Gray Sandstone Research Articles

Early Tree Growth in Reclaimed Mine Soils in Appalachia USA

Surface mining disturbs hundreds of hectares of land every year in many areas of the world, thereby altering valuable, ecologically-diverse forests. Reforestation of these areas after mining helps to restore ecosystem functions and land value. In Appalachia, native topsoil is normally replaced on the surface during reclamation, but waivers allow for brown and gray sandstone materials to be used as topsoil substitutes. Numerous studies report the growth of trees in these substitute mine soil materials, but few studies have compared the height of trees grown in reclaimed mine soils to the heights of trees grown in native soils. This study determined the growth of red oak (Q. rubra L.), white oak (Quercus alba L.), and tulip poplar (Liriodendron tulipifera L.) in two mine soil types which were compared to projected growth in native soils. Heights of tree seedlings in native soils at 11 years were estimated from site indices (SI) from USDA Soil Survey data. At the mine sites, areas with brown and gray mine soils (one site with a mulch treatment) had 12 tree species planted and growth was measured annually for 11 years. Mine soil pH after 11 years was 5.3 for brown mine soils, 6.6 for gray mine soils, 7.0 for mulched mine soils, and 4.1 to 5.2 for native forest soils. After 11 years, tree heights in gray mine soils were significantly lower (0.5 m) than tree heights in brown mine soils (2.8 to 4 m) for all three species. Trees in mulched mine soils were up to 0.7 m taller than trees in un-mulched brown mine soils. After 11 years, red oak height was 6.3 m in native soils and 3 m in brown and mulched mine soils (52% lower); white oak was 7.3 m tall in native soils compared to 3.6 m in brown mine soils (50% lower); and tulip poplar was 11.5 m tall in native soils and 3.5 to 4 m tall in brown and mulched mine soils (70% lower). In gray mine soils, trees were not growing at all. While the trees in brown mine soils are growing, tree growth has not reached projected levels of tree growth in native soils during the first 11 years after planting. The purpose of forestry reclamation is to restore ecosystem diversity and function. This study showed that one measure of ecosystem function, tree growth, was 50% lower on reclaimed mine soils than native forest soils. Maturing mine soils may develop properties over time that are similar to native soils and, with the increased rooting depth, may provide conditions where increased tree growth rates and height may be attained during the next several decades.

Geology of the area between Bardibas and Sindhuli Madi, Sub-Himalaya, Central Nepal

The Siwalik Group (Sub-Himalaya) is the east-west extending youngest mountain belt formed by the sediments derived from the rising Himalaya on the north. The Siwalik Group is separated from the Lesser Himalaya to the north by the Main Boundary Thrust (MBT), and the Indo-Gangetic Plain to the south by the Main Frontal Thrust (MFT). The study was carried out mainly along the Ratu Nadi, Kamala Nadi river sections and was lithostratigraphically divided into the Lower Siwalik, Middle Siwalik, and Upper Siwalik, from the bottom to the top section, respectively. The Lower Siwalik is composed of fine-grained greenish grey calcareous sandstone (subarkose and lithic arenite), variegated mudstone, and calcareous siltstone. The Lower Siwalik is exposed due to the Marine Khola Thrust in the Gadyauli Khola, and sandstone there is more indurated and non-calcareous. The Middle Siwalik is mainly comprised of the medium- to coarse-grained salt-and-pepper sandstone (arkose and subarkose) with large cross lamination, calcareous sand lenses, convolute bedding, dark grey siltstone and mudstone. Plant fossils are also present in the finely laminated clay bed of the Middle Siwalik along the Ratu Nadi section. The Upper Siwalik comprises of mud- to sand-supported pebble to cobble conglomerates.

Characteristics of Paleozoic tight gas sandstone reservoir: integration of lithofacies, paleoenvironments, and spectral gamma-ray analyses, Rub’ al Khali Basin, Saudi Arabia

The glaciogenic Sarah Formation (Hirnantian) is a potential tight gas sandstone reservoir in the Rub’ al Khali Basin and other basins in Saudi Arabia. This study investigated the facies heterogeneity and paleoenvironments of the Sarah Formation using cores, petrographic thin sections, and spectral gamma-ray (SGR) analyses. The study revealed four facies associations (FAs), including massive to ripple-laminated sandstone (FA1), gray massive sandstone (FA2), diamictites (FA3), and partially deformed, massive-graded sandstone (FA4), interpreted to have been deposited in fluvial, glaciofluvial, glaciolacustrine delta, and subglacial outwash environments, respectively. The sandstone varies from fine-, to medium-, and coarse-grained and is a moderately to poorly sorted quartz arenite, subarkose, and to sublithic arenite. The integration of facies analysis with SGR analysis allowed us to classify the facies further into low matrix and argillaceous sandstones in the fluvial and glaciofluvial facies, mixed sandstones in the glaciolacustrine delta facies, and clast-supported and matrix-supported diamictites with shales in the subglacial facies. The results of this study might provide guidelines for facies identification and the prediction of reservoir-quality targets in the tight sandstone in the subsurface. This classification could facilitate the identification of and distinction between the glaciogenic lithofacies of tight gas reservoirs in the subsurface and provides a tool for correlating the lithofacies. This work might also provide guidelines for the exploration and development of Paleozoic tight gas sandstone reservoirs in the subsurface that are deeply buried and show a wide range of facies, paleoenvironments, and paleogeographic settings.

Green altered sandstone related to hydrocarbon migration from the uranium deposits in the northern Ordos Basin, China

The formation of sandstone-hosted uranium deposits has been linked to upward migration of hydrocarbons in many sedimentary basins. However, hydrocarbon-induced diagenetic alterations associated with uranium mineralization and preservation are rarely discussed. Here, we report the bleaching of red sandstone to green in the Middle Jurassic Zhiluo Formation from the uranium deposits in the northern Ordos Basin, China. The original gray sandstone underwent oxidation and was reddened by the downward flow of meteoric water from the northern margin of the basin during the Late Cretaceous–Cenozoic uplift. This process resulted in the leaching of preore-stage uranium concentration and oxidation of preore pyrite in the organic matter-rich sandstone. Uranyl and sulfate ions were carried downward through the host sandstone by oxygenated groundwater. Meanwhile, hydrocarbons migrated upward and reacted with the downward flowing oxidizing fluids, which induced uranium mineralization at the redox interface between the red and gray sandstone where iron was reduced to Fe2+ and incorporated into pyrite cement. The highly negative 34S values (−58.0‰ to −33.4‰ V-CDT) of the pyrite indicate that it originated from bacterial sulfate reduction during hydrocarbon biodegradation. Abundant organic acids and CO2 were generated from hydrocarbon oxidation, resulting in the dissolution of feldspars and the precipitation of kaolinite in the mineralized sandstone. With the formation of the Cenozoic Hetao graben to the north, the gravity-driven flow of meteoric water was limited, resulting in progressive halting of epigenetic uranium mineralization. Then, the upward hydrocarbons dominated the fluid system throughout the northern slope of the basin and bleached the previous red sandstone updip, which set up a strong reducing environment and protected the early formed uranium deposits at the paleo-redox front from oxidation and remobilization. Due to the oxygen and sulfur supply absence, the iron released from hematite during bleaching was immobilized and incorporated into Fe-rich chlorite that imparts the green color, rather than into pyrite or reprecipitation as hematite. This study provides insights for the processes of hydrocarbon-water-rock interactions associated with uranium mineralization and preservation, which can serve as exploration guides for sandstone-hosted uranium deposits.

Evaluating the integrity of clayey sandstone rocks flooded with high pH EDTA chelating agent solutions

Abstract Understanding the interactions between the injected enhanced oil recovery (EOR) fluids and sandstone reservoir rock minerals during the flooding processes requires special attention due to the presence of several types of highly reactive clays and non-clay minerals with different concentrations which interact with the injected non-native solutions and affect the effeciency of the oil recovery process. In this study, four coreflood experiments were carried out using two different sandstone core samples namely Gray Berea and Gray Bandera sandstone having clay contents of 8 wt% and 12 wt%, respectively, to evaluate the integrity of the clayey sandstone rocks flooded with 5 wt% and 10 wt% EDTA solutions with pH of 12. To study the presence and distribution of the clay and non-clay minerals into these sandstone rocks, x-ray diffraction (XRD), scanning electron microscope (SEM), and nuclear magnetic resonance (NMR) were used to characterize the core samples before the coreflooding tests. After the coreflooding experiments, XRD analysis was used to identify the precipitated minerals, and the alteration in the flooded rocks integrity was investigated through application of NMR, computed tomography (CT) scan analyses, and permeability measurements. The exchangeability of the chelated iron from the sandstone rocks to the EDTA solutions was studied by analyzing the produced effluents through inductively coupled plasma (ICP) analyses. The pressure drop observed during the coreflooding experiments revealed the compatibility of the injected solutions and the core samples. The results of this study dominates that Gray Berea sandstone is compatible with the 5 wt% and 10 wt% of the EDTA solutions as confirmed by the permeability measurements, CT scan analysis, NMR results, and the pressure drop during the flooding tests; which indicates that there was no fine migration, clay minerals swelling, and/or non-clay minerals dissolution caused by the interaction of Gray Berea with the EDTA solutions. On the other hand, Gray Bandera core samples were found to exhibit incompatibility with a solution of more than 5 wt% of EDTA as indicated by the CT scan and the high permeability enhancement because of the interaction of EDTA with ankerite mineral.

Middle Jurassic palaeoenvironment and palaeobiogeography of the Tabas Block, Central Iran: palynological and palaeobotanical investigations

We performed a palynological study on Jurassic successions of the Hojedk Formation, Central Iran. The sampled material was recovered from well no. 233, South Kuchak-Ali area belonging to the Tabas Block. The lithology comprises 475.80 m of green–grey shales and sandstones. Palynological assemblages were recovered including spores, pollen grains, dinoflagellate cysts, woody debris and amorphous organic matter (AOM). Furthermore, 22 taxa of plant macrofossils were identified. We analysed 48 samples which resulted in identification of 13 spore species (belonging to 11 genera) and three pollen species (from three genera) with fair preservation quality. Trilete spores dominate while pollen grains only represent 11.5% of the total particulate organic matter. Representatives of the fern spore Klukisporites are particularly abundant and the K. variegatus acme zone, which is of biostratigraphical importance, is identified in the host strata. The abundance of K. variegatus and K. scaberis suggests a Middle Jurassic (Bajocian–Bathonian?) age for the host strata. This age designation corroborates previous stratigraphic interpretations, mainly based on plant macrofossils for this formation. The palynomorphs indicate deposition in an oxygenated environment close to the shoreline in a deltaic system. The presence of subordinate marine palynomorphs (proximate dinoflagellate cysts) is probably indicative of intermittent sea level transgression. The affinity of the palynological assemblages from the Hojedk Formation indicates a diverse parental flora of, in descending quantitative order, ferns, bryophytes and gymnosperms, the latter mainly represented by conifers and ginkgophytes. Comparisons with modern plant ecology indicate accumulation of palynomorphs under a moist warm climate during the Middle Jurassic (Bajocian–Bathonian?) time. The comparison of parental plants with previous palaeofloristic studies indicates that the Tabas Block was located in the Mid-Asian part of the Indo-European floristic province of the Northern Hemisphere.

Microfacies characteristics and reservoir potential of Triassic Baikouquan Formation, northern Mahu Sag, Junggar Basin, NW China

By using data such as lithology, thin sections, sedimentary structure, particle size, logging facies signs, mercury intrusion, porosity and permeability from 34 wells, 11 types of sedimentary microfacies were divided in this study. Upon analysis, sedimentary microfacies exert significant control on reservoirs, and high quality reservoirs are primarily developed with the following sedimentary microfacies: gray sandy conglomerate in underwater distributary channels microfacies of fan delta fronts sub-facies, river-estuary dams and gray sandstones of distal bars on the front edge of the fan delta that have strong hydrodynamic conditions and good stability. Relatively good reservoirs are primarily distributed in the braided channel in fan-delta plains with brown sandy conglomerates, main channel of underwater distributary channels on the front edge of the fan delta with gray conglomerates and underwater distributary channel ends on the front edge of the fan delta with gray fine sandstones. With the stable tectonic background, Triassic sedimentary microfacies in the Mahu sag control the distribution and development of reservoirs. Therefore, sites of high quality reservoirs can be predicted by sedimentary microfacies, and this study provides guidance for oil and gas exploration.

Multiphase dolomitization in the Jutana Formation (Cambrian), Salt Range (Pakistan): evidences from field observations, microscopic studies and isotopic analysis

Excellent dolomite exposures are observed in the eastern Salt Range (Pakistan), where the Cambrian Jutana Formation consists of two distinct units (i.e. oolitic – pisolitic unit and massive dolomite unit). Field observations revealed that the lower, oolitic-pisolitic unit mostly comprises medium to thick bedded, interlayered brown yellowish dolostone containing ooids/pisoids and faunal assemblages, and grey whitish sandstone with distinct depositional sedimentary features (i.e. trough-, herringbone- and hhummocky crossbedding). The upper massive dolostone unit consists of thick bedded to massive dolostone. These two units are separated by shale. Petrographic studies identified three dolomite types, which include: fine crystalline dolomite (Dol. I), medium-coarse crystalline dolomite (Dol. II) and fracture associated, coarse crystalline dolomite (Dol. III). Stable isotope studies indicate less depleted δ 18 O values for Dol. I (-6.44 to -3.76‰V-PDB), slightly depleted δ18O values for Dol. II (-7.73 to -5.24‰V-PDB) and more depleted δ 18 O values for Dol. III (-7.29 to -7.20‰V-PDB). The δ 13 C values of the three dolomite phases are well within the range of Cambrian sea-water signatures. Furthermore, δ 26 Mg-δ 25 Mg signatures (Dol. I; δ 26 Mg=-1.19 to -1.67, δ 25 Mg=-0.61 to -0.86 and Dol. II; δ 26 Mg=-1.34 to -1.59, δ 25 Mg=-0.70 to -0.83) indicate three phases of dolomitization in different diagenetic settings. First, an initial stage of dolomitization during the early Cambrian resulted from altered marine, Mg-rich fluids associated with the mixing zone mechanism. Second, a late stage of dolomitization was associated with burial during late Permian. A third dolomitization phase was related to post-Eocene times.

Geochemistry and geochronology of the Paleozoic sedimentary rocks in the Shar Khutul area, Central Mongolia

The study area is located in the central part of Tsetserleg terrane in the southwestern margin of the Khangai-Khentey orogenic system. The paper presents new data on geochemistry and geochronology of sedimentary rocks from the Shar Khutul area, where the Tsetserleg terrane consists of Silurian-Devonian oceanic plate stratigraphic unit and Carboniferous shallow water sediment. The Upper Silurian to Middle Devonian Erdenetsogt Formation (S3-D2er), which is an oceanic plate stratigraphic unit, is mainly composed of siliceous siltstone, volcanites, tuffs, quartzite, and cherts. The shallow water sediments are divided into Upper Devonian to Lower Carboniferous Tsetserleg Formation (D3-C1cc) and Lower–Middle Carboniferous Dzargalant Formation (C1-2dz). The Tsetserleg Formation (D3-C1cc) consists of only sedimentary rocks such as bluish-grey sandstones and siltstones, and Lower–Middle Carboniferous Dzargalant Formation (C1-2dz) is principally composed of medium- to coarse-grained, brown-greenish grey sandstones with thin-layers of dark siltstones and gravelites. 
 The SiO2 content of the Shar Khutul area sandstones ranges from 63.85 to 67.95 wt.% and the average content of TiO2 is 0.72 wt.% and Al2O3 content is 14.38 wt.%. The Chemical Index of Alteration (CIA) value ranges from 48.71 to 56.94 and the range of Index of compositional variations (ICV) is from 0.98 to 1.24. Moreover, the samples studied show that most of the sandstones are generally immature and were derived from weakly weathered source rocks.
 The ratios of Eu/Eu* (0.83), La/Sc (3.81), La/Co (5.30), and Cr/Th (13.81) indicate that the derivation of the Shar Khutul area sandstones from felsic rock sources and confirm the signatures of a felsic igneous provenance and suggest an active continental margin tectonic setting of the source area.
 The clastic zircons from the medium grained sandstone (Erdenetsogt formation) yield ages between 2.5 Ga and 236 Ma and the detrital zircons exhibit four peak ages at 1.7-2.5 Ga (n = 13), 455-499 Ma (n = 6), 337-382 Ma (n = 13) and 236–250 Ma (n = 5).

Spoil Type Influences Soil Genesis and Forest Development on an Appalachian Surface Coal Mine Ten Years after Placement

Surface mining for coal (or other mineral resources) is a major driver of land-use change around the world and especially in the Appalachian region of the United States. Intentional and well-informed reclamation of surface-mined land is critical for the restoration of healthy ecosystems on these disturbed sites. In Appalachia, the pre-mining land cover is predominately mixed hardwood forest, with rich species diversity. In recent years, Appalachian mine reforestation has become an issue of concern, prompting the development of the Forestry Reclamation Approach, a series of mine reforestation recommendations. One of these recommendations is to use the best available soil substitute; however, the characteristics of the “best” soil substitute have been an issue. This study was initiated to compare the suitability of several types of mine spoil common in the Appalachian region: brown sandstone (Brown), gray sandstone (Gray), mixed spoils (Mixed), and shale (Shale). Experimental plots were established in 2007 with each spoil type replicated three times. These plots were planted with a mix of native hardwood species. Ten years after plot construction and planting, tree growth and canopy cover were highest in Brown, followed by Shale, Mixed, and Gray. Soil conditions (particularly pH) in Brown and Shale were more favorable for native tree growth than Mixed or Gray, largely explaining these differences in tree growth and canopy cover. However, soil chemistry did not clearly explain differences in tree growth between Brown and Shale. These differences were more likely related to differences in near-surface soil temperature, which is related to soil color and available shade.

The aftermath of the CPE and the Carnian–Norian transition in northwestern Sichuan Basin, South China

The northwestern Sichuan Basin (South China) was a portion of eastern Tethys where, during the Late Triassic, a sharp lithological transition from oolitic–bioclastic limestones and sponge reef mounds to dark grey terrigenous clays, siltstones and sandstones is visible in several localities. The timing and significance of this major facies transition is still unclear. Here we report new biostratigraphic and carbon stable isotope data from Hanwang and Jushui, northwestern Sichuan Basin. Sporomorphs, ammonoids, conodonts and halobiid bivalves show that the lithological change is Late Carnian to Early Norian in age. This amended age determination facilitates recalibration of the magnetostratigraphy in the area allowing correlation between the Late Triassic of the Sichuan Basin and the Astrochronostratigraphic Polarity Time Scale. A carbon stable isotopic perturbation across the Carnian–Norian Boundary (CNB) is missing in our sections, or it is concealed because of the mixed organic matter sources. Our findings pinpoint the position of the CNB to a short stratigraphic interval of c. 12 m thickness in the Sichuan Basin. The studied sections greatly extend the palaeogeographical documentation of the CNB and provide novel information on biostratigraphy and chemostratigraphy that should be considered in defining the best position of the Norian Global Stratotype Section and Point.

Geology and geochemistry of the Kadamzhai and Chauvai gold-antimony-mercury deposits: Implications for new province of Carlin-type gold deposits at the Southern Tien Shan (Kyrgyzstan)

The Tien Shan Belt extends for over 2500 km, from western Uzbekistan, through Tajikistan, Kyrgyzstan and southern Kazakhstan to western China, and represents a part of the Altaid Orogenic Collage. The Tien Shan is one of the largest gold provinces on Earth and hosts several world-class gold deposits. The Turkestan-Alay and Southern Fergana regions, located within the South Tien Shan, host an important Hg–Sb mineral province with proven reserve of over 5 Mt Sb and 0.8 Mt Hg. In Soviet times, during the intensive study and exploitation of the mercury-antimony deposits, increased gold content of these ores has been noted. But the focus on only the main ore components (Hg-Sb), as well as the absence of “working” exploration geological and genetic models of Carlin type deposits, did not allow to fully assess the gold potential of the ore belt. Meanwhile, gold exploration in the region during the past two decades has identified a few deposits, now recognized as Carlin type. The studied Chauvai and Kadamzhai Hg-Sb deposits belong to the central part of the South Fergana antimony-mercury belt and, together with other Hg-Sb deposits (Abshyr, Khaidarkan), form a large ore province. They are located in the northern arms of the Alay ridge extending along the southern flank of the Kauzan antiform. The South Fergana antimony-mercury belt is commonly associated with the North-Katran regional deep fault (located between the southern edge of the Fergana depression and the foot of the Alay and Turkestan ridges). The host rocks are represented by alternating grey inequigranular gradational-layered sandstones, gravel, associated with sandstones by gradual transitions, and dark-grey carbonaceous siltstones, enriched in organic matter. Gold mineralization is confined to the main contact of the Tolubai Formation and Alay limestone. The rocks of the Tolubai Formation and Alay limestones have undergone pervasive hydrothermal alteration near the “main contact”. Based on the study of host rocks, three main types of gold-associated alteration have been recognized, such as jasperoides, decarbonatization, and sulfidization. Mineral composition of the Kadamzhai and Chauvai deposits is similar to gold deposits located in Nevada and Guizhou province. These deposits contain both Au and Sb-Hg. The main minerals in gold ore are pyrite, marcasite, arsenopyrite, orpiment, and realgar. The Sb-Hg ores are represented by cinnabar and stibnite. Deposits contain invisible gold (no observed native gold) associated with arsenic, antimony, mercury, and thallium, and have high gold-silver ratios. The distribution of gold is structurally controlled and is disseminated in the wall rocks. Structural settings for gold mineralization at the Kadamzhai and Chauvai deposits are transpressional regime. Based on geology, geochemical signatures and mineral composition of the Kadamzhai and Chauvai deposits that these deposits can be classified as Carlin type.

A revised stratigraphy of the Bida Basin, Nigeria

The Bida Basin is a NW-SE trending inland basin, stretching from Shegwa (NW) to Dekina (SE). It is approximately 350 km long and varies in width from 75 to 150 km. It is roughly elliptical in ground plan and runs perpendicularly to the western margin of the NE-SW trending Benue Trough Complex. Unlike other sedimentary basins in Nigeria, it is characterized by the absence of volcanics, carbonates and rocks of Tertiary age. Dedicated fieldwork carried out over the past four years revealed that the basin is underlain by mainly continental sediments with minor occurrence of marginal/shallow marine to freshwater flood-plain deposits. The initial basin fill is characterized largely by several cycles of simple, but amalgamated and/or stacked fanglomerates (alluvial fan) systems developed from several single stream breaches onto the proximal setting of the basin. These fanglomerates directly overly the Basement Complex and display a fining upward sequence. This unit is generally accepted as the Lokoja/Bida Sandstone. Our studies revealed that the Lokoja/Bida Sandstone is overlain directly by the oolitic/pisolitic ironstone of the Agbaja/Sakpe Ironstone which is in turn succeeded by a sequence of rocks generally referred to as the Patti/Enagi Formation, which is comprised of predominantly fine to medium-grained, grey and white sandstones, grey clays, carbonaceous silts and shales, and ubiquitous concretionary ironstone bands. This observation is opposed to the widely accepted view of previous workers that considered the Agbaja Ironstone as the youngest formation in the basin. This study further revealed that the sequence of rocks used to define the Patti Formation does not exist at the location of Mount Patti in Lokoja, rather, it is found in road cut sections, quarries and boreholes around the Ahoko Village. Following the rules for stratigraphic nomenclature, it is hereby proposed that the name ‘Patti Formation’ should be changed to ‘Ahoko Formation.’ A new geological map was made for the basin which clearly demonstrates the relationship of the formations.

Experimental investigation on the impact of connate water salinity on dispersion coefficient in consolidated rocks cores during Enhanced Gas Recovery by CO2 injection

Connate water salinity is a vital property of the reservoir and its influence on the displacement efficiency cannot be overemphasised. Despite the numerous analytical literature on the dispersion behaviour of CO2 in CH4 at different parametric conditions, studies have so far been limited to systematic effects of the process while parameters such as connate water salinity of the reservoir has not been given much attention and this could redefine the CO2CH4 interactions in the reservoir. This study aims to experimentally determine the effect of connate water salinity on the dispersion coefficient in consolidated porous media under reservoir conditions. A laboratory core flooding experiment depicting the detailed process of the CO2CH4 displacement using Grey Berea sandstone core sample at a temperature of 50 °C and at a pressure of 1300 psig was carried out to determine the optimum injection rate, from 0.2 to 0.5 ml/min, for the experimentation based on dispersion coefficients and methane recovery in the horizontal orientation. This was established to be 0.3 ml/min. At the same conditions, the effects of connate water saturation of 10% and a salinity of 0 (distilled water), 5, and 10% wt. with a CO2 injection rate of 0.3 ml/min on the dispersion coefficients was investigated. The results from the core flooding process indicated that the dispersion coefficient decreases with increasing salinity, hence the higher the density of the immobile phase (connate water) the lower the dispersion of CO2 into CH4. This is a significant finding given that the inclusion of the connate water and its salinity have an effect on the mixing of the gases in the core sample and should be given importance and included during simulation studies for field scale applications of Enhanced Gas Recovery (EGR). This is the first experimental investigation into the relationship between the connate water salinity and the dispersion coefficient in consolidated porous media.

Effects of different intertidal hard substrates on the recruitment of Crassostrea gigas

Physical properties, distribution, and abundance of natural hard substrates are important variables modulating the potential distribution of sessile aquatic species. In this study, we analyze the effects of the geological origin of different rock types common in intertidal environments of Argentina on the recruitment success of the nonindigenous Pacific oyster Crassostrea gigas, accounting for spatial and interannual variation. A series of experiments showed that although recruitment occurs on all of the five most widespread hard substrates in the region (i.e., pelitic mudstone, limestone, conglomeradic sabulitic sandstone, gray sandstone, and volcanic rock) it is significantly higher on pelitic mudstone. Accounting for the geographic distribution of these substrate types along the coast of Argentina, it is concluded that the Valdes Peninsula and central San Jorge Gulf areas, where pelitic mudstone outcrops are the dominant intertidal hard substrate, are the regions with highest potential for C. gigas intertidal reef formation. Pelitic mudstone displayed the highest mean values of specific heat and porosity as well as high values of luminosity.

Occurrence characteristics and influential factors of movable fluids in pores with different structures of Chang 63 reservoir, Huaqing Oilfield, Ordos Basin, China

Abstract Exploration and development of Chang 63 reservoir in the Huaqing Oilfield, Ordos Basin is challenging because of the complex geological features, including strong heterogeneity, complicated microscopic pore structures, low saturation of movable fluids, and distinct fluid distribution characteristics. Confronted with this challenge, this study used the nuclear magnetic resonance (NMR) technique to quantitatively evaluate the movable fluids in pores with different structures. Moreover, microscopic experiments were conducted to analyze the occurrence characteristics and influential factors of movable fluids in pores with different structures, including conventional physical property analysis, image porosity measurement, casting thin section observation, SEM analysis, high pressure mercury intrusion testing, and constant pressure mercury intrusion testing. The results showed that gray and grayish brown lithic feldspar sandstones were the dominant types of sandstone. Residual intergranular pores and feldspar dissolved pores were the main pore types, with unevenly distributed pore throat radii, among which small pores and micropores were primary. Four types of pore structures could be divided according to comprehensive analysis of capillary pressure curves, namely Types I, II, III, and IV, and they were featured by movable fluids with distinct occurrence characteristics in them. Reservoir permeability was well correlated with movable fluid saturation. Multiple factors were demonstrated to influence the movable fluid saturation in pores with different structures, including pore throat radius, pore-throat radius ratio, sorting coefficient, effective pore and throat volume, maximum mercury saturation in pores and throats, and interstitial clay minerals. Generally, good physical properties led to larger variation of movable fluid saturation. Among them, effective pore throat radius and pore-throat radius ratio were the dominant factors, effective pore and throat volume as well as sorting coefficient had some degree of influence, and maximum mercury saturation and physical properties had little effect on the movable fluid saturation.

ENGINEERING GEOLOGICAL STUDY ON THE SLOPE FAILURE ALONG THE KIMANIS TO KENINGAU HIGHWAY, SABAH, MALAYSIA

The geology along the Kimanis to Keningau Highway provides a favourable setting for engineering geological instability. The area is underlain by the Crocker Formation (Late Eocene to Early Miocene age) to vary recent Quaternary alluvial materials which are still being deposited. Crocker Formation consists mostly of interbedded grey sandstones and grey mudstones or shales. The sandstones are texturally immature where angular to subrounded quarts grains are cemented by clay minerals and occasionally by calcite. The Crocker Formation has also undergone intense deformation. The tectonic complexities influenced the physical and mechanical properties of the rocks, resulting in a high degree of weathering and instability. The weathered materials are unstable and may experience sliding due to by high pore pressure and intensively geomorphological processes. In this study, a total of 28 selected critical slope failures were studied and classified into two main groups: rock slope and soil slope. Failures in soil slopes (including embankments) are 18 (64 %) whereas 10 of all failures (36 %) of rock slope. Soil slope failures normally involved large volumes of failed material as compared much rock slopes, where the failures are mostly small. Of the 18 failures in soil slopes, 6 (33 %) are embankment failures making them 21 % of all types of failures. Kinematics rock slope analyses indicates that the variable potential of circular, planar, wedges and toppling failures modes as well as the combination of more than one mode of aforementioned failure. Rock and soil slopes stability analysis indicates that the factor of safety value as unsafe (0.50 to 0.96). The main factors causing slope failure occurrences in the study area are natural (geology, meteorology, topography and drainage system) and human factors (lack of proper planning, human activities and community’s attitude). Development planning has to consider the hazard and environmental management program. This engineering geological study should be prioritized and take into consideration in the initial step in all infrastructures program and it may play a vital role in landslide hazard and risk assessment to ensure the public safety.

Microscopic pore structure of Chang 63 reservoir in Huaqing oilfield, Ordos Basin, China and its effect on water flooding characteristics

Chang 63 reservoir in Huaqing oilfield, Ordos Basin, China is featured by strong pore structure heterogeneity, which leads to prominent Jamin effect in the water flooding, difficult development process, low productivity, and massive residual oil. Accordingly, this study aims to explore the microscopic pore structure of Chang 63 reservoir and investigate its influence on the water flooding efficiency, based on a series of comprehensive analyses, including physical property analysis, casting thin section observation, scanning electron microscopy measurement, high-pressure mercury injection, constant rate mercury injection, and microscopic real sandstone water flooding model. It is demonstrated that gray and gray-brown feldspathic sandstone are the main reservoir lithology in the study area, with dominant pore types of residual intergranular pores and feldspar dissolution pores. Pore throat radius is unevenly distributed, and small and micro pores take the majority. Based on the comparison of capillary pressure curve characteristics and comprehensive analysis of corresponding parameters, the pore structure of the Chang 63 reservoir is divided into four types, namely types I–IV. They have different reservoir spaces, and their reservoir and seepage capacities decrease in the order of types I–IV pore structures. Moreover, displacement patterns in them are also different, with the finger-like-reticular displacement as the primary. In addition, pore throat radius and distribution play a critical role in the water flooding. It is also demonstrated that the water flooding efficiency increases with permeability and porosity, pore structure quality, and pore throat distribution evenness.

Calcareous nannofossil stratigraphy of the Upper Cretaceous–lower Paleocene sequence from the Dokan section, Sulaimani, Kurdistan- Iraq

The boundary of the Cretaceous/Tertiary in the Kurdistan region of Iraq is still under debate. Most previous studies consider the Danian sediments to be absent. This paper examines theboundary in the Dokan area northwest of the Sulaimani city of Kurdistan in northern Iraq. This research analyzes calcareous nannofossil assemblages and the biostratigraphy of theboundary. The sequence in the study section is characterized by alternations of olive green to greenish gray sandstone, siltstone, shale and marlstone of the Tanjero Formation of the lateCampanian- Maastrichtian and the overlying Kolosh Formation of the early Paleocene. The upper part of the section includes thick sandstone beds and a reworked bioclasticconglomerate bed in addition to a dark- grey, silty calcareous shale. The study shows that deposition across the boundary is continuous. The boundary is biostratigraphically delineatedby the last occurrence of Maastrichtian taxon and the first occurrences of Biantholithus sparsus, Cruciplacolithus spp. and Coccolithus pelagicus of biozone NP1, which indicate nohiatus. This succession highlights the occurrence of the early Danian sequence at the bottom of the Kolosh Formation.

Clay minerals damage quantification in sandstone rocks using core flooding and NMR

Sandstone oil reservoirs consist of different clay minerals such as kaolinite, illite, and chlorite. These clay minerals highly affect the formation damage during enhanced oil recovery (EOR) and well stimulation operations in these reservoirs. No attention was paid to investigate the effect of these clay minerals on the formation damage during different reservoir processes. In addition, no solution was introduced to mitigate the effect of clay minerals on the formation damage in sandstone reservoirs. In this study, the effect of clay mineral contents and type on the formation damage was studied in detail by injecting water and HCl as damaging fluids. Bandera grey, Berea, and Bandera brown sandstone rocks with various clay mineral contents were studied. XRD was used to characterize the sandstone rocks to determine the clay type and content in each rock. Two core plugs from each rock were selected for HCl and water injection. Core flooding experiments were performed to measure the initial and final permeability. In the core flooding experiments, fluids were injected into the cores at 25 °C and at a backpressure of 1000 psi. SEM was carried out before and after flooding for the tested rocks to locate the change in the clay distribution inside the rocks. The NMR analysis of core samples was done before and after flooding with the damaging fluid to quantify the formation damage and to find the possible damaging mechanism. NMR was used to locate the damage inside the rock due to the migration of clay minerals. Based on the core flooding, SEM, and NMR analysis, the maximum damage by the fresh water took place in Berea sandstone core due to fine migration and clay swelling. The illite clay mineral and chlorite can cause the formation damage on HCl injection. Illite can break down and migrates in the cores during the acid injection. In sandstone acidizing, chlorite clay mineral caused iron hydroxide precipitation inside the cores during treatment with mud acid. NMR showed that clay minerals plugged the pore throats of the rocks and reduced the rock permeability during the injection of fresh water.