Effect of Salinities on Supercritical CO_2 Foam Stabilized by a Betaine Surfactant for Improving Oil Recovery

摘要

A zwitterionic surfactant, hexadecyl hydroxypropyl sulfo betaine, was examined for its ability to stabilize supercritical CO2 (SC-CO2) foam, with the goal of improving the oil recovery from mature oil fields with high temperatures and salinities. Herein, we present a detailed investigation of the effect of salinity on SC-CO2 foam. First, the bulk foaming capacity was assessed for a betaine surfactant with different salinities, using a high-temperature, high-pressure (HTHP) foam generation apparatus. The effect of salinity on the rheology, flow resistance, and foam texture of the SC-CO2 foams was characterized using a flow loop apparatus with a capillary tube and high-pressure visual cell that was under HTHP conditions. The stabilization mechanisms of the salinity for the SC-CO2 foam were also explored by means of a HTHP interfacial tensiometer. Experimental results showed that the foaming volume slightly decreased, whereas the stability and apparent viscosity of the SC-CO2 foam increased with increasing salinity. The foam half-life increased approximately 1.6-fold, from 22.2 to 35.2 min, while the apparent viscosity increased from 43.4 to 62 mPa s at 16 s(-1). The resistance factor of the steady-state CO2 foam increased from 48 to 53 with increasing salinity, and the bubble size was approximately 10-20 mu m during the core flooding experiments. The experiments indicated that the salinity could enhance the stability of the foam against film drainage and bubble coalescence. The interfacial experiments presented evidence that salt ions could drive more betaine surfactant molecules to adsorb on the lamella interface. The greater surfactant adsorption provided the large steric repulsion between bubble lamellae and enhanced the disjoining pressure, thereby improving the foam stability.