Impact of Wettability Alteration on CO₂ Residual Trapping in Oil-Wet Sandstone at Reservoir Conditions Using Nuclear Magnetic Resonance

Abstract

Oil reservoirs have hydrophobic surfaces, wherein surface-active chemical components from the oil phase deposit onto the surface of the rock matrix and render it hydrophobic. This pore-scale property drastically impacts the Darcy-scale (macro-scale) flow functions, including P c and K r, in porous media. However, quantitative measurement of CO2 in oil-wet formations via capillary trapping remains a prime challenge despite extensive lab research. This is primarily due to inconsistent existing experimental data sets in the literature. Moreover, substantial insecurities yet exist in relations of foreseeing the wettability of the CO2-rock at reservoir conditions–which are detrimental for CO2 trapping. Thus, we used the robust Nuclear Magnetic Resonance (NMR) T 1-T 2 2D Map to image the fluid configuration and measured T 2 to systematically quantify Wettability Indices (WIs) using the United States Bureau of Mines (USBM) scale in an oil-wet San Saba to predict carbon capture and storage capacity (CCS) and containment integrity. The T 1/T 2 ratio was used to measure the microscopic wettability subsequent to each flooding mechanism, and the P c-S w and K r-S w characteristic curves subsequent to drainage/imbibition cyclic water saturations were measured as well. Comparison of the results was made with analogous water-wet core results, and general consistency was found. The NMR T 2 response was also correlated to physical properties, Pore Size Distributions (PSDs), and a 12% residual CO2 trapping was measured which is significantly lower than that in an analogous water-wet sandstone. Importantly, the NMR T 2 distribution measurements demonstrated that water was displaced from small pores by CO2 flooding, whereas in the water-wet analogue rocks, capillary trapping occurs in the large pores. This work thus provides a comprehensive data set on the effect of pore-scale properties on Darcy flow functions which ultimately aid and advance industrial-scale implementation of CGS and EOR project schemes in oil-wet reservoirs.

Effect of Organic Acids on CO2 Trapping in Carbonate Geological Formations: Pore-Scale Observations Using NMR

“…Thus, CO 2 flow connectivity increases via connected conduits of thin-film drainage of nonpolar CO 2 , leading to a significant reduction of residual CO 2 saturation. 14,24,72 This has also been observed previously for mixed-wetting systems. 24,29,72,73 Furthermore, the CO 2 layers provide continuous desaturation corridors for the CO 2 phase even in pores and throats invaded by water, that is, CO 2 can still flow, albeit slowly, via such layers.…”

“…Figure 2h (the red band slightly vanished), Figure 4b (the curve did not fully recover to the initial value), and Table 2 indicate that CO 2 was captured by snap-off in the meso-and micropores that rapidly separated the ganglia from flow (immobilized). 24,44,69,72 Moreover, lower CO 2 residual trapping (14%) was achieved. 14,24,72 We infer that hydrophobic systems have two main processes: (a) Haines jump, wherein water invades the narrow throats and fills the neighboring (adjoining) pores, and (b) snap-off (local and distal), wherein water retracts from some throats to fill the sites (pores).…”

“…After 10 PV of "live" brine was reinjected, S w increased again for both the water-wet and oil-wet cores to 82 and 86%, respectively (from 71 and 72% at S wirr ; Table 2), consistent with the literature. 24,60,72,74 However, the brine reinjection did not displace all CO 2 ; instead, a fraction of the scCO 2 remained trapped in the cores. In the water-wet core, trapping was predominately attained in the macropores, while CO 2 trapping mainly occurred in the meso-and micropores in the CO 2 -wet core, consistent with the literature (e.g., compare).…”

Residual Co2 Trapping and Enhanced Oil Recovery in Carbonate Reservoirs: Three-Phase Flow Dynamics Examined Via Nmr

“…4), which was trapped by capillary forces [21]; while a tertiary oil recovery factor of R o = 37% was achieved. This can happen via threephase displacement (water displacing gas displacing oil) [7,25,60], and, notably, Scanziani et al (2020) [13] showed that gas trapping increased in the presence of oil and brine, and, similarly, Alhosani et al (2019) [51] observed efficient gas trapping in the presence of spreading oil layers and during subsequent water flooding. They also found that gas trapping is lower for near-miscible systems (as gas is surrounded by oil layers, preventing direct contact between gas and water [13]).…”

“…Carbon Geosequestraion combined with Enhanced Oil Recovery (CO 2 -EOR) is a promising technique to minimize the impact of the climate change caused by the emission of anthropologic CO 2 from fossil fuel combustion, as the recovery of the additional oil can offset the cost associated with CO 2 disposal [5,37,60]. However, there is a substantial lack of understanding of the pore-scale multi-phase flow through the porous media, despite their vital importance for residual CO 2 saturation and enhanced oil recovery efficiency [5,37].…”