Development of formation leakage model and process simulation for bullheading well control

Abstract

In the drilling process of exploiting natural gas, improper wellbore pressure control will lead to gas kicks, which will cause formation gas to enter the wellbore. If the gas reaches the ground, toxic gases such as H2S will cause environmental pollution and even large amount of drilling fluid overflow will further cause major safety accidents such as blowout. Bullheading killing is to inject killing fluid by applying pressure at the wellhead, and push the gas in the wellbore back to the formation. However, it is difficult to obtain formation parameters in high temperature and high pressure environment, and the distribution in wellbore gas is unclear, which makes it difficult to accurately simulate the well killing process and provide reference for actual construction. Therefore, through the characteristics of wellhead overflow in the process of gas kicks, combined with particle swarm optimization (PSO) algorithm, the formation parameters are solved, and then a new leakage model is derived to describe the resistance of gas being pushed back to the formation. Well W2 and Well X3 are taken as examples to verify the model. The results show that the error between wellhead pressure and actual wellhead pressure data is 6.3% and 6.9% respectively, which shows satisfactory calculation accuracy. The specific process of obtaining construction parameters for this engineering technology is put forward. The research in this paper is of great significance for modeling and guiding well killing operation by bullheading killing.