Sandstone Content Research Articles

Short-stasis signatures in Cambrian and Ordovician shallow-marine sandstones: Implications for the ichnological record and time preserved at outcrop

Shallow-marine sandstones are an archetypal facies in the stratigraphic record of the Cambrian Explosion and the Ordovician Radiation but have been considered uninformative due to erosional signatures, time-incompleteness, and unfossiliferous outcrops. New analyses of the Carnedd-y-Filliast Grits (Furongian, Wales) and littoral sandstone successions from Laurentia and Baltica reveal that bedding planes in such outcrops commonly register sedimentary stasis. Most stasis intervals were brief, reflecting 1) a high sedimentation frequency; 2) post-depositional substrate resculpting by wave action during ‘active-layer stasis’, inhibiting infaunal colonization and rendering the surface representative of only the interval immediately preceding burial; and 3) the low preservation-potential of longer-stasis surfaces, which mainly occur within heterolithic packages that, in low-subsidence settings, are commonly eroded and replaced by amalgamation surfaces between sandstones. The short-stasis signature of littoral sandstones renders meter-scale architectural elements relatively time-complete but biases their fossil record at outcrop. Short-stasis surfaces are high-resolution snapshots but form incomplete representations of ancient ecosystems compared to surfaces that capture longer intervals. As such, the predominance of short-stasis surfaces contributed to the low ichnodiversity and sparse fossil content of littoral sandstones, implying that early Palaeozoic littoral ecosystems were more biodiverse than their known record suggests.

Controls of low injectivity caused by interaction of reservoir and clogging processes in a sedimentary geothermal aquifer (Mezőberény, Hungary)

Low injectivity is often experienced in geothermal doublets installed in sandstone reservoirs. This even led to a shutdown of the Mezőberény (Hungary) geothermal site. An on-site campaign was carried out in January 2021 to prepare a stimulation aiming to enhance the transmissivity of the sedimentary reservoir and the near-wellbore zone of this site. Previous studies have concluded that insufficient injectivity may be linked to a high skin effect in the near well-bore zone and pore clogging in combination with the low net sandstone content of the fluvio-deltaic reservoir. A chemical soft stimulation based on the injection of hydrochloric acid (HCl) was successfully used to unclog and recover the well injectivity. Despite such empirical evidence, the geochemical mechanisms leading to both, detrimental formation of clogging and the HCl-driven transmissivity restoration, have not yet been elucidated. This work presents the results of a novel analysis aiming at (a) predicting the dominant type of clogging forming in the near-well bore zone; (b) quantifying the drop in hydraulic conductivity as clogging occurs; and (c) supporting the optimization of the HCl dosage during the chemical soft stimulation. The study is supported by new experimental datasets never presented before from the Mezőberény site and a geochemical model set-up simulating the main mechanisms involved in the clogging and unclogging processes. It is concluded that the biofilm formation was the dominant, while the precipitation of calcite and amorphous ferrihydrite—later reduced to magnetite by microbes—was the secondary clogging mechanism: In the long-term (yearly scale) simulating the hydraulic conductivity showed a decline with forming scales; therefore, biofilm was presumably responsible for the experienced rapid (1 month) clogging. When modelling the chemical stimulation, the estimated amount of precipitated minerals was dissolved already with 2.5 mol of HCl per liter of water (~ 10 m/m%). Therefore, the 20 m/m% of HCl chosen during the field campaign might had a beneficial effect dissolving the potentially higher amount of scaling and/or the carbonate minerals of the matrix near the wellbore. Overall, it is concluded that the chemical and the microbial analyses together with the geochemical model were critical to tailor the remediation attempts and to propose further development or reconstruction of the surface system before going into operation to prevent recurrent impairments. Our findings highlight the importance of interactions of various clogging mechanisms with each other as well as with the reservoir processes and provide approaches to tackle the issue of injectivity drop by characterizing and quantifying their effects.

Structural and Reservoir Characteristics of Potential Carbon Dioxide Storage Sites in the Northern South Yellow Sea Basin, Offshore Eastern China

The geological storage of carbon dioxide (CO2) in offshore saline aquifers stands as a primary option for reducing CO2 emissions in coastal regions. China’s coastal regions, particularly Shandong and Jiangsu provinces, face significant challenges in CO2 reduction. Therefore, evaluating the feasibility of CO2 geological storage in the adjacent seas is critical. To assess the suitability of a CO2 storage site, understanding its structural and reservoir characteristics is essential to mitigate injection and storage risks. In this study, we analyzed the structural characteristics and potential traps of the Yantai Depression in the South Yellow Sea Basin based on seismic data interpretation. We further conducted well logging analysis and post-stack seismic inversion to obtain lithological data, including acoustic impedance and sandstone content percentages from the Cenozoic Funing Formation, Dainan–Sanduo Formation, and Yancheng Formation. Our findings highlight that the Yantai Depression in the South Yellow Sea Basin exhibits diverse structural traps and favorable reservoir–caprock combinations, suggesting promising geological conditions for CO2 storage. This area emerges as a suitable candidate for implementing CO2 geological storage initiatives.

Evolving fill‐and‐spill patterns across linked early post‐rift depocentres control lobe characteristics: Los Molles Formation, Argentina

ABSTRACTInherited rift topography controls the sediment routing, timing of sand supply, and sedimentary linkage of early post‐rift depocentres. Exhumed examples of early post‐rift turbidite systems are rare and previous studies have examined the evolution of individual depocentres; in contrast, the detailed evolution of early post‐rift turbidite systems across multiple depocentres has never been documented. Current fill‐and‐spill models do not detail the stratigraphic architecture and evolution of sedimentological characteristics of multiple intraslope fans developed across topography, including bed type distributions. Here, the evolution of three intraslope fans that developed across two early post‐rift depocentres is documented along an 18 km long transect in the southern Neuquén Basin, Argentina. The relative chronology of sand supply in depocentres is constrained with new U–Pb ages, and sediment source areas with provenance analysis. The early post‐rift intraslope fans record progradation of the system and progressive sedimentary linkage of post‐rift depocentres, transverse to local syn‐rift structures, with sediment routing subparallel to the cratonic basin margin. The large‐scale stratigraphic architecture of intraslope fans indicates an evolution as a fill‐and‐spill system, with initial confinement through flow stripping and overspill to spillover with erosion and bypass across a transverse topographic high separating the depocentres. Changes in early post‐rift intraslope fan characteristics, including thickness, sandstone content, lobe complex stacking patterns, stratal termination patterns and bed type distribution, record changing confinement through time within a depocentre, and spatially across depocentres. The strong spatial and vertical stratigraphic variability of transitional flow deposits and hybrid event beds reflects enhanced erosion, sediment bypass and flow transformation across transverse relief between the two depocentres during the spillover phase. These findings advance current understanding of early post‐rift turbidite systems and refine fill‐and‐spill models, which will help the prediction of spatial and vertical changes in rock quality and connectivity in subsurface hydrocarbon reservoirs and CO2 storage sites.

Characterizing coal gas reservoirs: A multiparametric evaluation based on geological and geophysical methods

The gas content of coal seams is a key parameter to guide the development of coalbed methane (CBM). While most studies focused on geological features, geophysical methods provide a powerful tool for the analysis of the differential distribution of CBM. In this paper, we present a comprehensive model for the quantitative evaluation of gas content in coal seams based on the computation of multiple parameters including lithology coefficient, deformation coefficient, and ash content. Based on the results of industrial analysis and isothermal adsorption tests of 135 coal samples, logging data of 76 CBM wells, as well as 10 2D seismic lines, a geophysical evaluation method of lithology inversion, structural curvature calculation, and ash content identification was established. Our study reveals the differential distribution characteristics of gas content in coal seams under the coupling effect of the three parameters. The results from this method were applied in the southeastern margin area of the Ordos Basin where 5# coal seam with sandstone and mudstone is interbedded as the roof and floor, and the mudstone in the roof contributes more to the sealing ability of surrounding rock. For the 8# coal seam with stabilized limestone and thinly interbedded mudstones as the roof, the limestone contributes most to the sealing ability. The sealing ability of surrounding rock is poorer in the area with large sandstone content in the roof and floor of coal seams and large structural curvature. The lithological combination of the 5# coal seam is the most critical gas controlling factor, whereas deformation coefficient is found to be least significant. However, for the 8# coal seam with little change in the lithology of the roof, the effect of deformation coefficient on gas content increases, and the adsorption capacity is the most important factor influencing the differential distribution of CBM.

Gas prediction in tight sandstones based on the rock-physics-derived seismic amplitude variation versus offset method

Estimating gas enrichments is a key objective in exploring sweet spots within tight sandstone gas reservoirs. However, the low sensitivity of elastic parameters to gas saturations in such formations makes it a significant challenge to reliably estimate gas enrichments using seismic methods. Through rock physical modeling and reservoir parameter analyses conducted in this study, a more suitable indicator for estimating gas enrichment, termed the gas content indicator, has been proposed. This indicator is formulated based on effective fluid bulk modulus and shear modulus and demonstrates a clear positive correlation with gas content in tight sandstones. Moreover, a new seismic amplitude variation versus offset (AVO) equation is derived to directly extract reservoir properties, such as the gas content indicator and porosity, from prestack seismic data. The accuracy of this proposed AVO equation is validated through comparison with the exact solutions provided by the Zoeppritz equation. To ensure reliable estimations of reservoir properties from partial angle-stacked seismic data, the proposed AVO equation is reformulated within the elastic impedance inversion framework. The estimated gas content indicator and porosity exhibit favorable agreement with logging data, suggesting that the obtained results are suitable for reliable predictions of tight sandstones with high gas enrichments. Furthermore, the proposed methods have the potential to stimulate the advancement of other suitable inversion techniques for directly estimating reservoir properties from seismic data across various petroleum resources.

Internal Force Mechanism of Pisha Sandstone as a Soil Amendment to Improve Sandy Soil Structural Stability in Mu Us Sandy Land

Compounding Pisha sandstone (PSS) with sandy soil in Mu Us Sandy Land is a viable agronomical measure to effectively reduce soil erosion and improve soil quality due to the complementary characters and structures of the two materials. Aggregate stability is an important indicator to assess sandy soil erosion resistance and quality, which could be largely affected by soil surface electrochemical properties and particle interaction forces. However, the effect of the compound ratio and particle interaction forces on the aggregate stability of compound soils with Pisha sandstone and sandy soil is still unclear. Therefore, in this study, the electrochemical properties, particle interaction forces, and their effects on the aggregate stability of PSS and sandy soil at five volume ratios (0:1, 1:5, 1:2, 1:1, and 1:0) were determined to clarify the internal force mechanism of PSS to increase sandy soil structural stability in a 10-year field experiment. Experiments were measured by a combined method for the determination of surface properties and aggregate water stability. A ten-year field study revealed that the incorporation of Pisha sandstone significantly enhanced the soil organic carbon (SOC) and cation exchange capacity (CEC) (p < 0.05), while the CEC value notably increased from 4.68 to 13.76 cmol·kg−1 (p < 0.05). The soil surface potential (absolute value) and the electric field intensity gradually decreased with the increase in the Pisha sandstone content. For the compound soil particle interaction force, the addition of Pisha sandstone enhanced the van der Waals attraction force, reduced the net repulsive force between compound soil particles, and promoted the agglomeration of aeolian sandy soil. The overall trend of the aggregate breaking strength of compound soils under different addition ratios of PSS was 1:0 > 1:1 > 0:1 > 1:5 > 1:2. When the Pisha sandstone content in the compound soils was <50%, the aggregate stability was mainly influenced by compound soil particle interaction forces, and the interaction force increase was the key reason for the aggregate breakdown. When the Pisha sandstone content in the compound soils was ≥50%, the aggregate stability was affected by the combined effects of the compound soil particle composition and particle interaction forces. These results indicate that PSS addition ratios and particle interaction force are important factors affecting the structural stability of compound soils, in which the volume ratio of PSS to sandy soil of 1:2 is the appropriate ratio. Our study provides some theoretical references for further understanding of the compound soil structure improvement and sandy soil erosion control in Mu Us Sandy Land.

Reservoir Quality Under the Control of Gravity Flows in the C7 Member of Yanchang Formation in the Jinghe Oilfield, Ordos Basin, China

The late Triassic sandstone reservoir in the C7 member of the Jinghe oilfield southern Ordos basin is a typical deep-water gravity flow tight oil reservoir. Sedimentary microfacies, physical properties, and petrographic analysis were being examined for quality determination. Pore structure and physical properties data together combined with, thin sections, and scanning electron microscope and core images were used to identify factors controlling reservoir physical properties. The depositional system under debates of different gravity flows including debris flow, seismite slumping, and turbidity flows. Among which sandy debris flow facies shows a better distribution of porosity and permeability followed by seismite-slump, where turbidity facies are the poorest. The petrophysical analysis shows that the study oil interval is a typical tight sandstone reservoir with an average porosity of 9% and permeability average being 0.025mD. The rock classification criteria of the C7 sandstone reveal the sub-categories of lithic feldspar sandstone and feldspar lithic sandstone. Average quartz sandstone contents of 48.25%, average feldspar sandstone content being 25%, and lithic fragments content of 29%. The formation lithology comprises mostly fine-grained sandstone and small pore size, which disclose that the porosity-permeability distribution increases proportional to the average and median pore throat radius, and decreases with average and median pressure. The microfacies distribution shows that the depositional facies controlled physical properties. The sandstone primary pores are affected by the mineral composition of quartz, feldspar, illite, smectite, kaolinite, calcite, and dolomite. Features such as dissolved pores and intergranular pore filling by feldspar, silky-like aggregates of illite-smectite intergranular pore filling and most diagenetic minerals influenced the sandstone pores beside the compaction.

Estimation of unfrozen water content of saturated sandstones using nuclear magnetic resonance, mercury intrusion porosimetry, and ultrasonic tests

The unfrozen water content (UWC) is a crucial parameter that affects the strength and thermal properties of rocks in relation to engineering construction and geological disasters in cold regions. In this study, three different methods were employed to test and estimate the UWC of saturated sandstones, including nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), and ultrasonic methods. The NMR method enabled the direct measurement of the UWC of sandstones using the free induction decay (FID). The MIP method was used to analyze the pore structures of sandstones, with the UWC subsequently calculated based on pore ice crystallization. Therefore, the MIP test constituted an indirect measurement method. Furthermore, a correlation was established between the P-wave velocity and the UWC of these sandstones based on the mixture theory, which could be employed to estimate the UWC as an empirical method. All methods demonstrated that the UWC initially exhibited a rapid decrease from 0 °C to −5 °C and then generally became constant beyond −20 °C. However, these test methods had different characteristics. The NMR method was used to directly and accurately calculate the UWC in the laboratory. However, the cost and complexity of NMR equipment have precluded its use in the field. The UWC can be effectively estimated by the MIP test, but the estimation accuracy is influenced by the ice crystallization process and the pore size distribution. The P-wave velocity has been demonstrated to be a straightforward and practical empirical parameter and was utilized to estimate the UWC based on the mixture theory. This method may be more suitable in the field. All methods confirmed the existence of a hysteresis phenomenon in the freezing-thawing process. The average hysteresis coefficient was approximately 0.538, thus validating the Gibbs–Thomson equation. This study not only presents alternative methodologies for estimating the UWC of saturated sandstones but also contribute to our understanding of the freezing-thawing process of pore water.

Influence of sedimentary architecture on static connectivity and geothermal doublet performance (Mezőberény, SE Hungary)

Although the Pannonian Basin in Hungary boasts significant geothermal potential, most geothermal wells in the region suffer from reinjection issues. The aim of this study is to examine the impact of the sedimentary architecture of a paralic lacustrine succession on the static connectivity of a geothermal aquifer. This problem was examined for a case-study geothermal doublet drilled in Mezőberény, southeast Hungary, which experienced injectivity problems shortly after commencing operations in 2012, ultimately leading to shut-in of the wells. A characterization of the architecture of the deltaic aquifer has been undertaken through a novel workflow that combines sedimentological and sequence stratigraphic analysis of the well-doublet and stochastic 3D modelling techniques to assess the likely static connectivity between the production and injection wells. Planform dimension of aquifer-forming mouth-bar elements and fluvial channel bodies were estimated from geological analogues, selected based on the thickness values of such sedimentary bodies interpreted on the gamma-ray logs of the well doublet and nearby hydrocarbon wells. In total five mouth-bar and two fluvial channel input geometry groups were selected, and fifty object-based realizations were constructed to analyse the static connectivity of different geological scenarios. The internal lithology of mouth-bar and fluvial-channel elements were modelled by sequential indicator simulations (ten realizations). Results of connected volume analysis indicate that the sandstone content of the aquifer is located within vertically segmented fluvial-channel and mouth-bar elements separated by mud-prone prodelta and lower delta-front deposits. This architectural configuration, in combination with low net-sandstone content suggests limited connectivity between the wells. Across the set of stochastic realizations, the volume of sandstone connecting the injection and production wells is ∼4% of the total aquifer volume, on average. Results of this study shows that simplified reservoir models can lead to over-estimation of connectivity of geothermal doublets. The proposed workflow combines sedimentological analysis and 3D modelling supported by geological analogues to predict sandstone reservoir connectivity of deltaic geothermal reservoirs. The described workflow can be carried out in target areas using existing boreholes to assist borehole planning.

Longshore changes in the microfacies and distribution of clastic barrier coastal sandbodies: a case from the Benxi formation in the Ordos Basin, China

AbstractThe Benxi Formation in the Ordos Basin is an important gas-producing layer in the Yanchang gas field. There are critical changes in the microfacies type and extension trend of sandbodies, which affects the understanding of reservoir formation and the deployment of development wells. Based on many core and thin section observations, as well as statistical analyzes of sandstone thickness and percentage of sandstone content from 1446 wells, we analyzed the coastal changes and control factors of the microfacies type, planar morphology and distribution of the Benxi Fm sandbodies in the field. The results indicate that the Benxi Fm of the Yanchang gas field is generally composed of terrigenous coastal clastic barrier deposits in a medium to small tidal range environment, but the wave action in the southern region is weak, forming typical barrier sandbars and backbarrier deposits. The wave actions in the north change more strongly, forming three major microfacies sandbodies: reworked barriers, shoals and incised valley filled tidal channels. The barrier sandbodies are arranged in a belt or bead-like pattern parallel to the shoreline and are distributed longshore near the provenance. The oval-shaped shoal sandbodies are dispersed further from the shoreline, and the filling of tidal channel sandbodies is controlled by ancient geomorphic grooves. This research has important guiding significance for the identification and evaluation of reservoirs in the Yanchang gas field and similar geological settings.

Performance of Ecological Pervious Concrete Prepared with Sandstone/Limestone-Mixed Aggregates

To understand the performance of ecological pervious concrete prepared with mixed sandstone/limestone aggregates, limestone and sandstone were used as two aggregates. The sandstone-to-limestone volume ratio was calculated in 0 : 1, 0.25 : 0.75, 0.5 : 0.5, 0.75 : 0.25, and 1 : 0 in coarse aggregate to prepare ecological pervious concrete specimens. The compressive test, water permeability test, cooling test, evaporation test, alkaline test, and scanning electron microscope (SEM) tests were carried out with qualified compressive strength as the indicator to determine the optimum sandstone-to-limestone volume ratio for the ecological pervious concrete. The results show that the water permeability, cooling property, and evaporation property of the ecological pervious concrete increase with the sandstone content. When the sandstone-to-limestone volume ratio is less than 0.32 : 0.68 (the substitution rate of sandstone for limestone in ecological pervious concrete is 32%), the strength of ecological pervious concrete meets the requirements of 5 MPa and achieves the best permeability coefficient of 9 mm/s. This realizes the full use of net water storage and cooling capacity of the ecological pervious concrete and makes the ecological pervious concrete meet the construction requirement of slope protection in sponge cities in the south.

Estimation of the unfrozen water content of saturated sandstones by ultrasonic velocity

The unfrozen water content (UWC) of rocks at low temperature is an important index for evaluating the stability of the rock engineering in cold regions and artificial freezing engineering. This study addresses a new method to estimate the UWC of saturated sandstones at low temperature by using the ultrasonic velocity. Ultrasonic velocity variations can be divided into the normal temperature stage (20 to 0 ℃), quick phase transition stage (0 to −5 ℃) and slow phase transition stage (−5 to −25 ℃). Most increment of ultrasonic velocity is completed in the quick phase transition stage and then turns to be almost a constant in the slow phase transition stage. In addition, the UWC is also measured by using nuclear magnetic resonance (NMR) technology. It is validated that the ultrasonic velocity and UWC have a similar change law against freezing and thawing temperatures. The WE (weighted equation) model is appropriate to estimate the UWC of saturated sandstones, in which the parameters have been accurately determined rather than by data fitting. In addition, a linear relationship between UWC and ultrasonic velocity is built based on pore ice crystallization theory. It is evidenced that this linear function can be adopted to estimate the UWC at any freezing temperature by using P-wave velocity, which is simple, practical, and accurate enough compared with the WE model.

Possible influence of CaO admixture in the Pre-Ural Foredeep terrigenous rocks on the determination of the source rocks composition based on geochemical data

Research subject. The article discusses the analysis results of correlations between the calcium oxide content and a number of other rock-forming oxides in the Asselian sandstones and in the Middle–Upper Permian clay rocks of the Pre-Ural trough with some of their inherent ratios of rare and trace elements (La/Sc, Th/Cr, Th/Co, Ce/Cr, etc.), which act as traditional indicators of source rocks composition. Methods. Our main method is to analyze the correlation coefficients values between different pairs of oxide-indicator ratios. During the discussion, we proceeded from the fact that a statistically significant (both positive and negative) correlation between calcium oxide, ignition loss, or magnesium oxide, on the one hand, and the values of indicator ratios of rare and trace elements, on the other hand, suggest the dependence of the noted ratios on the features of the aluminosilicate matrix replacement with carbonate minerals. Results. We have established, there is a statistically significant positive or negative correlation between the calcium oxide content in Permian terrigenous rocks (different sedimentary intervals of the Pre-Ural Foredeep) and some indicator ratios of rare and trace elements (Asselian sandstones – Th/Cr, Ce/Cr and Eu/Eu*, Urzhum–Viatsk clay rocks – La/Sc, Th/Co, (La/Yb) N , etc.). As a result, the values of these ratios depend to some extent on the carbonate minerals content (mainly calcite) in terrigenous rocks. These carbonate minerals corrode the aluminosilicate matrix and in one way or another change the primary contents and ratios of impurity elements. On the contrary, there is no significant correlation between the CaO content in the Asselian sandstones and the values of La/Sc, Th/Co, etc. There is no correlation between the CaO content and the Ce/Cr ratio in the Urzhum–Viatsk clay rocks. Conclusions. We suggest, the correlation (not statistically significant at 5% confidence level) between calcium oxide content (in sandstones and clay rocks) and some indicator ratios of rare and trace elements can be considered as an indication that such ratios can be used to reconstruct the source rocks composition.

Elastic and electrical properties of calcite-cemented artificial sandstones based on a new manufacturing method

Calcite cement is widely existing in sandstones and can significantly affect the elastic and electrical properties of sandstones. Accordingly, understanding the effects of calcite cement on the elastic and electrical rock properties is of key importance for the accurate characterization of sandstone reservoirs through seismic and electromagnetic surveys. To obtain such knowledge, we design and implement dedicated laboratory experiments to investigate the effects of calcite cement and porosity on the P- and S-wave velocities and electrical resistivity of synthetic calcite-cemented sandstones made using a new recipe. The experimental results show that elastic velocities and electrical resistivity generally decrease with increasing porosity when the content of the calcite cement keeps constant, whereas the elastic and electrical rock properties exhibit complex variation with cement content in sandstones with approximately the same porosity. Analyses and interpretation of the experimental data indicate that the elastic and electrical rock properties are affected jointly by porosity, the content and distribution of the calcite cement, as well as the microstructure of the pore space resulting from the different axial stress employed for the consolidation of the rock samples. The results have revealed the mechanisms of how porosity and calcite cement affect the elastic and electrical properties of calcite-cemented sandstones, and provided a theoretical basis for the accurate characterization of sandstone reservoirs through seismic and electromagnetic surveys.

Deep learning based on self-supervised pre-training: Application on sandstone content prediction

Deep learning has been widely used in various fields and showed promise in recent years. Therefore, deep learning is the future trend to realize seismic data’s intelligent and automatic interpretation. However, traditional deep learning only uses labeled data to train the model, and thus, does not utilize a large amount of unlabeled data. Self-supervised learning, widely used in Natural Language Processing (NLP) and computer vision, is an effective method of learning information from unlabeled data. Thus, a pretext task is designed with reference to Masked Autoencoders (MAE) to realize self-supervised pre-training of unlabeled seismic data. After pre-training, we fine-tune the model to the downstream task. Experiments show that the model can effectively extract information from unlabeled data through the pretext task, and the pre-trained model has better performance in downstream tasks.

Different Response of Soil Microbial Carbon Use Efficiency in Compound of Feldspathic Sandstone and Sand

The stoichiometry of efficient soil microbial carbon use is a sensitive index for measuring changes in soil quality and plays a crucial role in research on ecological stoichiometry in the soil nutrient cycle. To further understand the effect of feldspathic sandstone and sand compound ratios on microbial carbon use efficiency (CUE), we simulated the field conditions of the feldspathic sandstone-sand compound layer in the Mu Us sandy land and analyzed the soil C:N:P ratio, microbial biomass, extracellular enzyme activity, and microbial carbon use efficiency in soils with different compound ratios. The results demonstrated that an increase in the feldspathic sandstone content had insignificant effects on the soil C:N:P ratio. The maximum values for microbial biomass nitrogen (MBN) and microbial biomass phosphorus (MBP) were observed at compound ratios of 1:5 and 1:2, respectively. Calculations of microbial carbon use efficiency and vector analysis revealed that the microbial carbon use efficiency increased as the feldspathic sandstone content increased, P limitation existed in all compound soils, and soil with a 1:1 compound ratio may be substantially less limited. In conclusion, our research indicated that adding feldspathic sandstone to sand improved soil quality, and the compound ratio affected soil microorganisms; nevertheless, it did not significantly change soil nutrient restriction. Our study provides a theoretical basis for the development and utilization of desert land resources.

Shallow shear wave velocity structure of the Dongshan sag area using surface wave data in a deep reflection profile of the Yuanmou area of Yunnan province, China

Deep reflection seismic data contain abundant surface wave information for which the velocity structure in the near-surface shallow underground can be obtained using multichannel analysis of surface waves (MASW). This paper uses the MASW method to process deep reflection data in the Yuanmou area in Yunnan province, China. The MASW method uses the phase velocity spectral transformation of Rayleigh waves to obtain its dispersion curve. The initial model for different lithology classifications is established to invert the underground velocity structure. This study obtains a two-dimensional shear wave velocity structure profile to investigate the shear wave velocity structure. Generally, the study results have shown that the shear wave velocity structure obtained by the MASW method corresponds well with the surface conditions and accurately reflects faults' changes, folds, and lithology. Moreover, the formation sand content calculation shows a large difference in Dongshan sag's formation sand content. The sand contents of Cretaceous and Middle Jurassic strata are over 30% similar, and the sandstone content of underlying Early Jurassic strata is mostly 30% lower. The stratum buried depth of Early Jurassic strata is between 0– 800 m. The dip angle of LZJF at this location is 90°. The west side of the LZJF is based on Proterozoic uplift, and the Quaternary sedimentary thickness exceeds 300 m above the uplift stratum. Whereas on the east side of the LZJF, the stratum of the Dongshan sag section is mainly a synclinal structure.

Coalbed methane gas content and its geological controls: Research based on seismic-geological integrated method

Gas content is a crucial indicator in the process of coalbed methane (CBM) exploration and development. However, the strong heterogeneity of CBM reservoirs makes it difficult to predict gas content by conventional geological methods. In this paper, we proposed a seismic-geological integrated method that is based on main controlling factors to predict coalbed gas content. The first step is to construct parameters such as deformation residual, fault density, net-to-gross ratio, and coal thickness to quantitatively analyze the effect of geological factors on gas content. Results show that tectonic deformation, fault systems, burial depth, and the sandstone content of the sequence after coal accumulation are key factors controlling the gas content, whereas coal thickness is weakly correlated with the gas content. Then, the degree of tectonic deformation and displacement were quantitatively calculated on the basis of 3D seismic interpretation, and the spatial distribution of sedimentary bodies and coal thickness was acquired by seismic sedimentology and facies-controlled inversion. Finally, a weighted fusion method was proposed to construct a multivariate linear model to quantitatively predict the gas content. The relative error of gas content predicted by the integrated method is 10.2%–28.4%, indicating that this new method is applicable and feasible. In addition, according to the combination of gas controlling factors, the CBM enrichment scenarios in the study area were divided into three types, in which the deep-buried, local concave, muddy roof regions are most favorable for CBM accumulation (Type Ⅲ, located in the southeast and north parts of the study area). This study provides a new way for block-scale CBM enrichment prediction under complex geological conditions.

Gouge formation and dilation impacts to flow during fracture shearing

Flow in fractures is of critical importance to fluid flow in low-permeability shales, particularly when they restrict vertical migration from reservoirs. The Mt. Simon Sandstone is a target for geologic CO 2 sequestration and the overlying Eau Claire Formation is the sealing formation capping this reservoir. The lower Eau Claire, a primary barrier to upward migration of CO 2 from the Mt. Simon, is lithologically heterogenous with a mixture of sandstone and shale. We use a series of flow-through experiments on fractured samples from the Eau Claire to document the morphological changes taking place in the fracture and surrounding rock as it is sheared in a stepwise fashion. The samples were imaged using computed tomography after each shearing episode and flow resistance was calculated based on the pressure differential across each core. We found that gouge accumulations in the fracture plane led to specific instances of self-sealing behavior despite the fact that most samples increased in average fracture aperture and transmissivity . Gouge limited the increase or, in some cases, decreased flow through these samples. Fractures adjacent to shale-rich zones and concordant with bedding were more likely to show evidence of self-sealing, while increased sandstone content and fracture orientation perpendicular to bedding planes was more likely to result in fracture dilation and fracture permeability increases. Reactivation and shearing of vertical fractures in lithologically heterogenous caprocks is more likely to pose risks to long term CO 2 storage scenarios. • Computed Tomography illustrates fracture shearing in Eau Claire formation. • Fracture transmissivity and dilation can be limited by gouge during shearing. • Mixed lithologies and diagenetic cements increase likelihood of gouge creation. • Shale-adjacent fractures are more likely to show localized sealing. • Self-sealing behaviors are less likely in fractures perpendicular to bedding.