Calculation of the timing for polymer flooding upward return in the second-class oil layers of D oilfield

In order to reasonably determine the economic limit of water cut under different economic conditions, and fully consider the maximization of oilfield benefits and evaluate economic benefits of oilfield production, we propose a new method based on the principle of profit and loss balance and the law of production decline to clarify the timing of upward development, in response to the issue of the replacement and production timing of polymer flooding potential layers in the second-class oil layers. Breaking the industry standard of selecting the value of 98% as the limit of water cut, based on oil prices using the input-output balance theory, a calculation model for the economic limit water cut of individual wells undergoing polymer flooding is derived based on economic parameters such as oil prices, actual oilfield output, costs, and taxes. The production decline law is used to predict the future trends in water cut changes in oil layers during the subsequent water flooding stage. Combined with the economic limit of water cut, we determine the break timing for reaching the even point, i.e., the timing of replacing the layer system for production. Taking the second-class oil layer of D oilfield as an example, the economic limit water cuts under different oil prices and liquid production scales are calculated, evaluating whether oil well production is economically viable and predicting changes in water cut, thereby clarifying the development and production timing. The results indicate that the economic limit water cut is positively correlated with oil prices and daily liquid production. For chemical flooding reservoirs with a high oil recovery rate, the limit water cut can reach 99.02% at high oil prices, significantly exceeding the industry standard. The predicted development and production timing based on the established economic limit water cut model extends the lifespan of economically productive periods during high water cut phases, greatly enhancing economic efficiency and providing important guidance for the chemical flooding development of oilfields.