SPE Journal
Volume 18,
Number 1,
February 2013,
pp. 124-133
Summary
The goal of this work was to pursue strategies to improve oil recovery in
highly fractured carbonate reservoirs by altering the wettability from oil-wet
to preferentially water-wet at high temperature (100°C or above), high
salinity, and especially in high-hardness environments. Cationic surfactants
and anionic surfactants were investigated for their compatibility with hard
brine at a high temperature. Sequestration agents were added to improve aqueous
solubility. The performance of surfactant formulations was evaluated by
measuring contact angles on calcite plates and spontaneous imbibition in
originally oil-wet dolomite cores. Cationic surfactants altered the wettability
of oil-aged calcite plates toward a more water-wet state in the presence of
hard brines; oil recovery by spontaneous imbibition from dolomite cores was 50
to 65% of original oil in place (OOIP). Anionic surfactant formulations changed
the carbonate wettability to strongly water-wet only when the brine salinity
and divalent-ion concentration were reduced. The wettability could be altered
in hard brines if a sequestration agent [e.g., ethylene diamine tetraacetic
acid (EDTA)] is added to anionic surfactant formulations; up to 45% of OOIP was
recovered by spontaneous imbibition. EDTA provides alkalinity, saponification,
chelation of divalent ions, and dissolution of dolomite, which may contribute
to the increase of imbibition rate and ultimate oil recovery in fractured
carbonates.
© 2013. Society of Petroleum Engineers
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History
- Original manuscript received:
14 February 2012
- Meeting paper published:
14 April 2012
- Revised manuscript received:
11 June 2012
- Manuscript approved:
13 June 2012
- Published online:
9 January 2013
- Version of record:
28 February 2013
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