Effect of Dissolution of CO2 and CH4 on the Flow Curve of Drilling Fluids

When drilling a well, careful choice of drilling fluid is essential to allow, among others, for well stabilization and lubrication of the drill bit. The apparent viscosity of a drilling fluid is one of its major properties affecting the ability to be pumped and to transport particles. However, when the drilling fluid is circulated in a well, it may meet components that affect its properties. Here we investigate the case of a gas kick, i.e., fluid from the rock formation entering the wellbore, and evaluate how the reservoir fluid dissolution affects the apparent viscosity of the fluids. The drilling fluid-reservoir fluid mixtures are prepared at high pressure (400 bar) in a 1L piston bottle, and the apparent viscosity is measured with a high-pressure Couette cell provided by Anton Paar. Several drilling fluids are tested, and as reservoir fluids, we perform experiments with CO2, CH4, or a mix of both. The results show that reservoir fluid dissolution decreases the apparent viscosity of the fluids at given temperature and pressure conditions. The experimental results will be used to calibrate numerical models in order to improve a well-control evaluation software.