evaluation of the potential for gas leakage along wellbores in the st lawrence lowlands basin quebec canada wellbore attributes i e deviation casings and plugging characteristics for 85 wells in the st lawrence lowlands basin of southern quebec were compiled from drilling reports and abandonment programs to provide an overview of the abandoned well characteristics and to establish a diagnosis on the long term reliability of the completion and abandonment practices carried out by the companies since the beginning of oil and gas exploration using these data the conventional and unconventional wells were divided into four categories 1 conventional wells drilled before 1950 2 conventional wells drilled between 1950 and 1970 3 conventional wells drilled after 1970 and shale gas wells all drilled after 2000 very little information was available for wells drilled before 1950 more information was available for the wells drilled from 1950 to 1970 which is considered a transition period between old and modern technology conventional and unconventional wells drilled after 1970 were generally well documented and their attributes corresponded to api standards a decision tree inspired from the methodology proposed by watson and bachu spe drill complet 24 1 115 126 2009 https doi org 10 2118 106817 pa was then created to assess the potential of leakage of each of the conventional and unconventional wells using the compiled attributes the factors defining the probability of well leakage were wellbore deviation height of cement in casing annuli partially or fully cemented type of abandonment plugs cement or mechanical plugs and drilling date before or after 1970 among the 85 wells assessed by this tree the probability of leakage was higher than 50 for 55 wells 65 of wells wellbore deviation and lack of information on the construction and abandonment methods were respectively the primary and secondary causes of high probability of leakage of these wells

numerical investigation of methane and formation fluid leakage along the casing of a decommissioned shale gas well methane and brine leakage rates and associated time scales along the cemented casing of a hypothetical decommissioned shale gas well have been assessed with a multiphase flow and multicomponent numerical model the conceptual model used for the simulations assumes that the target shale formation is 200 m thick overlain by a 750 m thick caprock which is in turn overlain by a 50 m thick surficial sand aquifer the 1000 m geological sequence being intersected by a fully penetrating borehole this succession of geological units is representative of the region targeted for shale gas exploration in the st lawrence lowlands quebec canada the simulations aimed at assessing the impact of well casing cementation quality on methane and brine leakage at the base of a surficial aquifer the leakage of fluids can subsequently lead to the contamination of groundwater resources and or in the case of methane migration to ground surface to an increase in greenhouse gas emissions the minimum reported surface casing vent flow measured at ground level for shale gas wells in quebec 0 01 m3 d is used as a reference to evaluate the impact of well casing cementation quality on methane and brine migration the simulations suggest that an adequately cemented borehole with a casing annulus permeability kc 1 md can prevent methane and brine leakage over a time scale of up to 100 years however a poorly cemented borehole kc 10 md could yield methane leakage rates at the base of an aquifer ranging from 0 04 m3 d to more than 100 m3 d depending on the permeability of the target shale gas formation after abandonment and on the quantity of mobile gas in the formation these values are compatible with surface casing vent flows reported for shale gas wells in the st lawrence lowlands quebec canada the simulated travel time of methane from the target shale formation to the surficial aquifer is between a few months and 30 years depending on cementation quality and hydrodynamic properties of the casing annulus simulated long term brine leakage rates after 100 years for poorly cemented boreholes are on the order of 10 5 m3 d 10 ml d to 10 3 m3 d 1 l d based on scoping calculations with a well mixed aquifer model these rates are unlikely to have a major impact on groundwater quality in a confined aquifer since they would only increase the chloride concentration in a pristine aquifer to 1 mg l which is significantly below the commonly recommended aesthetic objective of 250 mg l for chloride

geochemical evidence for possible natural migration of marcellus formation brine to shallow aquifers in pennsylvania the debate surrounding the safety of shale gas development in the appalachian basin has generated increased awareness of drinking water quality in rural communities concerns include the potential for migration of stray gas metal rich formation brines and hydraulic fracturing and or flowback fluids to drinking water aquifers a critical question common to these environmental risks is the hydraulic connectivity between the shale gas formations and the overlying shallow drinking water aquifers we present geochemical evidence from northeastern pennsylvania showing that pathways unrelated to recent drilling activities exist in some locations between deep underlying formations and shallow drinking water aquifers integration of chemical data br cl na ba sr and li and isotopic ratios 87sr 86sr 2h h 18o 16o and 228ra 226ra from this and previous studies in 426 shallow groundwater samples and 83 northern appalachian brine samples suggest that mixing relationships between shallow ground water and a deep formation brine causes groundwater salinization in some locations the strong geochemical fingerprint in the salinized cl 20 mg l groundwater sampled from the alluvium catskill and lock haven aquifers suggests possible migration of marcellus brine through naturally occurring pathways the occurrences of saline water do not correlate with the location of shale gas wells and are consistent with reported data before rapid shale gas development in the region however the presence of these fluids suggests conductive pathways and specific geostructural and or hydrodynamic regimes in northeastern pennsylvania that are at increased risk for contamination of shallow drinking water resources particularly by fugitive gases because of natural hydraulic connections to deeper formations

the utica shale and gas play in southern quebec geological and hydrogeological syntheses and methodological approaches to groundwater risk evaluation abstract the risk of groundwater contamination from shale gas exploration and development is a major societal concern especially in populated areas where groundwater is an essential source of drinking water and for agricultural or industrial use since groundwater decontamination is difficult or nearly impossible it is essential to evaluate exploration and production conditions that would prevent or at least minimize risks of groundwater contamination the current consensus in recent literature is that these risks are primarily related to engineering issues including casing integrity and surface activities such as truck traffic equipment and fluid haulage waste management mainly drill cuttings and water storage and treatment when hydraulic fracturing is utilized concerns have also been raised with respect to groundwater contamination that could result from potential fracture or fault interconnections between the shale unit and surficial aquifers which would allow fracturing fluids and methane to reach the surface away from the wellbore despite the fact that groundwater resources are relatively well characterized in some regions there is currently no recognized method to evaluate the vulnerability or risks to aquifers resulting from hydrocarbon industry operations carried out at great depths this paper focuses on the utica shale of the st lawrence platform quebec where an environmental study aiming to evaluate potential risks for aquifers related to shale gas development has been initiated to provide the context of these research efforts this paper describes the regional tectono stratigraphic evolution and current stress regime of the cambrian ordovician st lawrence platform as well as the utica shale internal stratigraphy mineralogy and thermal maturation then the hydrogeological context of the st lawrence platform is discussed finally the methodology for this environmental study based on geological geophysical geomechanical hydrogeological and geochemical data is presented

deep water facies processes and models a review and classification scheme for modern and ancient sediments abstract a review of previous work on modern and ancient deep water facies processes and models is presented with a new classification scheme involving 40 distinct facies related to 15 conceptually distinct facies groups these facies are fixed points in a spectrum of facies generated in a process continuum from resedimentation processes through semi permanent bottom currents to pelagic settling in essence the scheme is descriptive of the sedimentary attributes of sediments although it is designed to aid interpretation of possible sediment transport deposition processes the classification scheme is three tier with facies classes groups and constituent facies and is hierarchical to allow flexibility in its use there are seven facies classes with classes a e defined largely on the basis of grain size differences class f on the basis of internal organization and class g on composition the facies classes are class a gravels muddy gravels gravelly muds and pebbly sands with 5 gravel grade class b sands with 80 sand grade and 80 mud 40 silt and 0 20 sand class e muds and clays with 95 mud grade for the purpose of large scale mapping or reconnaissance fieldwork either the level of facies classes or groups may be appropriate whereas for more detailed sedimentology the more detailed facies level will be necessary

dehydration melting and the granulite transition in metapelites from southern namaqualand s africa in a prograde amphibolite granulite transition zone in the namaqualand metamorphic complex metapelites show an interbanding of the amphibolite facies association biotite sillimanite quartz with the granulite facies association garnet cordierite k feldspar relict graded bedding shows that compositional banding is of sedimentary origin the garnet cordierite k feldspar gneisses contain quartzofeldspathic segregations surrounding garnets and have more fe rich bulk compositions than the biotite sillimanite schists

predicting capillarity of mudrocks abstract this study provides a compilation evaluation and correlation of published petrophysical datasets determined for 233 rock samples 165 mudrocks 27 sandstone 25 carbonate 11 anhydrite and 5 marlstone datasets with predominant focus on mudrocks a review of the methods used for determination of capillary breakthrough and snap off pressures is given additionally based on more recent data previously published empirical correlations are critically investigated knowledge about these two critical pressures is important for both the prediction of the capillary sealing capacity of natural gas reservoirs or co 2 storage sites but also for production estimates from tight gas or shale gas plays capillary pressure experiments when performed on low permeability core plugs are difficult and time consuming laboratory measurements on core plugs under in situ conditions are mostly performed using nitrogen but also with methane and carbon dioxide therefore mercury injection porosimetry mip measurements are preferably used in the industry to determine an equivalent value for the capillary breakthrough pressure these measurements have the advantage to be quick and cheap and only require cuttings or trim samples when evaluating the database in detail we find that 1 mip data plot well with the drainage breakthrough pressures determined on sample plugs while the conversion of the system hg air to gas brine e g ch 4 co 2 using interfacial and wettability data does not provide a uniform match potentially caused by different wettability characteristics 2 brine permeability versus capillary breakthrough pressure determined on sample plugs shows a good match and could provide a first estimate of p c values since permeability is easier to determine than capillary breakthrough pressures for imbibition snap off pressures a good correlation was found for ch 4 measured on sample plugs only 3 porosity shows a fairly good correlation with permeability for sandstone only and with plug derived capillary breakthrough pressures for sandstones carbonates and evaporates no such correlations exist for mudrocks 4 air and brine derived permeabilities show an excellent correlation and 5 from the data used we do not infer any direct correlations between specific surface area ssa mineralogy or organic carbon content with permeability or capillary pressure however we were able to better predict permeabilities using a more sophisticated model that relies on a combination of these parameters

sedimentation under deep sea storms fast currents high concentrations of suspended sediment and grooved mud beds are associated with erosion in frequent abyssal storms where a fast deep mean flow is augmented or reversed by intense intermittent currents this occurs about 5 km below the gulf stream or its rings the waning phase of a storm results in development of bedforms and rapid deposition of a mud blanket several other regions of the world ocean display evidence of abyssal storm activity

the transformation of amphibolite facies gneiss to charnockite in southern karnataka and northern tamil nadu india amphibolite facies metamorphic grade gives way southward to the granulite grade in southern karnataka as acid gneisses develop charnockite patches and streaks and basic enclaves develop pyroxenes petrologic investigations in the transitional zone south of mysore have established the following points 1 the transition is prograde amphibole bearing gneisses intimately associated with charnockite at kabbal and several similar localities are not retrogressive after charnockite as proved by patchy obliteration of their foliation by transgressive very coarse grained charnockite high fluorine content of biotite and amphibole in gneisses and high large ion lithophile element contents in gneisses and charnockites these features are in contrast to very low fluorine in retrogressive amphiboles and biotites very low large ion lithophile element contents and zonal bleaching of charnockite in clearly retrogressive areas as at bhavani sagar tamil nadu 2 metamorphic temperatures in the transitional areas were 700 800 c pressures were 5 7 kbar and h2o pressures were 0 1 0 3 times total pressures based on thermodynamic calculations using mineral analyses dense co2 rich fluid inclusions in the kabbal rocks confirm the low h2o pressures at the first appearance of orthopyroxene farther to the south in the nilgiri hills and adjacent granulite massif areas peak metamorphic temperatures were 800 900 c pressures were 7 9 kbar and water pressures were very low so that primary biotites and amphiboles those with high f contents are rare 3 the incipient granulite grade metamorphism of the transitional areas was introduced by a wave of anatexis and k metasomatism this process was arrested by drying out under heavy co2 influx charnockites so formed are hybrids of anatectic granite and metabasite of metabasite and immediately adjacent gneiss or are virtually isochemical with pre existing gneiss despite gross recrystallization to granulite mineralogy these features show that partial melting and metasomatism are attendant rather than causative in charnockite development copious co2 from a deep crustal or mantle source pushed ahead of it a wave of more aqueous solutions which promoted anatexis granulite metamorphism of both neosome and paleosome followed the process is very similar to that deduced for the madras granulites by weaver 1980 the massif charnockites for the most part extremely depleted in lithophile minor elements show many evidences of having gone through the same process

experimental investigation of matrix permeability of gas shales predicting long term production from gas shale reservoirs has been a major challenge for the petroleum industry to better understand how production profiles are likely to evolve with time we have conducted laboratory experiments examining the effects of confining stress and pore pressure on permeability experiments were conducted on intact core samples from the barnett eagle ford marcellus and montney shale reservoirs the methodology used to measure permeability allows us to separate the reduction of permeability with depletion because of the resultant increase in effective confining stress and the increase in permeability associated with knudsen diffusion and molecular slippage also known as klinkenberg effects at very low pore pressure by separating these effects we are able to estimate the relative contribution of both darcy and diffusive fluxes to total flow in depleted reservoirs our data show that the effective permeability of the rock is significantly enhanced at very low pore pressures because of the slippage effects we use the magnitude of the klinkenberg effect to estimate the effective aperture of the flow paths within the samples and compare these estimates to scanning electron microscopy image observations our results suggest effective flow paths to be on the order from tens of nanometers in most samples to 100 200 nm in a relatively high permeability eagle ford sample finally to gain insight on the scale dependence of permeability measurements the same core plugs were crushed and permeability was again measured at the particle scale using the so called gas research institute method the results show much lower permeability than the intact core samples with very little correlation to the measurements on the larger scale cores

the geological evolution of the magondi mobile belt zimbabwe abstract the zimbabwe archaean craton is flanked to the nw by the magondi mobile belt within this belt magondi supergroup volcanics and sediments were deposited during the early proterozoic before being deformed and metamorphosed 1850 ma ago in the south the belt is a typical thin skinned thrust belt with magondi supergroup rocks thrust se onto the archaean craton northwards the character of the belt changes with the structural style changing to a more thick skinned type metamorphic grade increasing from greenschist to granulite facies and with increasing amounts of early proterozoic basement gneisses imbricated within the sedimentary sequence metamorphism in the northern part of the belt is explained by thermal relaxation after the overthrusting of hot early proterozoic rocks from the west effectively sandwiching the magondi rocks between archaean basement below and allochthonous early proterozoic basement above flat lying isograds that date from this event were subsequently folded along s plunging axes during continued orogenic squeezing the rocks within the magondian belt are essentially unaffected by subsequent pan african deformation and metamorphism the evolution of the belt seems to fit the emerging pattern of cratonisation of the african plate within which pattern the magondian mobile belt may be correlated with other eburnian cycle belts in south africa but not with any of the tectonothermal provinces to the north of the pan african zambezi damara belt

metamorphism and geochronology of granulites and migmatitic granulites from the magondi mobile belt zimbabwe the magondi mobile belt which crops out to the west of the zimbabwe archaean craton is an early to mid proterozoic feature within which sediments of the magondi supergroup were deformed and metamorphosed metamorphic grade increases northwards along the strike of the belt from greenschist facies in the south to granulite facies in the north the granulite facies rocks were partially melted during metamorphism at pressures of 5 7 kbar and temperatures of about 700 750 c with fluids buffered to low values of pfl late stages of partial melting were driven by vapour poor dehydration melting reactions an age for the metamorphism is indicated by rb sr ages of 1890 260 ma from enderbitic granulites at the rukomeshe river causeway east of makuti and of 1780 280 ma from garnet bearing and granitic granulites from the nyaodza region just east of lake kariba these ages confirm an early proterozoic age for the magondi orogeny which can be correlated with deformation in the kheis belt occupying a similar position on the western margin of the kaapvaal craton later brittle deformation and cataclasis distributed throughout the granulites but locally concentrated in n s striking shear zones are the result of deformation in the footwall of the south verging pan african thrust sheets

breakthrough pressure and permeability in partially water saturated shales using methane carbon dioxide gas mixtures an experimental study of carboniferous shales from the eastern qaidam basin china as an important unconventional and alternative resource shale gas has attracted worldwide attention the breakthrough pressure is a major factor in the generation and migration of shale gas as well as in the evaluation of the caprock sealing capacity carboniferous shales are considered to have great potential for the exploitation of shale gas thus investigations of the breakthrough pressure and gas effective permeability are significant two shale samples taken from the carboniferous hurleg formation in the eastern qaidam basin china were chosen to conduct breakthrough experiments to investigate the effects of water saturation and co2 ch4 mixed mole fractions on the breakthrough pressure and gas effective permeability prior to the experiments various relevant parameters e g the porosity mineral composition and organic geochemistry the total organic content thermal maturity and kerogen type and microstructure of these samples were also measured the results of our breakthrough experiments show that the breakthrough pressure increases with the water saturation and decreases with the co2 mole fraction in the gas mixture the situation for the gas effective permeability is just the opposite pore size distribution measurements indicate that there are many nanoscale micropores that can easily be blocked by water molecules this results in the reduced connectivity of gas pathways thus the breakthrough pressure increases and the gas effective permeability decreases with increasing water saturation the breakthrough pressure decreases with the co2 mole fraction because the interfacial tension of the co2 water system is smaller than that of the ch4 water system the viscosity of the co2 ch4 mixture was found to increase with the co2 mole fraction by fitting a series of values under the same temperature and pressure conditions leading to an increase in the gas effective permeability furthermore co2 molecules are smaller than ch4 molecules making it easier for co2 to move across pathways after each breakthrough experiment the co2 mole fraction in the effluent was less than that in the injected gas and it increased over time until reaching the initial injected gas composition this is because the adsorption and solubility of co2 in water are greater than those of ch4 this study provides practical information for further investigations of shale gas migration and extraction and the sealing capacities of caprocks

present day stress analysis of the st lawrence lowlands sedimentary basin canada and implications for caprock integrity during co2 injection operations abstract a geomechanical analysis of the st lawrence lowlands sedimentary basin is important to reliably estimate the maximum sustainable fluid pressures for co 2 injection that will not reactivate pre existing faults in the caprock thereby inducing a breeched co 2 reservoir this requires the determination of prevailing stresses orientations and magnitudes fault and fractures geometries and rock strengths the average maximum horizontal stress orientation s hmax is estimated n59 e 20 in the st lawrence lowlands the stress orientations were obtained from stress induced wellbore breakouts inferred from four arm dipmeter caliper data in 17 wells these wellbore failure features are confined to paleozoic lithological units of the st lawrence platform succession and frontal thrusts of the quebec appalachians at depths from 250 m to 4 km our results are consistent with the regional ne sw s hmax stress orientation trend that is generally observed in eastern canada and the u s the stresses pressure gradients estimated for the st lawrence lowlands depths hmin 20 5 3 kpa m s v 25 6 kpa m s hmax 40 7 5 kpa m pore pressure p p 9 8 kpa m indicating a strike slip stress regime s hmin v hmax the high angle ne sw regional faults and fractures in the paleozoic sedimentary succession and the grenvillian basement are oblique to the s hmax stress orientations 10 to 36 and could be reactivated slip tendency 0 34 to 0 58 under the present day stress field if fluid pressures exceeded the critical threshold further refinement of regional geomechanical model is required to estimate the maximum sustainable injection pressure necessary for shear reactivation along the regional faults the regional pore pressure stress coupling ratio under assumed parameters is about 0 5 0 65 and may contribute to reduce the risk of shear reactivation of faults and fractures the maximum sustainable p p that would not cause opening of vertical tensile fractures during co 2 operations is about 18 5 20 mpa for the depth of 1 km

grain size sensitive deformation of upper greenschist to lower amphibolite facies metacherts from a low p high t metamorphic belt abstract to identify the dominant deformation mechanism in continental middle crust at an arc trench system we used an sem ebsd system to measure the lattice preferred orientations of quartz grains in fine grained metachert from the low grade chlorite and chlorite biotite zones part of the low p high t ryoke metamorphic belt sw japan quartz c axis fabrics show no distinct patterns related to dislocation creep although the strain magnitudes estimated based on deformed radiolarian fossils are high enough that a distinct fabric might be expected to have formed during deformation fabric intensities are very low indicating a random distribution of quartz c axes quartz grains are equant in shape and polygonal and free of intracrystalline plasticity these observations suggest that the dominant deformation mechanism in the metacherts was grain size sensitive flow diffusion creep accompanied by grain boundary sliding rather than dislocation creep possibly reflecting the relatively low strain rate or low flow stress compared with that in high strain zones the development of grain size sensitive flow in metamorphic tectonites at mid crustal conditions would result in a significant decrease of the rocks strength of the continental middle crust

tectonic cycles in southern africa abstract the recurrence of major geological events within the 3600 ma stratigraphic record of southern africa suggests a periodicity of320 25ma for at least the last 3200 ma this periodicity is reflected in major episodes of continental volcanism granitoid plutonism orogeny reciprocity of terrestrial and marine dominated sequences platform carbonate sedimentation glaciation and first order changes in sea level these serve to define 11 completed megacycles each introduced by a major rifting event accompanied by listric faulting alluvial sedimentation in restricted fault bound troughs volcanism and a type granitoid plutonism prior to 3200 ma continental rift magmatism occurred subaqueously due to very high early archean sea levels resulting in pillow lavas and a lack of interbedded terrigenous siliciclastics the long term reciprocity of terrestrial and marine dominated sequences records eustatic first order changes in sea level with highstands characterized by generally humid warm continental climates low relief and tropical afforestation on the other hand lowstand climates were hot and arid with high relief and widespread desertification thick marine sequences accumulate in areally extensive epeirogenic basins without significant volcanism or faulting and commonly are divided into an early phase of open shelf sedimentation followed by deposition in a brackish marine foreland basin within openshelf environments an early phase of biochemical precipitation and or siliciclastic reworking along linear shorelines is separated from a later phase involving rapid deposition of immature siliciclastics along lobate shorelines evolution of the foreland basin is related to orogenic activity and the isolation of an epeiric sea which sometimes developed the characters of a barred basin marine dominated sequences display a deterministic stacking of lithofacies important glacial epochs commonly occur midway through first order regression sometimes with lesser events closely following peak transgression potentially they display 320 ma periodicity but with an unexplained mid proterozoic gap glaciation is related to the combined effect of climatic cooling associated with first order regression and depletion of atmospheric co2 by biological uptake associated with platform carbonate development terrestrial volcanism is believed to be the main contributor of atmospheric co2 climatic change is accompanied by cyclical patterns of cratonic weathering and pedogenesis

fe mg mixing in cordierite constraints from natural data and implications for cordierite garnet geothermometry in granulites from chemicaldata on 108 pairs of naturally occurring garnet and cordierite the interchange energy of fe mg mixing in cordierite wo and the free energy change of the exchange equilibrium feralrsiro t t zmgraiosiro y mgralrsiro yzferalosiro in the temperature range of 700 850 c have been extracted using standard methods of linear regression analysis the input thermochemical parameters for multicomponent camg fe mn garnet solid solutions are based on the updated and revised values after ganguly and saxena 1984 e g wr 2500 cal w w 3000 cal calculated on the basis of one third formula unit on the basis of the derived values at 710 760 800 and 850 c fe mg mixing in cordierite has been approximated to a symmetric regular solution the fe mg substitution shows positive deviation from ideality in cordierite with tzi 1 9 34 4 54kj mol of divalent cation the values derived for the free energy of mixing at xi d xi ds 0 5 are 3 26 kj at 700 c and 4 39 kl at 900 c the ag value in joules for the above equilibrium can be expressed as 15079 8 552 incorporating these parameters the geothermometric expression for the exchange equilibrium is

effects of in situ conditions on relative permeability characteristics of co2 brine systems carbon dioxide capture and geological storage ccgs is an emerging technology that is increasingly being considered for reducing greenhouse gas emissions to the atmosphere deep saline aquifers provide a very large capacity for co2 storage and unlike hydrocarbon reservoirs and coal beds are immediately accessible and are found in all sedimentary basins proper understanding of the displacement character of co2 brine systems at in situ conditions is essential in ascertaining co2 injectivity migration and trapping in the pore space as a residual gas or supercritical fluid and in assessing the suitability and safety of prospective co2 storage sites because of lack of published data the authors conducted a program of measuring the relative permeability and other displacement characteristics of co2 brine systems for sandstone carbonate and shale formations in central alberta in western canada the tested formations are representative of the in situ characteristics of deep saline aquifers in compacted on shore north american sedimentary basins the results show that the capillary pressure interfacial tension relative permeability and other displacements characteristics of co2 brine systems depend on the in situ conditions of pressure temperature and water salinity and on the pore size distribution of the sedimentary rock this paper presents a synthesis and interpretation of the results

quaternary mud turbidites from the south shetland trench west antarctica recognition and implications for turbidite facies modelling a piston core from the basinal part depth of 5188 m of the south shetland trench west antarctica yielded a terrigenous mud section 11 m long which can be subdivided with great precision into turbidite and hemipelagite layers mud turbidites mean bed thickness 44 cm alternate regularly with and are best distinguishable from their hemipelagite host mean bed thickness 17 cm by the following features i sharp basal contacts ii terrigenous sand free textures except basal well sorted silt laminae and the absence of outsized ice rafted components iii a laminated little to non bioturbated internal structure iv distinct textural and compositional grading and v marked steps on water content and sediment density logs mud turbidites recovered from the south shetland trench differ from an earlier model mud turbidite sequence by their i excessive about six times larger bed thickness ii complex internal organization manifested in multiple repetitions up to four of the same structural interval s in sequential or nonsequential order iii distinctive very fine grained cap of highly porous clay rich in fragments of siliceous biogenics iv widespread zones of penesyndepositional deformation and v evidence of flow reversals these features are interpreted to record deposition from large muddy turbidity currents subjected to flow transformations including soliton and or seiche related reversals induced by ponding and interactions of the flow with the topographical confinements of the trench it is concluded that contained muddy turbidites cannot be adequately modelled using published sequences differentiation of single model and contained mud turbidites offers obvious advantages in basin analysis and in understanding the plethora of turbidity current related depositional mechanisms of deep sea mud

water activity changes across an amphibolite granulite facies transition broken hill australia phase compositions in pelitic and mafic gneisses place tight constraints on pressure ranging from 3 up to 6 kb and to a lesser extent on temperature 500 up to 800 c during prograde regional metamorphism of the willyama complex broken hill se australia these limits allow an evaluation of water activity across the terrain using various equilibria in pelitic and mafic gneisses the stability of cummingtonite and biotite over much of the terrain places upper limits on temperature and the presence of syn metamorphic partial melts in the metasediments places lower limits on a h2o garnet biotitesillimanite k feldspar quartz relations combined with the partial melting data suggest a decrease in water activity from near 1 0 in the lower grade zones to 0 5 0 2 in the broken hill little broken hill part of the two pyroxene zone this result is compatible with less precise hornblende orthopyroxene clinopyroxene quartz relations

lithospheric structures and precambrian terrane boundaries in northeastern botswana revealed through magnetotelluric profiling as part of the southern african magnetotelluric experiment 1 within the framework of the southern african magnetotelluric experiment a focused study was undertaken to gain improved knowledge of the lithospheric geometries and structures of the westerly extension of the zimbabwe craton zim into botswana with the overarching aim of increasing our understanding of southern african tectonics the area of interest is located in northeastern botswana where kalahari sands cover most of the geological terranes and very little is known about lithospheric structures and thicknesses some of the regional scale terrane boundary locations defined based on potential field data are not sufficiently accurate for local scale studies investigation of the nnw sse orientated 600 km long zim line profile crossing the zimbabwe craton magondi mobile belt and ghanzi chobe belt showed that the zimbabwe craton is characterized by thick 220 km resistive lithosphere consistent with geochemical and geothermal estimates from kimberlite samples of the nearby orapa and letlhakane pipes 175 km west of the profile the lithospheric mantle of the ghanzi chobe belt is resistive but its lithosphere is only about 180 km thick at crustal depths a northward dipping boundary between the ghanzi chobe and the magondi belts is identified and two middle to lower crustal conductors are discovered in the magondi belt the crustal terrane boundary between the magondi and ghanzi chobe belts is found to be located further to the north and the southwestern boundary of the zimbabwe craton might be further to the west than previously inferred from the regional potential field data

thermobarometry and fluid evolution of enderbites within the magondi mobile belt northern zimbabwe abstract metamorphic conditions within arenaceous calcareous and argillaceous supracrustal rocks of the magondi mobile belt zimbabwe range from greenschist to granulite facies within the high grade segment basement gneisses of early proterozoic age and argillaceous rocks of the mid proterozoic piriwiri group are intruded by charnockites and enderbites metamorphic mineral assemblages and thermobarometric data for enderbitic granulites of nyaodza show temperatures of 700 800 c and pressures of 5 7 kbar for the peak of granulite facies metamorphism microthermometry and raman microspectroscopy reveal that co 2 associated with minor n 2 has been the dominant fluid phase during granulite facies metamorphism the chronology of the co 2 inclusions and the development of microtextures and mineral assemblages in the enderbites indicates that isolated negative crystal shaped co 2 inclusions in quartz and plagioclase porphyroclasts entrap syn metamorphic fluids of medium high densities 0 88 0 90 g cm 3 lower density 0 71 0 77 g cm 3 co 2 inclusions in trails and clusters within the same minerals were formed from local re equilibration and re entrapment of the former near peak granulitic co 2 inclusions as in many other granulites syn metamorphic co 2 is associated with intrusives emplaced near the peak of metamorphism

fracture healing and transport properties of wellbore cement in the presence of supercritical co2 this paper investigates the process and rate of carbonation reaction of class a wellbore cement exposed to co2 saturated solution at confined conditions similar to those employed in geological storage of co2 the main goal was to investigate whether reaction improves or degrades the sealing healing capacity of fractured type a cement plugs batch reaction experiments were performed for up to three months on both intact and fractured class a portland cement cylinders at a constant confining pressure of 30 mpa a temperature of 80 c and a co2 pressure of 10 mpa the experiments were carried out on water saturated samples exposing them to the supercritical co2 at one end all samples were jacketed in sleeves to seal them from the high pressure confining medium the results indicate that cement carbonation front advanced in time leading to a densification of the material extrapolation of the reaction rates to 1 year period indicates a carbonation depth of about 1 38 mm and about 7 56 mm after 30 years of exposure to co2 saturated solution thermogravimetric analyses scanning electron microscopy observations and permeability measurements indicate that carbonation of wellbore cement leads to a decrease of the porosity of the material on the reaction front and moreover has the potential for healing pre existent fractures and for improving the sealing properties of good quality cement samples in time at reservoir conditions

mississippian barnett shale fort worth basin north central texas gas shale play with multi trillion cubic foot potential the mississippian barnett shale serves as source seal and reservoir to a world class unconventional natural gas accumulation in the fort worth basin of north central texas the formation is a lithologically complex interval of low permeability that requires artificial stimulation to produce at present production is mainly confined to a limited portion of the northern basin where the barnett shale is relatively thick 300 ft 92 m organic rich presentday total organic carbon 3 0 thermally mature vitrinite reflectance 1 1 and enclosed by dense limestone units able to contain induced fractures the most actively drilled area is newark east field currently the largest gas field in texas newark east is 400 mi 2 1036 km 2 in extent with more than 2340 producing wells and about 2 7 tcf of booked gas reserves cumulative gas production from barnett shale wells through 2003 was about 0 8 tcf wells in newark east field typically produce from depths of 7500 ft 2285 m at rates ranging from 0 5 to more than 4 mmcf day estimated ultimate recoveries per well range from 0 75 to as high as 7 0 bcf efforts to extend the current barnett play beyond the field limits have encountered several challenges including westward and northward increases in oil saturation and the absence of lithologic barriers to induced fracture growth patterns of oil and gas occurrence in the barnett in conjunction with maturation and burial history data indicate a complex multiphased thermal evolution with episodic expulsion of hydrocarbons and secondary cracking of primary oils to gas

oil and gas wells and their integrity implications for shale and unconventional resource exploitation data from around the world australia austria bahrain brazil canada the netherlands poland the uk and the usa show that more than four million onshore hydrocarbon wells have been drilled globally here we assess all the reliable datasets 25 on well barrier and integrity failure in the published literature and online these datasets include production injection idle and abandoned wells both onshore and offshore exploiting both conventional and unconventional reservoirs the datasets vary considerably in terms of the number of wells examined their age and their designs therefore the percentage of wells that have had some form of well barrier or integrity failure is highly variable 1 9 75 of the 8030 wells targeting the marcellus shale inspected in pennsylvania between 2005 and 2013 6 3 of these have been reported to the authorities for infringements related to well barrier or integrity failure in a separate study of 3533 pennsylvanian wells monitored between 2008 and 2011 there were 85 examples of cement or casing failures 4 blowouts and 2 examples of gas venting in the uk 2152 hydrocarbon wells were drilled onshore between 1902 and 2013 mainly targeting conventional reservoirs uk regulations like those of other jurisdictions include reclamation of the well site after well abandonment as such there is no visible evidence of 65 2 of these well sites on the land surface today and monitoring is not carried out the ownership of up to 53 of wells in the uk is unclear we estimate that between 50 and 100 are orphaned of 143 active uk wells that were producing at the end of 2000 one has evidence of a well integrity failure

experimental study of fluid transport processes in the matrix system of the european organic rich shales ii posidonia shale lower toarcian northern germany abstract a laboratory study has been conducted to investigate the transport of gases he ar ch 4 and water in the matrix of lower toarcian posidonia shale samples from three shallow boreholes in northern germany the maturity of the organic matter of the shale samples ranged between 0 53 and 1 45 vitrinite reflectance vr r the measurements were performed at effective stresses ranging between 6 and 37 mpa and a temperature of 45 c the effects of different controlling factors including permeating fluid maturity anisotropy moisture content and effective stress on the fluid conductivity were analyzed and discussed permeability coefficients measured perpendicular and parallel to bedding 3 10 22 to 9 7 10 17 m 2 were within the range previously reported for other shales and mudstones they exhibited a strong dependence on permeating fluid maturity anisotropy moisture content and effective stress the permeability coefficients measured with helium as permeate were consistently higher up to two times than those measured with argon and methane permeability coefficients measured with water were up to three orders of magnitude lower than klinkenberg corrected gas permeability coefficients measured with helium and methane under similar experimental conditions among the samples studied the lowest porosity and permeability coefficients were measured on samples of intermediate thermal maturity 0 88 vr r oil window permeability coefficients he ch 4 measured parallel to bedding were up to more than one order of magnitude higher than those measured perpendicular to bedding permeability coefficients measured with he and ch 4 on a dry sample were up to two times higher than those measured on a sample with the as received moisture content all samples showed a nonlinear reduction in permeability parallel to bedding with increasing effective stress 6 37 mpa the permeability anisotropy and stress dependence of permeability were controlled by the mineralogy

alluvial eolian and lacustrine sedimentology of a paleoproterozoic half graben baker lake basin nunavut canada the northeast trending baker lake sub basin was a volcanically active half graben during deposition of ca 1 85 1 76 ga baker lake group drainage was oriented along transverse and axial directions with flow to playa lake and deeper perennial lacustrine depocentres basin marginal streamflow dominated alluvial fans were concentrated along the southern margin and provided sediment from archean crystalline basement rocks these fed transverse gravel and sand bed braided streams alluvial dynamics were characterized by channel aggradation and abandonment abandoned channel belts were sites of floodplain and eolian deposition basin axial braided streams fed northeast and southwest to a depocentre near christopher island where eolian playa and lacustrine environments were intimately linked felsic minette flows were initially erupted from localized centres contemporaneous sedimentary deposits typically contain minor volcaniclastic components that increase in abundance basinward voluminous and widespread younger minette flows prograded outward from volcanic centres contributing significant additional basin infill

partial melting and the formation of granulite facies assemblages in namaqualand south africa abstract dehydration melting reactions in which water from a hydrous phase enters the melt leaving an anhydrous solid assemblage are the dominant mechanism of partial melting of high grade rocks in the absence of externally derived vapour equilibria involving melt and solid phases are effective buffers of ah2 o the element partitioning observed in natural rocks suggests that dehydration melting occurs over a temperature interval during which for most cases ah2o is driven to lower values the mass balance of dehydration melting in typical biotite gneiss and metapelite shows that the proportion of melt in the product assemblage at t 850 c is relatively small 10 20 and probably insufficient to mobilize a partially melted rock body granulite facies metapelite biotite gneiss and metabasic gneiss in namaqualand contain coarse grained discordant unfoliated anhydrous segregations surrounded by a finer grained foliated matrix that commonly includes hydrous minerals the segregations have modes consistent with the hypothesis that they are the solid and liquid products of the dehydration melting reactions bt sil qtz pi grt crd kfs l metapelite bt qtz pl opx kfs l biotite gneiss and hbl qtz opx cpx pl l metabasic gneiss the size shape distribution and modes of segregations suggest only limited migration and extraction of melt growth of anhydrous poikiloblasts in matrix regions development of anhydrous haloes around segregations and formation of dehydrated margins on metabasic layers enclosed in migmatitic metapelites all imply local gradients in water activity also they suggest that individual segregations and bodies of partially melted rock acted as sinks for soluble volatiles the preservation of anhydrous assemblages and the restricted distribution of late hydrous minerals suggest that retrograde reaction between hydrous melt and solids did not occur and that h2o in the melt was released as vapour on crystallization this model combined with the natural observations suggests that it is possible to form granulite facies assemblages without participation of external fluid and without major extraction of silicate melt

radiogenic heat production in the lithosphere of sulu ultrahigh pressure metamorphic belt abstract the chinese continental scientific drilling ccsd project is located at the sulu ultrahigh pressure metamorphic uhpm belt it offers a unique opportunity for studying the radiogenic heat production of both shallower and deeper rocks based on the concentrations of radiogenic elements u th and k on 349 samples from main hole of ccsd ccsd mh pilot holes and exposures we determined radiogenic heat productions of all major rock types in the sulu uhpm belt results show the mean values of orthogneiss and paragneiss are respectively 1 65 0 81 and 1 24 0 61 w m 3 due to different composition and grade of retrogressive metamorphism the eclogites display significant scatter in radiogenic heat production ranging from 0 01 to 2 85 w m 3 with a mean of 0 44 0 55 w m 3 the radiogenic heat production in ultramafic rocks also varies within a large range of 0 02 to 1 76 w m 3 and the average turns out to be 0 18 0 31 w m 3 based on the measurements and crustal petrologic model the vertical distribution model of heat production in sulu crust is established the resulting mean heat production 0 76 w m 3 contributes 24 mw m 2 to the surface heat flow 1 d thermal model indicates that the temperature at the moho reaches above 750 c and the thermal thickness of the lithosphere is 75 km in good agreement with the geophysical results the high teat flow 75 mw m 2 together with thin lithosphere presents strong support for the extension events during the late cretaceous and cenozoic

assessing potential impacts of shale gas development on shallow aquifers through upward fluid migration a multi disciplinary approach applied to the utica shale in eastern canada abstract potential impacts of shale gas development on shallow aquifers has raised concerns especially regarding groundwater contamination the intermediate zone separating shallow aquifers from shale gas reservoirs plays a critical role in aquifer vulnerability to fluid upflow but the assessment of such vulnerability is challenging due to the general paucity of data in this intermediate zone the ultimate goal of the project reported here was to develop a holistic multi geoscience methodology to assess potential impacts of unconventional hydrocarbon development on fresh water aquifers related to upward migration through natural pathways the study area is located in the st lawrence lowlands southern quebec canada where limited oil and gas exploration and no shale gas production have taken place a large set of data was collected over a 500 km2 area near a horizontal shale gas exploration well completed and fracked into the utica shale at a depth of 2 km to investigate the intermediate zone integrity this project integrated research results from multiple sources in order to obtain a better understanding of the system hydrodynamics including geology hydrogeology deep and shallow geophysics soil rock and groundwater geochemistry and geomechanics the combined interpretation of the multi disciplinary dataset demonstrates that there is no evidence of and a very limited potential for upward fluid migration from the utica shale reservoir to the shallow aquifer microbial and thermogenic methane in groundwater of this region appear to come from the shallow organic rich fractured sedimentary rocks making up the regional aquifer nonetheless diluted brines present in a few shallow wells close to and downstream of a normal fault revealed that some upward groundwater migration occurs but only over a few hundred meters from the surface based on the isotopic signature of methane the methodology developed should help support regulations related to shale gas development aiming to protect groundwater

calculation and application of clinopyroxene garnet plagioclase quartz geobarometers recently published thermodynamic and experimental data in a variety of chemical systems have been evaluated to derive gibbs free energies for hedenbergite and pyrope these were used to calculate the geobarometric equilibria

three dimensional numerical simulations of methane gas migration from decommissioned hydrocarbon production wells into shallow aquifers three dimensional numerical simulations are used to provide insight into the behavior of methane as it migrates from a leaky decommissioned hydrocarbon well into a shallow aquifer the conceptual model includes gas phase migration from a leaky well dissolution into groundwater advective dispersive transport and biodegradation of the dissolved methane plume gas phase migration is simulated using the dumux multiphase simulator while transport and fate of the dissolved phase is simulated using the bionapl 3d reactive transport model methane behavior is simulated for two conceptual models first in a shallow confined aquifer containing a decommissioned leaky well based on a monitored field site near lindbergh alberta canada and secondly on a representative unconfined aquifer based loosely on the borden ontario field site the simulations show that the lindbergh site confined aquifer data are generally consistent with a 2 year methane leak of 2 20 m3 d assuming anaerobic sulfate reducing methane oxidation and with maximum oxidation rates of 1 10 5 to 1 10 3 kg m3 d under the highest oxidation rate dissolved methane decreased from solubility 110 mg l to the threshold concentration of 10 mg l within 5 years in the unconfined case with the same leakage rate including both aerobic and anaerobic methane oxidation the methane plume was less extensive compared to the confined aquifer scenarios unconfined aquifers may therefore be less vulnerable to impacts from methane leaks along decommissioned wells at other potential leakage sites site specific data on the natural background geochemistry would be necessary to make reliable predictions on the fate of methane in groundwater

bib sem study of the pore space morphology in early mature posidonia shale from the hils area germany abstract this contribution reports on the study of the pore space morphology in two early mature vr r 0 59 and 0 61 samples of posidonia shale from the hils syncline in germany using broad ion beam bib polishing and high resolution scanning electron microscopy sem this allows imaging pores with resolution down to 10 nm in equivalent diameter d eq and quantitative estimation of porosity using a combination of bse and se detectors and semi automatic segmentation of the gigapixel images the representative elementary area of the samples on the scale of a few mm is inferred to be about 140 140 m 2 pore morphologies and pore sizes are clearly related to the mineral fabric with large differences very large typically several microns pores with internal faceted crystal morphology in recrystallized calcite clasts and smaller pores d eq cf schizosphaerella nanofossils typically 200 nm pores are less common in organic material and in pyrite aggregates pore characteristics are very similar for both samples and porosity resolvable by bib sem is 2 75 and 2 74 pore size distribution can be described by a power law with an exponent about 2 0 and 2 2 respectively for the pore population excluding the fossils pores in the carbonate fossils show dual power law distribution with power law exponents of about 1 and 3 by extrapolating the power law distribution for each sample total porosity is estimated to be 4 8 0 9 1 7 and 6 5 2 7 7 2 respectively this estimate can be compared with 3 4 3 7 and 3 3 3 6 as measured by mercury injection porosimetry we interpret this difference to reflect the unconnected for mercury part of the porosity comparison of imaged pores and mercury injection porosimetry suggest a very high pore body to pore throat ratio this results in a pore model where large pores represented mainly by pores in fossils and calcite grains are connected via a low porous and low permeable clay rich matrix with pore throats below 10 nm in both samples

proterozoic tectonic provinces of southern africa abstract recent investigations in southwestern africa i e the nw cape province and namibia require a consistent hierarchy of tectonic provinces subprovinces belts and terranes in order to provide an adaptable framework table i and fig 1 for further progress in crustal evolution studies the proterozoic continental crust of southwestern africa originated during three major orogenic cycles known elsewhere in africa as the eburnean kibaran and pan african episodes

an overview of canadian shale gas production and environmental concerns abstract production of hydrocarbons from canadian shales started slowly in 2005 and has significantly increased since natural gas is mainly being produced from devonian shales in the horn river basin and from the triassic montney shales and siltstones both located in northeastern british columbia and to a lesser extent in the devonian duvernay formation in alberta western canada other shales with natural gas potential are currently being evaluated including the upper ordovician utica shale in southern quebec and the mississippian frederick brook shale in new brunswick eastern canada this paper describes the status of shale gas exploration and production in canada including discussions on geological contexts of the main shale formations containing natural gas water use for hydraulic fracturing the types of hydraulic fracturing public concerns and on going research efforts as the environmental debate concerning the shale gas industry is rather intense in quebec the utica shale context is presented in more detail

sedimentological significance of mudstone microclast intervals in upper proterozoic turbidites central dobrogea romania abstract the basement of the moesian platform exposed in central dobrogea is represented by the upper proterozoic histria formation this is a thick turbidifc succession which includes two sandstone dominated channelised mid fan members separated by a distal fan abyssal plain sequence a typical feature of this fine grained member is the occurrence at the top of the t e bouma divisions of tiny flat intraclasts defining a parallel lamination this interval with millimetric to centimetric thicknesses was designated the e i interval it usually occurs at top of t 7 or between t 3 and t 4 subdivisions of muddy turbidites the internal structure and the geometric position of the e interval suggests that the depositional mechanism involved erosion of muddy surface sediments by active turbiditic or thermohaline bottom currents followed by redeposition of the resulted intraformational microclasts by slow settling

hydraulic fractures how far can they go the maximum reported height of an upward propagating hydraulic fracture from several thousand fracturing operations in the marcellus barnett woodford eagle ford and niobrara shale usa is 588 m of the 1170 natural hydraulic fracture pipes imaged with three dimensional seismic data offshore of west africa and mid norway it is 1106 m based on these empirical data the probability of a stimulated and natural hydraulic fracture extending vertically 350 m is 1 and 33 respectively constraining the probability of stimulating unusually tall hydraulic fractures in sedimentary rocks is extremely important as an evidence base for decisions on the safe vertical separation between the depth of stimulation and rock strata not intended for penetration