Micro-nano Pores Research Articles

Characterization of micro-nano pore networks in shale oil reservoirs of Paleogene Shahejie Formation in Dongying Sag of Bohai Bay Basin, East China

Abstract For typical blocky, laminated and bedded mudrock samples from the Paleogene Shahejie Formation in the Dongying Sag of Bohai Bay Basin, this work systematically focuses on their structure characterization of multiple micro-nano pore networks. A use of mercury injection capillary pressure (MICP) documented the presence of multiple μm-nm pore networks, and obtained their respective porosity, permeability and tortuosity. Different sample sizes (500-841 μm GRI fractions, 1 cm-sized cubes, and 2.54 cm in diameter and 2-3 cm in height core plugs) and approaches (low-pressure N 2 gas physisorption, GRI matrix permeability, MICP, helium pycnometry, and pulse decay permeameter) were used to measure pore size distribution, porosity and permeability. The average porosity and matrix permeability determined from MICP are (6.31±1.64)% and (27.4±31.1)×10 -9 μm 2 , the pore throat diameter of pores is mainly around 5 nm, and the median pore throat diameter based on 50% of final cumulative volume is (8.20±3.01) nm in shale. The pore-throat ratios decrease with a decrease of pore size diameter. Moreover, the permeability of shale samples with lamination is nearly 20 times larger than matrix permeability. The geometrical tortuosity of the nano-scale 2.8−10.0 nm pore networks is 8.44 in these shales, which indicates a poor connectivity of matrix pore network and low flow capability. Overall, the variable and limited pore connectivity of shale samples will affect hydrocarbon preservation and recovery.

Reservoir Classification of Tight Sandstone and Its Micro-Nano Pores Characteristics, Songliao Basin, Northeast China

Reservoir Classification of Tight Sandstone and Its Micro-Nano Pores Characteristics, Songliao Basin, Northeast China

Microscopic surface wettability electrochemical characterization of tight sandstone with infrared spectra testing

The distribution of charge density on the surface of microscopic tight oil is studied by using Stern double electric layer theory, and the mathematical flow model of polar fluid with micro powers in tight oil reservoir is established. The Fourier transform infrared (FTIR) were used to investigate the interaction of rock surface functional groups with fluids. The results show that: (1) When the external fluid of the polar group passes through the dense micro-nano pore, it will form an electric double layer on the surface of the rock, there will be a certain thickness of the liquid membrane, the fluid migration has a certain Of the electrical viscosity effect, will have a certain flow resistance. (2) The Fourier transform infrared spectroscopy of the Chang 7 tight reservoir rock samples exists and distributes different kinds of peaks. The left peak trend determines the presence of hydroxyl groups. The four fronts and types of the right side can be used to obtain that calcium carbonate CO32- exists. (3) There are CO32- and hydroxyl functional minerals in the Chang 7 tight sandstone samples. It is consistent with the basic mineral analysis measured by X-ray diffraction. When the external fluid affects the rock surface, the surface will occur in the physical van der Waals force and chemical bond interaction, so it will affect the flow of water on the surface.

Fabrication of a controllable nanopesticide system with magnetic collectability

In this work, we constructed a multifunctional nanopesticide system, a pH-responsively controlled-release pesticide (PRCRP) with magnetic collectability performance, to effectively improve the pesticide utilization efficiency (UE). Herein, herbicide (glyphosate) and pesticide (cypermethrin) were respectively loaded in the micro-nano pores of diatomite/Fe3O4, a magnetic nanocarrier, which was fabricated through in-situ deposition method. Afterwards, the resulting pesticide/diatomite/Fe3O4 was coated by chitosan which can be dissolved in acid condition so as to control the release of pesticide. The magnetism resulted from Fe3O4 endowed PRCRP a feasible magnetic collection performance. After the release of pesticide, PRCRP could be separated conveniently from water and soil with a high collection ratio. PRCRP displayed a high adhesion capacity on the weed surface and pest epidermis, a significantly controlled-release performance, a high UE, an outstanding control efficacy on weed and pest, and potential collectability in practice. Therefore, this technology may have a promising application potential in reducing pesticide residue and risk to the environment.

Continental shale pore structure characteristics and their controlling factors: A case study from the lower third member of the Shahejie Formation, Zhanhua Sag, Eastern China

Since shale oil and gas primarily occur in micro-nano pores and fractures, research on pore structure characteristics is important to understand shale oil and gas accumulation mechanisms. Studies on the pore structure of the lower third member of the Shahejie (Es3l) Formation in Zhanhua Sag, Jiyang Depression, Bohai Bay Basin, Eastern China, are quite limited, thereby, restricting further investment on shale oil and gas exploration. We studied continental shale pore structure characteristics and their controlling factors by using a series of laboratory experiments on core samples taken from the Luo-69 Well. The results demonstrate that the Es3l continental shale has a high proportion of calcareous minerals, low siliceous minerals, and low clay minerals. It is characterized by low total organic carbon (TOC) content, low thermal maturity, and Type I and II organic matter. Five different kinds of pore spaces are developed in the shale samples: organic matter-hosted pores, intergranular pores, intercrystalline pores, dissolution pores, and micro-fractures, with the majority of slit-shaped and ink-bottle-shaped pores. Macropores make the greatest contribution to the total pore volume, whereas micropores provide the major surface area. As the organic-rich laminated calcareous shale (ORLCS) presents a larger pore volume, surface area, and mercury withdrawal efficiency, it is a favourable shale lithofacies for shale oil and gas storage and flow. Compared with the Longmaxi marine shale, macropores well-developed in the Es3l shale make great contribution for free hydrocarbon accumulation. Samples with different TOC contents, mineral compositions, thermal maturities, and lamellar layers exhibit distinct differences in pore structure. Mineral composition and thermal maturity primarily affect micropores and mesopores. Macropores are influenced by mineral composition, TOC content, thermal maturity, and lamellar layers.

Micron-to nano-pore characteristics in the shale of Longmaxi Formation, southeast Sichuan Basin

For shale of Lower Silurian Longmaxi Formation in Chongqing, southeast Sichuan Basin, characteristics of micro-nano pores in marine shale reservoirs were well studies by means of Field-Emission Scanning Electron Microscope and Low-temperature Low-pressure Adsorption Experiment of CO2 and N2. Results showed that six types of pore were developed in the shale of Longmaxi Formation, i.e., organic pores, intergranular pores, intragranular pores, intercrystalline pores, dissolution pores and microfractures, among which the organic pores and intragranular pores in interlayers of clay minerals were most developed, and a plenty of dissolution pores were also well developed because of high thermal evolution degree. BET specific surface area of the shale in Longmaxi Formation ranged from 3.5 to 18.1 m2/g, BJH total pore volume was from 0.00234 to 0.01338 cm3/g, DA specific surface area of micropores vaired from 1.3 to 7.3 m2/g, and DA pore volume ranged from 0.00052 to 0.00273 cm3/g. The specific surface area of micropores in the shale accounted for 23.1%–80.2% of total specific surface area with an average of 50.3%, and the pore volume of micropores accounted for 12.1%–48.5% of total pore volume with an average of 32.3%. Micropore was the main storage space in shale reservoir for methane adsorption, that because capacities of specific surface area provided by micropores were considerably greater than those provided by mesopores and macropores. Pore size distribution of the shale was complex, and multiple different peaks occurred in the pore size curves, showing two or three peaks in the range from 0 to 100 nm and four peaks occasionally. TOC had a good linear relationship with pore structure parameters of micropores, mesopores + macropores and total pores in the shale, indicating that TOC was the most important control factor for micron-to nano- pore structure in the shale. After normalization of pore structure parameters to TOC, the pore structure parameters of total pores and mesopores + macropores, had positive linear relationships with content of clay minerals but negative linear relationships with content of brittle minerals, indicating that clay minerals and brittle minerals mainly controlled development of mesopores and macropores in the shale.

Spontaneous imbibition in asymmetric branch-like throat structures in unconventional reservoirs

Unconventional reservoirs, especially shale plays, have abundant micro-nano pores. Large volume water was injected into the reservoir during hydraulic fracturing. Fracturing fluid can displace gas in pore spaces spontaneously, called spontaneous imbibition (SI), which has significant effects on the gas production after hydraulic fracturing. Throat structure in matrix is one of the key factors to influence SI process. In this work, at first, complex pore space is simplified as a spatial self-similar branch-like structure composed of several asymmetric sub-throats. Then, within asymmetric branch structure, the imbibition process is calculated by a newly established mathematical model, and the influence of both pore structure and fluid characteristics, including contract angle, viscosity, surface tension, are discussed. Finally, some lab experiments, especially SI tests, are included on shale and sandstone core plugs to verify our model. Results show that the coherence in wettability between the reservoir and the fracturing fluid is important to enhance the microscopic replacement effect. Pore size also has effect influence on imbibition curve. In addition, both in models and experiments, imbibition index n is useful to describe imbibition properties of rocks. In unconventional rock samples like shale, n is less than 0.4, while high-permeability sandstone, n approach to 0.5. These conclusions are useful to investigate the mechanism of spontaneous imbibition and microscopic displacement in unconventional reservoirs.

Some key issues on the unconventional petroleum systems

AbstractOil and gas currently still hold a leading role in the global energy mix. The recent drastic increase in unconventional oil and gas production contributes significantly to strike a balance between the global demand and supply of oil and gas. However, a range of important fundamental questions about the unconventional oil and gas resources have not been adequately answered. Little is known about the distribution and accumulation patterns, as well as the exploration and development characteristics of unconventional oil and gas. The current status of global oil and gas exploration was reviewed and four key theoretical issues regarding the unconventional oil and gas geology were identified: (1) the traditional concept and definition of “petroleum system” needs to be revisited. The concept of a “holistic-process accumulation” model of a “total petroleum system” in petroliferous basins was proposed to analyze the unconventional hydrocarbon accumulation mechanisms from four key aspects of quantitative studies on hydrocarbon generation–expulsion–migration–accumulation processes. (2) The second issue is related to fine-grained sedimentary system and sedimentary facies of tight reservoirs. Through analyzing the relationship between fine-grained sediments and unconventional hydrocarbon accumulation, three research integration areas were put forward. (3) The third issue is on the micro-nano pore system and fluid phase behavior in shales and tight reservoirs. Five aspects of micro-nano pore system were identified to focus on unconventional hydrocarbon research, and the characteristics of micro-nano pore development and fluid phase behavior in micro-nanopores were elucidated. (4) The fourth issue is related to unconventional hydrocarbon accumulation patterns and resource evaluation. Based on the characteristics of unconventional hydrocarbon accumulation, an evaluation system for unconventional hydrocarbon resources was established and optimized.

Influencing factors of micropores in the graptolite shale of Ordovician Pingliang Formation in Ordos Basin, NW China

Abstract Multiple tests were conducted on graptolite shale samples from Middle Ordovician Pingliang Formation in three typical areas in Ordos Basin to investigate the relationship between micro-nano pore structure, graptolite content, rock composition, TOC, maturity, main and trace elements and gas content. The graptolite of Pingliang Formation concentrates in the black shale at the lower section of this layer. Pores in the shale are diverse in types, including pores made by extracellular polymeric substance (EPS), in bio-graptolite body, as inter-granular void of clay minerals, intra-granular, interstitial space between mineral crystals, micro-fractures, and intra-granular dissolution structures etc. Tests show that graptolite affected the sedimentary environment and shale gas accumulation; graptolites content is positively correlated to TOC, in a certain range, specific surface area is positively correlated to TOC and maturity, etc., as overall a lithologic inorganic and organic ratios. The rare earth elements (REE) patterns of the three areas are similar, indicating the same provenance. REE, Fe, Al and Ti content are negatively correlated to TOC, indicating the high REE content is not caused by organic matter enrichment, but related to the absorption of minerals particles. Gas content is positively correlated to specific surface area, TOC and maturity. The above factors contribute to space and size distribution of micro-nano pores in shale.

Pore characteristics of shale gas reservoirs from the Lower Paleozoic in the southern Sichuan Basin, China

Data was acquired from both the drillings and core samples of the Lower Paleozoic Qiongzhusi and Longmaxi Formations' marine shale gas reservoirs in the southern Sichuan Basin by means of numerous specific experimental methods such as organic geochemistry, organic petrology, and pore analyses. Findings helped determine the characteristics of organic matter, total porosity, microscopic pore, and pore structure. The results show that the Lower Paleozoic marine shale in the south of the Sichuan Basin are characterized by high total organic carbon content (most TOC>2.0%), high thermal maturity level (RO = 2.3%–3.8%), and low total porosity (1.16%–6.87%). The total organic carbon content and thermal maturity level of the Qiongzhusi Formation shale are higher than those of the Longmaxi Formation shale, while the total porosity of the Qiongzhusi Formation shale is lower than that of the Longmaxi Formation shale. There exists intergranular pore, dissolved pore, crystal particle pore, particle edge pore, and organic matter pore in the Lower Paleozoic Qiongzhusi Formation and Longmaxi Formation shale. There are more micro-nano pores developed in the Longmaxi Formation shales than those in the Qiongzhusi Formation shales. Intergranular pores, dissolved pores, as well as organic matter pores, are the most abundant, these are primary storage spaces for shale gas. The microscopic pores in the Lower Paleozoic shales are mainly composed of micropores, mesopores, and a small amount of macropores. The micropore and mesopore in the Qiongzhusi Formation shale account for 83.92% of the total pore volume. The micropore and mesopore in the Longmaxi Formation shale accounts for 78.17% of the total pore volume. Thus, the micropores and mesopores are the chief components of microscopic pores in the Lower Paleozoic shale gas reservoirs in the southern Sichuan Basin.

Study on pore structure characteristics of marine and continental shale in China

Shale gas is a key natural gas resource and has been a certain success in China. The Weiyuan marine shale (1#), Jiaoshiba marine shale (2#), Yaoqu tuff (4#) and Yaoqu continental shale (5# and 6#) were selected and subjected to thin section analyses, ice field emission scanning electron microscope (FE-SEM), mercury intrusion capillary pressure (MICP) and gas adsorption tests to study the pore structure characteristics of typical marine and continental shale. Results of pore structure characteristics and controlling factors, puts forward a new standard of pore size naming for hydraulic fracturing technology. Pore distribution uniformity coefficient hu is proposed to describe the continuity of different pore size distribution of shale. The test results of N2 adsorption and CO2 adsorption can be unified to attain continuous distribution of nanometer pore by using density function theory (DFT) model. The pore development degree of the samples from high to low are from 2#, 5#, 1#, 6# to 4# in the pore range of 2–100 nm while for the pore range of 10–100 μm the pore development degree from high to low are 2#, 1#, 4#, 6# to 5# in that order. Micro-nano pore of sample 2# and 5# are more developed compared to the other samples. Also gas storage capacity of sample 2# and 5# are stronger. The results can thus be used to guide the shale gas development, optimize shale location and increase production of shale gas.

Fabrication and Cell Responsive Behavior of Macroporous PLLA/Gelatin Composite Scaffold with Hierarchical Micro-Nano Pore Structure.

Scaffolds providing a 3D environment which can effectively promote the adhesion, proliferation and differentiation of cells are crucial to tissue regeneration. In this study, the polyllactic acid (PLLA) scaffold with hierarchical pore structural was fabricated via two-step thermally induced phase separation (TIPS). To mimic both physical architecture and chemical composite of natural bone extracellular matrix (ECM), gelatin fibers were introduced into the pores of PLLA scaffolds and formed 3D network structure via TIPS. Human adipose tissue-derived stem cells (ADSCs) were harvested and seeded into PLLA/gel hybrid scaffolds and cultured in vitro for biocompatibility assay. The surface morphology, porosity and compressive modulus of scaffolds were characterized by scanning electron microscopy (SEM), density analysis and compression test respectively. The results showed that hybrid scaffolds had high porosity (91.62%), a good compressive modulus (2.79 ± 0.20 MPa), nanometer fibers (diameter around 186.39~354.30 nm) and different grades of pore size from 7.41 ± 2.64 nm to 387.94 ± 102.48 nm. The scaffolds with mild hydrolysis by NaOH were modified by 1-ethyl-3-(3-dimethyl ami-nopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS). Gelatin was performed onto PLLA scaffold via TIPS aiming at enhancement cell-material interaction. In comparison with PLLA scaffold, the PLLA/gel scaffold had better biological performance and the mechanical properties because the gelatin fibers homogeneously distributed in each pore of PLLA scaffold and formed 3D network structure.

Petrophysical and capillary pressure properties of the upper Triassic Xujiahe Formation tight gas sandstones in western Sichuan, China

The tight sandstones of the Upper Triassic Xujiahe Formation (T3x) constitute important gas reservoirs in western Sichuan. The Xujiahe sandstones are characterized by low to very low porosity (av. 5.22% and 3.62% for the T3x4 and T3x2 sandstones, respectively), extremely low permeability (av. 0.060 mD and 0.058 mD for the T3x4 and T3x2 sandstones, respectively), strong heterogeneity, micronano pore throat, and poor pore throat sorting. As a result of complex pore structure and the occurrence of fractures, weak correlations exist between petrophysical properties and pore throat size, demonstrating that porosity or pore throat size alone does not serve as a good permeability predictor. Much improved correlations can be obtained between permeability and porosity when pore throat radii are incorporated. Correlations between porosity, permeability, and pore throat radii corresponding to different saturations of mercury were established, showing that the pore throat radius at 20% mercury saturation (R20) is the best permeability predictor. Multivariate regression analysis and artificial neural network (ANN) methods were used to establish permeability prediction models and the unique characteristics of neural networks enable them to be more successful in predicting permeability than the multivariate regression model. In addition, four petrophysical rock types can be identified based on the distributions of R20, each exhibiting distinct petrophysical properties and corresponding to different flow units.