Hasil untuk "Petrology"

Miguel Ángel Rogerio Candelera, Alba Fuentes Porto, Timoteo Rivera Jiménez et al.

This paper presents multi-disciplinary research undertaken between 2022 and 2024 at El Riscal, the only rock art station known in Seville (Andalusia, Spain), a territory otherwise very rich in Late Prehistoric archaeological remains. Discovered in the 1980s and first published in the early 1990s, El Riscal presents engraved motifs not documented in other parts of southern Spain, where schematic-style painted rock art is prevalent. The set of methods employed in this research includes petrology, chemical characterisation (XRD, SEM-EDS), digital photogrammetry and digital image analysis, archaeological prospection and archaeoastronomy. The results throw new light on the characteristics and temporality of the site, with a pervasive significance through time. This, in turn, invites a new approach to the geographical distribution of the various traditions and styles present in Iberian rock art. This research also suggests that re-examining previously published rock art sites could lead to a better understanding of styles, chronologies and traditions.

Teresa Rivas, José Santiago Pozo-Antonio, Daniel Jiménez-Desmond et al.

Historical tempera paints exposed to pollutant gases suffer chemical and mineralogical deterioration which manifests through physical changes. Knowledge about these changes is fundamental to develop strategies for preventive conservation of wall paintings. In this research, binary tempera mock-ups composed of calcite, gypsum or lead white mixed with a proteinaceous binder (i.e., egg yolk or rabbit glue) were exposed to an aging test by using SO₂-rich atmosphere exposure to learn about the degradation mechanisms and forms related to the pigment–binder interaction. Reference (unaltered) and aged mock-ups were studied from a physical point of view, characterizing the morphological changes by using stereomicroscopy and profilometry, color variations by using spectrophotometry, gloss changes, and reflectance changes by using a hyperspectral camera. Also, mineralogical and chemical changes were studied by means of X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Egg-yolk-based paints showed higher chromatic changes than their counterparts made of rabbit glue binder. Also, sulfate and sulfite salts precipitated on the surface of the aged paints regardless of their binder, influencing the painting reflectance which subsequently increased. Egg-yolk-based mock-ups exhibited roughness increases while the rabbit-glue-based paints showed roughness reduction, with the exception of lead-white-based paints. Therefore, the important influence of the type of binder and the interaction between the binder and the pigment on the durability of tempera paints in atmospheres rich in SO₂ was confirmed.

Biao Yin, Hejun Zou, Jie Liu et al.

Abstract In the later stages of gas field development, corrosion and erosion wear often occur in elbow-shaped connections used for gas transportation. Combined with laboratory corrosion experiments, the paper is based on CFD to study the distribution characteristics of pressure and velocity in the flow field for the elbow with pre-set corrosion defects. Simultaneously, the specific procedure is designed to track the formation of Dean vortices, thereby revealing the impact patterns of different corrosion defect features on the erosion outcomes of the elbow. Accordingly, the effect of different arrangement, number and form of corrosion defects on erosion wear was systematically analyzed. The results show that: (1) A comparative analysis of the three different defect distribution forms indicates that erosion occurs mainly at the bend near the outlet Section (45° ~ 60°). Double corrosion defects in the radial distribution will significantly accelerate the rate of pipe erosion, changing the location of maximum erosion rate. (2) By controlling the number of corrosion defects to represent the size of the corroded area, the study reveals as the number of defects increases, the rate and area of erosion in surface of the target material increases significantly. Thus, the area of the corrosion will explicitly change the effect of erosion. (3) As the depth of the defects (corrosion rate) increase, the erosion rate around the radial and axial defects increases exponentially compared to the absence of corrosion, reaching a maximum of 7.8 × 10−6 kg/(m2·s). Corrosion and erosion are two complementary forms of damage to pipe in the production process. The presence of corrosion defects leads to faster erosion rates and changes in the overflow area, reducing service life. Hence, only a reasonable control of both types of wear can ensure the longevity of gas production and transportation.

Daniel Rodrigues dos Santos, André Ricardo Fioravanti, Vinicius Eduardo Botechia et al.

Abstract Enhancing oil recovery in reservoirs with light oil and high gas content relies on optimizing the miscible water alternating gas (WAG) injection profile. However, this can be costly and time-consuming due to computationally demanding compositional simulation models and numerous other well control variables. This study introduces WAGeq, a novel approach that expedites the convergence of the optimization algorithm for miscible water alternating gas (WAG) injection in carbonate reservoirs. The WAGeq leverages production data to create flexible solutions that maximize the net present value (NPV) of the field, while providing practical implementation of individual WAG profiles for each injector. The WAGeq utilizes an injection priority index to rank the wells and determine which should inject water or gas at each time interval. The index is built using a parametric equation that considers factors such as producer and injector relationship, water cut (W CUT), gas–oil ratio (GOR), and wells cumulative gas production, to induce desirable effects on production and WAG profile. To evaluate WAGeq’s effectiveness, two other approaches were compared: a benchmark solution named WAGbm, in which the injected fluid is optimized for each well over time, and a traditional baseline strategy with fixed 6-month WAG cycles. The procedures were applied to a synthetic simulation case (SEC1_2022) with characteristics of a Brazilian pre-salt carbonate field with karstic formations and high CO2 content. The WAGeq outperformed the baseline procedure, improving the NPV by 6.7% or 511 USD million. Moreover, WAGeq required fewer simulations (less than 350) than WAGbm (up to 2000), while delivering a slightly higher NPV. The terms of the equation were also found to be essential for producing a WAG profile with regular patterns on each injector, resulting in a more practical solution. In conclusion, WAGeq significantly reduces computational requirements while creating consistent patterns across injectors, which are crucial factors to consider when planning a practical WAG strategy.

A. A. Borisov

Jorge Otero

Abstract Global cultural heritage is a lucrative asset. It is an important industry generating millions of jobs and billions of euros in revenue yearly. However, despite the tremendous economic and socio‐cultural benefits, little attention is usually paid to its conservation and to developing innovative big‐picture strategies to modernize its professional field. This perspective aims to compile some of the relevant current global needs to explore alternative ways for shaping future steps associated with the 2030 Agenda for Sustainable Development. From this perspective, it is conceptualized how emerging artificial intelligence (AI) and digital socio‐technological models of production based on democratic Peer‐2‐Peer (P2P) interactions can represent an alternative transformative solution by going beyond the current global communication and technical limitations in the heritage conservation community, while also providing novel digital tools to conservation practitioners, which can truly revolutionize the conservation decision‐making process and improve global conservation standards.

Runze Yang, Xianzheng Zhao, Changyi Zhao et al.

The Wumaying buried hill experienced multi-stage tectonic movements, which resulted in a complicated and unclear nature of the hydrocarbon accumulation process. To solve these problems, in this study—based on the structural evolution and burial–thermal history of the strata, using petrology, fluid inclusion microthermometry, geochemical analysis of oil and gas, Laser Raman spectrum, and fluorescence spectrum—the history of hydrocarbon charging was revealed, and the differences in hydrocarbon charging of different wells was clarified. The results indicate that the only source for Permian oil and gas reservoirs are Carboniferous–Permian coal-measure source rocks in the Wumaying buried hill. There are three periods of hydrocarbon charging. Under the channeling of faults and micro cracks, low-mature oil and gas accumulation was formed in the first period, and the accumulation time was 112–93 Ma. In the late Cretaceous, a large-scale uplift exposed and damaged the reservoirs, and part of the petroleum was converted into bitumen. In the middle–late Paleogene, the subsidence of strata caused the coal-measure to expel mature oil and gas, and the accumulation time of mature oil and gas was 34–24 Ma. Since the Neogene, natural gas and high-mature oil have been expelled due to the large subsidence entering the reservoir under the channeling of active faults; the accumulation time was 11–0 Ma. The microfractures of Permian reservoirs in the Wumaying buried hill are the main storage spaces of hydrocarbons, and the fractured reservoirs should be explored in the future. The first period of charging was too small and the second period was large enough in the WS1 well, resulting in only a late period of charging in this well.

X. Zhong, X. Zhong, M. Dabrowski et al.

<p>Raman elastic thermobarometry has recently been applied in many petrological studies to recover the pressure and temperature (<span class="inline-formula"><i>P</i></span>–<span class="inline-formula"><i>T</i></span>) conditions of mineral inclusion entrapment. Existing modelling methods in petrology either adopt an assumption of a spherical, isotropic inclusion embedded in an isotropic, infinite host or use numerical techniques such as the finite-element method to simulate the residual stress and strain state preserved in the non-spherical anisotropic inclusions. Here, we use the Eshelby solution to develop an analytical framework for calculating the residual stress and strain state of an elastically anisotropic, ellipsoidal inclusion in an infinite, isotropic host. The analytical solution is applicable to any class of inclusion symmetry and an arbitrary inclusion aspect ratio. Explicit expressions are derived for some symmetry classes, including tetragonal, hexagonal, and trigonal.</p> <p>The effect of changing the aspect ratio on residual stress is investigated, including quartz, zircon, rutile, apatite, and diamond inclusions in garnet host. Quartz is demonstrated to be the least affected, while rutile is the most affected. For prolate quartz inclusion (<span class="inline-formula"><i>c</i></span> axis longer than <span class="inline-formula"><i>a</i></span> axis), the effect of varying the aspect ratio on Raman shift is demonstrated to be insignificant. When <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi>c</mi><mo>/</mo><mi>a</mi><mo>=</mo><mn mathvariant="normal">5</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="40pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="f5d3c7503b34dfd63ac2429dac7e9fda"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="se-12-817-2021-ie00001.svg" width="40pt" height="14pt" src="se-12-817-2021-ie00001.png"/></svg:svg></span></span>, only ca. 0.3 cm<span class="inline-formula">⁻¹</span> wavenumber variation is induced as compared to the spherical inclusion shape. For oblate quartz inclusions, the effect is more significant, when <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi>c</mi><mo>/</mo><mi>a</mi><mo>=</mo><mn mathvariant="normal">0.5</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="49pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="3a103ffbd4517c04cefd7e3f3fe2326e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="se-12-817-2021-ie00002.svg" width="49pt" height="14pt" src="se-12-817-2021-ie00002.png"/></svg:svg></span></span>, ca. 0.8 cm<span class="inline-formula">⁻¹</span> wavenumber variation for the 464 cm<span class="inline-formula">⁻¹</span> band is induced compared to the reference spherical inclusion case. We also show that it is possible to fit an effective ellipsoid to obtain a proxy for the averaged residual stress or strain within a faceted inclusion. The difference between the volumetrically averaged stress of a faceted inclusion and the analytically calculated stress from the best-fitted effective ellipsoid is calculated to obtain the root-mean-square deviation (RMSD) for quartz, zircon, rutile, apatite, and diamond inclusions in garnet host. Based on the results of 500 randomly generated (a wide range of aspect ratio and random crystallographic orientation) faceted inclusions, we show that the volumetrically averaged stress serves as an excellent stress measure and the associated RMSD is less than 2 %, except for diamond, which has a systematically higher RMSD (ca. 8 %). This expands the applicability of the analytical solution for any arbitrary inclusion shape in practical Raman measurements.</p>

M. Sadegh Rajabi, Rasoul Moradi, Masoud Mehrizadeh

Abstract The wettability preference of carbonate reservoirs is neutral-wet or oil-wet as the prevailing of hydrocarbon reserves that affects approximately half of the total production of hydrocarbons of the world. Therefore, due to surface wettability of carbonate rocks the notable fraction of oil is held inside their pores in comparison with sandstones. Since shifting the wettability preference toward water-wet system is of great interest, numerous components were used for this purpose. In this experimental research, the wettability alteration of dolomite surface by interacting with a novel nano-surfactant–alkaline fluid has been investigated in order to diminish its adhesion to crude oil droplets. The solutions were prepared by homogenous mixing of nanosilica particles with cetyl trimethyl ammonium bromide and sodium carbonate, respectively, as a cationic surfactant and alkaline agent. The maximum wettability alteration from oil-wet to water system was obtained by employing a mixture of nanoparticles in association with surfactant–alkaline. Then, the fluids were employed in core-surface from detached and attached forms to compare their interfacial effects on saturated thin sections by crude oil and to measure the wettability. In addition, the interfacial tension (IFT) between solutions and crude oil was investigated and the maximum IFT reduction was obtained from nano-surfactant. Finally, all chemical solutions were flooded to the dolomite plugs separately after water flooding in order to evaluate the maximum oil recovery factor acquired by nano-surfactant.

A. A. Feyzullayev, I. Lerche, I. M. Mamedova et al.

Abstract The scientific basis of the paper is the concept of renewability of oil and gas resources. In accordance with this concept, the purpose of this paper is to estimate the volumetric rate of natural replenishment of the reservoir with oil and gas using the example of long-developed Bibieybat oil and Garadag gas condensate fields in the South Caspian Basin (SCB). The methodological approach of this assessment is based on the authors' assumption that at the late stage of field development, the recoverable amount of hydrocarbon fluids is compensated by the amount of their natural inflow, as a result of which oil or gas production stabilizes. The analysis of the dynamics of hydrocarbon production for the Bibieybat oil field covered the period from 1935 to 2018, and for the Garadag gas condensate field from 1955 to 1979. The rate of natural oil replenishment calculated for 29 operating facilities of the Bibieybat field varies per well within 0.32–1.4 ton/day (averaging 0.76 ton/day) or about 277 ton/year. The rate of natural gas inflow at the Garadag gas condensate field is about 5.2 thousand m3/day per well.

Primož Mlakar, Boštjan Grašič, Marija Zlata Božnar et al.

The paper presents the construction and operation of a cave information system on the example of the Postojnska jama cave. It thoroughly describes the construction of the basic modules of the cave information system, such as an automatic cave measuring station with sensors for measuring air temperature, air flow and CO2 concentration, and a central unit for collecting, saving, processing and displaying data. The system provides quality automatic measurements for the scientific study of the micrometeorology of karst caves. Its construction is based on good practices stemming from many years of experience in taking measurements in the external atmosphere and in karst caves. The paper is rich and comprehensive guideline for automatic cave measuring system construction for scientific and tourist management purposes.

S. V. Pribavkin, A. V. Коrovko, I. A. Gottman

Research subject. The geological structure and rock composition of the Nizhne-Sinyachikhinsky plagiogranite massif, which is part of the Alapaevsk-Sukholozhsky zone, is promising for the Cu(Au,Mo)-porphyric mineralization type, were studied. The aim was to determine the formation features of these rocks and compare them with the productive granitoids of Ural porphyry deposits of similar age. Materials and methods. The mineral composition of the rocks was determined using a JEOL JSM 6790LV scanning electron microscope with an INCA Energy 450 X-Max 80 EDS spectrometer and a CAMECA SX-100 electron microprobe analyser. The rock composition was obtained by X-ray fluorescence spectrometry on a SRM-35 and XRF-1800 spectrometers with the titrimetric determination of FeO. The concentrations of rare and rare-earth elements were determined on an ELAN 9000 inductively coupled plasma mass spectrometer at the Geoanalitik Center for Collective Use of the Ural Branch of the Russian Academy of Sciences. Results. For the first time, an early tonalite-plagiogranite series was identified in the structure of the massif. This series is represented by tonalites of the hypabyssal appearance, broken through by the dikes of plagiogranite-porphyry. It was shown that the separation of plagiogranite-porphyry melts from magmas of the mafic composition occurred at the base of the island-arc construction, and their crystallisation was carried out in an intermediate chamber at a pressure of 1.8–2.3 kbar. In contrast, the plagiogranites of the main phase of the massif were separated from the parent melt in an intermediate chamber located at the level of the upper crust, and their crystallisation occurred at a pressure of 1.5–2.0 kbar. Conclusions. A comparison of the main phase plagiogranites and the isolated early-series plagiogranite-porphyry indicates their similar composition, as well as their similarity in age with the granitoids of the Southern Urals, productive in terms of the porphyry mineralisation type. The concentrations of F, Cl and S in the apatites and amphiboles of the rocks under study is an argument in favour of their belonging to andesitoid formations that are productive in terms of the Cu (Au)-porphyry mineralisation type. The absence of the sulphide mineralisation of this type can be explained by a more significant depth of rock formation and their erosion section.

Krisztián Fintor, Andrea Varga

In the basement areas of the southern Pannonian Basin, Central Europe (Tisia Composite Terrane, Hungary), Variscan blocks are essential components. The existing paleogeographic reconstructions, however, are often unclear and contradictory. This paper attempts to give a contribution for paleogeographic correlation of the Tisia using paleohydrological features (e.g., vein mineralization types, inclusion fluid composition and origin) of the Pennsylvanian continental succession and neighboring crystalline complexes. Vein-type mineralization in the studied samples dominantly forms blocky morphological types with inclusion-rich quartz and carbonate crystals. The evolution of hydrothermal mineralization and host rock alteration in the study area comprises three major stages. The first one is characterized by chloritization, epidotization, and sericitization of metamorphic rocks together with subsequent formation of Ca-Al-silicate and quartz-sulfide veins (clinopyroxene-dominant and epidote-dominant mineralization). The related fluid inclusion record consists of high-temperature and low-salinity aqueous inclusions, corresponding to a reduced retrograde-metamorphic fluid phase during the Late Westphalian (~310 Ma). The next mineralization stage can be related to a generally oxidized alkaline fluid phase with a cross-formational character (hematite-rich alkali feldspar-dominant and quartz-dolomite veins). High-salinity primary aqueous inclusions probably were originated from the Upper Permian playa fluids of the region. The parent fluid of the third event (ankerite-hosted inclusions) was derived from a more reductive and low-salinity environment and can represent a post-Variscan fluid system. Fluid evolution data presented in this paper support that the W Tisia (Mecsek–Villány area) belonged to the Central European Variscan belt close to the Bohemian Massif up to the Early Alpine orogenic phases. Its original position is presumably to the northeast from the Bohemian Massif at the Late Paleozoic, north to the Moravo-Silesian Zone. The presented paleofluid evolution refines previous models of the paleogeographic position of the Tisia and puts constraints on the evolution of the Variscan Europe.

Olusola J. Ojo, Ayoola Y. Jimoh, Juliet C. Umelo et al.

Abstract The Patti Formation which consists of sandstone and shale offers the best potential source beds in the Bida Basin. This inland basin is one of the basins currently being tested for hydrocarbon prospectivity in Nigeria. Fresh samples of shale from Agbaja borehole, Ahoko quarry and Geheku road cut were analysed using organic geochemical and palynological techniques to unravel their age, paleoecology, palynofacies and source bed hydrocarbon potential. Palynological data suggest Maastrichtian age for the sediments based on the abundance of microfloral assemblage; Retidiporites magdalenensis, Echitriporites trianguliformis and Buttinia andreevi. Dinocysts belonging to the Spiniferites, Deflandrea and Dinogymnium genera from some of the analysed intervals are indicative of freshwater swamp and normal sea conditions. Palynological evidence further suggests mangrove paleovegetation and humid climate. Relatively high total organic carbon TOC (0.77–8.95 wt%) was obtained for the shales which implies substantial concentration of organic matter in the source beds. Hydrocarbon source rock potential ranges from 0.19 to 0.70 mgHC/g.rock except for a certain source rock interval in the Agbaja borehole with high yield of 25.18 mgHC/g.rock. This interval also presents exceptionally high HI of 274 mgHC/g.TOC and moderate amount of amorphous organic matter. The data suggests that in spite of the favourable organic matter quantity, the thermal maturity is low as indicated by vitrinite reflectance and T max (0.46 to 0.48 Ro% and 413 to 475 °C, respectively). The hydrocarbon extracts show abundance of odd number alkanes C27–C33, low sterane/hopane ratio and Pr/Ph > 2. We conclude that the source rocks were terrestrially derived under oxic condition and dominated by type III kerogen. Type II organic matter with oil and gas potential is a possibility in Agbaja area of Bida Basin. Thermal maturity is low and little, or no hydrocarbon has been generated from the source rocks.

Biplab Kumar Mukherjee, G. Karthikeyan, Karanpal Rawat et al.

Abstract Shale is the primary rock type in the shallow marine section of the Mahanadi Basin, East Coast of India. Shale, being intrinsically anisotropic, always affects the seismic data. Anisotropy derived from seismic and VSP has lower resolution and mostly based on P wave. The workflow discussed here uses Gardner equation to derive vertical velocity and uses a nonlinear fitting to extract the Thomsen’s parameters using both the P wave and S wave data. These parameters are used to correct the sonic log of a deviated well as well as anisotropic AVO response of the reservoir. The presence of negative delta was observed, which is believed to be affected by the presence of chloride and illite in the rock matrix. This correction can be used to update the velocity model for time–depth conversion and pore pressure modelling.

Sandro Galdenzi

Research on the cave and karst water in the area of Monte Lago polje (Central Apennines) has revealed an articulate drainage pathway, influenced by the karstfication degree and geological setting. A fast drainage occurs from the ponor in the polje to the main temporary resurgence in the valley of San Giovanni, impeding the karst water in achieving thermal equilibrium with the rock. The water temperature in the resurgence decreases to very low values (~3 °C) during the winter, and the daily thermal cycles are clearly recognizable. These inputs of vadose water from the ponor have only a minor influence on the chemo-physical characteristics of San Giovanni spring, the largest emergence in the area, located a few hundred meters downstream in the same valley and fed by the main basal aquifer. The two nearby springs are recharged by different hydrostructures divided by low permeability levels in the Jurassic carbonate succession. This reduces the cross-formational communication mainly for the descending vadose fluxes. The fast drainage of karst water in the transfer vadose zone is due to a high karstfication, confirmed by the typology and distribution of the karst caves. A more regular discharge in the springs fed by the basal aquifer is probably related to a minor karstfication in the lower part of the limestone massifs. Key words: Monte Lago, Central Apennines, Karst, Groundwater monitoring. Kraško polje Monte Lago, študija vpliva geološke zgradbe in stopnje zakraselosti na tok podzemne vode v Centralnih Apeninih (Italija) Raziskave jam in kraške vode na območju kraškega polja Monte Lago (Centralni Apenini) so razkrile obstoj drenažne mreže, na katero vplivata stopnja zakraselosti in geološka zgradba. Med ponorom na polju in glavnim občasnim izvirom v dolini San Giovanni se pojavlja hiter tok, ki preprečuje uravnoteženje temperature vode s temperaturo kamnine. Pozimi ima voda v izviru zelo nizko temperaturo (~3 °C), jasno so vidni dnevni temperaturni cikli. Ti dotoki vadozne vode iz ponora imajo le majhen vpliv na fizikalno-kemijske značilnosti izvira San Giovanni, največjega izvira na tem območju, ki je lociran nekaj sto metrov dolvodno v isti dolini in se napaja iz glavnega spodnjega vodonosnika. Dva sosednja izvira se napajata iz različnih hidrostruktur, ločenih s plastmi slabše prepustnosti v jurskem karbonatnem zaporedju. To zmanjšuje prehajanje predvsem navzdol tekočih vadoznih vod skozi formacije. Hitro pretakanje kraške vode v vadozni coni je posledica dobre zakraselosti, ki jo potrjujeta tipologija in razpored kraških jam. Bolj enakomeren pretok izvirov, ki se napajajo iz spodnjega vodonosnika, je verjetno povezan z manjšo zakraselostjo v spodnjem delu apnenčastega masiva. Ključne besede: Monte Lago, Centralni Apenini, kras, monitoring podzemne vode.

Rajaa Bouamoud, Ely Cheikh Moine, Raphaèl Mulongo-Masamba et al.

Abstract The Democratic Republic of the Congo holds important reserves of oil shale which is still under geological status. Herein, the characterization and pyrolysis kinetics of type I kerogen-rich oil shale of the western Central Kongo (CK) were investigated. X-ray diffraction, Fourier-transform infrared spectroscopy and thermal analysis (TG/DTA) showed that CK oil shale exhibits a siliceous mineral matrix with a consistent organic matter rich in aliphatic chains. The pyrolysis behavior of kerogen revealed the presence of a single mass loss between 300 and 550 °C, estimated at 12.5% and attributed to the oil production stage. Non-isothermal kinetics was performed by determining the activation energy using the iterative isoconversional model-free methods and exhibits a constant value with E = 211.5 ± 4.7 kJ mol−1. The most probable kinetic model describing the kerogen pyrolysis mechanism was obtained using the Coats–Redfern and Arrhenius plot methods. The results showed a unique kinetic triplet confirming the nature of kerogen, predominantly type I and reinforcing the previously reported geochemical characteristics of the CK oil shale. Besides, the calculation of thermodynamic parameters (ΔH*, ΔS* and ΔG*) corresponding to the pyrolysis of type I kerogen revealed that the process is non-spontaneous, in agreement with DTA experiments.

Wen-Dong Wang, Yu-Liang Su, Qi Zhang et al.

Abstract The paper presents a novel hydraulic fracturing model for the characterization and simulation of the complex fracture network in shale gas reservoirs. We go beyond the existing method that uses planar or orthogonal conjugate fractures for representing the “complexity” of the network. Bifurcation of fractures is performed utilizing the Lindenmayer system based on fractal geometry to describe the fracture propagation pattern, density and network connectivity. Four controlling parameters are proposed to describe the details of complex fractures and stimulated reservoir volume (SRV). The results show that due to the multilevel feature of fractal fractures, the model could provide a simple method for contributing reservoir volume calibration. The primary- and second-stage fracture networks across the overall SRV are the main contributions to the production, while the induced fracture network just contributes another 20% in the late producing period. We also conduct simulation with respect to different refracturing cases and find that increasing the complexity of the fracture network provides better performance than only enhancing the fracture conductivity.

D. K. Richter, Th. G�tte, J. G�tze et al.

Fang Guo, Daoxian Yuan, Zhengjiao Qin

Approximately 33% of China is karstic. The most extensive karst areas are in southwestern China and cover approximate­ly 540,000 km2. Southwestern China hosts some of the most typical karst landforms in the world and has important high-quality karst water resources. Due to the rapid development of China, karst waters are threatened by various types of con­tamination. Detail field and laboratory investigations in five provinces including several cities in southwestern China were conducted in 2008 and 2009. Eighty-three springs and under­ground rivers were surveyed and water samples collected from eachfor laboratory analyses for major ions. Four main types of karst aquifer contamination were identified based on con­taminant sources: rural and agricultural pollution, pollution from urban development and industry, pollution from mining, and accidental groundwater pollution. Several representative instances for eachtype of contamination and their impacts on the environment are discussed in more detail. Contamination countermeasures of karst waters and a framework for overall management of karst water resources in southwestern China are provided.