Page 44 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

26 David A. Wood and Bin Yuan

LSFW is also effective in carbonate reservoirs with a range of potential
mechanisms proposed to explain its impacts on oil recovery, e.g., wetta-
bility (Al Shalabi et al., 2013), with IFT suggested as having a bigger
impact on LSWF in carbonate reservoirs, with contact angle controlling
final oil recovery (Al-adasani and Bai, 2012). Studies on chalk reservoirs
have identified that wettability alterations are impacted by the concentra-
tion of calcium and magnesium ions in the presence of sulfate (i.e., the
divalent ions: Ca 21 ,Mg 21 ,SO 4 22 ) and the overall salinity level of the
injected water (Zhang et al., 2006; Yousef et al., 2010; 2012; Hamouda
and Gupta, 2017). Many offshore carbonate reservoirs (e.g., North Sea
chalk reservoirs) have traditionally been flooded with sea water; so,
LSWF core experiments often compare the impacts of injected fluids of
various diluted brines with that of sea water. In doing so, Hamouda and
Gupta (2017) found that brines diluted 1:10 versus sea water were more
effective in terms of oil recovery from chalk reservoir than brines diluted
1:50. Also, the sulfate-rich brines performed the best, and were associated
with an increase in pH of the fluids, changes in the Ca 21 and Mg 21 ion
concentrations and pressure drop that suggested ion exchange and precip-
itation of magnesium minerals. Experiments conducted on oil-wet low-
permeability limestones (Gandomkar and Rahimpour, 2015) suggested
different outcomes for LSWF in secondary recovery mode versus tertiary
recovery mode; with no benefits observed for the latter due to an increase
in water relative permeability.
The uptake of LSWF in a wide range of reservoirs is now high for
several reasons: (1) low capital expenditure and incremental operating
costs for those reservoirs already developed with water injection
facilities and wells; (2) ease of injection into most oil reservoirs; (3) high
incremental recovery gains for light to medium gravity oil reservoirs; (4)
reduction in the scaling and corrosion of wellbore tubulars and surface-
water-handling facilities (Collins, 2011); and (5) potentially avoid
reservoir souring.

2.3 FINES MIGRATION: DETACHMENT, TRANSPORT,
AND REDEPOSITION

Khilar and Fogler (1984) identified that low-salinity water injected
into oil-bearing sandstones could cause significant formation damage