pore characterization of isolated organic matter from high matured gas shale reservoir abstract knowledge of pore structure of isolated organic matter om provides guidance for better understanding the origin distribution and characterization of pore system in gas shale reservoir and can be used to better comprehend the storage and transport mechanism of natural gas in shale reservoir pore structure characteristics of isolated organic matters and its corresponding bulk shales were investigated for five high matured marine shale samples from the lower silurian longmaxi formation in south china using x ray diffraction xrd total organic carbon content toc tests field emission scanning electron microscope fe sem observation and ultra low pressure nitrogen gas physisorption the results indicate that om hosted pores are abundant in bulk shale samples under fe sem observation the bet surface area and the bjh pore volume of isolated om are approximately three times greater than that of bulk shale samples pore size distribution psd of isolated om from five shale samples show a consistent variation pattern additionally with increasing toc content the psd curves of isolated om gradually grow down as result of the ductility of om bimodal psd in surface area and unimodal psd in pore volume exist in both isolated om and bulk shale samples indicating surface area is mainly associated with micropores and fine mesopores

spectrum of pore types and networks in mudrocks and a descriptive classification for matrix related mudrock pores matrix related pore networks in mudrocks are composed of nanometer to micrometer size pores in shale gas systems these pores along with natural fractures form the flow path permeability network that allows flow of gas from the mudrock to induced fractures during production a pore classification consisting of three major matrix related pore types is presented that can be used to quantify matrix related pores and relate them to pore networks two pore types are associated with the mineral matrix the third pore type is associated with organic matter om fracture pores are not controlled by individual matrix particles and are not part of this classification pores associated with mineral particles can be subdivided into interparticle interp pores that are found between particles and crystals and intraparticle intrap pores that are located within particles organic matter pores are intrap pores located within om interparticle mineral pores have a higher probability of being part of an effective pore network than intrap mineral pores because they are more likely to be interconnected although they are intrap om pores are also likely to be part of an interconnected network because of the interconnectivity of om particles in unlithifed near surface muds pores consist of interp and intrap pores and as the muds are buried they compact and lithify during the compaction process a large number of interp and intrap pores are destroyed especially in ductile grain rich muds compaction can decrease the pore volume up to 88 by several kilometers of burial at the onset of hydrocarbon thermal maturation om pores are created in kerogen at depth dissolution of chemically unstable particles can create additional moldic intrap pores

specific surface area and pore size distribution in clays and shales one of the biggest challenges in estimating the elastic transport and storage properties of shales has been a lack of understanding of their complete pore structure the shale matrix is predominantly composed of micropores pores less than 2 nm diameter and mesopores pores with 2 50 nm diameter these small pores in the shale matrix are mainly associated with clay minerals and organic matter and comprehending the controls of these clays and organic matter on the pore size distribution is critical to understand the shale pore network historically mercury intrusion techniques are used for pore size analysis of conventional reservoirs however for unconventional shale reservoirs very high pressures 414 mpa 60 000 psi would be required for mercury to access the full pore structure which has potential pitfalls current instrumental limitations do not allow reliable measurement of significant portions of the total pore volume in shales nitrogen gas adsorption techniques can be used to characterize materials dominated by micro and mesopores 2 50 nm a limitation of this technique is that it fails to measure large pores diameter 200 nm we use a nitrogen gas adsorption technique to study the micro and mesopores in shales and clays and compare the results from conventional mercury porosimetry techniques our results on pure clay minerals and natural shales show that i they have a multiscale pore structure at different dimensions ii fine mesopores with a characteristic 3 nm pore size obtained with n2 gas adsorption are associated with an illite smectite group of clays but not with kaolinite iii compaction results in a decrease of pore volume and a reduction of pore size in the inter aggregate macropores of the illitesmectite clays while the fine intra tachoid mesopores are shielded from compaction iv for natural shales mineralogy controls the pore size distributions for shales and the presence of micropores and fine mesopores in natural shales can be correlated with the dominance of the illite smectite type of clays in the rock our assessment of incompressible 3 nm sized pores associated with illite smectite clays provides an important building block for their mineral modulus

transience and persistence in the depositional record of continental margins 1 continental shelves and coastal plains are large persistent depositional landforms which are stationary nonmigrating at their proximal ends and characterized by relatively steady long term growth in detail however their surface form and stratigraphic record is built of transient freely migrating landscape elements we derive the timescales of crossover from transient to persistent topographic forms using empirical scaling relations for mean sediment accumulation as a function of averaging time based upon tens of thousands of empirical measurements a stochastic noisy diffusion model with drift predicts all the gross features of the empirical data it satisfies first order goals of describing both the surface morphology and stratigraphic completeness of depositional systems the model crossover from noise dominated to drift dominated behavior corresponds to the empirical crossover from transport dominated autogenic transient behavior to accommodation dominated subsidence persistent behavior which begins at timescales of 102 103 years and is complete by scales of 104 105 years because the same long term scaling behavior emerges for off shelf environments it is not entirely explicable by steady subsidence fluctuations in sediment supply and routing probably have significant influence at short term transient scales the exponents of the scaling relations vary with environment particularly the prevalence of channeled sediment transport at very small scales modeling sediment transport as a diffusive process is inappropriate our results indicate that some of the timescales of interest for climate interpretation may fall within the transitional interval where neither accommodation nor transport processes are negligible and deconvolution is most challenging

theory connecting nonlocal sediment transport earth surface roughness and the sadler effect earth surface evolution like many natural phenomena typified by fluctuations on a wide range of scales and deterministic smoothing results in a statistically rough surface we present theory demonstrating that scaling exponents of topographic and stratigraphic statistics arise from long time averaging of noisy surface evolution rather than specific landscape evolution processes this is demonstrated through use of elastic langevin equations that generically describe disturbance from a flat earth surface using a noise term that is smoothed deterministically via sediment transport when smoothing due to transport is a local process the geologic record self organizes such that a specific sadler effect and topographic power spectral density psd emerges variations in psd slope reflect the presence or absence and character of nonlocality of sediment transport the range of observed stratigraphic sadler slopes captures the same smoothing feature combined with the presence of long range spatial correlation in topographic disturbance

stratigraphy and remanence acquisition of a palaeomagnetic reversal in alluvial siwalik rocks of pakistan a high resolution record of a palaeomagnetic reversal is documented in miocene alluvial rocks of pakistan we examined lateral variability of lithostratigraphy and palaeomagnetic stratigraphy through the same palaeomagnetic reversal in six correlated sections each section contains one or more palaeomagnetic sites with directions between fully reversed and fully normal the position of the reversal illustrates local relief in the study area and the time transgressive nature of certain stratigraphic units variability in the thickness of the transitional interval indicates contemporaneous variability in sediment accumulation rates different characteristics of palaeomagnetic remanence are associated with the depositional and postdepositional history of these sediments variability in patterns of remanence behaviour is the basis for inferences about post depositional processes we discuss two magnetic parameters that express coherency of palaeomagnetic samples the maximum angle of deviation and the circular standard deviation of particular interest are samples with incoherent palaeomagnetic signals the incoherency of samples is inversely correlated with the thickness of the transitional interval a low rate of sediment accumulation suggested by a thin transitional interval may facilitate a prolonged period of remagnetization through pedogenic or hydrological processes alternatively transition intervals defined by coherent magnetization may be thin as a result of pedogenically induced incoherency

a quantitative approach to understanding dated dune stratigraphies attempts to reconstruct past changes in climate related forcing of dryland landscapes are hampered by the lack of an adequate quantitative framework for understanding the production and interpretation of dated sedimentary records in drylands as in other environments information on past forcing conditions is progressively modified degraded and removed from the available stratigraphic record by a series of filters involving changes in the primary forcing factors themselves geomorphological processes and the sampling dating procedures in this paper we describe a quantitative model that includes these effects and use the model to examine the nature of preserved dryland sedimentary records and their relationships to primary forcing conditions thicker preserved sedimentary records reflect periods of more intense aeolian activity localized switching between erosion and deposition results in discontinuous and highly variable stratigraphic sequences a preservation bias towards younger deposits is observed potentially leading to a continuum of accumulation that decays approximately in proportion to time periods not represented by deposition can in some cases be interpreted as periods of higher precipitation and or lower wind energy an asymmetry exists between the efficiency with which past drier and wetter episodes can be identified which relates to the time separation of depositional periods and the correct distinction between hiatuses due to forcing conditions and those due to under sampling relevant to this is the effect of random dating errors statistical uncertainty which increasingly with age filter out higher frequency events from the record a new data treatment method termed accumulation rate variability provides an efficient proxy for accumulation rates and therefore the intensity of aeolian activity with significant improvements over existing date frequency methods the filtering problem discussed applies to all attempts at understanding the timing and nature of past events independent of the proxies and dating methods employed further explicit analysis of these issues would be beneficial copyright 2013 john wiley sons ltd

simulated thermal maturation of type i and iii kerogens in the presence and absence of calcite and montmorillonite abstract the effects of a mineral matrix on hydrocarbon generation from different types of kerogen were examined simulated thermal maturation of type i iii a and iii b kerogens alone and mixed with minerals was investigated using anhydrous pyrolysis both calcite and montmorillonite modified the products of simulated thermal maturation of the kerogens montmorillonite slightly reduced and calcite slightly enhanced the formation of oil like products from the coals type iii a and iii b kerogens at higher levels of maturation however the catalytic effect of calcite resulted in cracking of the pyrolysates for retention of the pyrolysis products of type i kerogen montmorillonite proved to be a very active matrix whereas the products were less affected by calcite the amount of soluble bitumen extracted from heated type i kerogen was higher in the presence of minerals than in their absence on the contrary the amount of soluble bitumen obtained from heated type iii a kerogen was smaller in the presence of minerals in the case of type iii b kerogens this effect of minerals changed as a function of the temperature of simulated thermal maturation

papoose flat pluton forceful expansion or postemplacement deformation intense solid state deformation in the margin of the papoose flat pluton white mountians california and severe attenuation of nearby wall rocks encouraged earlier workers to suggest that this pluton was emplaced by blistering or in situ radial expansion reexamination of the pluton and wall rocks indicates that many features present in and around the pluton are not compatible with this model these features include the following 1 lack of compositional zoning or magmatic foliations in the pluton 2 lack of high temperature solid state deformation or a transition from magmatic to high temperature solid state flow 3 the presence of widespread moderate to low temperature deformation in the pluton 4 a northwest southeast trending stretching lineation and associated kinematic indicators of sinistral shear everywhere within and adjacent to the western half of the pluton 5 significant cleavage transposition after the growth of porphyroblasts in the contact metamorphic aureole and 6 upright to inclined folds with a steeply dipping axial planar cleavage in wall rocks that postdate aureole cleavages and porphyroblasts many other plutons in the white and inyo mountains also have deformed western or northwestern margins and weakly deformed eastern margins instead of interpreting all of these plutons as post tectonic and inferring that they all expanded in a western direction more the authors suggest that significant cretaceous regional deformation occurred during and after emplacement of these plutons less

pore structure and spontaneous imbibition characteristics of marine and continental shales in china the pore structure of shale has a significant effect on hydrocarbon migration and the long term gas supply of shale gas wells the present study investigates the spontaneous imbibition characteristics to evaluate the pore connectivity and wettability of marine longmaxi shale samples from the southeastern chongqing area and continental yanchang shale samples from the ordos basin the pore size distribution obtained from n2 adsorption and mercury intrusion porosimetry field emission scanning electron microscopy and focused ion beam scanning electron microscopy photos are used to interpret the imbibition behaviors our results show that the difference in dominant pore type between marine and continental samples which is dominated by thermal maturity controls on their imbibition behaviors as well as their wettability organic matter om pores within yanchang samples are poorly developed because of their low thermal maturity and a large amount of water wet inorganic pores are preserved in these samples because of relatively weak compaction oil wet om pores are well developed in longmaxi samples with higher thermal maturity and inorganic pores have been largely eliminated because of strong compaction the low pore connectivity to water for both the longmaxi and yanchang samples is indicated by the low water imbibition slopes furthermore the more oil wet property of the longmaxi samples and more water wet characteristics of the yanchang samples are obtained by comparing the directional water oil imbibition slopes in addition the positive meaning of quartz in the protection of pore spaces is found in both the longmaxi and the yanchang samples used in this study

the importance of shale composition and pore structure upon gas storage potential of shale gas reservoirs abstract the effect of shale composition and fabric upon pore structure and ch 4 sorption is investigated for potential shale gas reservoirs in the western canadian sedimentary basin wcsb devonian mississippian d m and jurassic shales have complex heterogeneous pore volume distributions as identified by low pressure co 2 and n 2 sorption and high pressure hg porosimetry thermally mature d m shales 1 6 2 5 vro have dubinin radushkevich d r co 2 micropore volumes ranging between 0 3 and 1 2 cc 100 g and n 2 bet surface areas of 5 31 m 2 g jurassic shales which are invariably of lower thermal maturity ranging from 0 9 to 1 3 vro than d m shales have smaller d r co 2 micropore volumes and n 2 bet surface areas typically in the range of 0 23 0 63 cc 100 g co 2 and 1 9 m 2 g n 2 high pressure ch 4 isotherms on dried and moisture equilibrated shales show a general increase of gas sorption with total organic carbon toc content methane sorption in d m shales increases with increasing toc and micropore volume indicating that microporosity associated with the organic fraction is a primary control upon ch 4 sorption sorption capacities for jurassic shales however can be in part unrelated to micropore volume the large sorbed gas capacities of organic rich jurassic shales independent of surface area imply a portion of ch 4 is stored by solution in matrix bituminite solute ch 4 is not an important contributor to gas storage in d m shales structural transformation of d m organic matter has occurred during thermal diagenesis creating and or opening up microporosity onto which gas can sorb as such d m shales sorb more ch 4 per weight percent wt toc than jurassic shales inorganic material influences modal pore size total porosity and sorption characteristics of shales clay minerals are capable of sorbing gas to their internal structure the amount of which is dependent on clay type illite and montmorillonite have co 2 micropore volumes of 0 78 and 0 79 cc 100 g n 2 bet surface areas of 25 and 30 m 2 g and sorb 2 9 and 2 1 cc g of ch 4 respectively dry basis a reflection of microporosity between irregular surfaces of clay platelets and possibly related to the size of the clay crystals themselves mercury porosimetry analyses show that total porosities are larger in clay rich shales compared to silica rich shales due to open porosity associated with the aluminosilicate fraction clay rich sediments low si al ratios have unimodal pore size distributions

repetitions and cycles in stratigraphy abstract stratigraphic sections show repetitions of similar or identical conditions on all scales from millimeters to many hundreds of meters representing time intervals from possibly seconds to many millions of years any such repetitions have been called cycles to understand the reason why cycles occur a time scale is essential beds can be with or without time information the latter are known as event stratifications the event which triggers the formation of beds or any succession of sediments could be a random effect or it could be part of a mechanism in which cyclic behaviour is due to an oscillating physical system such systems are dynamic systems which means that they involve the transport of masses over distances and in definite time intervals cycles generated by such systems can be used as time units a special example is the earth solar system which can generate cycles from daily periods to orbital variations of thousands and millions of years orbital variations are known as milankovitch cycles and they are the subject of cyclostratigraphy proper the recognition of milankovitch cycles or of any other cycle associated with oscillating systems rests on the regularity or time periodicity of such patterns the correct ways of analysing such cycles are the methods of time series analysis repetition patterns representing time intervals of millions and possibly many hundreds of millions of years are known from sequence stratigraphy we know as yet very little about the mechanisms which generate such long periods of repetition it has been suggested that the earth s crust has reached a state of self organized criticality bak p 1996 how nature works springer new york 212 pp in which case sequence formation could be part of the complexity which undoubtedly is an attribute of the earth s crust and history

real and apparent changes in sediment deposition rates through time 1 field measurements show that estimated sediment deposition rate decreases as a power law function of the measurement interval this apparent decrease in sediment deposition has been attributed to completeness of the sedimentary record the effect arises because of incorporation of longer hiatuses in deposition as averaging time is increased we demonstrate that a heavy tailed distribution of periods of nondeposition hiatuses produces this phenomenon and that observed accumulation rate decreases as t 1 over multiple orders of magnitude where 0 1 is the parameter describing the tail of the distribution of quiescent period length by using continuous time random walks and limit theory we can estimate the actual average deposition rate from observations of the surface location over time if geologic and geometric constraints place an upper limit on the length of hiatuses then average accumulation rates approach a constant value at very long times our model suggests an alternative explanation for the apparent increase in global sediment accumulation rates over the last 5 million years

numerical forward modeling of carbonate platform dynamics an evaluation of complexity and completeness in carbonate strata abstract it is clear that carbonate strata are complex and incomplete but the nature and origins of the complexity and the origin and distribution of hiatuses remain poorly understood a three dimensional numerical forward model of carbonate platform systems has been used to investigate how variations in complexity and completeness arise in carbonate strata the model includes depth dependent carbonate production occurring as a stochastic mosaic of producing elements across a topographic surface it also includes depth dependent sediment erosion transport and deposition governed by a regional transport direction that can vary stochastically through time and by wave refraction that causes local variations in transport direction combined mosaic production and variable sediment transport create a complex distribution of prograding islands generating self organizing shallowing upward parasequences of variable thickness and variable lateral extent hiatuses occur throughout the parasequences not just at the base and top generated by nondeposition due to mosaic production and by erosional scour this erosion is triggered by variations in water depth and fetch distance created by complex island morphologies preserved strata represent between 15 and 60 of total elapsed time measured at a 2 ky resolution and much of the preserved thickness represents punctuated deposition with depositional events spanning only a few thousand years stratigraphic completeness depends on subsidence rate and sediment transport rate so that completeness generally increases with increasing subsidence rate and decreasing transport rate but shows a nonlinear relationship with subsidence rate this suggests that reliable estimates of completeness of ancient carbonate strata require more than knowledge of subsidence rate and sea level change particularly because the real situation is likely to be considerably more complex than represented in this model the stochastic production mosaic and stochastic variations in regional transport direction create complex strata whereas the self organizing island progradation process creates simpler ordered strata a combination of the two processes creates an intermediate level of complexity producing strata consisting of laterally impersistent parasequences with numerous erosion surfaces and complex stacking patterns and complex thickness distributions this has important implications for parasequence correlation in outcrop and the subsurface

condensation processes in shallow platforms abstract sequence stratigraphy allows elucidation of the time space relationships of deposits in sedimentary basins however the relative distribution of unconformities and condensed sections can neither be used as diagnostic criteria for particular palaeogeographic settings nor as indicators of maximum regional transgressions condensation processes also occur in the shallowest portions of platforms and during maximum regression episodes three separate processes of condensation are here distinguished stratigraphic sedimentary and taphonomic these three categories of condensation can be used to analyze patterns of sediment distribution and also to estimate lateral and vertical variations in sedimentation rates contrary to the usual interpretation the maximum values of rate of sedimentation and degree of accommodation of sediments as well as the highest relative sea level occur in the lowest levels of the shallowing upward sequences the distinction between these condensation processes allows one to predict that the degree of sedimentary and stratigraphic condensation will be higher towards the distal portions of the platforms whereas the stratigraphic condensation processes without sedimentary condensation will show the maximum intensity and frequency in the shallowest portions of the platforms

patterns of stratigraphic cyclicity abstract all stratigraphic cyclicity results from cyclic sedimentation therefore patterns of stratigraphic cyclicity can be interpreted correctly only once cyclic sedimentation has been properly understood cyclic sedimentation occurs at any site at which there is cyclic variation in either or both of the two proximate controls on sedimentation these are sediment budget here defined as a generalization of sediment supply and sedimentation capacity here defined as a generalization of accommodation different patterns of cyclic variation in these controls produce different types of sedimentation cycle which result in different patterns of stratigraphic cyclicity a quantitative model for cyclic sedimentation suggests that the possible types of sedimentation cycle fall naturally into four families of these families the most difficult to use for reconstructing sedimentation conditions is the sawtooth family sawtooth cyclicity occurs when changing sedimentation conditions prevent stability from ever being reached the model shows that sequence boundaries in cyclic successions need not be closely tied to inflection points in baselevel curves sequences can start at any time from shortly after the baselevel null point on a cycle s falling baselevel limb to shortly before the baselevel high point on a cycle s rising baselevel limb i e a time range of almost three quarters of a cycle the model also suggests that cyclic successions may intrinsically be more complete than noncyclic ones

impact of rock fabric on water imbibition and salt diffusion in gas shales abstract understanding water uptake of gas shales is critical for designing fracturing and treatment fluids previous imbibition experiments on unconfined gas shales have led to several key observations the water uptake of dry shales is higher than their oil uptake furthermore water imbibition results in sample expansion and microfracture induction this study provides additional experimental data to understand the effects of rock fabric complex pore network clay swelling and osmotic potential on imbibition behavior we systematically measure and compare the imbibition rates of deionized water and oil into wet dry and confined unconfined rock samples from different shale members of the horn river basin we also measure the ion diffusion rate from shale into water during imbibition experiments the results show that initial water saturation decreases the water uptake of shale samples however it has no effect on oil imbibition rates the liquid imbibition and ion diffusion rates along the lamination are higher than those against the lamination the results also suggest that confining the shale samples decreases the water imbibition rate parallel to the lamination however it has a negligible effect on water uptake perpendicular to the lamination furthermore confining does not significantly affect the ion diffusion rates the comparative study suggests that for both confined and unconfined samples water uptake is higher than oil uptake however previous experiments on crushed shale samples show that the oil uptake of crushed packs is higher than their water uptake xu and dehghanpour 2014 the data suggest that the connected pore network of the intact samples is water wet while the majority of rock including poorly connected pores is oil wet this argument is backed by bse images and complete spreading of oil on fresh break surfaces of the rock

the role of minerals in the thermal alteration of organic matter iii generation of bitumen in laboratory experiments abstract a series of pyrolysis experiments utilizing two different immature kerogens from the monterey and green river formations mixed with common sedimentary minerals calcite illite or namontmorillonite was conducted to study the impact of the mineral matrix on the bitumen that was generated calcite has no significant influence on the thermal evolution of bitumen and also shows virtually no adsorption capacity for any of the pyrolysate in contrast montmorillonite and illite to a lesser extent alter bitumen during dry pyrolysis montmorillonite and illite also display strong adsorption capacities for the polar constituents of bitumen by this process hydrocarbons are substantially concentrated within the pyrolysate that is not strongly adsorbed on the clay matrices the effects of the clay minerals are significantly reduced during hydrous pyrolysis the strong adsorption capacities of montmorillonite and illite as well as their thermocatalytic properties may in part explain why light oils and gases are generated from certain argillaceous source rock assemblages whereas heavy immature oils are often derived from carbonate source rocks

organic matter hosted pore system marcellus formation devonian pennsylvania the marcellus formation of pennsylvania represents an outstanding example of an organic matter om hosted pore system most pores detectable by field emission scanning electron microscopy fe sem are associated with om instead of mineral matrix in the two wells studied here total organic carbon toc content is a stronger control on om hosted porosity than is thermal maturity the two study wells span a maturity from late wet gas vitrinite reflectance ro 1 0 to dry gas ro 2 1 samples with a toc less than 5 5 wt display a positive correlation between toc and porosity but samples with a toc greater than 5 5 wt display little or no increase in porosity with a further increasing toc in a subset of samples 14 across a range of toc 2 3 13 6 wt the pore volume detectable by fe sem is a small fraction of total porosity ranging from 2 to 32 of the helium porosity importantly the fe sem visible porosity in om decreases significantly with increasing toc diminishing from 30 of om volume to less than 1 of om volume across the range of toc the morphology and size of om hosted pores also vary systematically with toc the interpretation of this anticorrelation between om content and sem visible pores remains uncertain samples with the lowest om porosity higher toc may represent gas expulsion pore collapse that was more complete as a consequence of greater om connectivity and framework compaction whereas samples with higher om porosity lower toc correspond to rigid mineral frameworks that inhibited compactional expulsion of methane filled bubbles alternatively higher toc samples may contain om low initial hydrogen index relatively unreactive that is less prone to development of fe sem detectable pores in this interpretation om type controlled by sequence stratigraphic position is a factor in determining pore size distribution

variations in flood magnitude effect relations and the implications for flood risk assessment and river management abstract in spite of major physical impacts from large floods present river management rarely takes into account the possible dynamics and variation in magnitude impact relations over time in flood risk mapping and assessment nor incorporates feedback effects of changes into modelling using examples from the literature and from field measurements over several decades in two contrasting environments a semi arid region and a humid temperate region temporal variations in channel response to flood events are evaluated the evidence demonstrates how flood physical impacts can vary at a location over time the factors influencing that variation on differing timescales are examined the analysis indicates the importance of morphological changes and trajectory of adjustment in relation to thresholds and that trends in force or resistance can take place over various timescales altering those thresholds sediment supply can also change with altered connectivity upstream and changes in state of hillslope channel coupling it demonstrates that seasonal timing and sequence of events can affect response particularly deposition through sediment supply duration can also have a significant effect and modify the magnitude relation lack of response or deposits in some events can mean that flood frequency using such evidence is underestimated a framework for assessment of both past and possible future changes is provided which emphasises the uncertainty and the inconstancy of the magnitude impact relation and highlights the dynamic factors and nature of variability that should be considered in sustainable management of river channels

synthetic stratigraphy with a stochastic diffusion model of fluvial sedimentation abstract models of stratigraphic completeness and bed formation in fluvial depositional environments have most often assumed that successive depositional and erosional events deposit or erode amounts of sediment independently this results in a random walk model for the total amount of deposited sediment locally as a function of time we consider an extension of the random walk model of sedimentation in an alluvial plain in which deposition or erosion is concentrated in randomly avulsing channels and sediment transport is modeled by the diffusion equation culling s model in contrast to the random walk model this model results in an anticorrelated sequence locally as a function of time i e after an area has aggraded it has a higher elevation and a lower rate of future aggradation in a p evious paper we analyzed the topography generated by the model and argued that porosity variations could be associated with topographic variations the power spectrum s the square of the coefficients in a fourier series of one dimensional transects of topography and porosity horizontally and vertically in this model have a power law dependence on wave number k s k k s with values of s close to those observed in this paper we show that the model deposits sediment with a rate depending on time interval as a power law with exponent 3 4 more consistent with observations than the random walk model the model produces an exponential bed thickness distribution with a skew depen ent on the sedimentation rate of the basin in accordance with observations we also examine the persistence in the series of bed thicknesses as a function of depth for the stochastic diffusion model of sedimentation no persistence is observed if the model fully characterizes the autocyclic dynamics in fluvial sedimentary basins the lack of persistence in the synthetic bed sequences suggests that observed persistence and cyclicity in real bed thickness sequences must be the result of allocyclic processes

laboratory measurement of water imbibition into low permeability welded tuff abstract laboratory imbibition and vapor diffusion experiments were developed and conducted to measure accurately water imbibition and vapor condensation into welded tuff of low permeability automatically recorded balance readings were used to quantify the uptake of water into rock cores by imbibition and or vapor condensation the total uptake of water was checked against independent weighings of the sample before and after each experiment as water was imbibed into the sample and evaporated from the reservoir the buoyant force on the sample decreased balance readings corrected for the buoyancy effect agreed very well with independently measured total uptake sorptivity was calculated from the slope of a plot of corrected cumulative imbibition versus square root of time vapor condensation can provide a significant contribution to the water uptake into cores during imbibition experiments rock cores were coated with epoxy on the sides and covered on the top except for a small hole that allowed air to escape to minimize the vapor condensation contribution comparison of the sorptivity values between different core treatments shows that a consistent fraction about 20 of water uptake actually enters the core by vapor condensation overall methods for separating the confounding effects of buoyant force change and vapor condensation result in more accurate measurement of sorptivity as exhibited by the consistent and reproducible results of triplicate measurements these methods for buoyancy and vapor condensation correction are expected to be very useful for measuring imbibition rates on a wide range of porous materials especially very low permeability materials

hydrocarbon generation and shale gas accumulation in the longmaxi formation southern sichuan basin china abstract the gas bearing longmaxi formation fm records a complex tectonic history in which variations in structural and burial history directly effect the hydrocarbon maturation process through analysis of the tectonic burial history hydrocarbon maturity and easy r o numerical simulations we examine three areas representing the full spectrum of geological variability in the southern sichuan basin the changning area the luzhou area and the zigong area zishen well 1 following deposition of the longmaxi fm all three areas underwent five major tectonic events of subsidence and uplift showing an overall long term oscillation of the basin the longmaxi fm has undergone three major heating stages caledonian hercynian orogenesis time the high geothermal gradient field of hercynian and indosinian time approximately 200 300 ma and the yanshanian himalayan stage the high geothermal gradient stage is associated with extensive emeishan flood basalts or concealed basalts which could have played an important role in hydrocarbon maturation the maturation process can be divided into five stages caledonian hercyninan indosinian yanshanian and himalayan in the yanshan period the highest heating temperature of organic matter exceeded 200 c and the maturation level was more than 2 4 producing large amounts of natural gas which is the main accumulation period of shale gas in the longmaxi fm due to the large amount of hydrocarbon generated a large number of micropores were formed from organic matter evolution especially nanoscale pores during the middle diagenesis stage the longmaxi fm shale gas accumulation process is divided into four periods the source reservoir cap deposition period the initial accumulation period the main accumulation period and the adjustment period in the main accumulation period pyrolysis gas was dominant which was stored within the pores diagenetic fractures and structural fractures in adsorbed and free state ways forming the basic pattern of the longmaxi fm shale gas the current burial depth and structural stability of the longmaxi fm are critical to gas reservoir protection

study of the reed dolomite aided by remotely sensed imagery central white inyo range easternmost california remote sensing methods are of great value in assessing the stratigraphy and geologic structure of inaccessible terrains especially where lithologic contrasts are marked in this paper we show that such techniques can be successfully applied to a massive carbonate unit the reed dolomite exposed in the waucoba mountain blanco mountain and mount barcroft quadrangles of east central california airborne ns 001 satellite landsat tm and spot panchromatic imagery combined with conventional geologic mapping were employed to demonstrate that observed spectral variations on false color images were caused by subtle compositional variations of the dolomite based on reflectance differences and field investigations six discrete bedding units were recognized in exposures of th reed dolomite from lower to upper they are 1 very coarse grained granular gray pisolitic blocky dolomite 2 medium grained white oolitic massive dolomite 3 fine to coarse grained light gray oolitic massive crystalline dolomite and rare interbedded rusty quartzarenite 4 medium fine grained cross stratified locally ocherous brown interlayered quartzarenite tan siltstone and sandy dolomite 5 fine grained thin bedded sparsely oolitic buff dolomite and 6 fine grained fissile dull white dolomite subunit 4 and underlying subunit 3 appear to interfinger with subunit 4 representing a more proximal shelf facies in the southeast corner of the mapped area subunit 4 is present and subunit 3 is absent with the situation reversed along the western and northern portions of the range subunit 5 thins to a feather edge on the north near the barcroft granodiorite thickness variations of the different reed stratigraphic entities in the eastern and northern white inyo range may reflect attenuation caused by granitoid intrusion as well as original stratigraphic variations the broad expanse of reed dolomite directly northeast of the sage hen flat pluton is due to north south trending folds details of the white inyo anticlinorium are now better resolved in the central portion of the ra ge where previously undetected folds faults and homoclinal sections are revealed in false color imagery of the macroscopically featureless reed dolomite thickness trends and facies boundaries for the newly recognized subunits trend north south or north northeast throughout the study area locally reflecting the gentle west northwest continental shelf paleoslope of the passive margin of western north america during latest precambrian early cambrian this study is important to petroleum geologists because it demonstrates that detailed stratigraphy and structure can be determined using remote sensing techniques in semiarid regions where massive indistinct carbonate units crop out in some cases no single processing method allows spectral discrimination of all lithostratigraphic entities furthermore the spectral characteristics of a specific unit have been shown to vary even within a single image hence our work underscores the site specific limitations of individual multispectral methods and illustrates why a combination of diverse methods needs to be employed finally geologic lessons learned within the study area may be extrapolated to similar terrains elsewhere within the basin and range province end page 1008

experimental investigations on the geometry and connectivity of pore space in organic rich wufeng and longmaxi shales abstract the nano scale pore systems of organic rich shale reservoirs were investigated from upper ordovician wufeng and lower silurian longmaxi formations in southeast sichuan basin these two formations are the most important target plays of shale gas development in china the purpose of this article is to assess the geometry and connectivity of multi scale pore systems and to reveal the nature and complexity of pore structure for these over mature gas shales to achieve these objective total organic carbon mineralogy image analyses by focused ion beam sem low pressure nitrogen adsorption mercury injection capillary pressure micp and spontaneous fluid deionized di water and n decane imbibition were performed most of the visible pores from sem work in wufeng and longmaxi shales are within nm and m size regimes and belong to organic matter om pores the shapes of om pore in longmaxi samples are elliptical bubble like irregular or rounded wufeng pores are mainly irregular linear and faveolated even though two shales have small depth difference as well as similar thermal maturity kerogen type and toc content nano scale pores in longmaxi are mainly associated with narrow platelike or slitlike pores with pore size of 3 50 nm while inkbottle pores are dominant in wufeng samples and over 88 of the pore volume is contributed by pores with diameter

rates of sedimentation and stratigraphical completeness the most obvious result of sedimentation processes is the change in the thickness of accumulated sediment with time whenever the net change over a period of time is positive a record is left of a sedimentation system s existence a stratigraphical section for the stratigrapher the problem that such a section poses is to determine the detailed correspondence of thickness to time1 for the sedimentologist the problem is to infer the nature of the parent sedimentation system and to estimate its parameters a simple stochastic model is used here 1 to illustrate some basic stratigraphical results of clastic sedimentation processes 2 to offer an explanation for the commonly cited systematic decrease of mean sedimentation rate with increasing time span and 3 to assess the concept of stratigraphical completeness it will be assumed that all post depositional non erosional processes such as compaction can be identified and their effects on stratigraphical thickness allowed for

depo sequence as tool to convert shoreline trajectory from space domain to time domain abstract deposystems are complex and governed by discrete depo events with variable intervals of stasis or erosion in between since shoreface sediments indicate sea level depo events of shoreline facies are discrete samples of sea level only if these samples are sufficiently regular and frequent will the shoreline trajectory in the space domain accurately reflect the sea level curve in the time domain this study presents a method to convert shoreline trajectory in the space domain to sea level curve in the time domain from artificial miniature deltas one obtains the depo sequence as function of time and uses it to convert depo sequence from time to space domain correlate depo sequence to shoreline trajectory in the space domain and convert shoreline trajectory from space to time domain for natural deltas one would extract the depo set in the frequency domain i e the probability density function of stasis intervals between depo events from the experimental depo sequence and use it to convert shoreline trajectory from space to time domain and infer a range of possible sea level curves this method therewith explicitly includes the uncertainty of the inferred sea level curve

on the directional nature of stratigraphic correlation in every correlation exercise the diachroneity of the lithostratigraphic boundaries determines the discrepancy between lithostratigraphic correlation and time correlation here it is shown that diachroneity varies in degree as a simple function of the direction in which correlation is made and hence that stratigraphic correlation must take that direction into account when the direction of correlation is not known a sound strategy for time correlation of lithostratigraphic boundaries is to assume that each is at its most diachronous

optimizing significance testing of astronomical forcing in cyclostratigraphy the recognition of astronomically forced milankovitch climate cycles in geological archives marked a major advance in earth science revealing a heartbeat within the climate system of general importance and key utility power spectral analysis is the primary tool used to facilitate identification of astronomical cycles in stratigraphic data but commonly employed methods for testing the statistical significance of relatively high narrow band variance of potential astronomical origin in spectra have been criticized for inadequately balancing the respective probabilities of type i false positive and type ii false negative errors this has led to suggestions that the importance of astronomical forcing in earth history is overstated it can be readily demonstrated however that the imperfect nature of the stratigraphic record and the quasiperiodicity of astronomical cycles sets an upper limit on the attainable significance of astronomical signals optimized significance testing is that which minimizes the combined probability of type i and type ii errors numerical simulations of stratigraphically preserved astronomical signals suggest that optimum significance levels at which to reject a null hypothesis of no astronomical forcing are between 0 01 and 0 001 i e 99 99 9 confidence level this is lower than commonly employed in the literature 90 99 confidence levels nevertheless in consonance with the emergent view from other scientific disciplines fixed value null hypothesis significance testing of power spectra is implicitly ill suited to demonstrating astronomical forcing and the use of spectral analysis remains a difficult and subjective endeavor in the absence of additional supporting evidence

pore throat sizes in sandstones tight sandstones and shales pore throat sizes in siliciclastic rocks form a continuum from the submillimeter to the nanometer scale that continuum is documented in this article using previously published data on the pore and pore throat sizes of conventional reservoir rocks tight gas sandstones and shales for measures of central tendency mean mode median pore throatsizes diameters are generally greater than2 mm in conventionalreservoir rocks range from about 2 to 0 03 mm in tight gas sandstones and rangefrom0 1to0 005 mminshales hydrocarbonmolecules asphaltenes ring structures paraffins and methane form another continuum ranging from 100 a 0 01 mm for asphaltenes to 3 8 a 0 00038 mm for methane the pore throat size continuum provides a useful perspective for considering 1 the emplacement of petroleum in consolidated siliciclastics and 2 fluid flow through fine grained source rocks now being exploited as reservoirs

shale compaction and statistical physics summary after a short historical outline of the development of the ideas on the compaction of clays and shales it is shown that the exponential porosity depth dependence of compacted shales expressed by athy s law can be derived using standard methods of statistical physics the main result of the paper states that the exponential compaction law expresses the maximum entropy equilibrium state of the pores in the rock that is compaction is an irreversible process where clay particles tend towards a statistically defined final equilibrium connections with the classical theory of consolidation are pointed out

experimental investigations of the wettability of clays and shales 1 wettability in argillaceous materials is poorly understood yet it is critical to hydrocarbon recovery in clay rich reservoirs and capillary seal capacity in both caprocks and fault gouges the hydrophobic or hydrophilic nature of clay bearing soils and sediments also controls to a large degree the movement of spilled nonaqueous phase liquids in the subsurface and the options available for remediation of these pollutants in this paper the wettability of hydrocarbons contacting shales in their natural state and the tendencies for wettability alteration were examined water wet oil wet and mixed wet shales from wells in australia were investigated and were compared with simplified model shales single and mixed minerals artificially treated in crude oil the intact natural shale samples preserved with their original water content were characterized petrophysically by dielectric spectroscopy and nuclear magnetic resonance plus scanning electron optical and fluorescence microscopy wettability alteration was studied using spontaneous imbibition pigment extraction and the sessile drop method for contact angle measurement the mineralogy and chemical compositions of the shales were determined by standard methods by studying pure minerals and natural shales in parallel a correlation between the petrophysical properties and wetting behavior was observed these correlations may potentially be used to assess wettability in downhole measurements

precipitation as meteoric sediment and scaling laws of bedrock incision assessing the sadler effect abstractalthough it has been several decades since sadler 1981 first showed that sediment accumulation rates exhibit a negative power law dependence on measurement interval i e the sadler effect only recently has a manifestation of covariance in rate with duration become more widely appreciated in degradational settings because our collective understanding of rates of deposition and erosion are widely utilized to constrain the importance of active tectonism and climate forcing in shaping the surface of our planet cognizance of the dependence of rate on duration of observation is of critical importance relations between elevation change deposition erosion and rate scaling laws have often been examined by stochastic random walk simulations but this approach is generally confounded by insufficient data on amounts of land surface change on durations of land surface change and on hiatal durations separating time intervals of change deposition or erosion rates measured over short intervals suc

late cenozoic exhumation model of new zealand impacts from tectonics and climate abstract late cenozoic convergence between the australian and pacific plates has led to extensive crustal deformation and exhumation in new zealand over the past five decades the convergence associated exhumation history of the palaeozoic mesozoic new zealand basement has been studied using various thermochronometric techniques here we compile 992 published ages and invert them to estimate the temporal and spatial variation in exhumation rates since 25 ma which we then interpret with a plate tectonic reconstruction model the results reveal widespread increases in the exhumation rates at 6 4 ma a time correlated with accelerations in the relative plate motion the absolute increases in exhumation rates are however not uniformly distributed over new zealand since the plio pleistocene the inferred models suggest variable response of exhumation to global cooling in the non glaciated eastern north island the hikurangi subduction margin the million year average exhumation rates have remained relatively low 5 km myr have been observed in the collision zone of the central southern alps of south island where both tectonic deformation and precipitation rates are highest in fiordland the puysegur subduction margin despite the weak crustal deformation the exhumation rates have been high 0 5 3 km myr which we suggest is due to intensified glacial erosion our findings highlight the determining role of tectonics in setting up the regional exhumation pattern but both strong tectonic deformation and efficient erosion are required to maintain rapid exhumation rates the influence of climate on mountain erosion can only be distinguished in regions under slow to mediate exhumation

pore structure wettability and spontaneous imbibition of woodford shale permian basin west texas abstract even after more than 30 years of exploration and production low total recovery of shale gas

wettability and connectivity of overmature shales in the fuling gas field sichuan basin china the fuling gas field in sichuan basin china has produced greater than 1 5 1010 m3 0 53 tcf of natural gas from overmature upper ordovician wufeng and lower silurian longmaxi shales to systemically investigate the characteristics of wettability and connectivity and to understand the underlying causes of production behavior we study five samples of wufeng and longmaxi shales with different total organic carbon contents and mineral compositions complementary approaches include mercury intrusion capillary pressure micp contact angle measurement spontaneous imbibition and saturated diffusion and tracer both nonsorbing and sorbing migration mapped via laser ablation inductively coupled plasma mass spectrometry according to measured contact angles and imbibition tests conducted on aqueous deionized water and brine and oleic n decane phases wufeng and longmaxi shales are strongly oil wet and moderately strong water wet the lower boundary of estimated permeability obtained from n decane imbibition can reach 137 nd which is higher than the geometric mean permeability derived from the micp method 5 5 68 8 nd effective diffusion coefficients of the wufeng and longmaxi shales are in the range of 10 13 m2 s 1 1 10 12 ft2 s tests of imbibition and saturated diffusion using tracer containing brine show that concentrations of nanometer sized tracers decrease rapidly a factor of 10 over a migration distance of a few millimeters from the sample edge suggesting the presence of poorly edge connected water wet pores sparsely connected hydrophilic pores mixed wettability and highly restricted pathways collectively contribute to the limited migration of nano sized tracers which probably results in the production behavior of initial steep decline and low overall recovery in the fuling gas field

geochemical characteristics of marine and terrestrial shale gas in china abstract although the annual production of shale gas in china was 13 10 8 m 3 in 2014 a systematic study on geochemical and isotopic characteristics of these unconventional gases has not been well addressed in the present study almost all shale gas samples available in china including marine shale gas from the wufeng longmaxi formation in the sichuan basin o 3 w s 1 l and terrestrial shale gas from chang 7 member t 3 y 7 in the ordos basin were collected and analyzed for their geochemical and isotopic compositions the shale gas from the wufeng longmaxi shale is dry gas with an average methane content of 98 38 and records a highest content of ch 4 in the world 99 59 which is consistent with the very high thermal maturity levels of the gas shales that have equivalent vitrinite reflectance eqvro values between 2 4 and 3 6 the 13 c 1 values are correspondingly heavy and record a heaviest 13 c 1 values 26 7 for the shale gases found in the world as well the average values of 13 c 1 13 c 2 and 13 c 3 for the wufeng longmaxi shale gas are 31 3 35 6 and 47 2 respectively displaying a complete carbon isotopic reversal i e 13 c 1 13 c 2 13 c 3 2 h ch4 and 2 h c2h6 has an average value of 148 and 173 respectively also yielding a hydrogen isotopic reversal i e 2 h ch4 2 h c2h6 the chang 7 shale has an average toc content of 13 81 with vitrinite reflectance vro values between 0 7 and 1 2 the chang 7 shale gas is wet gas with an average methane content of 84 90 and is rich in heavy gaseous hydrocarbons c 2 c 5 the respective values of 13 c 1 13 c 2 and 13 c 3 are 48 7 36 4 and 31 3 displaying a positive carbon isotopic distribution pattern i e 13 c 1 13 c 2 13 c 3 the average 2 h ch4 2 h c2h6 and 2 h c3h8 values are 256 244 and 188 respectively and are characterized by a positive distribution pattern i e 2 h ch4 2 h c2h6 2 h c3h8 the differences in gas wetness and carbon and hydrogen isotopic distribution patterns between the shale gases from the wufeng longmaxi and chang 7 shale are attributed to variations in thermal maturity levels co 2 is present in low content in both the wufeng longmaxi and chang 7 shale gases mostly less than 1 13 c values for the co 2 in the wufeng longmaxi formation are between 8 9 and 9 2 indicating an inorganic origin from the cracking of carbonate mineral in the shales under high temperatures in contrast 13 c values of the co 2 in the chang 7 shale gas range from 8 2 to 22 7 indicating an organic origin from the thermal degradation of organic matter helium in both the wufeng longmaxi and chang 7 shale gases is dominantly of curst origin in terms of their r ra ratios that vary from 0 01 to 0 08 positive carbon isotopic distribution pattern is typical of primitive thermogenic gas however it can be converted into complete or partial carbon isotopic reversal patterns due to secondary alteration the causes that yield carbon isotopic reversal include 1 mixing of gases with the same source but different thermal maturity levels 2 secondary cracking of oil or wet gas 3 formation water involved reactions 4 gas diffusion and 5 carbon isotope exchange between alkane gases at high temperature among them carbon isotopic exchange between alkane gases at high temperature is a key factor nine plots have been drawn based on the shale gases from china usa and canada among them the plot of 13 c 2 versus wetness demonstrates a lying s shape with two inflection points on the gas wetness axis the wetness value of 1 4 represents a critical point from pyrolytic gas primary cracking gas to cracking gas secondary cracking gas and whereas the wetness value of 6 marks the end of oil generation on the diagram of wetness versus 13 c shale gases with wetness values greater than 1 6 are characterized by positive carbon isotopic distribution pattern whereas a complete or partial carbon isotopic reversals are observed for shale gases with wetness values less than 1 6

stratigraphic completeness and resolution in an ancient mudrock succession funded by nerc fellowship grant number ne i02089x 1 santander student project scholarship grant

temporal distribution of diastems in deposits of an open coast tidal flat with high suspended sediment concentrations abstract based on field observations of the preservation potential and genesis of couplets and small sequences diastems occur within tidal flat deposits at scales of semi tidal daily monthly and yearly intervals thus tidal flat deposition is riddled with more diastems of different scales than previous assumptions units that are apparently complete when examined at longer time scales actually contain many diastems when examined at a shorter time scale diastems within tidal flat deposits are generated not only by high magnitude storm waves which occur during typhoon seasons but also by daily erosion produced by tides and weak waves during calm weather seasons the missing intervals in diastems generated by storm waves can be several days to several years preservation potential of storm generated small sequences is of the order of one third diastems generated by erosion by tides and weak waves can have spans from a semidiurnal cycle to several days they are easily overlooked because of the low magnitude destruction and lack of distinctive sedimentary features net erosion by tides and weak waves is unexpectedly increased by day to day processes alternations of sandy and muddy laminae are related to tidal rhythm but individual laminae can be separated by a significant diastem documentation of erosion by tides and weak waves under normal non typhoon conditions is the principal focus of this report

structure emplacement and lateral expansion of the san jose tonalite pluton peninsular ranges batholith baja california mexico abstract the 108 km2 san jose pluton forms part of the jurassic to cretaceous peninsular ranges batholith of northern baja california mexico the pluton was formed by three nested southward migrating intrusive pulses and the internal contacts between them indicate juxtaposition while the adjoining pulses were magmas shrimp u pb zircon data indicate that the entire pluton was emplaced in less than 4 4 m y ages of the individual pulses cannot be separated at the 95 confidence interval owing primarily to low uranium content of zircon detailed structural data and geologic mapping are consistent with a component of asymmetrical lateral expansion at the site of emplacement the direction of maximum lateral expansion may have been controlled by thermal compositional and resulting rheological gradients in the surrounding wall rocks a carapace of predominantly solid state deformation marks the northern two thirds of the pluton and the early stages of this fabric may have formed in the presence of a small amount of melt lack of evidence for syn to post emplacement regional ductile deformation around the pluton suggests that this carapace was deformed during the lateral expansion of the pluton

conditions of contact metamorphism papoose flat pluton eastern california usa implications for cooling and strain histories petrological study of highly strained carbonate and pelitic rocks within the contact aureole surrounding the western part of the papoose flat pluton yields thermal profiles plots of metamorphic temperature versus distance across the aureole that show temperature gradients which are relatively flat and narrow 100m the gradients occur close to the contact and indicate a slight decrease in temperature from 500 550 c at the pluton wall rock contact to 450 500 c at the outer margin of the aureole one thermal profile across low strain metasedimentary rocks located in the southern part of the aureole shows that thermal effects from emplacement extend no further than 600 m from the contact coexistence of andalusite and cordierite in pelitic rocks of the aureole constrain pressures to 4 kbar thermal modelling using an analytical solution of the conductive heat flow equation for a rectangular shaped pluton reproduces the observed thermal maxima and profile shape conductive rather than convective cooling also is supported by isotopic and field evidence for limited fluid flow along the strongly deformed margin of the pluton simple thermal models coupled with observed high temperature deformation features and a measured 90 attenuation of stratigraphic units in the plastically deformed western part of the pluton s aureole indicate that strain rates may have been of the order of 10 12s 1 evidence for episodic heating such as two distinct generations of andalusite growth in pelites from the aureole alternatively may indicate a longer heating event and therefore slower strain rates thermal models also indicate that parts of the pluton still may have been above the solidus during deformation of the pluton margin and aureole

can we distinguish flood frequency and magnitude in the sedimentological record of rivers consideration of the origin of alluvial deposits and their paleoenvironmental interpretation has traditionally involved two schools of thought that they are either the result of processes that on average have acted uniformly through time or that they are related to exceptional events that occur infrequently despite the long running debate of gradualism versus catastrophism within the earth sciences there are surprisingly few quantitative data to assess the magnitude of events that produce alluvial sedimentary successions this paper reports on a unique natural experiment where surface digital elevation model dem and subsurface ground penetrating radar gpr data were taken immediately prior to and after a large 1 in 40 yr flood event on the sandy braided south saskatchewan river canada results show that although this high magnitude flood reworked the entire braidplain the scale of scour and style of deposition was similar to that associated with lower magnitude annual floods the absence of a distinct imprint of this large flood within the deposits is related to the fact that as river discharge rises and begins to flow overbank channel width increases at a much faster rate than flow depth and thus the rate of increase in channel bed shear stress declines hence rather than being a product of either frequent or rare events alluvial deposits will likely be created by a range of different magnitude floods but discriminating between these different scale events in the rock record may be extremely difficult

characterizing the pore structure of low permeability eocene liushagang formation reservoir rocks from beibuwan basin in northern south china sea abstract the hydrocarbon exploration from low permeability 50 nm mainly contribute to the total pore spaces for most samples with lower shale content mesopores 2 50 nm dominate the pore spaces of samples with higher shale content which leads to the relatively large surface area of these samples permeability of these low permeability rocks is positively related with average pore throat radius and negatively related with relative sorting coefficient while no such a close relationship exists between permeability and porosity fractal dimension has a negative relationship with average pore throat radius and permeability in summary this work comprehensively investigates the pore structure characteristics of low permeability liushagang formation reservoir rocks from beibuwan basin using multiple complementary approaches which helps to further understand the hydrocarbon migration and accumulation mechanism of these low permeability reservoirs

quaternary continental stratigraphy and neocatastrophism abstract recent papers on pre quaternary stratigraphy have emphasized that the rock record represents only a small portion of geologic time with the gaps representing the majority of elapsed time quaternary continental stratigraphy also yields such evidence in abundance time between dated organic sites in glaciated areas is commonly depicted as filled by glacial ice yet there is much evidence of rapid sedimentation and most deposits could be laid down in short time spans non glaciated areas yield similar evidence because of gaps over which depositional rates are averaged calculated rates are often lower than they really are continental stratigraphy requires attention from many workers supported by much improved dating methods to establish time spans and gaps for the rock record

porosity of devonian and mississippian new albany shale across a maturation gradient insights from organic petrology gas adsorption and mercury intrusion the evolution of porosity in shales with increasing maturity was examined in a suite of five new albany shale samples spanning a maturity range from immature vitrinite reflectance ro 0 35 to postmature ro 1 41 devonian to lower mississippian new albany shale samples from the illinois basin used in this study contain marine type ii kerogen having total organic carbon contents from 1 2 to 13 0 wt organic petrology co2 and n2 low pressure adsorption and mercury intrusion capillary pressure techniques were used to quantify pore volumes pore sizes and pore size distributions increasing maturity of the new albany shale is paralleled by many changes in the characteristics of porosity the total porosity of 9 1 vol in immature new albany shale decreases to 1 5 vol in the late mature sample whereas total pore volumes decrease from 0 0365 to 0 0059 cm3 g in the same sequence reversing the trend at even higher maturity the postmature new albany shale exhibits higher porosity and larger total pore volumes compared to the late mature sample with increasing maturity changes in total porosity and total pore volumes are accompanied by changes in pore size distributions and relative proportions of micropores mesopores and macropores porosity related variances are directly related to differences in the amount and character of the organic matter and mineralogical composition but maturity exerts the dominant control upon these characteristics we conclude that organic matter transformation due to hydrocarbon generation and migration is a pivotal cause of the observed porosity differences

2d and 3d nanopore characterization of gas shale in longmaxi formation based on fib sem abstract studying complex pore structures is the key to understanding the mechanism of shale gas accumulation fib sem focused ion beam scanning electron microscope is the mainstream and effective instrument for imaging nanopores in gas shales based on this technology 2d and 3d characteristics of shale samples from lower silurian longmaxi formation in southern sichuan basin were investigated 2d experimental results show that the pores in shale are nanometer sized and the structure of those nanopores can be classified into three types organic pores inorganic pores and micro fractures among the three types organic pores are dominantly developed in the om organic matter with three patterns such as continuous distributed om om between clay minerals and om between pyrite particles and the size of organic pores range from 5 nm to 200 nm inveresly inorganic pores and micro fractures are less developed in the longmaxi shales 3d digital rocks were reconstructed and segmented by 600 continuous images by fib cutting and sem imaging simultaneously the pore size distribution and porosity can be calculated by this 3d digital core showing that its average value is 32 nm and porosity is 3 62 the 3d digital porosity is higher than its helium porosity which can be regarded as one important parameter for evaluation of shale gas reserves the 2d and 3d characterized results suggest that the nanometer sized pores in organic matter take up the fundamental storage space for the longmaxi shale these characteristics have contributed to the preservation of shale gas in this complex tectonic area

estimation of completeness of stratigraphical sections using empirical data and theoretical models the completeness of a stratigraphical section is the fraction of time intervals of some specified length t that have left a record a record is left when some sediment is deposited during the interval and is not subsequently eroded a complete section contains no hiatuses longer than t the completeness of a section varies with t and its accumulation rate varies with the length of the time span over which it is measured plots of measured accumulation rate against time span are an empirical means of estimating completeness simple theoretical models help extrapolate meagre data and identify bias completeness at time scale t can depend upon three general properties of the accumulation history the age of the section the long term net accumulation rate drift and the unsteadiness of the sedimentation rate the way unsteadiness is measured depends upon the kinds of fluctuations that can be recognized in the accumulation rate to describe random fluctuations a standard deviation of rates is sufficient one dimensional brownian motion is a model of random fluctuations that explains many aspects of stratigraphical completeness regular periodic fluctuations in accumulation rate may be described in terms of wavelength and amplitude completeness is an increasing function of t drift and in the periodic case the wavelength of fluctuations it decreases with increasing standard deviation of accumulation rate and the amplitude of periodic fluctuations the completeness and thickness of stratigraphical sections are weakly positively associated

measured rates of sedimentation what exactly are we estimating and why abstract data on rates of sedimentation are essential in studies of sedimentation systems these data are obtained in three main study contexts 1 the study of sedimentation systems that are active today 2 the source to sink study of sedimentation systems that no longer are active and 3 the study of the relationship between accumulation rate and measurement timespan the aim of this paper is to question the meaning of measured rates of sedimentation and their interpretability particularly in these three contexts individual measurements of rate of sedimentation must always be interpreted with care firstly there are different definitions for instance with different statistical support or measurement dimension values that are defined differently cannot be compared directly secondly appropriate sampling schemes must have been used for the measurement this minimises sampling bias thirdly the inherent limitations of the data sources must be taken into account rates of sedimentation can usually be measured successfully in active sedimentation systems the same is not true for systems that are no longer active these can only be studied using the stratigraphic successions left behind rates of erosion can never be measured successfully in stratigraphic successions rate of sedimentation is essentially a ratio an amount of sedimentation per length of time therefore the obvious strategy to use in determining it is first to measure the amount and the time independently then to combine the values the amount can be measured in terms of thickness or volume or mass per unit area the duration of the time interval can be preset using quasi continuous measurement techniques or site reoccupation or it can be identified from interval specific sedimentary structures or it can be measured using dated horizons an alternative strategy is to use a surrogate measurement variable rates of erosion in ancient systems are usually measured in this way using cosmogenic radionuclide concentrations these two strategies are reviewed in this paper sets of measurements made in systems that are active today can certainly be used to estimate the rate of sedimentation for the system as a whole this estimation is best carried out using geostatistical estimation techniques the alternative is simply to average the measured rate values this latter approach should not be used however because the mean sedimentation rate in a system gives information only about the net sediment movement at the system boundaries it says nothing at all about how the system is operating or about its spatial and temporal variability measurements of rates of sedimentation made for source to sink studies are necessarily made in stratigraphic successions the measurements are used to estimate quantities in the sediment mass budget equation the amount of decumulation is inherently incapable of being measured in stratigraphic successions therefore there are always unknowns in the mass budget equation whenever the lithic surface at the start of the time interval considered cannot be recognised everywhere this means that the mass budget equation is applicable in practice only when all the systems involved in the study are entirely non erosional for that entire time interval a highly unrealistic situation the consistently inverse relationship documented between accumulation rates and measurement timespan is taken usually to indicate that this relationship is substantially scale invariant this in turn is often taken as indicating that the stratigraphic record is fractal in nature there are nevertheless grounds for doubt all of which relate to the ways that the data are collected and used for estimation the relationship is in fact the natural mathematical result of last in first out lifo operation and is produced in any type of system in which addition and removal processes both operate it says nothing particular about sedimentation processes the future analysis of accumulation rate data collected from stratigraphic successions will sensibly be framed in the context of estimating the parameters of a lifo model

micro and nano size pores of clay minerals in shale reservoirs implication for the accumulation of shale gas abstract a pore is an essential component of shale gas reservoirs clay minerals are the adsorption carrier second only to organic matter this paper uses the organic maturity test field emission scanning electron microscopy fe sem and x ray diffraction xrd to study the structure and effect of clay minerals on storing gas in shales results show the depositional environment and organic maturity influence the content and types of clay minerals as well as their structure in the three types of sedimentary facies in china clay minerals develop multi size pores which shrink to micro and nano size by close compaction during diagenesis micro and nano pores can be divided into six types 1 interlayer 2 intergranular 3 pore and fracture in contact with organic matter 4 pore and fracture in contact with other types of minerals 5 dissolved and 6 micro cracks the contribution of clay minerals to the presence of pores in shale is evident and the clay plane porosity can even reach 16 close to the contribution of organic matter the amount of clay minerals and pores displays a positive correlation clay minerals possess a strong adsorption which is affected by moisture and reservoir maturity different pore levels of clay minerals are mutually arranged thus essentially producing distinct reservoir adsorption effects understanding the structural characteristics of micro and nano pores in clay minerals can provide a tool for the exploration and development of shale gas reservoirs

prevalence of exponential bed thickness distributions in the stratigraphic record experiments and theory 1 stratigraphy preserved in alluvial basins holds important information for reconstructing past environmental conditions via inversion methodologies in this paper we explore through the use of physical and numerical experiments the forward problem that is we quantify how the probabilistic structure of the processes that govern the evolution of depositional systems relates to the probability distribution of the preserved bed thicknesses we demonstrate that the extreme variability as evidenced by heavy tailed distribution of the surface elevation increments largely cancels itself out in the resulting stratigraphy specifically we show that bed thickness is well described by an exponential distribution even when erosional and depositional increments characterizing the surface evolution exhibit heavy tailed statistics i e large infrequent events have a significant chance of occurrence we attribute this finding to the symmetric nature of the distribution of elevation increments both erosional and depositional events and the additive nature of the stratigraphic filter we also show that the variability of surface elevation increments as measured by the interquartile range of their probability distribution has a robust and well defined relationship with the preserved mean bed thickness

the effects of pore structure on wettability and methane adsorption capability of longmaxi formation shale from the southern sichuan basin in china the lower silurian longmaxi formation shale in the sichuan basin is one of the most promising shale gas plays in china pore structure has a significant impact on hydrocarbon migration within shales this study conducts systematic experiments to analyze the pore structure wettability and methane adsorption capacity of the longmaxi formation shale samples from the southern sichuan basin the pore size distributions obtained from n2 adsorption high pressure mercury intrusion porosimetry and statistical analysis of representative field emission scanning electron microscopy photographs of organic matter om are compared to evaluate the contribution of om pores to total pore spaces shale wettability was determined by contact angle measurements and spontaneous imbibition experiments the results reveal that these samples could be divided into three wettability categories more water wet samples z1 more oil wet samples z4 and intermediate wet samples z2 and z3 although samples z1 and z4 have similar total organic carbon toc contents om pores within sample z4 have a larger average pore size and occupy a greater proportion of the total pore spaces compared with sample z1 whereas inorganic pores contribute more to the total pore spaces of sample z1 sample z4 has a larger methane adsorption capacity than sample z1 with a higher brunauer emmett teller bet surface area which may be caused by the difference in their om pore types samples z2 and z3 with less toc content have lower porosities and bet surface areas as well as lower methane adsorption capacities consequently the pore structure significantly affects the wettability and methane adsorption capacity of the longmaxi shale

the middle eocene seeb formation of oman an investigation of acyclicity stratigraphic completeness and accumulation rates in shallow marine carbonate settings abstract the middle eocene seeb formation represents deposition on one of the earliest modern style carbonate platforms i e influenced by seagrasses and mangroves and presents an opportunity to explore controls on the preservation of cenozoic carbonate lithofacies in the study area the seeb fm is dominated by an anomalously thick approximately 250 m and uniform package of shallow marine platform interior sediments these nodular indistinctly bedded shallow subtidal sediments display no evidence for relative sea level change such as subaerial exposure features and lack the shallowing upwards cyclothems that have characterized carbonate sediments deposited in platform interior settings throughout much of the rock record particularly during greenhouse periods we conclude that this is a consequence of thorough bio retexturing of the sediment by burrowing organisms and the roots of marine vegetation which destroyed primary fabrics facies diversity evidence for cyclicity and missing time horizons such as cycle bounding exposure surfaces it seems possible that the remarkable thickness of apparently acyclic seeb fm sediment that built up may reflect increased bio disturbance of the shallow marine environment following the late cretaceous expansion of seagrasses and mangroves a similar lack of peritidal cyclothems may be common to many cenozoic shallow marine carbonate deposits missing time horizons in limestones reflecting erosion or nondeposition have been identified by some authors to explain discrepancies between low calculated accumulation rates of ancient sediments and higher rates measured in comparable modern environments however our studies of the seeb fm suggest that the significance of such missing time horizons in ancient sediments may have been overstated and that apparent differences between modern and ancient accumulation rates are a consequence of the extrapolation of unrepresentative localized high rates of modern sediment production to large platform scale areas our study reinforces the idea that modern sediment production and accumulation rates may be much lower than previously thought because they are typically measured in highly productive areas such as seagrass beds and do not take into account the highly variable nature of carbonate production storage erosion and destruction across platforms therefore far less missing time needs to be inferred for ancient sediments to account for any imbalance between modern and ancient sediment accumulation rates

the effect of moisture on the methane adsorption capacity of shales a study case in the eastern qaidam basin in china this study investigated the effects of moisture on high pressure methane adsorption in carboniferous shales from the qaidam basin china the shale characteristics including the organic inorganic compositions and pore structure volume and surface distribution were obtained using various techniques gibbs adsorption measurements were performed over a pressure range up to 6 mpa and temperatures of 308 15 k on dry samples and moisture equilibrated samples to analyze the correlations between organic inorganic matter pore structure and moisture content on the methane sorption capacity compared to dry samples the sorption capacity of wet samples 0 44 2 52 of water content is reduced from 19 7 5 3 to 36 1 6 1 langmuir fitting is conducted to investigate moisture dependent variations of adsorbed methane density langmuir pressure and volume by combining the pore volume and surface distribution analyses our observations suggested that the main competition sites for ch4 h2o covered pores of approximately 2 7 nm whereas the effective sites for methane and water were predominantly distributed within smaller 10 nm respectively regarding the compositional correlations the impact of moisture on the amount of adsorbed methane shows a roughly linearly decreasing trend with increasing toc content ranging from 0 62 to 2 88 whereas the correlation between the moisture effect and various inorganic components is more complicated further fitting results indicate that illite smectite mixed formations are closely related to the methane capacity whereas the illite content show an evident connection to the pore structural volume and surface variations in the presence of moisture

wettability of mississippian barnett shale samples at different depths investigations from directional spontaneous imbibition because of its significant impact on relative permeability capillary pressure stimulation methods and ultimate recovery the wettability of reservoir rocks is a critical factor of the petroleum recovery process however characterizing the wettability of shale with extremely low matrix permeabilities is a challenging task because of the dominant presence of nanopores in shale and high heterogeneity of shale compositions at multiple scales from spontaneous imbibition behavior that uses two types of imbibing fluid water and n decane the present study examines the wettability characteristics of gas window barnett shale samples taken from four different depths of texas united 1 blakely core in wise county in texas imbibition experiments were conducted in two directions parallel and transverse to the lamination of the samples a scaling method was used to analyze imbibition data and observed imbibition behaviors were interpreted to infer the different wettability conditions of four samples with different mineralogy total organic carbon content and pore throat size distribution our results show that wettability significantly affects fluid imbibition behavior and that four tested samples can be divided into three wettability categories more water wet mixed wet and more oil wet overall the variable wettability of barnett samples will affect hydrocarbon storage distribution and production

pore types in the barnett and woodford gas shales contribution to understanding gas storage and migration pathways in fine grained rocks the identification of organoporosity microscale and nanoscale pores within organic matter in shales its importance to storage and perhaps transfer of gas molecules through shales and methods for gathering three dimensional images of the pores such as by argon ion milling and or field emission scanning electron microscopy have all been well documented and discussed for unconventional gas shales however other types of pores exist within shales that can be important to storage and migration of gas and oil and other technologies are available for their identification and imaging the different pore types found in the barnett and woodford shales are described and classified in this article scanning electron microscopy revealed the presence of porous floccules in both the barnett and woodford shales which appear similar to laboratory produced floccules and to those in other ancient shales published experimental and observational studies indicate that floccules are hydraulically equivalent to coarser grains and are transported by traction processes current induced microsedimentary structures and textures within the barnett and woodford shales as well as the preserved floccules suggest such processes were active during transport and deposition pore spaces between the floccules are open and can provide storage space as well as permeability pathways for gas molecules through the shales pores are also found within organic matter that occurs both as discrete particles and as adsorbed coatings around clay grains in the shale they are referred to here as organopores porous fecal pellets are also common in the barnett shale preserved fossil fragments such as organic walled spores and inorganic sponge spicules have hollow central chambers which may remain partially or completely open even after burial intraparticle pores occur between grains of various minerals e g pyrite framboids microchannels within shale matrix which may be the bounding surfaces of scours or microsedimentary structures may also provide permeability pathways for hydrocarbon migration mircrofractures are also common and their initiation might be related to mineral crystal structure when present in sufficient quantity these pore types offer potential gas and oil molecule storage spaces and permeability pathways through the shales

effect of lithofacies on pore structure and new insights into pore preserving mechanisms of the over mature qiongzhusi marine shales in lower cambrian of the southern sichuan basin china abstract research on shale pore structures has furthered the understanding of shale oil and gas accumulation however understanding of mechanisms of shale lithofacies that affect pore structures remains poor restricting evaluations of marine shale and accurate estimations of gas content this study focuses on the over mature qiongzhusi marine shales in lower cambrian of the southern sichuan basin a series of laboratory experiments were conducted on core samples including x ray diffraction xrd scanning electron microscopy sem low pressure gas adsorption n2 and co2 and high pressure mercury intrusion porosimetry mip xrd results show that four main types of shale lithofacies are found in the qiongzhusi formation according to the content of siliceous carbonate and clay minerals including silica rich argillaceous shale lithofacies sal argillaceous rich siliceous shale lithofacies asl carbonate argillaceous containing siliceous shale lithofacies c asl and argillaceous siliceous mixed shale lithofacies a sml sem images reveal that three kinds of pores within the shale samples organic matter intergranular and dissolved pores with the majority being slit like and narrow slit like pores silica rich argillaceous shale lithofacies exhibit the highest pore surface areas and volumes while other shale lithofacies and carbonate clay containing siliceous shale lithofacies exhibit relatively lower pore surface areas and volumes it can be inferred that silica rich argillaceous shale lithofacies facilitate shale gas storage and flow both toc and clay mineral content are more positively correlated with the microscopic pore structure parameters of micropores than that of mesopores and thus further interpreted as two dominant factors controlling the development and distribution of micropores a relatively high quartz content in qiongzhusi shale of lower cambrian are conductive to contribute a large macropore volume but most importantly the development of rigid frameworks established by authigenic quartz pyrite and clay minerals are favorable for the preservation of primary organic matter micropores by providing effective grain supporters clay rich siliceous shale could be deemed as one of the most typical lithofacies types displaying this unique pore preserving mechanism shale lithofacies with different toc and mineral compositions exhibit distinct differences in pore structures

stochastic and deterministic controls on stratigraphic completeness and fidelity compilations of sedimentation rates determined across a large range of time spans and different sedimentary environments attest to the discontinuous nature of sedimentation and support the reasoning that hiatuses pervade sedimentary successions at multiple spatial and temporal scales the relationship between sedimentation rate and time span of observation also emphasises how stratigraphic completeness is a time span dependent concept the scaling of stratigraphic completeness with time span alludes to the likely stochastic and fractal nature of the stratigraphic record it also implies that the relationship between stratal thickness and time is inherently non linear and this has obvious implications for the way we should expect temporal processes to be recorded stratigraphically order within the stratigraphic record may arise from deterministic processes in stratigraphy most notably through astronomically influenced sedimentation intuitively a strongly ordered stratigraphic record due to the presence of cyclicity in sedimentation increases stratigraphic completeness at time spans equal to and longer than the time span of the cyclicity and minimises the non linearity between stratal thickness and time here geological data and simple modelling are used to support this supposition but these results also highlight how stochastic variability inherent in depositional processes may sensitise certain successions to missed cycles and incompleteness even in the presence of strong cyclicity this stochastic variability has the potential to mask evidence of astronomical forcing of sedimentation it is also shown how hiatuses affect the ability of a succession to faithfully record temporal processes and this is true regardless of whether hiatuses are deterministically controlled or random or indeed whether a succession is considered complete or not consequently stratigraphic completeness and stratigraphic fidelity are not synonymous terms

the stratigraphic filter and bias in measurement of geologic rates 1 erosion and deposition rates estimated from the stratigraphic record frequently exhibit a power law dependence on measurement interval this dependence can result from a power law distribution of stratigraphic hiatuses by representing the stratigraphic filter as a stochastic process called a reverse ascending ladder we describe a likely origin of power law hiatuses and thus rate scaling while power law hiatuses in certain environments can be a direct result of power law periods of stasis no deposition or erosion they are more generally the result of randomness in surface fluctuations irrespective of mean subsidence or uplift autocorrelation in fluctuations can make hiatuses more or less heavy tailed but still exhibit power law characteristics in addition we show that by passing stratigraphic data backward through the filter certain statistics of surface kinematics from their formative environments can be inferred

inferring autogenically induced depositional discontinuities from observations on experimental deltaic shoreline trajectories palaeo shoreline is a commonly used proxy for palaeo sea level but only if deposition is continuous and constant will shoreline trajectory t l completely capture sea level time series e t artificial deltas were generated in the eurotank flume facility under stepwise tectonic subsidence periodic sea level fluctuation and two periodic water discharge scenarios one in phase and the other out of phase with sea level independent input variables tectonic subsidence y sea level e and water discharge q controlling sediment supply s were varied and dependent output variable shoreline trajectory twas monitored these experiments confirm that deposition is discontinuous even for continuous sediment supply and this hinders the inference of sea level curve from shoreline trajectory these results justify the here developed methodology for converting shoreline trajectory from the space domain to the time domain thereby improving the accuracy of the inferred sea level curve 2015 john wiley sons ltd

estimating the error of age interpolation in sedimentary rocks magnetostratigraphic data can provide information on rates of sediment accumulation within a single sedimentation system over time spans from 104 to 106 yr the short term rate of sediment deposition varies with time the apparent average rate over any longer interval also depends on the relative durations of periods of deposition stasis non deposition and erosion while the average rate can be used to infer the time of occurrence of an event from its stratigraphical position the inferred age has an uncertainty deriving from the variability in rate of sediment accumulation over all shorter timescales we analyse here variability in sediment accumulation rates provided by the magnetostratigraphy of miocene siwalik sediments from pakistan for long periods 106 yr sediment accumulation is approximately linear through time over short intervals 104 105yr however there is considerable variability to provide an error term for an absolute age interpolated between boundaries of polarity units we use a resampling technique similar to the statistician s bootstrapping we illustrate this approach by estimating a standard error for the interpolated age of a biostratigraphical datum the first appearance of hipparionine equids in the siwalik sequence near the town of khaur the first appearance of hipparion in the khaur sequence is 9 22 0 09 myr

geometric interpretation of time scale dependent sedimentation rates abstract empirical rate data show that aggradation and progradation rates are negatively correlated with the duration they are averaged over this means that we cannot understand deep time sedimentation rates in terms of the abundant rate data we have from modern environments we are addressing this by investigating how growth of a sediment volume in multiple directions affects time averaged accumulation rates that do not necessarily measure all directions of growth we derive a mathematical model from mass balance considerations of a sedimentary deposit that grows without erosion we show that the non linear relationship between the lengths areas and volumes of growing objects require that time averaged sedimentation rates are time scale dependent when a deposit grows in multiple directions we generate rate compilations from simple synthetic stratigraphies which show that we can reproduce the empirical rate compilations by requiring only that deposition occur in a dynamic mosaic of sequential patches in which the areal extent of deposition increases with time scale as described by our mathematical model our model has two implications with application in stratigraphic analysis the first is that it provides a theoretical model of why we cannot expect high stratigraphic completeness if we measure a deposit in fewer directions than it has grown the second is that it provides a framework by which to attribute anomalies in the stratigraphic completeness of a one dimensional or two dimensional sample to scaling effects or erosional hiatuses

quantifying the stratigraphic completeness of delta shoreline trajectories understanding the incomplete nature of the stratigraphic record is fundamental for interpreting stratigraphic sequences methods for quantifying stratigraphic completeness for one dimensional stratigraphic columns defined as the proportion of time intervals of some length that contain stratigraphy are commonplace however quantitative assessments of completeness in higher dimensions are lacking here we present a metric for defining stratigraphic completeness of two dimensional shoreline trajectories using topset foreset rollover positions in dip parallel sections and describe the preservation potential of a shoreline trajectory derived from the geometry of the delta surface profile and the kinematics of the geomorphic shoreline trajectory two end member forward models are required to fully constrain the preservation potential of the shoreline dependent on whether or not a topset is eroded during base level fall a laboratory fan delta was constructed under nonsteady boundary conditions and one dimensional stratigraphic column and two dimensional shoreline completeness curves were calculated results are consistent with the hypothesis derived from conservation of sediment mass that completeness over all timescales should increase given increasing dimensions of analysis stratigraphic trajectories and completeness curves determined from forward models using experimental geomorphic trajectories compare well to values from transects when subsampled to the equivalent stratigraphic resolution as observed in the actual preserved sequence the concept of stratigraphic completeness applied to two dimensional trajectory analysis and the end member forward models presented here provide novel tools for a conceptual understanding of the nature of stratigraphic preservation at basin scales

fractured shale gas systems the first commercial united states natural gas production 1821 came from an organic rich devonian shale in the appalachian basin understanding the geological and geochemical nature of organic shale formations and improving their gas producibility have subsequently been the challenge of millions of dollars worth of research since the 1970s shale gas systems essentially are continuous type biogenic predominant thermogenic or combined biogenic thermogenic gas accumulations characterized by widespread gas saturation subtle trapping mechanisms seals of variable lithology and relatively short hydrocarbon migration distances shale gas may be stored as free gas in natural fractures and intergranular porosity as gas sorbed onto kerogen and clay particle surfaces or as gas dissolved in kerogen and bitumen five united states shale formations that presently produce gas commercially exhibit an unexpectedly wide variation in the values of five key parameters thermal maturity expressed as vitrinite reflectance sorbed gas fraction reservoir thickness total organic carbon content and volume of gas in place the degree of natural fracture development in an otherwise low matrix permeability shale reservoir is a controlling factor in gas producibility to date unstimulated commercial production has been achievable in only a small proportion of shale wells those that intercept natural fracture networks in most other cases a successful shale gas well requires hydraulic stimulation together the devonian antrim shale of the michigan basin and devonian ohio shale of the appalachian basin accounted for about 84 of the total 380 bcf of shale gas produced in 1999 however annual gas production is steadily increasing from three other major organic shale formations that subsequently have been explored and developed the devonian new albany shale in the illinois basin the mississippian barnett shale in the fort worth basin and the cretaceous lewis shale in the san juan basin in the basins for which estimates have been made shale gas resources are substantial with in place volumes of 497 783 tcf the estimated technically recoverable resource exclusive of the lewis shale ranges from 31 to 76 tcf in both cases the ohio shale accounts for the largest share

quantifying stratigraphic completeness a probabilistic approach using paleomagnetic data although sedimentary hiati of variable magnitude are abundant in most stratigraphic sections quantification of the degree of completeness for individual sections has proven difficult a new method of estimating stratigraphic completeness is developed for sections that preserve a detrital remanent magnetic reversal history because the timing of geomagnetic reversals is independent of sedimentation events the distribution of reversals in a stratigraphic section can be used to evaluate completeness the most direct method in which sections are sampled at the top and base of each stratigraphic unit evaluates the frequency of reversals within units versus at unit contacts the more complete a section the greater the probability that reversals occurred during depositional events and are recorded as within unit reversals the less complete a section the greater the probability that reversals occurred during depositional hiati and are recorded as unit contact reversals monte carlo simulations suggest that

morphology genesis and distribution of nanometer scale pores in siliceous mudstones of the mississippian barnett shale research on mudrock attributes has increased dramatically since shale gas systems have become commercial hydrocarbon production targets one of the most significant research questions now being asked focuses on the nature of the pore system in these mudrocks our work on siliceous mudstones from the mississippian barnett shale of the fort worth basin texas shows that the pores in these rocks are dominantly nanometer in scale nanopores we used scanning electron microscopy to characterize barnett pores from a number of cores and have imaged pores as small as 5 nm key to our success in imaging these nanopores is the use of ar ion beam milling this methodology provides flat surfaces that lack topography related to differential hardness and are fundamental for high magnification imaging nanopores are observed in three main modes of occurrence most pores are found in grains of organic matter as intraparticle pores many of these grains contain hundreds of pores intraparticle organic nanopores most commonly have irregular bubblelike elliptical cross sections and range between 5 and 750 nm with the median nanopore size for all grains being approximately 100 nm internal porosities of up to 20 2 have been measured for whole grains of organic matter based on point count data from scanning electron microscopy analysis these nanopores in the organic matter are the predominant pore type in the barnett mudstones and they are related to thermal maturation nanopores are also found in bedding parallel wispy organic rich laminae as intraparticle pores in organic grains and as interparticle pores between organic matter but this mode is not common although less abundant nanopores are also locally present in fine grained matrix areas unassociated with organic matter and as nano to microintercrystalline pores in pyrite framboids intraparticle organic nanopores and pyrite framboid intercrystalline pores contribute to gas storage in barnett mudstones we postulate that permeability pathways within the barnett mudstones are along bedding parallel layers of organic matter or a mesh network of organic matter flakes because this material contains the most pores

nano scale pore structure and fractal dimension of organic rich wufeng longmaxi shale from jiaoshiba area sichuan basin investigations using fe sem gas adsorption and helium pycnometry abstract much attention have been recently paid to the upper ordovician wufeng shale o3w and lower silurian longmaxi shale s1l in the jiaoshiba area of sichuan basin which is now the largest producing shale gas field in china field emission scanning electron microscopy fe sem low pressure gas n2 and co2 adsorption helium pycnometry x ray diffraction and geochemical analyses were performed to investigate the pore structure and fractal dimension of the pores in o3w s1l shale formation in the jiaoshiba area fe sem images show that organic matter om pores are dominant in the organic rich samples and these pores are often irregular bubble like elliptical and faveolate in shape while in organic poor samples limited and isolated interparticle interp intraparticle intrap and om pores are observed reversed s shaped isotherms obtained from nitrogen adsorption are type and hysteresis loops indicate that the shape of micropore in the samples is slit or plate like bet surface areas and total pore volume vary from 12 2 to 27 1 m2 g and from 1 8 10 2 to 2 9 10 2 cm3 g with an average of 19 5 m2 g and 2 3 10 2 cm3 g respectively adsorption volume from both n2 and co2 adsorption increases with respect to toc contents porosities obtained from helium porosimetry are comparable with these from gas co2 and n2 adsorption in o3w s1l shale however porosity determined by quantitative fe sem analysis is much smaller which is mainly related to limited resolution and the small areas of investigation based on the frenkel halsey hill fhh model of low pressure n2 adsorption fractal dimensions of the pores varied from 2 737 to 2 823 relationships between pore structure parameters and toc content mineral composition and fractal dimension reveal that the fractal dimension is mainly associated with micropores samples with higher toc content higher quartz content and lower clay content tend to contain more heterogeneous micropores resulting in higher fractal dimensions and more complicated pore structure in shales therefore fractal dimension is an effective parameter to reflect the complexity of pore structure and the degree of micropore development in o3w s1l shale