Abstract Pre-salt reservoirs are located in ultra-deep Brazilian waters. The petroleum production from these reservoirs is characterized by a high gas-oil ratio (GOR) and high content of CO2 in the associated gas. The challenges for production in such the pre-salt reservoir conditions include understanding the unusual phase behavior observed in the laboratory from field samples. In this paper, we discuss the phase equilibrium data and thermodynamic modeling of the systems containing CO2/n-C16H34, CH4/CO2/n-C16H34 and CH4/CO2/n-C16H34/C14H10. Transitions observed during this study were liquid-liquid (LL), vapor-liquid (VL), and vapor-liquid-liquid (VLL). The phase behavior investigated includes equilibrium conditions observed at temperatures from 293.1 K to 353.1 K and at pressures up to 58 MPa. The Peng-Robinson equation of state with classical van der Waals mixing rule was used to correlate the obtained experimental data. Results show a complex phase behavior for the binary system CO2/n-C16H34 at 298 K, featuring two liquid-liquid regions and barotropic inversion near the VLL transition. The addition of methane to the previous system (1/1 mol ratio relative to CO2) induces a phase behavior alteration in which the liquid-liquid transition disappears. The addition of a polyaromatic component (phenanthrene), whose influence over the mean molecular weight of the mixture under test is little, increased the saturation pressure. This study contributes to show that the use of a model representing the live-oil is a good strategy to understand how chemical and physical-chemical characteristics can induce complex phase behaviors, such as those observed in reservoirs with high carbon dioxide content.

中文翻译：

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高 CO2 含量系统的相行为：实验和热力学建模

摘要 盐下储层位于巴西超深水域。这些储层的石油生产具有高油气比 (GOR) 和伴生气中高 CO2 含量的特点。在这种盐下储层条件下生产的挑战包括了解实验室从现场样品中观察到的异常相行为。在本文中，我们讨论了含有 CO2/n-C16H34、CH4/CO2/n-C16H34 和 CH4/CO2/n-C16H34/C14H10 的系统的相平衡数据和热力学模型。在本研究中观察到的转变是液-液 (LL)、汽-液 (VL) 和汽-液-液 (VLL)。研究的相行为包括在 293.1 K 至 353.1 K 的温度和高达 58 MPa 的压力下观察到的平衡条件。使用具有经典范德华混合规则的 Peng-Robinson 状态方程来关联获得的实验数据。结果显示二元系统 CO2/n-C16H34 在 298 K 下的复杂相行为，具有两个液-液区域和 VLL 转变附近的正压反转。将甲烷添加到之前的系统中（相对于 CO2 的摩尔比为 1/1）会引起相行为改变，其中液-液转变消失。添加聚芳烃组分（菲），其对被测混合物的平均分子量影响很小，增加了饱和压力。这项研究有助于表明使用代表活油的模型是了解化学和物理化学特性如何诱导复杂相行为的好策略，