Layered injection technology for chemical flooding of Class-III oil reservoirs in the Daqing Oil Fields complex, Songliao Basin, Northeast China

The Class-III oil reservoirs of Lasaxing oilfield in the Daqing Oil Fields complex have geological oil reserves of 1.86 billion tonnes, an oil recovery of 39%, with remaining reserves accounting for more than 45% of the total geological reserves of the oilfield. Therefore, they have considerable potential for future oil production. The current layered injection technologies fail to achieve effective control over the low single-layer injection rates since they can only produce low throttle differential pressure under low injection rates (5–20 m3/d). In this study, a symmetrically-structured double-offset-hole injection allocator and a novel throttling component were developed. Their spatial layout was constructed and mechanical parameters were optimized using finite element analysis, which allows for expanding the flow rate range at low injection rates. According to experimental results, the throttle differential pressure increased from 0.2 MPa to 0.8 MPa at an injection rate of 5 m3/d, and the range of the single-layer flow rates expanded from 20 – 70 m3/d to 5–70 m3/d. The field test results show that the effective production of oil layers with medium and low permeability was achieved and that the ratio of producing oil layer thickness to the total reservoir thickness increased by 9.7% on average. Therefore, this study provides valuable technical support for the effective chemical-flooding-based development of Class-III oil reservoirs. [Display omitted] •Effective layered injection at low flow rate for chemical flooding in Class-III oil layers.•Overcoming the limitations of small chuck distances and thin barriers.•Producing reserves of Class-III oil layers achieved in field test.