Page 54 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

36 David A. Wood and Bin Yuan

aquifer (as was the case in Zichebashskoe oil field) results in lower incre-
mental oil recovery than LSWF injection directly into the oil zone. This
second effect could be due to the usually high sweep efficiency of water
injection directly into the aquifer; (3) reservoir heterogeneity limits the
field-wide impacts of LSWF and fail to efficiently sweep the low-
permeability flow channels.
Gamage & Thyne (2011) compared experimentally the impacts of
LSWF conducted as either a secondary or tertiary recovery mode and as a
two-phase (secondary plus tertiary) mode. They used cores from the
Berea sandstone outcrops and the Minnelusa Donkey Creek sandstone
reservoir (Permian, Powder River Basin Wyoming) and two crude oils

from other Minnelusa oil fields (API gravity 29 and 34 ; viscosity 11.5
and 8.0 cp). Their results showed increased oil recovery for LSWF in
both secondary and tertiary recovery modes (2 8% OOIP) for the Berea
sandstone, with the secondary modes at the top end of that oil recovery
range. The Minnelusa tests showed no impacts on oil recovery in tertiary
mode, but oil recovery increased significantly in secondary mode
(10 22% OOIP) with both types of crude oils. pH increased in the
effluent brine from the cores in all experiments, but less so for the
Minnelusa cores.
The experience of LSWF at the Zichebashskoe oil field and the
experiments conducted by Gamage & Thyne (2011) suggest that in plan-
ning LSWF IOR projects, the best results are likely to be achieved by
commencing LSWF from the outset of field development in secondary
recovery mode. The outcomes of the Zichebashskoe oil field suggest that
it is also prudent to consider injecting LSW directly into the oil leg of
the reservoir in some fields, and to carefully consider reservoir heteroge-
neities when selecting the locations for the injection wells.

2.6.3 Enhanced sweep efficiency by induced fines migration
during LSW flooding
The issues associated with fines migration induced by chemical environ-
ments of low-salinity fluids have aroused significant debate, due to its
positive and negative impacts. Fines migration may carry small amounts
of residual along with detached oil-coated particles from rock grains, i.e.,
improve the displacement efficiency (Aksulu et al. 2012). In addition, the
reduction of the effective permeability of the local water-phase in water-
swept areas caused by the blockage of mobile fines can provide mobility
control to enhance the sweep efficiency of the reservoir (Lemon, 2011;