CO2 Well Control Scenario Prediction Using Experimentally Verified Models

Abstract Objectives/Scope With the expected upscaling of the Carbon Capture and Storage (CCS) activity in coming years, the need for drilling infill wells for CO2 sequestration, i.e. wells that penetrate formations that already contain stored CO2, will inevitably arise. Hence, the risk of a CO2 well control event must be considered. This paper describes an approach to well control evaluation using software based on experimentally verified models, demonstrated through simulations of realistic case scenarios. Methods, Procedures, Process In order to achieve a software tool for evaluating potential well control scenarios for CO2 infill wells, it is crucial to obtain a good understanding of the behaviour of drilling fluids when exposed to CO2. This involves several aspects, such as density, phase state, rheology, robustness, particle sedimentation and risk of hydrate formation. Extensive laboratory studies have been performed to fill knowledge gaps in these areas and to obtain data for calibrating mathematical models describing the CO2-drilling fluid interaction. These models are then integrated into an existing hydraulic flow model framework, which is used in a well control evaluation software. Results, Observations, Conclusions Results from simulations using a well control software upgraded with capabilities for handling CO2 influx are presented and discussed. The input data for the simulations represent a case scenario supplied by an operator. In particular, the impact of CO2 influx on volume expansion and kick severity as the influx volume of CO2 is transported up the wellbore is discussed. Furthermore, the simulation software includes integrated models as resulting from laboratory studies of drilling fluid exposed to CO2. In a well control context, the thermophysical properties of CO2 may in many ways be more challenging than those of methane, e.g. with the presence of the critical point inside the typical operational envelope. It is also observed from the laboratory experiments that the impact of CO2 on drilling fluids is different than of methane. How these aspects contribute to different requirements for the models is discussed. Novel/Additive Information This study contributes to improved understanding of how a CO2 influx and its impact on drilling fluid properties affect the severity of well control incidents. For supporting the understanding, differences and similarities with respect to natural gas influx are presented.