Measurement and modeling of methane dissolution in synthetic liquids applied to drilling fluid formulation for deep and ultradeep water wells

Most of the Brazilian oil and gas reserves are located in offshore fields. There is also a great production potential in offshore reservoirs in deep and ultradeep water depths. The drilling scenario at those depths is quite complex and the risk of blowouts should be mitigated. A well control problem would incur in loss of human lives, equipment and catastrophic environmental damages. In order to overcome technical and environmental restrictions, synthetic liquids have been applied in the formulation of drilling fluids. Synthetic based drilling fluids show excellent lubricity and shale stabilization characteristics and may be the only option when drilling in high temperature and high pressure environments. The better understanding of the interaction between formation gas and a synthetic based drilling fluid during a kick detection and circulation situation would contribute to safely and economically drill the offshore wells. The present work involves PVT measurements and thermodynamic modeling of three mixtures of methane and organic liquids (n-paraffin, ester and a iso-paraffin : n-paraffin mixture), currently applied in drilling fluid systems for deep and ultradeep water drilling, in Campos Basin (Rio de Janeiro, Brazil). The measurement of thermodynamic properties of the methane–liquid mixtures, such as bubble point pressure, solubility, oil formation volume factor, gas formation volume factor and liquid density, were performed for 70 and 90 °C temperatures. The measurements were conducted in two different apparatuses: an Hg system and an Hg-free PVT system. The thermodynamic modeling of the gas–liquid system was based on Krichevsky–Kasarnovsky correction of Henry's law. The results showed that the precise accounting of formation gas solubility in the fluid under downhole conditions and during the kick circulation is a very important issue for safely drill deep and ultradeep water wells.