Sandstone Layers Research Articles

The First Dinosaur from the Kingdom of Cambodia: A Sauropod Fibula from the Lower Cretaceous of Koh Kong Province, South-Western Cambodia

The first discovery of a dinosaur bone from the Kingdom of Cambodia is reported in this paper. It consists of a sauropod fibula from a sandstone layer on Koh Paur island, in Koh Kong province, in south-western Cambodia. The dinosaur-bearing bed belongs to the non-marine Grès Supérieurs series and is apparently of Early Cretaceous age. On the basis of various characters, notably the development of the anteromedial crest, the dinosaur fibula from Koh Paur is referred to a euhelopodid titanosauriform. This first dinosaur discovery in Cambodia suggests that the thick non-marine formations which cover vast areas in the south-western part of the country are potentially an important source of continental Mesozoic vertebrates.

Lacustrine sedimentation by powerful storm waves in Gale crater and its implications for a warming episode on Mars

This investigation documents that the Rugged Terrain Unit, the Stimson formation, and the Greenheugh sandstone were deposited in a 1200 m-deep lake that formed after the emergence of Mt. Sharp in Gale crater, Mars, nearly 4 billion years ago. In fact, the Curiosity rover traversed on a surface that once was the bottom of this lake and systematically examined the strata that were deposited in its deepest waters on the crater floor to layers that formed along its shoreline on Mt. Sharp. This provided a rare opportunity to document the evolution of one aqueous episode from its inception to its desiccation and to determine the warming mechanism that caused it. Deep water lacustrine siltstones directly overlie conglomerates that were deposited by mega floods on the crater floor. This indicates that the inception phase of the lake was sudden and took place when flood waters poured into the crater. The lake expanded quickly and its shoreline moved up the slope of Mt. Sharp during the lake-level rise phase and deposited a layer of sandstone with large cross beds under the influence of powerful storm waves. The lake-level highstand phase was dominated by strong bottom currents that transported sediments downhill and deposited one of the most distinctive sedimentological features in Gale crater: a layer of sandstone with a 3 km-long field of meter-high subaqueous antidunes (the Washboard) on Mt. Sharp. Bottom current continued downhill and deposited sandstone and siltstone on the foothills of Mt. Sharp and on the crater floor, respectively. The lake-level fall phase caused major erosion of lacustrine strata that resulted in their patchy distribution on Mt. Sharp. Eroded sediments were then transported to deep waters by gravity flows and were re-deposited as conglomerate and sandstone in subaqueous channels and in debris flow fans. The desiccation phase took place in calm waters of the lake. The aqueous episode we investigated was vigorous but short-lived. Its characteristics as determined by our sedimentological study matches those predicted by an asteroid impact. This suggests that the heat generated by an impact transformed Mars into a warm, wet, and turbulent planet. It resulted in planet-wide torrential rain, giant floods on land, powerful storms in the atmosphere, and strong waves in lakes. The absence of age dates prevents the determination of how long the lake existed. Speculative rates of lake-level change suggest that the lake could have lasted for a period ranging from 16 to 240 Ky.

Characterization of tight sandstone and sedimentary facies using well logs and seismic inversion in lacustrine gravity-flow deposits

Lacustrine gravity-flow deposits are common in sedimentary basins, and sand bodies formed in the basin center mingled with organic rich mudstone may form excellent tight reservoirs of hydrocarbons. However, the complex architecture and intensive heterogeneities of lacustrine gravity-flow deposits commonly pose great risks for hydrocarbon exploration and development. To address this problem, a new workflow for predicting tight sandstone is proposed in this work. The workflow combines well log analysis, intelligent seismic inversion and 3D geological modelling to improve the prediction effectiveness of tight sandstone and sedimentary facies. The original 3D seismic data was firstly decomposed into three components with low, middle and high frequencies to improve the resolution of seismic inversion, and a nonlinear relationship between well logs and the decomposed 3D seismic data was then established by using an algorithm of support vector machine. A 3D lithofacies model was subsequently established integrating well logs and the seismic inversion result. The distribution of sand thickness was imaged relying on the lithofacies model. Correlations between the actual and predicted sand thickness based on the seismic attributes and the seismic inversion result was improved from 0.66 to 0.79. The prediction of sand bodies was further improved through the 3D lithofacies modelling, especially for these thin sandstone layers. Sedimentary facies of the Chang_7 member in the Qingcheng Oilfield, Ordos Basin, were characterized based on the distribution of sand bodies. Fan-shaped sand bodies are mapped in each zone of the Chang_7 member, revealing that the entire Chang_7 successions are of sub-lacustrine fan in origin. The Chang_7 member mainly contains six sedimentary architectural elements: main channel, branch channel, lobe, lobe edge, slump body and inter lobe/inter channel. The distribution of sedimentary facies is different in different zones, and appears to be largely related to the change of base-level. A horizontal well was designed according to the prediction of sand bodies, which show a higher probability of drilling into sandstone by approximately 10% compared with that of other horizontal wells.

Support Optimization of Open TBM Tunneling in Luohe Formation Sandstone by CT Test and Numerical Simulation

As underground engineering extends into the western and deeper regions of China, more and more Luohe Formation sandstone layers will be encountered, which have weak cementation and high water content. It is a significant challenge to apply the open TBM, and the support system is crucial in determining whether TBM can excavate quickly and safely. Therefore, in order to optimize the support scheme, this paper analyzes the pore structure and porosity through CT scanning, the results indicate that the volume percentage of pores ≥34 μm is 2.3% and 1.5%, respectively, the large pore apertures are predominant, the surrounding rock has strong permeability, and there is a high risk of rock burst and roof collapse accidents, hence requiring reinforced support measures. On this basis, numerical simulations were conducted to evaluate the support effectiveness. The results show that replacing the “bolt + mesh” with a “bolt + cable + mesh + steel belt”, and replacing the top three bolts with 7.3 m anchor cables, can better control the deformation and provide sufficient thrust force for the TBM, ensuring excavation speed. After the implementation of this scheme at the Kekegai coal mine in Shaanxi, China, the TBM excavation speed increased by 70%, from the previous 10 m/day to 17 m/d, significantly reducing the project duration and construction costs.

Study on mechanical characteristics and damage model of layered sandstone after high temperature action

Rock engineering, which includes slopes, tunnels, and mines, often encounters stratified rocks. These projects are also frequently exposed to special environments of high temperatures, such as deep underground or fire-related conditions. It is of significant importance to conduct research on the damage characteristics and constitutive models of stratified rocks under high-temperature conditions to accurately reflect the influences of rock structure characteristics, geological conditions, and load effects on the damage and deformation characteristics of rock engineering. Under five temperature conditions (20, 200, 400, 600, 800 ℃), the intact sandstone rock samples and the layered sandstone samples are subjected to high-temperature treatment, followed by triaxial compression tests. Based on existing research on statistical damage constitutive models for rocks, a high-temperature layered rock statistical damage constitutive model is established by introducing the Weibull distribution function and high-temperature, bedding, and load coupling damage variables, under the condition that the microelement strength follows the Drucker-Prager (D-P) criterion. The results indicate that the peak strength, damage threshold, elastic modulus, and longitudinal wave velocity show a "U"-shaped trend with an increasing bedding angle, with an opening upwards. As the temperature increases, the anisotropy of the rock initially increases and then decreases, with obvious ductile characteristics after the temperature reaches 600 ℃. The analysis of damage threshold, stress-strain curve, and macroscopic failure morphology shows that the 60° dipping angle sandstone is prone to undergo compressive-shear failure along the weak plane of bedding, exhibiting low toughness mechanical characteristics. Theoretical curves of the statistical damage constitutive model for high-temperature rock are in good agreement with the Triaxial shear test curve of sandstone, which indicates that the constitutive model can reflect the stress-strain process of layered sandstone after high-temperature action, and verifies the applicability of the model. This model does not include unconventional mechanical parameters and can reflect the ductility, brittleness, and strength characteristics with clear physical meanings. The findings of the study can offer theoretical support for computing and numerically modeling rock mechanics after high-temperature action.

Rock core VOC profiles diagnostic of aquitard occurrence and integrity in a multi-layered sedimentary rock aquifer flow system

Aquitard assessment poses a challenge for practitioners and researchers managing dense non-aqueous phase liquid (DNAPL) contaminants in sedimentary rock aquifer systems. Within these systems, DNAPL migration and bulk hydraulic properties are controlled by fracture networks which are difficult to characterize at relevant scales with conventional methods. A previous study at a DNAPL contaminated site used contrasts in high-resolution vertical gradients to delineate four aquitards and two surfaces with poor vertical connectivity within a thick (>200 m) sedimentary rock aquifer system primarily composed of layered sandstones. In this study, we corroborate that method by using the existing DNAPL contamination as a tracer to identify and characterize the aquitards in the sequence and assess aquitard integrity. Closely spaced samples of rock from four continuous cores were collected and analyzed for volatile organic compounds (VOCs). The cores were collected along a transect perpendicular to groundwater flow and 75 m downgradient of the DNAPL source zone. Dissolved phase contaminant concentrations were collected using high-resolution multilevel systems placed along the plume centerline, downgradient from the source. The rock core and groundwater VOC concentration profiles suggest a primary aquitard limits vertical migration of both DNAPL and the associated dissolved phase contaminants, despite relatively large, downward gradients across its lower boundary. A calibrated, three-dimensional numerical groundwater flow model indicates an anisotropy factor of 1,000 for this aquitard. The Kv values for all four aquitards are only slightly lower than the values for the aquifers. However, the aquitard Kv values are 1–3 orders of magnitude less than their Kh values, and the aquitard Kh values are often similar to or even greater than the Kh values for the aquifers. Therefore, large anisotropy, rather than exceptionally low Kv values, distinguish the aquitards from the aquifers in this system. Fracture network characterization of nearby outcrops showed the anisotropy of the aquitards can be attributed to laterally extensive, bedding parallel partings coupled with short, frequently terminating, and poorly connected vertical fractures. In addition, the rock VOC profiles combined with fracture network data show that fracture termination surfaces can be powerful inhibitors of downward DNAPL migration providing additional evidence for the importance of these features in sedimentary rock flow systems. Ultimately, this study reveals the important influence of anisotropic aquitards on DNAPL migration, accumulation, and persistence, as well as associated plume migration. Furthermore, it demonstrates that subtle contrasts critical to aquitard integrity may be easily missed with long screened wells and other conventional, low resolution site characterization methods.

Pore-Scale Characterization of CO2 Trapping and Oil Displacement in Three-Phase Flow in a Heterogeneous Layered Sandstone

Summary Permeability variation in the vertical direction, a typical sandstone reservoir heterogeneity, can trap a large amount of oil in the low-permeability layer. We performed water-alternating-gas (WAG) injection and CO2 foam flooding on a specially constructed millimeter-sized layered sandstone and investigated fluid distribution using high-resolution X-ray microtomography. Based on the segmented images, CO2 capillary-trapping capacity, oil recovery, Euler number, shaper factor, capillary pressure, and fluid flow conductivity were calculated. Our results show that increasing the number of WAG cycles favored CO2 capillary trapping, and oil recovery was enhanced by the WAG strategy. However, there was still a significant amount of oil trapped in the low-permeability layer. After the WAG injection, the connectivity of the residual oil clusters decreased, the capillary pressure of the oil clusters increased, and oil flow conductivity decreased. This was not conducive to further oil recovery. The subsequent injection of CO2 foam effectively recovered the oil in the low-permeability layer. During the no-injection period, we observed a crossflow phenomenon caused by gravity segregation (the high-permeability layer was located below the low-permeability layer), i.e., oil in the low-permeability layer decreased while oil in the high-permeability layer increased, which is beneficial for subsequent oil production. Furthermore, CO2 moved upward driven by gravity, and although capillary barriers could prevent CO2 from escaping, subsequent water injection was essential to improve the stability of CO2 capillary trapping. This work accurately quantifies the distribution of oil and gas in high- and low-permeability layers, thus providing fundamental data for oil recovery and CO2 trapping in reservoirs with vertical heterogeneity. Although the sample used in the experiment was not natural reservoir rock, our results imply that when the permeability ratio between the two layers is greater than 2, sufficient attention must be paid to the fluid distribution differences caused by this layered heterogeneity. Different displacement strategies, such as WAG and CO2 foam flooding, or gravity differences between oil and gas can be used to enhance oil recovery.

An attempt to use machine learning algorithms to predict strong tremors during longwall mining of a coal seam

Strong tremors during longwall mining are usually associated with the fracturing of thick sandstone layers. The prediction of such tremors is important and can be treated as a form of rockburst prevention. The article presents the possibility of predicting the occurrence of strong tremors based on the random forest algorithm in the 48-h forecast horizon. The study concerns a longwall panel in coal seam No. 506 in one of the hard coal mines in the Upper Silesian Coal Basin, Poland. The extraction of this longwall panel was carried out at a great depth, surrounded by thick layers of sandstone and with the occurrence of edges in the previously mined seams. Therefore, seismic activity was high and strong tremors occurred. Based on the seismic catalogue and data related to the longwall face advance, 12 parameters were selected that were most significantly positively or negatively correlated with the occurrence of strong tremors. Based on 10 randomly selected datasets, models of the random forest algorithm were trained and then tested. Due to the much smaller number of cases of strong tremors compared to days when there were no strong tremors, the set of training data was balanced using the ADASYN algorithm. The obtained models had an average recall value of 0.79, and average accuracy equalled 0.912. The trained models showed high efficiency in predicting minority cases of days with strong tremors for up to 48 h and a relatively low percentage of misclassifications.

Magnetic fabric and sedimentological constraints on the paleocurrent changes within the early devonian strata from the northwestern Tarim, China

The magnetic fabric technique is widely used to measure the direction of paleocurrent and paleostress due to its speediness, precision, and cheapness. However, correlating unique magnetic fabric patterns in weakly deformed rocks with hydrodynamic or tectonic regimes remains challenging. The Early Devonian sedimentary rocks in the Keziertage Formation have well-preserved sedimentary structures and were deformed by the Cenozoic non-plunging fold. This sequence offers a prime opportunity to explore the relationship between magnetic fabric evolution, paleocurrents, and weakly deformation. Furthermore, the paleocurrent characteristics of the Keziertage Formation reflect the provenance changes during the opening of the South Tianshan Ocean. Here, we report 120 sedimentary structure-based paleocurrents and 382 magnetic fabric data from the Keziertage Formation in the Kalpin area, Xinjiang. We find that: (1) During the weakly deformation stage, the minimum axis of susceptibility's imbrication direction serves as a reliable indicator for detecting paleocurrents at the coarse sandstone layer with well-developed cross-bedding; (2) While the maximum axis of susceptibility is more consistent with the tectonic stress rather than paleocurrents. Consequently, the complexity of magnetic fabric needs to be clearly verified when it is applied in the weakly deformed strata. In the northwest margin of Tarim, both the minimum susceptibility axes of magnetic fabrics and sedimentary structures indicate a shift in the paleocurrent direction, transitioning from southwest to northeast in the mid-to-upper Keziertage Formation. This indicates significant channel changes, potentially linked to a regional change in provenance due to the Early Devonian opening of the South Tianshan Ocean.

Petrophysical interpretation of logging-while-drilling borehole measurements in the presence of electrical anisotropy, mud-filtrate invasion, noise, and well deviation effects

Petrophysical interpretation of logging-while-drilling (LWD) borehole measurements in the presence of electrical anisotropy, mud-filtrate invasion, noise, and well deviation effects remains a challenge in formation evaluation. In high-angle and horizontal (HAHZ) wells penetrating electrically anisotropic sandstones, phase and attenuation apparent resistivity logs often exhibit values larger than resistivity parallel to bedding planes. Consequently, traditional interpretation methods often fail to accurately estimate hydrocarbon saturation when using only the long-spacing phase apparent resistivity log (P40H) in petrophysical calculations. We implement two approaches (analytical and Bayesian) to estimate horizontal and vertical resistivities from apparent resistivity measurements. The first analytical approach is based on the numerical simulation of LWD resistivity measurements using synthetic models under various conditions of electrical anisotropy and well inclination to derive analytical models. The relative error of analytical approximations is less than 6%. In the presence of measurement noise and shoulder-bed effects, we implement a Bayesian method for well-log inversion and uncertainty quantification. The relative error of Bayesian inversion is less than 2%. Estimates of horizontal and vertical resistivities then can be used for petrophysical analysis. A challenging set of synthetic and field examples of HAHZ wells penetrating electrically anisotropic formations is selected for examination and verification of the new methods. For radial lengths of invasion less than 20 cm (8 in), sensitivity analysis indicates that the effects of conductive mud-filtrate invasion on long-spacing resistivity logs are negligible. The long-spacing phase (P40H) and attenuation (A40H) apparent resistivities are used to estimate horizontal and vertical resistivities. In the field examples under study, electrical anisotropy is caused by intercalated laminations of coarse- and fine-grained sandstones; the volumetric concentration of shale is negligible. Considering that Archie’s parameters are direction dependent, sensitivity analysis indicates that the effective value of the saturation exponent parallel to bedding planes is less sensitive to the volumetric concentration of fine-grained sandstone layers compared with the saturation exponent perpendicular to bedding planes. Thus, water saturation of grain-laminated sandstones in HAHZ wells can be estimated using horizontal resistivity with Archie’s parameters that are consistent with petrophysical interpretations performed in vertical wells. Estimates of water saturation in the field examples using horizontal resistivity agree with saturation-height models. Compared with conventional interpretation methods that use P40H as the formation resistivity, the new approach improved the estimation of hydrocarbon saturation by 10%.

Utilizing shallow seismic reflection for mitigating seismic and geo-environmental hazards in the development project of Gabal Ataqa Area, Cairo–Suez District, Egypt

Nowadays, development projects are becoming so rapid in many developing countries worldwide. The study of interest focuses on Cairo–Suez District, which represents the most important location in Egypt for major infrastructure projects and urbanization expansion. Consequently, it is very important to reduce the hazards surrounding this area from natural disasters, so all information that supports geo-environmental hazards assessment is importantly needed. The Gabal Ataqa area has socioeconomic importance as it is considered the industrial zone in the national project for developing the northern part of the Gulf of Suez. The situation of Gabal Ataqa area for being rich with numerous geological structures, and its socioeconomic importance calls the need for the delineation of the subsurface structural features in this area using the appropriate method. The geological framework has recognized all Quaternary faults in the Gabal Ataqa area as they are exposed to the surface, at the same time, no seismic reflection data has been acquired in the Gabal Ataqa area. Accordingly, the shallow seismic reflection method is applied in the Gabal Ataqa area to detect the Quaternary faults that are not exposed to the surface and also to detect any subsurface features that may cause construction problems, such as water-wet sands, sabkhas, and limestone cavities. Three lines of 2D seismic profiles are acquired in the study area. After applying seismic data processing and interpretation, two Quaternary faults have been recognized in the first and third lines. The location of the first seismic line has been chosen to be between two historic earthquake events, increasing the probability that the sources causing these two events will be located on the newly recognized quaternary fault. A dim spot has been recognized in the second seismic line at a depth of 50 m, which may indicate the presence of a groundwater aquifer or wet sandstone layer. Based on these results, changing the industrial zone place to another side to be away from the area of the three seismic lines is highly recommended.

The Assessment of Groundwater Availability in Sedimentary Environments Using the Electrical Resistivity Method: A Case of Ekpoma and Its Environs, Southern Nigeria

Groundwater resources are an ephemeral aspect of the ecosystem, especially in the university town of Ekpoma, where the issue of severe water shortages brought on by failed or unproductive boreholes has lingered over time. This study makes an effort to thoroughly define the groundwater-bearing zones and estimate their thicknesses and depths in order to identify the cause(s) of groundwater scarcity in Ekpoma and its peri-urban area. In order to accomplish the objectives of the work, fifteen (15) Vertical Electrical Soundings (VES) were conducted across the study location, leveraging Schlumberger electrode array, with current electrode spacing varying from 5.00 to 550.00 m. The results show there were five distinct geoelectrical strata identified: top soil, clayey sandstone, sand, consolidated sandstone, and unconsolidated sandstone. The unconsolidated sandstone layer constituted the aquifer units in the area, whose depth ranges between 103.00 m and 258.00 m. Besides, this study showed that there is strong indication/evidence of saturation of the aquifer identified in the Imo Shale Formation surrounding Irrua with highly porous and permeable materials atop it, justifying the region's highly productive wells and boreholes. The aquifers delineated in and around the Ekpoma community, on the other hand, have relatively high resistive values (3404.20–5303.00 ?m), indicating less saturation, and are equally overlain by less porous and permeable materials, establishing why Ekpoma (located within the Bende-Ameki and Ogwashi Asaba Formations) has a perennial groundwater shortage. The shallow aquifer units in the area of study were discovered to be rather thin, with the majority having a thickness of less than 30 m, making them less sustainable for long-term groundwater abstraction and resulting in failed boreholes in most portions of Ekpoma town. The study indicates that the groundwater prospects of Ekpoma and its environs are poor, and deep boreholes reaching a minimum depth of 250.00 m should be drilled since it is sustainable due to its significant thickness to serve the Ekpoma community and its environs. The present investigation findings can aid in improving knowledge of underlying geological conditions, evaluating the feasibility of the researched area for predicted urban and economic development, and sustaining water supply for connected activities.

Micromechanical Contrast of Ordos Basin Sandstone‐Mudstone Interbedded Layered Rocks

AbstractLayered rocks are heterogeneous media composed of multiscale minerals with contrasting geomechanical properties. It remains unclear how the mechanical responses of constituent minerals among different adjacent layers vary in a microscale. Based on the grid nanoindentation tests assisted by high‐resolution scanning electron microscopy and energy‐dispersive spectroscopy techniques, we quantified the mechanical responses of various minerals in an interbedded sandstone‐mudstone core sample and provided visual mineralogies and indentation patterns of different adjacent layers. Results show that the Young's modulus, hardness, and elasticity index of quartz and dolomite decrease, whereas their fracture toughness and plastic work ratio increase from the sandstone layer to the mudstone layer. Quartz displays elastic‐dominated deformations in the sandstone layer whereas transforms into medium‐plastic deformations in the mudstone layer. The mean values of Young's modulus, hardness, and elasticity index of quartz in the sandstone layer are 1.28, 2.00, and 1.56 times higher than that in the mudstone layer, respectively. Dolomite and phyllosilicate minerals show prominently plastic‐dominated deformations in each layer. When an indenter encounters multiple minerals simultaneously, the mechanical responses are determined by the softer phases and irregular indent impressions are generated. Shear and radical cracks are prone to occur in the elastic‐dominated minerals, while chipping damage is induced in the plastic‐dominated minerals. This work provides new insights and fundamental understandings in geomechanical properties contrasts in multilayered rocks, and can facilitate the geomechanical modeling and upscaling schemes in multilayered formations.

Płuczki wiertnicze w skomplikowanych warunkach: przegląd

The review in this article focuses on various aspects of drilling extended reach (ERD) wells. Reaching extreme depths and setting world records for deviation illustrates the importance of well design and operating strategies. Studies of articles describing various locations, including Sakhalin Island in Russia and offshore Vietnam, provide insight into ERD operations. Furthermore, the challenges of drilling in specific geological conditions, such as layered sandstones and reactive clay, are considered. Particular attention is paid to issues related to wellbore instability and drilling fluid optimization. The results of technical studies highlight the key role of maintaining wellbore stability in achieving successful ERD results. The articles emphasize the importance of understanding geomechanical factors, employing optimal mud weight, lubrication, and specialized drilling fluids to counteract instability. It demonstrates that maintaining appropriate mud weights and employing specific drilling techniques are crucial for mitigating instability-related issues. The integration of mechanical and chemical approaches is advocated for effectively managing shale-related instability. The utilization of innovative materials and fluid systems is central to the successful resolution of stability-related problems. The incorporation of micronized sealing polymers in conjunction with conventional plugging materials is detailed as an effective approach to counter wellbore instability. The synergistic combination of materials, additives and mud salinity is showcased to achieve effective shale stabilization and optimize drilling time. The authors emphasize the importance of selecting the optimal composition for each well based on experience and laboratory testing and present laboratory-tested solutions that have been successfully applied in field operations. In summary, these articles collectively offer insights into a range of strategies to combat wellbore instability. They cover the use of advanced materials, innovative fluid systems, and chemical approaches to maintain wellbore stability, improve drilling efficiency, and reduce nonproductive time.

Mohr–Coulomb and Modified Hoek–Brown Strength Criteria of Layered Sandstone Considering the Unloading Effect and Anisotropy

The Mohr–Coulomb (M-C) and Hoek–Brown (H-B) strength criteria are widely used in various engineering fields, such as mining engineering, tunnel engineering and so on. To investigate the M-C and H-B strength criteria considering the unloading effect and anisotropy, series of triaxial loading (unloading) tests on layered sandstone were conducted. The results revealed that the peak strength was significantly affected by the unloading effect. Moreover, the cohesion and internal friction angle had a significant nonlinear relationship with the bedding angle. Additionally, the M-C and modified H-B strength criteria were established considering the unloading effect and anisotropy. Then, according to the strength criteria established, the peak strength could be estimated theoretically. Furthermore, compared to the M-C strength criteria, the modified H-B strength criteria were more appropriate for accurately estimating the triaxial compressive strength of layered sandstones. The conclusions obtained could provide certain references for the stability control of deep excavation engineering.

Dessert Optimization and Oil Potential Analysis of M9 Block in W Oilfield

This article first explains the fine structure of the M9 block, and the encryption equal value line is finely constructed into a diagram to identify the micro -amplitude structure. Use the block drilling to complete the inner plane and vertical distribution statistics of the block. Essence Using the seismic section interpretation technology, multi -attributes and detailed portrayal of the broken layer, implement the overall structural characteristics and TEZHEN characteristics of the block, carry out multi -attribute analysis and research on the oil layer sandstone group, preferably seismic attributes sensitive to the development of sandstone, and obtain each through the calculation of the well -shaking combination calculation. Unit sandstone thickness quantitative prediction diagram, analyze the characteristics of the oil and water distribution of the block, combine the favorable positions of the well deployment, combine the characteristics of the structure, the break, and the sandy body distribution, and prefer the dessert area. The original large sedimentation law understands that the “single structure favorable oil control zone” is required to re -evaluate the high -risk zone, and combine the fine structure interpretation with the sand body reservoir prediction. Improve the success rate of the evaluation control well in the dessert area, and follow the deployment of the block well after the guidance.

Petrophysical Properties and Identification of Electrofacies from Well Log Data of Nahr Umr Formation in Subba Oilfield, Southern Iraq

The main purpose of this study is to identify electrofacies and evaluate the petrophysical properties of the Nahr Umr Formation in four wells: A, B, C, and D in the Subba oilfield, southern Iraq. The petrophysical properties, such as shale volume, porosity, water saturation, hydrocarbon saturation, and bulk water volume, were computed and interpreted using Techlog software. According to the interpretation of density, neutron, and gamma ray sonic logs and deep resistivity logs using the IPSOM technique, four electrofacies were identified as sandstone, shaly sand, sandy shale, and shale electrofacies. The formation was divided into three parts based on well log interpretation and petrophysical analysis: the upper part, middle part, and lower part Interpretation of formation lithology and petrophysical parameters shows that the lower part consists mainly sandy shale with layers of sandstone and shale high porosity and high oil saturation whereas middle part consists mainly of sandstone, alternating with thin bedded of sandy shale and shale with high porosity and medium oil saturation. The upper part consists mainly of a sandy shale alternating with shale and shaly sand with high porosity, hydrocarbon saturation, and lower water saturation.

Seismoelectric wave conversions at an interface: a quantitative comparison between laboratory data and full-waveform modelling

SUMMARYSeismo-electromagnetic phenomena, electrokinetic in nature, take place whenever a seismic wave propagates in fluid-bearing media, its energy depending mainly on the electrical properties of the fluid and the hydraulic properties of the porous medium. They result from a conversion of mechanical into electromagnetic (EM) energy due to the transient ionic interactions occurring at the pore scale. Two of these phenomena are usually studied: the electric field accompanying seismic waves, and the EM field that travels independently, generated at discontinuities of physicochemical properties in the porous medium. Although the first event is sensitive to physical parameters of the surrounding medium, the second catches information about interfaces in the subsurface, with the resolution of seismic methods, making it very attractive to near surface exploration. In this context, we propose a new experimental setup where both phenomena can be simultaneously studied. At first, we use a porous medium composed of homogeneous water-saturated sand and study the characteristics of the coseismic electric field. Afterwards, a thin layer of Vosges sandstone is inserted into the sand, which allows the study of the EM waves generated at the two closely spaced sand-sandstone interfaces. We record the seismic displacement field at the upper surface of the sand volume using a laser vibrometer, and use stainless steel electrodes buried in the sand to acquire individual electric potentials rather than electric fields, seeking to favour the measurement of the EM interface-generated signals. With the help of direct numerical simulations, we compare experimental measurements and theoretical predictions, based on a well established set of seismoelectric governing equations. In both types of experiments, this comparison shows very good agreements between experimental and numerical waveforms, thus confirming the relevant theory. The electric potential data also show that the EM signals generated at interfaces are clearly recorded at distances of about 10 seismic P wavelengths away from the interface. By contrast, the same events are barely noticeable near the inserted layer when measured using classical electric dipolar arrays.

Studies on the Source and Phase Characteristics of Oil and Gas: Evidence from Hydrocarbon Geochemistry in the Pingbei Area of Xihu Sag, the East China Sea Shelf Basin, China

The Pingbei area is the main accumulation area of oil and gas in the Xihu Sag. The phase characteristics of oil and gas in this area are complex, and the understanding of their genesis is still unclear. In this paper, based upon discussions of crude oil and natural gas geochemical data, integrated with local geological features, we discuss the sources, migration, and phase state characteristics of oil and gas in the Pingbei area of the Xihu Sag. The study results show that the crude oil and natural gas in the Pingbei area are coal-derived and the oil and gas produced by the humic organic matter during the mature stage. The oil and gas source correlation showed that crude oil and natural gas have good affinity with the Eocene Pinghu Formation (PH) coal-bearing source rocks. Crude oil has the characteristics of near-source accumulation and short-distance migration while natural gas is supplied from a dual source: the coal-derived hydrocarbon rocks of PH in the deep part of the study area, supplemented by the coal-derived hydrocarbon rocks of PH on the bottom of the slope, and adjacent hydrocarbon-bearing sub sag. The distribution characteristics and geochemical migration indices of hydrocarbon show that the oil generated from the hydrocarbon source rocks of PH in the deep Pingbei area mainly migrates vertically along the fault connecting the reservoir and the source rocks to the trap, where it accumulates, while the natural gas exhibits deep and large faults that mainly migrate vertically, supplemented by its lateral migration along the composite transport system composed of faults and sandstone layers in the slope zone. The whole area presents the phase characteristics of “upper oil and lower gas, west oil and east gas”. The mechanisms of produced-exhausted and geochromatographic effects (PGE), as well as evaporative fractionation (EF) and phase-controlled migration fractionation (PMF), result in the obvious discrepancy of hydrocarbon’s properties on the vertical profiles.

Quantitative Evaluation of Suspended Solid Runoff from Large-Scale Landslide Areas Presumed to Be the Source of Turbid Water

In the uppermost stream of the Mimikawa River, in northern Miyazaki Prefecture, the contribution to river turbidity of a huge, collapsed slope alternating sandstone and mudstone layers was qualitatively shown in our previous study. In this study, the water level and turbidity were continuously observed, to obtain a quantitative estimation of this contribution. The conversion equation from the water level to the flow rate is required, but field measurements during the flooding term in the mountainous site are difficult. In this study, a high-resolution survey was conducted, and the relationship was determined via a small-scale hydraulic model shaped using a 3D printer from the survey results, to determine the relationship between the water level and the flow rate. The flow rate time series was reproduced with the distributed runoff model that is verified with the flow rate converted from the water level. The flow rate and turbidity load time series were also estimated from the long-term rainfall. The area of the bare soil surface of each small basin was obtained via satellite image analysis, and the soil yield from each surface condition was calculated. Furthermore, the amount of turbidity produced upstream of Kamishiiba Dam was calculated for each small basin. It was estimated that 24% of the turbidity was generated from the small basin covering 5.7% of the total catchment area. This study showed that it is possible to verify the hydrological model by obtaining the water-level–discharge relationship, even in the mountains, where it is difficult to observe the discharge on-site, via small-scale hydraulic model experiments.