Prediction Method of Cutting Settling Velocity in Gas-Liquid Two-Phase Flow Based on Multi-Gene Genetic Programming

: The cuttings settling process becomes erratic in the complex gas-liquid mixture under gas kick, it is very difficult to accurately describe the migration process of cuttings. Meanwhile, the traditional empirical formula based on fitting experimental data is difficult to accurately predict the complex cuttings settlement. Neural network and other intelligent models with high prediction accuracy are difficult to be popularized and applied due to their black box properties. Multi-gene genetic programming can accurately describe complex nonlinear problems and automatically optimize the structure and parameters of the mathematical model, so as to effectively reduce the complexity of the model. Based on the multi-gene genetic programming algorithm, this study used a variety of input parameters to predict the settling velocity, explored the relationship between the input variables and the result, and established an explicit mathematical model of settling velocity with RMSE of 0.0896 in test set and R2 of 0.9292, which breaks the accuracy limits of traditional empirical model and the inexplicability of neural network model. This new method for predicting cuttings settling velocity in gas-liquid mixture can provide theoretical guidance for efficient cuttings migration in wellbore during gas kick. 1. INTRODUCTION The migration of bottom-hole cuttings during oil and gas well drilling and the migration of solid proppant in cracks during fracturing are examples of particle settling in the field of petroleum engineering (Xu et al, 2017). When the particles settle freely in the fluid, they will be affected by their own gravity, buoyancy and resistance (Nouri et al, 2014). When these three forces reach an equilibrium state, the particles will reach a stable settling velocity, which is called the particle terminal settling velocity (McCabe et al, 2004). Understanding the settling law and properties of solid particles in their fluid environment, such as rock cuttings and fracturing proppant, is critical for enhancing drill cleaning efficiency and fracturing design. Until now, Many industry specialists and academics have devoted a significant amount of time and effort to the study of particle settling velocity.