Research of Water quality in Typical Low Permeability Oilfield Produced Water Treatment

It is significative to study sewage treatment process in low permeable oil fields. It could enhance the oil recovery. The water quality characteristics and oil/water separation characteristics were researched during different period process by GC-MS. It shows that there are about 108 kinds of organic matters, including 45 kinds of aliphatic hydrocarbon, 7 kinds of aine, 5 kinds of sulfocompound and 9 kinds of hexacyclic compounds, such as Benzene, phenol, naphthalene and anthracene. The percent of oil droplets which size was less than 10 mu m is 57.3%, compared to 91.6% which size was more than 50 mu m. It is difficult to separate the water and oil. The remaining oil was emulsified oil. The process was hard to decrease COD, and some pollutants were existed in water, such as Arsenic, Selenium, Mercury, Cadmium and Cr6+. It is further proposed to optimize and develop this process to removal oil and suspended solids. There are lots of low permeability oil reserves about one hundred million tons of more than 50 in China now. More than a half of the total proven reserves are unused. Low permeability oil field production accounted for 37.6% of the total national output in 2008. the ratio would be increased because high permeability oilfield had been in the late development. Low permeable oil fields are widely distributed in our country, which could been distributed in Daqing, Jilin, Jindong, North China, Xinjiang, Sichuan with Daqing distribution of 760 million tons at most. Low permeability oil field production accounted for 20.7% in Daqing oilfield, in which are 540 million tons unused([1]). Because of environment and technology, low permeability oil field need to be sought further. It had been built 86 low permeable oil produced water treatment stations with capacity of swage treatment reaches 77x10(4)m(3) per day in Daqing oil field, which can meet the needs of the development and production of low permeability reserviors([2]). The treatment stations provided the water for Xing Shugang oilfield, La Madian oilfield, Sa Ertu oilfield, as well as the peripheral low permeability and low permeability oil field injection water. The produced treatment technology of low permeability in old oilfield is mainly: the produced water after treatment of water, then through two levels of pressure filter, which accounts for 65.1% of the low permeability produced water treatment technology. The produced water treatment technology of low permeability in peripheral oilfield are mainly: two-stage sedimentation and two-stage filtration process, which combined with the common water treatment and advanced treatment processes, and accounts for 15.1% ([3 similar to 5]). In order to achieve the goal of oil displacement, it is very important to meet sewage flooding back control indicators in low permeability reservoir. The return water can achieve the complementary injected underground stratum losses, otherwise it will damage the formation, affect of crude oil production and improve recovery ([6 similar to 8]). In the paper, water quality and characteristics of organic matter are researched, and the different processes are monitored. In order to further improve the efficiency of the wastewater treatment process, the existing problems of low permeability sewage treatment process must be studied, which would provide technical and theoretical support.