| Low permeability reservoirs play an important role in meeting China’s energy needs,however,due to the characteristics of low porosity,low permeability,strong heterogeneity,and strong sensitivity in low permeability reservoirs,the oil recovery of water flooding was low,and crossflow was easy to cause during gas/water flooding.Foam has been widely used as an effective profile control system in conventional reservoirs,but in low permeability reservoirs,on the one hand,because the polymer component was difficult to inject,traditional polymer reinforced foam system was difficult to apply;On the other hand,microbubbles(referring to bubbles with a diameter between 1-100 μm)is a new foam system,they can prevent gas migration and further improve the oil recovery after water flooding,therefore,the application of microbubbles to low permeability reservoirs to improve oil recovery is getting more and more attention.Based on this,a microbubble flooding system with a diameter of micrometer was firstly constructed from the screening of bubble production method,bubble generating agent and stabilizing agent.Then through the bubble stability in the microtube,the seepage and profile control experiments in the core model,the stability and profile control ability of the microbubble system in the core throats were investigated.Finally,with the aid of microscopic visualization model,single and double tube parallel models,the oil displacement characteristics and heterogeneous adaptability of the microbubble system were studied.The research showed:(1)Porous media shearing method was a better method to generate microbubbles than high-speed stirring method;In order to avoid the adverse effects of poor injection caused by the addition of foam stabilizers such as polymers to strengthen microbubbles,this article adopts a foaming system without foam stabilizers(2)Stability and seepage experimental research showed,a dilute microbubble system with uniform bubble diameter distribution and no Plateau boundary was obtained by the porous medium shear method;The microbubbles all broke up in the bulk phase in 91 min,but could be exist for at least 455 min in both the microtubes and the porous medium,indicating that the stability of the microbubbles in the microtubes and the porous medium were much greater than their stability in the bulk phase;In the porous media,there was a clear correlation between the microbubbles generated in porous media and the core hole roar.The microbubbles only need to transport a short distance to achieve a effect that the diameter was compatible with the pore throat of the rock,that is,the microbubbles were easily matched to the rock;Seepage experiments with microbubbles showed that the lower the permeability,the higher the retention of the residual resistance coefficient relative to the resistance coefficient and the better the plugging effect;Profile control effect,the limit permeability contrast that the microbubbles can use was 245.3,microbubbles can play a profile control effect in a wide range of heterogeneity.(3)Displacement research showed,under homogeneous conditions,with the decrease of core permeability,the oil recovery of microbubble flooding and subsequent waterflooding were getting higher and higher.Microbubbles can increase the oil recovery of low permeability cores by more than 27.8%;Under heterogeneous conditions,when the permeability contrast was 11.9and below,microbubbles can improve the recovery of low permeability cores.If the range was exceeded,the microbubbles profile control and oil displacement capability would be significantly weakened. |
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