Mechanism of imbibition and production enhancement of nanoemulsion in tight sandstone oil reservoirs

Abstract

Nanoemulsion， as a kind of nanoscale colloidal dispersion system， has been widely applied in unconventional oil reservoir development due to its outstanding interfacial properties and enhanced oil recovery effects. Water-in-oil type nanoemulsion systems are prepared based on the low-energy emulsification method. The intrinsic relationships among the static adsorption， wettability alteration， and spontaneous imbibition of nanoemulsion are determined by laboratory experiments， elucidating the mechanism of imbibition and production enhancement of nanoemulsion in tight sandstone oil reservoirs. The laboratory results show that the average droplet size of nanoemulsion is less than 10 nm， which can meet the droplet size requirement of entering most of the pore throat of tight sandstone and can fully diffuse and migrate in the tight pore throat， thus expanding the imbibition range. The critical micelle mass fraction of the nanoemulsion is 0.015%， which can effectively reduce the oil-water interfacial tension to about 2 mN/m. The adsorption isotherm of the nanoemulsion conforms to the Langmuir adsorption model， and the wettability alteration mechanism is mainly adsorption. The nanoemulsion can dissolve the crude oil， further disperse the crude oil through emulsification， reduce the size of oil droplets in the emulsion， and weaken the Jamin effect when oil droplets pass through the pore throat， reducing seepage resistance. Core wettability will affect the spontaneous imbibition recovery， and the imbibition recovery will increase with the increase in core hydrophilicity. There are differences in the oil recovery at the pore scale in different wettability core spontaneous imbibition， and the addition of nanoemulsion can significantly improve the recovery of small pores in the oil-wet core. Meanwhile， increasing nanoemulsion concentration and boundary openness can improve the spontaneous imbibition recovery efficiency. This is mainly because tight sandstone imbibition is dominated by capillary force， increasing boundary openness can expand the contact area of nanoemulsion， and increasing nanoemulsion concentration can improve the wettability alteration and emulsification， thus improving the effect of spontaneous imbibition.

Keywords

• tight sandstone
• nanoemulsion
• wettability alteration
• static adsorption
• spontaneous imbibition