Preliminary study on nanopores,nanofissures,and in situ accumulation of Gulong shale oil

The Qingshankou Formation shale oil in the Gulong Sag is an important oil and gas reservoir in the Daqing oilfield,with geological resources of 15.1 billion tons.The fabric of shale can reflect not only its genesis but also the nature of the reservoir space,its physical properties,oil content,and development value.Here,the characteristics of clay minerals in the Gulong shale oil reservoir were studied via electron microscopy,with the primary focus on the microfabrics and reservoir space;thereafter,the in situ accumulation was studied and discussed.Electron backscattering patterns revealed that nanometer pores and fissures were well developed in the Gulong shale oil reservoir.The nano pores were mostly 20-50 nm in diameter(median 20-30 nm),irregularly shaped,mostly,polygonal,and connected with nanofissures.The widths of nanofissures ranged mostly between 10-50 nm(median 20-30 nm);moreover,these fissures were mainly formed by F-F condensation of clay sheets(clay domains).The coagulation of clays was closely related to organic matter,especially algae.The clay colloids were negatively charged due to isocrystalline replacement;hence,metal cations were absorbed around the clay,forming a positive clay group.The positively charged clays subsequently adsorbed negatively charged humic acid(organic matter)and initially degraded algae to form an organic clay flocculant.When the organic clay flocculates reached the threshold for hydrocarbon generation and expulsion,the volume of organic matter decreased by 87%;thereafter,the generated and expelled hydrocarbon filled the nearby pores formed by this contraction.Moreover,the discharged hydrocarbon could not migrate due to capillary resistance(~12 MPa)of the nanopores;hence,the nanopores formed a unique continuous in situ reservoir within the Gulong shale oil.This study demonstrated that the Gulong shale oil reservoir is an actual clay-type shale reservoir with numerous nanopore and fissures.During coagulation,a large amount of organic matter(including layered algae)was absorbed by the clay,forming an organic clay condensate that could have provided the material foundation for hydrocarbon generation at a later stage.Thermal simulation experiments revealed that the volume of organic matter decreased sharply after hydrocarbon generation and expulsion.

A transient model integrating the nanoconfinement effect and pore structure characteristics of oil transport through nanopores

Understanding the integrated transport behavior of oil in shale nanopores is critical to efficient shale oil development. In this paper, based on the time-dependent Poiseuille flow momentum equation, we present a novel transient model to describe oil transport in unsteady and steady states. The model incorporates the effect of the critical shift density, apparent viscosity, slip length, and alkane property, as well as pore tortuosity and surface roughness. We evaluated our model through a comparison with other models, experiments, and molecular dynamics simulations. The results show that the development rates of the volume flows of C_(6)–C_(12) alkane confined in inorganic nanopores and C_(12) alkane confined in organic nanopores were faster than that of the corresponding bulk alkane. In addition, the critical drift density positively promoted the volume flow development rate in the unsteady state and negatively inhibited the mass flow rate in the steady state. This effect was clearest in pores with a smaller radius and lower-energy wall and in alkane with shorter chain lengths. Furthermore, both the nanoconfinement effect and pore structure determined whether the volume flow enhancement rate was greater than or less than 1. The rate increased or decreased with time and was controlled mainly by the nanoconfinement effect. Moreover, as the wall energy increased, the flow inhibition effect increased;as the carbon number of alkane increased, the flow promotion effect increased. The results indicate that the proposed model can accurately describe oil transport in shale nanopores.

Molecular insight into the oil displacement mechanism of CO_(2) flooding in the nanopores of shale oil reservoir

With the increasing demand for petroleum,shale oil with considerable reserves has become an important part of global oil resources.The shale oil reservoir has a large number of nanopores and a complicated mineral composition,and the effect of nanopore confinement and pore type usually makes the effective development of shale oil challenging.For a shale oil reservoir,CO_(2) flooding can effectively reduce the oil viscosity and improve the reservoir properties,which can thus improve the recovery performance.In this study,the method of non-equilibrium molecular dynamics(NEMD)simulation is used to simulate the CO_(2) flooding process in the nanoscale pores of shale oil reservoir.The performance difference between the organic kerogen slit nanopore and four types of inorganic nanopores is discussed.Thus,the effects of nanopore type and displacement velocity on the nanoscale displacement behavior of CO_(2) are analyzed.Results indicate that the CO_(2) flooding process of different inorganic pores is different.In comparison,the displacement efficiency of light oil components is higher,and the transport distance is longer.The intermolecular interaction can significantly affect the CO_(2) displacement behavior in nanopores.The CO_(2) displacement efficiency is shown as montmorillonite,feldspar>quartz>calcite>kerogen.On the other hand,it is found that a lower displacement velocity can benefit the miscibility process between alkane and CO_(2),which is conducive to the overall displacement process of CO_(2).The displacement efficiency can significantly decrease with the increase in displacement velocity.But once the displacement velocity is very high,the strong driving force can promote the alkane to move forward,and the displacement efficiency will recover slightly.This study further reveals the microscopic oil displacement mechanism of CO_(2) in shale nanopores,which is of great significance for the effective development of shale oil reservoirs by using the method of CO_(2) injection.

Pressure-driven membrane inflation through nanopores on the cell wall

Walled cells,such as in plants and fungi,compose an important part of the model systems in biology.The cell wall primarily prevents the cell from over-expansion when exposed to water,and is a porous material distributed with nanosized pores on it.In this paper,we study the deformation of a membrane patch by an osmotic pressure through a nanopore on the cell wall.We find that there exists a critical pore size or a critical pressure beyond which the membrane cannot stand against the pressure and would inflate out through the pore and further expand.The critical pore size scales linearly with the membrane tension and quadratically with the spontaneous curvature.The critical pressure is inversely proportional to the pore radius.Our results also show that the fluid membrane expansion by pressure is mechanically different from the solid balloon expansion,and predict that the bending rigidity of the membrane in walled cells should be much larger than that of the mammalian cells so as to prevent membrane inflation through the pores on the cell wall.

Shale gas transport in nanopores with mobile water films and water bridge

Gas flow properties in nanopores are significantly determined by the flow patterns. Slug flow pattern is a potential water–gas two phase flow pattern, in which gas molecules flow in form of gas slugs and water molecules separate gas slugs. Considering water slippage, a portion of water molecules accumulates at the wall with lower mobility, while the remaining water molecules take the shape of a water bridge. Adopting foam apparent viscosity model to represent slug rheological behavior, how water bridge disturbs on gas flow capacity is estimated. The results are compared with the water–gas two phase flow model that assumes annular flow pattern as well as the single gas flow model without the consideration of water. The comparison illustrates that gas molecular movement is significantly hindered by flow space reduction and loss of gas slippage. The impact from water phase of slug flow pattern is more significant than that of annular flow pattern on gas flow capacity. It is discovered that larger nanopores improve gas flow capacity while maintaining bulk water layer thickness and increasing water bridge thickness tend to reduce gas transport ability. A better understanding of the structure and transport of water and gas molecules is conducive to figure out the specific gas–water flow behavior and predict shale gas production.

A biosensor based on graphene nanoribbon with nanopores:a first-principles devices-design

A biosensor device, built from graphene nanoribbons （GNRs） with nanopores, was designed and studied by first- principles quantum transport simulation. We have demonstrated the intrinsic transport properties of the device and the effect of different nucleobases on device properties when they are located in the nanopores of GNRs. It was found that the device＇s current changes remarkably with the species of nucleobases, which originates from their different chemical compositions and coupling strengths with GNRs. In addition, our first-principles results clearly reveal that the distinguished ability of a device＇s current depends on the position of the pore to some extent. These results may present a new way to read off the nucleobases sequence of a single-stranded DNA （ssDNA） molecule by such GNRs-based device with designed nanopores

Highly Efficient Power Conversion from Salinity Gradients with Ion-Selective Polymeric Nanopores

A polymeric nanopore membrane with selective ionic transport has been proposed as a potential device to convert the chemical potential energy in salinity gradients to electrical power. However, its energy conversion efficiency and power density are often limited due to the challenge in reliably controlling the size of the nanopores with the conventional chemical etching method. Here we report that without chemical etching, polyimide （PI） membranes irradiated with GeV heavy ions have negatively charged nanopores, showing nearly perfect selectivity for cations over anions, and they can generate electrical power from salinity gradients. We further demonstrate that the power generation efficiency of the PI membrane approaches the theoretical limit, and the maximum power density reaches 130m W/m2 with a modified etching method, outperforming the previous energy conversion device that was made of polymeric nanopore membranes.

Molecular insights on Ca^(2+)/Na+separation via graphene-based nanopores:The role of electrostatic interactions to ionic dehydration

Ca^(2+)/Na+separation is a common problem in industrial applications,biological and medical fields.However,Ca^(2+)and Na+have similar ionic radii and hydration radii,thus Ca^(2+)/Na+separation is challenging.Inspired by biological channels,group modification is one of the effective methods to improve the separation performance.In this work,molecular dynamics simulations were performed to investigate the effects of different functional groups(COO,NH3+)on the separation performance of Ca^(2+)and Na+through graphene nanopores under an electric field.The pristine graphene nanopore was used for comparison.Results showed that three types of nanopores preferred Ca^(2+)to Na+,and Ca^(2+)/Na+selectivity followed the order of GE-COO(4.06)>GE(1.85)>GE-NH3+(1.63).Detailed analysis of ionic hydration microstructure shows that different nanopores result in different hydration factors for the second hydration layer of Ca^(2+)and the first layer of Na+.Such different hydration factors corresponding to the dehydration ability can effectively evaluate the separation performance.In addition,the breaking of hydrogen bonds between water molecules due to electrostatic effects can directly affect the dehydration ability.Therefore,the electrostatic effect generated by group modification will affect the ionic hydration microstructure,thus reflecting the differences in dehydration ability.This in turn affects the permeable and separation performance of cations.The results of this work provide perceptive guidelines for the application of graphene-based membranes in ion separation.

3-83 Influence of Electrolyte Concentration on the Rectification of Single Conical Nanopores

A fundamental understanding of the rectification effect in the nanopores and the ion transport near charged surfaces on the nanometer length scale can push towards high performance energy storage devices[1]. Typically,nanopores are constructed within polymers, glass, or silica, and have internal and external surfaces that are electrically charged.

An analytical model for water-oil two-phase flow in inorganic nanopores in shale oil reservoirs

The existence of water phase occupies oil flow area and impacts the confined oil flow behavior at the solid substrate in inorganic nanopores of shale oil reservoirs,resulting in a completely different flow pattern when compared with the single oil phase flow.This study proposes an analytical model to describe the water-oil two-phase flow.In this model,water slippage at the solid substrate is considered while oil slip is introduced to calculate the oil movement at the solid-oil boundary in dry conditions.It is proven that the oil flow profiles of both the two-phase model and single-phase model show parabolic shapes,but the oil flow capacity drops when water takes up the flow space and the impact of water is more significant when the pore dimension is smaller than 30 nm.Also,the oil flow velocity at a pore center is found to drop linearly given a larger water saturation in wet conditions.The effects of surface wettability and oil properties on water-oil flow are also discussed.Compared with the existing singlephase models,this model describes oil flow pattern in the wet condition with the incorporation of the influence of nanopore properties,which better predicts the oil transport in actual reservoir conditions.Water-oil relative permeability curves are also obtained to improve oil yield.

Effects of nanopores and sulfur doping on hierarchically bunched carbon fibers to protect lithium metal anode

Studies on three-dimensional structured carbon templates have focused on how to guide homogeneous lithium metal nucleation and growth for lithium metal anodes(LMAs).However,there is still insufficient evidence for a key factor to achieve their high electrochemical performance.Here,the effects of nanopores and sulfur doping on carbon-based nanoporous host(CNH)electrode materials for LMAs were investigated using natural polymer-derived CNHs.Homogeneous pore-filling behaviors of lithium metal in the nanopores of the CNH electrode materials were first observed by ex situ scanning electron microscopy analysis,where the protective lithium metal nucleation and growth process led to significantly high Coulombic efficiency(CE)of~99.4%and stable 600 cycles.In addition,a comparison study of CNH and sulfurdoped CNH(S-CNH)electrodes,which differ only in the presence or absence of sulfur,revealed that sulfur doping can cause lower electrochemical series resistance,higher CE value,and better cycling stability in a wide range of current densities and number of cycles.Moreover,S-CNH-based LMAs showed high electrochemical performance in full-cell Li-S battery tests using a sulfur copolymer cathode,where a high energy density of 1370Wh kgelectrode−1 and an excellent power density of 4120Wkgelectrode−1 were obtained.

Effect of confinement on the three-phase equilibrium of water-oil-CO_(2)mixtures in nanopores

Accurate characterization of fluid phase behavior is an important aspect of CO_(2) enhanced shale oil recovery.So far,however,there has been little discussion about the nanopore confinement effect,including adsorption and capillarity on the phase equilibrium of water-oil-CO_(2) mixtures.In this study,an improved three-phase flash algorithm is proposed for calculating the phase behavior of water-oil-gas mixture on the basis of an extended Young-Laplace equation and a newly developed fugacity calculation model.The fugacity model can consider the effect of water-oil-gas adsorption on phase equilibrium.A water-Bakken oil-CO_(2) mixture is utilized to verify the accuracy of the flash algorithm and investigate the confinement effect.Results show that the confinement effect promotes the transfer of all components in the vapor phase to other phases,while the transfer of water,CO_(2),and lighter hydrocarbons is more significant.This leads to a large decrease,a large increase,and a small increase in the mole fraction of the vapor,oleic,and aqueous phases,respectively.When the confinement effect is considered,the density difference of vaporoleic phases decreases,and the interfacial tension of vapor-oleic phases decreases;however,the density difference of vapor-aqueous phases increases,the interfacial tension of vapor-aqueous phases still decreases.

Ion and water transport in charge-modified graphene nanopores

Porous graphene has a high mechanical strength and an atomic-layer thickness that makes it a promising material for material separation and biomolecule sensing. Electrostatic interactions between charges in aqueous solutions are a type of strong long-range interaction that may greatly influence fluid transport through nanopores. In this study, molecular dynamic simulations were conducted to investigate ion and water transport through 1.05-nm diameter monolayer graphene nanopores, with their edges charge-modified. Our results indicated that these nanopores are selective to counterions when they are charged. As the charge amount increases, the total ionic currents show an increase-decrease profile while the coion currents monotonically decrease. The co-ion rejection can reach 76.5% and 90.2% when the nanopores are negatively and positively charged, respectively. The Cl-ion current increases and reaches a plateau, and the Na＋current decreases as the charge amount increases in systems in which Na＋ions act as counterions. In addition, charge modification can enhance water transport through nanopores. This is mainly due to the ion selectivity of the nanopores. Notably, positive charges on the pore edges facilitate water transport much more strongly than negative charges.

Probing conformational change of T7 RNA polymerase and DNA complex by solid-state nanopores

Proteins are crucial to most biological processes, such as enzymes, and in various catalytic processes a dynamic motion is required. The dynamics of protein are embodied as a conformational change, which is closely related to the flexibility of protein. Recently, nanopore sensors have become accepted as a low cost and high throughput method to study the features of proteins. In this article, we used a SiN nanopore device to study the flexibility of T7 RNA polymerase（RNAP） and its complex with DNA promoter. By calculating full-width at half-maximum（FWHM） of Gaussian fits to the blockade histograms, we found that T7 RNAP becomes more flexible after binding DNA promoter. Moreover, the distribution of fractional current blockade suggests that flexibility alters due to a breath-like change of the volume.

Nanopores/Nanochannels Based on Electrical and Optical Dual Signal Response for Application in Biological Detection

Cancers and chronic diseases have always been global health problems. The occurrence and development of such diseases are closely related to the abnormalities of proteins, nucleic acids, ions or small molecules in the body. Nowadays, nanopores/nanochannels have emerged as a powerful platform for detecting these biomolecules based on the electrical signal variation caused by biomolecules passing. However, detection relied on the electrical signal easily suffered from the clogging defects, low throughput, and strong background signals. Fortunately, the emergence of designing nanopores/nanochannels based on electrical and optical dual signal response has brought innovative impetus to biological detection, which can also identify the chemical compositions and conformations of the biomolecules. In this review, we summarize the reasonable preparation of nanopores/nanochannels with electrical and optical dual signal response and their application in biological detection. According to different biomolecules, we divide the targets into four types, including nucleic acids, small molecules, ions and proteins. In each section, the design of representative examples and the principle of dual signal generation are introduced and discussed. Finally, the prospects and challenges of nanopores/nanochannels based on electrical and optical dual signal response are also discussed.

Enhanced piezo-catalysis in ZnO rods with built-in nanopores

Strategies to improve the efficiency of piezoelectric catalysis have long focused on piezo-optical coupling and construction of heterojunctions.However,it is a challenge to reinforce the performance of piezoelectric catalysis in a single material.Herein the built-in nanopores in single crystal ZnO rods are employed to form stress to intensify piezo-catalytic efficiency.The piezo-catalytic efficiency of the ZnO rods with built-in nanopores(holey ZnO NRs)for degrading dyes was about 1.7 times that of the ZnO rods without built-in nanopores(ZnO NRs).X-ray diffraction and Raman peaks of holey ZnO NRs appeared blue-shifted in comparison to ZnO NRs,uncovering the existence of tensile stress in holey ZnO NRs.The piezoelectric coefficient d_(33) of holey ZnO NRs increased by 1.92 times,triggering the amplification of piezoelectric catalytic property.Additionally,the piezoelectric current,carrier lifetime,and diffusion length of holey ZnO NRs were larger than that of ZnO NRs,respectively.These factors all contribute to the enhanced piezoelectric catalytic efficiency of holey ZnO NRs.This work demonstrates that the method of induced stress with built-in nanopores is a promising strategy for improving the piezoelectric catalytic efficiency of single-crystal ZnO rods.

Molecular force mechanism of hydrodynamics in clay nanopores

Nanopores are prevalent within various clay morphologies,and water flow in clay nanopores is significant for various engineering applications.In this study,we performed non-equilibrium molecular dynamics(NEMD)simulations to reveal the molecular force mechanisms of water flow in clay nanopores.The water dynamic viscosity,slip length,and average flow velocity were obtained to verify the NEMD models.Since the water confined in the nanopores maintained a dynamic mechanical equilibrium state,each water lamina can be regarded as a simply supported beam.The applied driving force,the force from clay crystal layers,the force from compensating sodium ions,and the force from other water laminae were further calculated to investigate the force mechanisms.The van der Wals barrier above the surface and hydraulic gradient lead to distribution differences in water oxygen atoms,which contribute to a net van der Waals resistance component of the force from clay crystal layers.Meanwhile,the water molecules tend to rotate to generate the electrostatic resistance component of the force from clay crystal layers and balance the increasing hydraulic gradient.Due to the velocity difference,the water molecules in the slower lamina have a higher tendency to lag and generate a net electrostatic resistance force as well as a net van der Waals driving force on the water molecules in the faster lamina,which together make up the viscous force.

Instant formation of nanopores on flexible polymer membranes using intense pulsed light and nanoparticle templates

The development of simple and high-throughput approaches to yield solid-state nanopores on large surface membranes may facilitate the prevalence of nanopore analysis technology and in-vitro diagnosis using portable devices.However,solidstate nanopores are typically realized by complex and highend nanofabrication equipments.Here,we present a method to achieve nanopores on polymer membranes using,silver nanoparticles(AgNPs)as templates and intense pulsed light(IPL)as a heating source.The density and size of nanopores are controllable by adjusting the spin coating rate,the concentration of nanoparticle suspension,and the size of nanoparticles(NPs).The temperature of the AgNPs can rapidly reach 1132 K under instant heating of photothermal effect through light irradiation in 2 ms,resulting in localized melting and decomposition of an underneath polycarbonate(PC)membrane to yield nanopores with sizes ranging from 10 to 270 nm.After removing the nanoparticle residues,the flexible membrane with nanopores can be integrated into a flow cell to achieve a nanopore sensor that has been used to measure the translocation behaviors of bovine serum albumin(BSA).The results have demonstrated the capability of the sensor in protein denaturation identification.This low-cost and highthroughput technique to fabricate solid-state nanopores on flexible polymeric membranes may facilitate the development of more nanopore-based flexible sensors that can be integrated with other flexible components for wearable diagnosis.

Water-bearing characteristics and their effects on the nanopores of overmature coal-measure shales in the Wuxiang area of the Qinshui Basin, north China

In this study,a group of overmature coal-measure shale core samples was collected in situ from an exploration well located in the Wuxiang area of the Qinshui Basin,north China.The pore water contents(CPW)of the shales under as-received conditions,equilibrium water contents(CEW)of the shales under moisture equilibrium conditions(relative humidity:100%),and nanopore structures of the shales under both as-received and dried conditions were measured.The results indicate that the CPW values of these shales are much lower than their CEW values,which implies that the bulk pore systems of these shales have low water-bearing extents.In addition,approximately half of the total pore volumes and surface areas of the as-received shales are occupied by pore water,and the effects of pore water on shale nanopores with various pore types and widths are different.The average water-occupied percentages(PW)are 59.16%−81.99%and 42.53%−43.44%for the non-micropores and micropores,respectively,and are 83.54%−97.69%and 19.57%−26.42%for the inorganic-matter hosted(IM)and organic-matter hosted(OM)pores,respectively.The pore water in shales not only significantly reduces the storage of shale gas by occupying many pore spaces,but also causes the shale gas,especially the absorbed gas,to be mostly stored in the OM pores;meanwhile,the IM pores mainly store free gas.Therefore,the water-bearing characteristics and their effects on the pore structures and gas-bearing properties of coal-measure shales should be noted for the evaluation and exploration of shale gas in the Qinshui Basin.

Electrokinetic transport of nanoparticles in functional group modified nanopores

Nanopore detection is a hot issue in current research.One of the challenges is how to slow down the transport velocity of nanoparticles in nanopores.In this paper,we propose a functional group modified nanopore.That means a polyelectrolyte brush layer is grafted on the surface of the nanopore to change the surface charge properties.The existing studies generally set the charge density of the brush layer to a fixed value.On the contrary,in this paper,we consider an essential property of the brush layer:the volume charge density is adjustable with pH.Thus,the charge property of the brush layer will change with the local H+concentration.Based on this,we established a mathematical model to study the transport of nanoparticles in polyelectrolyte brush layer modified nanopores.We found that pH can effectively adjust the charge density and even the polarity of the brush layer.A larger pH can reduce the transport velocity of nanoparticles and improve the blockade degree of ion current.The grafting density does not change the polarity of the brush charge.The larger the grafting density,the greater the charge density of the brush layer,and the blockade degree of ion current is also more obvious.The polyelectrolyte brush layer modified nanopores in this paper can effectively reduce the nanoparticle transport velocity and retain the essential ion current characteristics,such as ion current blockade and enhancement.