regional variability in the frequency and magnitude of large explosive volcanic eruptions quantifying the frequency at which volcanic eruptions of different size occurs is impor tant for hazard assessment volcanic records can be used to estimate the recurrence rate of large magnitude eruptions magnitude 4 but recording biases that impact data complete ness complicate analysis to overcome these biases we conceptualize the volcanic record as a series of individual and unique time series associated by a common behavior thus we approach issues of completeness on a volcano by volcano basis and use a hierarchical bayes ian approach to characterize the common frequency magnitude f m behavior for different groups of volcanoes we identify variations in the f m relationship between different volcano types and between different volcanic arcs by accounting for systematic under recording in the volcanic record we also calculate the global recurrence rates for large magnitude erup tions during the holocene which are similar to previous estimates however higher recur rence rates for smaller magnitude events are observed which is a result of our adjustments for data completeness quantifying how the f m relationship varies between different groups of volcanoes provides an opportunity to understand how the tectonic setting in uences f m behavior which is important to quantify long term regional volcanic hazard

reservoir characteristics and their effects on hydrocarbon accumulation in lacustrine turbidites in the jiyang super depression bohai bay basin china abstract a great difference exists between the hydrocarbon charging characteristics of different tertiary lacustrine turbidites in the jiyang super depression of the bohai bay basin east china based on wireline log data core observation and thin section analyses this study presents detailed reservoir property data and their controlling effects from several case studies and discusses the geological factors that govern the hydrocarbon accumulation in turbidite reservoirs the lacustrine fluxoturbidite bodies investigated are typically distributed in an area of 0 5 10 km2 with a thickness of 5 20 m the sandstones of the tertiary turbidites in the jiyang super depression have been strongly altered diagenetically by mechanical compaction cementation and mineral dissolution the effect of compaction caused the porosity to decrease drastically with the burial depths especially during the early diagenesis when the porosity was reduced by over 15 the effect of cementation and mineral dissolution during the late stage diagenesis is dominated by carbonate cementation in sandstones high carbonate cement content is usually associated with low porosity and permeability carbonate dissolution secondary porosity zone and primary calcite dissolution is believed to be related to thermal maturation of organic matter and clay mineral reactions in the surrounding shales and mudstone two stages of carbonate cementation were identified the precipitation from pore water during sedimentation and secondary precipitation in sandstones from the organic acid dissolved carbonate minerals from source rocks petrophysical properties have controlled hydrocarbon accumulation in turbidite sandstones high porosity and permeability sandstones have high oil saturation and are excellent producing reservoirs it is also noticed that interstitial matter content affects the oil bearing property to some degree there are three essential elements for high oil bearing turbidite reservoirs excellent pore types low carbonate cement 15 and average permeability 10 md

how porosity and permeability vary spatially with grain size sorting cement volume and mineral dissolution in fluvial triassic sandstones the value of geostatistics and local regression although it is well known that sandstone porosity and permeability are controlled by a range of parameters such as grain size and sorting amount type and location of diagenetic cements extent and type of compaction and the generation of intergranular and intragranular secondary porosity it is less constrained how these controlling parameters link up in rock volumes within and between beds and how they spatially interact to determine porosity and permeability to address these unknowns this study examined triassic fluvial sandstone outcrops from the uk using field logging probe permeametry of 200 points and sampling at 100 points on a gridded rock surface these field observations were supplemented by laser particle size analysis thin section point count analysis of primary and diagenetic mineralogy quantitative xrd mineral analysis and sem edax analysis of all 100 samples these data were analyzed using global regression variography kriging conditional simulation and geographically weighted regression to examine the spatial relationships between porosity and permeability and their potential controls the results of bivariate analysis global regression of the entire outcrop dataset indicate only a weak correlation between both permeability porosity and their diagenetic and depositional controls and provide very limited information on the role of primary textural structures such as grain size and sorting subdividing the dataset further by bedding unit revealed details of more local controls on porosity and permeability an alternative geostatistical approach combined with a local modeling technique geographically weighted regression gwr subsequently was used to examine the spatial variability of porosity and permeability and their controls the use of gwr does not require prior knowledge of divisions between bedding units but the results from gwr broadly concur with results of regression analysis by bedding unit and provide much greater clarity of how porosity and permeability and their controls vary laterally and vertically the close relationship between depositional lithofacies in each bed diagenesis permeability and porosity demonstrates that each influences the other and in turn how understanding of reservoir properties is enhanced by integration of paleoenvironmental reconstruction stratigraphy mineralogy and geostatistics

sandstone diagenesis and reservoir quality prediction models myths and reality models and concepts of sandstone diagenesis developed over the past two decades are currently employed with variable success to predict reservoir quality in hydrocarbon exploration not all of these are equally supported by quantitative data observations and rigorous hypothesis testing simple plots of sandstone porosity versus extrinsic parameters such as current subsurface depth or temperature are commonly extrapolated but rarely yield accurate predictions for lithified sandstones calibrated numerical models that simulate compaction and quartz cementation when linked to basin models have proven successful in predicting sandstone porosity and permeability where sufficient analog information regarding sandstone texture composition and quartz surface area is available analysis of global regional and local data sets indicates the following regarding contemporary diagenetic models used to predict reservoir quality 1 the effectiveness of grain coatings on quartz grains e g chlorite microquartz as an inhibitor of quartz cementation is supported by abundant empirical data and recent experimental results 2 vertical effective stress although a fundamental factor in compaction cannot be used alone as an accurate predictor of porosity for lithified sandstones 3 secondary porosity related to dissolution of framework grains and or cements is most commonly volumetrically minor 2 exceptions are rare and not easily predicted with current models 4 the hypothesis and widely held belief that hydrocarbon pore fluids suppress porosity loss due to quartz cementation is not supported by detailed data and does not represent a viable predictive model 5 heat flow perturbations associated with allochthonous salt bodies can result in suppressed thermal exposure thereby slowing the rate of quartz cementation in some subsalt sands

sandstone porosity as a function of thermal maturity sandstone porosity decreases in the subsurface as a power function of thermal maturity phi a m sup b where phi is porosity and m is a measure of thermal maturity representing integrated time temperature history a and b are constants for a given sandstone of homogeneous properties but vary between data sets the commonly observed exponential dependence of sandstone porosity upon depth follows as a special case from this power function relation when temperature increases linearly with depth the consideration of sandstone porosity in terms of time temperature exposure offers advantages in the comparison of porosity data from diverse geologic settings the recognition of unusual porosity within a sandstone sequence and the prediction of porosity ahead of the drill and at times in the geologic past

facies related diagenesis and multiphase siderite cementation and dissolution in the reservoir sandstones of the khatatba formation egypt s western desert in the fluvio deltaic quartz arenitic sandstones of the jurassic khatatba formation in the salam field egypt9s western desert diagenesis and sedimentary facies control reservoir quality fluvial channel sandstones have the highest porosities 10 15 and permeabilities 100 600 md in part because of siderite cementation which 1 inhibited compaction and quartz cement and 2 was later dissolved creating intergranular secondary porosity 1 4 of total porosity fluvial crevasse splay and marine sandstones have the lowest reservoir quality because of an abundance of depositional kaolin matrix and pervasive shallow burial fe dolomite cement respectively siderite precipitation was multiphase and separated by distinct dissolution events the earliest siderite precipitated near surface within suboxic tropical coastal swamps containing predominantly meteoric waters some influence of marine waters is indicated by local enrichments in mg and ca the next major siderite generation shows a trend to decreasing mn and ca contents and is of shallow burial origin the last major siderite phase is mg rich and interpreted as deeper burial in origin some dissolution occurred during shallow burial related to climatically controlled meteoric water fluxing under unconformities the most important dissolution however occurred during deep burial resulting in 1 a major corrosion surface predating the last mg rich zone 2 selective dissolution of some earlier zones and 3 secondary porosity this burial dissolution is interpreted to have been caused by cooling of compactional waters expelled from the basin along major faults other diagenetic phases observed include early diagenetic pyrite kaolin quartz bitumen and late diagenetic barite and illite kaolinite precipitated at shallow depths 130 c during and or after rapid late cretaceous burial quartz developed in two phases separated by oil migration this paper illustrates that in fluvio deltaic quartz arenites deposited under the influence of humid tropical climate reservoir quality can be largely controlled by the contrasting pathways of carbonate diagenesis followed by the different sedimentary facies this paper also documents a case in which siderite dissolution generated significant secondary porosity in reservoir sandstones and where both siderite cementation and dissolution took place in multiple phases during different diagenetic stages including early shallow burial and deep burial diagenesis the present study also shows that in multiphase siderite cements the earlier growth zones can be selectively dissolved and replaced by later siderite zones i e recrystallized during burial diagenesis these findings contrast with the general thought that siderite cements are not susceptible to generation of significant secondary porosity by dissolution and that earlier formed siderites are essentially stable during diagenesis

geochemistry of trace elements in coals from the zhuji mine huainan coalfield anhui china the abundances of nine major elements and thirty eight trace elements in 520 samples of low sulfur coals from the zhuji mine huainan coalfield anhui china were determined samples were mainly collected from 10 minable coal seams of 29 boreholes during exploration the b content in coals shows that the influence of brackish water decreased toward the top of coal seams marine transgression and regression occurred frequently in the lower shihezi formation a wide range of elemental abundances is found weighted means of na k fe p be b co ni cr se sb ba and bi abundances in zhuji coals are higher and the remainder elements are either lower or equal to the average values of elements in coals of northern china compared to the chinese coals the zhuji coals are higher in na k be b cr co se sn sb and bi but lower in ti p li v and zn the zhuji coals are lower only in s p v and zn than average u s and world coals potassium mg ca mn sr as se sb and light rare earth elements lree had a tendency to be enriched in thicker coal seams whereas fe ti p v co ni y mo pb and heavy rare earth elements hree were inclined to concentrate in thinner coal seams the enrichment of some elements in the shanxi or upper shihezi formations is related to their depositional environments the elements are classified into three groups based on their stratigraphic distributions from coal seams 3 to 11 2 and the characteristics of each group are discussed lateral distributions of selected elements are also investigated the correlation coefficients of elemental abundances with ash content show that the elements may be classified into four groups related to modes of occurrence of these elements

diagenesis and reservoir quality evolution of incised valley sandstones evidence from the abu madi gas reservoirs upper miocene the nile delta basin egypt abstract elucidation of the distribution of diagenetic alterations in incised valley sandstones within a sequence stratigraphic framework allows a better understanding of their reservoir quality evolution during burial gas reservoirs of the upper miocene abu madi formation present day depth 3350 m temperature 116 the nile delta basin egypt consist of lowstand systems tract lst fluvial and transgressive systems tract tst estuarine sandstones deposited in an incised valley these sandstones have a wide range of porosity 2 to 29 and permeability 0 01 to 6071 md which reflect both depositional facies and diagenetic controls diagenetic events that influenced the reservoir quality evolution include mainly the formation of extensive grain rimming fe mg chlorite mechanical compaction of ductile grains pressure dissolution of quartz and quartz cementation the chlorite rims distributions of which are not clearly related to sequence stratigraphy have preserved reservoir quality by inhibiting quartz cementation but have increased microporosity values in the reservoirs calcite cementation 18o 13 5 to 6 0 13c 14 3 to 1 0 and 87sr 86sr 0 707124 to 0 708181 has not influenced the overall reservoir quality evolution of the sandstones because of its localized occurrence other diagenetic events that have little influence on reservoir quality include the more frequent formation of kaolin in the lst fluvial sandstones and formation of pyrite in the tst estuarine sandstones this study demonstrates the possibility of constraining and evaluating the impact of diagenetic alterations on reservoir quality evolution in incised valley deposits and their sequence stratigraphic distribution and thus has an important impact on hydrocarbon exploration in such settings

sandstone reservoir quality prediction the state of the art joanna ajdukiewicz joined exxon production research company in 1980 she was reservoir quality assessment and prediction team lead there from 1991 to 1995 and at imperial oil research centre in calgary from 1995 to 1997 subsequently she has worked a variety of exploration company assignments in the north sea gulf of mexico and middle east her current interests are in predicting the distribution of early diagenetic controls on deep reservoir quality rob lander develops diagenetic models for geocosm llc he obtained his ph d in geology from the university of illinois in 1991 was a research geologist at exxon production research from 1991 to 1993 and worked for rogaland research and geologica as from 1993 to 2000 he is also a research fellow at the bureau of economic geology to guess is cheap to guess wrongly is expensive chinese proverb reservoir quality predictive models will be a useful element of risk analysis until remote sensing tools are invented that accurately measure effective porosity and permeability ahead of the bit this issue of the aapg bulletin highlights recent advances in a new generation of reservoir quality models that have successfully predicted porosity and permeability in diverse siliclastic reservoirs under many different burial conditions most previous attempts at predrill reservoir quality prediction have relied on empirical correlations or on first principle geochemical simulations that incorporate laboratory derived input parameters wood and byrnes 1994 the new reservoir quality models differ from previous approaches in that although incorporating theory inspired algorithms they include terms with values that are explicitly designed to be calibrated by and tested against data sets of high quality petrographic analyses that are linked to thermal and effective stress histories petrographic observations therefore provide essential constraints in these models on the types timing and rates of key geologic processes affecting sandstone pore systems this approach avoids the pitfalls inherent

carbonate cementation patterns and diagenetic reservoir facies in the campos basin cretaceous turbidites offshore eastern brazil massive turbidite arkoses contain more than 80 of the oil reserves of the campos basin the main petroleum province of brazil the porosity and permeability distribution in the namorado albian cenomanian and carapebus turonian santonian sandstones is

the yellowstone magmatic system from the mantle plume to the upper crust the yellowstone supervolcano is one of the largest active continental silicic volcanic fields in the world an understanding of its properties is key to enhancing our knowledge of volcanic mechanisms and corresponding risk using a joint local and teleseismic earthquake p wave seismic inversion we revealed a basaltic lower crustal magma body that provides a magmatic link between the yellowstone mantle plume and the previously imaged upper crustal magma reservoir this lower crustal magma body has a volume of 46 000 cubic kilometers 4 5 times that of the upper crustal magma reservoir and contains a melt fraction of 2 these estimates are critical to understanding the evolution of bimodal basaltic rhyolitic volcanism explaining the magnitude of co2 discharge and constraining dynamic models of the magmatic system for volcanic hazard assessment

seismic and hydroacoustic effects of the may 29 2010 submarine south sarigan volcanic explosion energy release and interpretation abstract the may 2010 submarine volcanic crisis of the shallow south sarigan seamount marianas arc ended on may 29 by a violent explosion that emitted a 12 km high atmospheric plume and created a crater 350 m in diameter the application of the multiphase localization method to the pg p t phases of this explosion allows us to refine considerably mainly based on the intense and impulsive t phases the location of their source that fits the position of the newly formed south sarigan crater we highlight the numerous similarities of this final explosion with artificial underwater explosions conventional or nuclear tests of known energy especially the explosive nature of the source in the volcanic basement is confirmed by the similarity of the p phases with those of underground nuclear tests and the application of discriminating criteria ms mb the explosive nature of the source in the water is also confirmedby the application of the identification criteria for hydroacoustic sources and the t phases exceptionally impulsive and of short durations these similarities allow us to provide a rough evaluation of the energy released by the south sarigan final explosion using the methods commonly applied to man generated explosions we estimate a minimal released energy of 1 kt 4 2 1012 j for the seismic effects of the shock and ca 1 t of equivalent tnt i e 4 2 109 j for the hydroacoustic effects of the explosive source in the water the processes leading to this final explosion are discussed on the basis of the sequence of the earlier seismic and eruptive events within the comprehensive nuclear test ban treaty framework this explosion that affected concomitantly the solid liquid and subaerial media is the first well documented one having generated intense waves p hydroacoustic t acoustic infrasounds and tsunamis

reservoir quality modeling of tight gas sands in wamsutter field integration of diagenesis petroleum systems and production data the late cretaceous almond formation is a lithic rich tight gas sandstone reservoir in wamsutter field wyoming the almond has measured porosities of less than 12 and permeabilities that are generally less than 0 1 md this is the result of significant mechanical and chemical compaction precipitation of carbonate cements and authigenic clays and deep burial cementation by quartz despite the advanced diagenesis and poor reservoir quality of this tight gas sandstone touchstone diagenetic modeling was used successfully to simulate rock properties during burial basin modeling and fluid inclusion data were integrated with touchstone simulations to constrain the timing of petroleum charge into the reservoir model results indicate that the almond was initially charged by liquid petroleum when the reservoir retained high porosity and permeability subsequent gas charging flushed most of the liquids from the system as the reservoir continued to experience porosity and permeability reduction from continued quartz cementation the almond touchstone model was applied to 15 well locations throughout the field ranging from areas of low thermal stress to high thermal stress a comparison of touchstone predicted permeability and standard thermal stress yielded a correlation that was used to build a pseudopermeability reservoir quality risk map across the wamsutter area a comparison of this map with historical production data demonstrates that the map successfully predicts areas of enhanced well performance the method used to build this risk map may be applied elsewhere as a quick means of high grading areas of risk during field development

the global magnitude frequency relationship for large explosive volcanic eruptions abstract for volcanoes as for other natural hazards the frequency of large events diminishes with their magnitude as captured by the magnitude frequency relationship assessing this relationship is valuable both for the insights it provides about volcanism and for the practical challenge of risk management we derive a global magnitude frequency relationship for explosive volcanic eruptions of at least 300 mt of erupted mass or m4 5 our approach is essentially empirical based on the eruptions recorded in the lameve database it differs from previous approaches mainly in our conservative treatment of magnitude rounding and under recording our estimate for the return period of super eruptions 1000 gt or m8 is 17 ka 95 ci 5 2 ka 48 ka which is substantially shorter than previous estimates indicating that volcanoes pose a larger risk to human civilisation than previously thought

super volcanic investigations multi disciplinary analyses of earth s most destructive volcanic systems show that continuous monitoring and an understanding of each volcano s quirks rather than a single unified model are key to generating accurate hazard assessments

ignimbrite morphology and the effects of erosion a new zealand case study ignimbrite morphology previously generalised using aspect ratios is here quantified as the relationships between the various thicknesses of material forming an ignimbrite and the areas and volumes represented by those thicknesses the morphology can be measured for the deposit in its present day eroded condition or reconstructed for the original deposit the reconstructed morphology of the 22 500 year bp ca 11 500 km2 ca 300 km3 oruanui ignimbrite in new zealand is documented to illustrate the latter approach the oruanui ignimbrite is an intermediate aspect ratio deposit and shows broadly linear relationships between 1 in thickness and the cumulative area occupied by that thickness or less of material and 2 thickness and the volume represented by that thickness or less of material two theoretical morphologies one where thicknesses exponentially decay with distance from a maximum and the other of uniform thickness slab are compared with the oruanui data limited comparative data suggest that low aspect ratio violently emplaced ignimbrites will show upward concave curves at one extreme following the exponential decay model and high aspect ratio gently emplaced ignimbrites downward concave curves with the slab model as an extreme when plotted on diagrams where the oruanui data show linear trends the effects of erosion on oruanui and model ignimbrite morphologies are modelled using two theoretical erosion scenarios 1 material is evenly removed from the land surface and 2 thinner non welded material is preferentially removed for the oruanui ignimbrite data area is lost much more rapidly in the first instance than volume for example 5 m of erosion is sufficient to remove 50 area whereas 40 m scenario 1 or 120 m scenario 2 of erosion is required to remove 50 volume in old ignimbrites volume estimates may be reasonably accurate even after strong erosion provided the original thicknesses of ponded landscape forming material can be inferred but estimates of original area and aspect ratio will be inaccurate an envelope enclosing all known outcrops of an ignimbrite will give a better estimate of original area and aspect ratio than simply summing the areas of known outcrops

factors controlling reservoir properties and hydrocarbon accumulation of lacustrine deep water turbidites in the huimin depression bohai bay basin east china abstract lacustrine deep water turbidite plays are a novel area for exploration in the huimin depression bohai bay basin turbidites in the shang 847 block a typical turbidite play in the huimin depression provide an opportunity to study the factors controlling the reservoir properties and hydrocarbon accumulation in lacustrine turbidite sandstones the reservoir quality of turbidite sandstones very fine grained moderately to well sorted mainly lithic arkose in this study area are mainly controlled by the distribution patterns of carbonate cements and pseudomatrix significant inverse relationships exist between the volume of carbonate cement and both porosity and permeability of the turbidite sandstones carbonate cement is located preferentially near the margins of the sandstone bodies sandstones with distance from the sandstone mudstone contact surface less than 0 7 m or with thickness less than 1 2 m are commonly tightly cemented carbonate cement 15 with low porosity and permeability lower than 10 and 0 1 md respectively the source of carbonate cement was most likely external probably derived from the surrounding mudstone most pore filling carbonate cements occurred during late diagenesis at burial depths greater than 2200 m the petrophysical properties of turbidites have a positive relationship with the content of kaolinite and chlorite but have a negative relationship with the content of illite 2 d and 3 d reconstructions of non oil bearing and oil bearing layers indicate that dissolution of carbonate cement feldspars and unstable rock fragments was more developed in oil bearing layers than in non oil bearing layers and hance oil bearing layers have higher porosity and larger pore sizes petrophysical property appears to have a significant effect on the hydrocarbon accumulation in the turbidite sandstones sandstones with porosities lower than 9 and or permeabilities lower than 0 78 md are not prone to contain oil

note on the importance of hydrocarbon fill for reservoir quality prediction in sandstones oil emplacement retarded the rate of quartz cementation in the brae formation deep water sandstone reservoirs of the miller and kingfisher fields united kingdom north sea thus preserving porosity despite the rocks being buried to depths of 4 km and 120 degreesc quartz precipitation rates were reduced by at least two orders of magnitude in the oil legs relative to the water legs important contrasts in quartz cement abundances and porosities have emerged between the oil and water legs where reservoirs have filled with hydrocarbons gradually over a prolonged period of time 15 m y the earlier the hydrocarbon fill the greater is the degree of porosity preservation failure to consider this phenomenon during field development could lead to overestimation of porosity and permeability in the water leg potentially leading in turn to poor decisions about the need for and placement of downflank water injectors during exploration the retarding effect of oil on quartz cementation could lead to the presence of viable reservoirs situated deeper than the perceived regional economic basement

sources of uncertainty in the mazama isopachs and the implications for interpreting distal tephra deposits from large magnitude eruptions estimating the area of tephra fallout and volume of large magnitude eruptions is fundamental to interpretations of the hazards posed by eruptions of this scale this study uses the tephra from the caldera forming eruption of mount mazama crater lake or usa to demonstrate the challenges faced when working with large prehistoric tephra deposits and outlines the methodologies required to determine eruption volume and magnitude we combine 250 mazama tephra occurrences reported by a range of disciplines including archaeology paleoclimatology and volcanology with new field studies to better understand the extent of the distal tephra we find that the mazama tephra has been remobilised to varying degrees over the past 7000 years so each tephra locality was appraised for the likelihood that it records primary tephra fallout we designated 45 of the distal 100 km from source tephra sites as suitable for use in the production of isopachs using a spline fitting method the new distal isopachs were then integrated with proximal fallout data and estimates of the ignimbrite volume from previous studies to revise the estimated bulk erupted volume from the climactic mazama eruption to 176 km3 61 km3 dense rock equivalent dre this study demonstrates the importance of collating tephra localities from a range of disciplines and that even remobilised deposits provide valuable information about the extent of the deposit interpreting remobilised deposits can provide insight into post eruptive processes that could potentially pose secondary hazards following large magnitude eruptions we also show that in some circumstances remobilised deposits preserve important physical properties such as grain size

fault control on hydrocarbon migration and accumulation in the tertiary dongying depression bohai basin china shengli oil field the second largest oil and gas field in china is located in the tertiary dongying graben system in the southern bohai basin three petroleum systems one for each mapped source rock and as many as seven reservoir rocks are documented in the dongying graben system representing a complex migration and accumulation pattern in addition both the source and the reservoir facies are distributed unevenly throughout the system requiring a complex distribution of possible migration pathways stratigraphic conduits that is sandy and conglomeratic facies are mostly present in the northern graben flank area where coarse sediments provide possible migration pathways over most of the basin however faults active at different times throughout basin evolution add important additional conduits for petroleum migration as well as acting locally as seals depending on their surrounding lithology and their respective sealing or leaking properties through time this article aims to show that the shengli oil field provides an excellent example of how three dimensional petroleum systems modeling allows the assessment of fault behavior and timing to predict the distribution of hydrocarbons in a system

the origin and fate of silt sized carbonate in subsurface miocene oligocene mudstones south texas gulf coast combined petrographic and geochemical data document several kinds of detrital carbonate in subsurface miocene oligocene mudstones of the texas gulf coast in the extreme south of texas in muddy sediments deposited by ancient precursors to the modern rio grande mudstone carbonate is dominated by extrabasinal detritus derived from cretaceous limestones of the edwards plateau further north oligocene mudstones contain carbonate that is mostly syndepositional skeletal material minor amounts of authigenic carbonate are found as replacements of silt sized feldspars in all the mudstones depth related shifts in 18ocalcite and 13ocalcite suggest that small amounts of authigenic carbonate also form by replacement of detrital carbonate recrystallization although this cannot be demonstrated petrographically pervasive carbonate cementation in primary pores in mudstones is not generally observed textural evidence of carbonate loss through pressure dissolution is widespread providing a mechanism for the depth related decline in carbonate content observed in many gulf coast wells carbonate dissolution in mudstones and export of the caco3 implies a massive acid source probably resulting from silicate reactions within the mudstones during burial diagenesis

tomography from 26 years of seismicity revealing that the spatial extent of the yellowstone crustal magma reservoir extends well beyond the yellowstone caldera the yellowstone volcanic field has experienced three of earth s most explosive volcanic eruptions in the last 2 1 ma the most recent eruption occurred 0 64 ma forming the 60 km long yellowstone caldera we have compiled earthquake data from the yellowstone seismic network from 1984 to 2011 and tomographically imaged the three dimensional p wave velocity vp structure of the yellowstone volcanic system the resulting model reveals a large low vp body interpreted to be the crustal magma reservoir that has fueled yellowstone s youthful volcanism our imaged magma body is 90 km long 5 17 km deep and 2 5 times larger than previously imaged the magma body extends 15 km ne of the caldera and correlates with the location of the largest negative gravity anomaly a 80 mgal gravity low this new seismic image provides important constraints on the dynamics of the yellowstone magma system and its potential for future volcanic eruptions and earthquakes

vertically extensive and unstable magmatic systems a unified view of igneous processes volcanoes are an expression of their underlying magmatic systems over the past three decades the classical focus on upper crustal magma chambers has expanded to consider magmatic processes throughout the crust a transcrustal perspective must balance slow plate tectonic rates of melt generation and segregation in the lower crust with new evidence for rapid melt accumulation in the upper crust before many volcanic eruptions reconciling these observations is engendering active debate about the physical state spatial distribution and longevity of melt in the crust here we review evidence for transcrustal magmatic systems and highlight physical processes that might affect the growth and stability of melt rich layers focusing particularly on conditions that cause them to destabilize ascend and accumulate in voluminous but ephemeral shallow magma chambers

magnetotelluric images of magma distribution beneath volcan uturuncu bolivia implications for magma dynamics the altiplano puna volcanic complex in the central andes records a history of major caldera forming eruptions over the past 10 m y geophysical and geodetic data indicate that magma is still present and perhaps mobile in the crust broadband magnetotelluric data were used to generate two dimensional and three dimensional electrical resistivity models of the altiplano puna magma body apmb with a focus on the zone of inflation around volcan uturuncu in southern bolivia low electrical resistivities 20 the upper surface of the apmb is shallowest beneath uturuncu and the geometry is consistent with geodynamic models that require the upward movement of a melt layer at this location the shallower resistivity structure is characterized by discrete electrically conductive bodies oriented east west near sea level depth of 5 km which are interpreted as a combination of partial melt and fluids

calcite cement in permian deep water sandstones delaware basin west texas origin distribution and effect on reservoir properties calcite cement is the dominant control on reservoir quality in turbidite sandstones of the upper permian bell canyon formation delaware basin these well sorted very fine grained arkoses were deposited in a basin floor setting by channel levee systems terminating in broad lobes calcite cement distribution in the east ford and geraldine ford fields was mapped using core log and thin section data calcite is concentrated in tightly cemented zones that are mostly less than 1 ft 0 3 m thick areas that have high percentages of calcite cemented sandstone 20 occur along the margins of the sandstone bodies in overbank and lobe deposits where sandstone pinches out into siltstone areas that have the lowest percentage of calcite cemented sandstone 10 occur where the sandstone is thickest in the channel facies isotopic composition of the calcite 13c 1 8 to 3 0 relative to the peedee belemnite pdb 18o 4 6 to 6 3 pdb is consistent with the source of calcium carbonate being from dissolution of detrital carbonate rock fragments and marine skeletal debris because internal sources of calcite were apparently insufficient to account for the cement volume cement components are interpreted as having been transported into the sandstones from organic rich basinal siltstones and limestones feldspars buffered acidic formation waters near where they entered the sandstone resulting in calcite concentrated near the sandstone margins the calcite formed near maximum burial depths of 4800 ft 1 5 km and temperatures of 104f 40c from marine pore waters with 18o of approximately 0 relative to standard mean ocean water most of the calcite cemented zones are interpreted as being concretions that extend no more than a few meters laterally production data and geophysical log correlations suggest that some cemented zones are laterally continuous at least 1000 ft 300 m and cause vertical reservoir compartmentalization laterally extensive calcite layers may be associated with the base of turbidite deposits

the impact of diagenesis on the heterogeneity of sandstone reservoirs a review of the role of depositional facies and sequence stratigraphy diagenesis exerts a strong control on the quality and heterogeneity of most clastic reservoirs variations in the distribution of diagenetic alterations usually accentuate the variations in depositional porosity and permeability linking the types and distribution of diagenetic processes to the depositional facies and sequence stratigraphic framework of clastic successions provides a powerful tool to predict the distribution of diagenetic alterations controlling quality and heterogeneity the heterogeneity patterns of sandstone reservoirs which determine the volumes flow rates and recovery of hydrocarbons are controlled by geometry and internal structures of sand bodies grain size sorting degree of bioturbation provenance and by the types volumes and distribution of diagenetic alterations variations in the pathways of diagenetic evolution are linked to 1 depositional facies hence pore water chemistry depositional porosity and permeability types and amounts of intrabasinal grains and extent of bioturbation 2 detrital sand composition 3 rate of deposition controlling residence time of sediments at specific near surface geochemical conditions and 4 burial thermal history of the basin the amounts and types of intrabasinal grains are also controlled by changes in the relative sea level and therefore can be predicted in the context of sequence stratigraphy particularly in paralic and shallow marine environments changes in the relative sea level exert significant control on the types and extent of near surface shallow burial diagenetic alterations which in turn influence the pathways of burial diagenetic and reservoir quality evolution of clastic reservoirs carbonate cementation is more extensive in transgressive systems tract tst sandstones particularly below parasequence boundaries transgressive surface and maximum flooding surface because of the abundance of carbonate bioclasts and organic matter bioturbation and prolonged residence time of the sediments at and immediately below the sea floor caused by low sedimentation rates which also enhance the formation of glaucony eogenetic grain coating berthierine odinite and smectite formed mostly in tst and early highstand systems tract deltaic and estuarine sandstones are transformed into ferrous chlorite during mesodiagenesis helping preserve reservoir quality through the inhibition of quartz cementation the infiltration of grain coating smectitic clays is more extensive in braided than in meandering fluvial sandstones forming flow barriers in braided amalgamated reservoirs and may either help preserve porosity during burial because of quartz overgrowth inhibition or reduce it by enhancing intergranular pressure dissolution diagenetic modifications along sequence boundaries are characterized by considerable dissolution and kaolinization of feldspars micas and mud intraclasts under wet and warm climates whereas a semiarid climate may lead to the formation of calcrete dolocrete cemented layers turbidite sandstones are typically cemented by carbonate along the contacts with interbedded mudrocks or carbonate mudstones and marls as well as along layers of concentration of carbonate bioclasts and intraclasts commonly hybrid carbonate turbidite arenites are pervasively cemented proximal massive turbidites normally show only scattered spherical or ovoid carbonate concretions improved geologic models based on the connections among diagenesis depositional facies and sequence stratigraphic surfaces and intervals may not only contribute to optimized production through the design of appropriate simulation models for improved or enhanced oil recovery strategies as well as for co2 geologic sequestration but also support more effective hydrocarbon exploration through reservoir quality prediction

the relative roles of compaction and early cementation in the destruction of permeability in carbonate grainstones a case study from the paleogene of west central florida u s a abstract how compaction can yield a progressive decrease in the permeability and pore structure of carbonate grainstones is not well documented in this study the destruction of permeability by compaction relative to early cementation is examined in forty five shallow buried 30 440 m grainstones with a range in permeability of 12 to 5180 md compaction and cementation indices calculated from thin section point count data indicate a group of grainstones dominated by cementation and another by compaction log linear cross plots of permeability versus these indices suggest that permeability loss in these two groups occurs by different processes the nature of those processes is elucidated by capillary pressure data and the distribution of cement and compaction fabrics as a function of permeability as cement abundance increases in the cement dominated samples a continuous distribution of cement develops along grain surfaces which is followed by the development of partial and then complete pore filling mosaics permeability is progressively reduced with this succession of cement fabrics and an increasingly greater percentage of pore space is positioned behind progressively smaller throats permeability loss results from porosity reduction progressive constriction of pore throats and increased tortuosity of flow paths once permeability is reduced to tens of millidarcies effective pore radii are all less than 1 m and many are less than 0 1 m but there is no evidence for complete blocking of all pore throats in this suite of samples in absolute terms the pore lining cements reduce permeability by thousands of millidarcies whereas the pore filling cements reduce permeability only by hundreds of millidarcies mechanical compaction is the dominant cause of permeability reduction between 5000 and about 500 md in the compaction dominated samples linear grain contacts and embayed grains become more abundant and close to overly close packing textures become more homogeneously distributed as permeability decreases however there is no concurrent change in the amount of pore space accessed by large or small throats indicating that mechanical compaction does not uniformly constrict or seal pore throats instead the data suggest that mechanical compaction reduces permeability by reducing porosity lengthening pore throats and increasing tortuosity at about 500 md the compaction dominated trend steepens on the log linear plot of permeability versus porosity a change that corresponds to the development of grain to grain pressure solution unlike mechanical compaction grain to grain pressure solution constricts and eliminates pore throats and isolates pore space resulting in a loss of large throats and an increase in the amount of pore volume accessed by small throats in contrast to cement dominated samples the most effective pore radii are still greater than 1 m at tens of millidarcies of permeability such low amounts of permeability can be reached even when pressure solution is not pervasively distributed throughout a sample

revised estimates for the volume of the late bronze age minoan eruption santorini greece the late bronze age minoan eruption of santorini greece occurred from within an existing caldera low temperature pyroclastic flow emplacement on shallow slopes outside the caldera can only be consistent with the caldera being filled with eruption products that are not preserved field observations and seismic reflection surveys suggest that this missing material has been downfaulted the volume of the caldera infill is estimated as 18 26 km 3 dense rock equivalent dre increasing the total of the minoan eruption deposits to 78 86 km 3 dre and making it the largest known holocene eruption this study highlights a general mechanism whereby caldera eruption volumes could be significantly underestimated

sequence stratigraphic distribution of diagenetic alterations in coal bearing paralic sandstones evidence from the rio bonito formation early permian southern brazil linking siliciclastic diagenesis to sequence stratigraphy allows a better understanding of the parameters controlling the spatial and temporal distribution of diagenetic alterations and hence of reservoir quality a study of the coal bearing alluvial deltaic estuarine and shallow marine sandstones of the rio bonito formation early permian parana basin southern brazil reveals that the distribution of diagenetic alterations and of related reservoir quality evolution can be constrained within a sequence stratigraphic framework calcite dolomite siderite kaolinite and pyrite cementation is consistently linked to sequence and parasequence boundaries transgressive and maximum flooding surfaces and is systematically distributed within lowstand transgressive and highstand systems tracts diagenesis of coal layers at parasequence boundaries has promoted the formation of stratabound calcite detectable in resistivity wire line logs concretionary pyrite and kaolinite and of silicate grain dissolution in sandstones located above and below these boundaries particularly in the transgressive systems tract meteoric water diagenesis caused grain dissolution and the formation of kaolinite in sandstones below sequence boundaries and in lowstand systems tract sandstones carbonate bioclasts and low sedimentation rates in lag deposits at parasequence boundaries transgressive and maximum flooding surfaces favoured the formation of grain rimming siderite the results of this study are relevant to the exploration of coal bed methane and other coal bearing reservoirs where it is crucial to unravel and predict the distribution and quality of reservoirs and compartments

identification of sedimentary diagenetic facies and reservoir porosity and permeability prediction an example from the eocene beach bar sandstone in the dongying depression china abstract accurate prediction of reservoir porosity and permeability is essential for prospecting hydrocarbon reserves and petroleum production capacity we propose an innovative reservoir porosity and permeability prediction method through identifying sedimentary diagenetic facies determining the porosity permeability trends using core measurement data extrapolating the spatial distribution of the sedimentary diagenetic facies using log data through the bayes discriminant analysis and predicting the reservoir porosity and permeability the essence of the method was illustrated and its effectiveness was demonstrated using the eocene beach bar sandstones in the dongying depression bohai bay basin eastern china the eocene beach bar sandstones are classified into fine sandstone siltstone and argillaceous siltstone based on grain sizes sorting and matrix contents the major diagenetic processes that influence the porosity and permeability of the beach bar sandstones are compaction carbonate cementation and feldspar dissolution seven sedimentary diagenetic facies were identified in the beach bar sandstones based on the lithological types and their corresponding diagenesis and influence extent on reservoir properties the variation ranges of porosity and permeability log k of these sedimentary diagenetic facies are typically less than 6 and 1 2 respectively both the porosity and permeability have well defined functional relationships with depth the sedimentary diagenetic facies can be identified effectively from logging data through the use of the bayes discriminant analysis and corresponding cross plots the porosity and permeability log k of the well evaluated in the study were predicted with errors in the range of 3 and 0 6 respectively based on the distribution and the fitting equation of the trend lines for the seven sedimentary diagenetic facies the predicted porosities and permeability of sedimentary diagenetic facies match the measured porosities and permeability well

mass and energy budgets of explosive volcanic eruptions analysis of the frequency size relationship of explosive volcanic eruptions for the past 2000 years reveals that the time averaged eruptive mass flux of tephra from subaerial explosive eruptions is 3 104 kg s 1 this mass flux corresponds to a thermal energy release of 4 1010 w half of the long term 10 year mass and thermal energy release from explosive volcanic eruptions is accounted for by eruptions of 10 km of tephra