Research and Practice of the Early Stage Polymer Flooding on LD Offshore Oilfield

Abstract

Literature survey shows that polymer flooding was generally conducted during high water-cut stage (WCT>80% to 90%). Even the first China Offshore polymer flooding project was carried out in SZ when water cut was 60%. By then, conduction of polymer flooding in early phase (WCT<10%) was just discussed in theory. For offshore oilfield, the treatment of water could be costly. Because polymer improves mobility ratio of replacement fluid over oil and sweep efficiency, less water is injected and less water is produced. So, we did enormous research about the polymer flooding on early stage by theoretical analysis, series of experiments and chemical flooding simulation. Based on these researches, we carried out the first field test of polymer flooding on early stage in LD. Single well polymer injection test was started in Mar 2006 when the water cut in the pattern was lower than 10%. After the trial, there were other 5 water injectors being converted to polymer injectors from 2007 to 2009. The polymer flooding controlled reserve was about 25,250,000 m3. 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 producing 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 merely water flooding. In addition, we observed the drop-down on the water cut in some wells, such as A11, A12, A13, A15, etc. For the well A11, the highest water cut reduction reached 41% after the injectors (A5/A10) profiles controlled, and net incremental oil for A11 even reached 154,510 m3. By Dec 2014, the total incremental oil by polymer flooding was about 754,650 m3, and the stage oil recovery efficiency was enhanced by 3.0%. The polymer flooding is still effective, and we will get more oil from the polymer flooding.