The influence of pore characteristics on rock fragmentation mechanism by high-voltage electric pulse

High-voltage electric pulse(HVEP)is an innovative low-energy and high-efficiency technique.However,the underlying physics of the electrical breakdown within the rock,and the coupling mechanism between the various physical fields involved in HVEP still need to be further understood.In this study,we establish a 2D numerical model of multi-physical field coupling of the electrical breakdown of porous rock with randomly distributed pores to investigate the effect of pore characteristics(porosity,pore media composition)on the partial electrical breakdown of rock(i.e.the generation of a plasma channel inside the rock).Our findings indicate that the generation of a plasma channel is directionally selective and extends in the direction of a weak electrical breakdown intensity.As the porosity of the rock increases,so does the intensity of the electric field in the‘electrical damage’region—the greater the porosity,the greater the effectiveness of rock-breaking.As the fraction of pore fluid(S_(water)/S_(air))gradually declines,the generation time of the plasma channel decreases,and the efficacy of rock-breaking by HVEP increases.In addition,in this study,we conducted an indoor experiment utilizing an electric pulse drill to break down the rock in order to recreate the growth mode of the plasma channel in the rock.Moreover,the experimental results are consistent with the simulation results.In addition,the development of this type of partial electrical breakdown is confirmed to be related to electrode polarity and pore characteristics via the experiment of the symmetrical needle-needle electrode arrangement,which further demonstrates the mechanism of partial electrical breakdown.This research is significant for comprehending the process of electric impulse rock-breaking and gives theoretical guidance and technological support for advancing electric impulse drilling technology.

Favorable lithofacies and pore characteristics of the Permian Longtan Formation shale in the southern Sichuan Basin

The marine–continental transitional shale (MCTS) reservoirs of the Longtan Formation (LTF) are widely distributed in the Sichuan Basin. However, the LTF shale exhibits considerable variations in mineral composition and pore characteristics, which makes identifying the 'sweet spot'a challenging task. To address this issue, 10 samples from four typical shale gas wells in the LTF in the southern Sichuan Basin were selected and analyzed for total organic carbon (TOC) content, whole-rock composition using X-ray diffraction (XRD), low-pressure gas adsorption, and high-pressure mercury intrusion. The lithofacies distribution and pore structure of the MCTS were studied to determine the pore structural characteristics and the primary factors influencing pore formation in different types of shale lithofacies in the LTF. The lithofacies of the LTF shale in the study area can be classified into three categories: siliceous clay shale, clay shale and mixed shale. Mineral content has a significant impact on the pore characteristics, while TOC content has a minor effect on the pore volume and specific surface area of micropores and mesopores. It can be inferred that the mesopores in the MCTS are mainly related to clay mineral pores, and mineral dissolution and TOC content are not the primary factors contributing to pore formation.

Pore Characteristics of the Fine-Grained Tight Reservoirs in the Yabulai Basin, Northwestern China

This work investigated the pore structure characteristics and reservoir features of the finegrained tight reservoirs in the lower member of the Xinhe Formation(J2x1) in the Xiaohu subsag,Yabulai Basin based on core samples through various techniques. Interbedded silt/fine sandstones and mudstones are developed in the study area. Scanning electron microscopy(SEM) images were used to delineate different types of pores, including primary intergranular pores, secondary intergranular and intragranular pores, organic pores and fractures. The pore types were distinguished by pore size, pore area, location and formation process. The pore radii of the fine-grained rocks range from 1 nm to 1.55μm, mainly concentrated between 5 and 300 nm by low pressure N2adsorption and MICP analyses. The pore structure parameters of pore throat size and pore throat sorting coefficient are both positively correlated with porosity, while pore throat sorting coefficient has a negative correlation with permeability. The pore structures of the studied samples are much related to the mineral type and content and grain size, followed by TOC content. In these rocks with relatively low TOC and low maturity, the rigid minerals protect pores with pressure shadow from collapse, and dissolution-related pores contribute a lot to inorganic porosity. In contrast, these rocks with abundant TOC contain a large number of organic pores. The permeability of the fine-grained tight reservoir is mainly dominated by larger pore throats, while a large number of small pores(mostly <0.1 μm) contribute considerably to porosity. These results have deepened our understanding of the interbedded fine-grained tight reservoirs and can be applicable to fine-grained reservoirs in a similar setting.

Pore Characteristics and Factors Controlling Lacustrine Shales from the Upper Cretaceous Qingshankou Formation of the Songliao Basin,Northeast China:A Study Combining SEM,Low-temperature Gas Adsorption and MICP Experiments

To investigate pore characteristics and the factors controlling lacustrine shales,geochemical,mineralogical and petrophysical experiments were performed on 23 shale samples from the Qingshankou Formation of the Songliao Basin,China.A comparison of mercury injection capillary pressure(MICP)and low-temperature N2 adsorption pore-size distribution showed that MICP has a higher pore-size distribution(PSD)line in its overlapping pore diameter range,which may be elevated by the higher pressure of MICP.Therefore,in the overlapping range,low-temperature N2 adsorption data were preferred in pore characterization.Negative correlations were observed between pore volumes and TOC content,indicating organic matter pores are not well-developed in the studied samples.This may be related to their low grade of maturity and type I kerogens.There existed negative relationships between pore volumes and S1,which illustrated that liquid hydrocarbons occupied some pore space.Micropore volume had a better correlation with S1 than mesopore and macropore volumes,which suggests that liquid hydrocarbons preferentially occur in micropores.No obvious relationships between pore volumes and quartz or feldspar were observed,while pore volumes increased with the increasing clay mineral content.These relationships indicate that intraparticle pores in clay minerals represent the principal pore type.

Nanoscale Pore Characteristics of the Upper Permian Mudrocks from a Transitional Environment in and around Eastern Sichuan Basin, China

Nanoscale pore characteristics of the Upper Permian Longtan transitional mudrocks and their equivalent strata Wujiaping Formation marine mudrocks in and around the eastern Sichuan Basin was investigated using field emission scanning electron microscopy(FE-SEM)and low-pressure N2 adsorption experiments.The results indicate that the Upper Permian mudrock is at a mature stage with total organic carbon(TOC)values ranging between 0.47%and 12.3%.The Longtan mudrocks mainly contain vitrinite,and their mineral composition is primarily clay.In contrast,the Wujiaping mudrocks are dominated by sapropelinite and solid bitumen,and their mineral compositions are mainly quartz and a notably high amount of pyrite.The FE-SEM reveals that clay mineral pores and microcracks are the common pore types in the Longtan mudrocks.The specific surface area and pore volume depend on the clay content but are negatively correlated with the TOC.The generation of nanometer pores in the Longtan mudrocks is caused by high clay mineral contents.Meanwhile,the Wujiaping mudrock mainly contains OM pores,and the pore parameters are positively correlated with the TOC.The OM pore development exhibits remarkable differences in the Longtan and Wujiaping mudrocks,which might be related to their sedimentary facies and maceral fractions.Vitrinite and inertinite appear as discrete particles in these mudrocks and cannot generate pores during thermal maturation.Sapropelinite often contains many secondary pores,and solid bitumen with large particles,usually with several pores,is not the major contributor to the pore system of the investigated mudrock.

Organic matter pore characteristics of over-mature marine black shale: a comparison of organic fractions with different densities

Organic matter pores are considered to be the most important type of pore for preserving hydrocarbon gases in shale gas reservoirs.The organic matter in each over-mature marine shale sample was separated into two organic fractions with densities of greater than and less than 1.25 g/cm^(3),and then their molecular compositions and pore characteristics were quantitatively evaluated using solid state 13C-nuclear magnetic resonance(NMR)and gas(N2 and CO_(2))adsorption analyses,respectively.The results revealed that aromatic carbon is the dominant molecular composition of the over-mature organic matter in the Lower Cambrian Niutitang shale.During the over-mature stage,the organic fractions with densities of greater than and less than 1.25 g/cm^(3) have no significant differences in molecular composition.The organic fractions with densities of greater than and less than 1.25 g/cm^(3) do have significant differences in their organic pore characteristics.In contrast to the high density organic fraction,the low density fraction contained abundant micropores and lacked mesopores and macropores.The organic pore structures of the different occurrence states of organic matter were significantly different.The C/O of organic matter in different occurrence states are obviously different,which proves that the organic pore structure is closely related to both the occurrence state and density of the organic matter.However,these relationships are still unclear and require further study.

NMR-based analysis of the effect of moisture migration on sandstone pore structure under alternating wetting and drying conditions

The wetting-drying(W-D)cycle is a type of water–rock interaction.The pore structure of rock,such as shape,size,distribution and pore throat,affects fluid storage and transport.Fractal theory and experimental research on the evolution characteristics of pore damage during the wet-dry erosion process are highly important for determining W-D damage.The mass and velocity of liquid migration are related to the pore size,porosity,fluid properties,etc.Experimental data show that the water absorption quality and velocity in rocks decrease with the number of wet-dry cycles.At the same test time,the mass and velocity of the SI water absorption method are smaller than those of the FI method.Under these two conditions,the amount and rate of water absorption represent the degree of water–rock interaction.Considering the pore evolution during the wet-dry cycling,an equation describing the motion of liquid in porous media was derived based on the imbibition-type separation model.The experimental data are in excellent agreement with the calculated values of the model.Permeability characteristics can affect the area and degree of rock deterioration as well as the development rate of pores and microcracks.Based on the interaction between permeability and pores,quantitative analysis of the weakening process(local damage)of rocks under W-D cycles can provide good reference indicators for evaluating the stability of geotechnical engineering.

Pore Characteristic Design Method of High-strength Pervious Concrete Based on the Mechanical Properties and Rainstorm Waterlogging Resistance

High-strength pervious concrete(HSPC) with porosity ranging from 0.08% to 2.011% was prepared. The mechanical properties and rainstorm waterlogging resistance of HSPC were evaluated,and a design method of HSPC pore characteristics(porosity and pore diameter) based on the mechanical properties and rainstorm waterlogging resistance was proposed. The results showed that the reduction of effective cross-sectional area caused by artificial channels was the main factor affecting flexural strength but had limited influence on compressive strength. Compared with the concrete matrix without artificial channels,the compressive strength of HSPC with porosity of 2.011% decreased by 7.4%, while the flexural strength decreased by 48.3%. The permeability coefficient of HSPC can reach 16.35 mm/s even at low porosity(2.011%).HSPC can meet the requirements of no rainstorm waterlogging, even if exposed to 100-year rainstorms. When the mechanical properties and rainstorm waterlogging resistance are compromised, the recommended porosity ranges from 1.1% to 3.5%, and the recommended pore diameter ranges from 0.8 to 2.7 mm.

Characteristics of microscopic pore heterogeneity and development model of Wufeng‒Longmaxi Shales in the Pengshui area of south-east Chongqing

Normal-pressure shale gas reservoirs are widely distributed in south-eastern Chongqing and show good potential for resource exploration.This paper reports the organic matter(OM),physical,and pore characteristics,mineral composition,and gas content of representative shale samples from the Upper Ordovician Wufeng Formation and Member 1 of the Lower Silurian Longmaxi Formation(Long 1 Member).Microscopic pores within different shale layers of the Long 1 Member were classified,quantitatively evaluated,and their development mechanisms were systematically studied.We found that OM characteristics,mineral composition,and pore type were the main factors affecting the enrichment and preservation of shale gas.The characteristics of the Long 1 Member are mainly controlled by changes in the sedimentary environment.There are evident differences in total organic carbon content and mineral composition vertically,leading to a variable distribution of pores across different layers.Organic matter abundance controls the degree of OM pore development,while clay minerals abundance control the development of clay mineral-related pores.Total organic carbon content generally controls the porosity of the Long 1 Member,but clay minerals also play a role in OM-poor layers.Pore connectivity and permeability are influenced by the development of pores associated with brittle minerals.We propose a microscopic pore development model for the different layers.Combining geochemical data and this pore development model,layers 1‒4 are considered to be excellent shale gas preservation and enrichment reservoirs.Poor preservation conditions in layers 5‒7 result in high levels of shale gas escape.Layers 8‒9 possess a better sealing condition compared with layers 5‒7 and are conducive to the enrichment and preservation of shale gas,and can thus be used as future potential target strata.This research provides a theoretical basis for exploring and evaluating shale gas potential in the studied region or other complex normal-pressure shale blocks.

Pore structure characterization and seepage analysis of ionic rare earth orebodies based on computed tomography images

Pore network structure of ore body is a diffusion channel of leaching agent solution that exerts a significant influence on seepage.The ore body structure,pore distribution,pore and throat size,and pore network characteristics of topsoil,weathered,and semiweathered layers of ionic rare earth ore in southern Jiangxi Province were explored in this study.The effect of leaching operation on the pore structure was investigated,and main factors affecting the seepage were analyzed.Results showed that the semiweathered layer presents a dense structure and a small number of unconnected pores.Pores of topsoil and weathered layers are mainly long and narrow column openings with some planar fractures.Even pore distribution and large size span were observed.Compared with the weathered layer,the topsoil layer demonstrates larger voids,smaller average pore volume and equivalent radius,and fewer coordination throats;however,the average equivalent radius of the throat in the topsoil layer is larger and largescale channels exist through ore body vertically.Hence,permeability of the topsoil layer is significantly higher than that of the weathered layer.Colloidal clay minerals migrate easily and the occurrence of silting in the small porosity blocks the throat and significantly decreases the permeability of the ore body in the leaching process.The equivalent radius of the throat is the key to the seepage.Reducing the migration of fine particles is an effective measure to protect the throat and shorten the leaching period.

Pore size distribution,their geometry and connectivity in deeply buried Paleogene Es1 sandstone reservoir,Nanpu Sag,East China

The study or pore characteristics is or great importance in reservoir evaluation,especially in deeply buried s andstone.It controls the storage mechanism and reservoir fluid properties of the permeable horizons.The first member of Eocene Shahejie Formation(Esl)sandstone is classified as feldspathic litharenite and lithic arkose.The present research investigates the pore characteristics and reservoir features of the deeply buried sandstone reservoir of Esl member of Shahejie Formation.The techniques including thin-section petrography,mercury injection capillary pressure(MICP),scanning electron microscopy and laser scanning confocal microscope images were used to demarcate the pores including primary intergranular pores and secondary intergranular,intragranular,dissolution and fracture pores.Mercury injection test and routine core analysis were led to demarcate the pore network characteristics of the studied reservoir.Pore size and pore throat size distribution are acquired from mercury injection test.Porosity values range from 0.5%to 30%,and permeability ranges 0.006-7000 mD.Pore radii of coarse-grained sandstone and fine-grained sandstone range from 0.2 to>4μm and 1 nm to 1.60μm,respectively,by MICP analysis.The mineral composition also plays an important role in protecting the pores with pressure from failure.Fractured sandstone and coarse-grained sandstone consist of large and interconnected pores that enhance the reservoir porosity and permeability,whereas fine-grained sandstone and siltstone consist of numerous pores but not well interconnected,and so they consist of high porosity with low permeability.

Study on Reservoir Geological Characteristics and Potential Damage Mechanism of FIOC Oilfield in Sargiz

With the in-depth development of the Sargiz oilfield in Kazakhstan, oil layer protection plays an extremely important role in the development process. The petrological characteristics and pore types of the reservoir were analyzed by X-ray diffraction and electron microscopy. The average face ratio of the reservoir was 19.30%. The main pore type was intergranular pore and the face rate was 17.52%. The total amount of clay minerals in the reservoir core is 7% - 10%, and the clay minerals are mainly illite, Yimeng, kaolinite and chlorite;the shale content of the main oil-bearing layer is about 3% - 10%. Refer to relevant industry standards for speed, water, stress, acid, and alkali sensitivity experiments to study the potential damage mechanism of the reservoir. According to the above experiments, the oilfield reservoirs have no speed-sensitive damage and are weakly water-sensitive reservoirs;the reservoirs are highly stress-sensitive and easy to produce sand when the stress changes;they have moderately weak acid sensitivity and weak-medium weak alkaline.

Analysis of microscopic pore structures of rocks before and after water absorption

Hydrophilic characteristics of rocks are affected by their microscopic pore structures,which clearly change after water absorption.Water absorption tests and scanning electron microscopic（SEM） experiments on rock samples,located at a site in Tibet,China,were carried out Changes of rock pore structures before and after water absorption were studied with the distribution of pore sizes and fractal characteristics of pores.The results show that surface porosities,fractal dimensions of pores and the complexity of pore structures increased because the number of new small pores produced increased or the original macropore flow channels were expanded after rocks absorbed water.There were points of inflection on their water absorption curves.After water absorption of other rocks,surface porosities and fractal dimensions of pores and complexity of pore structures decreased as the original pore flow channels became filled.Water absorption curves did not change.Surface porosity and the pore fractal dimensions of rocks have good linear relationships before and after water absorption.

Reservoir characteristics of Donghe well No.1 in Tarim Basin

Based on the techniques of X-ray diffraction analysis, identification of the thin sections of core cast, phys- ical analysis and scanning electron microscopy analysis, this paper studied the reservoir characteristics of the Carboniferous strata in Donghe well No.1 of Tarim region. The results show that the reservoir lithology is mainly the fine-grained quartz sandstone with ferrocalcite and pyrite, mud cement-based, the permeability concentrated in 5-40 × 10-3 μm2, a small part of the high permeability up to 150-327 ×10-3 μm2 and porosity ranged from 10% to 20%. The most part of the reservoirs is low perme- ability with a small part of the layer in moderate-high permeability. The types of reservoir space include intergranular pores, intra particle-molding pores, micro-pores and cracks, which mainly are intergranular pores with the pore diameter of 15-200 μm, 95.5μm on average. And the types of the throats are comolex with the main tvne of constricted l：hroats in this area and large contribution to the permeability.

Quantifying the Mechanical Properties of White Sandstone Based on Computer Fractal Theory

The work presented in this paper was conducted to quantify the relationship between the pore characteristics and mechanical properties of white sandstone.The study include tests carried out under the coupling effects of chemical corrosion,temperature,nuclear magnetic resonance,and mechanical tests.Computer fractal theory was employed to describe and quantify the characteristics of the growth of pores in white sandstone under the same coupling effect.A custom developed program code,in the MATLAB software platform,was used for calculating the growths of the pores in white sandstone when subjected to coupling effects.The correlation between the computer fractal dimension of the growth of the pores in rock and characteristics of mechanical damage was accordingly analyzed.The results showed that when the temperature was set at a level lower than 100°C,it caused damage to the rock and strength reduction,primarily due to the rates of chemical reactions,the generation,and evolution of pores in the rock mass under the coupling effects of chemical corrosion and temperature.Overall,it was observed that the higher the value of the computer fractal dimension,the higher the growth of the pores,and the lower the uniaxial compressive strength of the white sandstone.

Evaluation and Analysis of the Effect of Lignin Amelioration on Loess Collapsibility

The road subgrade and road surface in collapsible loess area are prone to many engineering diseases such as uneven subgrade settlement,insufficient bearing capacity of soaked foundation,collapse and instability of sub-grade side slope due to the special properties of loess.As an environment-friendly,low-cost soil modifier with good adhesion and chelation properties,lignin has been considered to be used in highway subgrade construction.In order to explore the effect of lignin on loess,the compressive and collapsible properties of modified loess with different lignin contents were analyzed based on consolidation compression test.The improvement mechanism of lignin on loess collapsibility was studied by means of infiltration test and SEM test.The results show that lignin fibers can promote the agglomeration of loose particles and form a network structure in the soil particle pores,enhance the cementation strength between particles and soil skeleton,and reduce the permeability of loess.With the increase of lignin fiber content,the improvement degree of loess collaps ility shows a trend of first increasing and then decreasing.When the lignin fiber content is 2%,the effect is the best,and the improved loess ollapsi-bility is eliminated.

Research on infiltration clogging effect and its application prospect in anti-seepage project

Clogging effect,as a new concept in geological engineering,is a phenomenon of permeability decreasing under seeping in reservoir dam foundation of the alluvial and diluvial deposits with deep and thick layer,coarse particle and high permeability in mountains-gully rivers of Tibetan Plateau.A clogging infiltration instrument has been designed successfully and a series of simulation tests have been done.Based on large amounts of data,it is confirmed that the existence of the clogging effect and the law of infiltration clogging is found out.Three indexes are proposed such as "optimal size of particle","optimal size range of particle" and "characteristic pore",which are closely related with effect of infiltration clogging.The concept and results can offer a new idea to solve problems on anti-seepage of dam foundation in mountains-gully rivers environment and to study artificial clogging,meanwhile supplement of the concept of seepage deformation.

Biomimetic construction of oriented lamellar Col/nHAP composite scaffolds and mediation of macrophages to promote angiogenesis and bone regeneration

Pore characteristics have been identified as key design parameters for osteoimmunomodulation.The strategy reported here is to create an appropriate immune microenvironment by regulating pore characteristics of scaffolds,thereby promoting early angiogenesis and enhancing osteogenesis.A series of collagen/nanohydroxyapatite(Col/nHAP)composite scaffolds with ordered lamellar structures and different layer spacings were prepared by mimicking the ordered lamellar topology of the bone matrix.Our research indicated that the layer spacing and ordered topology of the scaffold exerted an important influence on phenotype transformation of macrophages and the secretion of angiogenic factors.The Col/nHAP-O(135)with large layer spacing not only supported cell attachment and diffusion in vitro,but also promoted early angiogenesis by timely switching from M1 to M2 macrophage phenotype.In vivo data showed that the layer spacing and the ordered structure of the scaffold synergistically regulated the inflammatory response and triggered macrophages to secrete more angiogenesis related cytokines.Col/nHAP-O(135)considerably promoted the neovascularization and new bone formation in the defect site,indicating that Col/nHAPO(135)could significantly enhance the osteogenic activity of stem cells with the involvement of macrophages.

Improvements on physical conditions of bauxite residue following application of organic materials

Soil formation and ecological rehabilitation is the most promising strategy to eliminate environmental risks of bauxite residue disposal areas. Its poor physical structure is nevertheless a major limitation to plant growth. Organic materials were demonstrated as effective ameliorants to improve the physical conditions of bauxite residue. In this study, three different organic materials including straw(5% W/W), humic acid(5% W/W), and humic acidacrylamide polymer(0.2% and 0.4%, W/W) were selected to evaluate their effects on physical conditions of bauxite residue pretreated by phosphogypsum following a 120-day incubation experiment. The proportion of 2-1 mm macro-aggregates, mean weight diameter(MWD) and geometric mean diameter(GWD) increased following organic materials addition, which indicated that organic materials could enhance aggregate stability. Compared with straw, and humic acid, humic acid-acrylamide polymer application had improved effects on the formation of water-stable aggregates in the residues. Furthermore, organic materials increased the total porosity, total pore volume and average pore diameter, and reduced the micropore content according to nitrogen gas adsorption(NA) and mercury intrusion porosimetry(MIP)analysis, whilst enhancing water retention of the residues based on water characteristic curves. Compared with traditional organic wastes, humic acid-acrylamide polymer could be regarded as a candidate according to the comprehensive consideration of the additive amount and the effects on physical conditions of bauxite residue. These findings could provide a novel application to both Ca-contained acid solid waste and high-molecular polymers on ecological rehabilitation at disposal areas.