Injection of Xanthan Gum and Guar Gum Through Carbonate Rocks Evaluated by Two-Phase Core Flooding

Polymer flooding is widely applied to enhance oil recovery in sandstone reservoirs. However, applications in carbonate formations are challenged by the possible high adsorption of anionic polymers such as polyacrylamides and xanthan gum. Non-ionic biopolymers such as guar gum could be used to minimize retention. Many investigations using guar flooding have been conducted, but none targeted carbonate reservoirs. This work compares oil recovery improvement, water production delay, mobility control, injectivity, and polymer utilization in carbonate core flooding at reservoir conditions (salinity of 30,905 ppm and 60 °C) with xanthan (700 ppm) and guar (2500 ppm) solutions. A rheological study was performed to select target polymer concentration and solution viscosity. Indiana limestone and light mineral oil (viscosity of 6.55 ± 0.05 mPa · s at 60 °C) were used to represent the reservoir rock and oil. Guar flooding led to faster oil recovery, water production delay, and better injectivity than xanthan flooding, although the polymer utilization factor was higher. The ultimate oil recovery increased by 12.7 ± 7.0% and 9.0 ± 6.1% over waterflooding after guar and xanthan injections. The inferior performance of xanthan gum can be attributed to higher retention, especially close to the core inlet (residual resistance factor of 28 ± 4), and lower in-situ viscosity. The results suggest that guar may be a promising candidate for polymer flooding in carbonate reservoirs at moderate temperatures and salinities. In contrast, xanthan applications in these reservoirs must be carefully evaluated due to its high retention potential.