Insights on the Effect of Phase
Separation on the Alkylphenol Composition
of Petroleum During Migration – a Pressure-Volume-Temperature (PVT) Experimental
Approach
Sandra Ortega-Lucach1, Thomas B. P. Oldenburg2,
Steve R. Larter2, Bernard F. J. Bowler3, Brian
Moffatt4, and Ed Clarke4
1 Instituto Mexicano del Petróleo, Mexico-City, Mexico
2 University of Calgary, Calgary, AB
3 University of Newcastle upon Tyne, Newcastle upon Tyne,
United Kingdom
4 BP group, Reading, United Kingdom
The main aim of this study was to examine the effects of phase
separation-migration related processes on the distribution of alkylphenols
between liquid and gas phases. Based on the similarity between the
pressure-temperature (PT) reduction process during petroleum migration and the
PT reduction process which occurs during reservoir engineering laboratory
pressure-volume-temperature (PVT) tests, we have therefore used a PVT
experimental approach to simulate the physical and chemical changes that
petroleum undergo during
phase
separation-migration. Results indicate that in
addition to the well known effects on the relative concentrations of light
aliphatic and aromatic hydrocarbon compounds, the physical partitioning of
petroleum components between the gas and the liquid
phase
in equilibrium in
petroleum reservoirs can affect even “high molecular weight” compounds, such as
alkylphenols. For example, there is a steady increase in alkylphenol
concentrations in the liquid
phase
with decreasing PT conditions whereas their
concentrations decrease in the gas
phase
during the PVT tests performed. A
general increase in the preferential partitioning of lower alkylated homologues
into the gas
phase
compared to higher alkylated homologues with decreasing PT
conditions was observed. Similarly, there was preferential partitioning of lower
boiling point isomers into the gas
phase
compared to higher boiling point
isomers. The results also indicate that the migration history (e.g. the
frequency and extent of multiple equilibrations between the gas and liquid
phases in a reservoir, and the release of the fluid phases during fill-spill
migration) is an important factor to be included in the geochemical
interpretation of petroleums.
AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005