INVESTIGATION OF THE EFFECTS OF WAX CONTENT ON MINIMUM MISCIBILITY PRESSURE OF CARBON DIOXIDE IN WAXY OIL

The reservoir engineer's objective is to produce from oil and gas reservoirs with the
highest economical recovery factor. For this reason, Enhanced Oil Recovery (EOR)
methods were developed. EOR methods can increase field recovery factor and prolong
field life, thus improving its economic value (E.Manrique and !.Wright, 2005). One of
EOR methods that is becoming favourable is miscible displacement. For this method,
there are a range of gasses suitable for miscible displacement (e.g. Propane and
Methane), however, Carbon Dioxide (C02) is most commonly used due to availability
and less expensive than Liquefied Petroleum Gas (LPG). C02 can also reduce the oil's
viscosity.
In miscible displacement, one of the most important parameters that need to be
investigated is minimum miscibility pressure (MMP). This is the pressure where the
crude oil and C02 gas will become miscible. MMP can be affected by wax content,
however to an unknown degree. Waxy oil constitutes that the oil has paraffin content in
it. After weighing the options, experimental work was chosen to determine MMP of oil
samples and the effects of wax content on C02 MMP; and a technique called the
Vanishing Interfacial Tension (VIT) will be employed. The basic principal of this
technique is that when MMP is achieved, the IFT between C02 and oil will become
zero. Several oil samples with varying wax content have been experimented to obtain
the pressure at which the IFT approaches zero, also known as MMP.
5 samples were concocted for the experiment. However, the experiment failed to obtain
one of the sample's MMP due to technical difficulties. MMP for the following samples
were obtained; 3446 psi, 3706 psi, 3391 psi and 3332 psi for 5%, 15%, 20% and 25%
wax content respectively. As noted from 5% and 15%, the MMP increases, however
from 15% to 25%, it suddenly decreases. The theory is that there may be insufficient
points to extrapolate because of equipment safety limitations. From the experiments, it is
concluded that with increasing wax content, the MMP will also increase.