Search

Identifying potential petroleum traps in petroleum basins is one of the key challenges in petroleum exploration. Specifically, it is the identification of probable petroleum traps within a set of stratigraphic traps of a particular location of source rock and carrier bed. One solution lies in understanding the behaviour of hydrocarbon flow during secondary migration, and the evaluation of the probability of successful transport from the source rock to the trap. Modern reservoir simulators rely on numerical methods to model the oil/gas secondary migration. Using numerical simulators is, however, cumbersome and requires high volumes of data and computation time, which affects successful decision-making in exploration planning. Yet, analytical models are fast and allow for multivariant analysis of hydrocarbon secondary migration requiring only a moderate amount of geological data. This study presents the analytical modelling of hydrocarbon buoyant transport in petroleum basins by including the (i) areal variation of stringers’ cross-section, (ii) chemical reactions including oil biodegradation and (iii) hydrological water flow. The explicit formula is provided for the first and last moments of hydrocarbon arrival at the trap, describing the dynamics of filling of the trap. Field data from Australian and Chinese basins are used to investigate the effects of the above-mentioned parameters on the first and last moments of hydrocarbon arrival at the trap.

Objectives Most laboratories have difficulties to determine their own reference intervals for the diagnostic evaluation of patient results by direct methods. Therefore, data is often just taken from the literature or package inserts of the analytical tests. Methods The section on Reference Limits of the German Society for Clinical Chemistry and Laboratory Medicine (DGKL) first uploaded the Reference Limit Estimator (RLE) as an R-program with MS Excel-interface on the DGKL home page and now this tool is implemented in the commercial Laboratory Information System OPUS::L (OSM AG Essen, Germany). We used this OPUS::L “Population specific Reference Limits” tool online with our laboratory database. First calculations were done using the example of lipase. Results The manufacturer’s original reference interval for lipase 12–53 U/L (adults) was changed to age dependent upper reference limits of 80 years). Conclusions By means of the OPUS::L “Population specific Reference Limits” tool we were able to establish our laborarotry specific reference interval for plasma lipase activity. The new reference limits helped to solve an old problem of implausible low elevated lipase values.

The focus of this study is formation damage due to fines migration induced by the leak-off of low salinity potassium chloride (KCl) fracturing fluids. The importance of this topic is determined by the wide utilization of KCl in drilling and fracturing fluids, as well as for fines fixing, and the widely reported skin in gas and oil wells. Scanning electron microscopy (SEM) imaging and energy dispersive X-ray (EDX) analyses from this study clearly indicated clay fines mobilisation, migration and straining, resulting in permeability decline. The breakthrough fines concentration was measured during the coreflooding experiments. The installation of a pressure sensor in the middle of the core allowed for pressure drop measurements across the first core section and the overall core. Permeability decline was observed during the injection of water with piecewise-constant decreasing KCl salinity. An analytical model based on the exact solution for one-dimensional fines transport was used to match the laboratory data. Close agreement between the laboratory and modelling data was observed. Moreover, the tuned model coefficients vary in the range of commonly reported values. It was found that neglecting fines breakthrough concentration (BTC) measurements permits laboratory-based prediction of formation damage during fracture fluid leak-off. However, fines BTC must be measured to fully characterise the fines migration system.

CO2CRC has made a significant investment into establishing the feasibility of conducting a CO2 injection experiment into a shallow fault. This world-leading experiment, located at the CO2CRC Otway International Test Centre in Victoria, Australia, would seek to improve our understanding of the conditions necessary for CO2 to move vertically up faults. The work undertaken during Phase 2 of the Otway Fault Project confirms the experiment is technically feasible and can be done safely. Two appraisal wells drilled and cored through the shallow Brumbys Fault indicate the fault extends to the base of the upper 2 m thick Hesse Clay layer, which forms the seal to the underlying Port Campbell Limestone aquifer. The fault does not have a defined core but an approximately 6-10 m wide fault cataclastic zone. Permeability within the Port Campbell Limestone is variable, ranging from tens to thousands of millidarcies. The rock strength is low, however, and it is recommended to conduct the experiment at approximately 80 m depth rather than the 40 m originally proposed. This provides more confining pressure and will ensure that the injection pressure does not exceed the fracture pressure. A deeper injection also provides better spatial and timing conditions for geophysical monitoring and tracking of the CO2 plume. Simulations indicate only a small 10 tonne CO2 injection experiment would be required to monitor CO2 migration using geophysical techniques. In addition to providing an opportunity to demonstrate semi-continuous, near real-time monitoring of CO2 migration up a fault, the planned CO2 injection experiment presents a unique opportunity to obtain field measurements on vertical fault permeability. It also provides an opportunity to predict fluid flow and potential metal remobilisation through comprehensive reactive transport modelling, collection and analysis of core post CO2 injection, and evaluate the effectiveness of the modelling versus field observations.

CO2CRC and its partners are undertaking a feasibility study for a planned CO2 controlled release and monitoring experiment on a shallow fault at the CO2CRC Otway Research Facility. In this project we plan to image, using a diverse range of geophysical and geochemical CO2 monitoring techniques, the migration of CO2 up a fault from a controlled release point at approximately 30 m depth. This paper describes the results of site characterisation and modelling work undertaken to date. It also includes a description of the activities planned that will enable for a more detailed characterization of the fault and proposed injection interval. Together these results will enable an assessment as to whether the planned injection experiment is feasible and how it can be optimally designed.

The CO2CRC is undertaking a feasibility study for a planned controlled release and monitoring experiment at a shallow fault at the CO2CRC Otway Project site in 2018. Interpretation of pre-2016 seismic data could trace the height of the fault to approximately 100 m below the ground surface, at which point the resolution of the existing seismic data was insufficient to delineate the fault any further. To better understand the shallow geology at the Otway Project site and to map the extent of the shallow fault, new geophysical surveys were acquired over the Otway site during 2016. This included a high resolution, shallow focused, 3D seismic survey to provide greater delineation of the newly identified fault in the Port Campbell Limestone on the Otway Project site, and a high resolution resistivity survey to map the vertical extent of the fault towards the ground surface. Aerial imagery and LIDAR data were also collected. The seismic survey data exhibit greatly improved vertical and lateral resolution compared to previous seismic surveys. Preliminary pre-stack time migration (PreSTM) processing of the data show that the target fault can be clearly imaged at 30 ms TWT and the fault tip can be mapped to within approximately 25 m of the surface. Approximately 5 m of throw is identified at approximately 140 m depth and the throw appears to decrease in magnitude as the fault extends towards the surface. This, plus an identified dip angle of ∼70° (east), suggests that it is most likely a normal fault. There is no evidence of topographical features associated with the surface expression of the shallow fault using LIDAR and aerial imagery. Electrical Resistivity Imaging (ERI) results indicate that there are 3 distinct layers in the shallow geology of the Otway site, including a higher resistivity, more clay influenced, 3-5 m thick layer at the surface. The resistivity is also surprisingly heterogeneous over the site, suggesting that the shallow geology is complex. Preliminary hydraulic conductivity measurements confirm that the Port Campbell Limestone is highly permeable in the vicinity of the Otway Project site. The target fault at the CO2CRC Otway Project site appears to be a suitable candidate for a shallow CO 2 injection experiment.

CO2CRC is undertaking a feasibility study for a planned CO2 controlled release and monitoring experiment on a shallow fault at the CO2CRC Otway Research Facility. In the first phase of the project, a series of geophysical surveys and groundwater permeability assessments were conducted at the Otway Research Facility to characterise the prospective experimental site and confirm the presence of a shallow fault. The data from the surveys have been integrated into a 3D model of the upper faulted shallow geology of the CO2CRC Otway site. Five properties (hydrostratigraphic unit, horizontal permeability, vertical permeability, fault permeability and P-velocity from refraction tomography) were populated in the 3D grid to produce the final static model. The model has been developed to assist with designing the experiment and conceptualising the shallow stratigraphy and fault structure at the Otway site. Dynamic modelling simulations based on the static model suggest that under certain scenarios it is possible that CO2 could migrate up the fault to the base of the Hanson Plain Sand if injected at approximately 30 m depth. This suggests that the planned fault injection experiment is feasible but additional data is required to validate the geological model and better constrain the modelling simulations.

The Pretty Hill Formation of the Otway Basin (Australia) has been studied as a natural analogue for geological storage of anthropogenic CO2 in order to examine the effects that CO2 concentration and reservoir heterogeneity have on CO2-related reactions. New petrographic data are presented, which validate the use of Hylogger™ as a tool to investigate high-resolution vertical changes in reservoir mineralogy. The integrated data set confirms earlier interpretations, showing that chlorite has been altered to kaolinite and siderite/ankerite in reservoir facies exposed to moderate and high CO2 concentrations, while chlorite remains the dominant clay mineral in all parts of the formation where CO2 content is low. Differences have been observed in the degree of CO2-related reaction relative to CO2 concentration and reservoir heterogeneity. Where CO2 content is very high (c. 98 mol%) and associated with high water saturations, both chlorite and detrital feldspars have undergone complete reaction in the reservoir facies, resulting in quartzose sandstones with a kaolinite matrix, and with siderite as the dominant carbonate precipitate. Conversely, where CO2 content is moderate (c. 29–57 mol%) and within the gas leg of the reservoir, chlorite has undergone significant reaction, but much of the original feldspar is preserved, suggesting relatively minor reaction. Carbonate cements from the moderate CO2 gas-leg comprise calcite, siderite and ankerite, occurring as cemented zones associated with rock heterogeneities and the present-day gas–water contact. Heterogeneities within the gas-leg are likely to have associated pore fluid contacts, whereby relatively high water saturations will be present in the fine-grained baffles and seals. The most advanced feldspar reaction occurs locally at the contact between baffles and reservoir rock, while reactions have been significantly impeded in the finer grained units due to their low permeabilities. Stable isotope data presented for carbonate cements analysed from wells with low and moderate CO2 levels show no clear distinction. Relatively early formed calcite has δ13C values that require an organic carbon source, suggesting precipitation unrelated to the reservoir CO2 in the Otway Basin. In contrast, diagenetically late calcite and siderite samples display two distinct δ13C groups (dependent on carbonate type), where the calculated fluid carbon isotope compositions are similar to documented magmatic CO2 reservoired in the nearby Caroline Field. This suggests that magma-derived CO2 may have been more prevalent through the Pretty Hill Formation than previously thought. Although the CO2 has not been contained over the long term in the low CO2 sites, it may have caused the local dissolution of carbonate and laumontite cement, and also contributed a source of carbon for late-stage calcite cements. These studies illustrate the importance of understanding both the reservoir composition and vertical heterogeneity of potential storage systems. Fluid–mineral reactions are likely to be advanced within stacked reservoir facies and impeded within siltstone layers, while the distribution of carbonate cement may increase the reservoir heterogeneity by the formation of cemented siltstone/sandstone layers, thereby creating impermeable barriers or baffles to CO2.

Given the prevailing use of saline reservoirs for geological CO 2 storage projects, limited data are available on the geochemical evolution of formation water chemistry during geological CO 2 storage in low-salinity formations. The low-salinity (total dissolved solids 2 storage, comprising three major siliciclastic formations with distinctly different mineral compositions. Contrasts in the geochemical responses of Jurassic sequence core samples have been identified during short-term CO 2 –water–rock experiments conducted under CO 2 storage conditions (Farquhar et al., in this issue). If persistent, such contrasts may serve as geochemical tracers of CO 2 migration within the Surat Basin. Here we use a combined batch experiment and numerical modeling approach to characterize the long-term response of the Jurassic succession to storage and migration of CO 2 and to assess reaction pathway sensitivity to CO 2 partial pressure. Reservoir system mineralogy was characterized for 66 core samples from Geological Survey of Queensland stratigraphic well Chinchilla 4, and six representative samples were powdered and reacted with synthetic formation water and high-purity CO 2 for up to 27 days at a range of pressures. Formation water alkalinity offers limited buffering at elevated CO 2 pressures and pH rapidly declines resulting in sustained enhancement of mineral dissolution rates. Batch reactor results exhibit regional groundwater-like 87 Sr/ 86 Sr values (0.7048–0.7066), less radiogenic than whole-rock results (> 0.7085) indicating incongruent dissolution of the reservoir matrix. Carbonate and authigenic clay dissolution are expected to be the primary reaction pathways regulating long-term formation water composition during geological CO 2 storage in the Surat Basin, with lesser contributions from dissolution of the clastic matrix.

At the Cooperative Research Centre for Greenhouse Gas Technology's (CO2CRC) field site in the Otway Basin of Victoria, Australia, investigations into the storage of CO2-rich gas in a depleted hydrocarbon gas field have been conducted in the Waarre C reservoir. The injected gas from the nearby Buttress field contained 75 mol% CO2, 21 mol% CH4 with the remaining balance being a mixture of wet hydrocarbons, condensate and nitrogen. Chemical tracers (sulphur hexafluoride, SF6; krypton, Kr; perdeuterated methane, CD4) were added on the basis of literature surveys and small volume trials at the Frio II Brine experiment in Texas. The aim of the project was to measure, monitor and verify the presence of injected CO2 in a depleted gas field and that the arrival of tracers was a major component of demonstrating breakthrough of CO2 at the monitoring well, Naylor-1. The paper focuses on methods developed for the injection, recovery and analysis of samples collected at the Naylor-1 well. Results of tracer analysis compare well with other data collected (including pH and density measurements) to demonstrate breakthrough. A slip-stream injection system was designed to deliver the tracers mixed with the CO2-rich gas into the subsurface at the CRC-1 well. The tracers were added to the gas stream 17 days after the start of injection (CO2 injection commenced 18th March, 2008) into the depleted natural gas field at Naylor. A U-tube system was used to retrieve the samples from the Naylor-1 monitoring well. Collected gas and formation water samples were analysed in detail for gas composition, tracers, isotopes (13C CO2 mainly) and inorganic geochemistry for the broader project. The tracer results confirm that CO2 breakthrough at the monitoring well occurred within the predicted times. However the interval between samples taken from the U-tubes was too coarse to resolve detailed differences in arrival times between the CO2 and tracers. Of the three tracers used, SF6 provided the clearest evidence of breakthrough at U-tube 2. Kr, because of its abundance in air, and its potential to be present in the subsurface, was more prone to contamination and had higher background levels prior to breakthrough. CD4 was expected to provide some more unique data based on the presence of abundant CH4 in the reservoir interval. With hindsight, larger volumes should have been injected to facilitate comparisons with the other tracers and add value to the data set. The test of CD4 however acted as a suitable proof of concept that CD4 could be used in such a high background of CH4. Further work is ongoing to generate data for partition coefficients between supercritical CO2, CH4 and water under the injection conditions.

Soil gas baseline and assurance monitoring was performed over the CO2CRC Otway Project demonstration site for six years (2007–2012). The main objective of the monitoring was assurance monitoring, to demonstrate to regulators that there were no adverse environmental impacts on soils. The use of the method for leakage detection was also of research interest. Soil gas sampling was carried out annually over a defined grid, in preparation for and during the experimental storage of 65,000 tonnes of carbon dioxide (CO2) into the Waarre C Formation at a depth of about 2 km. CO2, methane, oxygen and nitrogen were the main gases analysed. Advanced analytics included helium and δ C CO 2 13 measurements. Baseline monitoring allowed us to develop an understanding of the local variability in soil gas CO2 concentrations in anticipation of the CO2 injection. Interpretation of the concentrations of CO2 in terms of possible leakage rates (fluxes) is not possible without more detailed models and measurements of the possible transport mechanisms of CO2 to and through the vadose zone. However, the comparison of post-injection with baseline data, the examination of fixed gas relationships and C/ 13 C CO 2 12 isotopes showed that most CO2 in the soil was of biogenic origin. A deep subsurface source, which would indicate deep gas migration to the surface, was not apparent. This shows that there is little impact of the injected CO2 on the local ecosystem and, in conjunction with other monitoring data, helps to satisfy our regulatory requirements. Our work is a case study of a practical soil gas monitoring programme and illustrates both the utility and the limitations of the technique.

The CO 2 CRC Otway Project Stage 2B field test was a residual CO 2 saturation and dissolution experiment carried out on the Paaratte Formation in the Otway Basin of Australia. During the 87 day test a downhole U-tube sampling assembly was used to collect formation water samples at various time intervals. The waters were analysed for chemical composition, dissolved gas content and stable isotopic composition of H and O. Changes in the chemical and isotopic composition of the formation water were observed from the initial baseline samples collected through to the conclusion of the test. Systematic reoccurrences of relatively large linear changes in the alkalinity, Ca 2+ , Fe 2+ , Mg 2+ and SiO2(aq) were observed during different test sequences. Similar behaviour occurred for the δ 18 O and δ 2 H values suggesting a complex system controlled by at least two processes. The chemical evolution was consistent with CO 2 -water-rock interactions, dominated by carbonate dissolution with some silicate dissolution. The mineral dissolution driven changes in water composition are overlain by what was clearly mixing of the injected and in situ formation water. The isotopic composition of the water was used to confirm the role of mixing and the calculated residual gas saturation values were broadly consistent with those derived by other methods. The extent of reaction in the relatively short time frame of the test was used to evaluate the capabilities of kinetics based reaction path models. The models were generated using published reaction rate data with commonly used assumptions regarding upscaling of reactive surface area. These assumptions consist of reducing the calculated geometric surface area that accounts for grain shape and roughness by factors of 100 to 1000 depending on the mineral habit. The numerical models provided a very good fit to the field data indicating that the rate data and the associated assumptions are relatively robust.

The successful commercial scale deployment of carbon capture and storage (CCS) requires assurance of the confinement of the injected CO 2 at each potential storage site. The critical elements of the confinement of CO 2 are the caprock overlying the storage formation, and any faults or fractures which occur within the caprock. The most significant aspect of containment is the seal potential of the caprock, defined as the seal capacity, seal geometry and seal integrity. The seal capacity refers to the CO 2 column height that the caprock can retain before capillary forces allow the migration of the CO 2 into and possibly through the caprock. Determination of capacity is achieved primarily through petrophysical analyses such as mercury injection capillary pressure (MICP) tests. For storage in depleted fields, assessments of seal capacity can be made from empirical observations of actual hydrocarbon column heights and converting these to CO 2 physical properties (density, temperature, pressure). Where these data sources are unavailable, the use of analogs can be a viable alternative. Seal geometry refers to the thickness and lateral extent of the caprock. The caprock must have sufficient lateral extent to cover whatever structural, stratigraphic or hydrodynamic storage reservoir in which the CO 2 is trapped. In addition, its thickness should exceed the throw of any faults that cut so as to maintain an effective barrier despite faults through it. Seal geometry is evaluated through well data (stratigraphic, sedimentological and wireline log analyses) and seismic surveys, which are pre-requisites to any viable storage project. Seal integrity refers to the geomechanical properties of the caprock. These properties are controlled by caprock mineralogy, regional and local stress fields as well as any stress changes induced by injection or withdrawal of water or CO 2 . The modification of the stress field within a storage formation during and after injection of CO 2 can lead to reservoir and caprock mechanical failure. This failure can result in the generation of new faults and fractures, reactivation of existing faults and/or bedding parallel slip. The key parameters determining whether faults might act as conduits or as seals are the juxtaposition relationships of rocks on either side of a fault plane, the properties of the fault zone itself or the reactivation potential of the fault. The greatest likelihood of fluid migration up faults is during or immediately after reactivation. Thus, the mere existence of faults does not automatically rule out a site for geological storage of carbon dioxide. On the contrary, sealing faults commonly trap hydrocarbons and compartmentalize oil and gas reservoirs and could also form suitable confining barriers at CO 2 storage sites. Seal capacity, geometry and integrity interpretations must be tempered by the potential geochemical reactions between fluids and rocks and injected CO 2 as well as by the hydrodynamic environment above and below the seal which may modify the calculated pressure regimes.

Twelve clastic core samples from the Walloon Coal Measures, Surat Basin were tested for disintegration in artificially produced fluids varying in ionic strength. XRD data confirm the presence of smectite (water sensitive clay) in the samples. Flow-through rock disintegration experiments demonstrate that the higher the concentration of smectite and soluble plagioclase is, the quicker rock disintegrates in artificial low ionic strength fluid. Pre-soaking of rocks with high ionic strength fluid reduces rock disintegration rate in low ionic strength fluids. This is explained by very strong clay-clay and clay-sand attraction forces, evidenced through zeta-potential measurements, which inhibit rock degradation. For the studied samples it is clear that rock disintegration rate is proportional to fluid velocity. Experimental rock disintegration data are fitted by a power erosion model with two adjusted parameters: fluid ionic strength and Reynolds number. The experimental results satisfactorily agree with theoretical data. Rock disintegration rates are calculated as released particle volume per thickness of interburden layer per day at a fixed Reynolds number and low ionic strength. The laboratory work suggests that keeping wells under strong ionic fluid during shut-in times and a reduction of water production rate will preserve rock integrity for a longer period of time.

A four-stage soil gas monitoring study was conducted from March 2007 to March 2010 in the western Port Campbell Embayment of the onshore Otway Basin, SE Australia. This study evaluated existing vadose zone soil gases over the CO2CRC Otway Project’s site for CO2 storage, and nearby deep natural CO2 accumulations. Carbon dioxide, methane and helium were the main gases analysed and much of the time CH4 concentrations were too low for accurate analysis. Carbon dioxide concentrations ranged from atmospheric background levels of 0.033% up to about 10% of the total soil gas. The δ13CCO2 values are typical for organic matter decomposition as the main source of the CO2 in the soil gas. Modern radiocarbon ages, determined from 14C analysis, and low helium concentrations support the conclusion that CO2 in the soil gas is predominantly from modern organic sources. There was a relative increase in CO2 concentration measured in locations where the Port Campbell Limestone is near the ground surface, which implies additional CO2 has been produced from the weathering of limestone.

Two volcanic ash layer dominated marine gravity cores were recovered during research cruise RV Sonne 173/3 along the Pacific margin offshore Nicaragua. Thick ash layers dominate the recovered sediments. Pore water samples of these – one incoming plate and one slope site – sediment cores have been analysed for light rare earth elements, alkalinity, sulphate, phosphate, ammonia, calcium, and manganese contents. The data provide a systematic look at changes in REE during diagenesis proceeding from open ocean sediments to highly reducing near-shore sediments. The pore water patterns of all the dissolved species mentioned above suggest that volcanic glass alteration constitutes a major source for REE release in marine sediments when low rates of anaerobic degradation of organic matter, like typical for incoming plate/open ocean sediments, prevail. Under these conditions the release of REE results in fluxes of at least 0.04 nmol La cm− 2 yr− 1 and 0.09 nmol Ce cm− 2 yr− 1.

The research of fluids in the earth's crust is greatly benefiting from methodological (analytical) and experimental advances and the rapid development of increasingly powerful numerical modelling systems. New experimental data continuously refine the accuracy of numerical models aiming to quantitatively reconstruct geological processes. Geological modelling programs have moved on from linear or 2-dimensional approaches to integrating 3 or 4D geology with geothermal aspects, fluids flow and reactive transport processes into complex, quantitative scenarios. These combinations of refinement of the data base and advances in computational capacities are the stepping stones for the development of the predictive quality of mineralising models and hydrocarbon migration and accumulation, access to geothermal energy and the sequestration of CO 2 . This special issue presents a selection of contributions on “Fluids in Geological Processes” following the VIth GEOFLUIDS meeting in Adelaide in 2009, emphasizing on recent developments in the different research trends in this field.

The Otway Project in Victoria, Australia, run by the Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) began injecting gas (80% CO2: 20% CH4) in a supercritical state in April, 2008. It has been labeled with tracers (SF6, Kr and CD4) added via a purpose built slip-stream injector to unequivocally allow verification of the presence of the injected CO2 at various monitoring sites. A bottom-hole assembly installed in the Naylor-1 monitoring well enables multi-level sampling of fluids at reservoir pressure to allow the determination of hydrological and geochemical processes that control plume movement and water-rock- CO2 interactions in the subsurface.

This study focuses on the Carboniferous sediments of the Karawanken Mountains (Austria/Slovenia) to identify possible source areas and their geotectonic setting. Provenance analyses have been applied using petrographical and geochemical approaches what also lead to an evaluation of the used methods. Within the Hochwipfel Formation five stratigraphic related petrofacies groups can be defined using the sandstone component inventory. Homogenous provenance results based on major element and trace element data suggest an active continental margin/continental island arc with probably an intraplate signature. Provenance analyses of light minerals point to source areas with basement rocks (mainly metamorphic), arc material and sedimentary rocks. In combination, the rapid and highly variable change of provenance signatures within the stratigraphic succession of the petrofacies types excludes a single provenance in the western part of the Karawanken Mountains. Additionally, changes in composition of the individual petrofacies groups correlate with the stratigraphy in the eastern part. Varying contents of garnet, chromite, hornblende and epidote, within the sedimentary succession of the Hochwipfel sandstones, can partly be attributed to geodynamical changes in the hinterland. The chemical compositions of garnets, tourmalines, and chromites, confirm the results of both geochemistry and sediment petrography. In a quantitative approach based on petrography we can see an equal mixture of all source areas, whereas quantification with a geochemical approach results in c. 11% of material that can be attributed to a passive continental margin source, 28 to 37% to an active continental margin, c. 44% to a magmatic arc setting and 16 to 19% to an oceanic within-plate source area. The resulting model for the geodynamical setting of the Hochwipfel basin during the Late Palaeozoic can be best explained by a forearc basin in the eastern part and various pull-apart basins in the western part, connected through bypasses, at the continental margin of Gondwana and the Palaeotethys. As an additional outcome this study clarifies, that geochemically derived provenance results, based on bulk-rock and mineral composition, recognize best complex geodynamical settings and a mixture of sources since they incorporate best the provenance significant lithic components. On the other hand it points out that an application of additional petrological approaches does not necessarily lead to further information and an elimination of errors but could be essential to define general information of the investigated stratigraphy, like the correlation of deposits with stratigraphy (petrofacies groups).

Surface ocean iron (Fe) fertilization can affect the marine primary productivity (MPP), thereby impacting on CO2 exchanges at the atmosphere-ocean interface and eventually on climate. Mineral (aeolian or desert) dust is known to be a major atmospheric source for the surface ocean biogeochemical iron cycle, but the significance of volcanic ash is poorly constrained. We present the results of geochemical experiments aimed at determining the rapid release of Fe upon contact of pristine volcanic ash with seawater, mimicking their dry deposition into the surface ocean. Our data show that volcanic ash from both subduction zone and hot spot volcanoes (n = 44 samples) rapidly mobilized significant amounts of soluble Fe into seawater (35–340 nmol/g ash), with a suggested global mean of 200 ± 50 nmol Fe/g ash. These values are comparable to the range for desert dust in experiments at seawater pH (10–125 nmol Fe/g dust) presented in the literature (Guieu et al., 1996; Spokes et al., 1996). Combining our new Fe release data with the calculated ash flux from a selected major eruption into the ocean as a case study demonstrates that single volcanic eruptions have the potential to significantly increase the surface ocean Fe concentration within an ash fallout area. We also constrain the long-term (millennial-scale) airborne volcanic ash and mineral dust Fe flux into the Pacific Ocean by merging the Fe release data with geological flux estimates. These show that the input of volcanic ash into the Pacific Ocean (128–221 × 1015 g/ka) is within the same order of magnitude as the mineral dust input (39–519 × 1015 g/ka) (Mahowald et al., 2005). From the similarity in both Fe release and particle flux follows that the flux of soluble Fe related to the dry deposition of volcanic ash (3–75 × 109 mol/ka) is comparable to that of mineral dust (1–65 × 109 mol/ka). Our study therefore suggests that airborne volcanic ash is an important but hitherto underestimated atmospheric source for the Pacific surface ocean biogeochemical iron cycle.

This review covers the early diagenesis of the various types of deep-sea sediments. It uses pore-water profiles as a sensitive tool to gain insight in diagenetic processes, to depict the mineral reactions associated with the changes in the pore-water chemistry and to group deep-sea sediments into a limited number of diagenetic classes. In doing so, a sequence is followed from the simplest diagenetic systems encountered in pelagic sediments on the ocean crust with pore-water profiles lacking chemical gradients to the most highly reactive organic-matter rich sediments on the continental margins at the oxygen-minimum zone. Pore-water profiles are characteristic of specific sediment types only if they are reaction-controlled. In advection- and/or diffusion-dominated profiles, fluid-chemistry related to the nature of the host sediment is overprinted by ions derived from external sources. Advection and diffusion-dominated profiles are treated at the beginning of the chapter. The simplest type of pelagic sediment in terms of diagenesis and the first to be covered is the brown abyssal clay on the deep ocean floor below the calcite compensation level. The review of the early diagenesis of biogenic siliceous oozes which follows covers a wide range of topics from pore-water chemistry to burial-diagenetic stages, characteristics of the solid silica phases, nature of the conversion mechanisms and their interpretation in terms of Ostwald processes, crystallographic structural changes of opal-CT and quartz during progressive burial, rate-controlling factors of the diagenetic reactions, the formation of bedded chert and the physical diagenesis of biogenic siliceous deep-sea sediments. The next topic is the early diagenesis of biogenic pelagic carbonates which is characterized by recrystallization involving (pressure) solution and reprecipitation leading to the formation of chalk. It is accompanied by a marked redistribution of strontium isotopes in the pore waters. Rhythmic limestone/marlstone alternations are generally attributed to Milankovitch palaeoclimate cycles but may also be accentuated or even originate during burial diagenesis. For hemipelagic sediments the oxidation of organic matter becomes the driving force of diagenetic reactions. During early diagenesis the organic-matter of the sediments is decomposed mostly by bacteria. Microbial organic-matter oxidation is accomplished by five different oxidant-specific populations of bacteria (aerobic bacteria, nitrogen reducers, sulphate reducers, carbonate reducers or methanogens, and fermenters) that follow one another during burial in the order of decreasing energy efficiency of their metabolic reactions and give rise to the vertical sequence of organic-matter decomposition zones comprising (1) the oxidation zone, (2) the nitrate-reduction zone, (3) the sulphate-reduction zone, (4) the carbonate-reduction zone, and (5) the fermentation zone. The latter is followed by (6) the thermocatalytic decarboxylation zone. The oxidation zone corresponds to what is called ‘oxic diagenesis’, the nitrate-reduction zone to ‘suboxic diagenesis’, and the top of the sulphate-reduction zone to the top of ‘anoxic diagenesis’. The brown abyssal clay which is almost free of organic matter essentially remains in the oxidation zone during burial. A typical representative of suboxic diagenesis are manganese nodules and crusts, as are glauconitic sediments. Phosphorites are diagenetic in origin and frequently occur together with glauconite. Anoxic diagenesis in organic-matter rich hemipelagic sediments leads to the formation of gas-hydrates, if the water depth (i.e. pressure) is sufficient. Euxinic sediments are hemipelagic sediments undergoing anoxic diagenesis in stagnant basins under oxygen-free bottom water. Evaporite dissolution in the subsurface gives rise to a specific pore-water type, as does hydrothermal activity and the intrusion of igneous dykes and sills above sediment-covered mid-ocean ridges. Active margins affected by advective lateral fluid flow show typical step-curves of their pore-water profiles. Highly reactive volcanogenic sediments produce their own pore-water anomalies. A major section is devoted to early diagenetic mineralization reactions in anoxic deep-water sediments covering sulphide precipitation, authigenic carbonates (calcite, siderite, organogenic dolomite, complex authigenic carbonates) and barite. The final section deals with early diagenetic clay mineral formation.

[1] Sediment gravity cores collected on the Pacific slope and incoming plate offshore Central America reach up to 400 ka back in time and contain numerous ash layers from plinian eruptions at the Central American Volcanic Arc. The compositionally distinct widespread ash layers form a framework of marker horizons that allow us to stratigraphically correlate the sediment successions along and across the Middle America Trench. Moreover, ash layers correlated with 26 known eruptions on land provide absolute time lines through these successions. Having demonstrated the correlations in part 1, we here investigate implications for submarine sedimentary processes. Average accumulation rates of pelagic sediment packages constrained by bracketing tephras of known age range from ∼1–6 cm/ka on the incoming plate to 30–40 cm/ka on the continental slope. There are time intervals in which the apparent pelagic sedimentation rates significantly vary laterally both on the forearc and on the incoming plate where steady conditions are usually expected. A period of unsteadiness at 17–25 ka on the forearc coincides with a period of intense erosion on land probably triggered by tectonic processes. Unsteady conditions on the incoming plate are attributed to bend faulting across the outer rise triggering erosion and resedimentation. Extremely low apparent sedimentation rates at time intervals >50–80 ka suggest stronger tectonic activity than during younger times and indicate bend faulting is unsteady on a longer timescale. Submarine landslides are often associated with ash layers forming structurally weak zones used for detachment. Ash beds constrain ages of >60 ka, ∼19 ka, and

We collected 56 marine gravity cores from the Pacific seafloor offshore Central America which contain a total of 213 volcanic ash beds. Ash-layer correlations between cores and with their parental tephras on land use stratigraphic, lithologic, and compositional criteria. In particular, we make use of our newly built database of bulk-rock, mineral, and glass major and trace element compositions of plinian and similarly widespread tephras erupted since the Pleistocene along the Central American Volcanic Arc. We thus identify the distal ashes of 11 Nicaraguan, 8 El Salvadorian, 6 Guatemalan, and 1 Costa Rican eruptions. Relatively uniform pelagic sedimentation rates allow us to determine ages of 10 previously undated tephras by their relative position between ash layers of known age. Linking the marine and terrestrial records yields a tephrostratigraphic framework for the Central American volcanic arc from Costa Rica to Guatemala. This is a useful tool and prerequisite to understand the evolution of volcanism at a whole-arc scale.

This extended abstract summarises the objectives of a research project that will provide insight into hydrocarbon generation and accumulation in continuous-source reservoirs and how to best exploit such unconventional resources in Australia, specifically in the Cooper Basin. It compares and contrasts a productive shale from the US—the Bakken Formation—with shales from the Cooper Basin. Unconventional resources, such as the Devonian-Mississippian Bakken Formation, have been assumed to be continuous source-reservoirs where the oil is generated from organic-rich shales with minimal migration. It is possible, however, that the shale intervals are a waste zone (a leaked seal). These waste zones form when the buoyancy pressure of the hydrocarbon exceeds the capillary forces in the seal, resulting in tertiary migration. Oil saturation values strongly correlate with the hydrocarbon content parameter (S1/TOC) from Rock-Eval. Values of 120 mgHC/gC are typically indicative of non-indigenous or migrated hydrocarbons (reservoirs or leaked seals). Mercury injection capillary pressure (MICP) analysis of core samples can also diagnose whether a shale is a source or a seal. Organic shales with high capillary entry pressures generally have low hydrocarbon content, in line with in-situ generation; shales with low entry pressures have comparatively higher hydrocarbon content and indicate migration from an underlying accumulation. Once these waste zones are identified on a basin-scale, specific samples from the Bakken Formation will be analysed using micro-scale sealed vessel pyrolysis, combined with monitoring of the biomarkers and other organic compounds using mass spectrometry. As the composition of organic compounds is altered during migration, this will confirm whether they are generated locally or migrated.

Copyright © 2009 Elsevier B.V. All rights reserved. ScienceDirect® is a registered trademark of Elsevier B.V. Abstract of GEOFLUIDS VI., GEOFLUIDS VI. Sixth International Conference on Fluid Evolution, Migration and Interaction in Sedimentary Basins and Orogenic Belts Conference on Fluid Evolution, Migration and Interaction in Sedimentary Basins and Orogenic Belts

The CO2CRC Otway Project is an Australian-first, demonstration-scale CO2 geosequestration experiment. It incorporates a wide-ranging monitoring and verification operation, including the injection of chemical tracers and the geochemical characterisation of the subsurface fluids sampled from the Naylor—1 monitoring well multi-zone U-tube system. Following the successful collection of baseline gas and fluid samples, injection began in April 2008 and by September 2008 over 20,000 tonnes of the projected total of ∼100,000 tonnes of supercritical CO2 has been injected into the depleted Waarre C unit of the Naylor gas reservoir in the Otway Basin. Critical operational issues revolved around the timing of the chemical tracer injection at the CRC—1 injection well and the on-going maintenance and modifications to the U-tube sampling assembly. The latter resulted from two things:a hazard and operability study (HAZOP), which specifically addressed the continued integrity of the U-tube assembly and the safe collection and disposal of pressurised gases and formation waters, and the need for an innovative solution to mitigate against hydrocarbon wax precipitaton inside the U-tubes that would have jeopardise retrieval of sub-surface samples. A solvent delivery and retrieval system involving Solvesso—100TM was deployed following a mini-HAZOP. Breakthrough was initially confirmed by tracer detection at Naylor—1 approximately four months after injection began, whereas changes in the inorganic geochemical signatures were observed a few weeks later. This has validated the sub-surface monitoring strategy and resulted in refinements to fluid flow models and expanded our understanding of geochemical processes. Furthermore, supercritical CO2 injection has resulted in the lowering of the gas-water contact at Naylor—1 and the progressive gassing out of the deeper U-tubes. Weekly to fortnightly U-tube sampling will continue until supercritical CO2 is established at Naylor—1 following which the frequency of sampling will be reviewed for the rest of the injection period.

Geoscience Australia and the CO 2 CRC operate a greenhouse gas controlled release facility at an experimental agricultural station maintained by CSIRO Plant Industry in Canberra, Australia. The facility is designed to simulate surface emissions of CO 2 and other greenhouse gases from the soil into the atmosphere. Over 10 different near surface monitoring techniques were trialled at the Ginninderra controlled release site during 2012-2013. These included soil gas, soil CO 2 flux, soil analysis, eddy covariance, CO 2 laser, noble gas tracers, airborne hyperspectral, in-field phenotyping (thermal, hyperspectral and 3D imaging), and microbial soil genomics. Result highlights are presented. Different climatic conditions for the early 2012 release experiment (wet) and late 2013 release experiment (dry) resulted in markedly different sub-surface plume behaviour and surface expression of CO 2 . The differences between the years are attributed to changes in groundwater levels and drier conditions leading to a larger vadose zone during the 2013 experiment.

Residual CO 2 trapping (Sgr-CO 2 ) is a key mechanism for geological CO 2 storage. The CO2CRC undertook a sequence of field tests with the aim of comparing different ways of determining Sgr-CO 2 including a dissolution test. Dissolution test results show an unexpectedly early breakthrough and low maximum CO 2 concentrations in the back- produced water making the data inconclusive when using traditional data interpretation. Here, we consider two conditions to explain the observations: Firstly, residual CO 2 is vertically unevenly distributed and, secondly, the fluid and residual CO 2 are not in equilibrium. Furthermore, we postulate localised flow channels have formed during the 3- month test period caused by advective flow of CO 2 -saturated, low pH water leading to transport-controlled mineral dissolution.

The new method to assess permeability damage in geothermal reservoirs and predict well productivity decline is presented. The laboratory methodology developed aims to determine permeability decline from mobilisation, migration and straining of natural reservoir fines. Laboratory coreflood testing with constant and stepwise decreasing ionic strength has been performed with measurements of the pressure drop along the core and accumulated effluent particle concentration. Stabilisation of rock permeability occurs after injection of numerous pore volumes, suggesting slow drift of mobilised particles if compared with the carrier water velocity. Low ionic strength water increases electrostatic repulsion forces between clay particles and sand grain surfaces, further mobilising particles and resulting in formation damage. Kaolinite and illite/chlorite mixed layer clay minerals are identified by SEM-EDAX analysis and are the minerals primarily responsible for the permeability damage. The competitive effects of decreasing water viscosity and weakening electrostatic attraction on the attached particle concentration during temperature increase have been observed. The micro-modeling of the fine particle mechanical equilibrium shows that the water viscosity effect on the fine particle attachment dominates. It results in decreased fines detachment and permeability decline at high temperatures.