Study On The Oil-gas-water Multi-phase Seepage Law For Tight Sandstone Condensate Gas Reservoir

The tight sandstone condensate gas reservoir plays an important role in unconventional oil and gas reservoirs composition due to huge reserves, so studies on tight condensate gas reservoir have been paid much attention. However, there are still few reports on seepage characteristics of tight sandstone condensate gas reservoir. The few knowledge of complex multi-phase seepage mechanism for tight condensate gas reservoir becomes the bottleneck to efficient development. In allusion to these problems, some of the key problems of effective development for tight sandstone condensate gas reservoirs will be studied systematically by physical simulation experiments and theoretical analysis in this paper, such as reservoir permeability damage, stress sensitivity, threshold pressure characteristics and multi-phase seepage characteristics. The results reveal the oil-gas-water multi-phase seepage law and provide the theoretical and experimental basis for the development of tight condensate gas reservoirs.In this paper, the reservoir lithology and microscopic structure were first studied by using conventional core analysis method, the seepage experiments were designed to research the reservoir damage, reservoir protection and stimulation. The water lock effect, reservoir anti-imbibition damage and reservoir sensitivity were focused on to reveal reservoir damage mechanisms. The lithology characteristics of reservoir are studied. The reservoir is grey medium-giant coarse sandstone. There are three main pore types, which contains dissolution pore in grains, remaining pore between grains and micro-fractures. The pore throat is very narrow. Water lock effect and threshold pressure is caused by liquid phase adsorption. Water lock effect is obvious for tight sandstone reservoir. If the liquid phase precipitated too early, and condensate liquid polluted the near wellbore, the water lock effect would increase. On the basis of the reservoir characteristics, the experiments on the threshold pressure and gas-liquid seepage characteristics are carried out to study the generating mechanism of threshold pressure. The experiments show that the existence of adsorption boundary layer is the basic reason of threshold pressure gradient producing. A new method of non-steady driving-pressure balancing was designed to measure threshold pressure, which provides a precise three-phase threshold pressure measure method is significant for the productivity prediction. On the other hand, because the steady-state measure method is closer with the actual reservoir fluid seepage, we take this method to test the two phase and three phase relative permeability characteristics, and gas-liquid seepage law in tight sandstone condensate gas reservoir is obtained. Gas and liquid single-phase seepage area exists besides two-phase area in the relative permeability curve, which is different from the conclusions of the previous literatures of using non-steady method. Relative permeability of oil-phase and gas-phase are both functions of oil, gas and water three phase saturation degree, but water-phase relative permeability has nothing to do with oil-phase and gas-phase saturation degree, it is merely its own saturation degree function.Based on the above analysis, physical simulation experiment on the production performance has been carried out by using real core, and the result shows that the recovery is mid-range for tight sandstone condensate gas reservoir. By combining with the characteristics of tight sandstone condensate gas reservoir, and oil-gas-water three phase seepage mathematical model and productivity calculation method are established for tight sandstone condensate gas reservoir. By comparing the calculated results with the field productivity curve, the results show that the calculation method is reasonable. This method provides experimental and theoretical guidance for the field engineering practice.