Page 122 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

114 Hybrid Enhanced Oil Recovery using Smart Waterflooding

high- and low-salinity brines, the cores used in the condition, not in miscible condition, another assess-
experiments are determined as water-wet. The perfor- ment is performed to investigate the factors contrib-
mances of CGI and CO 2 WAG processes are assessed uting the oil production delay. The delay in oil
with CO 2 utilization factor and tertiary recovery factor. breakthrough is hardly observed in miscible condition
The CO 2 utilization factor is defined as the volume of because of an increasing CO 2 density. In the immiscible
CO 2 gas injected under the standard condition per a CGI process, brine type changes and the delay in
barrel of oil as defined in Eq. (5.1). It is conveniently oil production is evaluated. The higher salinity and
used to evaluate the feasibility of CO 2 injection project. monovalent condition injecting 5% NaCl brine shows
Tertiary recovery factor, defined as Eq. (5.2), is used to less delay in oil production compared with the low
normalize the tertiary oil production of CO 2 injection salinity and multicomponent condition injecting the
after secondary waterflood. In contrast to the simple Yates Field brine. The degree of delay in oil production
oil recovery analysis, they are more appropriate to is explained with the CO 2 solubility in immiscible con-
determine the contribution of CO 2 injected on the oil dition. Additional coreflooding confirms the role of
production by considering both the CO 2 amount CO 2 solubility in brine on the delay in oil production.
injected and remained oil amount. After the secondary waterflood using CO 2 -saturated
Yates Field brine or using normal Yates Field brine,
V CO 2 injection the tertiary recovery of CGI is investigated. In the results
¼ (5.1)
UF CO 2
V oil production
of tertiary recovery factor, the secondary injection of
CO 2 -saturated brine hastens the oil production of
V oil production
TRF ¼ (5.2) tertiary CGI. The observation from the coreflooding
V residual oil; waterflood V total CO 2 injection
confirms the role of salinity- or ionic composition-
indicates the CO 2 utilization factor; dependent CO 2 solubility in brine on the oil produc-
where UF CO 2
V CO 2 injection is the total volume of CO 2 injected; tion of CO 2 injection. This experimental study might
V oil production is the total volume of oil produced; TRF is not demonstrate the synergetic effects between LSWF
the tertiary recovery factor; V residual oil, waterflood is the re- and CO 2 injection. However, it is obvious that the ionic
composition and salinity of brine can be crucial factors
sidual oil volume after waterflood; and V total CO 2 injection
is the total pore volume of CO 2 injection. to influence the performance of CO 2 injection.
When the 5% NaCl brine is injected, tertiary CGI Aleidan and Mamora (2010) experimentally investi-
gated the effects of lowering water salinity on the oil
shows higher oil recovery by 9.2% than tertiary CO 2
WAG in the miscible condition (Fig. 5.1A). In the recovery of coreflooding of simultaneous water and
immiscible condition, both CGI and CO 2 WAG have CO 2 injection and CO 2 WAG processes. The study also
similar oil recovery of 23% (Fig. 5.1A). The higher oil carried out the waterflood and continuous CO 2
recovery of CGI is attributed to the higher CO 2 amount injection processes for a quantitative comparison. Before
injected. The analysis of tertiary recovery factor the limestone coreflooding experiments, the slim tube
reasonably compares the performances of CGI and experiment measures the MMP of West Texas dead oil

CO 2 WAG processes (Fig. 5.1B). The higher TRF is with 31 API. The MMP is determined as 1800 psi at
observed in CO 2 WAG over CGI in both miscible and which the oil recovery reaches to 90%. Making the
immiscible conditions. The lower TRF of CGI implies miscible condition system, the coreflooding experiments
the lower economics compared with CO 2 WAG process. are conducted at 1900 psi and 120 F. To observe the

Interestingly, the oil recovery by CO 2 injection in both effect of salinity, the salinity of brines is adjusted by
miscible and immiscible conditions is delayed controlling the NaCl concentration. For the waterflood
(Fig. 5.1B). The other CGI and CO 2 WAG processes experiment, two salinity levels of 0 and 6 wt% are
using Yates Field brine draw similar trend of total oil used. For the WAG process experiment, three salinity
recovery and tertiary recovery factor (Fig. 5.2). Miscible levels of 0, 6, and 20 wt% are prepared. The waterflood
condition is more favorable to oil recovery in both experiments injecting the distilled water and saline water
processes than immiscible condition. Although CGI show the equivalent oil recovery of 54% produced.
shows higher oil production than CO 2 WAG, tertiary Lowering salinity in brine hardly contributes to increase
recovery factor shows opposite result. Regardless of the oil production. It is explained that the system of
brine types, the CO 2 WAG is determined to produce waterflood does not satisfy the suggested conditions to
higher economics of tertiary recovery than CGI, provoke the mechanism of LSWF in carbonate rocks.
especially in miscible condition. Because the delay The brine does not have any potential-determining
in oil production is also observed in immiscible ions, and the temperature is low. These results screen