Enhanced Recovery From Organic-Rich Shales through Carbon Dioxide Injection: Molecular-Level Investigation

Alafnan, Saad; Falola, Yusuf; Mansour, Osamah Al; Alsamadony, Khalid L.; Awotunde, Abeeb A.; Aljawad, Murtada Saleh

doi:10.1021/acs.energyfuels.0c03126

Cited by 36 publications

(22 citation statements)

References 53 publications

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“…The convergence in the density is consistent with estimated mechanical moduli as shown in Figure 8. Similar observations of the number of units needed to form a realistic kerogen structure are reported in the literature [79][80][81][82][83][84].…”

Section: Resultssupporting

confidence: 83%

The Impact of Pore Structure on Kerogen Geomechanics

Alafnan

2021

Geofluids

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Production stimulation techniques such as the combination of hydraulic fracturing and lateral drilling have made exploiting unconventional formations economically feasible. Advancements in production aspects are not always in lockstep with our ability to predict and model the extent of a fracturing job. Shale is a clastic sedimentary rock composed of a complex mineralogy of clay, quartz, calcite, and fragments of an organic material known as kerogen. The latter, which consists of large chains of aromatic and aliphatic carbons, is highly elastic, a characteristic that impacts the geomechanics of a shale matrix. Following a molecular simulation approach, the objective of this work is to investigate kerogen’s petrophysics on a molecular level and link it to kerogen’s mechanical properties, considering some range of kerogen structures. Nanoporous kerogen structures across a range of densities were formed from single macromolecule units. Eight units were initially placed in a low-density cell. Then, a molecular dynamic protocol was followed to form a final structure with a density of 1.1 g/cc; the range of density values was consistent with what has been reported in the literature. The structures were subjected to petrophysical assessments including a helium porosity analysis and pore size distribution characterization. Mechanical properties such as Young’s modulus, bulk modulus, and Poisson ratio were calculated. The results revealed strong correlations among kerogen’s mechanical properties and petrophysics. The kerogen with the lowest porosity showed the highest degree of elasticity, followed by other structures that exhibited larger pores. The effect temperature and the fluid occupying the pore volume were also investigated. The results signify the impact of kerogen’s microscale intricacies on its mechanical properties and hence on the shale matrix. This work provides a novel methodology for constructing kerogen structures with different microscale properties that will be useful for delineating fundamental characteristics such as mechanical properties. The findings of this work can be used in a larger scale model for a better description of shale’s geomechanics.

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Section: Resultssupporting

confidence: 83%

The Impact of Pore Structure on Kerogen Geomechanics

Alafnan

2021

Geofluids

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“…The number of methane gas molecules hosted by the kerogen models was tracked through the Gibbs ensemble Monte Carlo calculations at different isothermal pressure stages, making it possible to plot the sorption profiles as a function of pressure for the six kerogen structures. A similar approach has been followed in prior studies. − …”

Section: Molecular Approachmentioning

confidence: 99%

Petrophysics of Kerogens Based on Realistic Structures

Alafnan

2021

ACS Omega

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Combining hydraulic fracturing with lateral drilling has allowed for economical hydrocarbon production from unconventional formations. Nevertheless, beyond hydraulic fracturing, our understanding of how hydrocarbons are stored and transported from the stimulated volume of a reservoir is still limited. Source rocks consist of organic materials finely dispersed within an inorganic matrix. Despite their small size, these organic pockets are capable of storing significant amounts of hydrocarbon due to their large surface area. The extent of the source rock’s storage capacity is determined by several factors, including the natural fracture abundancy, organic material content, type, and level of maturity. The petrophysical properties of organic materials, also known as kerogens, are subject to a high degree of uncertainty. Kerogens are difficult to isolate experimentally, which hinders accurate petrophysical analysis. The objective of this research was to use a molecular modeling approach to explore the petrophysical characteristics of kerogen. Kerogen macromolecules of different types and maturity levels were recreated via a computational platform. Then nanoporous structures representing these kerogens were obtained and characterized. Several elemental parameters, including porosity, density, pore size distribution, and adsorption capacity were closely delineated. The kerogen properties were found to correlate with the kerogen type and thermal maturity level. Kerogen type III showed the highest storage capacity, followed by types II and I, in a descending order. Moreover, in the same type of kerogen, a general trend of increasing storage capacity was observed as the maturity level increased. Methane adsorption capacity was modeled as a function of kerogen porosity. A transition flow regime was found to be the predominant mechanism. Such observations have significant implications for reservoir-scale modeling of unconventional resources.

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“…Despite its disadvantages, the literature shows multiple examples of the application of Molecular Dynamics for shale pore structure characterization, e.g., [71]. The method has been used mainly to understand the behavior and the diffusion of different gasses in porous media that could impact the adsorption capacity or related flow properties [47,[118][119][120][121][122].…”

Section: Advanced Methodsmentioning

confidence: 99%

Use of Gas Adsorption and Inversion Methods for Shale Pore Structure Characterization

Medina-Rodriguez

Alvarado

2021

Energies

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The analysis of porosity and pore structure of shale rocks has received special attention in the last decades as unconventional reservoir hydrocarbons have become a larger parcel of the oil and gas market. A variety of techniques are available to provide a satisfactory description of these porous media. Some techniques are based on saturating the porous rock with a fluid to probe the pore structure. In this sense, gases have played an important role in porosity and pore structure characterization, particularly for the analysis of pore size and shapes and storage or intake capacity. In this review, we discuss the use of various gases, with emphasis on N2 and CO2, for characterization of shale pore architecture. We describe the state of the art on the related inversion methods for processing the corresponding isotherms and the procedure to obtain surface area and pore-size distribution. The state of the art is based on the collation of publications in the last 10 years. Limitations of the gas adsorption technique and the associated inversion methods as well as the most suitable scenario for its application are presented in this review. Finally, we discuss the future of gas adsorption for shale characterization, which we believe will rely on hybridization with other techniques to overcome some of the limitations.

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Enhanced Recovery From Organic-Rich Shales through Carbon Dioxide Injection: Molecular-Level Investigation

Cited by 36 publications

References 53 publications

The Impact of Pore Structure on Kerogen Geomechanics

The Impact of Pore Structure on Kerogen Geomechanics

Petrophysics of Kerogens Based on Realistic Structures

Use of Gas Adsorption and Inversion Methods for Shale Pore Structure Characterization

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