Geomechanical Data Research Articles

Earth surface exchanges (ESEX) discussion of ‘Swelling and flow of expanding clays as a cause for nontectonic deformations in a glacial–interglacial environment: Holy Cross Mountains, Poland’ by E.Jurewicz, P.Karnkowski, A.Czarnecka‐Skwarek, E.Wójcik, I.Gawriuczenkow. Earth Surface Processes and Landforms2023: 1–16. https://doi.org/10.1002/esp.5609

AbstractIn a recently published report focused on the role of swelling of Triassic clays as the dominant process that led to the local steepening of competent Jurassic strata, its authors presented an opinion on the lack of evidence for the existence of the Gnieździska–Brzeziny strike‐slip fault along the contact between the Triassic and Jurassic rocks. This discussion presents the structural, geophysical, cartographic and geomechanical data indicating that the contact of Triassic and Jurassic rocks is defined by the vertical dextral strike‐slip Gnieździska–Brzeziny fault, which was formed after tilting of the beds in the Late Cretaceous. The presented evidence validates the tectonic deformation of Mesozoic rocks related to strike‐slip faulting. The dominant horizontal contraction across the fault planes within the restraining stepovers resulted in tilting of the beds, which is a well‐recognized phenomenon within the strike‐slip fault networks worldwide.

Geomechanics and Geology of Marine Terraces of the Crotone Basin, Calabria (Italy)

This study investigates the geomechanical behavior of five terrace orders in the Crotone Basin. The purpose is to understand the physical–mechanical parameters of these terraces to determine whether rock or soil mechanics principles should be applied for stability analysis. Samples were collected from each terrace following an extensive field survey. Laboratory analyses were conducted to measure pulse velocities, uniaxial unconfined compressive strength, and compressive strength with truncated conical platens. The findings revealed key physical–mechanical parameters of the rocks, which are crucial for stability assessments. The Crotone Basin, known for its mineral resources such as hydrocarbons and rock salts, has been studied geologically since before the 1950s, but there is a lack of geomechanical data in existing literature. Therefore, the results presented here are novel and provide a basis for future studies on the instability of rocky slopes composed of similar soft rock types. These results will aid in accurate geological–geotechnical model reconstructions. While the findings can be applied to similar cases, it is important to note that each analysis site, despite showing similar phenomena, is unique and requires individual investigation.

Mechanical Properties of Rock Salt from the Kłodawa Salt Dome-A Statistical Analysis of Geomechanical Data.

Rock salt is a potential medium for underground storage of energy resources and radioactive substances due to its physical and mechanical properties, distinguishing it from other rock media. Designing storage facilities that ensure stability, tightness, and safety requires understanding the geomechanical properties of rock salt. Despite numerous research efforts on the behaviour of rock salt mass, many cases still show unfavourable phenomena occurring within it. Therefore, the formulation of strength criteria in a three-dimensional stress state and the prediction of deformation processes significantly impact the functionality of storage in salt caverns. This article presents rock salt's mechanical properties from the Kłodawa salt dome and a statistical analysis of the determined geomechanical data. The analysis is divided into individual mining fields (Fields 1-6). The analysis of numerical parameter values obtained in uniaxial compression tests for rock salt from mining Fields 1-6 indicates an average variation in their strength and deformation properties. Upon comparing the results of Young's modulus (E) with uniaxial compressive strength (UCS), its value was observed with a decrease in uniaxial compressive strength (E = 4.19968·UCS2, R-square = -0.61). The tensile strength of rock salt from mining Fields 1-6 also exhibits moderate variability. An increasing trend in tensile strength was observed with increased bulk density (σt = 0.0027697·ρ - 4.5892, r = 0.60). However, the results of triaxial tests indicated that within the entire range of normal stresses, the process of increasing maximum shear stresses occurs linearly ((σ1 - σ3)/2 = ((σ1 + σ3)/2)·0.610676 + 2.28335, r = 0.92). A linear relationship was also obtained for failure stresses as a function of radial stresses (σ1 = σ3·2.51861 + 32.9488, r = 0.73). Based on the results, the most homogeneous rock salt was from Field 2 and Field 6, while the most variable rock salt was from Field 3.

Session 19. Oral Presentation for: Exploring for the Future: new geomechanical data in frontier Australian basins

Session 19. Oral Presentation for: Exploring for the Future: new geomechanical data in frontier Australian basins

Exploring for the Future: new geomechanical data in frontier Australian basins

Led by Geoscience Australia, Exploring for the Future (EFTF) is a A$225 million Australian Government program dedicated to exploring Australia’s resource potential and boosting investment. The EFTF program energy component aimed to attract industry investment by delivering a suite of new precompetitive geoscience data in prospective Australian sedimentary basins. Through EFTF, Geoscience Australia has acquired significant amounts of new geomechanical data from underexplored onshore sedimentary basins with identified hydrocarbon prospectivity, from both legacy and newly acquired samples. These data were acquired to build a better understanding of basin sediment rock properties, particularly looking at the reservoir and seal potential of postulated unconventional and conventional targets. Four major datasets are presented herein, representing prospective intervals from the Paleozoic Canning Basin of Western Australia, the Neoproterozoic-Paleozoic Officer Basin of South Australia and Western Australia, the Paleo-Mesoproterozoic South Nicholson region of the Northern Territory and northwest Queensland, and the Paleo-Mesoproterozoic Birrindudu Basin of the Northern Territory and Western Australia. Additionally, the Paleo-Mesoproterozoic McArthur Basin of the Northern Territory is represented by a small number of analyses. Tests include unconfined compressive strength tests, laboratory ultrasonic measurements, single and multi-stage triaxial tests and Brazilian tensile strength tests. These datasets are a precompetitive resource that can facilitate investment decisions in frontier regions, helping to identify elements of conventional and unconventional hydrocarbon systems as well as providing essential data to assess geological storage opportunities.

Defining the geomechanical operating limits for subsurface CO2 storage

Carbon capture and storage (CCS) is a critical component of proposed pathways to limit global warming, though considerable upscaling is required to meet emissions reduction targets. Quantifying and managing the risks of fault reactivation is a leading barrier to scaling global CCS projects from current levels of ~40 million tonnes of carbon dioxide(CO2) per year (to target levels of several gigatonnes of CO2 per year), because CO2 injection into reservoirs can result in increased pore-fluid pressure and temperature changes, which can reduce the strength of rocks and faults and induce brittle failure. This can result in induced seismicity, whilst hydraulic fracturing of seals could provide pathways for CO2 leakage. Consequently, identifying favourable geomechanical conditions (typically determined through data on pre-injection rock stress, mechanical and elastic properties, and pore-fluid pressures) to minimise deformation of reservoirs and seals represents a key challenge in the selection of safe and effective sites for CCS projects. Critically, however, such geomechanical data are typically spatially limited (i.e. restricted to wells) and mainly consist of pre-injection crustal stress orientation measurements, rather than a full 3D description of the stress tensor and related geomechanical properties. This paper reviews some key geomechanical issues and knowledge gaps (particularly those associated with data availability and limitations) that need to be understood to enable successful reservoir and seal management for CCS projects. We also highlight recent advances in multi-scale and dimensional geomechanical modelling approaches that can be used to assess sites for the secure storage of CO2 as well as other gases, including hydrogen.

Outcrops as windows to petroleum systems: Insights from the southern Bida Basin, Nigeria

The study assessed petroleum systems in the southern Bida Basin, Nigeria, focusing on the Cretaceous sediments. Reservoirs comprise Lokoja and Patti Formation sandstones, while shales, claystone, and siltstone serve as source rocks and stratigraphic traps/seals. Detailed studies delineating the key elements of the petroleum systems in the basin have not been conducted due to a lack of subsurface data. The goal of the current study was to use field observations, Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and geochemical and geomechanical data to evaluate key components of petroleum systems in the southern Bida Basin. The results presented in this investigation are intended to attain specific objectives, especially those lacking in the basin's study sections. Petrophysical analysis revealed that the Lokoja Sandstone has porosity of 37%–39.5% and moderate permeability of 23.22–42.29 mD. The Patti Formation sandstone reservoirs exhibited high porosity (38%–42%) and moderate to good permeability (31.54–66.48 mD), suggesting good potential reservoirs. SEM results revealed intragranular pores and micro-fractures in the Patti Shale, whereas the sandstone reservoirs in the Lokoja and Patti formations displayed fractures, facilitating hydrocarbon migration. Quartz was the dominant mineral in the sandstone units of both formations. XRD analysis revealed that brittle and clay minerals influenced the microstructure of Patti Shale. Geochemical analysis indicated promising petroleum potential in the Patti Shale, with a total organic carbon (TOC) content of 1.87 wt%, free hydrocarbon from kerogen (S1) of 0.41 mg/g, hydrogen index (HI) of 0.75 mg HC/g TOC, and production index (PI) of 0.17. The Patti and Lokoja formations' shale, claystone, and siltstone exhibited sealing potential, with a plasticity index of 24–35 and coefficient permeability of 2.8 × 10−4- 3.6 × 10−4 cm/s. Field studies, XRD, geochemical data, and geomechanical index values have confirmed the key components of the petroleum system, which in turn facilitate hydrocarbon generation, migration, accumulation, and entrapment in the basin.

Analysis of competition and interference mechanisms of multiple hydraulic fractures in deep-sea hydrate reservoirs in the South China Sea

Improving the fundamental theory of hydraulic fracturing in deep-sea hydrate reservoirs is of great significance in enhancing the efficiency of gas hydrate mining. In this paper, a multi-cluster fracturing model for a horizontal well was established with a three-dimensional extended finite element method and the measured geo-mechanical data from hydrate reservoirs in the South China Sea. The performance, fracture initiation, and expansion mechanisms of multi-hydraulic fractures are investigated under different fracturing sequences, hydrate saturation and cluster deployment patterns. Some interesting results have been discovered: In the case of three-cluster, the fractures produced by sequential fracturing are notably more affected by pre-existing fractures. Furthermore, the effect of fracture interference between simultaneous and sequential fracturing is reflected in the middle fracture is compressed by the fractures on its left and right sides. The increase in hydrate saturation enhances the cementing ability of the sediments and results in an increased difficulty of fracture initiation for the five-cluster simultaneous fracturing. It also results in a decrease in the geo-stress field, where the interaction between fractures plays a dominant role in the process of fracture expansion, leading to non-uniform expansion.

Rockfall Analysis from UAV-Based Photogrammetry and 3D Models of a Cliff Area

The application of Unmanned Aerial Vehicles (UAVs), commonly known as drones, in geological, geomorphological, and geotechnical studies has gained significant attention due to their versatility and capability to capture high-resolution data from challenging terrains. This research uses drone-based high-resolution photogrammetry to assess the geomechanical properties and rockfall potential of several rock scarps within a wide area of 50 ha. Traditional methods for evaluating geomechanical parameters on rock scarps involve time-consuming field surveys and measurements, which can be hazardous in steep and rugged environments. By contrast, drone photogrammetry offers a safer and more efficient approach, allowing for the creation of detailed 3D models of a cliff area. These models provide valuable insights into the topography, geological structures, and potential failure mechanisms. This research processed the acquired drone imagery using advanced geospatial software to generate accurate orthophotos and digital elevation models. These outputs analysed the key factors contributing to rockfall triggering, including identifying discontinuities, joint orientations, kinematic analysis of failures, and fracturing frequency. More than 8.9 × 107 facets, representing discontinuity planes, were recognised and analysed for the kinematic failure modes, showing that direct toppling is the most abundant rockfall type, followed by planar sliding and flexural toppling. Three different fracturation grades were also identified based on the number of planar facets recognised on rock surfaces. The approach used in this research contributes to the ongoing development of fast, practical, low-cost, and non-invasive techniques for geomechanical assessment on vertical rock scarps. In particular, the results show the effectiveness of drone-based photogrammetry for rapidly collecting comprehensive geomechanical data valid to recognise the prone areas to rockfalls in vast regions.

ОБ АКТУАЛЬНОСТИ И ВОЗМОЖНОСТИ ПРЕДУПРЕЖДЕНИЯ СЕЙСМИЧЕСКОЙ ОПАСНОСТИ НА ТЯНЬ-ШАНЕ

The problem of activation of the seismic regime of the Tien Shan and the possibility of strong earthquakes in its southern and northern foothills in the next few years in connection with the earthquake of January 23, 2024, which occurred in the southern foothills of the Central Tien Shan in Ushi County (Ukturpan) of Aksu Prefecture of Xinjiang Province of the People's Republic of China, an earthquake of magnitude 7.1 occurred near the city of Aksu. The Ushinsky earthquake of 23.01.2024 may mean the beginning of a new seismic activation of the Tien Shan. Here is the previous cycle of eight strongest earthquakes with M=6.9-8.3 in the northern and six with M=6.8-7.8 in the southern foothills of the Tien Shan, which lasted 100 years, began in 1885 with the Belovodsky earthquake (M=6.9 near Bishkek) and ended with the Kashgar earthquake (M = 7.0) in 1985. There was another strong Suusamyr earthquake with M = 7.3 in 1992 in the middle part of the Tien Shan, which is atypical in this region. With the earthquake of Usha, the period of calm for earthquakes with magnitudes 7.0 and more, which lasted for almost 40 years, ended. A brief overview of the current state of the issue of forecasting strong earthquakes is given. It is noted that there is a certain discrepancy between the basic concepts of the existing earthquake source models and the available geomechanical data on the fragile destruction of rocks. The latest achievements of tectonophysics in the field of studying the current stress state directly in rock massifs are presented. It is shown that, based on the results of tectonophysical reconstruction of natural stresses, it is possible to perform zoning of active faults according to the level of coulomb stresses responsible for the implementation of brittle fracture. The analysis of the results of active fault zoning performed in the foci of the strong Wenchuan earthquake (M=8.0, 2008) and the Karamushir earthquake (M=7.8, 2023) is given. The analysis of the possibilities for long-term and short-term forecasting based on a complex of seismic, seismotectonic and geophysical methods based on the results of tectonophysical zoning of active faults is performed.

Structural and Geomechanical Analysis of Natural Caves and Rock Shelters: Comparison between Manual and Remote Sensing Discontinuity Data Gathering

The stability of many shallow caves and rock shelters relies heavily on understanding rock discontinuities, such as stratification, faults, and joints. Analyzing these discontinuities and determining their orientations and dispersion are crucial for assessing the overall stability of the cave or shelter. Traditionally, this analysis has been conducted manually using a compass with a clinometer, but it has certain limitations, as only fractures located in accessible areas like the lower part of cave walls and entrances are visible and can be assessed. Over the past decade, remote sensing techniques like LiDAR and photogrammetry have gained popularity in characterizing rocky massifs. These techniques provide 3D point clouds and high-resolution images of the cave or shelter walls and ceilings. With these data, it becomes possible to perform a three-dimensional reconstruction of the cavity and obtain important parameters of the discontinuities, such as orientation, spacing, persistence, or roughness. This paper presents a comparison between the geomechanical data obtained using the traditional manual procedures (compass readings in accessible zones) and a photogrammetric technique called Structure from Motion (SfM). The study was conducted in two caves, namely, the Reguerillo Cave (Madrid) and the Cova dos Mouros (Lugo), along with two rock shelters named Abrigo de San Lázaro and Abrigo del Molino (Segovia). The results of the study demonstrate an excellent correlation between the geomechanical parameters obtained from both methods. Indeed, the combination of traditional manual techniques and photogrammetry (SfM) offers significant advantages in developing a more comprehensive and realistic discontinuity census.

Прогнозная оценка устойчивости борта карьера в тектонически напряженном массиве

The article presents an approach to determining the stability of the pit walls and benches using a set of methods. The results of numerical modeling of the stress-and-strain state are presented for the rock mass in vicinities of one of the quarries in the Khibiny Apatite Arc. Calculations were made using elastic approach to a three-dimensional finite-element model which incorporates basic geological, mining engineering and geomechanical data. The impact of gravitational and tectonic stress field is demonstrated on the stability of the pit wall and benches during its development. Potentially unstable areas have been determined in the wall and benches of the open pit design contour. The identified features of the stress-and-strain state of the rock mass in vicinities of the pit wall make it possible to increase the justification level of technical solutions for the development of surface mining operations and to design preventive measures that would ensure the stability of structural elements of the open pit.

Application of the Q-Slope Empirical Approach for Slope Stability Assessment of Spanish Mountain Roads in Winter—Combining Remote Techniques with Virtual Reality

The Q-slope (2015) geomechanical classification is the only empirical methodology for slope stability analysis that considers the effect of ice. This article shows the results of its application for icy slopes in Spain. Despite its sunny image, Spain is a mountainous country with cold winters. Slopes alongside a mountain road and a ski resort carpark have been studied in Puerto de Navacerrada (Madrid region) and Benasque (Pyrenees). This work combines the manual collection of geomechanical data on slope characteristics with an empirical analysis of slope stability and remote data acquisition techniques (Structure from Motion, SfM). The results of the field data collection are shown in a metaverse with two approaches: a 360° image virtual tour and a 3D image repository. One of the novelties of this work is that researchers who wish to replicate these analyses can access a table of input parameters and make a virtual field trip to see the parameters included in this study. The results show that the Q-slope methodology is useful for stability analysis and is conservative in terms of recommendations: All the slopes that are seen as unstable appear as such, but some slopes that do not present problems are shown as “transitional” slopes. The data and observations taken are useful for increasing the methodology database and for completing existing graphs of stable vertical slopes with good quality, as well as slopes with little slope and low quality.

A Case Study for Evaluating Effective Geomechanical Parameters and the Influence of the Biot Coefficient on the Stability of a Wellbore Wall in the Asmari Formation using Machine Learning

In oil extraction projects, knowledge of reservoir geomechanics is essential for estimating the stability of wellbore walls drilled at great depths. In this regard, mechanics of porous media according to the definition of Biot’s coefficient instead of Terzaghi effective stress can provide a more accurate estimate compared to other analyses. Additionally, using artificial intelligence and machine learning algorithms such as XGBoost and optimizing it with algorithms like Bayesian, along with using SHAP algorithm as an interpretable AI model, can provide us with deeper insights into available data. In this research, 1st geomechanical data of a well in Asmari formation in southwest Iran was obtained through well logs and operational reports and then analyzed by machine learning. Also, a 1-way coupled reservoir rock-fluid model was built to investigate the volume of fractured rock around the well. The interpretation of machine learning results helps us better understand the parameters affecting instability in this well’s wall. Moreover, finite element model results indicate that assuming a value equal to 1 for Biot coefficient (or Terzaghi effective stress) leads to incorrect results and overestimates the volume of fractured rock around this well up to 13 times more than actual values. Therefore, any proper analysis regarding wellbore wall stability and evaluating effective stresses requires accurate knowledge about real and existing values of this coefficient due to simultaneous behavior of stress and pore pressure. HIGHLIGHTS One of the major challenges in the oil industry is the factors affecting the stability of the walls of oil wells during the extraction process, which identifying and addressing these factors can greatly assist in reducing extraction costs Nowadays, the collection of precise and extensive data through well-logging is a reliable source for assessing reservoir geomechanics, which, alongside machine learning can help us better understand reservoir geomechanics Given the conditions of hydrocarbon reservoirs, the mechanics of porous media, along with the definition of the Biot coefficient, can provide us with a better understanding of how shear failure occurs in well walls The XGBoost algorithm is useful for data analysis through regression and classification, as it can easily be optimized using the Bayesian algorithm and interpreted using algorithms such as SHAP Assuming a value equal to 1 for the Biot coefficient, in comparison to its true and in-situ value can cause many errors in estimating the stress-pore pressure interaction and the sanding rate of the well due to shear failure in it GRAPHICAL ABSTRACT

Old core, new tricks: a comparative study of old and new mudstone cores for applications in the energy transition

Repurposing depleted oil and gas reservoirs for secondary storage may play an important role in the transition to low-carbon energy. The integrity of the cap rocks overlying the reservoirs is an important factor for gas storage and needs to be understood prior to repurposing. In some cases, old cap-rock cores collected during exploration and development of oil and gas fields may be available for characterization using modern techniques but after being stored for decades these cores are likely to have experienced many changes in moisture, which can lead to physical changes. A comparative study of samples taken from old, unpreserved mudstone core and samples from a recently acquired and preserved core taken from the same formation shows that the mineralogy, porosity and permeability results are relatively similar between the two cores. The differences in the porosity measurements between the old and new core samples are primarily due to natural variations in grain size, rather than the preservation status of the cores. Geomechanical data, however, show significant and non-systematic differences between the old samples and the new samples, suggesting that old core samples are not suitable for geomechanical characterization. In the absence of new, well-preserved core, old core samples may provide suitable porosity, permeability and mineralogical data, whereas the old, unpreserved core is unlikely to provide reliable geomechanical data. Supplementary material: Individual BIB-SEM porosity measurements for each sample are available at https://doi.org/10.6084/m9.figshare.c.6725765 Thematic collection: This article is part of the Fault and top seals 2022 collection available at: https://www.lyellcollection.org/topic/collections/fault-and-top-seals-2022

Review of Applicable Outlier Detection Methods to Treat Geomechanical Data

The reliability of geomechanical models and engineering designs depend heavily on high-quality data. In geomechanical projects, collecting and analyzing laboratory data is crucial in characterizing the mechanical properties of soils and rocks. However, insufficient lab data or underestimating data treatment can lead to unreliable data being used in the design stage, causing safety hazards, delays, or failures. Hence, detecting outliers or extreme values is significant for ensuring accurate geomechanical analysis. This study reviews and categorizes applicable outlier detection methods for geomechanical data into fence labeling methods and statistical tests. Using real geomechanical data, the applicability of these methods was examined based on four elements: data distribution, sensitivity to extreme values, sample size, and data skewness. The results indicated that statistical tests were less effective than fence labeling methods in detecting outliers in geomechanical data due to limitations in handling skewed data and small sample sizes. Thus, the best outlier detection method should consider this matter. Fence labeling methods, specifically, the medcouple boxplot and semi-interquartile range rule, were identified as the most accurate outlier detection methods for geomechanical data but may necessitate more advanced statistical techniques. Moreover, Tukey’s boxplot was found unsuitable for geomechanical data due to negative confidence intervals that conflicted with geomechanical principles.

Determining the drilling mud window by integration of geostatistics, intelligent, and conditional programming models in an oilfield of SW Iran

Accurate knowledge of pore and fracture pressures is essential for drilling wells safely with the desired mud weight (MW). Overpressure occurs when the pore pressure is higher than the normal hydrostatic pressure. There is a challenge regarding the pressure studies domain in an oilfield in SW Iran, where lack of geo-mechanical data limits exact mud window calculation. Also, the reservoir generally consists of carbonate rocks and contains no shale interbeds, so mechanical stratigraphy based on Gamma ray could not be applied. This study is to provide safe drilling considering MW to prevent the flow or loss in the vicinity of the new wells in the studied field. In this research, the formation pressures and mud window models are determined by combining geostatistical, intelligent, and conditional programming models and compared with real data. The conditional programming was also used to correct small out-of-range data. The highest correlation between the final effective pressure and velocity cube was observed in lower Fahliyan Formation with 0.86 and Ilam with 0.71.The modeled MW difference ranged between 2.5 and 30 PCF. Also, the maximum modeled MW is 150 PCF in the upper Fahliyan Formation. Heavy mud of more than 130 PCF is suggested for drilling the Khalij member and continues to the end of stratigraphy column. Best observed correlation comparing the drilled and modeled MW, especially achieved in the Fahliyan reservoir Formation with more than 100 PCF and the Ilam Formation with 80–100 PCF. Finally, 3D formation pressures are presented and recommended for further safe drillings.

3D structure tectonics model of Yenisei site of the Nizhnekansk Massif

In 2021, in the Yeniseisky region of the Nizhnekansk Massif in the Krasnoyarsk region, construction of an underground research laboratory (URL) was started to justify safety of high-level radioactive waste disposal. The URL investigations aimed to assess preservation of isolation properties of rock mass exposed to long-active rock pressure, tectonic stresses and heat flow within the whole period of effective radiobiological risk of radioactive waste. Based on the geological data analysis, the structure-and-tectonics model of the Yenisei site was developed, including tectonic faults, lithology, intrusives, as well as heavy fracturing and crushing zones. With no large-scale acquisition of geomechanical data on the Lower Kan Massif, the rock stability was estimated at outcrops on ground surface. The results proved the existing hypotheses of the dynamic impact exerted by the Muratov Fault on the Yenisei site. It was also confirmed that the zone of the dynamic impact of the major faults was less stable than the enclosing rock mass while the rock mass composed of dolerite dykes featured the highest stability.The authors appreciate participation of the researcher from the Nuclear Safety Institute, Russian Academy of Sciences, Candidate of Geological and Mineralogical Sciences O. A. Morozov in this study. This work was conducted in the framework of budgetary funding of the Geophysical Center of RAS, adopted by the Ministry of Science and Higher Education of the Russian Federation.The authors express their gratitude to the students of the NUST MISIS’ College of Mining A. V. Nikitenkova and A. K. Niyaz for the help in processing geological data.

Value of core for reservoir and top-seal analysis for carbon capture and storage projects

Abstract Carbon capture and storage (CCS) initiatives to mitigate greenhouse gas emissions are being planned in many countries, including offshore settings in the UK. To start with, almost all of these initiatives have utilized core that was originally collected to help with oil and gas exploration, appraisal and development projects. The objectives of core-based studies for CCS are subtly different to those for oil and gas studies. There are several significant reasons why core should be valued in CCS projects. Data from core provide a chance to calibrate lithology and porosity interpretations made from wireline logs that are used to characterize the subsurface and populate geocellular models. Permeability-related attributes, especially directional permeability ( k v and k h ) and relative permeability in CO 2 –water mixed fluid systems, are essential to predict CO 2 injection rates and CO 2 movement patterns in the reservoir and can only be acquired from core. Although many geomechanical data, necessary to undertake safe injection of CO 2 and avoid induced fracturing, can be acquired from wireline logs, borehole imaging and downhole tests, core samples from the reservoir and top-seal are required to reveal tensile strength and to calibrate elastic and other geomechanical properties acquired from logs. Top-seal performance is critical for carbon capture and storage; core samples from top-seals are the best way to determine capillary entry pressure and so define the maximum CO 2 column height and possible CO 2 leakage rates. The possibility of dissolution reactions between formation water, acidified by high pressure CO 2 , and minerals in both the reservoir and top-seal is best assessed by detailed petrographic and mineralogical study of core samples and a combination of modelling and core flow-through experiments. In summary, core is essential to CCS projects to determine CO 2 storage efficiency, CO 2 injection rates and the optimum way to safely store CO 2 .

Relationship between fissility, composition, rock fabric and reservoir properties in Vaca Muerta Formation (Neuquén Basin, Argentina): from outcrop to subsurface core data

The fissility is the ability of some rocks to split along relatively smooth surfaces parallel to the bedding. This property observed mostly in fine-grained rocks is particularly expressed in outcrops, where rocks are subjected to weathering processes. Most authors associate the fissility to the abundance of clay minerals and their orientation parallel to the bedding. The horizontal fabric can be promoted by depositional conditions such as sediment composition, quantity of total organic carbon content (TOC) and depositional mechanisms, giving rise to a primary fissility. Alternatively, the alignment of platy minerals can be linked to the burial history of the rock, by processes such as mechanical compaction or secondary mineral growth, resulting in a secondary fissility. The present study aims to identify the main controls of fissility development at the micro- and macroscopic scale in rocks of the Vaca Muerta Formation exposed in the Cerro Mulichinco area and in a 121-meter-long core extracted from a well within the Neuquén Basin. In outcrops, fissility is related to fine-grained laminated facies with low carbonate content, revealing the strong control exerted by lithology. The TOC measurements allow establishing a positive correlation between organic matter content and fissility intensity. Moreover, the analysis of the transgressive-regressive cycles shows that fissility is higher around the maximum flooding surfaces. Regarding their mechanical characteristics, the different interfaces observed in core are classified into first and second-order, the last one including fissility planes. Some of these interfaces evolve from potential (partially open) to effective (totally open) discontinuities in response to changes of stress conditions during the core extraction and due to the stress relaxation through time: weeks (T1), months (T2) and years (T3) after extraction. The time evolution of the effective core discontinuities points out rock intervals that are variably broken and core segments that remain intact. The Drying Alcohol Discontinuities (DAD) methodology reveals potential discontinuities within apparently intact core segments. By using this technique, a 4-class index is established as a proxy for fissility degree. When integrated with geological, petrophysical and geomechanical data, this index enables characterizing the main mechanisms controlling rock fissility that express through discontinuities promoting the loss of competence of a rock. Consequently, this mechanical property is considered to influence the efficiency of hydraulic fracture in shale reservoir completion.