Page 116 - Fundamentals of Enhanced Oil and Gas Recovery

104 Pouria Behnoudfar et al.

RBA is the other technique utilized for the estimation of the MMP parameter. Its
normal usage is for a fast and approximate range of gas oil miscibility. This technique is
qualitative in nature, which recognizes miscibility from visual observations. Subjective
interpretations of miscibility from visual observations are an advantage of this method,
whereas lack of quantitative data to support the results is a main disadvantage [23].
P X diagrams method is also time consuming, expensive, and requires a large
amount of fluids, and it is also subjected to some experimental errors [23].
The VIT technique has been recently developed and employed to measure the
miscibility conditions of various crude oils with different gases such as CO 2 [26 28].
The VIT technique is based on the measurement of equilibrium IFT between crude
oil and CO 2 as the pressure increases for the equilibrium IFT between the two phases,
which approach zero at miscible condition. Determination of MMP by using this
approach takes 4 6 hours, while slim-tube method takes 4 6 weeks [25]. In VIT
experiment, the equilibrium IFTs between an oil phase and a gas phase can be
accurately measured at different equilibrium pressures and reservoir temperature by
applying the ADSA technique for the pendant drop approach [29]. A schematic dia-
gram of the experiment setup used for measuring the dynamic/equilibrium IFT
between the dead/live crude oil and pure/impure CO 2 by applying the ADSA tech-
nique for the pendant drop case is reported in the relevant literature [30].
The major component of the above-mentioned experimental setup is a high-
pressure IFT cell. The light crude oil and CO 2 are stored in two transfer cylinders.
The temperature effects on the MMP and maximum injection pressure may be esti-
mated by applying the VIT technique. The following correlations could be utilized
for determination of MMP for cases which the test temperature T is considered as
show below [29]:

MMP 5 0:116ðT=KÞ 2 27:1 for dead oil and pure CO 2 system (4.1)
MMP 5 0:222ðT=KÞ 2 51:0 for dead oil and impure CO 2 system (4.2)

MMP 5 0:168ðT=KÞ 2 42:7 for live oil and pure CO 2 system (4.3)
MMP 5 0:194ðT=KÞ 2 42:2 for live oil and impure CO 2 system (4.4)
where MMP and T stand for minimum miscibility pressure in MPa and reservoir tem-
perature in K, respectively. In addition, the maximum injection pressure can be deter-
mined by the subsequent equations as follows [29]:
P max 5 0:384ðT=KÞ 2 102:8 for dead oil and pure CO 2 system (4.5)

P max 5 0:281ðT=KÞ 2 61:9 for dead oil and impure CO 2 system (4.6)
P max 5 0:417ðT=KÞ 2 113:5 for live oil and pure CO 2 system (4.7)

P max 5 0:247ðT=KÞ 2 50:8 for live oil and impure CO 2 system (4.8)