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Interpreting reservoir properties through log data and logging responses in complex strata is critical for efficient petroleum exploitation, particularly for metamorphic rocks. However, the unsatisfactory accuracy of such interpretations in complex reservoirs has hindered their widespread application, resulting in severe inconvenience. In this study, we proposed a multi-mineral model based on the least-square method and an optimal principle to interpret the logging responses and petrophysical properties of complex hydrocarbon reservoirs. We began by selecting the main minerals based on a comprehensive analysis of log data, X-ray diffraction, petrographic thin sections and scanning electron microscopy (SEM) for three wells in the Bozhong 19-6 structural zone. In combination of the physical properties of these minerals with logging responses, we constructed the multi-mineral model, which can predict the log curves, petrophysical properties and mineral profile. The predicted and measured log data are evaluated using a weighted average error, which shows that the multi-mineral model has satisfactory prediction performance with errors below 11% in most intervals. Finally, we apply the model to a new well "x" in the Bozhong 19-6 structural zone, and the predicted logging responses match well with measured data with the weighted average error below 11.8% for most intervals. Moreover, the lithology is dominated by plagioclase, K-feldspar, and quartz as shown by the mineral profile, which correlates with the lithology of the Archean metamorphic rocks in this region. It is concluded that the multi-mineral model presented in this study provides reasonable methods for interpreting log data in complex metamorphic hydrocarbon reservoirs and could assist in efficient development in the future. [ABSTRACT FROM AUTHOR]

The topography and geomorphology is complex, the lithology of the strata is varied and the metamorphic rocks are widespread distribution, which cause frequent landslide hazards in Shiyan City. In order to reduce the serious hazards caused by landslide hazards and achieve accurate early warning, the surface displacement monitoring(GNSS)data was selected from four metamorphic landslides that have been damaged in Shiyan City based on the improved tangential angle theory, combined with accumulate acceleration and accumulate accelerated acceleration. By drawing their T-t curves, accumulate acceleration-time curves and accumulate accelerated acceleration-time curves, the comprehensive classification of creep-slip stages of metamorphic landslides in Shiyan City were obtained. The following criteria were determined that the tangent angle of the T-t curvs was greater than or equal to 80°, the accumulate acceleration was greater than 0 and maintained a large positive value, and the accumulate accelerated acceleration was greater than 0 and continuously increased or maintained a high value. The results of the study are of great significance for the monitoring and warning of metamorphic landslides in Shiyan City, and can also provide reference for the monitoring and warning thresholds of other types of landslides. [ABSTRACT FROM AUTHOR]

Abstract Engineering rockmass classifications are an integral part of design, support and excavation procedures of tunnels, mines, and other underground structures. These classifications are directly linked to ground reaction and support requirements. Various classification systems are in practice and are still evolving. As different classifications serve different purposes, it is imperative to establish inter-correlatability between them. The rating systems and engineering judgements influence the assignment of ratings owing to cognition. To understand the existing correlation between different classification systems, the existing correlations were evaluated with the help of data of 34 locations along a 618-m-long railway tunnel in the Garhwal Himalaya of India and new correlations were developed between different rock classifications. The analysis indicates that certain correlations, such as RMR-Q, RMR-RMi, RMi-Q, and RSR-Q, are comparable to the previously established relationships, while others, such as RSR-RMR, RCR-Qn, and GSI-RMR, show weak correlations. These deviations in published correlations may be due to individual parameters of estimation or measurement errors. Further, incompatible classification systems exhibited low correlations. Thus, the study highlights a need to revisit existing correlations, particularly for rockmass conditions that are extremely complex, and the predictability of existing correlations exhibit high variations. In addition to augmenting the existing database, new correlations for metamorphic rocks in the Himalayan region have been developed and presented that can serve as a guide for future rock engineering projects in such formations and aid in developing appropriate excavation and rock support methodologies.

Engineering rockmass classifications are an integral part of design, support and excavation procedures of tunnels, mines, and other underground structures. These classifications are directly linked to ground reaction and support requirements. Various classification systems are in practice and are still evolving. As different classifications serve different purposes, it is imperative to establish inter-correlatability between them. The rating systems and engineering judgements influence the assignment of ratings owing to cognition. To understand the existing correlation between different classification systems, the existing correlations were evaluated with the help of data of 34 locations along a 618-m-long railway tunnel in the Garhwal Himalaya of India and new correlations were developed between different rock classifications. The analysis indicates that certain correlations, such as RMR-Q, RMR-RMi, RMi-Q, and RSR-Q, are comparable to the previously established relationships, while others, such as RSR-RMR, RCR-Qn, and GSI-RMR, show weak correlations. These deviations in published correlations may be due to individual parameters of estimation or measurement errors. Further, incompatible classification systems exhibited low correlations. Thus, the study highlights a need to revisit existing correlations, particularly for rockmass conditions that are extremely complex, and the predictability of existing correlations exhibit high variations. In addition to augmenting the existing database, new correlations for metamorphic rocks in the Himalayan region have been developed and presented that can serve as a guide for future rock engineering projects in such formations and aid in developing appropriate excavation and rock support methodologies. [ABSTRACT FROM AUTHOR]

Many methods have been developed to detect and predict the fracture properties of fractured rocks. The standard data sources for fracture evaluations are image logs and core samples. However, many wells do not have these data, especially for old wells. Furthermore, operating both methods can be costly, and, sometimes, the data gathered are of bad quality. Therefore, previous research attempted to evaluate fractures indirectly using the widely available conventional well-logs. Sedimentary rocks are widespread and have been studied in the literature. However, fractured reservoirs, like igneous and metamorphic rock bodies, may also be vital since they provide fluid migration pathways and can store some hydrocarbons. Hence, two fractured metamorphic rock bodies are studied in this study to evaluate any difference in fracture responses on well-log properties. Also, a quick and reliable prediction method is studied to predict fracture density (FD) in the case of the unavailability of image logs and core samples. Gene expression programming (GEP) was chosen for this study to predict FD, and ten conventional well-log data were used as input variables. The model produced by GEP was good, with R2 values at least above 0.84 for all studied wells, and the model was then applied to wells without image logs. Both selected metamorphic rocks showed similar results in which the significant parameters to predict FD were the spectral gamma ray, resistivity, and porosity logs. This study also proposed a validation method to ensure that the FD value predictions were consistent using discriminant function analysis. In conclusion, the GEP method is reliable and could be used for FD predictions for basement metamorphic rocks. [ABSTRACT FROM AUTHOR]

Inner fracture zones play a decisive role in the formation of high-quality reservoirs in buried hill reservoirs in covered metamorphic rock. Based on core, sidewall core, thin section, seismic, logging and reservoir physical property data, the fracture development characteristics of the Bozhong 13-2 block buried hill reservoir are described in detail and the controlling factors and the influence on reservoir quality are discussed. The results showed: (1) three groups of tectonic fractures developed in the study area—near-EW-striking, ENE-striking and nearly N–S-striking fractures—were controlled by the early Indosinian thrusting, the late Indosinian to early Yanshanian sinistral strike-slipping and the late Yanshanian late dextral strike-slipping in the Bohai Bay Basin, respectively. The ENE- and nearly-E-W-striking fractures are the most common, and the dip angles of the fractures are mostly between 35° and 75° and thus oblique. (2) The Indosinian-early Yanshanian was the main fracture-forming period, and the dextral strike-slip action in the late Yanshanian was the key to maintaining effective fractures. Imaging logging shows that 97.87% of the fractures are effective fractures. Based on thin section observation, 14.47% of the fractures are unmodified open fractures and 80.37% of the fractures are effective fractures due to reactivation. (3) The late Yanshanian strike-slip fault transformed the deformation adjustment zone formed by the early Indosinian thrust faulting and the core of the fold structure was more conducive to fracture development. The fracture density of a single well located within the deformation adjustment zone and at the core of the fold is between 0.93–1.49 m−1, the fracture density of a single well located only at the core of the fold is between 0.67–0.75 m−1 and that of a single well located at the wing of the fold is between 0.35–0.59 m−1. Diabase dike intrusions promoted the development of local fractures. (4) Fractures promote the migration and accumulation of oil and gas, and the fracture density in the oil layer is between 0.81–2.19 m−1. That in the nonoil layer is between 0.25–1.12 m−1. In addition, fractures not only provide storage space but also effectively improve the reservoir capacity of the inner fracture zones of buried hill reservoirs by concentrating dissolution. [ABSTRACT FROM AUTHOR]

The mechanical properties of metamorphic rocks are affected by foliation, which induces apparent anisotropy and heterogeneity. In this study, a series of pull-off and direct shear tests were performed to investigate the tensile strength, peak shear strength, and residual shear strength of the foliation in different metamorphic rocks (HY slate, RS schist, and SH schist). In addition, the effect of grout reinforcement on the fractured foliation was evaluated. Finally, a model was proposed to evaluate the shear strength of the cement-grouted foliation. The key findings of this study included the following: (1) The tensile and shear strengths of the schists were higher than those of slate. A nonlinear failure criterion for the foliation was adopted to reasonably describe their failure envelopes. (2) For the long-displacement shear tests, the friction angle of HY slate increased as the number of shearing cycles increased, and the friction angle of schists slightly decreased, which was related to the surface variations of the rocks. (3) Considering the grout reinforcement on the fractured foliation, the low strength of the grouted slate was attributed to the weak interface bonding between the cement and slate. In contrast, the strength of the grouted schists significantly increased. The high roughness strongly contributed to the grout reinforcement on the schist foliation. (4) Our proposed shear strength model for cement-grouted metamorphic rocks, which considered factors such as the joint roughness coefficient, uniaxial compressive strength of cement, residual friction angle, and interface tensile strength, provided reasonable predictions that aligned with the experimental test results. Highlights: A series of pull-off and direct shear tests were performed to investigate the strength of the foliation in metamorphic rocks. The effect of grout reinforcement on the fractured foliation was also evaluated. A model was proposed to evaluate the shear strength of the cement-grouted foliation. The proposed model provided reasonable predictions that aligned with the test results. [ABSTRACT FROM AUTHOR]

The formation process of metamorphic buried-hill reservoirs in Bohai Oilfield was complicated, which was affected bv tectonic movement, weathering and leaching, paleogeomorphologv and other geological factors, re-sulting in the diversified reservoir space and extremelv strong non-homogeneitv. liowever, the existing reservoir phvsical properties evaluation methods had problems such as low qualitv of collected data, strong multi-solutions and poor real-time accuracv. For this reason, the metamorphic buried-hill reservoir in Bohai Oilfield was taken as a target area, the field outcrop sampling was carried out, interval transit time and microdrill drilling experiments were carried out to obtain the interval transit time and mechanical specific energv values of rocks with different phvsical characteristics, and a mathematical model of phvsical propertv index and reservoir porositv were estab-lished. The studv shows that the interval transit time of the outcrops of the Archaeozoic metamorphic rocks of the Bohai Oilfield ranges from 371.75 to 617.29 xs/m, and the mechanical specific energv value ranges from 297.43 to 1207.47 MPa. The value of the mechanical specific energv shows an exponential function to decrease with the in-crease of the interval transit time, and the porositv shows a logarithmic function to decrease with the increase of the phvsical propertv index. The method has been popularized and applied in the metamorphic buried-hill reservoir of Bohai Oilfield, and the compliance rate with the logging interpretation results has reached more than 85%. This studv provide reference and basis for the identification of metamorphic buried-hill reservoirs. [ABSTRACT FROM AUTHOR]

Many methods have been developed to detect and predict the fracture properties of fractured rocks. The standard data sources for fracture evaluations are image logs and core samples. However, many wells do not have these data, especially for old wells. Furthermore, operating both methods can be costly, and, sometimes, the data gathered are of bad quality. Therefore, previous research attempted to evaluate fractures indirectly using the widely available conventional well-logs. Sedimentary rocks are widespread and have been studied in the literature. However, fractured reservoirs, like igneous and metamorphic rock bodies, may also be vital since they provide fluid migration pathways and can store some hydrocarbons. Hence, two fractured metamorphic rock bodies are studied in this study to evaluate any difference in fracture responses on well-log properties. Also, a quick and reliable prediction method is studied to predict fracture density (FD) in the case of the unavailability of image logs and core samples. Gene expression programming (GEP) was chosen for this study to predict FD, and ten conventional well-log data were used as input variables. The model produced by GEP was good, with R2 values at least above 0.84 for all studied wells, and the model was then applied to wells without image logs. Both selected metamorphic rocks showed similar results in which the significant parameters to predict FD were the spectral gamma ray, resistivity, and porosity logs. This study also proposed a validation method to ensure that the FD value predictions were consistent using discriminant function analysis. In conclusion, the GEP method is reliable and could be used for FD predictions for basement metamorphic rocks.

Inner fracture zones play a decisive role in the formation of high-quality reservoirs in buried hill reservoirs in covered metamorphic rock. Based on core, sidewall core, thin section, seismic, logging and reservoir physical property data, the fracture development characteristics of the Bozhong 13-2 block buried hill reservoir are described in detail and the controlling factors and the influence on reservoir quality are discussed. The results showed: (1) three groups of tectonic fractures developed in the study area—near-EW-striking, ENE-striking and nearly N–S-striking fractures—were controlled by the early Indosinian thrusting, the late Indosinian to early Yanshanian sinistral strike-slipping and the late Yanshanian late dextral strike-slipping in the Bohai Bay Basin, respectively. The ENE- and nearly-E-W-striking fractures are the most common, and the dip angles of the fractures are mostly between 35° and 75° and thus oblique. (2) The Indosinian-early Yanshanian was the main fracture-forming period, and the dextral strike-slip action in the late Yanshanian was the key to maintaining effective fractures. Imaging logging shows that 97.87% of the fractures are effective fractures. Based on thin section observation, 14.47% of the fractures are unmodified open fractures and 80.37% of the fractures are effective fractures due to reactivation. (3) The late Yanshanian strike-slip fault transformed the deformation adjustment zone formed by the early Indosinian thrust faulting and the core of the fold structure was more conducive to fracture development. The fracture density of a single well located within the deformation adjustment zone and at the core of the fold is between 0.93–1.49 m−1, the fracture density of a single well located only at the core of the fold is between 0.67–0.75 m−1 and that of a single well located at the wing of the fold is between 0.35–0.59 m−1. Diabase dike intrusions promoted the development of local fractures. (4) Fractures promote the migration and accumulation of oil and gas, and the fracture density in the oil layer is between 0.81–2.19 m−1. That in the nonoil layer is between 0.25–1.12 m−1. In addition, fractures not only provide storage space but also effectively improve the reservoir capacity of the inner fracture zones of buried hill reservoirs by concentrating dissolution.

The present work aims to characterize the processes of soil formation on shale metamorphic source rocks in a subhumid Mediterranean area in the north of Algeria (Algiers city). The study of the evolution of the horizon's total chemical composition of some elements (Si, Al, Fe, Ti, Ca, Mg, K, Na and Mn), allowed us to define rocks alteration mechanisms and redistribution of the alteration complex in two main profiles formed on metamorphic rocks. To do so, we conducted physical and chemical analyzes for both profiles. Then, the calculation of the Chemical weathering indices helped us to extract the alteration's balance. The results showed that silicium is the main chemical constituent of the studied soil profiles. The realized geochemical trends indicated enrichment of surface horizons by silicium and a decrease in iron and aluminium elements. Regarding the manganese, there is no clear pattern of distribution in the profiles. The concentrations of titanium, alkali and alkaline earth elements (Na2O, K2O, CaO and MgO) are irregular in the profiles and are generally lower than those of the parent materials. The weathering indices seem well suited to detect changes in the alteration intensity in the studied soils. The calculated chemical balances vary according to the targeted chemical elements. [ABSTRACT FROM AUTHOR]

The Dashuigou tellurium deposit is the world's only known independent tellurium deposit. By restoring metamorphic rocks' protolith, we seek to understand not only the development and evolution trajectory of the region but also the origin of the relevant deposits. While there are many ways to restore metamorphic rocks' protolith, we take the host metamorphic rocks of Dashuigou tellurium deposit and leverage various petrochemical eigenvalues and related diagrams previously proposed to reveal the deposit's host metamorphic rocks' protolith. The petrochemical eigenvalues include molecular number, Niggli's value, REE parity ratio, CaO/Al2O3 ratio, Fe3+/(Fe3+ + Fe2+) ratio, chondrite-normalized REE value, logarithmic REE value, various REE eigenvalues including scandium, Eu/Sm ratio, total REE amount, light and heavy REEs, δEu, Eu anomaly, Sm/Nd ratio, and silicon isotope δ30SiNBS−28‰, etc. The petrochemical plots include ACMs, 100 mg-c-(al + alk), SiO2-(Na2O + K2O), (al + fm)-(c + alk) versus Si, (FeO + Fe2O3 + TiO)–Al2O3–MgO, c-mg, Al2O3–(Na2O + K2O), chondrite-normalized REE model, La/Yb-REE, and Sm/Nd ratio, etc. On the basis of these comprehensive analyses, the following conclusions are drawn, starting from the many mantle-derived types of basalt developed in the study area of different geological ages, combined with the previously published research results on the deposit's fluid inclusions and sulfur and lead isotopes. The deposit is formed by mantle degassing in the form of a mantle plume in the late Yanshanian orogeny. The degassed fluids are rich in nano-scale substances including Fe, Te, S, As, Bi, Au, Se, H2, CO2, N2, H2O, and CH4, which are enriched by nano-effect, and then rise to a certain part of the crust in the form of mantle plume along the lithospheric fault to form the deposit. The ultimate power for tellurium mineralization was from H2 flow with high energy, which was produced through radiation from the melted iron of the Earth's outer core. The H2 flow results in the Earth's degassing, as well as the mantle and crust's uplift. [ABSTRACT FROM AUTHOR]

Through field surveys, sampling, and laboratory experiments, the content, enrichment, and migration characteristics of heavy metals in the rock–soil–tea system in the Guizhou metamorphic rock area were analyzed herein. The results show that the As and Hg contents in metamorphic sandstone in the study area are higher than those in slate, while the Mn, Zn, Pb, and Ni contents in slate are higher. The content of heavy metals in the sandstone of the Jialu formation of the Xiajiang group in Neoproterozoic is the highest, and that of the slate of the Fanzhao formation is the lowest. The content of As in the rock samples in the study area is higher than that in the Epicontinental crust, while Cd is found to be deficient. The heavy metals at some soil points exceed the standard, but this does not affect the growth and development of tea. The content of heavy metals in most tea is lower than the safety limit standards, and the THQ value is less than 1, indicating that the heavy metals in tea in Guizhou metamorphic rock areas pose no concern for human health. In the metamorphic rock distribution areas of Guizhou, tea does not enrich As, Cr, Hg, and Pb in soil, but enriches Mn, Cu, Ni, and Zn to varying degrees, with the enrichment of Mn being the strongest. [ABSTRACT FROM AUTHOR]

An albite deposit formed in orthogneiss has been operated using open pit mining process since 1996. However, landslides have occurred following the excavation works and heavy rainfalls. In the current state, the slopes are still susceptible to mass movement. For this reason, this study aimed to determine the root causes that are influencing continuous movements. In this context, two geometric features of the strike-slip faults that form tectonic slices in the pit were proposed. The first one (α-angle) is the acute angle between the dip direction of the overall slope and the general trend of the strike-slip fault and it was used for the kinematic evaluation of the sliding potential of the tectonic slices. The validity of α-angle was confirmed by investigating its relationship with the factor of safety values. The second one (undulation angle, i) was used to determine the effective surface friction angle (ϕeff). Thereafter, ϕeff value was used in the deterministic finite element (FE) slope stability analyses as well as back analyses. Its effect on the stability of overall slopes was investigated for static and pseudo-static conditions with different water table levels. The FE results confirmed the monitored field displacement measurements. It was found that as α-angle decreases, the ability to resist sliding also decreases since the low α-angle promotes block formation. This study also demonstrated that using the undulation angles on mapped profiles of large-scale discontinuities (≥270 m) would be a promising approach for slope stability assessments of open pit excavations in tectonically disturbed metamorphic rocks. [ABSTRACT FROM AUTHOR]

The rockslide systems along the Gepatsch reservoir in the Kaunertal valley are among the best investigated and monitored slopes in the Alps since TIWAG began operating the Kaunertal power plant in 1964. The rockslide systems consist of several individual slabs with variable activity. Only the deformation characteristics of the Hochmais slab shows transient behaviour and depends on external influences such as reservoir operation. No effects from heavy precipitation or snowmelt on the deformation characteristics were observed prior to 2019. The large amount of precipitation accumulated as snow in the winter of 2018/2019, combined with cool spring weather and low reservoir level, resulted in an increased deformation rate of the Hochmais slab due to excessive snowmelt in June 2019. The maximum deformation rate of several mm per week was the highest activity of the Hochmais slab since the end of the first impoundment period in 1966. In response to this exceptional situation, the engineers at TIWAG, in conjunction with external experts and the competent authorities, temporarily restricted the reservoir operation. The increased rates of deformation of the Hochmais slab decreased to the expected level in the late summer of 2019 [ABSTRACT FROM AUTHOR]

Bela Ophiolite and suture zone host several types of gemstones in the underlain and overlain rocks such as garnet (demantoid and almandine), quartz, brucite, malachite, chrysocolla, azurite, calcite, natrolite, green chert, jasper, serpentine, agate, epidote, augite and prehnite. However, the rare gemstones including demantoid garnet are found as dodecahedron green crystals associated with the altered peridotite rocks such as serpentinite. Brucite is found in the botryoidal habit in the ultramafic rocks of Bela Ophiolite associated with the chromite mines in the Baran Lak and Amorzai area of Wadh in the host rock dunite. The serpentine is found in several locations associated with the altered ultramafic rocks formed after the serpentinization of peridotite. Furthermore, one of the rare gemstones such as petroleum and diamond quartz is formed due to the hydrothermal intrusion in the sedimentary rocks such as limestone; calcite also occurs in limestone as dogtooth crystals. While azurite, malachite and chrysocolla are formed as secondary deposits in the oxidized zone of copper and sulphide mines in the Manjawi, Nal and Sonaro associated adjacent to basalt. Moreover, epidote is found as green crystals having porphyritic texture in the host rock granite mainly in the Bakhalo area, Wadh. Agate, jasper, green chert and several other kinds of chert are found associated with the basalt chert unit in the mélange and gossan. In addition to that natrolite is found in the Nal ophiolite mainly in the Hazarghanji town found associated with the cracks and vugs of dolerite dykes as fibrous and cylindrical crystals. In metamorphic sole rocks of Bela Ophiolite in the Sonaro area, marble and quartzite are associated with the metamorphic rocks such as greenschist and amphibolite facies that are formed during the e volution period of the ophiolite. In pegmatite gabbro, the elongated and prismatic black crystals of augite are found in the host rock gabbro near the Ornach cross area, and the prehnite gemstone is found associated with the basalt and gabbroic rocks transition zone in the Ornach area.

Abstract One of the most important issues in tunnels to be constructed with tunnel boring machines (TBMs) is to predict the excavation time. Excavation time directly affects tunnel costs and feasibility. For this reason, studies on the prediction of TBM performance have always been interesting for tunnel engineers. Therefore, the purpose of the study is to develop models to predict the rate of penetration (ROP) of TBMs. In accordance with the purpose of the study, a new database including 5334 cases is obtained from the longest railway tunnel of Turkey. Each case includes uniaxial compressive strength, Cerchar Abrasivity Index, α angle, weathering degree and water conditions as input or independent variables. Two multiple regression models and two ANN models are developed in the study. The performances of the ANN models are considerably better than those of the multiple regression equations. Before deep tunnel construction in a metamorphic rock medium, the ANN models developed in the study are reliable and can be used. In contrast, the performances of the multiple regression equations are promising, but they predict lower ROP values than the measured ROP values. Consequently, the prediction models for ROP are open to development depending on the new data and new prediction algorithms.

The hydrocarbon accumulation pattern of the Mesozoic covered Archean buried hill in the Bohai Oilfield was not clarified before, which restricts the oil and gas exploration progress in this area. In recent years, reservoir development modes and reservoir prediction technologies have been researched after the structural evolution and stratigraphic distribution characteristics of the buried hill in the Bozhong sag were investigated based on new 3D seismic data and a large number of cores and logging data of newly drilling wells. Then, the hydrocarbon accumulation pattern of covered type Archean buried hill was analyzed. Finally, this pattern was applied to guide the oil and gas exploration deployment in Bozhong 13-2 structure, and a significant discovery of Bozhong 13-2 large monoblock volatile buried hill oilfield was realized. And the following research results were obtained. First, the structure in this area mainly experienced multi-period tectonic movements, such as Indosinian, Yanshanian and Himalayan, and it is characterized by compression and thrusting to form a hill during Indosinian-early Yanshanian, extension and inversion transformation during middle Yanshanian, and burial and finalization during Himalayan, forming Bozhong 13-2 Mesozoic covered Archean large buried hill trap. Second, under the effect of Mesozoic cover and the control of multi-stage stress superposition, the reservoir development in this area has the distribution characteristics of “different vertical top, internal lateral continuity”. Third, the fracture prediction technology based on smooth reflection strength filter is developed. And by means of this technology, multi-scale fractured reservoirs inside buried hills can be predicted effectively. Fourth, the hydrocarbon accumulation pattern of “overpressure injection-relay migration” for covered type buried hills is established, which provides a basis for long-distance migration and large-scale accumulation of oil and gas in covered type buried hills. In conclusion, these understandings guide the discovery of Bozhong 13-2 Oilfield, achieve a breakthrough in the oil and exploration of Mesozoic covered buried hill in the Bohai Oilfield and can be used as the reference for the oil and gas exploration in the similar covered type buried hills of the Bohai Bay Basin and other areas.

Hydrothermal fluid is one of the factors controlling Archean buried hill reservoirs in Bozhong 19-6. However, there are no clear studies focusing on the influence of hydrothermal alteration products and their lithological characteristics on reservoirs. Through characterization of the alteration reservoir and construction of a new subtraction model of the logging-rock mechanical alteration degree, the comprehensive uses of core, thin section, and electrical imaging logging data are considered as the research objects with metamorphic and igneous rocks. Thus, the relationship between lithologies with different alteration degrees and reservoir quality is revealed. The study shows that feldspar chloritization and sericitization are the main factors controlling the hydrothermal alteration of the reservoir; the overall alteration degree of igneous rocks is high, and the overall alteration degree of metamorphic rocks is low; the reservoir with strongly altered igneous facies is prone to forming dissolution pores, with strong reservoir inhomogeneity and poor reservoir performance (alteration degree is greater than 15%); the reservoir with weakly altered metamorphic facies is prone to developing fractures and a high reservoir productivity (alteration degree is 0); The reservoirs with altered metamorphic facies are numerous in the formation, spatially diverse in type, and second in reservoir quality only to those in the weakly altered metamorphic facies (alteration degree of 0–15%). This method is expected to provide a reference for quickly finding advantageous reservoirs in the Bohai Sag.

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Buried‐hill reservoirs are important targets for petroleum exploration. The number of buried‐hill oil–gas fields with reservoirs hosted in metamorphic rock is low, and metamorphic rock buried‐hill reservoirs deeper than 4,500 m (ultra‐deep) are even rarer. Ultra‐deep metamorphic rock buried‐hill reservoirs are characterized by highly heterogeneous lithologies and structure and have complex formation mechanisms, but such reservoirs have received relatively little research attention compared with reservoirs hosted in other rock types and at shallower depths. In the Bozhong Sag in the Bohai Bay Basin, Archean metamorphic rocks are buried at depths of 4,500–6,000 m, and their anticlinal structures are thus defined as ultra‐deep buried hills. Owing to their burial depth and compacted overburden, tectonism has been a key control on the formation of high‐quality reservoirs by causing deformation such as fractures. In this study, using results of drill‐core analyses, thin‐section imaging, and rock mechanical tests, we investigated the distribution and formation mechanisms of high‐quality reservoirs within the Bozhong 19‐A metamorphic rock buried hill. We also examined the formation mechanism of fractures in the Bozhong 19‐A buried hill with respect to early‐stage initiation by compression and late‐stage reactivation by transpression. Results show that intense compression‐related overthrusting caused by collision between the South China and North China plates during the Indosinian (252–237 Ma) orogeny generated initial fractures in the metamorphic rock buried hill and the formation of numerous NW‐trending nappe structures. Subsequent Yanshanian (163–66 Ma) sinistral transpression not only reactivated pre‐existing fractures, but also resulted in the development of numerous new fractures. In addition, in low‐stress regions such as anticline flanks and the lower parts of structures, compression closed the pre‐existing fractures, leading to lower fracture densities. Results of acoustic emission mechanical testing indicate that Himalayan (66–0 Ma) extensional stress was insufficient to produce large‐scale fracture systems in the Archean metamorphic rock, but was crucial for reactivating pre‐existing early‐stage fractures. Thus, the Himalayan period was a key interval for the formation of effective fractures. Therefore, rocks that underwent large‐scale overthrusting during early‐stage (Indosinian) fracturing and subsequent late‐stage (Yanshanian and Himalayan) reactivation favoured the development of ultra‐deep metamorphic rock buried‐hill reservoirs. This study should provide guidance for petroleum exploration in buried hills in superimposed basins that underwent early‐stage compression, late‐stage transpression, and final extension. [ABSTRACT FROM AUTHOR]

Abstract Faults in the rock mass of dam foundation are crucial in controlling dam deformation and stability. In particular, long‐term stability of dam foundation is an important factor for the safety of dam operations. The rock in the foundation of Dagangshan hydropower station is mostly granite, and there are many diabase dikes distributed in granite. Geological survey indicates that many faults exist along the interfaces between granite and diabase. Lots of diabase were metamorphosed to chlorites, which have very low strength. In order to investigate the deformation of faults in diabase dikes under long‐term loading, in situ shear creep tests were performed to estimate the creep performance of a fault. The shear creep displacement and the influence of displacement history of the specimen during multi‐level loading tests were measured and analyzed. The isochronous stress‐strain method was used to determine the long‐term strength of the fault in shear creep tests. Considering the instantaneous damage and strain softening, a new viscoelastic‐plastic softening creep model was proposed to describe the shear creep behavior of the fault. Comparisons confirmed that this creep model is capable of describing the shear creep behavior of the fault and the creep parameters were estimated accordingly using this model.

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Analytical lines play a crucial role in laser-induced breakdown spectroscopy (LIBS) technology. To improve the classification performance of LIBS, an image features assisted line selection (IFALS) method which based on spectral morphology and the characteristics of Harris corners was proposed. With this method, a classification experiment for 24 metamorphic rock samples was conducted with linear discriminant analysis (LDA) algorithm. The result showed that the classification accuracy was increased from 94.38% of the conventional classification model MLS-LDA (Manual line selection-linear discriminant analysis) to 98.54% of IFALS-LDA. Furthermore, the time required for the whole classification process was decreased from 2768.38 s of MLS-LDA to 4.36 s of the proposed method, thus the classification efficiency was greatly improved. In addition, compared with the existing automatic line selection method, the convergence rate of IFALS-LDA is significantly faster than that of ASPI (Automatic spectral peaks identification)-LDA. This study demonstrates that LIBS assisted with the image features in machine vision can promote the analytical performance of LIBS technology. Image 1 • A new line selection method named IFALS is first proposed in LIBS. • Image corner features instead of spectral features are used for analytical line selection. • Classification performance is significantly improved by IFALS-LDA. [ABSTRACT FROM AUTHOR]

Investigations on the Posiva Olkiluoto spalling experiment (POSE) at the nuclear waste disposal site in Olkiluoto, western Finland, have revealed that the presence of anisotropic veined gneiss (VGN) could affect the evaluation of spalling/damage strength of the host rock. In this study, the mechanical and damage behaviors of anisotropic VGN during complex true-triaxial in situ stress path loading is numerically investigated, considering the lifetime stress evolution of POSE. Overall, the discrete element numerical results show reasonable agreement with those of laboratory experiments for both strength and damage development. Numerical simulations at the microscale showed that the damage is concentrated within the discontinuous foliation bands and at the interfaces between weak and strong bonds when the mineral composition of the foliation bands is heterogeneous. It is possible that the varying stiffnesses of the two materials cause strain concentration at strong segments within the weak foliation bands or high strain gradients at the interfaces between the weak and strong bands, leading to tensile failure of the strong bonds. However, if continuous foliation bonds are employed, fractures mainly propagate within the weak bonds, indicating that the heterogeneity of the foliation bonds is a predominant factor affecting the failure of VGN. After weak bonds and interfaces failure, shear movements occur along the weak bonds, forcing the strong bonds to bear most of the load. The simulations also show that the unloading of σ2 and σ3 triggers microcracks in the early stages, revealing the role of unloading in rock damage. The change in the secant modulus in relation to the foliation angle is generally found to follow a U-shaped anisotropy and obtains the lowest value at 45°. For each test, the modulus gets the minimum value in the damage stage and recovers in the unloading stage, but it cannot reach its original value. Sample strength increases as the foliation orientation angle increases from 0° to 45° in relation to σ2, because the increase in normal stress from σ2 causes the role of the strong foliation bonds to become significant as the bonds strengthen. The damage to the strong bonds leads to a larger reduction in the modulus at the damage stage. [ABSTRACT FROM AUTHOR]

Faults in the rock mass of dam foundation are crucial in controlling dam deformation and stability. In particular, long‐term stability of dam foundation is an important factor for the safety of dam operations. The rock in the foundation of Dagangshan hydropower station is mostly granite, and there are many diabase dikes distributed in granite. Geological survey indicates that many faults exist along the interfaces between granite and diabase. Lots of diabase were metamorphosed to chlorites, which have very low strength. In order to investigate the deformation of faults in diabase dikes under long‐term loading, in situ shear creep tests were performed to estimate the creep performance of a fault. The shear creep displacement and the influence of displacement history of the specimen during multi‐level loading tests were measured and analyzed. The isochronous stress‐strain method was used to determine the long‐term strength of the fault in shear creep tests. Considering the instantaneous damage and strain softening, a new viscoelastic‐plastic softening creep model was proposed to describe the shear creep behavior of the fault. Comparisons confirmed that this creep model is capable of describing the shear creep behavior of the fault and the creep parameters were estimated accordingly using this model. [ABSTRACT FROM AUTHOR]

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Metamorphic rocks are widely exposed in the Pingxiang area of the western area of the Jiangxi province; the types of metamorphic rocks are various and complex, and the regional dynamic pressure metamorphic rocks are the main types present. According to a preliminary study of metallogenic trace elements on different metamorphic rocks in this area, the contents of Au, Ag, Fe, Pb, and Zn in the Pingxiang area are generally higher than those of the crustal clark, while the content of Zn is twice as high and Cu is relatively lower than that of crustal clark. In addition, Au and Ag contents in metamorphic sandstone are higher than the crustal clark value. The contents of Cu, Pb, Zn, V, Co, Ni, and other elements in argillaceous rocks vary greatly. Au, Ag, and Sn content is higher in the phyllite, at times even higher than the earth's crust clark values and several times higher than that of sedimentary rocks of eastern China. [ABSTRACT FROM AUTHOR]

This study presents the results of a more than 10-year-long field investigation and remote sensing monitoring campaign of a highly active deep-seated rock slide located in a glacial to periglacial environment (Bliggspitze, Tyrol, Austria). Data concerning (i) the terrain surface displacements based on imagery (webcam time-lapse, ortho-images) and both terrestrial and airborne laser scanning, and (ii) the geological-structural and geomorphological situation were analysed to develop a geological-geometrical model of the rock slide and to study the temporally variable activity behaviour and the formation of individual rock slide slabs. Results clearly show that at least seven rock slide slabs were formed at different times and under different slope stability conditions. Some of these rock slide slabs were displaced at slow to moderate velocities and reached scarp offsets of several tens of metres, whereas other, shallower slabs collapsed and formed extremely rapid rock falls and avalanches. Generally, the rock slide is affected by rock mass cataclasis, fracturing and loosening, which in turn cause extensive mass loss accompanied by debris accumulation at lower parts of the slope. The cause for the development of the Bliggspitze rock slide is poorly understood. However, there are clear indications that permafrost degradation and/or glacial retreat, particularly at the foot of the slide, during the recent decades may have adversely affected the slope stability situation. [ABSTRACT FROM AUTHOR]

Veins and dikes are often oriented subparallel to the axial surfaces of folds in the adjacent layered or foliated rocks. This implies an awkward situation, since veins would lay in planes close-to-parallel to the maximum stretching axis. A series of geometric models have been conceived in order to gain insight into the possible mechanisms for their formation. The models are based on the analysis of a varied selection of field structures and on the review of similar structures in the existing literature. A first categorization consists on distinguishing between axial-planar veins achieved by either progressive or polyphase deformation. Five models of axial-planar veins resulting from progressive deformation are described and discussed: (1) fold-related veins associated with the standard folding mechanisms, (2) fracture arrays localized along the short limbs of folds (asymmetric fold-related veins), (3) folds associated with rotation of extension veins (vein-related folds), (4) high strain and transposition of early veins, and (5) high strain and late veins parallel to axial planar foliations (axial planar foliation-related veins). The axial planar geometry is achieved through variable amounts of progressive rotational strain, except in model 5, in which the co-planarity is acquired at the time of vein intrusion. The possibility for axial-planar veins to have developed in two distinct phases in the context of polyphase or polyorogenic tectonics has also been explored and discussed. This study contributes to a better understanding of the intriguing interplays between deformation, metamorphic and magmatic processes in orogenic belts. Image 1 • Veins oriented subparallel to the axial surfaces of folds are investigated. • Axial-planarity can be achieved by either progressive or polyphase deformation. • In progressive deformation, the structure is commonly attained by rotational strain. • A few models allow the co-planarity to be acquired at the time of vein intrusion. [ABSTRACT FROM AUTHOR]