Influence of Pore Structure on Shale Gas Recovery with CO₂ Sequestration: Insight Into Molecular Mechanisms

Abstract

Although the focus of shale gas recovery has shifted to CO 2 sequestration with enhanced gas recovery (CS-EGR) for overcoming the low recovery efficiency, the adsorption and recovery mechanism of methane (CH 4 ) and carbon dioxide (CO 2 ) considering the effect of pore structures remains to be revealed. In this work, we focus on the influence of pore structures on adsorption behaviors of CH 4 and CO 2 at different geological depths and recovery process in different pore structures with various injection gas pressures. The results demonstrate that the excess adsorption capacity of CH 4 and CO 2 is in the order of cylinder-shaped > bottleneck > wedge-shaped > slit-shaped. The adsorption capacities of both CH 4 and CO 2 increase initially with geological depth until reaching maximum and then decrease with the depth going deeper. As for competitive adsorption of CH 4 and CO 2 , the pore structures do not have much influence on the selectivity. However, the pore structures have significant impact on shale gas recovery, and the difficulty of CH 4 molecules being displaced in various pore structures is ordered as cylinder-shaped > bottleneck > slit-shaped > wedge-shaped pores, which is consistent with the system resistance. The displacement efficiency of CH 4 in cylinder-shaped pores is about 59%, much less than in other pore structures. The injection pressure has a negative effect on the speed of shale gas recovery and displacement efficiency of CH 4 for the reason that more molecules aggregate into clusters near the pore throat and the flow blocking effect become more obvious when the injection pressure increases. Based on this actuality, we proposed a probable reliable method for CS-EGR: lower injection pressure is initially set to improve recovery efficiency, and higher pressure is finally used to increase CO 2 sequestration amount.

Enhanced Gas Recovery in Kerogen Pyrolytic Pore Network: Molecular Simulations and Theoretical Analysis

“…Type IV kerogen (with a H/C ratio of less than 0.5) mainly consists of polycyclic aromatic hydrocarbons without the potential for gas production. As we mentioned above, different kerogen macromolecular models with diverse types are proposed by the scholars, and these models are subsequently employed to investigate the pyrolysis, − adsorption, ,, and diffusion ,− properties based on the kerogen matrix. Among these kerogen types, type II kerogen is the most revered and widely distributed kerogen in the world, and recently a kind of immature type II kerogen model was constructed by Wang et al This macromolecule is built based on the sample from the Songliao Basin in China, whose element component information is examined by element analysis (EA) and X-ray photoelectron spectroscopy (XPS).…”

“…Simulations always serve as powerful tools once carrying out experiments becomes unfeasible. Molecular dynamics (MD) simulations, based on the particle dynamic theory and statistical physics, show great ability in depicting the physical or chemical properties at atomistic/molecular scales, such as the nanoscale flow, − adsorption, − and chemical reactions, − and thus have been widely employed to reveal the nanoscale recovery behavior in shale matrix . Normally, current EGR0related MD simulations focus on the subjects of carbon dioxide injection and sequestration and can be roughly divided into two strategies.…”

Linking multi-scale 3D microstructure to potential enhanced natural gas recovery and subsurface CO2storage for Bowland shale, UK

“…They may act as flow porosity, in the form of Darcy flow, allowing the CH 4 and CO2 exchange between different compositions. The CH 4 /CO 2 displacement efficiency in these pores changes relatively rapid [41].…”

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.…”