| Wenxisan reservoir of Tuha oil field is of a low porosity and medium-low permeable layer. Its original rock pressure is 23.78 MPa, the formation temperature is 76℃ and the formation water salinity is above 20000mg/L, and its heterogeneity of interlayer and tabular surface is very severe. The development situation is very grim when the oil field is in the high water cut stage that means the compatibility of well pattern-layer system become worse gradually, block natural decline begin to increase, develop effect get worse step by step and the recovery ratio can’t meet the calibration value. At present, the CWI of pilot test area is 109.12×104m3, the cumulative liquid production is 32.31×104t, the cumulative oil production is 20.86×104t, the remaining oil is 59.6×104t, composite water cut is 50% and calibration recovery rate is 32%. But the degree of reserve recovery is low, only 25.93%. So, there are still more than 70% of the oil residue in the underground. Therefore, it is practically significant to improve the recovery rate of Wenxisan reservoir efficiently.Air EOR technology can not only take advantage of air as a medium to displace crude oil, but also take advantage of the characteristic of air which has an excellent injectivity to consume oxygen in the air so that release a lot of calories which can reduce crude oil viscosity and improve the water/oil mobility ratio at reservoir temperature. The flue gas is produced to increase the low permeability layer to produce oil and improve the sweep efficiency so as to improve oil recovery. However, because of the severe reservoir heterogeneity, the plane and vertical permeability contrast of reservoir is bigger, there is a phenomenon called gas channeling that results in low efficiency of air EOR technology when inject air. So we studied the way emphatically to improve sweep efficiency of air EOR technology by foam.In this paper, based on the part of well-block of Wenxisan reservoir as the research objection, the EOR of air drive has been completed in the lab. The parameter that influence the EOR of air drive has been attained through the analysis of the data. It has been researched by using foaming agent that has good foam performance for the differences to improve sweep efficiency of air EOR technology in various slug size of foaming liquid, then researching the influence factors of alternating injection time with foaming liquid and air to EOR. In the last, it has been used to optimize the research results by the method of numerical simulation, then predicting the sweep efficiency of air EOR technology by foam.The experimental results show that it is efficient to decrease injection pressure for air EOR technology than water flooding so that to solve the difficulty of injection in the scene. When the slug size of air is 0.3PV, the EOR number is 6.25% and the injection pressure reduce 0.03 MPa more than water flooding. But, the permeability contrast has bigger influence on the EOR of air drive. The higher permeability contrast, the worse EOR it is in the final. When the permeability contrast is from 1.3 to 15.7, the EOR number is reduce by 6.66%.It is found that the main part of increasing oil mass by air EOR technology is from high permeability pipe in lab research. In the condition of air EOR technology, it is limited for low permeability pipe to be actuated and sweep efficiency is relatively low. It shows that the air access to high permeability pipe more than the low one in the process of double pipes displacement.With the permeability contrast become bigger, the reduction curve of water cut for low permeability pipe is above the high one for the most, it means that the cumulative liquid production of low permeability pipe become less and less when the high one become more and more. This shows that since the degree of heterogeneity intensify, gas molecules flow easily, the water channeling and gas channeling happen in high permeability pipe so that the air intake reduce even stop in low permeability pipe which influence the water flooding effect.Foam that improve sweep efficiency of air EOR technology can obviously enhance oil recovery obviously than air EOR technology it alone. The foaming agent foam fully high permeability pipe can block the high permeability part and improve the double pipes’ heterogeneity, then actuate the low permeability pipe further and enlarge the swept volume of air EOR technology, thus enhance oil recovery largely. With the increase of foaming liquid slug size, the displacement characteristic is better. When the foaming liquid slug size is 0.04 PV and air slug size is 0.3 PV, the EOR number of foam that improve sweep efficiency of air EOR technology is 12.10% that increased by 5.85% when the one of air EOR technology is 6.25%.Alternating injection with foaming liquid and air can improve the displacement characteristics of foam that improve sweep efficiency of air EOR technology. And with alternating injection time increase, the EOR number of Foam that improve sweep efficiency of air EOR technology increase, too. When the alternate number is 8 times, the recovery rate is improved by 15.33%. The more alternating injection times, the more benefits to a good contact with air and foam liquid and foam production, then air and foam liquid can create synergy. With alternating injection times increase, air slug and foam liquid slug reduce relatively, but the quantum of air and foam liquid is fixed, and the foaming volume of foam fluid increase in the pores so that recovery ratio is improved gradually. Meanwhile, it is effective for foam that improve sweep efficiency of air EOR technology to improve the injection profile contrast with air EOR technology and make the low permeability layer to be actuated adequately, so that make the increased amount of oil of low permeability layer to be bigger significantly than the high permeability layer.The results of numerical simulation research show that, when air slug size is 0.25 PV, foaming liquid slug size is 0.05 PV, alternating injection time is 12 and injection rate are 1.0 times(160m3/d), the EOR number of pilot test area is 12.29%, increased amount of oil from air is 68.11t/105m3, cumulative gas production is 1.06×107m3, less than the gas drive by 83.36%. |
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