**4.1 Polymer flooding in S field**

*Enhanced Oil Recovery Processes - New Technologies*

**platform**

duced water treatment [17, 18].

polymer flooding projects.

**3.4 Treatment technology of chemical flooding produced fluid in offshore** 

Partially hydrolyzed polyacrylamides with high molecular weight (HPAM), after undergoing a series of chemical, mechanical, and thermal degradations, are back produced, making the oil-water interface highly electronegative and forming a strong electrical double layer. The repulsive force between oil droplets affects their aggregation and coalescence, and at the same time, the adsorbed polymers also increase the strength and viscoelasticity of the oil-water interface film. As a result, the emulsified oil droplets are of small particle size and strong stability. Therefore, the oil-water separation of produced fluid from polymer flooding is more difficult than that from water flooding. Hence, devices with much longer residence time and several times larger size are required for pro-

However, platform space is limited for offshore oil fields; the abovementioned practice cannot be implemented. At present, the treatment process of polymer-containing produced fluid in Bohai oil fields is a so-called three-stage treatment process similar to that of water flooding. For example, the comprehensive water content of the produced fluid is 78% in Bohai A oil fields, and the average polymer concentration is 150 mg/L. The oil treatment system includes a one-stage three-phase separator, a two-stage thermal settling separator, and a conventional electric dehydrator (**Figure 5**). The wastewater treatment system mainly includes a tilted plate separator, a gas flotation unit (GFU), a walnut shell filter, and a residue conversion system. The abovementioned process represents the traditional process of produced fluid treatment for water flooding oil fields. For different polymer flooding oilfields, the original water flooding process have different complexity and methods for adaptive modification for

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**Figure 5.**

*Treatment process of produced fluid in Bohai A oil field.*

S oil field is located at the coast of Liaodong, Bohai Bay, with stable distribution and good connectivity. Its reservoir rocks are feldspathic quartz sand composed mainly of fine sands. The crude oil in S oil field is highly viscous, varying from 13 to 380 mPa s, with an average of 70 mPa s at reservoir conditions. It was put into operation since 1993 with inversed 9-point well pattern. From the very beginning, the enhanced oil recovery technologies were taken into consideration, and polymer flooding showed great potential among these technologies. Since September 2003, the first single-well polymer injection pilot in China offshore field was successfully carried out in S field [19–21]. In October 2005, the well group polymer injection was carried out in AJ platform in S oil field, which consisted of four injectors and one central producer and seven peripheral producers. After 3 years of well group test, the expected incremental oil was obtained. Based on the well group polymer injection test result in S field, the expanded polymer injection project was implemented in mid-2008. Up to 2014, 24 wells were successively converted to polymer injectors, and significant incremental oil was achieved (**Figure 6**). By the end of 2017, 4.75 million cubic meters of cumulative oil were achieved, increasing recovery rate by 5.2%.
