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Carbonate rocks encompass about 15% of the exposed sedimentary sequences on the Earth. The Lesser and the Tethyan Himalayan units are sedimentary sequences in the Himalayan region that comprise carbonates along with pelites and arenites. It is critical to understand these carbonate rocks because of the impending large-scale infrastructure developments in the Himalayas. In this study, the petrographic traits and physico-mechanical properties of carbonate rock samples from the Deoban Formation, Lesser Garhwal Himalaya, India, have been attempted. The physico-mechanical behavior of carbonate rocks is governed by a variety of petrographic characteristics, such as grain size, grain shape, mineralogy, and the existence of microcracks and veins in the rock. It is also apparent that petrographical indices have a significant impact on the engineering attributes of the rocks. The association of the Uniaxial Compressive Strength (UCS), Brazilian Tensile Strength (BTS), and dry density with acoustic wave velocities (Vp and Vs) is markedly positive. In contrast to UCS with porosity, correlations between porosity and acoustic wave velocities, and porosity and tensile strength are weakly negative. The impact of grain size on UCS is more significant than that of other textural characteristics like form factor and aspect ratio. The study showed no strong correlations between acoustic wave velocities and aspect ratio, but it did uncover weak positive correlations between acoustic wave speeds and form factor, and weak negative correlations between acoustic wave velocities and grain size. [ABSTRACT FROM AUTHOR]

The effective exploitation of hydrocarbon from basement reservoirs requires an understanding of geomechanical parameters. Uniaxial compressive strength (UCS), Young's modulus (E), and Poisson's ratio (ν) are key attributes in addressing a range of geomechanical problems. The rock texture, which is chiefly dependent on the size, shape, orientation of grains, and their spatial distribution in the sample, provides valuable information about rock strength. In this study, we present the dependence of UCS on the rock texture in igneous and metamorphic basement rocks of western offshore India. A texture coefficient (TC) was calculated to quantify the rock texture, and an empirical relationship between TC and laboratory-derived UCS was standardized, which was then used to calculate UCS from TC. We also standardized new equations to calculate UCS from compressional (Vp) and shear wave (Vs) velocities using non-destructive technique (NDT). The static and dynamic values of E and ν were measured in laboratory, and new relations were standardized to calculate static from its dynamic equivalents. The results show that the dynamic values for ν are higher (approx. 22%) than the static values for all basement samples, whereas E exhibits a positive and a negative correlation between the dynamic and static values for mafic and felsic basement rocks, respectively. This study addresses the importance of rock texture in determining the UCS and the other associated elastic and geomechanical properties, which in turn will help in wellbore instability studies, planning hydrofracturing designs, and rock strength analysis of unconventional basement reservoirs of western offshore basin. [ABSTRACT FROM AUTHOR]

Pile foundation systems are used in India in many projects such as metro and railways, flyovers, and multi-story buildings. The pile transfers superstructure load to the substructure, i.e. to rock layers by means of skin resistance and end-bearing resistance. In this study, an attempt is made to observe the performance of socketed piles in soft rock. A series of socketed small-scale model pile load laboratory studies have been conducted using the loading frame. Load tests were performed on a model steel pile to calculate its axial load-bearing capability at various socket depths. An unconfined compression test was performed on pseudo-rock variations to find out the properties of the soft rock used. The results showed the ability of the drilled pile to enhance the strength of the pseudo rock. An attempt was also made to calculate the optimum depth for the socketed pile in soft rock. [ABSTRACT FROM AUTHOR]

Reservoir geomechanical studies play a decisive role in identifying wellbore instability and weak zones in offshore petroleum reservoirs. In this study, an integrated workflow developed with 1D Mechanical Earth Models (1D MEM), uniaxial compressive strength and swelling tests using well logs, drilling, and core data of production and exploratory wells from the North-Heera field, Mumbai offshore, India. Lithology-based correlations are utilized for calculating continuous profiles of rock mechanical properties by taking well logs as a primary source of input. Insights of fracture gradients and stresses are generated by interpretation of the pore pressure. UCS created from the well logs shows the low value of 15 MPa and high Poison's ratio of 0.38–0.45. Fracture pressure analysis of the wells specifies the lower fracture initiation pressures at 300 m are 5ppg–15ppg, which are shale and clay formation. Shale swelling tests are performed to know the hydration properties of shales present at shallow depths. The core samples' loading tests' results are very close to the UCS models constructed from the well logs. The combined analysis examines fracture pressures around wellbores, hydration of shales, weak zones identification, and wellbore instability. [ABSTRACT FROM AUTHOR]

The natural and cut slopes of a segment of the Dharasu-Uttarkashi Roadway (NH-108), located in the Lesser Himalayan Zone in India, have been studied for the first time adopting a multi-parametric integrated approach in terms of (1) distribution of magnitude of natural slope (2) engineering geological properties of intact rocks and rock masses, (3) kinematic analysis of slopes, (4) documentation of existing slope failures (5) rock- microstructural implications and (6) multiple geomechanical classification of slopes. Assessment of stability of slopes based on the combined study of the above parameters has been performed for twelve locations (L1−L12) on the road-cut sections where the slopes mostly have not yet failed. Magnitude of natural slopes overlooking the road section attains peak slope class of 41°−50°. Kinematic analysis characterizes the intact slopes in the above locations to possess conditions of wedge and toppling modes of failure, either in single or as combined. Existing failed slopes conform to combinations of planar, wedge, toppling and shallow circular failures. Rock microstructural study reveals development of strong shear-strength-weakening foliation anisotropy in the phyllites and schistose quartzites of the slopes that evidently serve as avenues of groundwater percolation and seepage and can promote failure along water-soaked foliation planes that 'day-light' on the road-cut slopes at locations L1, L8 L9 and L10. Based on Geomechanical classification systems applied to slopes including Continuous Slope Mass Rating, Q-Slope and Hazard Index, new stability charts have been developed that classify the slopes at each location to be one of the three types: severely unstable, unstable or stable. Based on the new stability charts, road-cut slopes at all twelve locations were found to be unstable and slopes at three locations − L7, L8 and L10 were observed to be severely unstable, particularly hazardous and require immediate mitigation. Highlights: Multiparametric integrated approach was adopted to study instability of road-cut slopes in the Dharasu-Uttarkashi highway for the first time New stability charts were developed combining three Geomechanical slope mass classification systems viz. the C-SMR, Q-Slope and Hazard Index. The impact of rock microstructure induced foliation anisotropy and water seepage along foliations and fractures on stability of slopes has been recognized. The stability of road-cut slopes were evaluated using newly developed stability charts and rock microstructure. [ABSTRACT FROM AUTHOR]

Seismic inversion is a geophysical technique used to estimate subsurface rock properties from seismic reflection data. Seismic data has band-limited nature and contains generally 10–80 Hz frequency hence seismic inversion combines well log information along with seismic data to extract high-resolution subsurface acoustic impedance which contains low as well as high frequencies. This rock property is used to extract qualitative as well as quantitative information of subsurface that can be analyzed to enhance geological as well as geophysical interpretation. The interpretations of extracted properties are more meaningful and provide more detailed information of the subsurface as compared to the traditional seismic data interpretation. The present study focused on the analysis of well log data as well as seismic data of the KG basin to find the prospective zone. Petrophysical parameters such as effective porosity, water saturation, hydrocarbon saturation, and several other parameters were calculated using the available well log data. Low Gamma-ray value, high resistivity, and cross-over between neutron and density logs indicated the presence of gas-bearing zones in the KG basin. Three main hydrocarbon-bearing zones are identified with an average Gamma-ray value of 50 API units at the depth range of (1918–1960 m), 58 API units (2116–2136 m), and 66 API units (2221–2245 m). The average resistivity is found to be 17 Ohm-m, 10 Ohm-m, and 12 Ohm-m and average porosity is 15%, 15%, and 14% of zone 1, zone 2, and zone 3 respectively. The analysis of petrophysical parameters and different cross-plots showed that the reservoir rock is of sandstone with shale as a seal rock. On the other hand, two types of seismic inversion namely Maximum Likelihood and Model-based seismic inversion are used to estimate subsurface acoustic impedance. The inverted section is interpreted as two anomalous zones with very low impedance ranging from 1800 m/s*g/cc to 6000 m/s*g/cc which is quite low and indicates the presence of loose formation. [ABSTRACT FROM AUTHOR]

Under certain suitable geological conditions, anthropogenic seismicity due to gold/coal mining, geothermal and natural gas/oil production, filling of artificial water reservoirs, and high-pressure fluid injection has been reported globally. The reservoir-triggered seismicity (RTS) is most prominent, having been reported from hundreds of with at least five sites where earthquakes exceeding M 6 occurred, claiming human lives and destruction of properties. The most important correlate for RTS to occur is the height of water column in the reservoir. Certain common characteristics of the RTS sequences have been identified, which discriminate them from normal earthquake sequences. Factors influencing RTS include the highest water levels reached in the reservoir, duration of the retention of high-water levels and rate of loading/unloading. The mechanism of RTS is reviewed. The absence of knowledge of physical properties of rocks and fluids in the fault zone does not permit us to comprehend the RTS mechanism. Koyna, India, is found to be a very suitable site for such investigations as the earthquakes have been occurring in a small region of 20 × 30 km, at shallow depths (mostly within 8 km), with no other seismic source in the vicinity, and the region being accessible for all kinds of observation and investigations. The suitability of Koyna for setting up of a deep borehole laboratory was discussed during International Continental Drilling Program (ICDP) workshop in 2011 and accepted. Suggestions were made for some additional scientific works, which were completed during 2011–2014. The second ICDP workshop in 2014 approved of going ahead. A 3-km-deep Pilot Borehole has been completed in the vicinity of Donachiwada fault that hosted the main 10 December 1967 M 6.3 earthquake and several earthquakes of M ~ 5. The investigations being carried out are providing the necessary input to set up the proposed ~ 7-km-deep borehole laboratory. In this article, an overview of RTS globally and at Koyna, India, specifically is focused. Article Highlights: Global review of the reservoir-triggered seismicity (RTS) sites Factors influencing RTS, their common characteristics and mechanism Continued seismicity at Koyna, India, and near-field studies [ABSTRACT FROM AUTHOR]

Physical properties of rocks have significant engineering value. Compressive strength and density of rocks are used in many rock mechanics related studies pertaining to civil and mining activities, stability of the excavations and estimation of the support required. In addition, rocks like granite are used as a building material and are encountered in many civil and infrastructure projects. However, these properties vary with increase or decrease in their temperature. A host of data exists on heat treatment of different rocks. In order to augment such studies and to further the know-how in this discipline, a comprehensive analysis of 56 samples of two types of granites from India was taken up in this study. The tests for compressive strength and density with increase in temperature from 35°C to 600°C were devised and conducted. The results revealed that the behaviour of two groups of the granite varied in a noticeable range on a linear scale. A reduction of 45% to 49% in strength from room temperature to 600°C in the two types of granites points to the loss of strength with increasing temperature. A reduction of 4.3% to 6.3% in density of the samples on heating can be considered to be mild. The rearrangement of grains, loss of water content initially and increase in volume on further heating are considered to be the major reasons for reduction of such physical properties in a linear manner. Colour changes have also observed in the heating process which needs to be explained in future. [ABSTRACT FROM AUTHOR]

Rock slope projects are often available with insufficient investigation data for rock properties due to involvement of high costs, manual efforts, geological complexities, etc., in testing. Support estimation performed by traditional approaches for slope failure mitigation could be highly inaccurate due to inaccuracies in the estimated statistics of properties. This article describes a computationally efficient re-sampling stochastic framework to overcome this issue by coupling the Advanced Re-Sampling Reliability Approach (ARRA) with deterministic and Target Reliability Approach (TRA) to estimate the required support for rock-slides mitigation with limited data. The proposed methodology was demonstrated for the support design to mitigate two massive rockslides along a rockslide-prone highway, i.e., Rishikesh-Badrinath National Highway (NH-58) in India. It was concluded that the limited data invokes uncertainties in the statistical parameters (mean and standard deviation) and distributions of properties. Support estimated using traditional approaches with the inaccurate statistics of input properties can result in inaccurate support estimates in the presence of insufficient data. Proposed methodology couples ARRA with traditional methods and evaluates the final support design by quantifying the uncertainty in the reliability index induced by the statistical uncertainties of input properties statistics. This improves the overall accuracy, efficiency, and the designer's confidence in the estimated support. [ABSTRACT FROM AUTHOR]

The Uttarakhand Himalaya which comprises of the Garhwal and Kumaon Himalaya lies in the central seismic gap region of India. Strong motion networks have been installed separately in the Garhwal and Kumaon Himalaya under various sponsored research projects funded by the Department of Science and Technology (DST) and Ministry of Earth Sciences (MoES). These networks have recorded several near field earthquakes in the recent past. Recorded data from these networks have been utilised to study the crustal attenuation characteristics of these two regions. The crustal attenuation characteristics of medium can be directly estimated from the frequency dependent quality factor 'Q'. Estimation of shear wave quality factor, coda wave quality factor and attenuation relations have been made by using same methodology in the data set obtained separately from these two regions. It has been found that there is a substantial difference in the attenuation characteristics of the crustal rocks in these two regions. Since shear wave attenuation has a close relation with the shear wave velocity, therefore, the shear wave velocity has been estimated at various locations of the Garhwal and Kumaon Himalaya by both active and passive methods. It has been found that the average shear wave velocity of crustal rocks in the Garhwal Himalaya is comparatively higher than that in the Kumaon Himalaya which clearly support the high attenuation property of the crustal rocks in the Kumaon Himalaya compared to the Garhwal Himalaya. [ABSTRACT FROM AUTHOR]

Lower Gondwana Kommugudem Formation of the Krishna‐Godavari (KG) Basin in the eastern coast of India records the deglaciation sequences of the Early Permian and is characterized by well‐preserved sandstone—shale—coal cyclothems. Kommugudem shales from six deep borewells of the KG Basin were studied for the organic petrological and geochemical compositions. The objective was to elucidate its source rock properties and depositional settings, which provide significant insights on the shifts in the Gondwanan palaeoenvironment and its climatic controls during the Early Permian. Maceral identification reveals the abundance of vitrinite that is distinctive to organic‐rich Permian Gondwana sediments. SiO2 enrichment with the dominance of quartz and clay minerals suggests moderate to strong weathering with palaeoclimate shift from cold, arid to hot, and semi‐arid during the Early Permian. The occurrence of higher short and mid‐chain alkanes with predominant n‐C18 and important biomarker ratios suggest a transitional fluvio‐marine environment of deposition, which is also supported by the enrichment of redox‐sensitive trace elements. Prevailing anoxia enhanced the preservation of organic matter, despite reduced primary productivity, as indicated by low P/Ti ratios. A depleted δ13Corg (mean = −21.55‰) in the shales, distinct to the interglacial period, reflects the changes in pCO2 of the Early Permian atmosphere. Sedimentary biomarkers, carbon isotopes, and trace elements explicate the palaeoceanographic conditions and sea‐level changes, indicative of marine influence in the dominantly fluvial regime. The deposition and preservation of organic‐rich sediments under anoxic (possibly euxinic) water‐column took place, forming the prolific Pre‐trappean Lower Gondwana Kommugudem source rock in the KG Basin. [ABSTRACT FROM AUTHOR]

Petrography and rock magnetic properties of the Dalma volcanics (DV) and associated meta-sediments of Singhbhum mobile belt (SMB) are presented to describe magnetic grain size and Fe-Ti oxide mineralogy of the volcano-sedimentary sequence. Petrography revealed the presence of Ti-magnetite, hematite, ilmenite and pyrite in quartz-biotite-sericite-muscovite schists, quartzites, and volcanic rocks. The average value of magnetic susceptibility (χ) is 5.6 × 10−7 m3/kg, anhysteretic remanent magnetization (ARM) is 2.25 × 10−5 Am2/kg, saturating isothermal remanent magnetization (SIRM) is 403.33 × 10−5 Am2/kg, soft IRM is 240.2 × 10−5 Am2/kg, hard IRM is 77.56 × 10−5 Am2/kg, and natural remanent magnetization (NRM) is 54.1 mA/m. The central tendency of the inter-parametric ratio ARM/χ is 0.06 kAm−1, SIRM/χ is 111.04 kAm−1 and S-ratio is 0.8. Based on results, magnetic mineralogy indicated that the bulk magnetic carrier is stable single domain (SSD) or pseudo single domain (PSD) grains of Fe-Ti oxides with minor iron sulphides such as pyrite, greigite and pyrrhotite. Petrography and rock magnetic studies suggest that the magnetic carriers are chiefly secondary in origin and the NRM is modified over time. [ABSTRACT FROM AUTHOR]

One of the major aspects of rock‐physics forward modelling is to predict seismic behaviour at an undrilled location using drilled well data. It is important to model the rock and fluid properties away from drilled wells to characterize the reservoir and investigate the root causes of different seismic responses. Using the forward modelling technique, it is possible to explain the amplitude responses of present seismic data in terms of probable rock and reservoir properties. In this context, rock‐physics modelling adds significant values in the prospect maturation process by reducing the risk of reservoir presence in exploration and appraisal phases. The synthetic amplitude variation with offset gathers from the forward model is compared with real seismic gathers to ensure the fidelity of the existing geological model. 'Prospect A' in the study area has been identified from seismic interpretation, which was deposited as slope fan sediments in Mahanadi basin, East Coast of India. The mapped prospect has shown class‐I amplitude variation with offset response in seismic without any direct hydrocarbon indicator support. The existing geological model suggests the presence of an excellent gas reservoir with proven charge access from the fetch area, moderate porosity and type of lithology within this fan prospect. But, whether the seismic response from this geological model will exhibit a class‐I amplitude variation with offset behaviour or 'dim spot' will be visible; the objective of the present study is to investigate these queries. A rock‐physics depth trend analysis has been done to envisage the possibilities of class‐I reservoir in 'Prospect A'. Forward modelling, using a combination of mechanical and chemical compaction, shows the synthetic gas gathers at 'Prospect A', which are class I in nature. The study has also depicted 2D forward modelling using lithology and fluid properties of discovery well within similar stratigraphy to predict whether 'dim spot' will be seen in seismic. The estimated change in synthetic amplitude response has been observed as ∼5% at contact, which suggests that the changes will not be visible in seismic. The study connects the existing geological model with a top‐down seismic interpretation using rock‐physics forward modelling technique to mature a deep‐water exploratory prospect. [ABSTRACT FROM AUTHOR]

Koyna region in western India experienced more than 1,00,000 earthquakes of different magnitudes (M ~ 1.0–6.3) in the past five decades. Earthquakes in this region are believed to be triggered by a change in fluid pressure due to the percolation of the reservoir (Koyna and Warna reservoir) water into the subsurface. A drilling program was set up by the Ministry of Earth Sciences, India and International Continental Scientific Drilling Program (ICDP) to study the deep subsurface lithology, structure, thermal attributes, etc. as the area is covered by ~ 950 m of thick Deccan basalts. This paper reviews all the hypotheses proposed by earlier workers to explain the mechanism of reservoir trigger causing earthquakes and summarizes such theories to a simple generic model. Slip tendency analysis was further carried out based on the proposed model to explain the dependence of fault slip on fault geometry, rock mechanical properties, stress and fluid gradients. Finally, faults at various depths were characterized (favourably oriented, unfavourably oriented and severely misoriented) based on their potential to go into failure. [ABSTRACT FROM AUTHOR]

This article presents the challenges encountered during the stability analysis and stabilization of two Himalayan rock slopes supporting the Chenab Railway Bridge in India, which will be the highest railway bridge in the world after completion. Owing to the importance of the project, extensive geological investigations, in situ and laboratory tests were carried out using conventional and advanced methods to evaluate various intact rock, rock joints, rock mass properties and rock mass quality present at the site. Once the conclusive results were made regarding these properties, stability of slopes were evaluated against both structurally controlled and stress-controlled failures using the developed probabilistic approach due to the presence of high variability in intact rock, rock mass and rock joints properties. It was observed that while the slopes were stable against stress-controlled failures, the possibility of structurally controlled failures exists as observed in the probabilistic approach in which the conventional deterministic approach was not able to detect. Different stabilization measures, i.e. rock bolts, slope flattening, grouting, drainage and shotcreting, were designed at the site to reduce the probability of failures for the slopes, deformability of rocks present due to cavities and high aperture joints, shallow block failures along the slope surface and pore-pressure build-up. To check the efficiency of the stabilization measures, cross-hole seismic tomography is carried out at the site and further in situ measured displacements are compared with the displacements estimated using the developed probabilistic approach. The case study used in this paper is a real-time ongoing bridge project of global interest and the data and analysis presented will be of great benefit to the researchers and practitioners working on similar problems. [ABSTRACT FROM AUTHOR]

India is the leading producer of sheet mica and a major part of this is exported. Nellore mica belt is the largest mica-producing area covering part of Nellore district in Andhra Pradesh, India. As most of the mines are old and privately operated, they are developed and operated purely based on local experiences. In this article, we highlight the problems associated with the present mica-mining practices in the Nellore mica belt, and scientific approaches that have been adopted for fixing different parameters associated with mica extraction. Based on detailed field study, geo-mechanical data and tested rock properties, extensive numerical modelling is done to suggest the best possible method of mining for safe and sustainable mica extraction from the area. [ABSTRACT FROM AUTHOR]

Probabilistic methods are the most efficient methods to account for different types of uncertainties encountered in the estimated rock properties required for the stability analysis of rock slopes and tunnels. These methods require estimation of various parameters of probability distributions like mean, standard deviation (SD) and distributions types of rock properties, which requires large amount of data from laboratory and field investigations. However, in rock mechanics, the data available on rock properties for a project are often limited since the extents of projects are usually large and the test data are minimal due to cost constraints. Due to the unavailability of adequate test data, parameters (mean and SD) of probability distributions of rock properties themselves contain uncertainties. Since traditional reliability analysis uses these uncertain parameters (mean and SD) of probability distributions of rock properties, they may give incorrect estimation of the reliability of rock slope stability. This paper presents a method to overcome this limitation of traditional reliability analysis and outlines a new approach of rock mass characterization for the cases with limited data. This approach uses Sobol's global sensitivity analysis and bootstrap method coupled with augmented radial basis function based response surface. This method is capable of handling the uncertainties in the parameters (mean and SD) of probability distributions of rock properties and can include their effect in the stability estimates of rock slopes. The proposed method is more practical and efficient, since it considers uncertainty in the statistical parameters of most commonly and easily available rock properties, i.e. uniaxial compressive strength and Geological Strength Index. Further, computational effort involved in the reliability analysis of rock slopes of large dimensions is comparatively smaller in this method. Present study also demonstrates this method through reliability analysis of a large rock slope of an open pit gold mine in Karnataka region of India. Results are compared with the results from traditional reliability analysis to highlight the advantages of the proposed method. It is observed that uncertainties in probability distribution type and its parameters (mean and SD) of rock properties have considerable effect on the estimated reliability index of the rock slope and hence traditional reliability methods based on the parameters of probability distributions estimated using limited data can make incorrect estimation of rock slope stability. Further, stability of the rock slope determined from proposed approach based on bootstrap method is represented by confidence interval of reliability index instead of a fixed value of reliability index as in traditional methods, providing more realistic estimates of rock slope stability. [ABSTRACT FROM AUTHOR]

Abstract H 2 O in the mantle is of great interest in the fields of geochemistry and geophysics on account of its significant influence on the melting and physical properties of mantle rocks. The abundance of water in derivative mantle melts beneath mid-ocean ridges can provide important insights into the abundance and distribution of water in the mantle. For this study, we analyzed the H 2 O, CO 2 , and major- and trace-element contents in basaltic glass samples collected from the slow-spreading Carlsberg Ridge from 59 ° E to 66 ° E in the India n Ocean. All of the studied samples are found to be normal mid-ocean ridge basalt (N-MORB) in composition. The H 2 O concentrations range from 0.13 to 0.29 wt% with a mean value of 0.22 ± 0.10 wt%. Along the ridge from 59 ° E to 66 ° E, H 2 O/La, H 2 O/Ce, and trace-element ratios show systematic variation whereby H 2 O/La and H 2 O/Ce ratios increase with longitude, whereas K 2 O/Ti 2 O and (La/Sm) N decrease. The Nb/U (36.4– 42.3) and Ce/Pb (17.6– 20.8) ratios of the samples are lower in comparison with typical values reported for global MORBs and OIBs (ocean island basalts) (Nb/U = ca. 47, Ce/Pb = ca. 25). In addition, the ratios of incompatible trace elements display wide variation (e. g., Ba/La and Nb/Zr values of 2.04– 6.02 and 0.02– 0.07, respectively). The limited variation in the degree of mantle melting cannot yield the observed level of variation in the basaltic glass trace-element ratios. Therefore, we suggest that the mantle source of the studied MORBs has been mixed with subducted oceanic/continental crust and that mantle heterogeneity is the main factor responsible for the chemical variation of MORB along the Carlsberg Ridge axis from 59 ° E to 66 ° E. Highlights • H 2 O content range from 0.13 wt% to 0.29 wt% in MORB from the Carlsberg Ridge. • Incompatible trace element ratios show systematic variation along the ridge from 59 ° E to 66 ° E. • Mantle heterogeneity is the main factor responsible for the chemical variation of MORB along the ridge. [ABSTRACT FROM AUTHOR]

Identifying dispersed organic matter (DOM) types present in shales with the help of a standalone scanning electron microscope (SEM) is often difficult to accomplish. Although reflected light microscopes are useful in identifying the organic matter type, they typically achieve magnification of 500× but cannot magnify beyond 2500×. Optical-electron correlative microscopy, a new technique that has recently gained popularity, involves first identifying the type of organic matter under an optical microscope before finding the same particle under SEM for a closer look at its microstructure. In this study, marginally mature in the early oil window (n = 2) and late mature at the boundary of oil window and condensate wet gas window (n = 2) shales from the Rajmahal (RM) and Jharia (Jh) Basins of India, respectively, were compared using the correlative technique. The source rock properties and the mineralogical composition of the shale samples were first evaluated using Rock-Eval 6 and X-ray diffraction (XRD) analysis, respectively. During electron microscopy analysis, SEM parameters such as brightness/contrast levels, acceleration voltage, and working distance were adjusted to make the DOM and mineral matter present in the shale samples clearly distinguishable from one another. At the acceleration voltage of 15 kV under backscattered (BSE)scanning mode and 10 kV under secondary electron (SE2) scanning mode the DOM and mineral matter were clearly discernible in both RM and Jh shale samples. However, without the correlative technique it was challenging to distinguish between the individual maceral types present in the shale samples, as all appear dark under SEM. Mineral matrix characterization using the correlative technique and energy dispersive spectroscopy (EDS) analysis enabled clay minerals in cell lumens of semifusinite to be identified in both RM and Jh shales. Under SEM, pyrite was associated with vitrinite in Jh shales, which was difficult to notice under the optical microscope. The correlative technique enabled the analysis of the organic matter-hosted porosity under SEM at higher magnifications. The sporinite in the RM shale samples was found to have SEM visible pores, whereas no pores were observed to be present within the sporinite in Jh shales. Both vitrinite and inerinite macerals observed in RM and Jh shale samples lacked any SEM-visible pore structure. The pores were found to be more obvious at a 5 kV acceleration voltage than at 10 kV in SE2 scanning mode. • First application of optical-electron correlative microscopy on Indian shales. • Identification of organic matter type under electron microscope using correlative technique. • 'Protocol' for reliable identification of organic and inorganic matter under electron microscope. • Association of organic matter and inorganic matter in shales. [ABSTRACT FROM AUTHOR]

The Puga geothermal reservoir is located in the south-eastern part of Ladakh (Himalayan region, India), and it is providing encouraging results towards heat production. We proposed an improved mathematical model for the fully coupled thermo-hydro-geomechanical model to examine the variations in the Puga geothermal reservoir at between 4500 m from the surface with three, four, and seven hydraulic fractures in the reservoir along with four-spot, five-spot, seven-spot, and nine-spot well patterns. The distribution of low-temperature region is found in each fracture, and it is low in the reservoir with seven hydraulic fractures. The changes in the rock and fluid properties are examined effectively. Thermal strain is dominated in the fractures, and mechanical strain is impressive in the rock matrix; it is dependent on the number of hydraulic fractures and well patterns. The thermal performance of the Puga reservoir is examined with the geothermal life, reservoir impedance, and heat power and found that the number of hydraulic fractures and well patterns are influenced significantly in the multistage modeling of the Puga geothermal reservoir. Thus, the proposed mathematical model can effectively evaluate and predict the variations that occur in the Puga geothermal reservoir with dynamic rock, fracture, and fluid properties. • Mathematical model improved by including the dynamic variations in the rock, fracture, and fluid properties. • Examined the performance of Puga geothermal reservoir with different well patterns. • Multistage model was proposed to the development of Puga geothermal reservoir. [ABSTRACT FROM AUTHOR]

This paper describes a comprehensive approach to improved lithofacies characterization using the simultaneous pre-stack inversion, Bayesian classification, and multiple-point geostatistics. This integrated workflow provides an enhanced lithofacies characterization by reproducing the continuity of geological facies in the meandering-fluvial sandstone reservoir from Upper Assam, India. The simultaneous pre-stack inversion provides the rock elastic properties of the reservoir, such as P- impedance, s-impedance, density, and V P /V S ratio. Next, the probabilistic modeling approach of Baye's theorem is used to integrates seismic elastic properties with well log lithofacies identified from the cross-plot analysis for probability volumes of lithofacies. Finally, the multiple-point geostatistics based on the Single Normal equation Simulation algorithm is used to generate the improved lithofacies model by constraining of the lithofacies probability volumes (soft data) and well logging data (hard data). These results were compared with the Bayesian lithofacies classification and proved that the adopted method had successfully improved the continuation of the reservoir lithofacies by reproducing the lithofacies, hence an improvement in the reservoir characterization. • An integrated workflow is used that provides better lithofacies characterization. • Estimation of seismic elastic properties using simultaneous prestack inversion. • Prediction probability volumes of lithofacies by Bayesian classification. • The SNESIM algorithm applied with constrained by probability volumes and well data. • Improved lithofacies volume generated by the multiple-point geostatistics. [ABSTRACT FROM AUTHOR]

The Panna Formation was deposited during the Paleocene period and is the oldest hydrocarbon-bearing tertiary sedimentary unit in the Western Offshore Basin (WOB). It is also believed to be the source rock above which hydrocarbons pools in. In the recent years, exploration activity in the Panna Formation has significantly increased, owing to its own potential hydrocarbon pools. The primary challenge encountered when drilling through the Panna Formation include well flows, mud losses, stuck pipe events, and limitation of using logging while drilling (LWD) tools due to high temperature which makes it tough for real-time monitoring without LWD. The stable-mud-weight window becomes narrow (<2 ppg), and the pore pressure seems to vary considerably from near-hydrostatic to ∼17.5ppg mud weight equivalent (EMW). This overpressure zone is correlated with relative thickness of Panna Formation and well locations in the region. The pore pressure ramp is observed to start either from the bottom of the Lower Bassein or Devgarh Formations (formation overlying Panna) or 120m–150 m inside the Panna Formation itself. Additionally, the transition of pore pressure from near-hydrostatic to overpressure zone is quite sudden. As a result, when the lithological seal isolating the high-pressure compartment is broken during drilling, well flow is encountered. In the process of well control, mud weight is increased to corresponding shut-in-drill-pipe pressure (SIDPP), which sometimes causes mud losses in the overlying formations because of insufficient fracture gradient. To delineate the area with overpressure and identify its mechanism, a comprehensive geomechanics study with lithology types has been carried out across 5 main blocks of WOB. The study integrates petrophysical, geological, and drilling information to give insight into the overpressure mechanism and safe drilling solutions through this complex setup. The pore pressure, rock mechanical properties, and stress profiles have been estimated in multiple wells to build robust geomechanical models and estimate the most stable mud weight windows. This study establishes the Type-II overpressure phenomenon with the help of crossplots between effective stress with velocity, density with compressional slowness, and pressure with porosity. There is a clear shift in the geothermal gradient associated with the overpressure interval. The casing policies for safe drilling have been discussed in different scenarios. The analysis has also outlined the occurrence of overpressure in triangular area adjacent to the Bombay High Oilfield. [ABSTRACT FROM AUTHOR]

[Display omitted] • Permian shales of India show distinctive oil and gas generation potential. • Shale reactivity is closely linked to kerogen type and thermal maturity. • Multi-heating-rate pyrolysis with kerogen petrography explain kinetic variations. • Contact metamorphism of organic-rich shales lowers their residual reactivity. • A substantial range of shale reactivity is associated with different kerogen types. Reconstructing hydrocarbon generation history for predicting the onset of oil/gas generation is an important step for petroleum system modeling, and for the purpose, source rock kinetic analysis is required. For evaluating the controlling factors that influence shale rock kinetics, Lower Permian Barren Measures Formation shales from two Damodar Valley sub-basins, India are evaluated in terms of their source rock properties and kinetics. Rock-Eval open-system programmed-pyrolysis is applied at heating-rates of 5, 15 and 25 °C/min to determine the shales' reaction kinetics. The results substantiate the importance of petrographic composition in controlling the shale source rock potentiality and reaction kinetics. North Karanpura Basin shales are shown to have liquid hydrocarbon generation potential, owing to their richness in type I-II kerogen. In contrast, the Raniganj Basin shales are richer in type III-IV kerogen and gas prone. The shales are grouped in distinct clusters on an E versus LnA (activation energy versus pre-exponential factor) kinetic distribution. The type I-II kerogen-bearing samples display the highest reactivity, while the type III-IV kerogen-bearing shales, and those with higher thermal maturity levels, display lower reactivity. The least reactivity is associated with a heat-altered shale from the Raniganj Basin, which also displays the highest Rock-Eval S2 T max , S4 T peak , and lowest HI (hydrogen index) value. This indicates the significant impact of igneous intrusions by removing hydrocarbons from shales and lowering their residual reactivity. The dominance of type I-II kerogen and presence of framboidal pyrite in the North Karanpura Basin shales also indicates some marine influence during their deposition. [ABSTRACT FROM AUTHOR]

This study aims to investigate the hydrocarbon potential and storage capacity of five shale samples collected from Barren Measure Formation of Damodar Valley in India. Characterization of source rocks was performed using rock eval pyrolysis and, pore volumes were measured using the MICP and low pressure CO 2 adsorption methods. Results of pyrolysis show excellent TOC content ranging between 4.24% and 9.78%. Variation in T max values from 437 to 447 °C indicates that the thermal maturity is within the oil window range. Values of HI (110–211 mg HC/gm TOC) and OI (3–36 mg HC/gm TOC) indicate a mixture of Type II and Type III kerogen which, can be a good source rock for oil and gas. Pore spaces present within the rock act as storage for the generated hydrocarbons. Pore volume and pore-size are the major influential factors for the storage and production capacities of hydrocarbon reservoirs. Results of MICP experiments show high porosity values (≥13%) for all the samples. Macro and mesopore volumes calculated using the MICP method are varying within the range between 0.074 and 0.17 cc/mg. Low-pressure adsorption using CO 2 gas was adopted to estimate the micropore volume of the samples. The volumes of micropores are varying between 2.3 cc/gm and 4.1 cc/gm. Pore volumes measured using both techniques were arithmetically summed up to calculate the total pore volume of the samples. Source rock characters shows a change in trend below 475 m. High pore volumes indicate a good storage capacity for the studied samples. Having the potential to be a good source rock for hydrocarbon and also containing higher pore volume to store hydrocarbon, Barren Measure shale can be considered as a good source as well potential hydrocarbon reservoir rocks among Indian shale formations. • Rock eval pyrolysis, MICP, and LP CO 2 -adsorption were carried out on Barren Measure shale samples. • Type II or Type III or mixed of both kerogen types are present. • Variable pore size distribution observed. • Micropore volume is higher than macro and mesopore volumes. • Source rock properties and micropore volumes show significant change below 475 m. [ABSTRACT FROM AUTHOR]

The causes of organic-rich sediments in contact with the perennial oxygen minimum zone (OMZ) on the continental slope off western India have been debated extensively, largely in relation to two main controlling factors: high productivity in the water column and enhanced preservation due to oxygen deficiency in bottom waters. In order to better understand the causes for organic-richness in sediments, three sediment cores recovered from the upper OMZ (UOMZ) at 500 m, middle OMZ (MOMZ) at 812 m and lower OMZ (LOMZ) at 1168 m water depths from the continental slope off Ratnagiri (west coast of India) were investigated for their organic matter (OM) and their stable isotopic (δ13C and δ15N), geochemical and rock magnetic parameters. The bottom water dissolved oxygen (DO) concentrations were 0.4 μM, 5.8 μM and 25 μM at UOMZ, MOMZ and LOMZ core locations respectively. Maximum age of the sediments recorded in these cores was 4500 yrs BP. Sedimentation rates in the upper sections of the UOMZ and MOMZ cores were lower (5 to 7 cm/kyr) than that in the LOMZ core (20 cm/kyr). Organic carbon (C org) content was highest (upto 7.9%) in the UOMZ core than in other cores (upto 4.9%). Enriched δ13C org values (−18.6 to −16.8‰) in the MOMZ core were indicative of reworked organic matter in the lower section. The δ15N values ranged from 4 to 7.4‰, however, with lower values for the reworked sediments at MOMZ site. The parameters representing productivity and redox conditions increased towards core top in all the cores, whereas terrigenous parameters decreased towards core top in the MOMZ and LOMZ cores. Despite the MOMZ core was always in OMZ in the lower section, very low C org content coinciding with high terrigenous and reworked OM were deposited in the sediments prior to 1700 years BP. Rock magnetic properties indicate that the degree of diagenetic conditions varied in different sections of the cores and also among the cores within OMZ. Authigenic magnetite and authigenic uranium occurred in the lower sections of UOMZ and LOMZ cores and, authigenic magnetite in the upper sections of MOMZ core. These results suggest that productivity played an important role in organic-richness of the sediments and bottom water oxygen concentration has little effect on the preservation of OM. Besides, sedimentation rates, reworked organic matter, and topography at the core site indeed contribute on the distribution of organic matter in the Late Holocene sediments. • Three sediment cores with varying bottom water DO concentrations were studied to understand the controls on OM distribution • Bottom water DO played a minimal role in the OM preservation compared to productivity in the eastern Arabian Sea sediments • In addition, sedimentation rates, winnowing and type of OM controlled the organic-richness in the late Holocene sediments • Rock magnetic properties indicate variable degree of diagenetic conditions among the cores within the OMZ [ABSTRACT FROM AUTHOR]