Carbonate Mineral Content Research Articles

Pore characteristics and micro-structure change of undisturbed loess induced by acid corrosion

With the rapid development of coal chemical base and urbanization construction in China's Loess Plateau, the phenomenon of acid corrosion induced loess geological disasters tends to occur frequently in this region. Loess is characterized by high water sensitivity, dense vertical joint surface, and rich in carbonate minerals, which providing a good precondition for acid solution corrosion. Due to the occurrence of chemical erosion, the changes of loess structure and strength become more complex, and there is a significant difference from the conventional water infiltration-induced loess disasters. In order to clearly grasp the internal mineral and structural damage characteristics of loess under acid dissolution conditions, this work studies the pore characteristics and micro-structure change of undisturbed loess under acid corrosion conditions with different pH values (7, 5 and 3) and dissolution times (5,10 and 15 days). It is found that the content of carbonate minerals in the undisturbed loess,and the combined structure characteristics are the two main factors affecting its acid corrosion effect. Specific findings include as: (1) With the decrease of pH, the dissolution of carbonate minerals such as calcite and dolomite intensifies (the element content of the precipitate: Ca96.58%, Mg1.26%), and the selective dissolution of silicate minerals (albite and chlorite) are obvious, which provides expansion space for pores. As a result, the change of the pore structure of undisturbed loess by acid leaching is as follows: Expansion of initial joints→Connectivity and enlargement of internal pores→The increase of new shallow pores. Meanwhile, under the action of acid dissolution, the cohesive substances were rearranged due to the dissolution, disintegration and rotation of the skeleton particles during the collapse, resulting in an increasing in the content of fine particles in the soil. (2) With the increase of corrosion time, the roundness increased from 7.19 to 25.98 which proves that the contact between the acid solution and mineral particles is more complete, and the effect of corrosion and particle aggregation is more significant. This results in a reciprocating unidirectional development of the pore structure. Flocculated particles with clay properties appear alternately in the soil structure. (3)The occurrence of acid-sensitive geological disasters in loess is mainly divided into three stages: The filling of the structural surface is eroded by acid→The horizontal and vertical erosion is intensify→The soil is broken down into particles that are washed away. This study has a certain reference for understanding the damage mechanism and early warning of loess eroded by acid solution in China's Loess Plateau.

Effect of saline sedimentary environment on pore throats of shale

Shale pore throat is one of the key factors affecting shale oil and gas exploitation. In order to study the effect of saline on shale pore throat in the continental lacustrine basin, the paleo-salinity of the lacustrine basin was analyzed using the Couth and Sr/Ba methods, and the pore throat characteristics of shale were observed by thin section and scanning electron microscope. The saline stage is divided into five stages: freshwater (0.5‰–1‰), brackish water (1‰–5‰), brackish water (5‰–15‰), brackish water (15‰–30‰), and high saltwater (>30‰). Shale is mainly reserved in micropores (organic, intercrystalline, and intergranular pores) and microcracks (along-layer, high pressure, structural, and mineral shrinkage cracks). Paleosalinity affects the pore throat characteristics of shale by controlling the mineral composition, rock combination type, and texture. Carbonate minerals tend to dissolve and form dissolution pores, resulting in pore throat enlargement and better physical properties. When salinity is low, the content of carbonate minerals increases with the increase in salinity. However, in the case of high salinity, the content of carbonate minerals gradually decreases, but that of sulfate and gypsum increases with the increase in salinity. The texture is conducive to the development of microcracks. With the increase in salinity, the number of textures first increases and then decreases. When the content is 15 ‰–30‰, there are most abundant textures, making it most likely to form microcracks. The results of this study play an important role in promoting the study of shale in the continental lacustrine basin.

Study on the accelerated carbonation of MSWI fly ash under ultrasonic excitation: CO2 capture, heavy metals solidification, mechanism and geochemical modelling

The current carbonation technology of municipal solid waste incineration fly ash (FA) has disadvantages such as low carbon sequestration efficiency, harsh conditions, and complicated equipment. An ultrasonic chemical method coupled with wet-carbonization technology is proposed. The effects of the FA ultrasonic carbonation (UC) method on CO2 capture, heavy metals (HMs) release and solidification were investigated, and geochemical model of FA was explored. The results showed that UC improved the CO2 capture capacity, and the carbonation efficiency increased from 14.1 % to 18.8 % because the ultrasonic physical and chemical excitation improved the mass transfer efficiency and strengthened the gas–liquid-solid three-phase carbonation reaction. UC inhibited the release of Pb and Zn into the liquid phase (0.002 mg/L and 0.004 mg/L) and increased the solidification efficiency of Pb and Zn in FA (99.99 % and 100 %) because free Pb and Zn converted carbonates completely. UC FA had a single component, small particle size, high degree of homogenization, and contained slender nano-CaCO3 crystals. The acid neutralization capacities of original FA, FA4, and FA9 were 10, 8, and 3 meq/g because the carbonation reaction neutralized the alkaline substance. The content of carbonate minerals was the highest in UC FA and the pH of carbonate-minerals controlled dissolution/precipitation was mainly between 6 and 10. The HMs were in a soluble state (pH < 6) and the amphoteric HMs were affected by soluble hydroxides, the leaching concentration increasing (pH > 10). Therefore, UC FA had the potential of economical, environmentally friendly, and resource-based applications when avoiding strong acid and alkali application scenarios.

Detecting Mineral Resources and Suggesting a Physical Concentration Flowsheet for Economic Minerals at the Northern Border Region of Saudi Arabia

There is a limited number of studies on sand deposit resources of Saudi Arabia, which cover nearly the one-third of the area of the country, whereas most of these studies deal with the environmental rather than the mineralogical or mining aspects. In this paper, and in the effort to detect the mineral resources of the Northern Border Region, the surficial Wadi sediments along the Ar'ar-Sakaka road are studied. The deposits of several Wadies (Al Aqra, Shiban al Hanzaliyat, and Arar) are mixed. The sediments of the collected samples are investigated to determine definite areas characterized by a relatively higher content of heavy minerals and a relatively lower content of carbonate minerals that are also friable enough to be investigated by some of the available physical concentration techniques. A large quantity of the surficial deposits, weighing 4.69 tons was collected from the stretch at the investigated area which is 3km long and 1.5km wide. Evaluation of the heavy minerals content, their types, and their ability for concentration and separation, was conducted. A suggested physical concentration flowsheet was concluded for concentrating and separating the contained economic minerals. The average heavy mineral content is 1.55 wt% and the identified economic minerals are magnetite, ilmenite, hematite, goethite, zircon, rutile, anatase, monazite, and xenotime. The other contained heavy minerals include monoclinic pyroxenes (diopside, and augite), monoclinic amphibole (winchite), and muscovite mica. Dolomite and calcite carbonate are also contained. The concluding results ensure that magnetite, zircon, TiO2 minerals, and monazite are mineable for separation in individual mineral concentrates. Most of the detected economic minerals are recorded in the area for the first time. Monazite, xenotime, and zircon are responsible for some recorded radioactivity in the area.

Comparison among brittleness, hardness and mineral composition of the Besa River Formation in the Liard Basin, Canada

Rock brittleness is regarded as one of the most crucial geomechanical properties affecting hydraulic fracturing in shale reservoirs. Numerous studies have been conducted to quantify rock brittleness, most of which were based on mineralogical and geomechanical properties. This study aims to clarify relationship between brittleness indices and multi-proxies of the Devonian Besa River Formation, which is a frontier shale gas play in Western Canada Sedimentary Basin and to suggest an ideal model for mineralogy-based brittleness index. To this end, we calculated Young's modulus and Poisson's ratio from well logs and measured the Leeb hardness from slabbed core surfaces. We also conducted geochemical and sedimentological analyses for the Besa River Formation. Hardness and brittleness are positively correlated with quartz content but negatively with clay mineral content in the formation, whereas carbonate mineral and total organic carbon (TOC) contents show no relationship with hardness and brittleness. Hardness measurements are also well correlated with rock brittleness from well logs and can be a good proxy for the brittleness of Besa River Formation. This study suggests an ideal model for a mineralogy-based brittleness index, considering the influence of biogenic and detrital quartz in the Formation. This model shows a high correlation coefficient with rock brittleness and can be useful to determine the brittleness of rocks with similar characteristics to Besa River Formation.

Coseismic fluid–rock interactions in the Yingxiu–Beichuan surface rupture zone of the Mw 7.9 Wenchuan earthquake and their implications for the structural diagenesis of fault rocks

The mechanisms by which fluids modify the mineralogy and geochemistry of fault zones and the role of rock–fluid interactions in fault weakening are subjects of debate. We assessed the mineralogical and geochemical variations in fault rocks in the Shaba area of the Yingxiu–Beichuan surface rupture zone of the Mw 7.9 Wenchuan earthquake using analyses of their mineralogical compositions, major elements, and the microstructural characteristics of wall rocks, damage zones, and oriented fault gouge samples from the principal slip zones. The elemental and mineralogical compositions show a certain regularity across the fault zone from the wall rocks to the fault gouge so that (1) Al2O3, Fe2O3T, and K2O contents increase and exhibit significant enrichments in the fault gouge; (2) Na2O and P2O5 contents decrease gradually and exhibit significant depletions in the fault gouge; (3) quartz, feldspar, and carbonate mineral contents decline; and (4) clay mineral contents increase dramatically. Isocon analysis indicates that mass losses in the Shaba fault zone occur with losses in the damage zone < the fault gouge. The mechanisms of material loss and transformation in the fault zone are complex, and mechanical fracturing, dehydration reactions, and fluid–rock interactions are important factors in changing and controlling the material compositions and fault zone evolution, with material losses and transformation especially important within the fault core. Moreover, due to the damage zone having a higher permeability than the fault core, it was conducive to hydrothermal upwelling, fluid–rock interactions, and fracture healing.

Petrology, Physical Properties and Geochemical Characteristics of Alkaline Lake Shale—Fengcheng Formation in Mahu Sag, Junggar Basin

There are rare comparative studies on the geological characteristics of shale in different members of Permian Fengcheng Formation in Mahu Sag, Junggar basin, China. In order to compare the mineral composition, physical properties, and geochemical characteristics of shale in three members of Fengcheng Formation in Mahu Sag, a large number of test data such as X-ray diffraction, high-pressure mercury injection, organic carbon, rock pyrolysis, and vitrinite reflectance were collected and analyzed. Results showed that the content of clay minerals in the shale of the third member of Fengcheng Formation (P1f3) is the highest. The content of carbonate minerals is the highest and the content of clay minerals is the lowest in the shale of the second member of Fengcheng Formation (P1f2). The content of felsic minerals is the highest and the content of carbonate minerals is the lowest in the shale of the first member of Fengcheng Formation (P1f1). The physical properties of the shale of P1f3 are the best, and the porosity of the shale of P1f2 is the smallest, but its permeability is relatively large, and the permeability of shale of P1f1 is the lowest. The organic matter abundance of shale of P1f2 is the highest, while that of P1f1 is relatively the lowest. Most of the organic matter types of shale of P1f3 are type I–II, those of P1f2 are mainly type II, and those of P1f1 section are distributed from type I–III. On the whole, the shale of Fengcheng Formation in the peripheral fault zone and slope area of Mahu Sag has reached the low mature to mature stage, and the shale in the central area of the sag has reached the mature stage. More than half of the shale samples of Fengcheng Formation belong to fair to good source rocks, especially the samples of P1f2. A few samples from P1f3 and P1f1 belong to non-source rocks. This study indicates that the shale of Fengcheng Formation in Mahu Sag has good hydrocarbon generation potential, especially the shale of P1f2, and can become the target of shale oil exploration.

Geochemical and physical alteration of clay-rich shales under supercritical CO2 conditions

The injection of Carbon Dioxide (CO2) into shale gas formations is a promising approach that not only reduces the impact of greenhouse gas on climate change but also enhances the gas recovery due to geochemical interactions between CO2 and clay minerals. However, these geochemical interactions have not been fully explored and changes in the petrophysical properties of shales have been reported over time. This paper evaluates the geochemical reactions and physical changes caused by the injection of supercritical carbon dioxide (ScCO2) on the properties of clay-rich shales. Samples from the Eagle Ford formation were collected and exposed to ScCO2 at different pressures ranging from 10 to 24 MPa at 70 °C. Analytical methods such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thin-section microscopy were used to characterize the ScCO2-treated samples. The results showed dissolution of clays and precipitation of quartz with increasing ScCO2 treatment pressure. The content of carbonate minerals was also reduced at high pressure, which can be attributed to the reactions of the dolomite with H+ to form magnesium carbonate. The percentage of absorption of aromatic hydrocarbons and oxygenated groups gradually increased with increasing pressure, which can be attributed to the increase in CO2 adsorption. On the other hand, the absorption of aliphatic and hydroxyl groups decreased after treatment. ScCO2 treatment pressure is an important factor to evaluate the CO2 adsorption capacity of clay-rich shales. The presented results enrich the understanding of the interactions between CO2 and shale under different pressures, which may be helpful to determine the feasibility of long-term injection and storage in shale.

The Influence of CO2 Saturated Brine on Microstructure of Coal: Implications for Carbon Geo-Sequestration

Carbon dioxide geological storage in deep underground oil and gas reservoirs or coal seam is considered a key technology to effectively mitigate carbon emissions. Deep coal seams are the potential host rock for CO2 storage, with chemical reactions occurring when coal is exposed to CO2-saturated brine. However, limited studies have been conducted to reveal the effect of chemical reaction, particularly to unveil how this importantly affects the coal seam porosity at the micrometer scale. In this study, the CO2 geological storage is simulated using a high-temperature and high-pressure reactor containing CO2-saturated brine and coal samples. The samples in the previous study on the effect of CO2 on coal mostly contained high content of carbonate minerals and sulfide minerals. However, the tested Collie coal samples, which are characterized by high content of kaolinite and siderite, are rarely used. This coal was quantitatively analyzed using a scanning electron microscope before and after reaction. The results show that the microstructure of coal matrix was largely changed due to acid exposure. Kaolinite and siderite in the coal matrix were dissolved, the size and morphology of the cleats increased, and the absolute effective porosity also increased significantly. Most importantly, the connectivity of cleat network was improved, leading to an increase in CO2 storage space and coal seam permeability. Therefore, it is concluded that the microstructure changes of coal can be measured on a microscopic scale, and it is better to be quantitatively evaluated to improve the accuracy and reliability of CO2 storage in deep coal seams.

Identification of lithofacies and prediction of mineral composition in shales – A case study of the Shahejie Formation in the Bozhong Sag

The identification of shale lithofacies is the basic work of shale gas exploration and development. Accurate quantitative characterization of different mineral components in fine-grained mixed shale is of great significance for the identification and classification of lithofacies types, the enrichment conditions of shale oil and gas (hydrocarbon generation, reservoir, occurrence and preservation), and the evaluation of shale oil potential (reservoir, oil bearing, fracturability and oil mobility). When organic-rich argillaceous laminae are moderately mixed with brittle laminae, the laminated shale is not only the favorable interval of shale oil and gas enrichment for hydrocarbon generation (organic-rich argillaceous laminae) and storage (brittle laminae), but also the excellent “sweet spots” for continental shale oil and gas optimization. Different shale lithofacies have distinct rock texture, fabric and composition, leading to different brittleness and rock physical properties. For the identification of shale lithofacies containing various components, the overlaps of different wire-line logging responses and the vague boundaries between various logging data cause the large deviation in the logging prediction of lithofacies by traditional methods. In this study, shale samples from the lower part of the third member of Shahejie Formation in Bozhong Sag of the Bohai Bay Basin are selected to carry out the reservoir characterization and then the data mining of logging information by a Back Propagation (BP) neural network coupled with Atomic Search Optimization (ASO) algorithm. The BP algorithm based on the identified shale lithofacies (expected output) and logging data index (input) is used to train the neural network. The complex and unrecognized nonlinear relationship between shale lithofacies and logging data is mapped onto the high-dimensional identifiable nonlinear quantitative relationship to establish the prediction model of the relative content of clay minerals, silicate minerals and carbonate minerals. This study reveals the main lithologic characteristics of lacustrine shale lithofacies from Shahejie Formation in Bozhong Sag, and the main controlling factors for shale lithofacies prediction based on logging data. Our results show that the main mineral composition of shale lithofacies associations can be effectively predicted through the whole rock X-ray diffraction data, wire-line log data and neural network analysis, which provides the basis for lithofacies identification shale interval in well locations lacking core and test data. • Based on the optimized algorithm, a neural network prediction model of mineral composition is established to mine the hidden information in conventional logging data to predict lithofacies, and the accuracy is improved compared with the conventional neural network model. • The prediction of lithofacies mineral composition data for a wider range of non-coring wells by neural network provides more geological basis for the selection and prediction of favorable lithofacies zone - dessert area in subsequent exploration.

Paleoenvironment and chemostratigraphy heterogenity of the Cretaceous organic-rich shales

The Cretaceous Qingshankou Formation in the Songliao Basin is rich in shale oil resources, which has become one of the most important exploration targets of lacustrine shale oil in China. Based on X-ray fluorescence element analysis, X-ray diffraction analysis, total organic carbon, rock pyrolysis, scanning electron microscope and nitrogen adsorption, the Paleoenvironment was reconstructed by comprehensive utilization of integrated prediction error filter analysis of chemical stratigraphy, and its relationship with organic geochemistry, mineralogy and pore structure was discussed. The results indicated that the Qingshankou Formation was deposited in the environment with fresh water-brackish water, semi-deep/deep water and strong reduction. The evolution of Paleoenvironment during the deposition of Qingshankou Formation changed from bottom to top, with increasing water depth, decreasing salinity and oxygen content. Paleosalinity was positively correlated with total organic carbon, residual hydrocarbon and carbonate mineral content. From bottom to top, the contents of carbonate and chlorite decreased, while the contents of plagioclase and clay minerals increased slightly. The pores were dominated by intra-illite pores, intra-I/S mixed-layer pores and intra-pyrite pores. Some intra-plagioclase pores and calcite dissolution pores were developed, and the organic matter pores are slightly few. Nitrogen adsorption data showed that the dominate pore size was 40-53 nm. This study clarifies the Paleoenvironmental evolution of the Qingshankou Formation, and may shed lights on lacustrine shale oil accumulation and sweet-spotting. Cited as : Guan, M., Wu, S., Hou, L., Jiang, X., Ba, D., Hua, G. Paleoenvironment and chemostratigraphy heterogenity of the Cretaceous organic-rich shales. Advances in Geo-Energy Research, 2021, 5(4): 444-455, doi: 10.46690/ager.2021.04.09

Chemical Nature of Hydrothermal Fluids Generated by Serpentinization and Carbonation of Komatiite: Implications for H2‐Rich Hydrothermal System and Ocean Chemistry in the Early Earth

AbstractH2‐rich ultramafic‐hosted hydrothermal systems are considered to be important places for the origin and early evolution of life. In this study, we conducted two hydrothermal serpentinization/carbonation experiments involving synthetic komatiite under CO2‐rich conditions to further understand the chemical nature of hydrothermal fluids in the komatiite‐hosted seafloor hydrothermal systems in the early Earth. The H2 concentration in fluid at 300°C is one order of magnitude lower than that under CO2‐free conditions, which revealed that the carbonation of komatiites suppressed H2 generation under CO2‐rich conditions. The steady‐state H2 concentrations in the fluid increased with increasing temperature, while the Fe content of carbonate minerals in the run products increased with decreasing temperature. This correlation suggested that Fe incorporation into the carbonate minerals would limit the H2 generation during the serpentinization of komatiites at each temperature. In addition, the pH of the fluid also depended on temperature. High‐temperature (&gt;300°C) fluids became alkaline, whereas low‐temperature fluids became acidic. Thermodynamic calculations show that the acidic fluids were attributed to high water/rock ratio during the hydrothermal reactions. Consequently, H2‐poor and acidic fluids were likely generated at low temperatures. In contrast, the H2‐rich and alkaline hydrothermal fluids were generated at temperatures above 300°C, which suggests that high‐temperature seafloor hydrothermal systems may be more favorable than lower‐temperature systems for the emergence and early evolution of life in the Hadean ocean in terms of the formation of energy and electrochemical potentials between hydrothermal fluids and ambient seawater.

Mineralogical and petrographic characteristics of the Ordovician-Silurian Wufeng-Longmaxi Shale in the Sichuan Basin and implications for depositional conditions and diagenesis of black shales

Depositional and diagenetic processes play important roles in controlling the fabric and petrophysical properties of black shales. In this study, an outcrop section of the Wufeng-Longmaxi Shale was studied through sedimentologic facies analysis, petrographic observations (both transmitted- and reflected-light microscopy and scanning electron microscopy), and X-ray diffraction analysis to investigate how depositional and diagenetic processes controlled the accumulation and evolution of organic-rich black shales. The studied Wufeng-Longmaxi Shale consists of over-mature black shales, with an equivalent vitrinite reflectance of 3.07%. Organic matter is dominated by pyrobitumen and graptolite, the former of which hosts abundant organic pores. Minerals mainly consist of quartz (average 42 wt %), carbonates (average 37.4 wt %), and clay minerals (average 15 wt %). Eighty percent of quartz is of biogenic origin, which occurs as siliceous fossils and microcrystalline quartz. Microcrystalline quartz forms a rigid framework and preserves organic pores from compaction. Clay minerals comprise dominantly (95 wt %) illite and mixed-layer illite/smectite. The vertical variations in lithofacies and quartz and carbonate mineral content exhibit three cycles, likely corresponding to three transgressive-regressive cycles. Within each cycle, quartz content first increases to reach a maximum at the maximum flooding surface, and then decreases. Although long being considered as deposited under quiescent and anoxic conditions, sedimentologic and petrographic analyses in this study indicate that the deposition of the Wufeng Formation and lower Longmaxi Formation was subject to intermittent reworking by bottom currents and bottom-water dysoxia. Meiofauna capable of tolerating low oxygen content could have lived in surficial sediments and disrupted the original fabric of sediments formed by bottom currents. Mineralogical and petrographic analyses in this study provide new insights into the accumulation mechanism of the organic-rich black shales of the Wufeng-Longmaxi Formations, calling for a critical reappraisal of other black shales that have conventionally been considered as deposited under mostly quiet and anoxic conditions. • Mineralogical and petrographic characteristics were studied. • Three stratigraphic cycles were identified. • Depositional conditions were not persistently quiescent and anoxic. • Intermittent reworking by bottom currents and bottom-water dysoxia existed.

Last Glacial central Mediterranean hydrology inferred from Lake Trasimeno’s (Italy) calcium carbonate geochemistry

There is still a paucity of hydrological data explaining the relationship between (rapid, millennial‐scale) climate forcing and Mediterranean rainfall since the Last Glacial. We show that distinct lake‐level fluctuations at Lake Trasimeno (Italy) are associated with changing aridity in the central Mediterranean during the last ~47 800 years. The lake‐level fluctuations are reconstructed based on carbonate mineral content and carbonate mineral species, as well as the stable oxygen and carbon isotope (δ18O and δ13C) geochemistry of endogenic carbonates. Low lake levels are linked to high carbonate, Mg‐calcite and aragonite contents, and high δ18O and δ13C values. Inferred hydrological changes are linked to glacial–interglacial and, tentatively within the limitations of our chronology, to millennial‐scale climate variability as well as the intensity of the Atlantic Meridional Overturning Circulation (AMOC). Prior to the Last Glacial Maximum (LGM), during intervals equivalent to Marine Isotope Stage 3 (MIS 3), a stronger AMOC associated with Greenland interstadial periods (Dansgaard/Oeschger (D/O) warm periods) and stronger Asian monsoon probably coincide with increased precipitation in central Italy as inferred from high lake levels at Lake Trasimeno. Periods of weak AMOC intensity such as during Greenland stadials (D/O cold periods), during Heinrich events, and weak Asian monsoons are correlated with lake level lowstands, which imply relatively dry conditions in central Italy. Lake Trasimeno’s water level during the LGM and the Lateglacial (MIS 2) is relatively stable, with recorded changes showing distinct similarities to orbital configurations. Although muted, high latitude climate forcing is still evident in the data during peak glacial conditions. The transition from D/O‐like hydrological variability at Lake Trasimeno during MIS 3 to orbitally controlled fluctuations during the Lateglacial to Holocene transition coincides with an increasing amplitude in local winter and summer insolation, probably indicating increasing seasonality and a larger temperature gradient between low‐ and high‐latitude settings.

Integration of sub- meter scale lithological heterogeneity in reservoir models for an improved quantification of CO2 trapping capacities

Sub-meter scale lithological heterogeneity in the form of sedimentary structures such as cross, planar and massive beddings is known to enhance carbon mineral trapping. However, this understanding is largely qualitative. Quantitative estimates of trapping capacities at this scale are limited by the availability of high-resolution field data. Additionally, such heterogeneity is typically not accounted for in conventional reservoir models due to computational restriction posed by the grid size resolution. As a result, the impact of sub-meter scale lithological heterogeneity on carbon trapping capacities is typically not accounted for in dynamic flow and reactive transport simulations at the reservoir scale. The present study aims to quantify the impact of intraformational baffles on carbon mineralization for a range of rock types. A series of 2-D multiphase reactive transport simulations were set-up to model the geochemical processes occurring at the interface of a baffle and a reservoir rock for a period of 1000 years. The study shows that the presence of baffles with certain rock properties within the reservoir rock can enhance or reduce carbon mineral trapping capacity relative to homogeneous reservoir rocks depending on clay and carbonate mineral content in baffles. Further, a new workflow is developed to build a 2D high-resolution reservoir model of the Paaratte Formation, Otway Basin while overcoming the technical challenges associated with sub-meter scale discretization of geological models.

Petrographic features and diagenetic alteration in the shale strata of the Permian Lucaogou Formation, Jimusar sag, Junggar Basin

Reservoir quality is the key parameter controlling shale oil enrichment. However, the complicated lithofacies, which control diagenesis, result in reservoir heterogeneity in the shale strata, creating challenges for reservoir prediction. Combining with the detail analysis of inorganic and organic geochemistry, characteristics of the main lithofacies and diagenetic alteration were investigated in Permian Lucaogou Formation, Jimusar sag, Junggar Basin. Laminated rocks with laminae combinations containing pyroclastic and terrigenous clastic laminae, terrigenous clastic and dolomite laminae, and pyroclastic and carbonate laminae were identified. Massive rocks mainly includes dolomicrite, dolomitic tuff, silt dolostone, dolomitic siltstone, and tuffaceous siltstone. Feldspar dissolution and carbonate cementation were the two dominant diagenetic types, further causing heterogeneity of the shale oil reservoirs. Feldspar dissolution generally occurred in laminated rocks containing pyroclastic laminae with low content of carbonate minerals (PL1), as well as in their adjacent interbedded siltstones. Carbonate cementation generally occurred in laminated rocks containing carbonate laminae, as well as in their adjacent interbedded siltstones. Whether in laminated and massive rocks, sparry carbonate crystals were also precipitated adjacent to organic matter and in microfractures. In the burial processes, enriched transition metal elements of V and Ti in pyroclastic laminae promote catalytic pyrolysis of organic matter. Abundant CO 2 produced during the catalytic pyrolysis promoted feldspar dissolution. Dissolution of sedimentary carbonate minerals by organic acids and CO 2 provided the material sources for secondary carbonate cements. It promoted the recrystallization and re-precipitation of sparry carbonate crystals adjacent to organic matter and in the terrigenous clastic laminae or interbedded siltstones. Ca 2+ , Mg 2+ Sr 2+ , Fe 2+ , and Mn 2+ produced by the transformation of smectite to illite in the pyroclastic laminae also provided Ca source for secondary carbonate cements. External diagenetic fluids providing materials along microfractures is another genesis of carbonate cements in the Permian Lucaogou Formation. • Petrographic features in the shale strata in Permian Lucaogou Formation were identified based on in situ analytical method. • Differential feldspar dissolution and carbonate precipitation generally occurred in different lithofacies. • Catalytic pyrolysis of organic matter in presence of transition metal elements in pyroclastic laminae promoted dissolution. • Development of carbonate cements in the shale strata were mainly provided by three material sources.

Conditions and processes controlling carbon mineral trapping in intraformational baffles

Carbon mineral trapping is commonly believed to be insignificant relative to other trapping mechanisms, yet, the role of cm-scale intraformational baffles is rarely considered in reservoir scale assessments. The present study aims to reveal conditions governing carbon mineral trapping and its quantification for a range of rock compositions in intraformational baffles. A series of 2-D multiphase reactive transport simulations were set-up to model the geochemical processes occurring at the interface of a baffle and a reservoir rock for a period of 1000 years. The study shows that the presence of baffles with certain rock properties within the reservoir rock can enhance or reduce carbon mineral trapping capacity relative to homogeneous reservoir rocks depending on clay and carbonate mineral content in baffles. The analysis shows that the precipitation of secondary carbonates occurs at the interface of the two rock types. Furthermore, it was found that higher clay and lower carbonate content of the baffle contribute towards enhancing mineral trapping while the mineralogy of reservoir rock does not have an important influence. The results are further utilized to derive averaged mineral composition for the integration of fine scale processes in coarser scale simulations.

Mineral Composition and Its Control on Nanopores of Marine-Continental Transitional Shale from the Ningwu Basin, North China.

There is a large difference between the sedimentary environment and maturity of organic matter between marine shale and marine-continental transitional shale. It is of great significance to discuss the effect of inorganicminerals on the pores for marine-continental transitional shale gas exploration. In this study, scanning electron microscopy (SEM), low temperature liquid nitrogen adsorption and Xray diffraction (XRD) were conducted on eight marine-continental transitional shale samples from the Ningwu Basin, Shanxi Province, China. The pore structure differences in the different minerals were discussed, and the relationship between the mineral content and pore parameters was analysed. The results show that the mineral composition of shale is dominated by clay minerals, quartz, carbonate minerals and a small amount of pyrite. The clay minerals content is between 39.5% and 77.0%, with an average of 59.9%. The quartz content ranges from 21.8% to 47.8%, with an average of 31.9%. The carbonate minerals content in shale is between 0.6% and 23.9%, and the average is 6.3%. The clay minerals are composed of mixed illite-montmorillonite layer, kaolinite and chlorite. The content of mixed illite-montmorillonite layer is between 13.8% and 27.4%, with an average of 20.4%. The kaolinite content ranges from 57.0% to 86.2%, with an average of 76.0%. The content of chlorite is between 0 and 15.6%, with an average of 5.7%. The types of pores are mainly intergranular pores and interlaminar pores, which are mostly presented as slit and parallel plates. The mixed illite-montmorillonite layer contributes more to the specific surface area, which is favourable for shale gas adsorption. The pores in kaolinite are more developed than those of the mixed illite-montmorillonite layer, but the pore diameter is relatively large. The quartz granule has a complete crystal type, and intergranular pores with a large pore size are often developed at the mineral contacts. Compared with clay minerals and quartz, the pore development in the carbonate minerals is relatively poor and develops more micro-fractures. The pyrite contributes a certain number of intergranular pores and mold pores.

Effects of Water Immersion and Acidification on Nano-Pores in Tight Sandstones-A Case Study of the Gaotaizi Reservoir, Songliao Basin.

Hydraulic fracturing and acidification are among the most commonly used methods for stimulating the tight oil reservoirs and improving oil recovery. Therefore, examining the effects of water immersion and acidification on tight oil reservoirs is important for oilfield development plans. Core flooding testing, which analyzes the influence of core permeability variations before and after acid injection on the reservoir quality, is the conventional research method; however, it is difficult to observe the changes in minerals and pores caused by acidulation and water immersion in situ. In this study, we conduct field-emission scanning electron microscopy (FE-SEM), MAPS, the quantitative evaluation of minerals through scanning electronic microscopy (QEM-SCAN), and describe the types of pores in tight sandstone. Further, the effects of water immersion and acidification on pores in tight sandstone were studied. The results indicate that: (1) intergranular pores, intragranular dissolution pores, clay mineral intercrystalline pores, and micro-cracks were developed in the Gaotaizi tight sandstone in Songliao Basin, with the intergranular pores observed to be dominant; (2) the hydration of clay minerals induced by water injection caused plugging of pores at the nanometer- micrometer scale, and plane porosity is slightly reduced (˜0.86%); (3) acidification resulted in the dissolution of carbonate minerals, increasing the porosity of the reservoir, therefore, the increase in porosity is influenced by the carbonate mineral content. We recommend that future studies should investigate the content, type, and distribution of carbonate minerals in the operation area. During the process of reservoir stimulation, such as acidification and CO₂ injection- and-production, the influence of carbonate minerals dissolution on oil production should be considered.

Distribution of total carbonate and iron oxides on catena at Duhok Governorate, Kurdistan Region, Iraq

The study area located at Zawita location, Duhok province, Kurdistan region, Iraq. Five pedons were digging on catena depending on the slope degree and slope aspects. Samples were air-dried, ground, and sieved using (2) mm sieve, in order to be used for physicochemical analysis. The soil texture varied from clay loam to sandy loam in the surface horizons of all pedons and became finer from the summit to foot slope in the south aspect, in contrast at the north aspect soil texture became coarser from the summit to foot slope). Study soils were less development and less differentiation of soil horizons in pedons at the summit and back slope in contrast to it at the foot slope of catena and were slightly alkaline non-saline soils. Soil organic matter in the north aspect was more than it in the south aspect. CEC in all horizons for pedon (1) at the summit was high value when compared with it for pedons at the back slope and foot slope. Studied soils consider as calcareous that have a high content of carbonate minerals as a result of the calcification pedogenic process in turn these soils have a high buffering capacity. Total carbonate at the summit, was less amount, in the surface horizon (Ah) then was gradually increased in the subsurface horizon (Bc) after that uniformity increased of carbonate distribution in soil horizons (C1st) and (C2k), whereas was decreased in surface horizons at the back slope at both aspects but in north aspect was less than it at south aspect. In surface horizons, at foot slope in both directions, total carbonate was decreased, whereas the vertical distribution indicated increasing it towards deep horizons of pedons at foot slope. Iron oxides in soil samples were fluctuated between increase and decrease with the exception of pedon (4) at the back slope in the south aspect. Part of the iron oxides was translocation downslope with runoff water and adds it to iron oxides at the foot slope and a considerable amount of it was present in the study location that is causing the change in soil color.