Rock Storage Research Articles

Energy storage and fracture characteristics of brittle rock with rockburst proneness after microwave irradiation

Microwave irradiation has been considered a promising solution for high-temperature cracking rock. Most of the current researches are concentrated on investigating the effects of microwave irradiation on the physical and mechanical properties of rock. However, there is a paucity of reports on the application of microwave irradiation for controlling rockburst disasters. The novelty of this investigation lies in the utilization of microwave irradiation to modify the energy storage capacity and fracture characteristics of brittle rock with rockburst proneness. Based on the phenomenon of overheating in rock under microwave irradiation, the concept of progressive damage in granite was proposed for the first time. The weakening of energy storage capacity due to microwave irradiation was evaluated by defining an energy storage coefficient. A novel index for assessing the rockburst proneness of brittle rock was proposed. By combining this index with the strain energy release rate, the potential value of microwave irradiation in reducing the proneness and intensity of rockburst was explored. This study also introduced the concept of "sensitive stress level" which influences the closure state of cracks, and found that SSL and mechanical properties show high sensitivity to microwave power. A threshold power of 4.5 kW was identified, at which numerous parameters undergo significant changes.

Analysis of dynamic characteristics and influencing factors of CO2 low-permeability coal reservoir sequestration

ABSTRACT Abandoned coal seams can be an important carrier for CO2 geological storage. Considering the gas seepage-diffusion and physical adsorption coupling characteristics in the process of CO2 adsorption and storage in coal and rock, a two-dimensional model of coupled flow-solidity for geological storage of CO2 in low-permeability reservoir with double voids was established by introducing the Zhang Hongbin model algorithm and adding the Klinkenberg effect and the compression effect of the rock skeleton in coal reservoirs in the controlling equation for rock deformation. The coupled flow-solid model was solved by using the PDE equation of COMSOL Multiphics program, and the simulation results difference between the new model and the traditional model in terms of sequestration dynamics were compared. The dynamic characteristic of reservoir gas pressure, formation stress, permeability and sequestration density in the process of CO2 geologic sequestration and injection were analyzed, and the influences of injection pressure and injection well diameter on the amount of CO2 sequestration were explored. The results show that the new model is more reasonable for calculating reservoir gas pressure and permeability compared with the Palmer-Mansoori model (PM model), and can simulate the free-state seepage movement of CO2 in the fracture system as well as its physical adsorption process compared with the single-heavy pore medium model. With continuous CO2 injection, the maximum sequestration density was raised to a limit value of about 1000 kg/m3 after 1 year. The date of reaching the limit of the sequestration volume was advanced by about 45 d when the positive pressure of the injected gas was increased from 10 kPa to 50 kPa. This model can reproduce the main parameters including, when affecting the effect, and realize the calculation of parameters such as CO2 density reaching the limit value, sealing limit day, sealing limit amount, which can provide a theoretical basis for further deep understanding of CO2 geological sealing law and scientific development of gas injection scheme.

Facilitating early boreal forest succession on waste rock using Ramial Chipped Wood mulch: A five-year study

After a mine is closed, waste rock storage areas must be revegetated to facilitate the return of ecosystem services and meet legal and social expectations. The restoration of forest ecosystems on waste rock through spontaneous colonization associated with primary succession can take decades and is still poorly studied. Adding a mulch of ramial chipped wood (RCW) could improve the physicochemical properties and microclimate conditions of waste rock, thus facilitating substrate colonization by plants. In 2016, a fully randomized block design was installed on waste rock from a closed gold mine located in the boreal forest in Abitibi-Témiscamingue, Quebec, Canada. The design included four treatments: scarified waste rock as the control (WR), 2 cm of RCW mulch on top of scarified waste rock (RCW/WR), and 10 cm layer of sand on top of scarified waste rock with or without 2 cm of RCW mulch (RCW/S and S, respectively). Over a period of five years, we followed the natural colonization of forest species as well as abiotic (substrate microclimate conditions and physicochemistry) and biotic (herbaceous plant colonization) factors influencing woody plant colonization success. Six boreal woody species spontaneously colonized the area (five individuals per m2, on average, all species combined). Salix sp. and Picea glauca seedlings were more abundant on substrates with RCW mulch (especially sand) than those without mulch, and P. glauca had greater aerial biomasses with RCW mulch. Substrate water content during the growing season and the presence of the weed species Tussilago farfara were determining environmental factors in substrate colonization by Abies balsamea. In the absence of Tussilago farfara, RCW mulch increased A. balsamea colonization. RCW mulch increased the total cover of colonizing herbaceous plants (23.3–58.2%) as compared to mineral substrates alone (4.78–52.3%), which negatively affected the number of A. balsamea individuals. The colonizing herbaceous species were mostly primary succession species, Pilosella caespitosa, Anaphalis margaritacea, and Tussilago farfara being dominant; no exotic species were observed. The results highlight the potential of RCW mulch in promoting forest recolonization on waste rock, including mid-successional species like Picea sp., which could be useful for facilitating ecosystem succession in post-mining landscapes.

Effects of length-to-diameter ratio and strain rate on strain energy accumulation and dissipation in sandstone

To investigate the influence of the length-to-diameter (L/D) ratio and strain rate on the evolution of strain energy of sandstone under uniaxial compression, experimental tests were conducted using the RMT-150B rock mechanics test system. Specifically, uniaxial compression experiments (UCE), uniaxial loading-unloading experiment(ULUE) and uniaxial cyclic loading-unloading experiments (UCLUE) were performed. The results show that: 1) Based on an investigation of the Kaiser effect in UCLUE, it is postulated that a small degree of loading-unloading has negligible impact on the storage of strain energy in rock masses. The hypothesis regarding the limited influence of loading-unloading on the elastic strain energy storage of rocks is confirmed through a comparative analysis between the elastic strain energy storage in UCLUE and ULUE. 2) By analyzing the ESED and ISED of sandstone under different L/D ratios and strain rates, it is found that it follows the linear energy storage law. The evolution of elastic strain energy is not affected by strain rate. Therefore, the UCLUE at any strain rate can analyze the elastic strain energy of uniaxial compression experiment with the same size at any strain rate, and provide a new method for strain energy analysis at different length-diameter ratios and strain rates. 3) When the stress of sandstone samples of equal size is equal, the smaller the strain rate, the longer the loading experiment of sandstone, the more time the friction development and interconnection of cracks in sandstone are, and the more dissipated strain energy and input strain energy are generated. 4) Smaller L/D ratios are associated with larger ESED and DSED values in sandstone. As the stress intensifies, the ESED and DSED of certain sandstones with larger L/D ratios experience a sharp increase when approaching the failure stress. Under equal stress levels, it is possible for sandstones with larger L/D ratios to exhibit higher ESED and DSED values compared to those with smaller L/D ratios.

Exploring hydrogen storage potential in depleted Western Australian hydrocarbon reservoirs: A petrophysical and petrographic analysis

Hydrogen, recognised as a clean and sustainable energy carrier with excellent transportation fuel properties, drives numerous countries towards a hydrogen-based economy due to its high utilisation efficiency and minimal environmental impact. However, the gaseous nature of hydrogen necessitates larger storage surface areas. Underground Hydrogen Storage (UHS) has emerged as a promising and efficient method to overcome this challenge. Currently, only a handful of UHS locations exist globally due to the novelty of this field. With its abundant depleted hydrocarbon reservoirs boasting significant storage capacity, Western Australia presents a suitable region for hydrogen storage.This paper comprehensively analyses petrophysical and petrographic characteristics, employing XRD, MIP, and Micro-CT techniques on sandstone and claystone samples obtained from several fields in Western Australia. The suitability of these samples for hydrogen storage is evaluated based on mineral composition and porosity. The analysis reveals that more than 96% of Quartz is present in the sandstone samples. The claystone samples exhibit a mineral composition comprising Quartz, Calcite, K-feldspar, Kaolinite, Pyrite, Albite, and Muscovite. The study suggests that hydrogen storage in formation rock is favourable due to the low reactivity of hydrogen with silicate minerals, but interactions with cap rock minerals should be considered.Micro-CT results indicate the connected porosity in the 17.23–4.67% range. Pore distribution in sandstones ranges from nanometers to millimetres, with a substantial proportion of connected pores in the intermediate range, which is conducive to hydrogen storage. This is particularly advantageous as the hydrogen-water system is highly water-wet, with hydrogen primarily occupying medium and larger pores, minimising hydrogen trapping. In claystone, most pores were below 3 nm, but instrumental constraints limited their quantification. In conclusion, the petrophysical and petrographic analysis underscores the potential of Western Australian depleted hydrocarbon reservoirs for hydrogen storage. Understanding the mineralogical reactions with cap rock minerals is crucial, while the favourable pore distribution in sandstones further supports the viability of hydrogen storage.

Core analysis in a changing world – how technology is radically benefiting the methodology to acquire, the ability to visualize and the ultimate value of core data

Abstract Core analysts principally study the storage, flow and saturation properties of porous rocks and sediments. Some of the derived parameters are specific to hydrocarbon production but many have commonality with other subsurface disciplines such as hydrology and soil science. Traditional core analysis involves direct physical experimentation on core plugs to derive a range of parameters used as calibration for conventional well logs, and to predict hydrocarbon reserves and recovery. The mechanisms and processes for obtaining such data have evolved significantly during the last century, from the manual instruments of the mid-twentieth century to the accredited digital data collection and recording of the 1990s onwards. X-ray micro- and nano-scale computed tomography (CT) imaging led to the development of the digital rock physics subdiscipline in the early 2000s. This has subsequently allowed direct visualization of fluid flow at the pore scale, imaging the wetting phase and multiphase fluid mobility. Multiscale imaging workflows are being developed to overcome issues around heterogeneous rock and the limited field of view associated with the highest resolution X-ray CT images. Hybrid workflows, which combine digital rock physics with traditional core analysis, are becoming increasingly common to meet the challenges associated with some of the most difficult to constrain properties, such as relative permeability. At a larger scale, the recent development of multisensor core logging (MSCL) tools has allowed the cost-effective acquisition of essentially continuous high-resolution 1D, 2D and 3D datasets from both slabbed and unslabbed whole core. Often aided by artificial intelligence to manage and interpret these large physical and chemical datasets, both new and legacy core can be rapidly screened to allow representative subsampling for detailed laboratory experimentation. The context and data provided by the MSCL then allows effective upscaling of these time- and cost-intensive point-source measurements. In the last decade, extended reality (XR) has resulted in a step change in the ability to visualize and integrate core and core-derived information with other subsurface datasets. A very wide range of scales can be managed effectively, from micrometre- to centimetre-scale petrographical and core analysis data, to metre-scale well logs and up to kilometre-scale 3D and 4D seismic. These tools allow stakeholders to work and meet from any location in a common workspace, and efficiently scale and interrogate data in a virtual 3D environment. The various advances in core analysis and associated technologies during the early twenty-first century mean that the study of porous media to help enable the energy transition looks assured. During the coming decades, applications as diverse as carbon capture, utilization and storage (CCUS), hydrogen storage, geothermal energy generation, mining for critical minerals, palaeoclimate studies, radioactive waste management, and site surveys for windfarms will all continue to benefit from the data and understanding derived from core analysis.

Energy conversion through deep borehole heat exchanger systems: Heat storage analysis and assessment of threshold inlet temperature

The heating capacity of deep borehole heat exchanger (DBHE) systems gradually attenuates due to the cold accumulation of rock and soil during long-term operation. Therefore, heat storage in rock and soil is crucial to alleviate thermal attenuation and ensure stable operation. However, the mechanism and design methods for heat storage are unclear. In this paper, heat extraction and storage models for DBHE systems are established, the effects of heat storage on system operation are revealed, and a design method for the threshold inlet water temperature of heat storage is proposed. The results show that the fluid in the DBHE should inflow from the inner pipe to release more heat into the rock and soil when adopting heat storage. The heat storage power under fluid inflow from the inner pipe is 10.81 kW higher than that from the annular space under the same operating conditions. Increasing the inlet water temperature is more beneficial than increasing the flow rate to enhance the heat storage power. After 2880 h of operation, the heating power of the DBHE is increased by 3.44% for the next heating season when the storage flow rate is increased from 8 m3/h to 38 m3/h. Thus, a high heat storage inlet temperature with a low flow rate should be adopted during the heat storage period. Furthermore, the threshold inlet water temperature of heat storage is highly dependent on the depth of the DBHE and the geothermal gradient, with percentage contributions of 57.14% and 39.26%, respectively. The multiple linear regression model (R2 = 0.972) has shown high predictive accuracy in the assessment of threshold inlet water temperatures, with a maximum relative error of −5.60%. The findings of this paper provide technical support for designing heat storage using DBHE systems.

Study on Multi-factor Optimization of Adjacent Underground Layered Salt Rock Gas Storage Based on RSM

To study the significance of different factors on adjacent underground laminated salt rock storage, 15 groups of simulation tests are designed by using the response surface methodology (RSM), the quadratic response surface model with the midpoint displacement and medial waist stress of the interlayer as the response values is constructed. By analyzing the main effect and interaction of the regression model, the influence of the interaction between pillar width, interlayer thickness, and the location of a single interlayer on the midpoint displacement of the interlayer and the internal waist stress of the adjacent ellipsoidal cavity is studied. The results show that the interlayer thickness is the main effect factor of the midpoint displacement of the interlayer. And the pillar width is the main effect factor of the medial waist stress. When the adjacent storage is designed with as 2.5D pillar width, 2 m interlayer thickness, and the midpoint of the interlayer is located at 0.3H above the cavity, the displacement and stress of the test model are relatively small. The above conclusions can provide a certain reference value for the mechanical analysis of adjacent underground layered salt rock gas storage.

Fracture and energy evolution of rock specimens with a circular hole under multilevel cyclic loading

Underground structures gradually face increasing multilevel cyclic loading as construction progresses. In this paper, the fracture and energy evolution of rock specimens with a circular hole under multilevel cyclic loading were investigated using an experimental-theoretical approach. A series of multilevel cyclic loading tests were conducted on two types of rock (sandstone and granite) using the MTS 815 rock mechanics test system. Digital image correlation (DIC) and acoustic emission (AE) techniques were employed to monitor the fracture behavior of the rock with deformation and acoustic emission data recorded respectively. The total energy density, elastic energy density, and dissipated energy density of specimens are obtained by theoretical calculation. The results indicate that, despite the similarity in cracking sequence and fracture evolution of rock specimens with a circular hole between multilevel cyclic loading and uniaxial compression tests, there are differences in the AE activity under these two loading conditions. Additionally, the cracks around the hole under multilevel cyclic loading display a distinct “open-close-reopen” behavior. The energy density of rock specimens with a circular hole grows nonlinearly with stress. The elastic and dissipative energy density exhibits a linear relationship with the total energy density before rock failure. The fitting value of the elastic and dissipative energy density can be regarded as the energy storage coefficient and the energy dissipation coefficient, which could be further used to quantify the energy storage and dissipation capacities of rock. Under multilevel cyclic loading, the propagation of remote fractures and their coalescence with the shear fractures is the primary resource of AE energy, with only a few supplies given by micro-fissure closure and primary fractures. The dissipation energy in the rock structure can be described by the growth of AE energy. The findings indicate that there are distinct stages of energy release during the fracture evolution of cracks around the circular hole. These stages can be predicted by changes in AE energy or macroscopic energy, revealing the evolution stages of cracks and the modes of failure.

Research on Microscopic Pore Structure Characteristics and Producibility of the Chang 9 Reservoir in the Wucangpu Block

The pore structure can affect the storage and flow properties of rock, which is an important research content in the study of unconventional tight reservoirs. This research hopes to clarify the reservoir characteristics and fluid seepage mechanism of the Chang 9 reservoir in the Wucangpu block and provide technical support for the development of horizontal wells with staged fracturing in this block. In this paper, the microscopic pore structure characteristics and producibility of the reservoir in the study area are analyzed in detail by means of constant-rate mercury intrusion and nuclear magnetic resonance. The research results show that the reservoir with permeability less than 0.076 mD is mainly composed of microthroat, the reservoir with permeability of 0.208-0.633 mD has a larger proportion of microthin throat, and the reservoir with permeability of 2.722-3.998 mD has a larger proportion of fine-middle throats. The results show that the oil/gas in the rock sample reservoirs with permeability greater than 1.0 mD is easy to produce.

Microstructure and mechanical behavior of cemented gold/tungsten mine tailings-crushed rock backfill: Effects of rock gradation and content

Without appropriate and responsible waste management in place, the cursory storage of tailings and waste rocks on the surface can cause devastating damage to the planet's ecosystems. To proactively manage or abolish the damage, some techniques such as mine backfill have been already used repeatedly in mines. Microstructure and strength behavior of cementitious tailings-crushed rock backfill (CTCRB) with gold/tungsten tailings and rock contents (e.g., 10%, 20%, 30%, 40%, and 50%) were conducted in this study by using both UCS (unconfined compressive strength) tests (e.g., peak strengths, stress-strain curves, failure modes) and SEM micro-graphs. Key conclusions were shown that: when gradation and content of crushed rock was considered as 1–3 mm and 50% respectively, the UCS value of gold tailings based backfills was 1.02 MPa. In contrast, the UCS value of tungsten mine tailings based backfills was 1.36 MPa when the amount of crushed rock within the filling matrix became 10%. Tungsten tailings based backfills were more sensitive to crushed rock gradation than gold tailings based backfills. CTCRB's stress-strain curvatures were up-concave in the step of pore compaction. With the increase in the content and gradation of crushed rock, tungsten tailings based backfills showed swelling and crushing in complete destruction. Tailings' particle size, crushed rock content and gradation utterly affected the failure modes of CTCRB. Ettringite/CSH gel was found to be the leading hydration materials in the backfill matrix. The micro-cracks within CTCRB specimens were unfavorably correlated with its UCS data. To conclude, this study's main outcomes could give a significant guide for CTCRB's industrial uses.

The Legacy of Potential Environmental Soil Contamination in an Antimony Mining Heritage Area

In the Valongo Belt, with an extension of about 90 km, located very close to Porto, northern Portugal, dozens of ore deposits of various metallic minerals and coal were exploited in the 19th and 20th centuries. One of the metals most intensely exploited was antimony, with or without associated gold mineralization. This research intends to verify the extent of the current environmental legacy of ancient antimony mining. A typical old mine was selected. The main objectives were to verify whether the environmental legacy still manifests today, how natural processes contributed to an environmental dispersion of the mining footprint and whether the environmental legacy was absorbed by developments in a new landscape modified by anthropic activities. The topography of the area was captured using a Light Detection and Ranging (LIDAR) based drone system. The regional background was characterized by the geo-referenced chemical analysis of 157 soil samples, collected in a 35 × 35 m grid. The former mining area was characterized by 58 supplementary samples. The mining area is distinct from the background by higher antimony and zinc levels, constituting two distinct populations, as confirmed by statistical tests. In the samples collected in the industrial zone, six elements were considered contaminants: As, Cu, Mo, Sb, Sn and Zn. The concentrations of these elements were statistically examined using multivariate statistical analyses (principal component analysis and correspondence analysis). The main conclusions are: (a) the mining heritage area is discernible from the highly mineralized background; (b) in the mining zone, it is possible to distinguish the processing industrial area from the waste rock storage; (c) the natural processes of environmental dispersion were of little relevance; (d) the environmental legacy was smoothed and mostly incorporated into the new post-industrial landscape created by anthropic activities.

Технологія складування безрудних гірських порід у виробленому просторі виведеного з експлуатації кар’єру

Технологія складування безрудних гірських порід у виробленому просторі виведеного з експлуатації кар’єру

Investigation on Energy Evolution and Storage Characteristic of CSTBD Red Sandstone during Mixed-Mode Fracture

To investigate the energy evolution and storage characteristics of the rock during the mixed-mode fracture failure, several single loading-unloading tests under preset different unloading levels were conducted on the cracked straight-through Brazilian disc (CSTBD) red-sandstone specimen with crack inclination angles of 10° and 20°. The input energy, elastic energy, and dissipated energy parameters were obtained by calculating the area integral of the load-displacement curve. Test results display that the total input energy, elastic energy, and dissipated energy of rock specimens increase in quadratic function with the increase of unloading level at different unloading levels. It was found that there are significant linear energy storage and dissipation laws of rock during the mixed-mode fracture process. The concepts of fracture energy storage coefficient (FESC) and fracture energy dissipation coefficient (FEDC) were proposed to express the energy variation of rock in the prepeak stage. Under the same loading conditions, FESC and FEDC remain unchanged regardless of crack inclination angles, indicating that the linear energy storage and dissipation laws are an inherent property of the rock. Besides, the peak fracture elastic-dissipation index W ed (the ratio of peak elastic energy to peak dissipation energy) was obtained through quantitative analysis and demonstrated its invariant feature.

Experiments on rockburst proneness of pre-heated granite at different temperatures: Insights from energy storage, dissipation and surplus

Many underground engineering projects show that rockburst can occur in rocks at great depth and high temperature, and temperature is a critical factor affecting the intensity of rockburst. In general, temperature can affect the energy storage, dissipation, and surplus in rock. To explore the influence of temperature on the energy storage and dissipation characteristics and rockburst proneness, the present study has carried out a range of the uniaxial compression (UC) and single-cyclic loading–unloading uniaxial compression (SCLUC) tests on pre-heated granite specimens at 20 °C–700 °C. The results demonstrate that the rockburst proneness of pre-heated granite initially increases and subsequently decreases with the increase of temperature. The temperature of 300 °C has been found to be the threshold for rockburst proneness. Meanwhile, it is found that the elastic strain energy density increases linearly with the total input strain energy density for the pre-heated granites, confirming that the linear energy property of granite has not been altered by temperature. According to this inherent property, the peak elastic strain energy of pre-heated granites can be calculated accurately. On this basis, utilising the residual elastic energy index, the rockburst proneness of pre-heated granite can be determined quantitatively. The obtained results from high to low are: 317.9 kJ/m 3 (300 °C), 264.1 kJ/m 3 (100 °C), 260.6 kJ/m 3 (20 °C), 235.5 kJ/m 3 (500 °C), 158.9 kJ/m 3 (700 °C), which are consistent with the intensity of actual rockburst for specimens. In addition, the relationship between temperature and energy storage capacity (ESC) of granite was discussed, revealing that high temperature impairs ESC of rocks, which is essential for reducing the rockburst proneness. This study provides some new insights into the rockburst proneness evaluation in high-temperature rock engineering. • The temperature does not change the pre-heated granite possess the linear energy storage law. • The peak strain energy of pre-heated granite is quantitatively calculated using the linear energy storage law. • The rockburst proneness of pre-heated granite at different temperatures can be accurately evaluated by the A EF . • The rockburst proneness of pre-heated granite initially increases and then decreases with the temperature increasing. • The rockburst proneness of pre-heated granite at 300 °C is the highest.

A structured procedure for the selection of thermal energy storage options for utilization and conversion of industrial waste heat

Thermal energy storage is a key enabling technology for the recovery and valorisation of industrial waste heat. Nevertheless, there is a wide gap between the variety of heat storage options investigated and the recurrent few types virtually implemented in the industries. To take advantage of a wider spectrum of solutions, a structured procedure is proposed in this work for the selection of storage material and layout. The algorithm developed consists of a preliminary storage design followed by a performance estimation of the overall system where the heat storage is integrated. The preliminary design allows a first screening and ranking of sensible, latent or thermochemical materials using a quasi-stationary approach. The performance estimation leads to the final selection of the heat storage system, which is based on the analysis of the dynamic thermal response of the heat storage along with physically based or input-output models for the load. The algorithm is applied to improve the heat recovery of a discontinuous and fluctuating flue gas at medium temperature from a steel industry, targeting the production of process steam or electricity. The results show that the integration of a packed bed heat storage, either of the sensible or latent type, allows the highest amount of steam to be generated in the discharging. Moreover, the combination of the same heat storage with an organic Rankine cycle or the Kalina cycle results in the highest amount of generated electricity. The investment in a packed bed rock storage was found to result in payback times of about seven years, whereas tank-based storage units appear not profitable due to the high cost of the silicone oil.

Techno-economic analysis of two-tank and packed-bed rock thermal energy storages for foil-based concentrating solar collector driven cogeneration plants

Concentrated solar power driven systems using thermal energy storage technology are an attractive solution for medium-scale dispatchable cogeneration plants. Recently, a novel concentrating solar collector system using a micro-structured polymer foil-based solar collector, with a potential of large cost reduction compared with current solar collector systems, was proposed. A techno-economic analysis of two-tank indirect storage, two-tank direct storage and packed-bed rock storage, respectively, for the foil-based solar field driven cogeneration plant is presented in this paper. The objectives are to identify the most suitable energy storage technology and to identify the optimal design for such system. Three different heat transfer fluids and two different rocks are considered in the analysis. The effects of solar field heat transfer fluid's operating and cost parameters on the selection of storage system are studied. The results suggest that the packed-bed rock (considering quartzite rock) thermocline storage with Therminol 55 as heat transfer fluid is the preferred option, attaining a minimum levelized cost of electricity and fresh water of 0.103 €/kWhe and 0.995 €/m3, respectively, for Antofagasta, Chile. The levelized costs of electricity and water are about 11.2% and 11.9% lower, respectively, compared to those of the conventional two-tank indirect storage based plant.

Construction simulation of large-spacing-two-well salt cavern with gas blanket and stability evaluation of cavern for gas storage

The single well or small-spacing two-well technologies with oil blanket has been gradually applied to construct salt cavern storage in recent years. In order to solve the problems of low efficiency, oil blanket sealing failure, cavern deformity, roof collapses, small volume and brine pollution in salt cavern construction. In this study, a large-spacing two-well (Wellhead spacing is greater than 20 m) with gas blanket (LSTW-GB) method was proposed to construct salt cavern. Firstly, through indoor physical simulation experiment, the feasibility of the LSTW-GB to construct cavern is verified and discussed. The experimental results show that increasing the two-well-spacing effectively increases the effective cavern volume, improve the cavern construction rate and obtain clear brine, but the increase of two-well-spacing will also increase the difficulty of connecting the two wells, so more attention should focus on the technology improvement on connecting the two wells. Secondly, combined with the experimental observations and field geological data in Jintan bedded salt rock of China, the stability of the LSTW-cavern for gas storage under different ratios of long axis to height (RLH) was analyzed by numerical simulations. The simulation results show that as the RLH increasing, the stability of the LSTW-cavern gradually decreases. In addition, under low-internal-pressure operation, the cavern is most likely to lose its stability, so much more attention should be paid to designing the value and duration of minimum operating internal pressure (Pmin). Finally, the working conditions of the LSTW-cavern gas storage are optimized, and it is proposed that the Pmin of the gas storage in the LSTW-cavern should be 33% ∼ 38% of the gravity stress at the casing shoe when RLH varies from 1.60 to 3.10. Comprehensive research results show that the LSTW-cavern has a good application prospect in the construction of gas storage of salt rock in China.

Mineralogy-dependent sulfide oxidation via polysulfide and thiosulfate pathways during weathering of mixed-sulfide bearing mine waste rock

Tracking the S oxidation pathway in sulfide-bearing mine waste-rock piles is complicated by variations in water content, O2 and Fe3+ concentrations, microbial diversity, mineralogy, the occurrence of a variety of S species associated with incomplete oxidation, and nonlinear coupling between physicochemical processes. Synchrotron-based S K-edge X-ray absorption near edge structure (XANES) spectroscopy facilitates the identification and quantification of S species (i.e., S2−, S22−, S8, S2O32−, and SO42−) in a weathered mine waste-rock pile containing pyrite, sphalerite, galena, pyrrhotite, and chalcopyrite. Mineralogy-dependent polysulfide and thiosulfate pathways both affect the S oxidation within the waste-rock pile. Currently, the polysulfide pathway, with S8 as the intermediate S species, generates high concentrations of dissolved metals (from the rapid oxidation of monosulfides including sphalerite, galena, pyrrhotite, and chalcopyrite). As these monosulfides are depleted, the thiosulfate pathway of pyrite oxidation, including intermediate oxidation products (i.e., S8 and S2O32−), will become the dominant oxidation pathway, resulting in the potential for generation of additional acidic drainage. This information highlights the importance of identifying the sulfide-mineral oxidation reaction pathways when attempting to estimate acid generation potential, and when developing remediation strategies for the storage and management of sulfide-bearing waste rock.

NMR AND WELL LOGS PETROPHYSICAL CHARACTERIZATION OF SANDSTONE FROM THE MARACANGALHA FORMATION, BAHIA, BRAZIL

The storage and production capacity of reservoir rocks can be estimated through some petrophysics characteristics involving the lithological identification of the constitute rocks, fluids nature in the porous space, porosity, permeability, saturation and clay content. The most popular tools for obtaining these petrophysical parameters are the conventional geophysical well logs. However, the determination of petrophysical parameters from tools based on the phenomenon of nuclear magnetic resonance (NMR) has gained prominence in recent decades. In this work, we analyzed rock samples from outcrops in Frades Island region, Bahia, Brazil, through laboratory NMR measurements, to estimate and evaluate the petrophysical properties of the Maracangalha Formation, one of the main hydrocarbons reservoirs in the Recôncavo Basin. The Sandstone samples were characterized in terms of porosity, permeability, saturation, and petrofacies. Finally, we calculated porosity, permeability, and clay content using data from gamma-ray, electrical and density logs, measured in a depth interval interpreted for Maracangalha Formation. These results corroborate with the obtained by NMR since, despite the effects of weathering and erosion on the samples used, the values of porosity and permeability obtained in NMR are in the range of values calculated from these profiles.