The characterization of kerogen nanopores is crucial for predicting the geostorage capacity and recoverability of natural gas in unconventional gas shale reservoirs.Towards this end,a powerful technique is presented w...The characterization of kerogen nanopores is crucial for predicting the geostorage capacity and recoverability of natural gas in unconventional gas shale reservoirs.Towards this end,a powerful technique is presented which integrates 2D NMR T_(1)-T_(2) relaxation measurements with molecular dynamics(MD)simulations of hydrocarbons confined in the nanopores of kerogen.The integrated NMR-MD technique is demonstrated using T_(1)-T_(2) measurements of kerogen isolates and organic-rich chalks saturated with heptane,together with MD simulations of heptane completely dissolved in a realistic kerogen model.The NMR-MD results are used to extract the swelling ratio and nanopore size distribution of kerogen as a function of depth in the reservoir.The effects of organic nanoconfinement on the T_(1) relaxation dispersion and T_(2) residual dipolar coupling of heptane are investigated,as well as the effect of downhole effective stress on the kerogen nanopore size as a function of depth and compaction.Potential applications in partially depleted gas shale reservoirs are discussed,including CO_(2) utilization/geostorage,geostorage of green H_(2),and integration of the NMR-MD technique with thermodynamic models for predicting the competitive sorption of gas mixtures in kerogen.展开更多
MRI is an indispensable diagnostic tool in modern medicine;however,understanding the molecular-level processes governing NMR relaxation of water in the presence of MRI contrast agents remains a challenge,hindering the...MRI is an indispensable diagnostic tool in modern medicine;however,understanding the molecular-level processes governing NMR relaxation of water in the presence of MRI contrast agents remains a challenge,hindering the molecularguided development of more effective contrast agents.By using quantum-based polarizable force fields,the first-of-its-kind molecular dynamics(MD)simulations of Gadobutrol are reported where the ^(1)H NMR longitudinal relaxivity r_(1) of the aqueous phase is determined without any adjustable parameters.The MD simulations of r_(1) dispersion(i.e.,frequency dependence)show good agreement with measurements at frequencies of interest in clinical MRI.Importantly,the simulations reveal key insights into the molecular level processes leading to r_(1) dispersion by decomposing the NMR dipole−dipole autocorrelation function G(t)into a discrete set of molecular modes,analogous to the eigenmodes of a quantum harmonic oscillator.The molecular modes reveal important aspects of the underlying mechanisms governing r_(1),such as its multiexponential nature and the importance of the second eigenmodal decay.By simply analyzing the MD trajectories on a parameter-free approach,the Gadobutrol simulations show that the outer-shell water contributes∼50%of the total relaxivity r_(1) compared to the inner-shell water,in contrast to simulations of(nonchelated)gadolinium-aqua where the outer shell contributes only∼15%of r_(1).The deviation between simulations and measurements of r_(1) below clinical MRI frequencies is used to determine the low-frequency electron-spin relaxation time for Gadobutrol,in good agreement with independent studies.展开更多
基金Vinegar Technologies LLC,Chevron Energy Technology Company,Rice University Consortium for Processes in Porous Media,and the American Chemical Society Petroleum Research Fund(No.ACS PRF 58859-ND6)for their financial support。
文摘The characterization of kerogen nanopores is crucial for predicting the geostorage capacity and recoverability of natural gas in unconventional gas shale reservoirs.Towards this end,a powerful technique is presented which integrates 2D NMR T_(1)-T_(2) relaxation measurements with molecular dynamics(MD)simulations of hydrocarbons confined in the nanopores of kerogen.The integrated NMR-MD technique is demonstrated using T_(1)-T_(2) measurements of kerogen isolates and organic-rich chalks saturated with heptane,together with MD simulations of heptane completely dissolved in a realistic kerogen model.The NMR-MD results are used to extract the swelling ratio and nanopore size distribution of kerogen as a function of depth in the reservoir.The effects of organic nanoconfinement on the T_(1) relaxation dispersion and T_(2) residual dipolar coupling of heptane are investigated,as well as the effect of downhole effective stress on the kerogen nanopore size as a function of depth and compaction.Potential applications in partially depleted gas shale reservoirs are discussed,including CO_(2) utilization/geostorage,geostorage of green H_(2),and integration of the NMR-MD technique with thermodynamic models for predicting the competitive sorption of gas mixtures in kerogen.
基金Ken Kennedy Institute,the Rice University Creative Ventures Fund(Faculty Initiatives Fund)the Robert A.Welch Foundation for the financial support.
文摘MRI is an indispensable diagnostic tool in modern medicine;however,understanding the molecular-level processes governing NMR relaxation of water in the presence of MRI contrast agents remains a challenge,hindering the molecularguided development of more effective contrast agents.By using quantum-based polarizable force fields,the first-of-its-kind molecular dynamics(MD)simulations of Gadobutrol are reported where the ^(1)H NMR longitudinal relaxivity r_(1) of the aqueous phase is determined without any adjustable parameters.The MD simulations of r_(1) dispersion(i.e.,frequency dependence)show good agreement with measurements at frequencies of interest in clinical MRI.Importantly,the simulations reveal key insights into the molecular level processes leading to r_(1) dispersion by decomposing the NMR dipole−dipole autocorrelation function G(t)into a discrete set of molecular modes,analogous to the eigenmodes of a quantum harmonic oscillator.The molecular modes reveal important aspects of the underlying mechanisms governing r_(1),such as its multiexponential nature and the importance of the second eigenmodal decay.By simply analyzing the MD trajectories on a parameter-free approach,the Gadobutrol simulations show that the outer-shell water contributes∼50%of the total relaxivity r_(1) compared to the inner-shell water,in contrast to simulations of(nonchelated)gadolinium-aqua where the outer shell contributes only∼15%of r_(1).The deviation between simulations and measurements of r_(1) below clinical MRI frequencies is used to determine the low-frequency electron-spin relaxation time for Gadobutrol,in good agreement with independent studies.
