Assessing the Feasibility of Improving the Performance of CO₂ and CO₂–WAG Injection Scenarios by CWI

Abstract

In water-wet systems, the oil recovery performance of CO2 and CO2–WAG injection scenarios is negatively affected when the injection pressure is below the minimum miscibility pressure and the spreading coefficient is negative. Under these conditions, the bypassed oil in the porous medium will have the minimum surface contact area with the injected CO2. Thus, injection strategies that can improve this contact can enhance the CO2 performance. This study aims to quantify the impacts of injecting carbonated water (CW) prior to CO2 injection on oil recovery by CO2 and CO2–WAG injection scenarios. For this aim, a series of integrated high-pressure and high-temperature coreflood, micromodel and IFT experiments were performed using live crude oil. Coreflooding tests indicate that the preflush of CW improved the sweep efficiency of CO2 injection by 6.6% of the original oil in place. According to micromodel experiments performed under the condition of coreflood tests, during CWI period, CO2 partitioning from CW into the remained oil led to oil swelling, which in turn led to an increase in the remained oil saturation. Oil swelling also led to rupturing of the water layers shielded isolated oil ganglions and thus reconnection of isolated oil ganglions. Due to these changes, more oil will be accessible to the CO2 stream which in turn can favor the CO2 recovery performance. More importantly, IFT experiments showed that the preflush of CW impacts the interfacial tensions between the fluids (oil–water–CO2) and the spreading coefficient. Preflush of CW shifted the spreading coefficient from a negative value to a positive value. In a water-wet system, this shift maximizes the oil spreading or surface contact area between the CO2 and oil, and consequently favors the oil recovery performance of CO2 injection.

Experimental Investigation of Oil Recovery Performance and Permeability Damage in Multilayer Reservoirs after CO2 and Water–Alternating-CO2 (CO2–WAG) Flooding at Miscible Pressures

“…Flooding with both CO2 and CO2-WAG are common EOR strategies which have been widely used in a significant number of oilfields [13][14][15] . Each flooding scheme has individual characteristics in terms of displacement effect, injection difficulty, and impact on the reservoir's physical properties [16][17][18][19] .…”

“…Flooding with both CO 2 and CO 2 –WAG are common EOR strategies which have been widely used in a significant number of oilfields. − Each flooding scheme has individual characteristics in terms of displacement effect, injection difficulty, and impact on the reservoir’s physical properties. − Since CO 2 has a lower viscosity and density at reservoir conditions, the pressure required for CO 2 injection during CO 2 flooding is small. However, the lower density of CO 2 promotes viscous fingering and gravity segregation which leads to early CO 2 breakthrough (BT), low CO 2 utilization efficiency, and low oil RFs. , This is especially the case when the actual oil-bearing reservoir consists of a series of thin layers with different permeabilities separated by restraining barriers.…”

Experimental Investigation on the Effects of CO2 Displacement Methods on Petrophysical Property Changes of Ultra-Low Permeability Sandstone Reservoirs Near Injection Wells

“…As the water saturation decreases during the CO 2 flooding, CO 2 gradually becomes the continuous phase and flows in the large pores, and the fine migration and blockage mainly occur in these pores. However, during the process of CO 2 -WAG flooding, when the CO 2 flooding period is over in a cycle, the CO 2 mainly retaines in the large pores, and when the subsequent brine flooding is carried out, the flow of the fluid in the large pores is hindered due to the influence of the Jamin effect ,which means the additional resistance effects when droplets (drops or bubbles) in two-phase percolation of liquid-liquid or gas-liquid pass through the pore throat or narrow pores [47,48], then the brine with CO 2 dissolved in flows in the relatively small pores, and the fine migration and blockage would also occur in those smaller pores, resulting in the changes in microstructure and size in more pores (Figure 13a,b).…”

Comprehensive Review of the Determination and Reduction of the Minimum Miscibility Pressure during CO2 Flooding

“…The other is that the part oil displacement efficiency of CO 2 gas injection highly depends on MMP . CO 2 miscible flooding can only be achieved when the pressure is higher than MMP, thereby enhancing oil recovery. , If the injection pressure is lower than MMP, miscible flooding will not occur, and only immiscible flooding can be achieved . In conclusion, as one of the key parameters affecting gas injection for improving oil recovery, MMP has great significance for reservoir exploitation …”

“…12,13 If the injection pressure is lower than MMP, miscible flooding will not occur, and only immiscible flooding can be achieved. 14 In conclusion, as one of the key parameters affecting gas injection for improving oil recovery, MMP has great significance for reservoir exploitation. 15 First, this article reviews the measurement methods for MMP, which consist of experimental and theoretical calculation methods.…”