Porous Model Research Articles

Analysing the effect of defects on stress concentration and fatigue life of L-PBF AlSi10Mg alloy using finite element modelling

Additive manufacturing (AM) is a developing manufacturing technology, which provides excellent attributes compared to other manufacturing techniques. However, one of the critical challenges is the presence of defects that hinder the mechanical properties of the parts, particularly the fatigue life. Experimental understanding of fatigue is a cumbersome process. Therefore, numerical prediction based on specified conditions (such as porosity and applied load) can be an alternative to experimental analysis at the design stage of AM parts. In this study, elastic–plastic finite element analysis (FEA) is performed to obtain the stress distribution around pores, and their resultant effect on fatigue life for L-PBF (laser powder bed fusion) produced AlSi10Mg alloy samples. The stress field is calculated for both single and multiple pore models, where stress concentration is evaluated as a function of the pore’s location and its size. It is found that both pore location and size affect the stress field; however, location effects dominate over pore size. For the same remote applied stress level, the stress concentration around the pore increases with an increase in pore size, and the local maximum stress occurs near the pores that are closest to the surface. The current study also evaluates the relative effect of porosity fraction, average pore size, and location. It is found that the magnitude and sensitivity of stress concentration are hierarchically controlled by porosity location, pore size, and porosity density. A multi-scale finite element (FE) model is proposed based on inherent porosity data measured using Computed Tomography (CT) to predict overall fatigue life. The fatigue cycles are calculated using the rainflow counting algorithm in FE Safe using the stress–strain data obtained from the proposed FEA model. Using the proposed model, it is possible to generate S–N curves for any loading condition for a given porosity condition (porosity density and average pore size). The S–N curve results obtained from the FE model are compared to the experimental observations. The predicted fatigue life shows approximately 5% error with experimental results at high stress loading conditions. However, the proposed model overpredicts the fatigue life at low stress loading by almost 30%.

Fracture strength and failure mechanism of graphene-containing grain boundaries and pores

Grain boundaries and pores commonly manifest in graphene sheets during experimental preparation. Additionally, pores have been intentionally incorporated into graphene to fulfill specific functions for various applications. However, how does the simultaneous presence of pores and grain boundaries impact the mechanical properties of graphene? This paper establishes uniaxial tension models of single-layer graphene-containing pores and three types of experimentally observed. The effect of interaction between pores and grain boundaries on the fracture strength of graphene was studied respectively for three types of grain boundaries by employing molecular dynamics simulations and considering factors such as pore size, the distance between pores and grain boundaries, and loading angle. A competitive mechanism between the intrinsic strength of pristine graphene with grain boundaries (referred to as pristine GGBs), which varies with the loading angle and the fracture strength of graphene sheets with pores that changes with the size of the pores, governs the fracture strength and failure modes of GGBs with pores. When the former exceeds the latter, the fracture strength of GGBs with pores primarily depends on the size of the pores, and fractures occur at the edges of the pores. Conversely, when the former is lower, the fracture strength of GGBs with pores relies on the loading angle and the distance between pores and grain boundaries, leading to grain boundary rupture. If the two strengths are comparable, the failure modes are influenced by the distance between pores and grain boundaries as well as the loading angle. The findings further elucidate the impact of coexisting grain boundaries and pores on the fracture behavior of graphene, providing valuable guidance for the precise design of graphene-based devices in the future.

Study on oil seepage mechanisms in lamellar shale by using the lattice Boltzmann method

The shale oil and gas resources in the world are rich and are an important part of unconventional oil and gas resources. In this paper, firstly, by comprehensively using CT scanning technology, the three-dimensional pore-fracture structure characteristics of shale core samples of different sizes is characterized, and a three-dimensional digital core is established; Secondly, SEM and FIB-SEM techniques are systematically used to describe the microstructure and fracture network development characteristics of shale matrix pores and fractures, and a three-dimensional pore and fracture network model is established; Thirdly, Combined with LBZ simulation method, the mechanism of two-phase fluid transport in shale cross-scale fracture network is explored. Results show that: (a) The relatively dispersed mesopores and macropores in space constitute the main storage space of methane. Some pores in the study area of shale samples have good connectivity, and some samples only have connected pores in the study area of their magnification. (b) A large number of intergranular pores and fissures developed together with the intergranular pores of clay minerals, forming a good network connection system between microscopic pores in laminated shale. (c) when the hydrophilic mineral proportion is increased from 30% to 70%, the relative permeability of oil phase at water saturations of 20%, 40% and 60% has an increase of 6.8%, 7.8% and 4.2%, respectively, and the relative permeability of water phase at water saturations of 20%, 40% and 60% has a decrease of 1.8%, 2.6% and 6.5%, respectively. (d) When the oil phase contact angle is increased from 30° to 70°, the relative permeability of oil phase at water saturations of 20%, 40% and 60% has an increase of 1.9%, 2.7% and 2.2%, respectively, and the relative permeability of water phase at water saturations of 20%, 40% and 60% has a decrease of 1.2%, 2.1% and 3.5%, respectively.

Resource recovery from RO concentrate using nanofiltration: Impact of active layer thickness on performance

Modelling the removal of monovalent and divalent ions from seawater via nanofiltration is crucial for pre-treatment in seawater reverse osmosis systems. Effective separation of divalent ions through nanofiltration and allowing the permeate containing only monovalent ions to pass through the reverse osmosis system produces pure NaCl salt from the concentrate. However, the Donnan steric pore model and dielectric exclusion assume a uniformly distributed cylinder pore morphology, which is not representative of the actual membrane structure. This study analyzed the impact of membrane thickness on neutral solute removal and investigated the effect of two different methods for calculating the Peclet number on rejection rates of monovalent and divalent salts. Results show that membrane thickness has a significant effect on rejection rates, particularly for uncharged solutes in the range of 0.5–0.7 solute radius to membrane pore size ratio. Operating pressures above 10 bar favour the use of effective active layer thickness over the membrane pore size to calculate the Peclet number. At low pressures, using the effective active layer can lead to overestimation of monovalent salt rejection and underestimation of divalent salt rejection. This study highlights the importance of appropriate Peclet number calculation methods based on applied pressure when modelling membrane separation performance.

Influence of pH and NaCl on the rejection of glycine and triglycine in binary solutions for desalination with diananofiltration

Nanofiltration can be used as the last step in the purification of the biomolecules that are present in many industrial by-products, such as biological protein hydrolysates. The present study explored the variation in glycine and triglycine rejections in binary solutions with NaCl at different feed pHs with two nanofiltration membranes: MPF-36 and Desal 5DK with molecular weight cut-offs of 1000 and 200 g mol−1, respectively. First, water permeability coefficient showed a n-shaped curve with feed pH, which was more evident for the MPF-36 membrane. Second, membrane performance with single solutions was studied and the experimental data were fitted with the Donnan steric pore model with dielectric exclusion (DSPM-DE) to explain the variations of solute rejection with feed pHs. Glucose rejection was assessed to estimate the membrane pore radius of the MPF-36 membrane, and a pH dependence was observed. For a tight membrane (Desal 5DK), glucose rejection was close to unity and the membrane pore radius was estimated from the glycine rejection in the feed pH range from 3.7 to 8.4. Glycine and triglycine rejections showed a pH-dependence with a u-shaped curve, even for the zwitterion species. In binary solutions, glycine and triglycine rejections decreased with NaCl concentration, especially in the MPF-36 membrane. Triglycine rejection was always higher than NaCl rejection and it was estimated that triglycine can be desalted using a continuous diananofiltration the Desal 5DK membrane.

Insight into the Desolvation of Quaternary Ammonium Cation with Acetonitrile as a Solvent in Hydroxyl-Flat Pores: A First-Principles Calculation.

Supercapacitors have a wide range of applications in high-technology fields. The desolvation of organic electrolyte cations affects the capacity size and conductivity of supercapacitors. However, few relevant studies have been published in this field. In this experiment, the adsorption behavior of porous carbon was simulated with first-principles calculations using a graphene bilayer with a layer spacing of 4-10 Å as a hydroxyl-flat pore model. The reaction energies of quaternary ammonium cations, acetonitrile, and quaternary ammonium cationic complexes were calculated in a graphene bilayer with different interlayer spacings, and the desolvation behavior of TEA+ and SBP+ ions was described. The critical size for the complete desolvation of [TEA(AN)]+ was 4.7 Å, and the partial desolvation size ranged from 4.7 to 4.8 Å. The critical size for the complete desolvation of [SBP(AN)]+ was 5.2 Å, and the partial desolvation size ranged from 5.2 to 5.5 Å. As the ionic radius of the quaternary ammonium cation decreased, the desolvation size showed a positive trend. A density of states (DOS) analysis of the desolvated quaternary ammonium cations embedded in the hydroxyl-flat pore structure showed that the conductivity of the hydroxyl-flat pore was enhanced after gaining electrons. The results of this paper provide some help in selecting organic electrolytes to improve the capacity and conductivity of supercapacitors.

Prediction of Adsorption and Diffusion of Shale Gas in Composite Pores Consisting of Kaolinite and Kerogen using Molecular Simulation.

Natural gas production from shale formations is one of the most recent and fast growing developments in the oil and gas industry. The accurate prediction of the adsorption and transport of shale gas is essential for estimating shale gas production capacity and improving existing extractions. To realistically represent heterogeneous shale formations, a composite pore model was built from a kaolinite slit mesopore hosting a kerogen matrix. Moreover, empty slabs (2, 3, and 4 nm) were added between the kerogen matrix and siloxane surface of kaolinite. Using Grand-Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations, the adsorption and diffusion of pure methane, pure ethane, and a shale gas mixture were computed at various high pressures (100, 150, and 250 atm) and temperature of 298.15 K. The addition of an inner slit pore was found to significantly increase the excess adsorption of methane, as a pure component and in the shale gas mixture. The saturation of the composite pore with methane was observed to be at a higher pressure compared to ethane. The excess adsorption of carbon dioxide was not largely affected by pressure, and the local number density profile showed its strong affinity to kerogen micropores and the hydroxylated gibbsite surface under all conditions and pore widths. Lateral diffusion coefficients were found to increase with increasing the width of the empty slab inside the composite pore. Statistical errors of diffusion coefficients were found to be large for the case of shale gas components present at low composition. A larger composite pore configuration was created to investigate the diffusion of methane in different regions of the composite pore. The calculated diffusion coefficients and mean residence times were found to be indicative of the different adsorption mechanisms occurring inside the pore.

Machine Learning Predictions of Simulated Self-Diffusion Coefficients for Bulk and Confined Pure Liquids.

Diffusion properties of bulk fluids have been predicted using empirical expressions and machine learning (ML) models, suggesting that predictions of diffusion also should be possible for fluids in confined environments. The ability to quickly and accurately predict diffusion in porous materials would enable new discoveries and spur development in relevant technologies such as separations, catalysis, batteries, and subsurface applications. In this work, we apply artificial neural network (ANN) models to predict the simulated self-diffusion coefficients of real liquids in both bulk and pore environments. The training data sets were generated from molecular dynamics (MD) simulations of Lennard-Jones particles representing a diverse set of 14 molecules ranging from ammonia to dodecane over a range of liquid pressures and temperatures. Planar, cylindrical, and hexagonal pore models consisted of walls composed of carbon atoms. Our simple model for these liquids was primarily used to generate ANN training data, but the simulated self-diffusion coefficients of bulk liquids show excellent agreement with experimental diffusion coefficients. ANN models based on simple descriptors accurately reproduced the MD diffusion data for both bulk and confined liquids, including the trend of increased mobility in large pores relative to the corresponding bulk liquid.

Elucidating the role of interlayer structure in the permeance-selectivity trade-off of ceramic nanofiltration membrane

Reasonable design of a rational interlayer in an asymmetric ceramic nanofiltration (NF) membrane facilitates water transport as well as solute retention. Nevertheless, the inherent relationship between the microstructure of the interlayer and the permselectivity in ceramic NF membrane remains to be unclear. In this study, a quantitative model is developed to predict the influence of the factors (i.e., particle diameter and layer thickness) controlling the structure of interlayer on the permselectivity by integrating the cake filtrated theory and Donnan-Steric Pore model with the Dielectric Exclusion model. The simulations demonstrate that interlayer thickness dominates the solute rejection rather than particle diameter that constitutes the interlayer when an appropriate top-layer structure is applied. However, the enhancement of water permeance requires simultaneous regulation of the microstructures of both interlayer and top layer. For negatively charged ceramic NF membranes, the comprehensive effect of diffusion, convection, and electro-migration is the transport mechanism of positively charged counter-ion (i.e., Na+), whereas the transport of negatively charged co-ion (i.e., SO42-) is merely dominated by diffusion. This study thereby elucidates the role of the interlayer in terms of improving the permeance-selectivity trade-off relationship, which is of great significance to the future development of a high-performance ceramic NF membrane.

Spouted fluidised bed reactor for kinetic measurements of the reduction of Fe2O3 in a CO/ CO2 atmosphere part II: An extended random pore model for solid-state diffusion

A generalised random pore model, including both gaseous diffusion and solid-state diffusion in the product layer was developed, and was successfully applied to the reduction of hematite to magnetite by CO. The initial surface rate constant, ks,0′ and effective diffusivity, DS in the original model were formulated to describe the surface reaction and solid-state diffusion in the product layer. This approach is also particularly useful to determine the solid-state diffusivity during the reduction of a metal oxide, which is difficult to obtain via direct measurement. As an extension of previous work, the generalised random pore model was satisfactorily applied to the kinetic data obtained from a spouted fluidised bed reactor for the reduction of pure iron oxide with CO. Kinetic and diffusion constants, ks,0′ and Ds, were derived by fitting the model to the kinetics data for temperatures up to 650 °C. The activation energy for ks,0′ and Ds were calculated to be 35 kJ mol-1 and 100 kJ mol-1. The overall reaction kinetics were likely to be control by both surface reaction and the product layer diffusion of iron ions, Fen+. The fitted random pore model was fed into a two-phase fluidised bed model to test against experimental measurements from the spouted fluidised bed reactor. The model outlet concentration was shown to agree closely with that observed in the experiment. This validated the key assumption required for intrinsic kinetic measurements using the fluidised bed reactor, and also give credence to the applicability of the random pore model to reactions limited by solid state diffusion.

Droplet Evolution from a Single Hydrophobic Pore in the Diffusion Media of Polymer Electrolyte Fuel Cells: A Conceptual Analysis

Maintaining a well-balanced water distribution is crucial for the operation of polymer electrolyte fuel cells. The water distribution depends to a large extent on the ease of liquid water transport in the diffusion media (DM) and in the flow field (FF) on the cathode side and, especially, on processes in boundary regions between these media. In this article, the droplet dynamics at the DM-FF interface are studied by a mechano-hydrodynamic pore model. The presented treatment allows droplet detachment to be rationalized, in dependence of pore radius and air flow velocity. Large pore radius and high air flow velocity favor droplet detachment during an earlier stage of growth, at which the contact line of the droplet remains pinned at the pore opening while the droplet volume expands during growth. We evaluate the trend of detachment time and detachment height of a droplet. Furthermore, we analyze the influence of the air flow velocity on the time-averaged liquid pressure at the pore exit. The physics governing the flooding behavior of the pore is discussed. The presented model-based analyses provide theoretical insights into material properties and operating conditions that improve water removal.

Three-dimensional Numerical Simulation of Entrained-Flow Gasifier and Influence of Coal Distribution at the Inlet

The research object in this paper is an industrial HTL gasifier in a plant. A three-dimensional model is built. The chemical percolation devolatilization (CPD) model is used to calculate the pyrolysis reaction. Considering the gas diffusion in the inner pores of the particle and the evolution of pore structure, the random pore model (RPM) was used to simulate the chemical reaction on the particle surface, and the gasification reaction kinetic parameter of char was measured by high-pressure thermogravimetry analysis. The slag model was constructed to describe the formation process and distribution of slag. Through the coupling of the above models, a simulation method that combines several submodels for the entrained flow gasifier is built, and the results from simulation are in good agreement with the industrial data. Furthermore, the effect of the uniformity of pulverized coal injection was analyzed by this method. The simulation results reflect that the asymmetric feed of coal will affect gas-solid mixing and reduce carbon conversion, and it leads to a higher local wall temperature and a lower ratio of crude slag to fine slag.

Simulation of adsorption and diffusion behaviors of H2O and O2 in low-rank coal pores

In this paper, Materials Studio software was used to construct 2–7 nm cylindrical pore models to study the adsorption and diffusion behaviors of H2O and O2. The results show that H2O is adsorbed in multiple layers or clusters in micro-mesoporous pores, while O2 is adsorbed in single layer·H2O occupied the adsorption site of O2, resulting in a decrease in the adsorption capacity of O2 by 5.44%∼31.38%. The diffusion coefficients of H2O and O2 are both on the order of 10−8 m2/s, but H2O will preferentially bind to high-energy sites, promoting the diffusion of O2.

Conventional Mercury Penetration and Constant Velocity Mercury Penetration Experiments Are Used to Quantitatively Characterize the Difference in Micropore Structure in Low Permeability Reservoirs and Its Influence on Movable Fluid Saturation

There are many research methods and experimental means for quantitative and semiquantitative evaluation of low permeability reservoirs. Generally, people do not use a single means to study them but use a variety of experimental means to verify and complement each other. Conventional mercury penetration and constant velocity mercury penetration are two important experimental methods for the quantitative evaluation of tight reservoirs. The micro characteristic parameters of reservoirs obtained by them are quite different, which bring some difficulties to people’s research. This paper first analyzes the reasons for the differences between the two from the aspects of experimental theory and model, experimental conditions, and experimental process. Taking C 6 and C 7 reservoirs in Ordos Basin as an example, a total of 13 representative pairs of samples were selected to analyze the difference in capillary pressure curve shape and pore throat distribution characteristics between the two experiments and to clarify the reasons for the difference in microscopic pore characteristic parameters measured by the two experiments. Finally, the correlation between the microscopic pore characteristic parameters and the movable fluid saturation parameters is analyzed. The results show that the theoretical model of conventional mercury penetration experiment is a capillary tube bundle model with different radii. The maximum injection pressure of experimental mercury is high and the experimental speed is fast. The theoretical model of constant velocity mercury penetration experiment is the pore and throat capillary model with different radii. The maximum injection pressure is low, the experimental speed is very slow, and the process is quasistatic. The parameters such as displacement pressure, total mercury saturation, and separation coefficient obtained by the latter are smaller than those measured by the former; however, the maximum throat radius, average throat radius, and other parameters obtained by the latter are larger than those measured by the former. According to the correlation chart drawn, it can be concluded that the correlation between the microscopic pore throat characteristic parameters and the movable fluid saturation in the constant velocity mercury penetration experiment is better than that in the conventional mercury penetration experiment. The influencing factors mainly include permeability, porosity, displacement pressure, maximum pore throat radius, and sorting coefficient. The maximum mercury injection saturation has little correlation.

Experimental and numerical investigations on damage evolution of concrete under sulfate attack and freeze-thaw cycles

The macro-microstructure tests of concrete under the alternating action of salt freezing (ASF) were conducted to investigate the macro-mechanical properties and microstructure pore evolution patterns of concrete. Combined with CT scanning and 3D pore model reconstructing technologies, we present the evolution equation of concrete porosity and the quantitative relation between the fractal dimension of concrete pores and the macroscopic strength under the ASF. Then, a macro-microscopic damage evolution model of concrete was proposed to study the structural performance evaluation of an aqueduct. The results show that the compressive strength (fc), splitting tensile strength (ft), and relative dynamic modulus (Erd) of concrete specimens under the ASF show a decreasing trend as a whole, and the mechanical properties of concrete gradually decrease with the increase of sulfate solution concentration. With the increase of the cycles of salt freezing alternation, the pore fractal dimension of the concrete gradually decreases and the porosity gradually increases. After the cycle of 8 times, the pore fractal dimension decreases by 6.06%, and the porosity increases by 7.30% compared with the initial state. The porosity of concrete is negatively correlated with the strength, while the fractal dimension of the pore structure is positively correlated with the strength. When the ASF reaches 8 times, the maximum compressive stress and tensile stress of the groove body are 9.48 MPa and 3.13 MPa, respectively, which appear at the ends of the lower chord. The displacements of the bottom and side wall plates are 0.384 mm and 3.289 mm, respectively. The penetrating cracks appear at the junction, and the structure severely deteriorates.

Hybrid ablation–expansion model for laser interaction with low-density foams

A sub-grid foam model is developed to describe numerically a sequence of processes transforming solid elements in the foam into a hot plasma under the energy deposition by lasers. We account for three distinct processes: accurate laser energy absorption and scattering on the sub-wavelength cylindrical solid elements, expansion of the foam element due to the energy deposition in its volume, and ablation of the solid element due to the energy deposition on its surface. The foam element dynamics is modeled via a self-similar isothermal expansion combined with a stationary ablation model, and it is described by a set of ordinary differential equations. The microscopic single pore model is incorporated in the macroscopic hydrodynamic codes, and numerical simulations show a good agreement with available experimental data.

Studies of some bio-inspired liquid crystals

ABSTRACTThe main phase transition of lipid bilayers corresponds to a defined change from an ordered (gel) to a disordered (fluid liquid crystal) state of hydrocarbon chains, occurring in general at a defined temperature Tm. However, aqueous dispersions of pure anionic phospholipids, and particularly DMPG, may exhibit a ‘melting regime’, from Tmon until Tmoff, over ~10°C. The melting process depends on pH, ionic strength and several details of sample preparation. This paper makes a review on seven papers of the author with different collaborations, with the original proposal of pores in the DMPG melting transition. The focus is on structural results obtained from X-ray scattering, varying concentration and temperature, but integrating with results from other experimental techniques. Initially the effect of salt addition was separated from the effect of DMPG concentration. At DMPG concentrations higher than 70 mM a lamellar phase starts and a detailed study of the temperature variation of 150 mM DMPG allowed arrival to detailed pore model, focused in the surface fractions of pores in the bilayers. The model admits large and small pores in the melting regime and agrees with the new Lamellar Phase with pores (Lp) starting at T3. The large biological relevance is stressed.

A new approach to evaluate abandoned mine methane resources based on the zoning of the mining-disturbed strata

Abundant abandoned mine methane (AMM) accumulates in the mining-disturbed coal/rock strata in abandoned coal mines. However, the simplified pore and fracture model of the mining-disturbed strata is often adopted to investigate AMM resources. In this case, AMM distribution needs to be more accurate, making it difficult to determine the appropriate location of surface wells. So the question is, how can the pore and fracture be characterized in different zones of the mining-disturbed strata? What is the distribution of AMM resources in the mining-disturbed strata? To address these problems, in this work, the mining-disturbed coal/rock strata of the abandoned mine are divided into five zones. The pore and fracture of the mining-disturbed strata in different zones are characterized by simulation experiments. On this basis, the new evaluation approach of AMM in the mining-disturbed strata is established to reveal the distribution of AMM in each zone. The results show that the mining-disturbed coal/rock strata are divided into five zones: stress concentration zone (I), shear fracture zone (II), separation fracture zone (III), compaction zone (IV), and bottom fracture zone (V). The pore and fracture of coal/rock strata and the distribution of AMM are different in each zone. The AMM resources in the mining-disturbed strata have great potential for development. The AMM in zone I account for 69% of the total, mainly the adsorbed gas in the remaining coal seam affected by mining disturbance. The AMM in the stress relief zone is mostly free gas remaining in the pore and fracture. The fractures in zone II are connected along the horizontal direction, forming a ring fracture body with abundant free AMM resources, which accounted for 19% of the total AMM resources. The AMM in zones III, IV, and V are limited. This work provides a new approach to evaluating the AMM and plays a guiding role in the layout of the surface wells in abandoned mines.

Engineering high post-electroporation viabilities and transfection efficiencies for elongated cells on suspended nanofiber networks

The impact of cell shape on cell membrane permeabilization by pulsed electric fields is not fully understood. For certain applications, cell survival and recovery post-treatment is either desirable, as in gene transfection, electrofusion, and electrochemotherapy, or is undesirable, as in tumor and cardiac ablations. Understanding of how morphology affects cell viability post-electroporation may lead to improved electroporation methods. In this study, we use precisely aligned nanofiber networks within a microfluidic device to reproducibly generate elongated cells with controlled orientations to an applied electric field. We show that cell viability is significantly dependent on cell orientation, elongation, and spread. Further, these trends are dependent on the external buffer conductivity. Additionally, we see that cell survival for elongated cells is still supported by the standard pore model of electroporation. Lastly, we see that manipulating the cell orientation and shape can be leveraged for increased transfection efficiencies when compared to spherical cells. An improved understanding of cell shape and pulsation buffer conductivity may lead to improved methods for enhancing cell viability post-electroporation by engineering the cell morphology, cytoskeleton, and electroporation buffer conditions.

Controlling effect of pore-throat structures on tight oil accumulation effectiveness in the upper Cretaceous Qingshankou formation, Songliao Basin

The Gaotaizi reservoir in the Qingshankou Formation, northern Songliao Basin is one of the most potential tight oil targets in China and it is underlain directly by the OM-rich shales of the Qingshankou Formation. Previous studies indicated a strong oil-bearing heterogeneity in the Gaotaizi reservoir, while the relationship between pore-throat system and oil-bearing property is poorly understood. Thin section, Soxhlet extraction, MICP, fluid inclusion PVTX simulation and basin modelling were combined to investigate the pore-throat structure, and its effect on oil-bearing abundance and the tight oil accumulation effectiveness. Three pore-throat structures in the Gaotaizi reservoir were identified. The pore-throat size distribution (PSD), pore-throat configuration, and the corresponding physical properties became worser from Type I to Type III, as well as the pore types. A close relationship between pore-throat structures and sedimentary facies was established. Type I and II were dominated in mouth bar sand, while Type II, and Type III were mainly distributed in distal sandbars and sheet sand, respectively. The fluid properties and oil-bearing grades in the Gaotaizi tight sandstones were significantly controlled by the pore-throat structures. There were few fluids produced from the tight sandstones with Type III pore-throat structures, whose pore-throat size was almost half of that in tight sandstones with oil production. The dynamic model and ratio of pore containing oil (RPO) parameter were proposed. The residual pressure difference between the source rock and reservoir was 4.1 MPa, and the corresponding lower limit of pore-throat radius for tight oil accumulation was around 180 nm considering the limited buoyancy. Under the same driving force, the RPO of the Type I, II, III pore-throat structure reservoir was 74.4%, 58.0%, 23.3%, respectively, caused by pore-throat structure differences. It shows that an optimal tight oil “sweet spot” formed in the Type I reservoir, and favourable tight oil zones typically developed in the Type II reservoir, whereas only poor tight oil or dry zones developed in the Type III reservoir. This research improves the understanding of continental tight oil enrichment mechanism and provides a reference for optimizing favourable area of tight oil exploration.