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Microfiltration technology | Treatment of oilfield reinjection water

In the process of oil field exploitation, especially in the middle and late stages of oil field exploitation, the pressure of oil layer gradually decreases with the extension of exploitation time. when the pressure of oil layer falls below the saturation pressure of oil and gas, the natural gas dissolved in oil will largely separate out from the oil layer. the output of oil well obviously decreases, the oil-gas ratio increases, and the nature of underground crude oil changes, resulting in viscosity increase and flow difficulty, making a large amount of degassed crude oil ( also called dead oil ) remain in the formation and cannot be mined out, thus reducing the exploitation efficiency of the oil field.  In order to maintain the reservoir pressure and prolong the self-injection period of the oil well, the main method currently adopted is to inject water into the formation to supplement the void volume of the crude oil that has been produced in the oil layer, so as to keep the reservoir pressure stable or rising, thus achieving the aim of high and stable oil well yield and improving the final recovery ratio.  Most of the existing oil fields in our country use water injection and oil recovery methods, and in order to improve the efficiency of subsequent production, water injection will begin at the peak of the oil field.  However, in the process of water injection and oil recovery, water injected into the ground to supplement formation pressure is produced together with crude oil. after oil-water separation, a large amount of oilfield waste water will also be produced.  This requires careful processing and re - injection.

At present, most oil fields in our country have entered the middle and late stages of oil exploitation. the water content in the produced fluid is 70 - 80 %, and in some oil fields it is even as high as 90 %. with the increase of exploitation time, the water content is also continuously increasing, so the amount of waste water produced in our country's oil fields is very large.  If such a large amount of produced water is drained out directly, it will cause a very serious environmental pollution problem and waste precious water resources at the same time.  If the oily wastewater is treated and re-injected into the formation to supplement the pressure of the formation, not only the environmental pollution can be avoided, but also a large amount of water resources can be saved.  The treatment and reinjection of oily wastewater is an important way to realize sustainable development in oil fields and to improve economic benefits and save costs in oil fields.

2 major existing problems

1 most of the existing reinjection water treatment processes are: walnut shell + quartz sand or walnut shell + primary quartz sand + secondary quartz sand filtration process. with the development of oil extraction technology, such as chemical flooding and the implementation of three-dimensional co-flooding process, the polymer content in water increases, and the existing equipment is gradually unable to meet the requirements of reinjection water.

2 the top of walnut shell and quartz sand filter tank is usually equipped with a stirrer to separate the filter material adhered by oil, but the actual effect is not ideal and the interception effect on suspended solids and oil needs to be improved.

3 because of the above problems, the existing treatment equipment has become more and more difficult to meet the design requirements. it is not that the equipment is not good, but that the water quality of the inlet water has deteriorated, while the outlet water requirements are still unchanged or higher.  Only upgrading can meet higher technical requirements.

4 as the proportion of reclaimed water in oil production is getting higher and higher, some of which have reached 90 %, the old equipment originally designed is not only unable to meet the technical requirements, but also difficult to meet the increasing water demand.

5 the following figure shows a field filtration effect sampling and three-stage filtration process for reinjection water in an oil field. flocculant is added before entering the first stage of filtration. the first stage is walnut shell and the second stage is quartz sand. due to the effect of water outlet does not meet the requirements, the third stage of quartz sand filtration is added, but the effect is not obvious.  The analysis causes include both flocculation and filtration accuracy.

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