Petrology Of Rocks Research Articles

Alluvial karstification and paleodoline development in Eocene limestones, a case study from west Sohag City, Egypt: implications for causes and impacts

The Late Oligocene pre-Eonile paleoriver flows northwesterly over the Eocene Limestone Plateau in the east central Western Desert, west of the Nile Valley (Sohag), building an alluvial plain and leading to the karstification of the limestone bedrock, as paleoerosional surfaces and paleodolines. Knowledge of this alluvial karstification is completed with the detailed studies of the sedimentary evolution of the fluvial system and its contemporary deposition. Analysis of the sedimentological and geomorphological features allows discussing the natural environmental conditions that favored karst in the past and its main genetic mechanisms. The architectural elements of the fluvial deposits indicate that they were deposited in a gravel-dominated braided fluvial system, characterized by high availability of water and sediment supplies. The current study proves that genesis of paleodolines was mainly related to this high water supply. Some of them were progressively filled by syn-sedimentary deformed unconsolidated deposits. Such deformation is due to dissolution of the underlying sagging synclinal limestone, conditioning the location of sinking waters where preferential dissolution and later suffosion took place. A model for the evolution of the paleodoline fills is proposed and interpreted in three different stages: (1) gravitational processes developed and disorganized gravels were remobilized and dragged toward the created paleodolines; (2) flooding of the paleodolines acted as lakes where Gilbert-type deltas and gravel slope deposits accumulated, exhibiting several unconformities interpreted as a result of continued subsidence of the paleodoline related to dissolution; and (3) nondeformed fluvial facies sealed the whole deposits, marking the end of the karstification process. Combinations of different types of factors that could cause karstic subsidence and associated hazards include soluble rock lithology, paleoclimate, and deformational structure.

The Quebrada del Diablo Lower West Au deposit (Gualcamayo mining district, Argentina): A Carlin-type mineralization?

The Gualcamayo Mining District (GMD), located in the eastern margin of the Argentini an Precordillera includes three Au deposits: Amelia-Ines, Magdalena, Quebrada del Diablo Main, and QDD Lower West. The district has reserves of 491,000 oz. and resources of 2.3 million oz of Au.The metallogenetic analysis of these Au deposits based on previous work and new micro-geochemistry (LA- ICP- MS), isotopic (C-O-S-Pb) and fluid inclusions studies revealed that they are genetically linked and share many characteristics with Carlin-type deposits, including the lithology of host rocks, structural control, geochemical signatures, ore paragenesis, and dissolution and decarbonization processes. However, they also display some noticeable differences. The sulfur isotopic composition supports a genetic link between these gold deposits and the precursor magmatism of the porphyry-type mineralization of the area. Besides, the fluids responsible for the Au mineralization proved to be neutral to slightly alkaline and Au-saturated. The link with the magmatism along with the character of the mineralizing fluids and the presence of significant base metal sulfides allowed classifying the GMD deposits as “distal disseminated gold deposits” that occur on the distal edges of magmatic-hydrothermal systems.

Alteration and mineralization styles of the orogenic disseminated Zhenyuan gold deposit, southeastern Tibet: Contrast with carlin gold deposit

Orogenic disseminated and Carlin gold deposits share much similarity in alteration and mineralization. The disseminated orogenic Zhenyuan Au deposit along the Ailaoshan shear zone, southeastern Tibet, was selected to clarify their difference. The alteration and mineralization from the different lithologies, including meta-quartz sandstone, carbonaceous slate, meta-(ultra)mafic rock, quartz porphyry and lamprophyre were researched. According to the mineral assemblage and replacement relationship in all types of host rocks, two reactions show general control on gold deposition: (1) replacement of earlier magnetite by pyrite and carbonaceous material; (2) alteration of biotite and phlogopite phenocrysts in quartz porphyry and lamprophyre into dolomite/ankerite and sericite. Despite the lamprophyre is volumetrically minor and much less fractured than other host rocks, it contains a large portion of Au reserve, indicating that the chemically active lithology has played a more important role in gold precipitation compared to structure. LA-ICP-MS analysis shows that Au mainly occurs as invisible gold in fine-grained pyrite disseminated in the host rocks, with Au content reaching to 258.95 ppm. The diagenetic core of pyrite in meta-quartz sandstone enriched in Co, Ni, Mo, Ag and Hg is wrapped by hydrothermal pyrite enriched in Cu, As, Sb, Au, Tl, Pb and Bi.Different host rock lithology has much impact on the alteration and mineralization features. Carbonate and sericite in altered lamprophyre show they have higher Mg than those developed in other of host rocks denoting that the carbonate and sericite incorporated Mg from phlogopite phenocrysts in the primary lamprophyre during alteration. The ore fluid activated the diagenetic pyrite in meta-quartz sandstone leading the hydrothermal pyrite enriched in Cu, Mo, Ag, Sb, Te, Hg, Tl, Pb and Bi, but the hydrothermal pyrite in meta-(ultra)mafic rock is enriched in Co and Ni as the meta-(ultra)mafic rock host rock contain high content of Co and Ni. However, Au and As shear similar range in both types of host rocks indicating that these two elements most likely come from the deep source fluid rather than the host rocks. It was shown in the disseminated orogenic gold deposit that similar hydrothermal alteration with mineral assemblage of carbonate (mainly dolomite and ankerite), sericite, pyrite and arsenopyrite develops in all types of host rocks. This is different from the Nevada Carlin type, in which alteration is mainly dissolution and silicification of carbonate host rock. On the other hand, Au mainly occur as invisible gold in both disseminated orogenic and Carlin gold deposits.

Numerical study on the effect of U-shaped deep-buried pipe type on heat transfer performance

In combination with a U-shaped deep-buried drilling project for heating buildings in Xi’an, three-dimensional (3D) full-size numerical calculation models with a depth of 1000 m were established for coupling the internal and external heat transfer of U-shaped and W-shaped pipes. This is based on the measured well temperature data of a drilling project and lithology of rock and soil obtained from the tests. Furthermore, by calculating and comparing the total heat transfer quantity and heat transfer per linear meter between two types of buried pipes during the simulation, the heat transfer effect of W-shaped buried pipe versus U-shaped buried pipe was analyzed. The simulation results show that under the same flow rate and inlet water temperature of buried pipe, there is no significant difference in heat transfer per linear meter between W-shaped and U-shaped buried pipes. Considering the outlet pipe diameter of W-shaped buried pipe, the flow rate of its inlet pipe and the spacing between buried pipes can be enhanced or enlarged in practical projects. It can be concluded that W-shaped buried pipe has a better heat transfer effect than U-shaped buried pipe under certain conditions. Therefore, similar solutions can be considered to increase the heat transfer capacity of deep-buried pipes in limited space sites for practical projects, and then the building heating area can also be expanded.

Basaltic Terrains in Idaho and Hawai'i as Planetary Analogs for Mars Geology and Astrobiology.

Field research target regions within two basaltic geologic provinces are described as Earth analogs to Mars. Regions within the eastern Snake River Plain of Idaho and the Big Island of Hawai‘i, the United States, provinces that represent analogs of present-day and early Mars, respectively, were evaluated on the basis of geologic settings, rock lithology and geochemistry, rock alteration, and climate. Each of these factors provides rationale for the selection of specific targets for field research in five analog target regions: (1) Big Craters and (2) Highway lava flows at Craters of the Moon National Monument and Preserve, Idaho, and (3) Mauna Ulu low shield, (4) Kīlauea Iki lava lake, and (5) Kīlauea caldera in the Kīlauea Volcano summit region and the East Rift Zone of Hawai‘i. Our evaluation of compositional and textural attributes, as well as the effects of syn- and posteruptive rock alteration, shows that basaltic terrains in Idaho and Hawai‘i provide a way to characterize the geology and major geologic substrates that host biological activity of relevance to Mars exploration. This work provides the foundation to better understand the scientific questions related to the habitability of basaltic terrains, the rationale behind selecting analog field targets, and their applicability as analogs to Mars.

Evaluating of lithological and structural controls on the barite mineralization by using the remote sensing, Fry and fractal methods, Northwest Iran

The most part of barite deposits in the NW Iran have been epigenetically formed in the form of veins, fracture, and/or open-space fillings. For this reason, structural evaluation is the important factor for investigation of the barite mineralization in the host rocks. Fault and fracture are the predominant structures that can be distinguished in the studied area. Two approaches are proposed for analyzing the structures; the first one is visual investigation. This approach produces a fracture density map and a fracture rose diagram. The second one is used to quantify the fracture distribution by using the fractal dimension. The results indicated that the fracture distribution is not only the controlling factor of the barite mineralization, but also the presence of hydrothermal fluids and the lithology of the host rock that are other important factors in the productivity of the fractures as well. For this reason, despite the high fractal dimension (1.92) in the SE of the studied area, the barite indices have not been introduced up until now, whereas several barite indices in the NW of the study area with low value of fractal dimension (1.62) have been found. Fry analysis data can help us to identify the trend of mineralization in barite deposits. Fry analysis results revealed that E-W trending fractures are the most important structures for barite vein emplacement and subsidiary N-S striking fractures also host for the barite veins, but NE-SW trending fractures are almost barren. In this research, pyrite strain firings were used for temporal evolution of ore deposition. Wrapping of barite around the porphyroblasts reveals that coeval growth of fractures and mineralization with deformation of shear zone and exhumation of host rocks are done by a set of thrust faults in the study area.

Genetic Types and Metallogenic Model for the Polymetallic Copper–Gold Deposits in the Tongling Ore District, Anhui Province, Eastern China

AbstractThe Tongling ore district is one of the most economically important ore areas in the Middle–Lower Yangtze River Metallogenic Belt, eastern China. It contains hundreds of polymetallic copper–gold deposits and occurrences. Those deposits are mainly clustered (from west to east) within the Tongguanshan, Shizishan, Xinqiao, Fenghuangshan, and Shatanjiao orefields. Until recently, the majority of these deposits were thought to be skarn‐ or porphyry–skarn‐type deposits; however there have been recent discoveries of numerous vein‐type Au, Ag, and Pb‐Zn deposits that do not fall into either of these categories. This indicates that there is some uncertainty over this classification. Here, we present the results of several systematic geological studies of representative deposits in the Tongling ore district. From investigation of the ore‐controlling structures, lithology of the host rock, mineral assemblages, and the characteristics of the mineralization and alteration within these deposits, three genetic types of deposits (skarn‐, porphyry‐, and vein‐type deposits) have been identified. The spatial and temporal relationships between the orebodies and Yanshanian intrusions combined with the sources of the ore‐forming fluids and metals, as well as the geodynamic setting of this ore district, indicate that all three deposit types are genetically related each other and constitute a magmatic–hydrothermal system. This study outlines a model that relates the polymetallic copper–gold porphyry‐, skarn‐, and vein‐type deposits within the Tongling ore district. This model provides a theoretical basis to guide exploration for deep‐seated and concealed porphyry‐type Cu (–Mo, –Au) deposits as well as shallow vein‐type Au, Ag, and Pb–Zn deposits in this area and elsewhere.

A Model of Hydrothermal Dolomite Reservoir Facies in Precambrian Dolomite, Central Sichuan Basin, SW China and its Geochemical Characteristics

AbstractHydrothermal mineral assemblages and related hydrothermally enhanced fracturing are common in the Precambrian Dengying Formation of Central Sichuan Basin. Petrographic and geochemical analyses of core samples show that the hydrothermal dolomite reservoirs of Dengying Formation consist of four main types of pores in the reservoir facies. These include: 1) hydrothermal dissolution vug (or pore), 2) intercrystalline pore, 3) residual inter‐breccia vug (or pore), and 4) enlarged dissolved‐fracture. There are three different fabrics dolomite in hydrothermal dolomite reservoirs, namely, saddle dolomite, fine‐medium dolomite and micritic dolomite. Micritic dolomite is the original lithology of host rock. Saddle dolomite with curved or irregular crystal faces was directly crystallized from hydrothermal fluids (average temperature 192°C). Fine‐medium dolomites are the products of recrystallization of micritic dolomite, resulting in abnormal geochemical characteristics, such as slight depletion of δ18O, significant enrichment of Mn‐Fe and 87Sr/86Sr, and positive Eu anomaly. A model for the distribution of various hydrothermal dolomite reservoir facies is proposed here, which incorporates three fundamental geological controls: 1) extensional tectonics and tectono‐hydrothermal events (i.e., the Xingkai Taphrogenesis of Late Sinian‐Early Cambrian, and Emei Taphrogenesis of Late Permian), 2) hydrothermal fluid storage in clastic rocks with large thickness (e.g., Nanhua System of Chengjiang Formation and part of Doushantuo Formation), and 3) confining bed for hydrothermal fluids (such as, the shale in Qiongzhusi Formation). The supply of hydrothermal fluid is critical. Large basement‐rooted faults and associated grid‐like fracture system may function as the channels for upward migration of hydrothermal fluid flow. The intersection of the above‐mentioned faults (including the conversion fault), especially transtensional sags above negative flower structures on wrench faults can serve as a key target for future hydrocarbon exploration.

The influence of fracture development on quality and distribution of volcanic reservoirs: a case study from the carboniferous volcanic reservoirs in the Xiquan area, eastern Junggar Basin

The distribution pattern of fractures in the Carboniferous volcanic rocks controls the oil and gas distribution in the Xiquan area located in the eastern Junggar Basin. This paper describes the types, characteristics, distribution of fractures in the volcanic rocks, and the evolutionary history of fractures, as well as the influence of fractures on the reservoir distribution in this area, based on analyzing cores, casting thin sections, imaging logging data, the measurement of the physical properties and integrated with the production testing. The lithology of these Carboniferous volcanic rocks is primarily andesite and volcanic breccia. Basalt, dacite, tuff, breccia lava, tuffaceous sandstone, and tuffite were also present. The fracture types are mainly shrinkage fractures, weathered fractures, dissolution fractures, and structural fractures, the majority of which are structural fractures and weathered fractures. The distribution of fractures has obvious zonation characteristics in the vertical direction. Fractures are mainly distributed at four intervals under the top surface of the Carboniferous unconformity: 0–50 m, 65–115 m, 125–155 m, and 170–210 m. There are mostly weathered fractures and dissolution fractures in the 0–50-m interval. The physical properties and oil production of andesite are the highest, and weathering fractures and dissolution fractures play a major role in controlling the secondary pores of volcanic lava and the formation of favorable reservoirs in this interval. The structural fractures were developed in the intervals of 65–115 m, 125–155 m, and 170–210 m. The physical properties and oil production of volcanic breccia are the highest, and therefore, structural fractures mainly control the formation of favorable reservoir in volcanic breccia in these three intervals. The evolution of fractures in the Carboniferous volcanic rocks experienced four phases: the condensation and shrinkage fracture stage, which developed the primary pores in the middle-late Carboniferous period; the weathered fracture and dissolution fracture stage, which greatly increased the porosity in the late Carboniferous period to the early-middle Permian period; the structural fracture and weathered fracture stage, which greatly increased the porosity and permeability of the reservoir from the end of the Triassic to the early Cretaceous period; and the filled fracture and dissolution fracture stage, which can also greatly increase the porosity of the volcanic reservoir and occurred wholly within the late Cretaceous period until the present.

Highly siderophile elements in Archaean and Palaeoproterozoic marine shales of the Kaapvaal Craton, South Africa

Determination of highly siderophile element (HSE; Au, Pt, Pd, Ir, Os, Rh and Ru) concentrations in relatively unweathered and unaltered marine shales from the Barberton, Witwatersrand and Transvaal supergroups in the Kaapvaal Craton revealed systematic differences, interpreted to reflect secular changes in the HSE content of Mesoarchaean to Palaeoproterozoic seawater. Most of the studied marine shales have HSE concentrations in the range given for average Archaean crustal rocks (0.5–5 ppb), with the exception of the shales in the Witwatersrand Supergroup. These shales contain up to three times more HSE, independent of source rock lithology in the granitoid-greenstone-dominated hinterland. Although sedimentary pyrite incorporated gold from synsedimentary to early diagenetic waters, its modal proportion (<3 vol.%) is too small to account for the total amount of Au and PGE in the studied marine shales. Instead, our results suggest that in addition to contributions from pyrite, some colloidal gold was attached to clay-sized sediments during source area weathering. Probably, colloidal gold and some of the platinum group elements were mechanically aggregated during sediment suspension and deposited synchronously with the host marine sediments.

Study on the risk assessment of water inrush in karst tunnels based on intuitionistic fuzzy theory

Water inrush is a major geological hazard that threatens the safety of karst tunnels. The risk assessment of water inrush is necessary in tunnel engineering. A new model based on intuitionistic fuzzy analysis was proposed to assess the risk of water inrush, which considered the subjective and objective weights of influencing factors. Seven factors were selected to constitute the set of evaluation attributes, namely, formation lithology, unfavourable geological conditions, groundwater level, landform and physiognomy, modified strata inclination, contact zones of dissolvable and insoluble rock, and layer and interlayer fissures. The proposed model was applied in a typical karst tunnel, Xiakou tunnel in China. The sensitivity of the changes in the index weights was analyzed. The results showed that the water inrush risk of section XJK0 + 110 to XJK0 + 060 in Xiakou tunnel was evaluated as grade I (high risk). The risk assessment results were more sensitive to the index weights of landform, formation lithology, and contact zones of dissolvable and insoluble rock than to those of the other indices. Landform was the most sensitive index. The obtained results were identical to the practical findings, and the rationality and feasibility of the model was verified. Intuitionistic fuzzy analysis is a new method for the quantitative risk assessment of water inrush in karst tunnels.

Characteristics and evaluation of Mesozoic source rocks in the southeastern East China Sea continental shelf

ABSTRACT Source rocks are the material basis of oil and gas generation and determine the potential resources of exploration blocks and have important research value. This paper studies the lithology, thickness, and geochemistry of Mesozoic source rocks in the southeastern East China Sea continental shelf. The results show that the Mesozoic source rocks are mainly dark mudstone and coal-bearing strata. The total thickness of Lower–Middle Jurassic source rocks ranges from 100 m to 700 m, and that of Lower Cretaceous source rocks ranges from 50 m to 350 m. The overall thickness of Mesozoic source rocks is distributed in the NE direction and their thickness center is located in the Jilong Depression. The Lower–Middle Jurassic source rocks are mainly developed shallow marine dark mudstone and transitional coal measure strata. Those of the Lower Cretaceous are mainly mudstone of a fan delta front. Lower–Middle Jurassic and Lower Cretaceous hydrocarbon source rocks are dominated by type III kerogen, with Lower–Middle Jurassic hydrocarbon source rocks having high organic matter abundance and being medium–good hydrocarbon source rocks, while Lower Cretaceous hydrocarbon source rocks have relatively poor quality. From northwest to southeast, the vitrinite reflectance Ro of Mesozoic source rocks increases gradually. Source rocks in the study area are divided into three types. The first hydrocarbon-generating area is mainly located in the southeastern region of the study area, and the Jilong Depression is the hydrocarbon-generating center. The results of this study can provide a basis for exploration of Mesozoic oil and gas resources in the southeastern East China Sea continental shelf. © 2019 China Geology Editorial Office.

Опыт применения ГИС для оценки эколого-геоморфологических условий особо охраняемых природных территорий Прионежья (в пределах Вологодской области)

The assessment of ecological-geomorphological conditions of Verkhneandomsky (on the Upper Andoma river), “Atleka” and Andomskaya Gora (Andoma Mountain) protected areas was performed by Moscow State University and Moscow State University of Geodesy and Cartography researchers during 2002–2017. The aim of the study was to evaluate conditions for the development of exogenous relief-forming processes under the influence of natural factors using geoinformation systems (GIS). Topographic maps (scale 1:100 000) were vectorized and transformed to the uniform coordinate reference system (Gauss-Krueger projection, Pulkovo-42 datum). The GIS allows carrying out the ecological-geomorphological analysis of exogenous relief-forming processes of specially protected natural areas (PAs), relying on the grouped materials in the database, adding the parameters of the “erosion layer” and conducting their subsequent processing. Spatial analysis in GIS environment made it possible to identify similarities in karst processes and the difference in their intensity, expressed in the thickness and spatial distribution of the “erosion stratum” of the landscape reserves of the Verkhneandomsky and “Atleka”, which is defined by the relief of the karst-glacial-lake basin and the “karst” plateau, respectively. On the Andomskaya Gora natural monument, the suffusion-karst process and ravine dominate, which is caused by lithology (sand and sandstones) of rocks and significant relative height of the coastal ledge. Topographic, geological, geomorphological, and thematic information, as well as the boundaries and unique characteristics of the protected areas, allowed us to compile a series of derived maps reflecting the purpose of the research.

Utilization of full-polarimetric SAR data (RADARSAT-2), ASTER and Landsat 8 data in geological mapping of the west Gebal Elba area, Halayeb district, South Eastern Desert, Egypt

The present study explored the potentiality of integrating principal component analysis, minimum noise fraction, independent component analysis transformation and spectral ratioing of selected bands of Landsat 8 and Advanced Spaceborne Thermal Emission and Reflection Radiometer for geological mapping in west Gebel Elba area, Halayeb district, South Eastern desert, Egypt. Data fusion of optical and radar remote sensing using Color Normalization Transformation showed an effective approach to further identify lithological units and rock boundaries. The Freeman–Durden decomposition method was used to determine the dominant scattering mechanisms and to identify the current state of the surface cover. This approach provided solution for geological mapping of the study area, which is impeded by difficult accessibility and could be generic methodology for similar studies. It enabled to identify and map rock units and lithological formations at range of validly from 73% for wadi deposits to 90 for quartz diorite.

Predicting Aquifer Storage Properties Integrating Geoeletric Methods with Dynamically Derived Geomechanical Parameters in Parts of Cross River State, Nigeria

Predicting subsurface rocks’ storage properties is a fundamental problem of groundwater prospecting and potential evaluation for planning of long term abstraction wells. Water in aquifers is stored and or released from elastic storage and gravity drainage. Aquifer storage parameters are traditionally determined from pumping tests data which are seldom available until wells have been drilled. Confined aquifer storativity (S) is estimated as a function of rock lithology and thickness of the aquifer using the rule of thumb equation S = 3.0 × 10-6b, but S = Ssb neglecting the effect of porosity and compressibility. The storativity equation assumes that all aquiferous rocks have a constant specific storage even though specific storage is directly dependent on rock porosity and most importantly rock grain compressibility which differs with lithology. In this study, apparent resistivity data derived from field resistance measurements in 31 locations were interpreted to infer geolectric layers lithologies and thicknesses. To determine the rock grain compressibility for computation of the specific storage, vertical stress at the aquifer depth was estimated using average densities of the interpreted subcrustal rocks. Results show that rock mineral grain compressibility varies from 7.915 × 10-7 to 9.235 × 10-5/Pa, porosity from 0.08 to 1.64 with the weathered overburden and sandstones having the higher porosities; specific storage vary from 8.32 × 10-6 to 1.80 × 10-3 and storativity ranges from 3.161 × 10-6 to 1.96 × 10-3. Clearly, results indicates that the specific storage differ predictably with rock type and consequently the storativity of the different aquifers.

Water-rock interaction of the Jilh and Tawil aquifers in the Wadi Sirhan Basin, NW Saudi Arabia

A total of 79 groundwater samples from the Upper Silurian-Lower Devonian Tawil and Triassic Jilh aquifers in NW Saudi Arabia were analysed for hydrochemical and strontium isotopic composition. A sequential extraction and 87Sr/86Sr analysis were conducted on 32 cutting samples from the groundwater host rocks and the underlying shale bed. The chemical composition of the groundwater was distinct from that of the host rock lithologies in terms of elemental abundance (i.e., Na+ was dominant in the groundwater and K and Ca were the main constituents of the aquifer units). Principal component analysis (PCA) of water samples showed a positive loading of Na+ and negative loadings of Ca2+ and SO42-. The replacement of gypsiferous waters by Na+-rich waters is suggested by this ion exchange. The shale rock samples showed Na to be the dominant chemical constituent. 87Sr/86Sr ratios of the groundwater (0.707673-0.711577) and host rock samples (0.707930-0.712477) suggest that groundwater inherits the Sr signature of the rock from the exchangeable, carbonate, and the oxides phase, reflecting reducing conditions in Tawil aquifer. The elevated groundwater 87Sr/86Sr ratios were found in deeper sections of the aquifers, which coincided with the radiogenic 87Sr/86Sr of the deeper aquifer lithologies and the underlying shale bed.

Development of an Empirical Equation To Predict Hydraulic-Fracture Closure Pressure From the Instantaneous Shut-In Pressure Using Subsurface Solids-Injection Data

Summary During hydraulic-fracturing operations, conventional pressure-falloff analyses (G-function, square root of time, and other diagnostic plots) are the main methods for estimating fracture-closure pressure. However, there are situations when it is not practical to determine the fracture-closure pressure using these analyses. These conditions occur when closure time is long, such as in mini-fracture tests in very tight formations, or in slurry-waste-injection applications where the injected waste forms impermeable filter cake on the fracture faces that delays fracture closure because of slower liquid leakoff into the formation. In these situations, applying the conventional analyses could require several days of well shut-in to collect enough pressure-falloff data during which the fracture closure can be detected. The objective of the present study is to attempt to correlate the fracture-closure pressure to the early-time falloff data using the field-measured instantaneous shut-in pressure (ISIP) and the petrophysical/mechanical properties of the injection formation. A study of the injection-pressure history of many injection wells with multiple hydraulic fractures in a variety of rock lithologies shows a relationship between the fracture-closure pressure and the ISIP. An empirical equation is proposed in this study to calculate the fracture-closure pressure as a function of the ISIP and the injection-formation rock properties. Such rock properties include formation permeability, formation porosity, initial pore pressure, overburden stress, formation Poisson's ratio, and Young's modulus. The empirical equation was developed using data obtained from geomechanical models and the core analysis of a wide range of injection horizons with different lithology types of sandstone, carbonate, and tight sandstone. The empirical equation was validated using different case studies by comparing the measured fracture-closure-pressure values with those predicted by using the developed empirical equation. In all cases, the new method predicted the fracture-closure pressure with a relative error of less than 6%. The new empirical equation predicts the fracture-closure pressure using a single point of falloff-pressure data, the ISIP, without the need to conduct a conventional fracture-closure analysis. This allows the operator to avoid having to collect pressure data between shut-in and the time when the actual fracture closure occurs, which can take several days in highly damaged and/or very tight formations. Moreover, in operations with multiple-batch injection events into the same interval/perforations, as is often the case in cuttings/slurry-injection operations, the trends in closure-pressure evolution can be tracked even if the fracture is never allowed to close.

Review of the Role of Remote Sensing Applications in Mineral Exploration and Sustainable Development in Oman

Applications of remotely sensed satellite data are wide and unique in the mapping of different lithologies, mineral resources, and ore deposits. Satellite images are capable in discriminating rock types useful for geological applications and significantly used in the identification of mineral resources. The techniques are low-cost and save time in mapping and exploration of such resources and are well-suitable and applicable to the arid region. Oman has the potential occurrence of the industrial minerals and ore deposits which mostly occur in inaccessible mountains and desert regions where it is difficult to do conventional geological mapping. Thus, understanding the capability of the techniques to map and ex­plore such potential resources by geologists is highly important. The absorption characters of spectral bands of Advanced Spaceborne Thermal Emission and Re­flection Radiometer (ASTER) and selected imaging processing methods namely decorrelation stretching, band ratios, linear spectral unmixing (LSU), and Mixture Tuned Matched Filtering (MTMF) demonstrates the sensor capability of ASTER to map several mineral deposits and different rock lithologies in Oman, which in­cludes limestone, marl, listwaenites, carbonatites, metamorphic zones, caves, karst, springs, vegetation’s, rock fall and slide, Moho, copper, chromite, awaruite, manganese, and gold deposit in different parts of the Sultanate of Oman. It demonstrates the spectral sensitivity of such rocks for simple interpretation over satellite data and describes and distinguishes them based on the absorptions of hydrous minerals in the spectral bands of ASTER for mapping and exploration studies.

Tungsten from typical magmatic hydrothermal systems in China and its environmental transport

Tungsten is of extraordinarily high concentrations in the geothermal waters discharging from several representative Tibetan magmatic hydrothermal systems (up to 1103 μg/L), which are also characterized by exceptionally high W/Mo molar ratios (up to 1182). The geochemical origins of the tungsten in these geothermal waters were investigated, with a comparison to those from Rehai, the sole magmatic hydrothermal system in Yunnan, which is another major part of the Yunnan-Sichuan-Tibet Geothermal Province of China. The results show that the lithology of reservoir host rocks is the primary factor controlling the tungsten concentrations of the geothermal waters, although the contribution of magmatic fluid input cannot be ruled out. In this study, the geothermal waters are generally rich in sulfide, and therefore the molybdenum in the reservoir fluids has been substantially precipitated as the form of molybdenite; in contrast, the reservoir fluids are well undersaturated with respect to tungstenite which is much more soluble than molybdenite. Thus the neutral/alkaline hot springs, i.e. the evolved reservoir fluids, have high W/Mo molar ratios as well. In the hot spring sediments, the distribution pattern of tungsten is quite different. The concentrations of tungsten are the highest in the sediments with high iron concentrations collected from the acid hot spring vents and outflow channels. The adsorption of aqueous tungsten onto iron-bearing minerals, like goethite or pyrite, is favorable at acid pH values and thereby responsible for the very high tungsten concentrations of these acid hot spring sediments. The proportions of thiotungstates in total tungsten are quite low for all the hot springs, as indicated by thermodynamic calculations, suggesting that thiolation of tungstate has little impacts on the environmental transport and fate of geothermal tungsten in the investigated hydrothermal areas. This is the first study to report the tungsten geochemistry of hot springs in mainland China.

Determination of Hydrocarbon Zones Using Logging Data Analysis in A Sandstone Reservoir (Case Study: Structure ‘TL’ Basin North West Java)

DOI: 10.17014/ijog.5.3.251-263Northwest Java Basin is one of the Indonesian basins that has the potential of hydrocarbon reservoir. A petrophysical analysis plays a role in determining the physical properties of reservoir rocks such as shale volume, porosity, and water saturation zones which is to analyze the hydrocarbon zone possibilities (net pay). A qualitative analysis and correlation of rock lithology study were carried out at seven wells, while a quantitative study was performed by calculating the volume of the shale with a linear method, density-neutron porosity, and water saturation using simandoux equation, then zoning the prospect zones was finally done. Based on the calculation and data analysis, Vsh cutoff value obtained is 23%, the porosity is 10.6%, and water saturation is 71%. Then, the zones of hydrocarbon prospects were recovered, that are the PI-08 wells (9.632 ft - 9.662 ft), PI-10 (9.420 ft - 9.468 ft, 9.475 ft - 9.516 ft, 10.155 ft - 10.175 ft), well PI-11 (9.268 ft - 9.288 ft), well PI-11ST (9.268 ft - 9.927 ft), well PI-12 (9.396 ft - 9.461 ft, 10.047 ft - 10.059 ft), and PI-13 wells (9.356 ft - 9.416 ft, 9.980 ft - 10.000 ft).