Page 44 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

36 Hybrid Enhanced Oil Recovery using Smart Waterflooding

potentially increases oil production. In addition, component with high polarity has nitrogen in the
the removal of the flakes leaves behind less organic aromatic molecules (R 3 N). Conventionally, the
materials on calcite surfaces and it makes the underly- acidic and basic materials at the oil-water interface
ing hydrophilic calcite to be exposed. Consequently, undergo the fast proton exchange reactions, which
the removal of preadsorbed organic-ionic ad-layer are sensitive to the pH of brine. The reactions at the
because of low ionic strength promotes the wetness interface are described in Eqs. (2.10) and (2.11). The
toward water-wet. The study concluded that the species of R-COOH and R 3 NH þ have the highest
increasing oil recovery via the LSWF is attributed to affinity to the negatively charged clay minerals.
the three different but interrelated mechanisms.

R-COOH þ H 2 O % R-COO þ H 3 O þ (2.10)
R 3 N: þH 2 O % R 3 NH þ OH (2.11)
þ
COMPARISON OF LSWF BETWEEN
SANDSTONE AND CARBONATE
RESERVOIRS • Formation water must be present and has divalent
2þ
Extensive mechanisms have been proposed to explain cations (Ca 2þ and Mg ).
the enhanced oil recovery of LSWF for both sandstone • Low-salinity water to be injected has salinity in
and carbonate reservoirs. Majority of the proposed mech- the range of 1000e2000 ppm TDS. LSWF effects
anisms have explained that physical and/or chemical have been observed with the salinity up to
phenomena are attributed to wettability alteration, 5000 ppm TDS.
consequently improving oil recovery. Because of the • There appears to be no effective temperature
striking differences (clay content and surface potential) conditions.
between sandstone and carbonate reservoirs, different • The produced water usually shows the increase in
physical and/or chemical reactions have been proposed pH. However, there is a controversy about whether
to explain the wettability modification underlain the pH increase is a necessary condition or just
in sandstone and carbonate reservoirs, respectively. experimental observation.
Carbonate reservoirs could contain slight clay, but it is • Experiments reported the effects of LSWF with and
not much and hardly exposed to the invading fluid. without production of fines.
Sandstone could have a wide range of clay content. In • Increasing pressure of injector is observed when
addition, inherent positively-charged carbonate and injecting brine is switched from high-salinity water
negatively-charged quartz and clay lead to different to low-salinity water.
potential reactions contributing to wettability alteration.
Conditions in Carbonate Rocks
The positively charged calcite surface can attract the
carboxylic organic component directly, and negatively • The calcite surface has positively charged potential
charged clay surface mostly needs cations to bind the because of complex molecular structure.
organic materials. Different mineralogy and surface • Crude oil must have the acidic polar component. The
potential require different conditions to explain the acidic polar component generates the negatively
wettability modification effect by LSWF for carbonate charged carboxylic materials, R-COO , as shown

and sandstone reservoirs. Following section summarizes in Eq. (2.10). The negatively charged component ad-
these conditions. sorbs on the positively charged carbonate surface. The
adsorption, initially, results in mixed- to oil-wetness
Conditions in Sandstone of carbonate reservoir. In terms of natural bases of
• Sandstone has negatively charged surface because of crude oil, they hardly coadsorb with the negatively
the abundant clay. The clay minerals are the hydrous charged carboxylic material on the chalk surface
aluminous phyllosilicates and include the several because of steric hindrance. Rather than, the acid-base
types of minerals. The clay minerals have the complexes form and they reduce the adsorption of the
negative charges occurring cation exchange, and carboxylic material implying less oil-wetness.
kaolinite and illite usually have higher capacity of • Low-salinity water to be injected must have SO 4 2
2þ
cation exchange. and Ca 2þ and/or Mg . The limitation regarding
• Crude oil has the basic and/or acidic polar compo- overall salinity is not reported.
nents. The acidic material usually has the functional • The effective temperature conditions are reported
group, the carboxylic group (-COOH). The basic with the range of 70e130 C.