Mineral Composition Of Rocks Research Articles

Logging evaluation of deep multi-type unconventional gas reservoirs in the Songliao basin, northeast China: Implications from continental scientific drilling

Multi-type unconventional gas-bearing reservoirs with different lithologies and gas accumulation potential occur in the deep part of the Songliao basin. However, the reservoirs are non-homogeneous, the gas components differ substantially, and not all types of gas-bearing reservoirs have been identified or evaluated. The International Continental Scientific Drilling Program (ICDP) is used as an example to conduct qualitative and quantitative evaluations of deep multi-type unconventional gas-bearing reservoirs using conventional and specialized logging data. The core test data are used to determine the physical properties. The porosity and permeability are compared and analyzed using different methods and models. The results show that the reservoirs have low to ultra-low porosity and ultra-low permeability. Based on the comparison of the rock mechanical parameters and mineral composition, brittleness evaluation parameters are proposed for different types of deep reservoirs in the study region. The mineral brittleness index is highly consistent with the brittleness index based on rock mechanics. An identification method for deep multi-type gas-bearing reservoir and a classification approach for different gas properties are established based on the logging response and parameter interpretation. The methane gas reservoirs have low density (DEN) and low compensated neutron logging (CNL) values and high acoustic (AC) time difference and high resistivity (RT) values. The CO2 gas reservoirs have lower RT values and higher CNL values than the hydrocarbon gas reservoirs. The comprehensive analysis of deep gas source rock conditions and of the source-reservoir relationship provides insights for the evaluation of deep multi-type unconventional gas reservoirs. The discovery of high hydrogen content is of significant importance for developing new areas for deep natural gas exploration.

Whole-rock geochemistry and mineral compositions of gabbroic rocks and the associated Fe–Ti (–V) oxide deposit in the Gonamsan intrusion, South Korea

The NS trending sill-like Gonamsan gabbroic intrusion in the central region of the Korean Peninsula intruded Neoproterozoic metasedimentary rocks composed of schists intercalated with gneisses, marbles, and quartzites. The intrusion has an east zone (EZ) composed of diorite–monzodiorite, diorite–gabbro, and oxide gabbro–monzodiorite, and a west zone (WZ) composed of quartz monzodiorite. These silicate rocks have similar primitive-mantle normalized trace elements and chondrite-normalized REE patterns, suggesting that they are co-magmatic. Plagioclase anorthite (An) contents (1.9–54.0), pyroxene MgO/ (MgO + FeO) (Mg#) (35.4–73.7), and olivine forsterite (Fo) values (14.5–20.9) show a wide range through the intrusive silicate suite, but each unit has narrow ranges, and reverse fractionation is absent. The Fe–Ti (–V) oxide mineralization only occurs in the EZ and is characterized by variations in morphology, size, mineral assemblages, and chemical compositions of the Fe–Ti oxide minerals. Stratiform Fe–Ti (–V) oxide mineralization interlayered with diorite–monzodiorite is restricted to metasedimentary host rocks in the central region of Gonamsan and comprises magnetite and ilmenite with lesser amount of olivine, tschermakite, apatite, spinel, pyroxene, and plagioclase. Lenticular mineralization occurs along the western margin of the diorite–gabbro and consists of magnetite and ilmenite with minor hornblende, apatite, chlorite, and spinel. Oxide gabbro interlayered with relatively thin monzodiorite bands forms cyclical units irregularly distributed throughout the EZ and consists of olivine and pyroxene with minor interstitial magnetite, ilmenite, and apatite. Magnetite is the principal Fe–Ti oxide mineral, and varies in chemical composition and microtextures in different ore zones. Overall, the compositions of magnetite from all mineralized zones fall in the compositional fields for magmatic Fe–Ti, V deposits defined by Dupuis and Beaudoin (2011). Magnetite from the stratiform Fe–Ti oxide mineralization is compositionally consistent with those from high-temperature silicate melts and displays complex ilmenite and spinel exsolution textures that resulted from re-equilibration of ulvöspinel–magnetite solid solution during cooling. In contrast, magnetite from the lenticular ore and oxide gabbro are compositionally consistent with being derived from evolved low-temperature melt. Based on the whole-rock geochemistry, mineral composition, and mineralization distribution, the Fe–Ti (–V) oxide mineralization in the Gonamsan intrusion seems to be related to Fe–Ti-rich melt formed from magmatic fractionation and migration along a relatively permeable zone, rather than other magmatic and post-magmatic processes.

Uranium in Source Rocks: Role of Redox Conditions and Correlation with Productivity in the Example of the Bazhenov Formation

The paper reports comprehensive analysis of different factors affecting uranium content in oil source rocks and the relationship between uranium content and productivity of source rocks. The analysis of data for 13 wells of the Bazhenov Formation (Western Siberia, Russia) was carried out. The uranium content of the rocks was measured by gamma-ray spectrometry on core samples. In order to analyze factors affecting uranium accumulation in source rocks, we studied content and characteristics of organic matter (Rock-Eval pyrolysis), and also mineral, element, and isotope composition of rocks. We have shown that redox conditions at the sedimentation stage have the most pronounced impact on the uranium accumulation in the rocks of the Bazhenov Formation. It was also shown that productive intervals, containing increased amounts of mobile hydrocarbons, are characterized by low (<20 ppm) concentration of uranium. However, the intervals, containing phosphorite minerals may show better reservoir properties and oil saturation at higher concentration of uranium. The analysis of correlations and relationships between uranium content and Rock-Eval pyrolysis indexes (oil saturation index and productivity index) enabled formulation of criteria for selection of oil-saturated intervals using the spectral gamma and pulsed neutron spectroscopy log data.

Mineral Composition and Grain Size Effects on the Fracture and Acoustic Emission (AE) Characteristics of Rocks Under Compressive and Tensile Stress

The influence of rock mineral composition and mineral grain size on basic rock strength performance and AE characteristics have been studied, 13 different rocks microstructures are analyzed in an optical microscope thin section using petrographic image analysis, making it possible to determine the mineral composition and mineral texture characteristics of rocks. Then, the basic strength parameters of rock and AE signals generated during fracture propagation were obtained by UCT (uniaxial compression test) and BIT (Brazilian intension test). Finally, the relationship between basic strength parameters and AE characteristics of rock with mineral composition and grain size was analyzed. The results showed that different mineral constituents have significant effects on rock strength. The positive influence of plagioclase content on igneous strength was obtained. Sedimentary rocks strength increases initially and then decreases with the increase of plagioclase content. Besides, with the increase in quartz and K-feldspar content, the strength of the rock was weakened obviously. It is also found that the greater the dimensional deviation of mineral grain, the greater the strength of the rock. The strength of igneous rocks was inversely proportional to the mineral grain size, but there is no correlation between the sedimentary rocks strength and the mineral grain size. Furthermore, the tension–shear crack propagation of rock can effectively distinguish by judging that the data set of the AF–RA density graph was nearby the AF axis or RA axis and the peak frequency data sets of below 100 kHz or more than. Alterations in the rock nature are the main key reasons for the differences between AE hit rate, AE count rate, AE energy, and cumulative energy. The plagioclase content and grain size play a decisive role in AE signal characteristics and failure mode.

Parameter Sensitivity Analysis of the Hydraulic Fracture Growth Geometry in a Deep Shale Oil Formation: An Experimental Study

The depth of shale oil of Fengcheng Formation in Mahu of Junggar Basin, China, is 4500-5000 m. The horizontal principal stress difference of deep shale reservoir is high, which makes it difficult to form complex fractures during fracturing reconstruction. In order to fully understand the law of hydraulic fracture propagation in the formation during fracturing construction, the anisotropy characteristics and basic reservoir physical parameters (mineral composition and rock strength parameters) of rock were obtained through mineral composition test and indoor rock mechanics test (Brazil splitting test), and it was found that the heterogeneity was strong. The true triaxial fracturing simulation experimental system is used to carry out experimental research on full-diameter core rock samples, and the propagation patterns of hydraulic fractures under the influence of different geological factors (in situ stress difference and natural fractures) and engineering factors (pumping rate and fracturing fluid viscosity) are compared and analyzed. The results show that the in situ stress is the most important factor affecting fracture propagation, which determines the direction and shape of fracture propagation. The natural weak surface (lamina/bedding and natural fractures, etc.) in shale reservoir is an important reason for complex fractures. The nature of the weak plane, occurrence, and in situ stress jointly determine whether the fracture can extend through the weak plane. With the increase of pumping rate (18 mL/min to 30 mL/min), the ability of hydraulic fractures to penetrate layers is continuously enhanced. The horizontal principal stress difference of deep shale reservoir is high, and the low viscosity fracturing fluid (10 mPa·s) tends to activate the horizontal bedding, while the high viscosity fracturing fluid (80 mPa·s) tends to directly penetrate the bedding to form the vertical main fracture. Therefore, the fracturing technology of alternating injection of prehigh viscosity fracturing fluid and postlow viscosity fracturing fluid can be adopted to maximize the complexity of fracturing fractures in deep shale reservoirs. The research results are designed to provide theoretical guidance for prediction of hydraulic fracturing fracture propagation in shale reservoir and have certain reference significance for field construction.

Brittleness evaluation based on shale fracture morphology

Fracture morphology of shales represents the main feature related to their brittleness, and plays an important role in affecting the complexity of fracture network in shale reservoirs. However, no brittleness index model based on fracture morphology has been developed so far. In the present research, a detailed analysis on morphological characteristics of shale fractures under triaxial compression has been performed, focusing on the Longmaxi Formation shale in the Weiyuan area, China. As a next step, the fractal theory is used to establish a method to characterize fracture complexity. As a next step, the correlation between rock mechanics parameters, mineral composition, stress-strain curve, dilatability, and shale fracture complexity is analyzed, determining the most influencing factors affecting brittleness, whose weight is analyzed by applying the gray correlation method. Furthermore, a novel brittleness evaluation method based on shale fracture morphology is established. Results show that Young's modulus, peak strain, and dilatancy angle of shales are characterized by the highest correlation values with fracture morphology (0.4745, 0.6302, and 0.579, respectively), while Poisson's ratio, mineral composition, peak, and residual stress, and strain have little correlation. The calculation and analysis of a shale horizontal well using the brittleness index calculation method in this paper shows that the established method has a good correlation with the number of events of MS after fracturing, the reconstruction volume, which provides technical support for the optimization of fracturing sweet spot in shale horizontal wells, and the evaluation of shale reservoir compressibility.

The Isotope Composition, Nature, and Main Mechanisms of Formation of Different Types and Subtypes of Salt Lakes in Transbaikalia

Abstract —More than a hundred lakes, groundwater, rivers, and precipitation of their catchments have been studied in Transbaikalia. The chemical composition of natural waters and the mineral composition of rocks and lacustrine bottom sediments have been analyzed. The isotope composition of waters, the isotope ratios in dissolved and deposited carbonates and in bacterial mats, and the content of heavy oxygen in the aluminosilicate fraction of bottom sediments and rocks in catchments have been determined. It is shown that all secondary minerals inherit the oxygen isotope composition of water, but their oxygen is isotopically much heavier than the water oxygen, because the water–rock interaction leads to the fractionation of oxygen and the transition of its heavy isotope into secondary carbonates and aluminosilicates. Bacterial mats using oxygen of carbon dioxide ions for their vital activity are also enriched in its heavy isotope. We have established that the water of soda lakes, being less saline than other lake waters, is more enriched in heavy oxygen isotope. Mineral analysis of lacustrine bottom sediments and material from sedimentation traps revealed chemogenic carbonates and secondary aluminosilicates. The performed thermodynamic calculations confirm their possible formation in lakes. It is shown that the lake water is in equilibrium not only with carbonates, clays, and hydromica but also with zeolites, and the most alkaline and mineralized water is in equilibrium with albite. The bottom sediments of soda lakes have a greater portion of clays and carbonates than those of fresh, chloride, and sulfate waters. The enrichment of salt lake waters with heavy isotopes is due not only to evaporation but also to the water–rock interaction. The contribution of aluminosilicate hydrolysis to oxygen fractionation is confirmed by the direct dependence of the “oxygen shift” value on pH, whose value is determined by the degree of the above interaction. We have established that the diversity of the chemical and isotope compositions of lake waters is due to their multifactorial formation related to the different degrees of lake water evaporation, the different mineralization of organic matter, and the different duration of the interaction of lake waters and groundwater with rocks.

The Effects of Physical and Geometrical Properties on Rock Brittleness Index Based on Numerical Modeling

Rock brittleness is a key parameter to quantify and evaluate the brittle nature of the rock. A better estimating technique of rock brittleness is crucial for acquiring an efficient stimulation of unconventional shale gas reservoirs such as hydraulic fracturing. One way to predict rock brittleness index is by using rock elastic moduli. These physical properties highly depend on the complexity of the microstructure, fluid content, and mineral composition. The other way is by measuring the rock mineral composition itself. This complexity of the microstructure can be accurately characterized by using imaging techniques such as micro-CT scans. This study used the finite element method to estimate rock brittleness index based on elastic properties on synthetic and digital rock images. We then evaluate the effect of physical and geometrical properties (pore aspect ratio, water saturation, and mineral composition) in determining the rock brittleness characteristic. The results indicate that there is an increase in Young’s modulus along with an increasing pore aspect ratio to 1, which in turn raises the rock brittleness. Fluid saturation, in this case, water saturation, causes brittleness to be increased. The rock mineral composition, such as abundant quartz and carbonate content, yields high brittleness values, while high clay content and porosity lower the rock brittleness. Overall, the results imply that pore geometry, fluid saturation, and mineral composition significantly alter the rock strength parameters.

Investigation on pore structure, fluid mobility and water huff-n-puff oil recovery of tight volcanic oil reservoir

The pore structure of tight volcanic oil reservoirs is very complex and the permeability is extremely low. The oil recovery effect of traditional water-driven and gas-driven development is not ideal. In this paper, we first analyzed the pore structure characteristics and fluid movability characteristics of tight volcanic rocks. Then, the feasibility of water huff-n-puff in tight volcanic rocks was analyzed. Finally, we investigated the oil recovery characteristics, pore motility characteristics, and ORM of water huff-n-puff in tight volcanic rocks by using a high temperature and ultra-high pressure water huff-n-puff physical simulation experimental device under NMR monitoring. The study shows that the mineral composition of tight volcanic rocks is relatively simple, but the pore structure is very complex. The pores are mainly amygdule pores, and contain some vesicular pores and matrix pores. The fractures include structural fractures, dissolution fractures, and shrinkage fractures. Fractures are of great significance for communicating relatively independent pores and improving the seepage ability of fluids in tight volcanic rocks. The fluid movable saturation of tight volcanic rocks is 32.93%–83.75%, and the minimum movable pore radius is 0.0178 μm. The seepage capacity of large pores (r > 0.1 μm) is 2.19–7.75 times that of middle pores (0.001 μm < r < 0.1 μm). The oil recovery efficiency (the ratio of the volume of recovered oil to the volume of injected water) of the first two cycles of water huff-n-puff of tight volcanic rocks exceeds 20%, which is high-efficiency oil recovery period. However, with the increasing huff and puff cycles, the recovery factor and oil change rate both decrease rapidly. After five cycles of water huff-n-puff, the recovery factor of tight volcanic rocks increases by 29.13%. For the selected experimental core, middle pores are the main oil-producing pores, and their contribution rates in natural energy depletion and five cycles of water huff-n-puff are 59.665% and 78.173%. In five cycles of water huff-n-puff, the contribution rates of elastic displacement are 96.491%, 93.846%, 86.667%, 64.706%, and 55.556%, and the effect of imbibition displacement is relatively small. Increasing the water injection pressure is beneficial to water huff-n-puff oil recovery of tight volcanic rocks. The research can provide a good theoretical basis for the efficient development of tight volcanic oil reservoirs.

Identifikasi Komposisi Mineral Batuan Teralterasi Menggunakan Spektroskopi SEM-EDX dan FTIR Pada Daerah Manifestasi Panas Bumi di Desa Mototompiaan Kecamatan Modayg Kabupaten Bolaang Mongondow Timur

Mototompiaan village is one part of the area that has geothermal potential, there are 2 types of manifestations that exist in the area that is in the form of hot springs and mud pool. The purpose of this study to determine mineral composition of rocks which is in the area around geothermal manifestation of hot springs by SEM-EDX and FTIR. Based on the result of identification using SEM-EDX in sample 1 shows that there are composition of Aluminium (Al) 6.11%, Fe 11,10% and Silica (Si) 82.79%, while sample 2 contains Aluminium (Al) 6.53%, Fe 9,16%, Co 2,85% and Silica (Si) 87.13%. The test result by FTIR spectroscopy can be known the types of minerals contained in rock samples are Hermatite, Arganite, Quartz, and Palygorskite.

What happened to the Early Precambrian granulite complexes of the Bug region (Ukrainian shield) and the Limpopo belt (South Africa) and how to stratify them? A tectonist’s view

The author reviews two alternative approaches (stratigenic-metamorphogenic and deformation-metamorphogenic) to the geology and mapping of the Earth’s oldest crust rocks that were metamorphized in РТ-conditions of the granulite facies, on the examples of two granulite belts — the Bug area complex (Ukrainian shield) and Limpopo belt (Southern Africa).&#x0D; There was shown a fairly good correlation of the composition and metamorphism (including the dynamometamorphism) of the rock complexes of both belts and their at least three-stage origin and transformation. The granulitic metamorphism processes within both belts happened before 3,0 b.y.a., 2,6—2,8, and c. 2,0 b.y.a. The structural-metamorphic transformations of the granulitic complexes, formation of their new structural plans with the destruction of the former (archean) by the following (proterozoan) do not allow falsifiably stratifying the archean granulitic complexes within the stratigenic-metamorphogenic approach already at the facies level. For the Bug area granulitic belt it is feasible only to isolate the Dniester-Bug and Bug series. Two of the important processes of the belt development are rock deformation in the compression and slip conditions and formation within the granulitic complexes of the sub-vertically-layered medium, slip folds with sub-vertical folds’ joints and wings. In both belts these processes began in the Neoarchean. This shows that in that time the tectonic processes were already to some significant degree propelled by plate tectonics mechanisms. Both belts had in common the formation of the linear-typeshearzonesat micro- to macroscale and their superimposition onto the deformation structures of the granulitic complexes of the preceding developmental stages. On their basis there formed the internal structure of the belts’ and their interconnections with the adjacent blocks of crust. Presumably, the archean charnokitoids and TTG-granitoids form the same structural layer of the crust, given their geochemical similarity and close age, and this layer is the base for the greenstone belts. The mineral composition, РТ-metamorphism conditions and age of granulitic belt rocks based on their U-Pb, Lu-Hf, Sm-Nd isotope systems compositions andoxygen isotope composition in Zirconium grains suggest that in the eo- and paleoarchean mantle and crust there should have already been amassed large quantities of medium-acidic matter which gave rise to the TTG complexes.

PDC bit optimization scheme for tight oil reservoirs in the Jidong Oilfield based on rock anti-drilling characteristics

The tight oil reservoir rocks in the Jidong Oilfield are generally characterized by high hardness, strong abrasiveness, and extremely unevenness, which seriously reduce the drilling efficiency. In view of this problem, the mineral composition, hardness, plasticity coefficient, and drillability of rocks were first determined. It was found that the rock integrity, compactness and high hardness are the main factors leading to the low rock breaking efficiency of PDC bits. Then, combined with logging data, the drilling resistance profile of the whole well section was established. According to the crushing mechanism of rocks under the action of a PDC bit, the mechanical model of a single composite plate under rock crushing conditions is established, and the influence of the back angle on the cutting force is analyzed. The flow field distribution of the drill bit surface under different nozzle combinations was calculated by finite element numerical simulation. Based on the experimental and simulation results, the optimal backward angle was 15°, and the optimal nozzle combination was two 16-mm central nozzles and five 14-mm peripheral nozzles. Finally, a personalized PDC bit design scheme for tight oil reservoirs in the Jidong Oilfield was proposed. The scheme includes the following: (1) a 5-blade straight-arc crown is profiled; (2) anti-impact cylindrical components are set; (3) the nozzle hydraulic structure adopts a bending type; and (4) the diameter-retaining teeth and diversion grooves are optimized. The optimized bit reduces stick–slip, improves stability, and has an obvious acceleration effect.

Multilevel Structural Characteristics of Jinshajiang Main Fault and Its Influence on Engineering

It is of great significance to study the geological characteristics of faults and the corresponding displacement patterns for the tunnel engineering crossing active faults. On the basis of field investigation and geological data analysis, it is found that the secondary weak structures, such as narrow cleavage bands, narrow joint bands, fault gouge zones, and small folds, often appear in the fault fracture zones and affected zones. The multilevel structure of fault is proposed from mechanics and engineering by summarizing their main characteristics. Taking the outcrop of fracture zones of Batang section, Jinshajiang main fault in the Qinghai-Tibet Plateau as the research object, the geometric characteristics of rock masses, the particle size, mineral composition, and mechanical characteristics of rocks in the fault are studied through field investigation, geological mapping, mineral composition analysis, and mechanical tests. In addition, a displacement model of multilevel structure fault is presented by numerical simulation. The results show that the Jinshajiang main fault comprises a primary structure and several secondary weak structures, which has a typical structure of multilevel fault. There are several secondary weak structures in the outcrop of the fracture zone. Compared with the rock masses in the primary structure, the joints of the rock masses in the secondary weak structure are more developed, and the rock particle size is smaller, the mud content is higher, and the mechanical strength is lower. The geometric morphology, mineral composition, and mechanical properties of the rock masses in the secondary weak structure are obviously different from those of the primary structure. The overall displacement mode of multilevel structural fault is S-shaped distribution, and the secondary weak structure will affect the displacement distribution pattern and have the possibility of sliding when the fault moves. Therefore, the secondary weak structure section in the tunnel should be a priority for prevention and control when designing tunnels through active faults. The multilevel structure of the fault, together with centralized structure, distributed structure, and stepped structure of the fault, can be used as a structure classification method of fault structure, which provides a reference for the study of disaster mechanisms, and prevention and control measures of tunnels crossing active faults.

Damage Characteristics of Thermally Deteriorated Carbonate Rocks: A Review

This review paper summarizes the recent and past experimental findings to evaluate the damage characteristics of carbonate rocks subjected to thermal treatment (20–1500 °C). The outcomes of published studies show that the degree of thermal damage in the post-heated carbonate rocks is attributed to their rock fabric, microstructural patterns, mineral composition, texture, grain cementations, particle orientations, and grain contact surface area. The expressive variations in the engineering properties of these rocks subjected to the temperature (&gt;500 °C) are the results of chemical processes (hydration, dehydration, deionization, melting, mineral phase transformation, etc.), intercrystalline and intergranular thermal cracking, the separation between cemented particles, removal of bonding agents, and internal defects. Thermally deteriorated carbonate rocks experience a significant reduction in their fracture toughness, static–dynamic strength, static–dynamic elastic moduli, wave velocities, and thermal transport properties, whereas their porous network properties appreciate with the temperature. The stress–strain curves illustrate that post-heated carbonate rocks show brittleness below a temperature of 400 °C, brittle–ductile transformation at a temperature range of 400 to 500 °C, and ductile behavior beyond this critical temperature. The aspects discussed in this review comprehensively describe the damage mechanism of thermally exploited carbonate rocks that can be used as a reference in rock mass classification, sub-surface investigation, and geotechnical site characterization.

Comparative analysis of lithological and geochemical features and conditions for the formation of oil and gas source rock strata

The typification according to the lithological and geochemical characteristics of the deposits that make up the sections of the two oil source strata: Domanik and Bazhen was carried out . Lithotypes are revealed. For each of the objects of study, a complex of laboratory studies of rocks and contained fluids was carried out. The relationships were revealed between the mineral composition of rocks, the content and types of contained organic matter, the degree of organic matter maturity,the chemical composition of the inorganic and component composition of the organic parts of study strata.

Preliminary research on developing the methodology for predicting and estimation of productive sulfide mineralization of the Norilsk type using polarizing-optical and petrophysical methods (on the example of the Talnakh Deposit)

The quantity of the mineral composition of ore and parent rocks was carried out. Ore sections from the core samples of two wells of the Talnakh field were used for these studying. Also a number of their physical, mechanical, magnetic and electrical properties were determined. The content of the main ore minerals and useful components in the studied samples were calculated due to comparison of these data of their petrophysical properties. Additionally petrophysical anomalies in the external contact of ore horizons were identified. Using of this methodology may contribute to improving the efficiency of survey and evaluation work on Norilsk type sulfide mineralization.

Rock shale mineral composition influence on oil and gas generation process (results from laboratory experiments)

The paper presents the results of the hydrothermal processes of organic matter transformation in the rocks of the Bazhenov Formation and the Domanik horizon laboratory modeling. Shortterm exposure of samples to high temperatures (350 C) and reservoir pressures (300 atm) in the presence of water made it possible to simulate the processes that could take place in the reservoir, and to transform kerogen up to 70% in the rocks initially containing immature kerogen or kerogen in the beginning of the oil window. It was found that the amount of liquid hydrocarbon compounds generated during cracking mainly linearly depends on the content of organic matter in the rocks, while the gas generation is described by a rate function. The mineral composition of rocks does not affect the size of the formed pores, but in some cases it controls the amount of formed hydrocarbon compounds and the composition of the liquid products. It is shown that the increase in the amount of carbonate material in the rocks inhibits oil and gas generation process, there are lower amounts of light components in the products, and some of hopanes are absent. At the same time, high concentrations of siliceous material in the rocks with low amount of other components and, probably, the presence of pyrite can stimulate the generation process, in some cases allowing an increase in the amount of produced “synthetic” oil and gas, to achieve a greater variety of reaction products. The results obtained in general make it possible to examine the processes of individual hydrocarbon compounds formation during hydrothermal processes, to identify catalysts and inhibitors of the generation mechanism, and also, from a practical point of view, to propose conditions for reservoirs stimulation and development of technologies for increasing oil production and generation of oil with a controlled composition in situ.

Petrography Characteristic of Porphyritic Dacite Rock in Olele Village, Kabila Bone, and Bone Bolango

Porphyritic Dacite volcanic rocks are abundant in Olele Village, Kabila Bone, Bone Bolango. This research aims to determine the petrography characteristics of porphyritic dacite rock in Olele. The methods used in this research were field observation and petrography analysis to determine rock texture, mineral composition, and micro-texture plagioclase. Olele Porphyritic Dacite has a porphyritic texture composed phenocryst of plagioclase, quartz, hornblende, sanidine, opaque mineral, and secondary minerals such as sericite and clay minerals. Rock textures include glomeroporphyritic, seriate, and embayment. The micro-textures in plagioclase are fine oscillatory zoning, synneusis, glomerocryst, fine sieve, coarse sieve, resorption surface, and broken crystal. Magmatic processes that occur in the magma chamber include fractional crystallization, magma injection, magma mixing, convection, adiabatic decompression, syn-eruption decompression, and undercooling. The secondary minerals indicated alteration hydrothermal process.

Mineralogical Characterization of Early Bronze Age Pottery from the Svilengrad-Brantiite Site, Southeastern Bulgaria

Several pottery sherds from the Svilengrad-Brantiite site, Bulgaria, were mineralogically and petrographically analyzed. The aim was to add information to the very scarce material data available for Early Bronze Age pottery in the southeastern Thrace plain, Bulgaria, in order to examine a possible raw-material source of the pottery. The characterization techniques applied were optical microscopy (OM), petrographic microscopy (PM), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), X-ray fluorescence (XRF) spectroscopy, and X-ray diffraction (XRD). The pottery samples consisted of two typological groups: a local-made type and a cord-impressed decoration type influenced by foreign cultures. All of the samples were produced from fine clay pastes that had a quite similar composition, with abundant mineral grains of similar mineral composition and fragments of metamorphic and granitic rocks. The chemical compositions of each mineral in the grains and fragments were almost identical, and consistent with those from metamorphic and granitic rocks from the Sakar-Strandja Mountains near the study site. The clay paste compositions corresponded to those of illite/smectite mixed-layer clay minerals or mixtures of illite and smectite, and the clay-mineral species were consistent with those in Miocene–Pleistocene or Holocene sediments surrounding the site.

Multiscale pore structure characterization of an ultra-deep carbonate gas reservoir

The pore structures of shallow and mid-deep carbonate gas reservoirs have been well explored. Totally different from these reservoirs, however, the pore structure of a target ultra-deep carbonate gas reservoir, the Qixia Reservoir in the Shuangyushi play is still unknown. Affected by tectonic movement and deep hydrothermal transformation, the lithology of this target reservoir has significantly changed and it has developed different scales of pores and fractures. Thus, a multiscale micro-CT (computed tomography) method is needed to combine different scales of its pore space to evaluate carbonate samples more realistically. In this study, the multiscale micro-CT method and other traditional methods including X-ray diffraction (XRD), casting thin section, scanning electron microscope (SEM), routine petrophysical measurements (RPM), and high-pressure mercury intrusion (HPMI) are first combined to quantitatively describe a distribution of multi-scale pores, throats, and fractures in the target ultra-deep carbonate gas reservoir. The results showed that micro pores (70%–90%), micro throats (>90%), and micro fractures (>90%) dominated in this reservoir. Dolomite accounted for more than 90% of the rock mineral composition in the Qixia reservoir with few clay minerals. Intercrystalline pores and micro fractures were the main pore types and the mean reservoir porosity was less than 2%. Micro fractures play a great role in improving reservoir permeability. The HPMI method presented with errors in the classification of ultra-deep carbonate reservoir types owing to the development of vugs, large pores, and fractures. In this study, a new classification method was proposed to classify this type of reservoirs based on porosity, permeability, and the studied parameters from the multiscale micro-CT method such as throat number and connected porosity proportion. The target reservoir was divided into the following four categories according to the new classification method: fracture macropore type (FMA), macropore type (MA), fracture micropore type (FMI), and micropore type (MI). According to the results of multiscale CT scanning, a strong linear relationship was observed between the number of throats, the connected porosity, and the permeability of the ultra-deep carbonate rock samples studied. Fractures improved the permeability of rock samples by aiding the connection of isolated pores and the expansion of the number of throats. Therefore, the MA and MI types of reservoirs should be properly fractured to increase their productivity.