Dynamics of <i>In Situ</i> CO<sub>2</sub> Foam Using Natural and Synthetic Surfactants under Different Injection Modes in Sandstones: Implications on Enhancing Oil Recovery and CO<sub>2</sub> Sequestration
Nirmala Dinesh, Alpana Singh, Tushar Sharma, P. Sivasankar
Abstract
The in situ CO 2 foam flooding (CFF) enhanced oil recovery (EOR) process is an efficient EOR technique to simultaneously improve oil recovery and sequestrate CO 2 at a larger scale. However, there is currently a lack of understanding about the influence of the injection mode (i.e., single- and three-cycle) and surfactant type (i.e., natural and synthetic surfactants) on the dynamic behavior of in situ CO 2 foam (i.e., generation, flow, and dissociation of in situ CO 2 foam) and its effects on enhancing oil recovery and CO 2 sequestration within sandstone reservoirs. To address this, five core sample flooding EOR experiments were conducted at 90 °C with a confining pressure of 2.06 × 10 7 N/m 2 . Initially, water flooding (WF) was carried out using seawater in each of the core samples that were earlier saturated with formation brine and crude oil. Subsequently, five different CO 2 EOR techniques were carried out using different injection modes and surfactant types (i.e., continuous CO 2 gas EOR process and single- and three-cycle modes of natural and synthetic surfactant-based in situ CFF EOR process), in which surfactant solutions for the CFF EOR process were prepared using DI water. The oil recovery during the WF process was found to vary from 29.75% to 35% (mean is 32.75%, standard deviation is 1.8%). The results showed that the three-cycle mode of the natural surfactant (NS) CFF EOR process generated in situ CO 2 foam with relatively higher apparent viscosity, which increased the capillary number to 3.79× 10 –5 and delayed CO 2 gas breakthrough. This allowed the three-cycle NS foam injection to recover 24% additional oil (i.e., 4% higher than single-cycle mode) and sequestrate 25% more CO 2 than the single-cycle mode of injection. Moreover, the present study proposed a new method of determining CO 2 breakthrough time from the capillary desaturation curve, which was found to be ≈ 98% accurate when compared with the actual CO 2 breakthrough time observed from core flooding experiments.