PVT behavior of methane and ester-based drilling emulsions

Well construction is especially complex in deep and ultra-deep water, where large Brazilian oil and gas reserves are located, demanding the use of synthetic-based drilling fluids, which have adequate characteristics such as lubricity, shale stabilization and low toxicity. Hydrocarbon gas kick will dissolve to some extent in any drilling fluid, but this effect can generally be ignored with a water-based drilling fluid. However, an operator working with synthetic-based drilling fluid must have training in gas solubility to avoid a blowout situation. Methane is the main component of natural gas, while ester can be used in the formulation of synthetic drilling fluids. To study phase equilibrium of these gas-liquid mixtures, at high pressures and high temperatures, found in bottom-hole conditions, specific, work and time intensive experimental tests were performed. The objective of this work is to present the experimental PVT data obtained from methane and ester emulsion mixtures. The fluid was loaded into a PVT cell and tests were carried out at desired conditions. Gas enrichment procedure was devised to cover temperature, pressure and methane concentration range with a long-term, single liquid amount test. Thermodynamic properties such as bubble pressure, solubility, density and formation volume factor of these mixtures were calculated up to 103 MPa and 130 °C, similar to bottom-hole conditions. A model based on the Peng-Robinson equation of state was used to predict the bubble point of the mixture.