Summary
This research fully investigates the impact of chelating agent pH, chelating agent’s type, water chemistry, and viscoelastic surfactant (VES) concentration on the rheology and stability of CO2 foam under harsh reservoir conditions. In this regard, a modified high-pressure high-temperature (HPHT) foam rheometer and HPHT foam analyzer were implemented to study the foam rheology and stability at 100°C and 1,000 psi. Additionally, the HPHT viscometer and drop shape analyzer were utilized to understand the role of physicochemical properties on the microstructure, stability, and rheology of CO2 foam. First, the role of L-glutamic acid N,N-diacetic acid (GLDA) pH on the foam properties and foam rheology was investigated; the results showed that GLDA has a significant effect on the viscosity, stability, and foamability of CO2 foam. The optimum foam viscosity was achieved with a GLDA pH of 3, while the highest stability was attained with a GLDA pH ranging between 4 and 7. The highest foamability was achieved with low GLDA pH (3 to 2) due to the formation of high bubble numbers with uniform fine texture. Second, different chelating agents were considered; low pH GLDA provided the highest foam viscosity and stability among diethylene triamine pentaacetic acid (DTPA) salt and ethylenediaminetetraacetic acid (EDTA) disodium salt, while high pH EDTA exhibited the highest foamability. Additionally, three types of water were studied: produced water, sea water, and formation water. The outcomes showed that water salinity significantly impacts the foam formation process, where the formation water presented poor foamability. Finally, the concentration of surfactant has a major effect on the viscosity of CO2 foam; it reached 150 cp at 100/s once the concentration increased to 6 wt%. This study provides a comprehensive understanding of the impact of additives and water chemistry on VES behavior for CO2 foam. Also, the usage of erucamidopropyl hydroxypropylsultain (SURF) is promising for the generation of high stability and foam viscosity at high salinity and high temperature and pressure.
