Page 78 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

70 Hybrid Enhanced Oil Recovery using Smart Waterflooding

salinity water as the makeup brine and evaluated the investigated the efficiency of secondary or tertiary injec-
benefits in terms of the overall economics. In compari- tion modes of LSWF and performance of LSPF on EOR
son with the conventional polymer flood, which uses potential. The synthetic seawater of 36,000 ppm TDS is
the seawater as the makeup brine, the hybrid LSPF intro- used for the connate water and injecting brine of con-
duces a number of advantages. The primary advantage ventional waterflood. The low-salinity water is prepared
underlying LSPF is the synergetic effect improving both by diluting the synthetic seawater by a factor of 10. The
wettability and mobility ratio. As a result, the LSPF im- commercial Flopaam 3630s is used for polymer injec-
proves both volumetric sweep and displacement effi- tion. The target oil is the diluted crude oil with 2.4 cp,
ciencies and enhances oil production. The deployment which is favorable for the coreflooding experiment.
of LSPF is also enabled to avoid a clay swelling and miti- Because the synthetic seawater and low-salinity water
gate critical issues, i.e., reservoir souring. In addition, it approximately have a viscosity of only 1 cp, the
expects to consume less amount of dosing polymers mobility ratio of the conventional waterflood is deter-
required to achieve a target viscosity of displacing fluid mined to be unfavorable. The coreflooding of LSWF
because of the inherent salinity-dependent viscosity of as secondary or tertiary modes indicates that the early
polymer. The lower concentration of salinity and hard- deployment of LSWF is beneficial for the increasing
ness in LSPF prevent the significant chemical degradation oil recovery. The tertiary LSWF hardly produces the
of polymer. The amount of polymer consumption deter- additional oil from the strongly water-wet cores and
mines the chemical procurement, transportation, stor- only recovers the limited oil from the intermediate-
age, and mixing and hydration requirements, and wet cores. However, the secondary LSWF is promising
operating costs in offshore environments. The less poly- to enhance oil production from the both water-wet
mer consumption requires the smaller facilities and re- and intermediate-wet cores. In addition, more
duces the capital expenditures (CAPEX) as well as enhancing oil production is observed in intermediate-
operating expense (OPEX). The saving cost in the CAPEX wet cores over water-wet cores. Although these observa-
and OPEX compensates the extra desalination costs. tions are contrast to other experimental observations
The study simulated the analysis of LSPF with the (Ashraf, Hadia, Torsaeter, & Medad Twimukye
HPAM polymer, Flopaam 3630s. The commercial Tweheyo, 2010; Rivet, Lake, & Pope, 2010), they clarify
polymer is most widely used for EOR applications the potential of LSWF to modify the wettability of Berea
sandstone core. The experiments analyze the perfor-
and approximately has 30% hydrolysis and 18e
20 million molecular weight. The viscosity of the poly- mance of LSPF using polymer or linked polymer, i.e.,
mer is experimentally measured at the various temper- gel, after tertiary LSWF. In the strongly water-wet cores,
ature and salinity conditions. The experimental results the applications of LSPF using linked polymer or poly-
estimate that the polymer concentration requirement mer of 300 ppm increase the pressure differential
achieving the specific target viscosity will be reduced without producing any additional oil. For the interme-
by a factor of 10 when the makeup brine is switched diate water-wet cores, the additional oil recovery up to
from seawater (35,178 ppm TDS) to the low-salinity 5% is obtained for the LSPF using the linked polymer.
designer water (650 ppm TDS). In addition, the study Interesting observation is that LSPF with the linked
simulated the hypothetical eight designs for LSPF pro- polymer of 300 ppm shows higher EOR potential
cess considering the injection capacity, viscosity of than LSPF with the linked polymer of 1000 ppm. It in-
polymeric solution, and existence of desalination pro- dicates that more favorable mobility ratio is a necessary,
cess and investigated the CAPEX, space, weight, and but not sufficient conditions for EOR. A following
OPEX operating LSPF process. The operating costs for experiment designs the successive deployment of
the desalination are assumed to be 6% of the total cap- LSWF, conventional polymer flood, and LSPF in the in-
ital costs. The analysis indicates that LSPF requires the termediate water-wet cores (Fig. 4.3). The polymer
higher capital cost by a factor of three and lower OPEX flood after LSWF shows an encouraging response.
costs per year by a factor of three compared with the Because the secondary injection of LSWF ahead of poly-
conventional polymer flood. The analysis of the pre- mer flood already establishes the favorable condition
sent value with 7% discount rate indicates that the for polymer flood, the polymer flood produces addi-
payout time corresponding to the extra desalination tional oil recovery of 12%. The significant enhanced
cost is less than 4 years. oil recovery by polymer flood after LSWF results in the
Shaker Shiran and Skauge (2013) experimentally negligible contribution of LSPF after the polymer flood
carried out coreflooding using strongly water-wet and on oil recovery. Additional experiments validate the
intermediate-wet Berea sandstones. The study mainly EOR potential of combined injections. They confirm