Production of gas from coal seams in the Upper Silesian Coal Basin in Poland in the post-injection period of an ECBM pilot site

A pilot site for CO₂ storage in coal seams was set-up in the Upper Silesian Coal Basin in Poland in the scope of the RECOPOL project, funded by the European Commission. About 760 tons CO₂ were injected into the reservoir from August 2004 to June 2005. Breakthrough of the injected CO₂ was established, which resulted in the production of about 10% of the injected CO₂ in this period. This paper reports on activities performed under the European Commission project MOVECBM that aimed at the assessment of the storage performance of the reservoir in the follow-up period, i.e. whether the injected CO₂ was adsorbed onto the coal or whether it was still present as free gas in the pore space. The injection well was used for this purpose, as the production well had to be abandoned for permitting reasons. Several operational periods can be defined between the last injection in June 2005 and the abandonment of the well in October 2007. In the first period the well was shut-in to observe the pressure fall-off, from about 15.0 MPa at the wellhead after the last injection until about 4.5 MPa at the end of 2005. This pressure fall-off curve showed that the reservoir permeability was very low. This seemed to confirm the observed swelling of the coal during the injection period. In the first months of 2006 the pressure at the wellhead was decreased by releasing gas in a controlled way. The amount and composition of the gas were measured. As a result of the pressure reduction, the well flooded with water. A production pump was placed on the former injection well, enabling active production from the coal from March to September 2007. Results of these operations showed that whereas the gas production rates were as expected based on the experience with the production well, the water production was remarkably low. This could be related to permeability issues or, alternatively, indicate a drying effect of the CO₂ in the reservoir. Further, the gas composition showed a predominance of CO₂ over CH₄ during the gas release that changed gradually into a predominance of CH₄ over CO₂ during the production phase. Although stabilization was not reached within the given production period, the composition approached a 60% methane, 40% CO₂ ratio. This indicates that the exchange of these gases is more complex than often envisaged. After removal of the pump the well was filled with water, which ceased the gas release. This indicates that the pressure in the reservoir was back to its original, hydrostatic, state. As the total volume of CO₂ produced was only a fraction of the amount that was injected, it can be concluded that the CO₂ was taken up by the coal and is currently adsorbed. This gives confidence in the long-term stability of the injected CO₂.     

Long lasting interactions between tectonic loading, unroofing, post-rift thermal subsidence and sedimentary transfers along the western margin of the Gulf of Mexico: Some insights from integrated quantitative studies

After Jurassic rifting, numerous carbonate platforms (i.e., the Orizaba, Cordoba and Golden Lane-Tuxpan platforms) developed during the Lower and Middle Cretaceous episode of thermal subsidence along the western passive margin of the Gulf of Mexico, with intervening basinal domains (i.e., the Tampico-Misantla, Zongolica, Veracruz and Deep Gulf of Mexico - DGM - basins).During the Late Cretaceous-Paleocene, the east-verging Sierra Madre Oriental thrust belt developed, resulting in tectonic uplift and unroofing of the allochthonous units (i.e. tectonic units made up of former Orizaba and Cordoba platforms and Zongolica Basin series). This new topography provided also an important source of clastics to feed the adjacent foredeep, where coeval tectonic loading accounted for the bending of the foreland lithosphere. However, shallow water facies or even emersion persisted until the Eocene in the forebulge area (at the present location of the Golden Lane), preventing locally the clastics to reach the DGM. This topographic barrier was ultimately bypassed by the clastics only during the Oligocene and Neogene, once (1) the prograding clastic wedge had exceeded accommodation, and (2) the long lasting thermal subsidence of the passive margin could overpass the effect of the bending and force the former bulge to sink.Numerous paleo-thermo-meters (Tmax, Ro), paleo-thermo-barometers (fluid inclusions), PVT and coupled forward kinematic and thermal modeling have been used to calibrate and date the progressive unroofing of the thrust belt. Coupled tectonic and sedimentologic modeling was applied in the foreland to predict the distribution of sand versus shale ratios in the Oligocene to Plio-Quaternary clastic sedimentary wedge of the passive margin, where gravitational gliding of post-Eocene series occurred during the Neogene along major listric faults.Mantle dynamics are advocated as the main process accounting for post-orogenic uplift and regional tilting of the basement, which initiated a massive transfer of sediments from the Cordillera towards the Gulf of Mexico, from Oligocene onward, resulting in a destabilization and gravitational collapse of the western slope of the Gulf of Mexico in Neogene times.     

Deep structure, recent deformation and analog modeling of the Gulf of Cadiz accretionary wedge: Implications for the 1755 Lisbon earthquake

The Gulf of Cadiz spans the plate boundary between Africa and Eurasia west of the Betic-Rif mountain belt. A narrow east dipping subduction zone descends beneath the Gulf of Cadiz and the straits of Gibraltar. The deep crustal structure of the Gulf and the adjacent SW Iberian and Moroccan margins is constrained by numerous multi-channel seismic reflection and wide-angle seismic surveys. A compilation of these existing studies is presented in the form of depth to basement, sediment thickness, depth to Moho and crustal thickness maps. These structural maps image an E-W trending trough, with thin (< 10 km) crust beneath the Gulf of Cadiz. This trough is filled by an eastward thickening wedge of sediments, reaching a thickness of 10-15 km in the eastern Gulf. These sediments are tectonically deformed, primarily along a series of westward-vergent thrust faults and represent a 200-250 km wide accretionary wedge. The northern and especially the southern limits of the accretionary wedge are marked by sharp morphological lineaments showing evidence of recent deformation. These tectonic limits are situated in an internal position with respect to the Miocene deformation front (external Betic and Rif allocthons), which has been abandoned. At the western boundary of the accretionary wedge, near the adjacent Seine and Horseshoe abyssal plains, an E-W trending basement high (Coral Patch Ridge) can be seen indenting the deformation front in an asymmetric manner. Analog modeling is performed using granular materials accreted against a semicircular backstop (representing the basement of the Rif and Betic mountain belts). The modeling initially produces a symmetric, arcuate accretionary wedge. The ensuing collision of an oblique rigid indenter retards accretion on one side, resulting in an embayment and a locally steeper deformation front. The deformation pattern observed in morphology and high-resolution seismic profiles suggests the accretionary wedge and underlying subduction system is still active. The implications of active subduction for the source region of the 1755 Lisbon earthquake and the regional seismic hazard assessment are discussed.     

A New Basal Neoceratopsian Dinosaur from the Middle Cretaceous of Jilin Province,China

A new basal neoceratopsian dinosaur, Helioceratops brachygnathus gen. et sp. nov., is described from the Quantou Formation (late Early Cretaceous or early Late Cretaceous) in the Liufangzi locality (Jilin province, China). Helioceratops differs from other basal neoceratopsians with its deep dentary ramus, its steeply-inclined ventral predentary facet, its heterogeneous dentary crowns, and by the denticles and secondary ridges asymmetrically distributed on either side of the primary ridge on its dentary teeth. Along with Auroraceratops and Yamaceratops, Helioceratops represents one of the most derived non-coronosaurian neoceratopsians. The palaeogeographical distribution of basal neoceratopsians appears limited to northern China and southern Mongolia in the current state of our knowledge. It is therefore probable that this region constituted the birthplace for more advanced, Late Cretaceous Coronosauria.     

The Markoye Shear Zone in NE Burkina Faso

Birimian supracrustal sequences in NE Burkina Faso are dominated by meta-volcaniclastic greywacke, intercalated meta-conglomerate, siltstone and shale. The sequences where subjected to two phases of deformation and contact metamorphosed to hornblende–hornfels facies during emplacement of pyroxenite–gabbro–norite (Yacouba Mafic complex), granodiorite–tonalite (Tin Taradat granodiorite–tonalite) and dolerite dykes.Structural studies indicated that the NE-trending, first-order crustal-scale Markoye Shear Zone (MSZ; Markoye Fault of [Jeambrun, M., Delfour, J., Gravost, M., 1970. Carte géologique de L’Oudalan. Bureau De Recherches Geologiques et Miniéres, Burkina Faso.]) has undergone at least two phases of reactivation concomitant to two phases of regional deformation. The first phase of deformation, D1, resulted in the formation of NNW-NW trending folds and thrusts during dextral-reverse displacement on the MSZ. The deformation is termed the Tangaean Event and predates the Eburnean Orogeny. D2 phase involved a period of SE–NW crustal shortening and sinistral-reverse displacement on the MSZ, and is correlated to the Eburnean Orogeny 2.1 Ga. Deformation in D2 is characterised by NE-trending regional folds (F2) and a pervasive NE-trending foliation (S2-C to S2). Within the MSZ, deformation is characterised by NNE-trending zones of mylonite that are bordered in the hangingwall and footwall by pseudotachylite veins. Buck quartz-carbonate veins and quartz cataclasite veins crosscut the mylonite zones and are, in turn, crosscut by quartz–chlorite–(muscovite) shears that formed during reactivation of the MSZ late in D2. Several generations of veins are recognised at the Essakane main deposit (EMZ): Arsenopyrite–pyrite–gold mineralization in quartz veins formed in D1 during metasomatic alteration of the host rocks; Vein-stockwork gold mineralization is interpreted to have formed late in D2.     

A transmission electron microscopy (TEM) investigation of opaque phases in shocked chondrites

Abstract— Shock defects in the most common silicate minerals of chondrites (olivine, pyroxenes and feldspars) have been investigated in detail, but there have been almost no studies of the shock defects in other components, like metal and sulfide. This probably stems from the fact that these latter phases are opaque in the optical microscope. The same reason explains why veins and melt pockets, which are constituted of microcrystalline or glassy phases (i.e., isotropic) are also poorly documented. We have investigated such phases by analytical transmission electron microscopy (ATEM) in two shocked chondrites, Tenham (L6) and Gaines County (H5). We have characterized shock defects in troilite very similar to those occurring in silicates (i.e., a mosaic texture and sets of straight and very narrow, ?10 nm, lamellae of amorphized FeS). There are many small regions in shocked chondrites that are composed of very fine grained (?1 μm) mixtures of metal and sulfide or of various silicates. They must result from local melting followed by a rapid cooling that prevented grain growth. We have determined the chemical compositions and the volume proportions of the tiny grains in these veins and melt pockets, which has allowed their temperature and pressure (T, P) history to be partially deciphered. Finally, we have observed a dense network of very narrow fractures (down to 10 nm) in the olivine and enstatite grains. These fractures are systematically filled with an amorphous (or cryptocrystalline) material that stems from the melt pockets and was injected when the fractures were opened by the rarefaction wave. This material was then quenched at the contact with the colder crystalline rims.     

Magnetic mapping of the western Alps: compilation and geological implications

Extracted from large surveys of France, Italy and Switzerland, airborne magnetic data covering the western Alpine Arc have been compiled into a single homogeneous map of magnetic anomalies at the constant altitude of 3000 m. For this purpose, each data set has been revised thoroughly and accurately to give a single coherent large-scale pattern.

The magnetic contour map reflects the anomaly pattern over the entire length of the Western Alpine collision suture. The distribution of polarities exhibits a large anomalous low located by reduction to the pole over the whole external part of the belt. The observed anomaly suggests a large gap of magnetization between the Adriatic microplate and the European crust. The analysis of the waveband shows that the broadest wavelengths are produced in the lower crust close to the transition zone, in the granulite facies. This highly magnetic layer is used as a marker to describe the geometry of the European and Adriatic deep seated crust. The main results are presented on a composite synthetic profile showing the sloping side of the European slab and an important crustal thinning to the southeast of the Adriatic slab. This feature is emphasized on the magnetic contour map by a linear magnetic low attributed to major transcurrent fault. This trend is called the Sestri-Voghera trend and extends from the Ligurian basin by the Sestri-Voltaggio Zone to the Judicarian system. Sinistral movements can be recognized along the whole axis as well as possible uplift of rift shoulders. The magnetic anomaly pattern over the complete length of the anomalous body of Ivrea as well as the Insubric-Canavese Line limit the extension of the Adriatic microplate by a well defined linear trend. The symmetrical shears deduced from consecutive anomalies are used to propose a structural scheme.