泡沫复合驱研究

Studies on Alkaline/Surfactant/Polymer Combinational Foam Flood in Daqing

讨论了泡沫三元复合驱的基本原理。介绍了室内实验研究结果。根据二元(AS)和三元(ASP)复合体系/天然气泡沫综合指数(Fq)等值图,选择石油磺酸盐ORS 41(及国产品AOS)为发泡剂;ORS 41浓度为1～4g/L、NaOH浓度为6～12g/L的二元体系产生超低界面张力,与天然气形成的泡沫按Fq具有中等强度,加入≤1 2g/L聚合物可使泡沫稳定,性能改善。在3个岩心上泡沫三元复合体系在水驱基础上提高采收率28 7%～39 4%。气液比越大,泡沫体系提高采收率幅度越大,但注入粘度越大。取气液比为1∶1。气液同时注入比交替注入的采收率高。在6个岩心上气液交替注入时,气液段塞越小,交替频率越大,采收率提高越多,在水驱基础上可提高30%以上。先导试验方案规定前置AP段塞0 02PV,气液比1∶1交替注入主段塞0 55PV和副段塞0 3PV,后续P段塞0 2PV,注入流量0 4PV/a。先导试验区6注10采,在大庆油田北二区东部,1984～1994年曾进行天然气驱,提高采收率12 9%,试验开始时采出程度43 8%,综合含水97 2%。试验于1997 02 20开始,2002 04先期结束,注天然气仅0 19PV,气液比0 34∶1,中心井含水91 5%,全区采收率增加21 85%,2口中心井采收率增加22 58%。试验动态和数值模拟表明采收率增加应>25%。图3表2参3。

The basic principles of ASP foam flood is discussed. The results of laboratory investigation on ASP foam flood are presented. As foaming agent, petroleum sulfonate ORS-41 and home made sulfonate AOS are chosen according to the isograms of composite foam index, F_q, for AS and ASP solution/natural gas (NG) systems. 1-4 g/L ORS-41+6-12 g/L NaOH solution creates ultralow interfacial tension with the crude oil and, mixed with NG, forms foam of moderate strength (F_q value in rang 5×10~3-1×10~4), which become more stable and is improved in properties when polymer is introduced at dosage ≤1.2 g/L. ASP foam enhances the oil recovery in 3 cores by 28.7-39.4% over that of water flood. The larger the gas to solution ratio (G/S), the larger the increment of enhanced oil recovery (EOR) by ASP foam is and the higher the viscosity of the foam becomes. The G/S taken is of 1∶1. Simultaneously injecting G and S gives higher EOR than alternatively injecting G and S. In experiments on 6 cores with alternative G and S injection, the smaller the volume of G and S slugs, that is, the higher the frequency of G and S slug alternation, the higher the EOR is: >30% over that of water flood. In the pilot trial program following slug structure is designed: 0.02 PV of AP pad; 0.55 PV of main and 0.30 PV of supplementary ASP multislugs to be injected alternatively with NG; 0.2 PV P postpad; injecting rate 0.4 PV/a. The pilot area in East of 2nd Northern District of Daqing, flooded by NG in 1984-1994 and characterized by oil recovery 43.8% and composite water cut 97.2%, covers 2 injection and 10 production wells. The trial was started Feb 20, 1997 and ended Apr 2002 ahead of schedule when only 0.19 PV of NG injected, G/S ratio 0.34∶1 reached and water cut in 2 central production wells (CPWs) raised to 91.5%. The EOR obtained is of 21.85% for whole area and of 22.58% for the CPWs and might be of >25% for whole area as shown by the performance and the digital simulation of the trial.