Fractures play an important role in the formation of shale-gas reservoirs because they can enlarge the transport channels and aggregation spaces and increase the specific surface area of the gas ...shale. For artificial hydraulic fracturing of these reservoirs, the natural fracture system must be fully integrated with the artificial fracture system to form an intact fracture system. In this study, we first comprehensively examined the fractures in 42 shale-gas wells using several approaches, including a systematic examination and description of the cores and the casting of thin sections, a compilation of the statistics of fracture feature parameters, and observation of various analytical and test data, such as the mineral composition, the organic carbon contents, and the rock mechanics properties for specimens from the corresponding fractured intervals. The data enabled us to thoroughly explore the developmental features and major factors affecting organic-rich shale fractures in the upper Paleozoic Carboniferous–Permian marine–continental transitional coal-bearing formation, which is located in the southeastern Ordos Basin. Our results reveal that, in comparison with the Paleozoic marine shale in the United States and southern China, as well as the Paleozoic basin transitional shale in northern China, the upper Paleozoic black shale in the Ordos Basin is primarily characterized by a relatively low content of brittle minerals and a high content of clay ingredients. The total content of brittle minerals, e.g., quartz, feldspar, and siderite, was approximately 33%, which included 27% quartz and 0.3% K-feldspar but did not include carbonate. The total content of clay minerals reached 64% and was dominated by mixed-layer illite–smectite (I/S), which accounted for more than 41% of the total clay ingredients. The shale accommodated the widespread development of various types of macro- and microfractures. In the core specimens, medium-angle slip fractures and horizontal bedding cracks were the most common types of fractures, whereas vertical and high-angle fractures and horizontal bedding cracks were underdeveloped. In the thin sections, microfractures arising in organic matter laminations or at their edges as well as those of tectonic origin were the predominant type of fractures, and they were mainly short, narrow, and open. Overall, the surface/fracture ratios of the thin sections were concentrated in a range of approximately 0.1–0.3%. The developmental level of the fracture was influenced by various factors, including tectonism, lithology, rock mechanics, and organic matter and mineral content. Thus, increased developmental level of fractures was correlated with higher paleostructural elevation and increased sand content, whereas the developmental level of microfractures was correlated with high lamellation development, high level of organic carbon (leading to more pronounced laminations), and high contents of quartz, mixed-layer I/S, and illite (leading to low levels of kaolinite). These findings were corroborated by other data generated in this study, including the rock mechanics results for the upper Paleozoic black shale and silty shale, the observation results from the cores and from the thin sections sampled from more than 40 shale-gas wells, and the anomalies of gas logging.
•Characteristics of fracture development in transitional shale-gas reservoirs.•Dominant factors of fracture development in transitional shale-gas reservoirs.•Conventional log response characteristics of shale fractures in reservoirs.•Petrological characteristics of shale-gas reservoirs in the Ordos Basin.
This paper proposes a phase field model for fracture in poroelastic media. The porous medium is modeled based on the classical Biot poroelasticity theory and the fracture behavior is controlled by ...the phase field model. Moreover, the fracture propagation is driven by the elastic energy where the phase field is used as an interpolation function to transit fluid property from the intact medium to the fully broken one. We use a segregated (staggered) scheme and implement our approach in Comsol Multiphysics. The proposed model is verified by a single-phase solid subjected to tension and a 2D specimen subjected to an increasing internal pressure. We also compare our results with analytical solutions. Finally, we show 2D and 3D examples of internal fluid injection to illustrate the capability of the proposed approach.
•A phase-field modeling approach of fracture propagation in poroelastic media is proposed.•The fracture propagation is driven by the elastic energy and no stress threshold is set.•2D and 3D examples are presented.
Rhenium (Re) is an extremely rare element, with a crustal abundance of approximately 0.4 parts per billion (ppb) and a sea water concentration of 8.3 parts per trillion (ppt). However, Re ...concentrations in anoxic marine sediments range from 2 to 184 ppb, which is attributed to reduction of the highly soluble perrhenate ion (Re(VII)Osub.4 sup.−) to insoluble Re(IV) species. Anoxic sediments typically contain Fe(II) and sulfide species, which could potentially reduce Re(VII) to Re(IV). In this study, we examined the interactions of KReOsub.4 with magnetite (Fesub.3Osub.4), siderite (FeCOsub.3), vivianite (Fesub.3(POsub.4)sub.2•8Hsub.2O), green rust (mixed Fe(II)/Fe(III) layered double hydroxide), mackinawite (FeS), and chemically reduced nontronite (NAu-1) using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to determine the valence state and speciation of Re. Uptake of Re by green rust was rapid, with ~50% associated with the solids within 2 days. In contrast, there was <10% uptake by the other Fe(II) phases over 48 days. Reduction of Re(VII) to Re(IV) was only observed in the presence of green rust, producing clusters of bidentate-coordinated Re(IV)Osub.6 octahedra.. These results suggest that except for green rust, the potential for other Fe(II)-bearing minerals to act as reductants for ReOsub.4 sup.− in sedimentary environments requires further investigation.
Palaeontology, the scientific study of fossils, has developed from a descriptive science to an analytical science used to interpret relationships between earth and life history. This book provides a ...comprehensive and thematic treatment of applied palaeontology, covering the use of fossils in the ordering of rocks in time and in space, in biostratigraphy, palaeobiology and sequence stratigraphy. Robert Wynn Jones presents a practical workflow for applied palaeontology, including sample acquisition, preparation and analysis, and interpretation and integration. He then presents numerous case studies that demonstrate the applicability and value of the subject to areas such as petroleum, mineral and coal exploration and exploitation, engineering geology and environmental science. Specialist applications outside of the geosciences (including archaeology, forensic science, medical palynology, entomopalynology and melissopalynology) are also addressed. Abundantly illustrated and referenced, Applications of Palaeontology provides a user-friendly reference for academic researchers and professionals across a range of disciplines and industry settings.
Previous studies of the availability of lithium for use in batteries to power electric vehicles (EVs) have reached the generally encouraging conclusion that resources are sufficient to meet growing ...demand for the remainder of the 21st century. However, these surveys have not looked past estimates of lithium resource to the geological constraints on deposit size and composition that will allow the resources to be converted to reserves from which lithium can be produced economically. In this survey, we review the relevant geological features of the best characterized pegmatite, brine and other types of lithium deposits and compare their potential for large-scale, long-term production.
The comparison shows that the average brine deposit (1.45Mt Li) is more than an order of magnitude larger than the average pegmatite deposit (0.11Mt Li) and that brine deposits, especially the large Atacama (Chile) and Uyuni (Bolivia) deposits, have a much larger total lithium resource (21.6Mt Li). Brine deposits clearly have a much greater capacity for large-scale, long-term production than do pegmatite deposits. However, individual brine deposits differ considerably and successful production from one deposit does not necessarily assure success at others. Conversion of brine resources to reserves will depend on the degree of compartmentalization of brine reservoirs, the extent to which brine can be recovered without dilution from recharge waters and degradation of salt-bearing reservoir rock, and whether other constituents of the brines, including potassium, magnesium, bromine and boron, restrict processing or the capacity of production to respond to changes in demand for lithium.
Despite their smaller size and total estimated resource (3.9Mt), pegmatites will remain of interest because of their wider geographic distribution and consequently lesser susceptibility to supply disruptions and their more lithium-dominant compositions, which might allow more flexible response to market changes. Some deposits will be amenable to large-scale mining, but significant production might also come from selective, underground mining of small deposits in areas with low labor costs. Even the largest pegmatite deposits, such as those at Greenbushes (Australia) and Manono–Kitolo (Democratic Republic of Congo) have estimated resources that are similar to only an average brine deposit. For this reason, continuous, long-term production from pegmatites will require extensive exploration and discovery of new pegmatite deposits and districts.
Two other types of lithium deposits, unusual rocks and unusual fluids, have also received attention. Deposits consisting of rocks and minerals that are enriched in lithium by interaction with brines and hydrothermal solutions, including the large Jadar (Serbia) and King Valley (USA) deposits, have estimated resources of about 3.4Mt Li. Unusual brines in oilfields and the Salton Sea geothermal field (USA) contain an estimated 2Mt Li. Both of these deposit types will require new processing methods but are likely to become important because of their lithium-dominant compositions and relatively large size.
The total lithium resource in these deposits (31.1Mt Li) far exceeds estimated lithium demand of up to 20Mt Li (including consideration for recycling) in all markets through 2100. The difference between these two estimates should be vied largely as a challenge rather than a comfort. Evaluation of the economic extractability of these resources will require large investments and result in only partial success. If prices provide sufficient encouragement and exploration is sustained, however, lithium resources should be available for the next century.
Chicago in Stone and Clay
explores the interplay between the city's most
architecturally significant sites, the materials they're made of,
and the sediments and bedrock they are anchored in. This
...unique geologist's survey of Windy City neighborhoods demonstrates
the fascinating and often surprising links between science, art,
engineering, and urban history.
Drawing on two decades of experience leading popular geology
tours in Chicago, Raymond Wiggers crafted this book for readers
ranging from the region's large community of amateur naturalists,
"citizen scientists," and architecture buffs to geologists,
architects, educators, and other professionals seeking a new
perspective on the themes of architecture and urbanism.
Unlike most geology and architecture books, Chicago in Stone
and Clay is written in the informal, accessible style of a
natural history tour guide, humanizing the science for the
nonspecialist reader. Providing an exciting new angle on both
architecture and natural history, Wiggers uses an integrative
approach that incorporates multiple themes and perspectives to
demonstrate how the urban environment presents us with a rich
geologic and architectural legacy.
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