Comparison of the Absolute Adsorption of CH₄, n-C₄H₁₀, and CO₂ on Shale

Abstract

Comprehensive knowledge of the absolute adsorption of light hydrocarbons and CO 2 is significant for shale reservoir assessment and CO 2 stimulation optimization. In this work, excess adsorption isotherms are first obtained for CH 4 , n-C 4 H 10 , and CO 2 on typical shale. The simplified local density (SLD) theory is then used to obtain the adsorption-phase density for CH 4 , n-C 4 H 10 , and CO 2 in organic pores, which is then employed for absolute adsorption calculation. The absolute adsorption of CH 4 , n-C 4 H 10 , and CO 2 is compared to prove the potential of CO 2 for shale hydrocarbon recovery as well as CO 2 sequestration in shale reservoirs. The results show that CH 4 , n-C 4 H 10 , and CO 2 can form adsorption layers and result in a much higher adsorbed phase density than that at the pore center. Based on the SLD theory, C 4 H 10 shows the highest adsorbed density on the shale surface than CO 2 and CH 4 at all pressure ranges. In addition, absolute adsorption is higher than the excess values in line with the previous molecular simulation methods. Absolute adsorption is calculated in the order of n-C 4 H 10 > CO 2 > CH 4 , indicating the suitability of CO 2 for CH 4 recovery but also that it may not be feasible for recovering heavier hydrocarbons, i.e., n-C 4 H 10 . This study provides insights into the mechanism of shale resources recovery using CO 2 method, which is theoretically crucial for shale resource assessment and production optimization.

Imbibition and Oil Recovery Mechanism of Fracturing Fluids in Tight Sandstone Reservoirs

“…Since the 1980s, NMR technology has been widely used to observe the fluid distribution and pore volume changes under different environmental conditions. − This technique can quantitatively characterize the change in the core pore volume parameters by measuring the transverse relaxation T 2 distribution of the sample; the two have a good corresponding relationship. − The NMR T 2 value reflects the size of the specific surface of the rock pore throat, which is proportional to the pore throat radius, indicating that a larger T 2 value corresponds to a larger core pore throat …”

Interactions of CO2 with Hydrocarbon Liquid Observed from Adsorption of CO2 in Organic-Rich Shale

“…Besides, the pore space would be too small to accommodate large amounts of CO 2 for storage. On the other hand, organic-rich shale rocks can adsorb CO 2 on organic matter, ,,− enabling an effective mechanism for retaining CO 2 in rocks. Because adsorbed CO 2 molecules are more densely packed and tightly held than in the free phase, adsorption of CO 2 in shale is a favorable scenario for a combined CO 2 enhanced recovery and CO 2 storage process.…”

Adsorption Behavior of CH4 and C2H6 on Shale under the Influence of CO2 and Flue Gas

“…Injecting CO 2 into shale gas reservoirs has been adopted as a suitable method for enhanced CH 4 recovery. As the dominant gas component, CH 4 recovery as a result of CO 2 injection is most investigated. − With the measurement of adsorption isotherms of CH 4 and CO 2 , it was found that CO 2 has higher adsorption capacity than CH 4 ; it implies that CO 2 could be a suitable agent for developing shale gas reservoirs. − In recent years, molecular simulation methods, such as molecular dynamic simulation, density functional theory, etc., are powerful in investigating the microphase behavior of fluids in nanopores. ,− On the basis of the molecular simulation results, CO 2 generally forms stronger adsorption layers on the shale surface compared to CH 4 , validating the efficiency of CO 2 for CH 4 recovery.…”