The thermogenic transformation of kerogen into hydrocarbons accompanies the development of a pore network within the kerogen that serves as gas storage locations both in pore space and the surface area for adsorbed gas with source rocks. Therefore, the successful recovery of gas from these rocks depends on the accessible surface area, surface properties, and interconnectivity of the pore system. These parameters can be difficult to determine because of the nanoscale of the structures within source rocks. This study seeks to investigate the pore structure, surface heterogeneity, and composition of isolated kerogens with progressively increasing thermogenic maturities from source rocks at a middle-east reservoir. Prompt gamma-ray activation analysis (PGAA), nitrogen and methane volumetric gas sorption, and small-angle neutron scattering (SANS) are combined to explore the relationship between the chemical composition, pore structure, surface roughness, surface heterogeneity, and maturity. PGAA results indicate that more mature kerogens have lower hydrogen/carbon ratios. Nitrogen gas adsorption indicates that the pore volume and accessible specific surface area are higher for more mature kerogens. The methane isosteric heat at different methane uptakes in the kerogens is determined by methane isotherms and shows that approximately two types of binding sites are present in less mature kerogens while the binding sites are relatively homogeneous in the most mature kerogen. The hysteresis effects of the structure during the adsorption and desorption processes at different CD 4 gas pressures are studied. An extended generalized Porod's scattering law method (GPSLM) is further developed here to analyze kerogens with fractal surfaces. This extended GPSLM quantifies the surface heterogeneity of the kerogens with a fractal surface and shows that more mature kerogen is chemically more homogeneous, consistent with the results from methane isosteric heat. SANS analysis also suggests a pronounced surface roughness in the more mature kerogens. A microporous region circling around the nanopores, which contributes to high surface roughness and methane storage, is shown to develop with maturity.
A nuclear magnetic resonance (NMR)-based method was developed to quickly and accurately determine porosities and densities of tight reservoir rocks from drill cuttings. The method combines low-field NMR and two mass measurements, one in the air and one in a fluid, to determine rock porosity, grain density, and bulk density. The method provides an inexpensive approach to deliver continuous data for evaluation of a drilled well and is especially useful for unconventional reservoirs for evaluating both vertical and horizontal sections of a well.
Spin relaxation, a defining mechanism of nuclear magnetic resonance (NMR), has been a prime method for determining three-dimensional molecular structures and their dynamics in solution. It also plays key roles for contrast enhancement in magnetic resonance imaging (MRI). In bulk solutions, rapid Brownian molecular diffusion modulates dipolar interactions between a spin pair from different molecules, resulting in very weak intermolecular relaxations. We show that in fluids confined in nanospace or nanopores (nanoconfined fluids) the correlation of dipolar coupling between spin pairs of different molecules is greatly enhanced by the nanopore constraint boundaries on the molecular diffusion, giving rise to an enhanced correlation for the spin pair. As a result, the intermolecular dipolar interaction behaves cooperatively, which leads to a large intermolecular dipolar relaxation rate and opposite in sign to the bulk solution. We found that the classical NMR relaxation theory fails to capture these observations in a nanoconfined fluid environment. Hence, we developed a formal theory and experimentally confirmed that enhanced correlation and cooperated relaxation are ubiquitous in nanoconfined fluids. The newly discovered phenomenon and the developed NMR method reveal new applications in a broad range of synthesized and naturally occurring materials in the field of nanofluidics to study molecular dynamics and structure as well as for MRI image enhancement.
Many different methods have been developed to investigate fluid–solid interactions in nanoporous systems. These methods either only work in the liquid phase or provide an indirect measurement by probing the fluid–solid interaction based on a measured property change of the fluid or solid under different sample conditions. Here, we report a direct measurement technique using NMR dipolar cross-relaxation between the nanoconfined fluids and the matrix solids. The method was tested using a methyl-functionalized mesostructured silica saturated with methanol as a model sample. A formal theory was established to describe the enhanced dipolar cross-relaxation interaction between the nanoconfined fluids and the matrix solids. Both the experiment and theory showed that nanoconfinement of the fluids enhances the dipolar cross-relaxation interaction between the fluid and the matrix solids, which can be applied to investigate the fluid–solid interaction for various materials of a similar nanostructure.
Many different methods have been developed to investigate fluid-solid interactions in nanoporous systems. These methods either only work in the liquid phase or provide an indirect measurement by probing the fluid-solid interaction based on a measured property change of the fluid or solid under different sample conditions. Here, we report a direct measurement technique using NMR dipolar cross-relaxation between the nanoconfined fluids and the matrix solids. The method was tested using a methyl functionalized mesostructured silica saturated with methanol as a model sample. A formal theory was established to describe the enhanced dipolar cross-relaxation interaction between the nanoconfined fluids and the matrix solids. Both the experiment and theory showed that nanoconfinement of the fluids enhances the dipolar cross-relaxation interaction between the fluid and the matrix solids, which can be applied to investigate the fluid-solid interaction for various materials of similar nanostructure.
Drill cuttings are available continuously over the entire depth of any drilled wells. The use of drill cuttings to obtain petrophysical data can add a significant value in formation evaluation. An update to the previous study is presented using NMR and Archimedes principle to determine petrophysical properties including porosity, bulk density, and matrix density from drill cuttings of organic-rich mudrock formations. In the original published method, sonication was used to clean and saturate the drill cutting samples. In this improved method, particulate samples were saturated using both sonication and pressure injection methods. The obtained results were compared with accepted lab measurement techniques. Results show that pressure saturation of particulate samples can provide accurate results of petrophysical properties. Obtaining reliable petrophysical data from drill cuttings can provide continuous and quasi-real-time data for the formation evaluation of reservoirs and can effectively reduce costs by reducing or eliminating expensive formation evaluation methods.
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