Abstract
The study of the interaction between the formation gas and the drilling fluid during offshore operations as well as in HPHT environment is essential to safely and economically drill the pay zone of the well. The environmental regulatory issues and the peculiar technical aspects involved in deep and ultradeep waters require low toxicity synthetic drilling fluids. The main objective of this study was to understand the PVT behavior of those fluids by the experimental determination and modeling of thermodynamic properties such as: solubility, specific gravity and formation volume factor of the fluid. Those properties have a direct impact on kick detection and circulation out of the well and should be addressed in well control planning and execution. The experimental work was conducted in a PVT lab, using mixtures of methane and n paraffin based emulsions as unweighted drilling fluids, tested at the temperatures of 158, 194 and 302o F. The pressure, temperature and fluid composition effects on those gas-liquid properties were analyzed and the experimental data for solubility and formation volume factor compared to predictions considering the additivity hypothesis and mathematical fittings based on the experimental data. A model for the methane and n paraffin system based on literature data and Peng-Robinson equation of state has also been fitted to the data in order to discuss the application of the additivity hypothesis for the emulsions. Pit gain evaluation based on the correlated experimental data for the synthetic drilling fluid has been performed and compared to the values expected for water based muds.
