Study On Mechanism And Efficiency Of Foam Flooding And Profile Controlling In Tahe Fracture-Cavity Carbonate Reservoirs

For the high temperature and high salinity reservoir,traditional chemical flooding cannot meet the demand of EOR.Foam flooding has been successfully used in sandstone reservoir to improve oil recovery efficiency because of its profile control and displacement characteristics.In this paper,the efficiency and mechanism of nitrogen foam flooding in fracture-cavern reservoir are studied by laboratorial visualization physical simulation experiment,which is based on the evaluation of foam system performance in Tahe high temperature and salt seam reservoir.The main work and results are as follows:(1)When the temperature was 100 ?,the foaming volume and half-life time of the nitrogen foam system NP increased with the increase of pressure.When the pressure increases to 20MPa,the half-life time is about 7 times when it's under normal pressure,and when the pressure is stable at 20MPa,the foaming volume of the system increases 9%(14mL)with the temperature rising from 80? to 120 ?.but the half-life time is reduced 18%(44s).(2)By detecting the resistance coefficient of foam flowing through porous media,the resistance coefficient increased from 20 to 95 with the increase of pressure,but the resistance coefficient decreased from 150 to 95 with the increasing of temperature.Using artificially carved hole-seam cores to evaluate the stability of the nitrogen foam in the hole-seam medium,the experimental results show that the foam resistance coefficient is 1?2 in the hole-seam media,and the pressure difference between the two sides of the core is small.(3)The profile controlling and oil flooding experiments using the two kinds of fracture-cavity visible models show that the foam has higher oil recovery efficiency when the oil viscosity is lower.In the fracture-cavity model with fixed seam width and cavern size changing,the foam flooding improves the recovery rate to 11.88%?30.31%,while the recovery rate is 7.5%?27.5%in the fracture-cavity model with fixed cavern size and seam width changing.In the former fracture-cavity model,the foam migration was observed,and the foam entered into the simulated "cave" with larger diameter.And it can exist more stable in the holes,the flow resistance when the foam flows to the exit crack of the hole can be increased,the subsequent entry of the foam can more spread to other remaining oil more parts,displacement efficiency is higher.But in the latter fracture-cavity model,the foam mainly enters the crack with large seam width,It breaks and gathers in the seam and is prone to channeling.In addition,with transparent acrylic plate carving-seam-hole model experimental results show that with the continuous foam entry,the foam leading edge can be uniformly advanced,there is a better "profile controlling +oil flooding" effect.In this paper,the efficiency and mechanism of nitrogen foam flooding in fractured-cavity reservoir are clarified through laboratory physical simulation experiment,and the research results have some reference value and referential significance for the application of nitrogen foam flooding in fractured-cavity reservoirs.