INVESTIGATION OF CRITICAL PARAMETERS AFFECTING ASPHALTENES PRECIPITATION DURING C02 INJECTION IN MALAYSIAN OILFIELD

The study was conducted to investigate the fundamental aspects of asphaltene
precipitation during CO2 flooding in EOR applications. The oil samples used in this
study are from peninsular Malaysia oilfield (PMO) and Sarawak oilfield (SKO).
Asphaltenes precipitation during CO2 injection for EOR applications in Malaysian
oilfield was evaluated using Near-Infra-Red Solids-Detection-System (NIR-SDS).
Five different samples from Malaysian oilfield were investigated in this study i.e.
four bottomhole samples and one recombined sample. Variation in pressure,
temperature and composition were thoroughly investigated to monitor their impact
on CO2 induced asphaltenes precipitation tendency. Only two out of five samples
shows tendency to develop asphaltenes precipitation problem during CO2 injection
study. Variation in temperature shows no influence on asphaltene precipitation if the
asphaltenes problem does not occur during pressure changes. (Only cover Reservoir
Temperature and Wellhead Temperature).
Physiochemical properties of the two samples were compared against the non�problematic samples. It was found that crude oil that has high GOR, high API and
low molecular weight have higher propensity to create asphaltene precipitation
problem during CO2 injection. Percentage of asphaltenes deposited and precipitated
from depressurization test was recorded by HPHT filtration technique. Results show
that most of solids asphaltenes in this case are in precipitation form and the
deposited asphaltenes on PVT cell wall are a very small amount.
Precipitated asphaltenes samples were then characterized by FTIR and NMR
spectroscopy. The spectroscopic analysis found that the solids were mainly wax,
while asphaltenes could be in a very small amount and was not detected by thesespectroscopy techniques. Asphaltene modeling was then conducted on five samples
using AEOS (Association Equation of State) as underlying theory in the modeling
tool named as DBR Solids software. Asphaltene precipitation modeling by this
technique required tuning of binary interaction parameter and asphaltene molar
volume. Comparison from asphaltene model and experimental works produce a
similar result.