延长油田典型“三低”油藏空气泡沫驱试验与认识

Experimental study and cognition on air foam flooding in the typical “three-low” oil reservoirs in Yanchang Oilfield

为了提高延长油田"三低"油藏开发效果,探索空气泡沫驱在该类油藏的可行性,在室内研究的基础上,分别选取东、西部具有代表性的唐80井区和旗35井区开展了空气泡沫驱矿场试验。结果表明:空气泡沫驱最终驱油效率可以达到80%以上。相比先水驱再空气泡沫驱,直接空气泡沫驱的驱动方式更有效,获得相同的较高驱油效率需要的总注入量更小。同时,据2个井区的矿场试验结果,单井月增油幅度最高达215%,单井累积增油幅度最高达近40%,单井含水率最高下降40个百分点以上;唐80井区综合含水率下降约16个百分点,自然递减率较注水区低13个百分点以上,降水增油效果非常明显。另据耗氧安全分析和矿场试验监测结果,套管气氧含量基本都在5%以内,且随时间的延长,氧含量均越来越低。通过上述研究和试验认为:空气泡沫驱在延长油田"三低"油藏具有经济和安全的双重可行性,打破了低温低压油藏不适合空气泡沫驱的常规理念,对同类油藏的实施具有借鉴和向导意义。建议矿场试验中采取有效措施减缓气窜的发生,加强油藏动态和产出气的监测与分析,保证在安全的前提下取得良好的驱油效果。

In order to improve the development results of"three-low"oil reservoirs(low permeability,low temperature and low pressure)in Yanchang Oilfield,it is necessary to explore the feasibility of air foam flooding in this type of oil reservoirs.In this paper,Well blocks Tang80and Qi35which are the typical well blocks in the east and west of Yanchang Oilfield respectively were selected on the basis of in-house study for field experiment of air foam flooding.It is indicated that the ultimate oil displacement efficiency of air foam flooding can reach over80%.Compared with the air foam flooding after water flooding,the direct air foam flooding is moreefficient and needs less injection for the same higher oil displacement efficiency.The field experiment results of both well blocks show that the maximum monthly oil increment per well is up to215%,maximum cumulative oil increment per well is nearly40%and maximum water cut decline per well is over40%.In Well block Tang80,the composite water cut drops by16%and natural decline rate is over13%lower than that of the water flooding zones,indicating remarkable effect of water cut decreasing and oil production increasing.The safety analysis on oxygen consumption and the monitoring results of field experiment show that the oxygen content of casing head gas is basically below5%and gets lower and lower as the time goes.It is concluded that air foam flooding is economically and safely feasible for"three-low"oil reservoirs in Yanchang Oilfield.The research and experiment results break the conventional concept that air foam flooding is not suitable for low temperature and low pressure oil reservoirs and they can be used as the reference and guidance for the development of similar oil reservoirs.It is recommended to take some effective measures in the field experiment to slow down gas channeling and strengthen the monitoring and analysis on oil reservoir performance and produced gas so as to realize good oil displacement effect while the safety is guaranteed.