The Mechanism And Parameter Optimization Of Water Control With Nitrogen Foam In Bottom Water Reservoir

Water coning is a major problem of reservoir with bottom water.With water coning occurred,a well can produce a huge amount of water than oil.In recent years,foam is used into controlling water course foam fluid is stable in water layer while defoaming with oil,making less damage to the formation.At present,the research on water control of the injected foam in the bottom water reservoir mainly adopts the physical model,which simulates the effect of controlling water and increasing oil,and does not directly show the mechanism of water control with foam.Therefore,it is necessary to study the mechanism of water control with nitrogen foam in bottom water reservoir using the visualization model.In this paper,Waring Blender method was used to evaluate the foaming performance of several foaming agents.Performance of several foaming agents under different salinity,temperature,pressure,and oil content have been tested.A foaming agent which is adapted to the reservoir conditions was selected as ZY21120 with properties of 0.5%.The water shutoff regulation of foam system was studied by core displacement experiment,the experimental results show that the ZY21120 foam system has the best plugging ability by gas-liquid co-injection and gas-liquid ratio 2:1.Permeability range is 100×10^-3μm² to 1000×10^-3μm²,with permeability increasing,resistance factor increases.When temperature increases,resistance factor reduces.With pressure increasing,resistance factor is greatly enhanced.When permeability contrast of formation permeability is smaller than 6 times,the injection foam system has better selective plugging,which can achieve the turnover of the high permeability and low permeability core diversion rate.The secondary emulsion forming capacity of the foaming agent solution and the crude oil was studied.The particle size of the emulsion was measured.The results showed that the emulsion was sealed with the increase of the pore diameter of the porous medium or the increase of the moisture content of the emulsion.Blocking ability is reduced.The two-dimensional visualization model was used to study the transport and evolution of nitrogen foam in porous media.The process of water control with nitrogen foam in bottom water reservoir was simulated.From the results,Mechanism of water control with nitrogen foam in bottom water reservoir can be summarized.:Foam blocks the area with high water saturation,bottom water flows around the foam area;foaming agent emulsifies crude oil,auxiliary foam plugging;foaming agent expands the oil deplacement efficiency of subsequent water flooding;After the gas floats,the residual oil at the top of the reservoir is used to increase the effect of subsequent bottom water flooding.The numerical simulation software was used to simulate and optimize the nitrogen foam water control technology in bottom water reservoir.The recommended nitrogen injection volume is 25×10⁴m³ to 30×10⁴m³,and the concentration is 0.5%foaming agent solution is312.5m³ to 375m³.The best injection timing is water content reaches 94%to 96%.The best soak time is 15d.The best production rate is 60m³/d to 80m³/d.The research shows that injecting nitrogen foam is an effective method to control water in the bottom water reservoir.The water control mechanism revealed in the experiment helps deepen the theoretical understandin.The optimized parameters can provide reference for field engineering.