Behavior of oil in interactions with aqueous solutions under elevated and high temperatures and pressures

The behavior of oil was studied, and the solubility of its light and heavy fractions in hydrothermal solutions was evaluated at 260–700°C and pressures of 30–200 MPa. The experiments were accompanied with simultaneous growth of quartz crystals containing fluid inclusions (in the same solutions). These inclusions allowed one to trace, by means of thermobaric geochemistry, the in situ behavior of oil within a wide range of temperatures and pressures. It was shown that the oil undergoes pronounced transformations under the interactions with hydrothermal solutions. Even at 260–300°C (pressures of 30–50 MPa), the oil was enriched in light fractions. The content of these fractions was pronouncedly increased at 330–350°C (70–80 MPa pressure). This process was accompanied by the appearance of mazut-like, semisolid, and solid bitumoids in amounts that increased manifold within the 400–700°C temperature range (up to 200 MPa pressure). The oil transformations were accompanied by an ample emission of methane. At 260–300°C, the oil in the hydrothermal solution occurred mainly as liquid drops. However, at temperatures near 400°C (about 100–150 MPa pressure), the solubility of light fractions increased to about 5–6 vol % which pointed to the ability to transfer significant amounts of oil not only in the liquid-drop form but also in the dissolved form.