An Evaluation of Spontaneous Imbibition of Water into Oil-Wet Carbonate Reservoir Cores Using a Nonionic and a Cationic Surfactant

Abstract

Some surface-active chemicals are able to improve the spontaneous imbibition of water into oil-wet carbonates. In this work, the oil recovery from oil-wet reservoir cores was compared using aqueous solutions of an ethoxylated alcohol (EA) and a cationic surfactant (C12TAB). The experiments were conducted at room temperature using short (∼5 cm) and long (∼30 cm) cores with initial water saturation in the range of 17-33%. Due to wide variation in porous structure, the cores were characterized into two groups, i.e., moldic and sucrosic. The former cores had more than 25% of the pore volume (PV) related to vugs, and the latter appeared more homogeneous. The permeability of the moldic and sucrosic cores varied between 20 and 180 and 80-350 mD, respectively. In general, the efficiency of C12TAB was superior to EA regarding spontaneous oil expulsion from the cores. For the short core experiments, about 40-45% of original oil in place (OOIP) was recovered using C12TAB, while only 10% was the average recovery using EA. The available data for the short cores gave no reasons to discriminate between moldic and sucrosic cores regarding oil expulsion. The long 162 mD sucrosic core expelled 65% of OOIP in the presence of C12TAB. The high oil recovery, compared to the short cores, was related to greater impact of gravity forces. The imbibition of EA solution into the long 45 mD core was very small, less than 5%, but large improvements were achieved when changing to C12TAB solution. Contact angle measurements on oil-wet calcite crystals confirmed that C12TAB was much more effective than EA in altering wettability toward more water-wet conditions.

Biosurfactants Produced From Agriculture Process Waste Streams To Improve Oil Recovery in Fractured Carbonate Reservoirs

“…25;31 Several researchers reported that dilute solutions of chemical surfactants can alter the wettability of carbonate rock toward a more waterwet state. [6][7][8][9][10][11][12][13] This wettability change can improve oil recovery in fractured carbonate reservoirs by accelerating the spontaneous imbibition process during water flooding. They also reported that surfactant loss due to adsorption and/or retention on reservoir rock can be significant even at dilute surfactant concentrations.…”

“…Several studies revealed that the injection of dilute surfactants into oil reservoirs could also modify the wettability of the reservoir rock. [6][7][8][9][10][11][12][13] This phenomenon can be very useful in fractured carbonate reservoirs where the wettability change can improve oil recovery by accelerating the spontaneous imbibition process. 14;15 The overall objective of this project is to evaluate the use of low-cost biosurfactants produced from agriculture process waste streams to improve oil recovery in fractured carbonate reservoirs.…”

Surfactant Based Enhanced Oil Recovery and Foam Mobility Control

“…Cationic surfactant has been used to alter wettability of carbonate formations to more water-wet conditions [1][2][3][4][5] . Standnes and Austad proposed the mechanism to be the formation of ion-pairs between surfactant monomers and the adsorbed carboxylates 1 .…”

Surfactant Based Enhanced Oil Recovery and Foam Mobility Control

“…Application of surfactants to alter wettability and thus enhance spontaneous imbibition has been investigated by Austad, et al [7][8][9][10][11] with chalk and dolomite cores. Chen, et al 12 , investigated enhanced spontaneous imbibition with nonionic surfactants.…”

“…Spinler, et al 13 , evaluated 46 surfactants for enhanced spontaneous imbibition in chalk formations. Standnes, et al 11 and Chen, et al 12 used either nonionic or cationic surfactant with a strategy to alter wettability but avoid ultra-low tensions. The work presented here differs from the previous work in that sodium carbonate and anionic surfactants are used to both alter wettability and reduce interfacial tension to ultra-low values.…”