Gas kick dynamic circulation in MPD operations with water based drilling fluid: Maximum casing pressure modeling and validation

Abstract

The use of water-based drilling fluids enables the rapid detection of a gas influx by pit gain monitoring due to the low solubility of gases in the aqueous medium. Moreover, as the influx remains as a free gas, it undergoes a process of expansion the further it rises through the well, changing the pressure profiles and producing a pressure peak when it reaches the surface. Therefore, the gas influx must be controlled appropriately. Otherwise, the maximum pressure experienced during the kick circulation may exceed the safety limits of surface equipment, placing the operation and the rig crew in a hazardous situation. The Managed Pressure Drilling (MPD) technique allows for a more precise detection and control of the influx while retaining the ability to circulate dynamically small volumes of gas kick through the riser, minimizing the risks involved and the non-productive time (NPT). However, the decision of when to apply dynamic or conventional circulation techniques must be considered carefully, taking into account factors such as predictions of pressure peaks, as well as intensity and volume of the kick. In this way, it is paramount that the maximum pressure during the circulation be estimated before the operation begins to ensure that the decision is made correctly. This paper presents the results of a gas kick circulation simulator specifically developed to predict pressure peaks. This simulator uses a mathematical model based on algebraic equations whose solution requires low computational effort and, therefore, regarding gas kick incidents, is an interesting tool that can aid in guiding decision-making. The results of pressure peaks were successfully validated by employing literature data, experimental drilling setup runs and simulations performed in a commercial software largely consolidated in the petroleum industry: Drillbench.