Page 42 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

34 Hybrid Enhanced Oil Recovery using Smart Waterflooding
(A) results and theoretical modeling. The main hypothesis is
Oil that increasing oil recovery is attributed to the lower adhe-
sion energy between crude oil and carbonate rock across
+ - + + - + - + + - + the brine. As a result, the lower adhesion energy releases
the crude oil from the surface and enables the crude oil
H O H 2 O
2
Counterions H 2 O H O H O to flow throughout the reservoir. This study suggested
2
H 2 O 2
not shown H O H OH OH O H O that three different mechanisms are interrelated and, syn-
2
2
2
2
2
ergistically, influence the adhesion energy of COBR by
- - - + - - + - - + - -
reducing ionic strength. The three different mechanisms
Mineral are (1) changes to the colloidal interaction forces; (2)
roughening, dissolution, and restructuring of the underly-
(B) ing calcite surfaces; and (3) removal of preadsorbed
organic-ionic layers (ad-layers)asflakes thatcarry withoil.
Oil The first mechanism is related to the colloidal inter-
2
H 2 O H O H O H O action forces: (1) EDL repulsion; (2) van der Waals; and
2
2
Mineral (3) hydration (structural) forces. The adhesion energy is
the result of the interaction forces between crude oil/
brine and brine/rock interfaces across the brine film.
FIG. 2.6 (A) Indirectly adhered oil through a three-layer oil/ These forces are collectively given by the extended
water/rock and (B) directly adhered oil on the rock. (Credit: Derjaguin-Landau-Verwey-Overbeek (DLVO) theory.
Brady, P.V., & Thyne, G. (2016). Functional wettability in
The extended DLVO theory calculates the adhesion
carbonate reservoirs. Energy and Fuels, 30(11), 9217e9225.
energy, and Eqs. (2.6) and (2.7) express the extended
https://doi.org/10.1021/acs.energyfuels.6b01895.)
DLVO between two spherical particles. The relationship
The carbonate surfaces have both cation- and anion- between the adhesion energy and wettability is quanti-
exchange sites. Crude oil has cationic surface groups fied with the Young-Dupré equation of Eq. (2.8),
þ
of eNH and eCOOCa , which links to the cation- which calculates the contact angle corresponding to
þ
exchange site of carbonate surface, and anionic surface the adhesion energy. Following the extended DLVO

group of eCOO , which links to anion-exchange site theory, adhesion energy decreases until ionic strength
of carbonate surface. In addition, the carbonate surface decreases and reaches to the critical ionic strength.
consists of the hydrated calcium and carbonate sites. With the Young-Dupré equation, the decrease in the
The surface charge involved with the calcite surface is adhesion energy results in decreasing contact angle
developed through the sites gaining or losing hydrogen and increasing water-wetness (Fig. 2.7). This result is
ions, i.e., surface acid-base reactions, and adsorption of attributed to the relatively higher EDL repulsive force
multivalent cations or anions on the charged sites. over other forces. However, the further reduction in
Then, the layer of the hydrated counterions is formed ionic strength below the critical ionic strength results
around the charged mineral surface to balance the in the increasing adhesion energy. This reversal trend
surface charge. Therefore, the EDL forms at the interface across the critical ionic strength is responsible for the
of mineral and water. At the interface of oil and water, effect of brine concentration at a specific distance on
another EDL generates. Conventionally, the oil the EDL repulsion force. The concentration of brine
and mineral surface charges are referred by measuring less than critical ionic strength makes negligible EDL
z-potential. However, this study suggested the develop- contribution. It implies optimum ionic concentration
ment of the predictive model, which employs surface to maximize the wettability modification toward
complexation models of the oil and carbonate inter- water-wetness and, consequently, oil recovery.
faces to describe the surface mechanisms quantitatively. 64k B T zej 0 2
The complexation models are constructed using a WðdÞ¼ k C tanh 4k B T expð kdÞ
diffuse layer model of the EDL. Then, the indirect adhe- 20 (2.6)
A d
sion of oil on the carbonate surface is formulated 2 þ d
12pðd þ DdÞ
through bridging between the two complexation
models of the oil and carbonate interfaces. where W is the colloidal interaction force; k 1 is the
Another study by Chen et al. (2018) formulated the Debye length; k B is the Boltzmann’s constant; T is the
interrelated mechanisms, consequently determining the temperature; C is the brine concentration; z is the brine
adhesion energy of COBR based on the experimental electrolyte valence; e is the elementary electronic charge;