The KT-1 layer of B oilfield is a weakly volatile and low-permeability layered carbonate reservoir with developed fractures and pores. During the construction phase from 2012 to 2015, the production decline rate was 51.18%. By 2109, after water injection development, the pressure retention rate was 62%, the oil recovery index was 7% of the initial stage, the water cut increase rate was as high as 26%, the production gas oil ratio was 2150 m3/t, and the development effect was poor. To improve the development efficiency of oil reservoirs, a refined numerical simulation model based on reservoir units is established to verify the material foundation and remaining oil distribution of the reservoir, determine the occurrence status and water flow advantage channels of the reservoir, optimize the injection production well network and production policies, propose encrypted well locations and production increase measures, and demonstrate the feasibility of gas injection to improve oil recovery. After the formation pressure is lower than the saturation pressure, secondary gas caps appear in local areas, and the density of crude oil in the formation increases. Fractures make the distribution of remaining oil after water injection more complex. Although the recovery rate of the reservoir is 9.6%, the remaining reserves of the reservoir in 2019 were only 87.49% of the original reserves due to formation degassing and water flooding, resulting in a reserve loss of 2.8%. Based on the research results of water flow advantage channels, the following conclusion is proposed: densify production wells to form a row and column injection production well network, conduct periodic water injection, implement nano water injection for wells with ineffective water injection, and gas injection is better than water injection. According to research results, from 2016 to 2019, 74 new wells were deployed in areas avoiding water flow advantage channels, with an average single well oil production of 17.7 tons, a water cut of 12.9%, and a cumulative oil increase of 48.5×104 tons. After cyclic water injection, the average single well oil increase was 2.1 tons/day, and the natural decline rate of production decreased from 40.65% in 2015 to 9.4% in 2019. The development effect has been significantly improved, and the adjustment measures provide reference significance for the development of similar oil reservoirs.