**4.3 Chemical flooding in JW field**

The water depth of W oil field is from 6.5 to 10.5 m; the reservoir depth is 1600– 1800 m with banded fault anticline structural form and 25 m average effective thickness. This reservoir has normal temperature and pressure system containing oil with *Development and Application of Chemical EOR Technologies in China Offshore Oil Fields DOI: http://dx.doi.org/10.5772/intechopen.88942*

**Figure 8.** *Field production curves in JW field.*

*Enhanced Oil Recovery Processes - New Technologies*

**120**

**Figure 7.**

**Figure 6.**

*Field production curves in S field.*

754,650 m3

**4.3 Chemical flooding in JW field**

*Water cut curves under water flooding, chemical flooding, and actual situation.*

is still effective, and more incremental oil will be obtained later.

injection pilot test was carried out since 2006 when the water cut in the pattern was lower than 10% [22–24]. After that, another five water injectors were converted to polymer injectors from 2007 to 2009. For the early-stage polymer flooding, the characteristics of the responses on producers were different from the case in which polymer flooding was conducted during high water cut stage. The water production of the producers continued to rise up after polymer flooding, but the simulation research showed that the water cut increasing rate was lower than the rate during water flooding. Of course, water cut drop was observed in some wells (**Figure 7**). By December 2014, the total incremental oil by polymer flooding was about

The water depth of W oil field is from 6.5 to 10.5 m; the reservoir depth is 1600– 1800 m with banded fault anticline structural form and 25 m average effective thickness. This reservoir has normal temperature and pressure system containing oil with

, and the stage oil recovery was enhanced by 3.0%. The polymer flooding

underground density of 0.87 g/cm3 and reservoir viscosity of 16–26 mPa s. The formation porosity is from 22 to 36% and permeability from 0.01 to 5 μm2 . There are many sub-reservoirs in the upper part of this oil field, with large permeability difference and serious heterogeneity [25, 26]. W oil field was put into production since 1999 with antinine-spot well pattern and 350–400 m well space. Water flooding began in December 2000. This oil field was considered as the best candidate for polymer flooding which has the lowest water salinity and medium oil viscosity in Bohai Bay. In order to improve the efficiency of water flooding and reduce the decline rate of production, eight polymer injectors were gradually implemented at field water cut of 79% since 2007. The injection rate was 0.045 PV/year, and the polymer injection concentration was 1200 mg/L. After polymer flooding, the characteristics of polymer flooding such as decreasing water cut drop, increasing oil production, and injection profile improvement were observed gradually. In order to improve the performance of chemical flooding, eight polymer injectors were transferred into polymer-surfactant injectors since February 2011. The field water cut was successfully controlled, and the oil recovery was further improved (**Figure 8**). By the end of 2017, oil recovery had increased by 5.5%.
