A novel early gas kick monitoring method using the difference between downhole dual measurement points pressure and a genetic algorithm-based model

Abstract

Prompt monitoring of early gas kicks is critical to drilling safety. Untimely detection or inappropriate control measures can easily lead to well-blowouts, resulting in enormous human and economic losses. Existing early gas kick monitoring methods need more functionality. They must provide solutions for qualitative detection and quantitative inversion of the annulus gas fraction. Firstly, this paper establishes a gas kick simulation model to describe the changes in annulus pressure accurately and verifies its accuracy using laboratory data. Secondly, the pattern of change in the annulus flow rate and its relationship with annulus gas fraction during gas kick are analyzed. In addition, the method for detecting gas kick and the model for calculating the annulus gas fraction are proposed. Finally, an annulus flow rate inversion method based on the difference between downhole dual measurement points pressure and a genetic algorithm is presented, the method's stability is analyzed, and the distance between two measurement points is optimized. The results indicate that a gas kick at the bottom of the well increases the annulus flow rate, which serves as a critical parameter for early gas kick detection. The method for annulus flow rate inversion is minimally affected by the accuracy of downhole pressure and temperature measurements. The gas kick monitoring method detects gas kicks 31.0 min earlier than the conventional pit gain method with an average relative error of less than 10% in the annulus gas fraction backward value. To improve the accuracy of the gas kick monitoring method, the optimal distance between two measurement points is 30 m, and the minimum annulus gas fraction is 3.85%. The combination of the early gas kick monitoring method with the downhole dual-measurement point measurement system has significant value in guiding the reduction of downhole gas kick risks and optimizing the well control scheme.