Page 78 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

60 David A. Wood and Bin Yuan

2.12 CONCLUSIONS

• Many experimental studies and several field tests have demonstrated
the benefits of the LSWF method in terms of increased oil recovery
factors and lower water cuts. However, the technique does not work
in all sandstone reservoirs and requires quite specific conditions to
work in carbonate reservoirs.
• Considering a wide range of recent studies, tests, and trials, it is appar-
ent that there are multiple factors and driving mechanisms at play in
LSWF. These include electrical DLE, MEI, the presence of calcium
and magnesium ions in the injected water, and multiwet fines migra-
tion. The net effect of the combined mechanisms is a desorption of
petroleum heavy ends from the clays present on the pore wall, result-
ing in a more water-wet rock surface, a lower remaining oil saturation,
and higher oil recovery.
• Some of the impact of the multiple mechanisms at work in LSWF
lead to both positive and negative formation damage outcomes (e.g.,
fines migration).
• The induced fines migration by low-salinity water delays water break-
through, improves sweep efficient by fines migration assisted mobility
control, and leads to uniform allocation of injected fluid entering each
layer. However, fines migration can also lead to troublesome forma-
tion damage resulting in a reduction in permeability and the decline
of well injectivity.
• Established correlations between residual oil saturation and the
wettability-related attributes, including contact angle, IFT, and capil-
lary pressure as functions of salinity help to improve the accuracy of
reservoir simulation predictions associated with LSWF. Recently
developed electrokinetic techniques offer potential to monitor the
dynamic changes in wettability as LSWF progress through streaming
potential and zeta potential measurements.
• As uncertainty exists concerning the main mechanisms at work in
specific reservoirs subjected to LSWF, there is the risk of it being
ineffective or less effective than expected. Consequently, the predictions
of core-flooding experiments and simulation analysis may be inaccurate,
due to incomplete or incorrect assumptions, meaning that pilot well test-
ing and/or field trials are typically required to confirm its performance.