The pre-salt discoveries in deep water have evidenced a challenging environment for drilling operations because of the technical demand and restriction and also environmental regulations fomenting technological development.

Inaccurate estimation of the pressure could lead to drilling problems such as kick, lost circulation and wellbore instability. In this context, understanding the drilling fluid and gas formation mixture behavior is essential in situations of gas influx from the formation into the wellbore. These evidence the drilling fluids importance for the drilling operational efficiency, safety and cost reduction.

Since the synthetic based drilling fluids are more sensitive to the pressure and temperature variations than water based drilling fluids, the effect of pressure, temperature and mixture composition on the thermodynamic properties such as density, formation volume factor, solubility ratio and saturation pressure were determined based on PVT (pressure/temperature/volume) experimental measurements for methane and olefin mixtures. Those properties are crucial for the mixture volumetric behavior knowledge at downhole conditions especially when gas enters into the wellbore.

The experiments were conducted in isothermal conditions and a gas enrichment experimental procedure was applied. The temperature was set at a range between 25°C and 80°C while the gas molar fraction ranged from 30% to 50% and pressures up to 70 MPa.

Additionally, the data collected was compared with the teamwork database for methane and n-paraffin mixtures and methane and ester mixtures. According to the literature, olefins show less toxicity and better biodegrability when compared to isomerized paraffins and esters, therefore olefins fit in with the new requirements present by the Brazilian Institute of Environment and Renewable Natural Resources (IBAMA), which restricted the disposal of cuttings associated with paraffins in offshore operations.

Moreover, as each base has its own particularity, the findings exhibited the importance of the methane and olefin mixtures behavior knowledge at downhole conditions to guarantee the operational safety and efficiency. The experimental data will be essential to bring well control software up to date, which helps the decision-making of the engineers during well control.

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