The target well is an offshore injection well designed with a two-section drilling scheme. The well has a total depth of 1,744 m and a maximum inclination angle of 34.5°. The injection intervals include four sublayers with excellent physical properties, featuring an average porosity of 36.5% and an average permeability of 3,416 mD.

The single well adopts a two-stage, three-point water injection method. However, the water injection distribution among the sublayers is uneven, with some sublayers failing to achieve the expected water injection rates.

Using wireline operations, fiber optics were deployed to the target intervals. Data from the entire wellbore, including temperature readings, wellhead flow, and pressure, were recorded under three distinct operating regimes. Based on this, distributed fiber optic sensing quantitative interpretation was conducted to accurately delineate the injection profile under graded water injection. The distribution characteristics of water injection rates for each sublayer were clearly identified.The results showed that all sublayers in the injection intervals absorbed some amount of water, but the L sublayer's water absorption was particularly low, accounting for only 7% of the total injection. This indicates insufficient water injection into the L sublayer, highlighting a significant injection-production imbalance.

Based on the interpretation results from the distributed fiber optic sensing, it is recommended that the operator adopt stratified water injection to enhance water injection into the L sublayer. This adjustment will help further clarify the pressure levels of each sublayer, providing a basis for adjusting the injection rates and pressures across the well group or reservoir in both the horizontal and vertical planes. These measures aim to improve water flooding efficiency and increase the production capacity of the single well.