Experimental Investigation of Asphaltene Deposition and Its Impact on Oil Recovery in Eagle Ford Shale during Miscible and Immiscible CO₂ Huff-n-Puff Gas Injection

Abstract

One of the challenges in extracting oil from unconventional resources using hydraulic fracturing and horizontal drilling techniques is the low primary recovery rate, which is caused by the ultra-small permeability of these resources. Consequently, it is essential to investigate gas injection methods to produce the trapped oil in shale formations. However, the injection process can cause asphaltene depositions inside the reservoir, leading to plugging of pores and oil recovery (OR) reduction. There has been limited research on using gas injection techniques to improve oil production in tight/unconventional resources, although carbon dioxide (CO2) and gas-enhanced oil recovery methods have been used in conventional resources. In order to determine whether or not the cyclic (huff-n-puff) CO2 process improves OR and aggravates asphaltene precipitation, a rigorous experimental investigation was undertaken utilizing filter membranes and Eagle Ford shale cores. After the minimum miscibility pressure was calculated for CO2, various injection pressures were selected to perform CO2 huff-n-puff experiments. Investigations were carried out at 70 °C on injection pressure, cycle number, production time, and huff-and-puff mode injection. The results demonstrated that when the pore size structure of the membranes used was smaller and gas injection cycles increased, a higher asphaltene weight percent (wt %) was determined during the static experiments (i.e., employing filter paper membranes). Miscibility improved OR in dynamic testing (i.e., using shale cores), but a more oil-wet system was detected in wettability measurements taken following CO2 huff-and-puff tests. The plugging impact of asphaltene particles on the pore structure was studied using optical microscopy and scanning electron microscopy imaging. Following the huff-and-puff tests, a mercury porosimeter revealed how severely the pores were plugged, and after the CO2 tests, the pore size distribution reduced as a consequence of asphaltene deposition. This study examines the significance of CO2 injection in OR under miscible/immiscible conditions to identify the critical parameters that could impact the effectiveness of CO2 huff-n-puff operation in unconventional formations.

Minireview of Microscopic CO2 Interactions with Fluids and Minerals in Shale: Advances and Outlook

“…Formation damage as a result of asphaltene deposition in conventional reservoirs has been reported . Asphaltene deposition can cause more serious plugging problems in shale as a result of its nanometer pore sizes. , For example, Shen et al measured the sizes of the asphaltene particle formed during CO 2 injection in the oil sample from the Wolfcamp shale reservoir. They compared asphaltene particle sizes to the pore size of cores and found that pore sizes (3–50 nm) are even smaller than asphaltene particle sizes (30 and 200 nm).…”

Recovery mechanisms and formation influencing factors of miscible CO2 huff-n-puff processes in shale oil reservoirs: A systematic review

“…Miscibility refers to the ability of substances to form a homogeneous mixture. CO 2 EOR means the dissolution of CO 2 into oil, requiring reservoir pressure exceeding the MMP (Elturki and Imqam, 2023). Achieving miscibility involves multiple contacts due to factors like reservoir conditions and oil composition, rather than first contact.…”

Critical Contribution of Water in Hybrid CO2/Water Enhanced Shale Oil Recovery: Insights from Molecular Dynamics

“…However, the practical applications of CO 2 -EOR do not always achieve the expectations, especially for shale oil extraction. One particularly noteworthy problem is that, though CO 2 injection could extract the light and medium components of shale oil first, and the initial recovery is improved, most of the heavy components still remain in the shale reservoirs, and the total oil recovery is limited. , Due to the recent research learning, there is serious restrictive effect of heavy polar components, such as the asphaltene molecules to the displacement of light and medium components of shale oil in the CO 2 flooding process; further solutions have to be conducted to solve the essential problem. Investigating the mechanisms and the influencing factors to discover clues that overcome the bottleneck problems is important for the development of the technique.…”

“…noteworthy problem is that, though CO 2 injection could extract the light and medium components of shale oil first, and the initial recovery is improved, most of the heavy components still remain in the shale reservoirs, and the total oil recovery is limited. 28,29 Due to the recent research learning, 30 there is serious restrictive effect of heavy polar components, such as the asphaltene molecules to the displacement of light and medium components of shale oil in the CO 2 flooding process; further solutions have to be conducted to solve the essential problem.…”