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We present U-Th/Pb data obtained for xenotime and monazite from the polycyclic eclogite-facies para- and ortho-gneisses of the Les Essarts Unit (Vendée, southern Armorican Massif, France), which have recorded an HT-LP cycle ending with a first retrogression and a subsequent HP eclogite-facies metamorphism similar to that of the neighbouring eclogites. Some paragneisses and orthogneisses are only slightly deformed and retrogressed, showing the structure of nebulitic migmatite or metagranite, respectively; both show well-preserved complex coronitic and pseudomorphic microstructures, due to the eclogite-facies metamorphism. Monazite I and xenotime crystallised during the HT stage providing an opportunity to date the early HT metamorphic event in the paragneiss and the emplacement of granite in the orthogneiss. U/Pb ages obtained from monazite I and xenotime of the cordierite-bearing migmatitic paragneisses range between 510 and 480 Ma (Late Cambrian-Early Ordovician). These ages may correspond to the crystallisation and/or re-equilibration of monazite and xenotime during the prograde stage of the HT cycle, close to the T peak. Consistent monazite and xenotime U/Pb ages around 496 Ma in the orthogneiss represent the age of the granite protolith. During subsequent HP overprint in the gneisses, numerous coronas developed at the expense of the early HT parageneses, in particular plagioclase. In both paragneiss and orthogneiss, monazite I in contact with HT plagioclase reacted to form apatite + zoisite + monazite II coronas. The small monazite II crystals could be dated in a paragneiss sample and gave a lower intercept age of 395 ± 9 Ma, interpreted as the age of the eclogite-facies HP metamorphism. This age is in agreement with those obtained in HP metamorphic rocks of the Upper Allochthon Unit of the Iberian-Armorican Arc (Bragança, Cabo-Ortegal, Audierne) representing the first evidence of convergence in the Variscan cycle.

It is well-acknowledged that the northern margin of the Gondwana supercontinent was affected by a major magmatic event at late Cambrian (Furongian) to early Ordovician (Tremadocian–Floian) times. However, an accurate assessment of its extent, origin, and significance is partly hampered by the incomplete characterization of the numerous gneiss massifs exposed in the inner part of the Variscan belt, as some of them possibly represent dismembered and deformed Furongian–Lower Ordovician igneous bodies. In this study, we document the case of the “Cézarenque–Joyeuse” gneiss complex in the Cévennes parautochthon domain of the French Massif Central. The gneisses form decametre- to kilometre-thick concordant massifs interlayered within a pluri-kilometric sequence of mica- and quartz schists. They encompass two main petrological types: augen gneisses and albite gneisses, both typified by their blue and engulfed quartz grains with the augen facies differing by the presence of centimetre-sized pseudomorphs after K-feldspar and the local preservation of igneous textures. Whole-rock geochemistry highlights that many gneisses have magmatic ferrosilicic (acidic with anomalously high FeOt and low CaO) compositions while others are akin to greywackes. Collectively, it is inferred that the bulk of the Cézarenque–Joyeuse gneisses represents former rhyodacite lava flows or ignimbrites and associated epiclastic tuffs. Volumetrically subordinate, finer grained, and strongly silicic leucogneisses are interpreted as microgranite dykes originally intrusive within the volcanic edifices. LA–ICP–MS U–Pb dating of magmatic zircon grains extracted from an augen gneiss and a leucogneiss brackets the crystallization age of the silicic magmas between 486.1 ± 5.5 Ma and 483.0 ± 5.5 Ma which unambiguously ties the Cézarenque–Joyeuse gneisses to the Furongian–Lower Ordovician volcanic belt of SW Europe. Inherited zircon date distributions, Ti-in-zircon and zircon saturation thermometry demonstrate that they formed by melting at 750–820 °C of Ediacaran sediments. Zircon Eu/Eu* and Ce/Ce* systematics indicate that the melts were strongly reduced (fO2 probably close to the values expected for the iron–wüstite buffer), possibly because they interacted during ascent with Lower Cambrian black shales. This would have enhanced Fe solubility in the melt phase and may explain the peculiar ferrosilicic signature displayed by many Furongian–Lower Ordovician igneous rocks in the northern Gondwana realm. We infer that crustal melting resulted from a combination of mantle-derived magma underplating in an intracontinental rift setting and anomalously elevated radiogenic heat production within the Ediacaran sedimentary sequences.

In order to clarify the sedimentary development law under the Cambrian Ordovician regional stratigraphic framework in Tadong area, and lay a theoretical foundation for further oil and gas exploration in the study area. The distribution, characteristics and evolution of main sedimentary facies belts of Cambrian Ordovician are studied by means of drilling core observation, cast thin section identification, logging curve feature analysis, seismic profile and well connection profile. The results show that the Cambrian middle lower Ordovician in Tadong area is equivalent to a second-order sequence and can be further divided into 12 thirdorder sequences. Each third-order sequence is mainly composed of transgressive and highstand tracts. Carbonate platform margin beach facies and Reef (mound) beach complex facies are favorable reservoir development facies belts in this area; Under the regional stratigraphic framework, three types of sedimentary facies can be identified in Cambrian Ordovician, and a total of 10 subfacies are developed; The evolution of sedimentary facies is mainly controlled by the rise and fall of sea level, which is characterized by the migration of platform margin facies and the change of platform facies.

The thermal reservoir in Taiyun area mainly consists of Ordovician and Cambrian carbonate formations. The target interval of example well contains more than 95% carbonate, being thick, argilliferous and have well-developed natural fissures and rich hot water. However, sometimes stimulation is necessary to achieve the designed water production rate. In this paper, multistage alternating injection acid fracturing technology is selected according to lithologic characteristics of geothermal reservoir. A gel acid, which is a composite of 20%HCl+0.8%SHY1+2% corrosion inhibitor+1.5% iron ion stabilizer+1% cleanup additive, is optimized and developed by experimental tests. Its viscosity can reach 27 mPa·s. Then, pumping schedule of multi-stage alternate injection acid fracturing is optimized by numerical simulator of acid fracturing design. It is shown from job pressure of field sample well that resistance reduction ability of gel acid needs to be further improved. Moreover, from the analysis results of pressure decline after acid fracturing, the fluid efficiency is 42.32%, net pressure is 3.3 MPa, and the dynamic fracture length is 107m, the maximum fracture width is 8.6mm by fitting treatment pressure. The water production increase factor reaches 1.2 after acid fracturing treatment. Therefore, the acid fracturing treatment is successful.

The transition from the Cambrian to Ordovician in Morocco is known to be characterized by a frequent Furongian hiatus, restricted extension of the Tremadocian marine deposits, and frequent unconformities at the base of the transgressive upper Floian deposits. In the present work, we first highlight the occurrence of Fe- and mica-rich, red silty/sandy formations in the Central and Eastern High Atlas between the Middle Cambrian and Upper Floian sequences. In the Tislyt type-locality, a synsedimentary hemigraben structure is defined, within which the red beds show frequent slump folds, debris flows and internal unconformities. The correlation with several coeval series of the Meseta domain allows us to define a shallow marine, ferruginous clastic Atlas-Meseta Red Beds (AMRB) basin during the Tremadocian-early Floian. The AMRB basin extended between the Meseta coastal block and the Anti-Atlas domain, being limited by the fault zones that became the West Meseta shear zone and the South Meseta fault, respectively, in the Variscan orogen. The AMRB basin compares with the coeval rifted basins of the central Iberian and Armorican massifs. The red beds were likely sourced from the east, from both the Precambrian basement and Early Ordovician magmatic rocks, contrary to the Ordovician deposits of the Sahara platform sourced from the south. Subsidence of the AMRB and central Iberian-Armorican basins of the NW-Gondwana border aborted during the Floian, whereas the opening of the Rheic ocean went on more to the west.

The basin of Maider is limited northly by the vast ensemble Oriental Saghro-Ougnate, from the east by the Tafilalet plain, from the west by the oriental Jbel Bani, finally from the south and south-east by the Cretaceous Hamada of Kern-Kem. During last decades, groundwater in the basin of Maider, is confronting degradation in both cases: Quantitative and qualitative, as a result of the drought, the overexploitation and the salinization. The aim of this action research is to understand the current state of water resources in the area of stady. At the end of this work, we can get the following conclusions: the general flow of the ordovician aquifer is always directed from the north to the south-east of the basin by following the principal axes of the wadis:Taghbalt, Hssiya and Fezzou. The recharge of the aquifer is primarily done, either by the underground flow, or by the surface runoff of torrential waters from the upstream of Jbel Saghro. The piezometric anomaly noticed at the level of Ait Saàdane, explained by overexploitation linked to the needs of irrigation water. The physicochemical approach for the Maider basin identifies two essential factors of the salinisation of groundwater: the dissolution of the aquifer which is rich in minerals with high temperature on the one hand, and the decrease of the piezometric surface due to the overexploitation and drought on the other hand.

The Gucheng region is oil and gas accumulation area of Tarim Basin，dominated by beach controlled lithologic oil and gas reservoirs，which has superior oil and gas accumulation conditions and broad exploration prospects. The lower Paleozoic strata in the Gucheng region are the Carboniferous, Ordovician, and Cambrian systems from top to bottom. The Silurian, Devonian, and Permian systems are missing. The lower Ordovician – Cambrian are the main exploration target layers in the area. There are four reservoirs: the Ordovician group, the Yingshan group, the Penglaiba group and the Cambrian group in The Gucheng region, The upper part of the Yijianfang formation and Yingshan formation are limestone reservoir, which is a set of potential reservoir. The lower part of the Yingshan formation, the Penglaiba formation, and the Cambrian formation developed three sets of dolomite reservoirs. The distribution of oil and gas in Gucheng region was mainly found in Yijianfang formation, Yingshan formation, Penglaiba formation and Cambrian of the Ordovician. The Yingshan group and the Hanwu group were the main exploration target layers. Yingshan formation and Cambrian are the main exploration targets, and Yijianfang formation and Penglaiba formation of Ordovician can be used as the concurrent exploration targets. Gucheng region can form two major realistic exploration areas: dolomite reservoir of Ordovician and reef beach of Cambrian. The Ordovician dolomite reservoirs are mainly searched for the inner shoal of the platform edge high-energy facies belt, and the Cambrian system is mainly search for the high-energy reef beach far away from the platform edge facies belt in the north of cherchen fault.

Taking the Late Ordovician Wufeng Formation (WFF) shale in the Upper Yangtze region as an example, we conducted a lithofacies distribution, thickness quantification, and paleo-topographic reconstruction of the Late Ordovician graptolite zones. Specifically, we focused on the Late Katian Dicellograptus complexus and the Early Hirnantian Metabolograptus extraordinarius within a chronostratigraphic framework, using the Geographic Information System (GIS) and 310 stratigraphic sections (incl. drilling) obtained from the Geobiodiversity Database (GBDB). Reconstruction of the geographic distribution indicates that the WFF and the synchronous sediments in the Upper Yangtze region contain 8 litho-stratigraphic units, which are geographically distributed across 7 provinces/municipalities and do not exhibit significant variations in lithofacies. The black graptolite shale extends in a broad swath from east to west within the basin, while the other lithofacies deposited during the same period are present on the periphery of the basin. All these strata were deposited in a normal neritic epicontinental sea environment, except for the flysch sediments in the southern Hunan area. The thickness reconstruction involves a comparison of three spatial interpolation methods, including Inverse Distance Weighting (IDW), Kriging, and the Radial Basis Function (RBF). Based on a general verification, IDW is considered to be the optimal method since it has the minimum standard deviation and variance. Based on the contours obtained from the IDW model, the WFF black shale is estimated to have an overall area of 0.67 × 106 km2, an average thickness of 6.2 m, and a total volume of 3902 km3. This shale was deposited over a 2.83 Ma period. Therefore, the volume of shale deposited per million years is estimated to be 1379 km3/my and the average thickness of shale deposited per million years is 2.37 m/my. The Hirnantian paleo-water-depth values obtained using 275 sections were used to infer the Late Katian paleo-topography. These results suggest that the Yangtze platform was surrounded by ancient highlands to the west, south, and north, exhibiting a paleo-geographic framework characterized by one uplift and four depressions. This setting blocked water circulation, causing the water to be contained and forming a closed and restricted marine environment, which was one of the major factors controlling the deposition of the organic-rich WFF shale. With the advent of the big data era of geology, the methodology of GIS-based technology is readily exportable to any resource play having spatial distribution pattern. Results can be provided rapidly and efficiently generated from geological data.

The identification of oceanic sutures is key to understanding the evolution of the Paleozoic Variscan belt and the structure of the West European lithosphere. In the French Massif Central, the suture of the ‘Mid-Variscan’ ocean would be stamped by distinctive lithological formations known as ’Leptynite–Amphibolite Complexes’ (LACs). These formations comprise various Cambrian–Ordovician (meta-)igneous associations, commonly interpreted as representing rifted-margin magmatism, and experienced Devonian (385–360 Ma) high-pressure metamorphism. Our study provides geochronological and geochemical data on mafic–felsic rocks from the Riverie LAC in the Monts-du-Lyonnais metamorphic complex. In the Riverie LAC, metaluminous, amphibole-bearing felsic gneisses represent former tonalites closely associated with mafic rocks (now amphibolites). LA–ICP–MS zircon U–Pb dating reveals a latest Ediacaran (c. 545 Ma) crystallization age for the melt that yielded the tonalites. Whole-rock geochemistry (notably pronounced Nb negative anomalies) and the highly radiogenic zircon Hf isotope compositions, with εHf(545Ma) of c. +11 (within the range expected for the Depleted Mantle reservoir), indicate that the parental melt of the tonalites ultimately originated from a mantle source metasomatized by oceanic slab-derived fluids. The (meta-)mafic rocks share a similar ’arc’ signature and were possibly generated from the same mantle source. The mafic–felsic association of the Riverie LAC is unrelated to the opening and closure of the Mid-Variscan ocean and does not represent its suture. Instead, it can be correlated to a juvenile Ediacaran magmatic event identified throughout the Variscan realm, interpreted as reflecting Cadomian arc/back-arc magmatism.

In order to address one of the most serious environmental concerns of our day, reducing carbon footprints, the globe has turned its attention to carbon dioxide (CO2) storage as a potential solution. Because of its unique features, shale is one of the most intriguing options in this area. Adsorption is the method through which CO2 is stored in shale, particularly in its supercritical condition. Adsorption isotherm models can be used to deduce the behaviour and mechanisms of this adsorption. Langmuir, Freundlich, Dubinin-Astakhov (D-A), and Brunauer-Emmett-Teller (BET) models are among the many available for CO2 modelling on shale. We attempted to fit these models to experimental data gathered from literature sources in this study, concentrating on four separate shale samples from various places in China. Among these samples are LMX1 and LMX2 from the Silurian Longmaxi Formation, WF1 from the Ordovician Wufeng Formation in the Sichuan Basin, and YC from the Ordos Basin's Yanchang Formation. The total organic carbon (TOC) content of these shales, three marine and one continental, ranged from 3.19 to 4.27. The experimental data used to fit the model was obtained at three different temperatures: 35, 45, and 55°C. The Langmuir and D-A models offered the best fit for the data across all samples and temperature. R2 values 0.93429 (for YC rock at 35°C) to 0.99287 (for WF1 at 35°C) for Langmuir and 0.88879 to 0.99201 LMX1 at 35°C. The theoretical underpinnings of these models, which account for the physical properties and adsorption dynamics of supercritical CO2 on shale, are responsible for their performance. Finally, this study adds to our understanding of CO2 adsorption on shale, giving useful insights for future research and potential practical uses in CO2 storage. More research is needed, however, to completely understand the mechanisms and influencing factors of CO2 adsorption in various types of shale, as well as to develop the models used to forecast this behaviour.

We present new constraints on the age, nature, and tectonic setting of mafic eclogite protoliths from the Maures-Tanneron Massif, southern Variscan belt. Whole-rock major and trace element geochemistry was combined with zircon dating using 206Pb/238U by LA‒ICP‒MS to improve the understanding of this key-target of the European Southern Variscides. Geochemical data show that protoliths of the mafic eclogites are typical MORBs, while REE and HFSE patterns suggest an E-MORB affinity. However, the geochemical study shows several signs of crustal contamination that increases with the degree of retrogression. A comparison with Sardinian eclogites, which belong to the same Variscan microplate, namely, “MECS” (Maures-Estérel-Corsica-Sardinia), demonstrates that the eclogites are included in migmatites, which is the case for the studied samples, are the most contaminated. The Maures-Tanneron mafic eclogites represent the remnant of an oceanic basaltic crust. Zircon cores display homogeneous Th/U ratios (0.3–0.4), which are consistent with a magmatic origin, and define an age peak at 499.5 ± 2.9 Ma that is interpreted as the most likely emplacement age of the basaltic protolith. This age suggests that this protolith was part of an oceanic floor that was older than the Rheic Ocean and located to the north of the Gondwana active continental margin as predicted by recent unified full plate reconstruction models. Although the studied eclogites are retrogressed, the study of mineral inclusions trapped in garnets combined with thermodynamic modelling yields a P−T range of 17.2–18.5 kbar and 640–660 °C, which is consistent with the standard oceanic subduction palaeo-geotherm. These new data suggest that eclogites recognized in the “MECS” Variscan microplate represent the closure of oceanic domains of different ages (Cambrian or Ordovician).

On suggère, comme une voie de recherche et de corrélations, que des réactions cycliques entre le volcanisme producteur de CO2 et les végétaux productifs d'oxygène contrôlent certains aspects de l'évolution et de la sédimentation, en particulier en ce qui concerne les composés du fer et la matière organique. Sous l'atmosphère anoxique archéenne et lors d'une évolution initiale très lente, les cycles étaient limités à la mer, avec des interrelations entre le fer ferreux et les bactéries oxydantes (Berckner et Marshall, Cloud). Le développement des algues bleues a augmenté la teneur en oxygène. Les Métazoaires apparurent mais sans coquilles (faune d'Ediacara) ce qui indique que la teneur en CO2 est restée élevée jusqu'au Cambrien inférieur, quand les coquilles apparurent. Les flores peu diversifiées impliquent d'amples cycles entre le Pré-Cambrien terminal et le Jurassique supérieur. La diminution en CO2 (Cambrien, Dévonien, Permien) favorisa le développement animal, spécialement celui des Vertébrés, ainsi que le dépôt de couches rouges, de calcaires, d'évaporites (faible nébulosité et climats contrastés) ; la recharge en CO2, liée aux activités volcaniques et orogéniques (Ordovicien, Dinantien, Trias supérieur) a stimulé la vie végétale, augmenté la nébulosité, réduit les contrastes climatiques mais les précipitations développent les calottes glaciaires aux pôles. les conditions réductrices facilement réalisées permettent l'accumulation de matière organique (Silurien, Pennsylvanien, Lias). Les dépôts ferrugineux marins apparaissent aux périodes de transition : Ordovicien inférieur, Dévonien inférieur et Lias supérieur. A partir du Jurassique supérieur, la complexité croissante des flores réduit l'amplitude des cycles atmosphériques, mais les tendances vers les couches rouges, les évaporites et les dépôts riches en matières organiques alternent cependant dans certaines mesures. It is proposed, as a line for research and correlations, that cyclic reactions between C02 producing volcanism and 02 producing plants govern some aspects of evolution and sedimentation, in particular that of iron and organic matter coumpounds. Under Archean anoxic atmosphere and slow initial evolution, cycles were limited to the sea, with feed-back oscillations between ferrous iron and oxydising bacteria (Berckner and Marshall, Cloud). Development of blue Algue increased the O content. Insoluble ferric oxydes were retained on the continents (first Red Beds). Metazoa appeared, but being shelless (Ediacara fauna), they indicate that C02 content remained high until Lower Cambrian, when shells appeared. Poorly diversified floras induce ample cycles between Upper Precambrian and Upper Jurassic. Depletion of CO2 (Cambrian, Devonian, Permian) favours animals especially Vertebrates development, deposition of Red Beds, limestones, evaporites (nebulosity low, climatic contrasts) ; recharge of CO2 through volcanic-orogenic-activity (Ordovician, Dinantian, Upper Trias) stimulates plant life, increases nebulosity, reduces climatic contrasts but precipitations develop polar ice caps. Easily achieved reducing conditions enable the accumulation of organic matter (Silurian, Pennsylvanian, Lias). Marine iron deposits occur at transition periods: Lower Ordovician, Lower Devonian, Upper Lias. From Upper Jurassic onwards, increasing complexity of floras reduce the amplitude of atmospheric cycles, but tendancies towards Red Beds, evaporites or organic matter deposits still alternate to some extent.

The ordovician limestone water inrush accident occurred during the excavation of 8228 working face in Tashan Coal Mine, Tongmei Group. On the basis of comprehensive geophysical exploration above and below the well, in order to find out the development boundary of the water flowing subsided column and the distribution characteristics of the broken body filled in it, and to control the subsided column by Grouting, the development boundary, the influence zone, the cementation of the fractured body and the distribution characteristics of the water flowing subsided column are found out by means of multi-layer and multi-branch surface directional horizontal drilling speed logging, drilling fluid leakage, cuttings logging and logging while drilling, and combined with data statistical analysis. The length and short axis of the collapse column is 410m - 200m, and the broken area is mainly distributed in the right front of the driving head of the belt roadway near the water inrush roadway. The 3d geological modeling of the spatial structure and development characteristics of the collapse column is carried out by using SURPAC software, and the main passageway area, fracture area and secondary fracture area are divided according to the crushing degree of the collapse column filling material. In view of the different zones of the collapse column broken body, the directional horizontal drilling control technology and the three-dimensional block grouting technology are used to construct the separate zones of the grouting technology. The safe mining of the working face is finally realized by the comprehensive treatment of cutting the source and reinforcing the water-flowing collapse column. The comprehensive exploration and treatment technology of directional horizontal drilling multi-branch collapse column provides a good reference for other similar projects.

In recent years, shale gas in the Upper Ordovician Wufeng Formation and lower Silurian Longmaxi Formation is gradually developing into deep strata in Sichuan Basin. Well 202-H1 is a evaluation well deployed to evaluate the productivity of horizontal Wells in longmaxi Formation and Wufeng Formation in The West Chongqing block. The well type is horizontal well. The main reasons for the poor production effect of Well Z202-H1 are as follows: Reservoir pores are not developed; continuous thickness of thin reservoir; insufficient fracturing treatment; low flowback rate, large water production and wellbore fluid accumulation. This article not only obtained the reasons for the difference between the test and production of well Z202-H1, but also provided a new research idea for the test and production tracking analysis of deep shale gas static in The Western Chongqing block.

Une nouvelle méthode de préparation des matières organiques dispersées, destinées à être étudiées au microscope, est décrite et proposée. Le montage de la matière organique est fait par des lames de verre. Il permet de faire tous les types d'observations microscopiques (lumière transmise, réfléchie ou fluorescente) sur une même préparation. Ses avantages sur la méthode classique d'imprégnation sur des briquettes sont illustrés par un exemple dans la séquence ordovicienne et siluro-dévonienne de l'île d'Anticosti et de l'est des Appalaches québécoises au Canada. This paper presents a new method to be used in the preparation of dispersed organic matter for microscopic studies. The organic matter is spread on a glass slide in order to permit all types of microscopic observation (transmitted, reflected or fluorescent light) on a single mount. An example of its application, taken from the Ordovician and Siluro-Devonian sequence of Anticosti Island and Eastern Appalachians of Quebec, shows the advantages of this new method over the traditional plugmethod.

Le Gisement de Rhourde el Baguel produit de l'huile à partir d'un réservoir gréseux du Cambro-Ordovicien aux qualités matricielles médiocres. La fracturation naturelle joue un rôle important sur la productivité. L'intensité de la fracturation paraît liée davantage aux paramètres lithologiques qu'à des variations d'épaisseur des bancs. Les directions des fractures relevées sur les carottes orientées d'un sondage ne sont pas en accord avec la direction des grandes failles proposée jusqu'ici. Les fractures et les blocs délimités par celles-ci sont présentés sous trois formes : un bloc diagramme simplifié qui montre la complexité du réseau et la faible représentativité d'un sondage à l'échelle du gisement; des blocs matriciels en trois dimensions à partir de l'utilisation d'un logiciel préexistant; une hauteur moyenne de bloc matriciel calculée à partir de l'application d'un modèle probabiliste. The Rhourde el Baguel field in Algeria is made up of a thick series of Cambro-Ordovician sandstone. This highly fractured formation can be subdivided into four terms: R3, R2, Ra and Ri (Fig. 2). Its structure has been interpreted as a horst bounded by two major faults trending NNE-SSW. The western fault has been traversed by well Rb 18, from which the 45° tilted sandstone core samples have been the subject of a special analysis. Different methods were used to evaluate the fracturing. The first consisted in linking the thickness of the beds with the intensity of fracturing (Aguilera method). This method was applied to 700 meters of core samples coming from four wells. Generally, it was found that the thicker a bed was, the more it was fractured, which runs counter to the commonly accepted theory. This finding might be linked to the lithology (the thinner the beds are, the larger the argillaceous matrix content is, and the thicker the argillaceous interbeddings are). Another methodology, based on an analysis of fracturing and the use of probabilistic models linked to the Poisson process, was implemented for well Rb 18, for which dipmeter measurements were available. Fracture directions (Fig. 9) are mainly E-W, which was not expected from the structural pattern accepted previously (Fig. 3). From measurements made in this well, three types of fracture network plots were made :(a) A three-dimensional plot in the form of a block diagram (cf. 2D illustration in Fig. 10). (b) A three-dimensional plot using a software (I-DEAS) (Fig. 11) enabling the blocks to be isolated easily. (c) A plot making use of a Poisson probabilistic model. The last two plots were used to evaluate a mean block thickness of about 45 cm. To conclude, this study illustrates a methodology for analyzing fracturing by using core samples, with these core samples having first been oriented. Since the tilting of the beds could be dated, a relative chronology could be determined for the activity and reworking of the fractures. Different approaches were also used to define the geometry of the matrix blocks having a mean thickness of 45 cm and to reveal the role of lithological parameters in the distribution and intensity of fracturing.

The main goal of the study was to enhance and improve information about the Ordovician and Silurian gas-saturated shale formations. Author focused on: firstly, identification of the shale gas formations, especially the sweet spots horizons, secondly, classification and thirdly, the accurate characterization of divisional intervals. Data set comprised of standard well logs from the selected well. Shale formations are represented mainly by claystones, siltstones, and mudstones. The formations are also partially rich in organic matter. During the calculations, information about lithology of stratigraphy weren’t taken into account. In the analysis, selforganizing neural network – Kohonen Algorithm (ANN) was used for sweet spots identification. Different networks and different software were tested and the best network was used for application and interpretation. As a results of Kohonen networks, groups corresponding to the gas-bearing intervals were found. The analysis showed diversification between gas-bearing formations and surrounding beds. It is also shown that internal diversification in sweet spots is present. Kohonen algorithm was also used for geological interpretation of well log data and electrofacies prediction. Reliable characteristic into groups shows that Ja Mb and Sa Fm which are usually treated as potential sweet spots only partially have good reservoir conditions. It is concluded that ANN appears to be useful and quick tool for preliminary classification of members and sweet spots identification.

More than 70 rock samples from so-called sweet spots, i.e. the Ordovician Sa Formation and Silurian Ja Member of Pa Formation from the Baltic Basin (North Poland) were examined in the laboratory to determine bulk and grain density, total and effective/dynamic porosity, absolute permeability, pore diameters size, total surface area, and natural radioactivity. Results of the pyrolysis, i.e., TOC (Total Organic Carbon) together with S1 and S2 – parameters used to determine the hydrocarbon generation potential of rocks, were also considered. Elemental composition from chemical analyses and mineral composition from XRD measurements were also included. SCAL analysis, NMR experiments, Pressure Decay Permeability measurements together with water immersion porosimetry and adsorption/ desorption of nitrogen vapors method were carried out along with the comprehensive interpretation of the outcomes. Simple and multiple linear statistical regressions were used to recognize mutual relationships between parameters. Observed correlations and in some cases big dispersion of data and discrepancies in the property values obtained from different methods were the basis for building shale gas rock model for well logging interpretation. The model was verified by the result of the Monte Carlo modelling of spectral neutron-gamma log response in comparison with GEM log results.