Successful Field Application of a New Polymer Flooding Technique Suitable for Mature Oilfields Against Low-oil-Price Background – A Case Study from East China

Abstract DGXJ is a sandstone reservoir with temperature of 113 °C, salinity of 36235mg/L, and calcium and magnesium content of 1152mg/L and 30mg/L respectively. The reservoir is not only vertically multilayered and severe heterogeneous, but also witnesses water flowing channels, irregular and imperfect injecting-production well patterns, high recovery degree (43%) and high water cut (97%). A new particle-type polymer (SMG) slug combined several small linked-polymer-gel (LPG)slugs and pregelled swellable particle (PSP) was applied during 2011-2015 and achieved remarkable technical and economic effect. The application area is composed of 16 injection wells and 22 production wells. Among the 22 wells, 17 get benefit from dual directions or multi directions, which account for 77.3%. Tracer test was applied for accurate identification of planar reservoir heterogeneity, while water injection profile was tested among injection wells to identify inter-layer difference of injectivity. On the basis those tests PI decision technology and Fuzzy Comprehensive Judgment Meth were applied for the identification and classification of inter-well advantageous flowing channels, after which parameters of new polymer flooding combined slug were setup. Tracer testing showed a relatively large difference of water flooding velocity in different directions within the same I/P well pattern with the slowest being 3.00m/d and the fastest being 11.30 m/d. It also showed over 6 times of inter-layer water intaking intensity as inter-layer differences. The total designed volume of slugs was 0.1 PV with the main slug applying the micrometer-level new particle-type polymer SMG of a concentration of 0.2%-0.5%, the pre-set and middle conformance control slugs apply LPG added PSP of concentrations between 0.3%-0.5% and 0.4%-0.5% respectively. During the application, volumetric proportion of conformance slug and SMG slug was increased from designed 1:9 to 4:6 and SMG diameter was adjusted to sub-millimeter level. Test data showed the planar heterogeneity of 15 injection well patterns was relieved with an increase of reservoir sweeping coefficient by 4.3%. By far the reservoir has witnessed production increase for five consecutive years with 51.2% daily oil production rise, 2.5% water cut decrease and 3.12% recovery factor increase. According to economic evaluation, the costs of water flooding and EOR are 41.1 and 28.56 USD per barrel oil produced respectively which heralds the break-even capability of EOR even against a backdrop of oil price plunging to 30 USD/bbl. The case study has proved that good technical and economic results can be achieved through new comprehensive EOR techniques for complex mature fields with late-stage development. Against the background of low oil price, the application of high-efficient EOR techniques is high likely an effective measure to maintain economic and sustainable development. The opinion of the paper may provide some reference for oil companies to make investment decision in low oil price period.