HBDY is a sandstone reservoir, which is vertically multi-layered, severe heterogeneous, and developed with water flowing channels. The injecting-production well patterns are imperfect. It has high recovery degree, 36.2%, and high water cut, 83.9%. The average reservoir crude oil viscosity is 6.3 mPa.s. The reservoir temperature is 90°C, and the formation water salinity is 10701mg/L. A new particle-type polymer slug combined with a linked polymer gel (LPG) pre-set slug was applied during May, 2014 to Feb., 2016, and technical and economic success was obtained.
The application area is composed of 12 injection wells and 29 production wells, among which 14 producers have got benefit from dual directions or multi directions. Tracer test was applied for accurate identification of areal reservoir heterogeneity. And water injection profiles were also tested to identify inter-layer difference of injectivity. Based on the above, core flooding experiment and numerical simulation were applied to optimize and design the combined slug parameters of new polymer flooding.
Tracer testing showed a relatively large difference of water flooding velocity in different directions within the same well pattern, with the lowest velocity of 1.35 m/d and the highest velocity of 7.04 m/d. It also showed over 30 times of inter-layer water intaking and liquid producing intensity as inter-layer differences. Using produced water to prepare the liquid, the total designed volume of slugs was 0.06 PV, in which the main slug was made of the nanometer-level new particle-type polymer SMG with the concentration of 0.3%, and the pre-set conformance control slug applies LPG with the concentration of 1.2%. During the execution, due to the poor gelling quality of the LPG, the preparing water for LPG slug was changed to clean water, but the SMG slug was still prepared by produced water. SMG diameter was adjusted to mirometer level from nanometer level. So far, the project has obtained cumulative oil incremental of 35,154.4 t and income of 11,469,000 USD. The operation cost per ton oil produced is 12.6 USD, and the input to output ratio is 1:4.9. Even calculated under low oil price of 30 USD/bbl, the input to output ratio can reach 1:3.3. The project is still in the effective duration, and the technical and economic effect is significant.
It has proved by the case study that good technical and economic results can be achieved through new comprehensive EOR techniques for complex mature fields with late-stage development. The scientific nature of the program design and the timely adjustment during program execution play important role in making the project successful. The experience and lessons learned from the case study provide valuable referencing significance for further optimizing and applying the technology.