Predictions of Swab/Surge Pressure of Tripping Under Pump Circulation Based on Narrow Slot Geometry

ABSTRACT: Swab/Surge pressure will increase the risk of wellbore stability such as lost circulation, wellbore collapse, kicks, and even blowouts, particularly in formations with narrow safe mud weight windows. The existing studies for predicting swab/surge pressures only consider pressure variations induced by tripping and hardly consider the effects of pump circulation during tripping. This paper presents a new steady-state model based on narrow slot geometry. The model aims to predict swab/surge pressure during tripping with pump circulation. Meanwhile, to mitigate the impact of fluctuation pressures on wellbore stability, the design of tripping speed, and pump displacement are investigated in this study. Results show pump circulation increases the pressure in the wellbore, partly offsetting swab pressure and increasing surge pressure. The faster the speed of tripping, the higher the fluctuation pressure. This study provides a theoretical foundation for predicting swab/surge pressure, which is of significant practical importance and application value in reducing wellbore instability caused by fluctuation pressure. 1. INTRODUCTION In deep and ultra-deep drilling, accurately predicting pressure variations in the wellbore is crucial, especially in formation with a narrow safe mud weight windows (Cayeux and Daireaux, 2017; SUN et al., 2024; Wei et al., 2024). Tripping, casing and cementing can generate pressure variations (Balanza et al., 2015). Pressure variations caused by tripping are referred to as fluctuation pressures, which include swab pressure and surge pressure. Swab pressure, which is usually defined as a negative value, reduces the pressure in the wellbore (Mohammad and Davidrajuh, 2022; Meng et al., 2019). Figure 1, excessive swab pressure lowers the wellbore pressure to an unbalanced state, increasing the risk of wellbore collapse. Formation fluids enter the wellbore, potentially leading to a kick and eventually a blowout (Huang et al., 2022; Wei et al., 2022). Conversely, surge pressure, which is usually defined as a positive value, increases the pressure in the wellbore that may be in an overbalanced state. Figure 2, excessive surge pressure can lead to formation fractures or continuous leakage of drilling fluid into the permeable formation, ultimately resulting in lost circulation. Fluctuation pressure is a cause of wellbore instability (Cao et al., 2014; Zhao et al., 2023; Fekete et al., 2015). Therefore, accurate prediction of fluctuation pressure is essential for safe and efficient drilling (He et al., 2016; Ettehadi and Altun, 2018; Erge et al., 2018).