| Abstract | Approximately half of the world oil production is a result of water flooding. A
major concern in this process is the mobility control of the injected phase with
unfavourable fluid mobility ratio, channelling through permeable zones and,
fingering effects can occur leading to an early water breakthrough and an
inefficient flooding.
Technically, it is possible to improve the flooding efficiency by applying
enhanced oil recovery (EOR) processes (e.g. polymer flooding, steam
injection and surfactant flooding). EOR processes intend to improve the
sweep efficiency by reducing the mobility ratio between injected and in-situ
fluids and/or to improve the displacement efficiency by reducing the capillary
and interfacial forces. Polymer flooding is an enhanced water flooding
process in which the water/oil mobility ratio is lowered by adding watersoluble
polymers to water to increase its viscosity.
The most applied polymer for EOR processes is the synthetic partially
hydrolyzed polyacrylamide (HPAM). Several field projects have been carried
out utilising HPAM, and the observed trend is that these polymers show low
shear stress stability, and low salt tolerance. They are also sensitive to
elevated reservoir temperature. Additionally, polymer retention and
adsorption affect the rheological properties of the polymer solution
significantly and reduce permeability. Therefore, polymers with greater
salinity resilient and temperature resistance are needed.
Hydrophobically modified polyacrylamide is a type of associative polymers
that has been introduced to oil field applications as an alternative to HPAM
for the past two decades. The main characteristics of these polymers are
their significant enhancement of water viscosity compared with the
conventional polymers such as HPAM, and their salinity tolerance and
temperature resistance that would be more important in the real application.
In this project, phenyl-polyacrylamide (PPAM), a hydrophobically modified
polyacrylamide is studied as a potential viscosifier in waterflooding process.
PPAM is synthesised by free radical micellar copolymerisation. The synthesised copolymer was characterised and the polymer composition was
determined. Viscosity average molecular weight of copolymer was measured,
and the rheological behaviour of the polymer was investigated in both,
distilled water and NaCl solution and the results were compared with those
obtained for HPAM. Greater viscosity values were observed for PPAM in
distilled water and saline brine than HPAM.
Comparative flow experiments for polymer solutions were carried out in sand
packs to investigate the interaction of polymer, sand, and brine, and also to
study the effect of the shear rate on viscosity of the polymer in-situ. The
polymer solutions exhibited a shear thinning, shear thickening and
degradation behaviour at different shear rates. The experiments were further
carried out to investigate the polymer retention at different polymer
concentrations, and brine salinity, and the results were compared with those
from conventional hydrolysed polyacrylamide. Greater polymer adsorption
was observed at higher brine salinity for HPAM than PPAM, however,
polymer adsorption for PPAM is slightly greater than HPAM in distilled water.
Oil displacement tests were further conducted through consolidated core
samples (Benthemier sandstone). The reduction of permeability to water was
estimated, and oil recovery was measured. A greater permeability reduction
to water was observed for PPAM than HPAM solution at low salinity which is
not desirable, however, oil recovery at higher concentration of PPAM was
greater than HPAM.
In summary, PPAM can be used as a good alternative to conventional HPAM
due to strong viscosity behaviour in high salinity and temperature. Intermolecular
association of hydrophobic monomers in copolymers of PPAM
form a bulky structure which causes great viscosity enhancement of polymer
solution in distilled water. PPAM solubility in high salinity water is proven to
be greater than HPAM and the results from polymer precipitation tests
showed much less polymer precipitation for PPAM than HPAM in high saline
brine. Moreover, the results for temperature effect on polymer viscosity
demonstrated stronger temperature resistance for PPAM than HPAM. |
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