Page 81 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

CHAPTER 4 Hybrid Chemical EOR Using Low-Salinity and Smart Waterflood 73

Vermolen, Pingo Almada, Wassing, Ligthelm, and the extra cost in OPEX/CAPEX for the desalination is
Masalmeh (2014) validated the prospective benefits much lower than the saving in OPEX for the less poly-
and synergetic effects, which can be drawn for LSPF. It mer injection, securing chemical stability of polymer us-
is summarized that the low salinity makeup brine can ing low-salinity makeup water significantly increases
secure a number of benefits to polymer flood: (1) chem- the economics of LSPF. The second experiment evalu-
ical stability; (2) mechanical stability, especially, at high ates the viscosity loss by the mechanical degradation
temperature condition; (3) less adsorption; and (4) less at different shear rate and salinity conditions. The exper-
scaling and souring problems. The benefits provide less iment calculates the degree of polymer degradation,
amount of polymer required to reach the target viscosity and it is observed that the viscosity loss by shear force
as observed in previous studies. In addition, it is sug- increases with an increase in salinity as shown in
gested that the LSPF introduces the mechanism of Fig. 4.6. The third experiment using dynamic (oscilla-
LSWF and using low-salinity water of makeup brine en- tory) frequency sweep measurements analyzes the
hances the elasticity of polymer. The mechanism of viscoelasticity of polymer varying polymer concentra-
LSWF confidentially modifies the wettability of reser- tion at different salinity conditions. It measures the rela-
voir. In addition, the elastic behavior of polymer poten- tion between storage (elastic) modulus and loss
tially reduces the residual oil saturation. Because of the (viscous) modulus and determines the relaxation time
wettability modification and more reduction in residual of the polymer from the relation. The higher relaxation
oil reduction, the LSPF can enhance the displacement time is observed with decreasing salinity, which means
efficiency compared with the conventional polymer the increasing viscoelastic characteristics of polymer.
flood. This study tried to demonstrate the benefits by The increasing viscoelastic characteristics of polymer
measuring the polymer behavior under various condi- mobilize the immobile oil and potentially increase
tions. The first experiment of the study measures the the oil recovery. The polymer adsorption during LSPF
amounts of HPAM polymer concentration to reach is also briefly investigated in two aspects. Firstly, the
the target viscosity of polymeric solution at the different low-salinity water as makeup brine leads to the less
salinity conditions of 7000 and 700 ppm TDS. About adsorption of polymer and the degree of the reduction
half amount of polymer is required to reach the target varies with polymer and rock types. Secondly, the effect
viscosity with 50 cp at a shear rate of 11.5 s 1 in low of mixing between displacing and displaced brines on
salinity compared with the high salinity conditions. the adsorption is investigated. When the low-salinity
Another experiment estimates 34 times reduction in polymeric solution displaces high-salinity connate
polymer concentration at the salinity of 1500 ppm water, polymer adsorption occurs and polymer propa-
TDS compared with the 260,000 ppm TDS. Because gation is retarded. Until the polymer adsorption reaches

70%
60%

50%
Degradation 40% 100 ml/min

30%
150 ml/min
20% 200 ml/min
10%
0%
0 1000 2000 3000 4000 5000 6000 7000
Salinity (ppm TDS)
FIG. 4.6 Shear degradation of viscosity of polymeric solution at different share rates and salinity conditions.
(Credit: From Vermolen, E. C. M., Pingo Almada, M., Wassing, B. M., Ligthelm, D. J., & Masalmeh, S. K. (2014).
Low-salinity polymer flooding: Improving polymer flooding technical Feasibility and economics by using low-
salinity make-up brine. Paper presented at the International petroleum technology conference, Doha, Qatar,
19e22 January. https://doi.org/10.2523/IPTC-17342-MS.)