Further Investigation of Effects of Injection Pressure and Imbibition Water on CO₂ Huff-n-Puff Performance in Liquid-Rich Shale Reservoirs

Abstract

Shale oil production has increased rapidly in the past decades, especially in the United States, and results in a revolution in the energy landscape. However, one main problem existing in the shale reservoir development is the sharp decline of liquids production in all the hydraulically fractured wells. In recent years, CO2 huff-n-puff injection has been proved to be a potential method to enhance the oil recovery. In this study, the effects of injection pressure and imbibition water on CO2 huff-n-puff performance were further investigated. Eagle Ford core samples and Wolfcamp dead oil were used in this experimental study. The microscopic pore characteristics of Eagle Ford shale core samples were analyzed, and the results show that 98.08% of the pore sizes are distributed between 3 nm and 50 nm. The experimental results demonstrate the great potential of CO2 huff-n-puff EOR. The cumulative oil recovery can reach 68% after seven huff-n-puff cycles. The oil recovered in each cycle deceases as injection cycle number increases due to the permeability damage caused by asphaltene precipitation, oil saturation reduction, and low injected CO2 sweep efficiency. The effect of injection pressure was studied by injecting CO2 at both immiscible and miscible conditions. CO2 huff-n-puff has better performance (more than 9.1% EOR) under miscible conditions than immiscible conditions. After that, a novel experiment was designed to saturate the core samples with both water (15 wt % KCl) and Wolfcamp dead oil to investigate the influence of imbibition water on CO2 huff-n-puff EOR performance. The existence of imbibition water impedes oil production in shale core samples. The oil recovery decreased about 45.3% after seven huff-n-puff cycles compared to the condition without water. A simulation study provides a better understanding of CO2 huff-n-puff application in liquid-rich shale reservoirs, which is fundamentally important for applying and optimizing CO2 huff-n-puff in field production.

A New Mechanism for Enhanced Oil Recovery by CO2 in Shale Oil Reservoirs

“…Figure 9 depicts average oil saturation in the core after three days. The gas saturation (Figure 8) of the improved case has reached 20% after 12 hours, which indicates an acceptable response time compared to normal huff and puff time-scales suggested for shale oils [3,13,[15][16][17]. On the other hand, using conventional approach, no gas was formed in the grid block as shown with pink curve on Figure 8, which indicates the importance of using realistic parameters for EOS.…”

Experimental and computational evaluation of cyclic solvent injection in fractured tight hydrocarbon reservoirs

“…There are now numerous studies of improved oil recovery in a variety of North American tight oil reservoirs that have examined the feasibility of incremental oil recovery using gas injection [1][2][3][4][5][6] . These studies have primarily focused on numerical 2,3,6 or laboratory-based approaches 1,[7][8][9] . Laboratory-based studies are important for assessing (1) the key mechanisms controlling injected gas transport into the reservoir, and miscibility with the oil 7,8,10 and (2) the influence of operational parameters including injection pressure/time, soaking time, production pressure/time-among other factors (e.g.…”

Experimental Investigation on Cyclic Huff-n-Puff with Surfactants Based on Complex Fracture Networks in Water-Wet Oil Reservoirs with Extralow Permeability

“…The oil far away from the channeling fractures remains unswept in place. Therefore, the technology of huff-n-puff for a single well can be an excellent substitute to recover the oil near the well and the fractures [18][19][20][21], particularly during the early production period. Huff-n-puff covers the injection, soaking, and production cycles, which requires substantial water transfer into or out of the oil formation [8].…”