. The variability of permeability quotiety were measured respectively with monotonously increasing and decreasing confining pressure in the coupling flow experiment.Through the flow experiment, it was confirmed that: 1) the convexity non-Darcy flow phenomenon with very small threshold pressure gradient exists distinctly in the low permeability rocks; 2) when the smaller permeability quotiety of the rock and the larger the viscosity of fluid is, the more obvious the non-Darcy phenomenon manifests; 3) permeability declines obviously with increasing effective confining pressure.Through the flow experiment, new phenomena were discovered that: 1) the higher heterogeneity degree of rock is, the more obvious the non-Darcy phenomenon manifests; 2) the migration of fine particles in low permeability media is one of the main reasons why non-Darcy flow phenomenon exists; 3) the relation between permeability ratio and effective confining pressure is approximate hyperbola at constant flow speed. Through the analyses of the results of the flow experiment combined with the results in the concerned literatures, it was discussed how to efficiently conduct low speed flow experiment on low permeability saturated rocks from the seven aspects of rock samples dimension, air permeability quotiety, flowing fluid, effective confining pressure, temperature, flowing speed and oscillatory wave.