modeling width adjustment in meandering channels widening in sinuous channels occurs when the retreat of the outer bank exceeds the advance of the opposite bank an analytical model is presented to simulate width adjustment in meandering channels of non cohesive bank material resulting from bank erosion of two interactive processes basal erosion and bank collapse bank collapse refers to the avalanche of non cohesive material in the upper part of bank above water surface resulting from over steepening of the bank surface due to basal erosion the rate of basal erosion including lateral erosion and bed degradation is calculated as a function of the longitudinal gradient of sediment transport rate and strength of secondary flow the transverse bed slope is treated as a variable that increases as channel sinuosity increases until the transverse bed slope reaches its maximum value by simplifying the bank collapse process for non cohesive materials the present study shows that the rate of bank line retreat is determined by lateral erosion rate near bank bed degradation rate sediment grain size and difference between flow depth and bank height the time dependent widening processes of two meandering channels in the laboratory are selected to test applicability of the model the result shows that the simulated bank lines at individual time intervals closely match the experimental measurements whether the sinuosity of a meandering channel will increase or decrease is primarily determined by didtribution of the lngitudinal gradient of sediment transport rate along the channel

hydraulic geometry river sediment and the definition of bedrock channels a growing literature deals with bedrock channels erosion processes within them and their role in landscape evolution formal definitions currently in use classify channels as bedrock when alluvial cover is discontinuous or thin this is equated with a physical property of the flow using up to date erosion laws and descriptions of channel dynamics we show that existing definitions are difficult to apply and may lead to conflicting classifications we propose the definition a bedrock channel cannot substantially widen lower or shift its bed without eroding bedrock applied to channels in taiwan this leads to a different classification than previous definitions by analysing at a station hydraulic geometry of these channels we show that the classification exposes different controls of sediment effects on dynamics of channels classified as alluvial and bedrock

simulation of multi period tectonic stress fields and distribution prediction of tectonic fractures in tight gas reservoirs a case study of the tianhuan depression in western ordos basin china abstract hydraulic fracturing technology which is emerging in low or ultralow permeability oil and gas and tight gas reservoirs has become a key technology for improving the development efficiency and economic benefit of unconventional gas reservoirs the success rate of hydraulic fracturing is closely related to the development and distribution of natural fractures data obtained from outcrops cores thin sections and image logging were used to determine the developmental characteristics of tectonic fractures in the study area to obtain a quantitative forecast of the distribution of gas reservoir fractures in the tianhuan depression with the aid of burial history analysis geologic interpretation seismic inversion logging evaluation rock mechanics and acoustic emission tests 3d geomechanical models were established using the finite element method in tianhuan depression to simulate the paleotectonic stress fields during indosinian yanshanian and himalayan periods the effects of different rock mechanics parameters on the development and distribution of tectonic fractures were identified a fracture density model was established to determine the quantitative development of tectonic fractures in the upper he8 member during the production of multi period tectonic stress fields the validity of the fracture density model was verified by the fracture statistics of drill core density and gas well productivity tests favorable areas for hydraulic fracturing were also determined simulation results indicate that the maximum and minimum principal stresses and the maximum shear stress during the indosinian yanshanian and himalayan periods are controlled by the distribution of the sand body rock mechanics parameters play important roles in the development of tectonic fractures in the sedimentary basin with less faults and folds the 3d models of the multi period tectonic stress fields and density calculation modelling are not only significant for tight gas sandstone reservoirs but also for predicting of other reservoir fractures

large flume experiments on the stable straight gravel bed channel a set of experiments is described that obtain the shape of stable straight uniform mobile bed channels with cohesionless banks these experiments were carried out in an outdoor flume at length scales at least twice those used by previous experimenters but otherwise using similar techniques including the use of a half channel against the flume wall in order to suppress meandering eight flume runs are reported including channels farther from threshold conditions than those previously tested the resulting data might prove useful both in validating theories for the stable shape of the straight channel and for advancing models of the adjustment to that shape

distribution of erosion across bedrock channels lateral erosion in bedrock rivers is an important control on the shape of channel crosssections and the coupling of channels and hillslopes recent observations link lateral erosionto the variability of flow we propose two mechanisms to explain this one is based on changing shear stress distributions within the channel with varying flood level the other on the competition between cover and tool effects in fluvial bedrock erosion we assess these processes for the liwu river taiwan and conclude that cover and tool effects dominate the partitioning of lateral and vertical erosion in this case

stable channels with mobile bed formulation and numerical solution natural rivers and streams are observed to maintain stable banks while transporting sediment over a central bed region the development of a numerical model that accounts for this essential feature of natural rivers and streams is discussed in this paper the model considers the concept of momentum diffusion and assumes a channel comprising a flat bed region and two curving bank regions the resulting boundary stress distribution is such that boundary particles in the flat bed region are subjected to stresses great enough to put them in motion while particles in the bank regions are only in a state of incipient motion it is the combination of this channel geometry and the phenomenon of momentum diffusion that allows for the successful simulation of the stable bank mobile bed condition experienced by rivers while this paper emphasizes the theoretical and numerical aspects of the problem a companion paper deals with the application and verification of the model it presents design equations and grap

fracture development in paleozoic shale of chongqing area south china part two numerical simulation of tectonic stress field and prediction of fractures distribution abstract a tectonics sedimentation evolution has been researched in southeast chongqing and the reasonable longmaxi shale highstand system tract hst and transgressive system tract tst geological model were built respectively based on the rock mechanical test and acoustic emission experiment which the samples are from field outcrop and the yuye 1 well the longmaxi shale two dimension tectonic stress field during the cenozoic was simulated by the finite element method and the distribution of fractures was predicted the research results show that the tectonic stress field and the distribution of fractures were controlled by lithology and structure as a result of cretaceous movement there are trough like folds wide spaced synclines battlement like folds similar spaces between synclines and anticlines and ejective folds wide spaced anticlines which are regularly distributed from southeast to northwest in the study area since the strain rate and other physical factors such as the viscosity are not taken into account and the stress intensity is the main factor that determines the tectonic strength therefore the stronger tectonic strength leads the higher stress intensity in the eastern and southeastern study area than in the northwest the fracture zones are mainly concentrated in the fold axis transition locations of faults and folds the regions where are adjacent to faults the fragile mineral contents such as siliceous rock carbonate rock and feldspar in the shelf facies shale from south of the study area are higher than in the bathyal facies and abyssal facies shale from center of the study area the shales characterized by low poisson s ratio and high elastic modulus from south of the study area are easily broken during cenozoic orogenic movement

unconventional shale gas systems the mississippian barnett shale of north central texas as one model for thermogenic shale gas assessment shale gas resource plays can be distinguished by gas type and system characteristics the newark east gas field located in the fort worth basin texas is defined by thermogenic gas production from low porosity and low permeability barnett shale the barnett shale gas system a self contained source reservoir system has generated large amounts of gas in the key productive areas because of various characteristics and processes including 1 excellent original organic richness and generation potential 2 primary and secondary cracking of kerogen and retained oil respectively 3 retention of oil for cracking to gas by adsorption 4 porosity resulting from organic matter decomposition and 5 brittle mineralogical composition the calculated total gas in place gip based on estimated ultimate recovery that is based on production profiles and operator estimates is about 204 bcf section 5 78 10 9 m 3 1 73 10 4 m 3 we estimate that the barnett shale has a total generation potential of about 609 bbl of oil equivalent ac ft or the equivalent of 3657 mcf ac ft 84 0 m 3 m 3 assuming a thickness of 350 ft 107 m and only sufficient hydrogen for partial cracking of retained oil to gas a total generation potential of 820 bcf section is estimated of this potential approximately 60 was expelled and the balance was retained for secondary cracking of oil to gas if sufficient thermal maturity was reached gas storage capacity of the barnett shale at typical reservoir pressure volume and temperature conditions and 6 porosity shows a maximum storage capacity of 540 mcf ac ft or 159 scf ton

impacts of the tectonic stress field on natural gas migration and accumulation a case study of the kuqa depression in the tarim basin china stress fluid and temperature are three of the major factors that impact natural gas migration and accumulation in order to study the influences of tectonic stress field on natural gas migration and accumulation in low permeability rocks we take the kuqa depression as an example and analyze the evolution of the structure and tectonic stress field at first then we study the influences of tectonic stress field at different tectonic episodes on fractures and fluid potentials through the numerical simulation method on the section across the kl2 gas field we summarize two aspects of the impact of the tectonic stress field on natural gas migration and accumulation firstly under the effects of the tectonic stress field the rock dilation increases with the added stress and strain and when the shear stress of rock exceeds its shear strength the shear fractures are well developed on one hand the faults which communicate with the hydrocarbon source rocks become the main pathways for natural gas migration on the other hand these positions where fractures are well developed near faults can become good reservoirs for natural gas accumulation secondly because fluid potentials decrease in these places near the faults where fractures are well developed natural gas can migrate rapidly along the faults and accumulates the impact of tectonic stress fields on natural gas migration and accumulation allows for hydrocarbon migration and accumulation in the low permeability rocks in an active tectonic compressive setting

river width adjustment i processes and mechanisms in 1993 a task committee tc of the asce was established to study the hydraulics bank mechanics and modeling of width adjustment in alluvial channels the work of the tc in reviewing width adjustment processes and mechanisms is reported in this paper a companion paper presents the findings of the tc with regard to width adjustment modeling this paper first establishes the geomorphic context within which width adjustments occur and it demonstrates that width adjustment may take place over a wide range of scales in time and space in the past engineering analyses of channel width have tended to concentrate on prediction of the equilibrium width for stable channels most commonly the regime extremal hypothesis and rational mechanistic approaches are used and these are reviewed herein more recently attention has switched to channels that are adjusting their morphology either due to natural instability or in response to changes in watershed land use river regulation or channel engineering chara

quantitative prediction of fractures using the finite element method a case study of the lower silurian longmaxi formation in northern guizhou south china abstract natural fractures have long been considered important factors in the production of gas from shale reservoirs because they can connect pore spaces and enlarge transport channels thereby influencing the migration accumulation and preservation of shale gas industrial level shale gas production has been initiated in the lower silurian longmaxi formation in northern guizhou south china however it is important to quantitatively predict the distribution of natural fractures in the lower silurian shale reservoirs to locate additional sweet spots in northern guizhou in this study data obtained from outcrops cores thin sections field emission scanning electron microscope fe sem images and x ray diffraction xrd were used to determine the developmental characteristics and controlling factors of these fractures correlation analysis indicated that the mechanical parameters of the longmaxi shale are mainly related to the total organic carbon toc quartz clay calcite and dolomite contents the spatial variations in the mechanical parameters of the longmaxi shale were determined based on the spatial variations in the toc and mineral contents then a heterogeneous geomechanical model of the study area was established based on interpretations of the fault systems derived from seismic data and acoustic emission ae experiments performed on samples of the relevant rocks the paleotectonic stress fields during the yanshanian period were obtained using the finite element method fem finally a fracture density calculation model was established to analyze the quantitative development of fractures and the effects of faults and mechanical parameters on the development of fractures were determined the results suggest that the main developmental period of tectonic fractures in the longmaxi formation was the early yanshanian period during this time the horizontal principal stress conditions were dominated by a se nw trending 135 315 compressional stress field and the longmaxi formation experienced a maximum tectonic stress of 110 120 mpa this simulated paleotectonic stress field was mainly controlled by faults and the contents of toc quartz clay calcite and dolomite at different positions along the same fault the degree of fracture development varies significantly overall the distribution of fractures in the longmaxi formation can be used to optimize well deployment and provides a basis for the future exploration of shale gas

least action principle equilibrium states iterative adjustment and the stability of alluvial channels the energy based least action principle lap has proven to be very successful for explaining natural phenomena in both classical and modern physics this paper briefly reviews its historical development and details how in three ways it governs the behaviour and stability of alluvial rivers first the lap embodies the special stationary equilibrium state of motion and so its incorporation with the principle of energy conservation explains why so many optimizing hypotheses have been proposed in fluvial geomorphology second the variational approach underlying the lap provides a more straightforward and simpler fuzzy object orientated method for solving river regime problems than do the various complex newtonian formulations third it is shown that in fluvial systems with surplus energy the surplus can be expended with slope and or channel geometry adjustments with the degree of channel geometry adjustment quantified by the dimensionless numbers f for depth dominated adjustment and h for width depth dominated adjustment different planforms are preferred at different energy levels with h providing a quantitative measure of the flow s efficiency for moving sediment in rivers with insufficient energy the interactions of endogenous and exogenous factors are shown to be capable in certain circumstances of achieving a stationary equilibrium condition which acts as the attractor state importantly this study describes how iterative changes enable systems to achieve such a stable equilibrium copyright 2007 john wiley sons ltd

stable width and depth of gravel bed rivers with cohesive banks an analytical model is developed to determine the influence of the bank stability on the stable width and depth of alluvial gravel bed rivers with cohesive banks the formulation of the model is based on the assumption that the stable width corresponds with an optimum condition that is equivalent to the maximum bed load transporting capacity the optimum condition develops when the channel banks are at their limiting stability with respect to either mass failure or fluvial erosion two basic channel types are identified bank height and bank shear constrained mass failure stability is estimated using a simple total stress approach a method for estimating the critical bank shear stress based on model calibration is proposed analysis of field data indicates that the effect of the bank vegetation on bank stability can be expressed in terms of the critical bank shear stress the average critical bank shear stress value calculated for riverbanks covered by vegetation with well developed root networks was fo

total petroleum system assessment of undiscovered resources in the giant barnett shale continuous unconventional gas accumulation fort worth basin texas undiscovered natural gas having potential for additions to reserves in the mississippian barnett shale of the fort worth basin north central texas was assessed using the total petroleum system assessment unit concept and a cell based methodology for continuous type unconventional resources the barnett paleozoic total petroleum system is defined in the bend arch fort worth basin as encompassing the area in which the organic rich barnett is the primary source rock for oil and gas produced from paleozoic carbonate and clastic reservoirs exploration technology and drilling in the barnett shale play have rapidly evolved in recent years with about 3500 vertical and 1000 horizontal wells completed in the barnett through 2005 and more than 85 of the them completed since 1999 using framework geology and historical production data assessment of the barnett shale was performed by the u s geological survey using vertical wells at the peak of vertical well completions and before a transition to completions with horizontal wells the assessment was performed after 1 mapping critical geological and geochemical parameters to define assessment unit areas with future potential 2 defining distributions of drainage area cell size and estimating ultimate recovery per cell and 3 estimating future success rates two assessment units are defined and assessed for the barnett shale continuous gas accumulation resulting in a total mean undiscovered volume having potential for additions to reserves of 26 2 tcfg the greater newark east fracture barrier continuous barnett shale gas assessment unit represents a core producing area where thick organic rich siliceous barnett shale is within the thermal window for gas generation ro 1 1 and is overlain and underlain by impermeable limestone barriers pennsylvanian marble falls limestone and ordovician viola limestone respectively that serve to confine induced fractures during well completion to maximize gas recovery the extended continuous barnett shale gas assessment unit which had been less explored defines a geographic area where barnett shale is 1 within the thermal window for gas generation 2 greater than 100 ft 30 m thick and 3 where at least one impermeable limestone barrier is absent mean undiscovered gas having potential for additions to reserves in the greater newark east assessment unit is estimated at 14 6 tcf and in the less tested extended assessment unit a mean resource is estimated at 11 6 tcfg a third hypothetical basin arch barnett shale oil assessment unit was defined but not assessed because of a lack of production data

modeling the evolution of channel shape balancing computational efficiency with hydraulic fidelity 1 the cross sectional shape of a natural river channel controls the capacity of the system to carry water off a landscape to convey sediment derived from hillslopes and to erode its bed and banks numerical models that describe the response of a landscape to changes in climate or tectonics therefore require formulations that can accommodate evolution of channel cross sectional geometry however fully two dimensional 2 d flow models are too computationally expensive to implement in large scale landscape evolution models while available simple empirical relationships between width and discharge do not adequately capture the dynamics of channel adjustment we have developed a simplified 2 d numerical model of channel evolution in a cohesive detachment limited substrate subject to steady unidirectional flow erosion is assumed to be proportional to boundary shear stress which is calculated using an approximation of the flow field in which log velocity profiles are assumed to apply along vectors that are perpendicular to the local channel bed model predictions of the velocity structure peak boundary shear stress and equilibrium channel shape compare well with predictions of a more sophisticated but more computationally demanding ray isovel model for example the mean velocities computed by the two models are consistent to within 3 and the predicted peak shear stress is consistent to within 7 furthermore the shear stress distributions predicted by our model compare favorably with available laboratory measurements for prescribed channel shapes a modification to our simplified code in which the flow includes a high velocity core allows the model to be extended to estimate shear stress distributions in channels with large width to depth ratios our model is efficient enough to incorporate into large scale landscape evolution codes and can be used to examine how channels adjust both cross sectional shape and slope in response to tectonic and climatic forcing

simulation of paleotectonic stress fields and quantitative prediction of multi period fractures in shale reservoirs a case study of the niutitang formation in the lower cambrian in the cen gong block south china abstract reservoirs where tectonic fractures significantly impact fluid flow are widespread industrial level shale gas production has been established from the lower cambrian niutitang formation in the cen gong block south china the practice of exploration and development of shale gas in the cen gong block shows that the abundance of gas in different layers and wells is closely related to the degree of development of fractures in this study the data obtained from outcrop cores and logs were used to determine the developmental characteristics of such tectonic fractures by doing an analysis of structural evolution acoustic emission burial history logging evaluation seismic inversion and rock mechanics tests 3 d heterogeneous geomechanical models were established by using a finite element method fem stress analysis approach to simulate paleotectonic stress fields during the late hercynian early indo chinese and middle late yanshanian periods the effects of faulting folding and variations of mechanical parameters on the development of fractures could then be identified a fracture density calculation model was established to determine the quantitative development of fractures in different stages and layers favorable areas for shale gas exploration were determined by examining the relationship between fracture density and gas content of three wells the simulation results indicate the magnitude of minimum principal stress during the late hercynian early indo chinese period within the cen gong block is 100 110 mpa with a direction of se nw 140 320 and the magnitude of the maximum principal stress during the middle late yanshanian period within the cen gong block is 150 170 mpa with a direction of nnw sse 345 165 during the late hercynian early indo chinese period the mechanical parameters and faults play an important role in the development of fractures and fractures at the downthrown side of the fault are more developed than those at the uplifted side folding plays an important role in the development of fractures in the middle late yanshanian period and faulting is a secondary control this 3 d heterogeneous geomechanical modelling method and fracture density calculation modelling are not only significant for prediction of shale fractures in complex structural areas but also have a practical significance for the prediction of other reservoir fractures

variation of in situ stress regime in coal reservoirs eastern yunnan region south china implications for coalbed methane production knowledge of in situ stress distribution is fundamental for coalbed methane production however it is poorly understood in the eastern yunnan region south china in this study the horizontal maximum shmax and minimum shmin principal stress and vertical stress sv were systematically analyzed for the first time the results indicated that the magnitudes of shmax shmin and sv showed positive correlations with burial depth in general three types of in situ stress fields were determined 1 shmax sv shmin in shallow layers with burial depths less than approximately 600 m 1970 ft below ground level bgl indicating a dominant strike slip faulting stress regime 2 in medium layers approximately 600 800 m 1970 2625 ft bgl the in situ stress state followed multiple relationships suggesting that the in situ stress regime was transformed and 3 sv shmax shmin in deep layers with burial depths greater than approximately 800 m 2625 ft bgl indicating a dominant normal faulting stress regime coal permeabilities obtained from injection falloff well tests showed that they were widely distributed and no obvious relationships were found between coal permeability and effective in situ stress magnitude in the study area the development and orientation of previously generated natural fractures combined with the present day in situ stress distribution controlled the permeability in coal reservoirs differential stress and presence of natural fractures significantly affected the geometry and pattern of hydraulic fractures in addition in the eastern yunnan region locations with relatively deep depths in vertical wells and approximately west northwest east southeast trending horizontal wells suffered high potential of borehole instability because of the high differential stress

analysis of the developmental characteristics and major regulating factors of fractures in marine continental transitional shale gas reservoirs a case study of the carboniferous permian strata in the southeastern ordos basin central china abstract fractures play an important role in the formation of shale gas reservoirs because they can enlarge the transport channels and aggregation spaces and increase the specific surface area of the gas shale for artificial hydraulic fracturing of these reservoirs the natural fracture system must be fully integrated with the artificial fracture system to form an intact fracture system in this study we first comprehensively examined the fractures in 42 shale gas wells using several approaches including a systematic examination and description of the cores and the casting of thin sections a compilation of the statistics of fracture feature parameters and observation of various analytical and test data such as the mineral composition the organic carbon contents and the rock mechanics properties for specimens from the corresponding fractured intervals the data enabled us to thoroughly explore the developmental features and major factors affecting organic rich shale fractures in the upper paleozoic carboniferous permian marine continental transitional coal bearing formation which is located in the southeastern ordos basin our results reveal that in comparison with the paleozoic marine shale in the united states and southern china as well as the paleozoic basin transitional shale in northern china the upper paleozoic black shale in the ordos basin is primarily characterized by a relatively low content of brittle minerals and a high content of clay ingredients the total content of brittle minerals e g quartz feldspar and siderite was approximately 33 which included 27 quartz and 0 3 k feldspar but did not include carbonate the total content of clay minerals reached 64 and was dominated by mixed layer illite smectite i s which accounted for more than 41 of the total clay ingredients the shale accommodated the widespread development of various types of macro and microfractures in the core specimens medium angle slip fractures and horizontal bedding cracks were the most common types of fractures whereas vertical and high angle fractures and horizontal bedding cracks were underdeveloped in the thin sections microfractures arising in organic matter laminations or at their edges as well as those of tectonic origin were the predominant type of fractures and they were mainly short narrow and open overall the surface fracture ratios of the thin sections were concentrated in a range of approximately 0 1 0 3 the developmental level of the fracture was influenced by various factors including tectonism lithology rock mechanics and organic matter and mineral content thus increased developmental level of fractures was correlated with higher paleostructural elevation and increased sand content whereas the developmental level of microfractures was correlated with high lamellation development high level of organic carbon leading to more pronounced laminations and high contents of quartz mixed layer i s and illite leading to low levels of kaolinite these findings were corroborated by other data generated in this study including the rock mechanics results for the upper paleozoic black shale and silty shale the observation results from the cores and from the thin sections sampled from more than 40 shale gas wells and the anomalies of gas logging

3d geomechanical modeling and numerical simulation of in situ stress fields in shale reservoirs a case study of the lower cambrian niutitang formation in the cen gong block south china abstract an analysis of the in situ state of stress in a shale reservoir was performed based on comprehensive information about the subsurface properties from wellbores established during the development of an oil and gas field industrial level shale gas production has occurred in the niutitang formation of the lower cambrian cen gong block south china in this study data obtained from hydraulic fracturing drilling induced fractures borehole breakout global positioning system gps and well deviation statistics have been used to determine the orientation of the maximum horizontal principal stress additionally hydraulic fracturing and multi pole array acoustic logging xmac were used to determine the vertical variations in the in situ stress magnitude based on logging interpretation and mechanical experiments the spatial distributions of mechanical parameters were obtained by seismic inversion and a 3d heterogeneous geomechanical model was established using a finite element stress analysis approach to simulate the in situ stress fields the effects of depth faults rock mechanics and layer variations on the principal stresses horizontal stress difference horizontal stress difference coefficient k h and stress type coefficient s p were determined the results show that the direction of the maximum principal stress is ese 120 additionally the development zones of natural fractures appear to correlate with regions with high principal stress differences at depths shallower than 375 m the stress type is mainly a thrust faulting stress regime at depths ranging from 375 to 950 m the stress type is mainly a strike slip faulting stress regime when the depth is 950 m the stress type is mainly a normal faulting stress regime depth fault orientation and rock mechanics all affect the type of stress the knowledge regarding the cen gong block is reliable and can improve borehole stability casing set point determination well deployment optimization and fracturing area selection

predicting the regional distribution of fracture networks using the distinct element numerical method previous research has shown the importance of understanding the relationship between fault geometry and current applied tectonic stresses in the prediction of critically stressed faults and their propensity for fluid flow via generated fracture networks along and or around the fault plane this article summarizes research aimed at increasing this understanding by applying the distinct element method dem to predict stress within a rock mass generated by far field stress on seismically resolvable faults within a modeled area we showed that increases in differential over regional stress can be correlated with the presence of fractured rock as detected by petrophysical logs and core and drilling data a case study example is used to illustrate the methodology from the penola trough otway basin south australia modeled using two dimensional dem assuming a reasonable understanding of 1 rock properties 2 structure and 3 far field or regional stress then the technique described in this article provides a valid workflow to increase confidence in the prediction of the generation of fractures and their spatial distribution

paleotectonic stress field modeling and prediction of natural fractures in the lower silurian longmaxi shale reservoirs nanchuan region south china abstract natural fractures serve as significant storage spaces for hydrocarbons and are favorable for fluid flow in shale gas reservoirs therefore predicting the intensity and distribution of natural fractures within reservoirs are of extreme significance for shale gas exploration and development natural fractures in the nanchuan region are generally in high dip angles and the dominant fracture strikes are in the ne sw and nw se directions most natural fractures within the longmaxi formation are formed in the late yanshanian period therefore in this study the late yanshanian paleotectonic stress field was numerically investigated the comprehensive rupture rate crr was defined and calculated as an indicator to quantitatively predict the intensity and distribution of natural fractures within the longmaxi formation the results indicated that regions with well developed fractures were mainly located in around fault zones and fold zones among fault fold orientations change and at fault tips the intensity and distribution of natural fractures in the longmaxi formation of nanchuan region were influenced by many factors including tectonic activities mineral compositions etc the present study provides preliminary insights into natural fractures within the longmaxi formation of nanchuan region south china which can guide and support shale gas exploration and development

correction to transient rift opening in response to multiple dike injections in the manda hararo rift afar ethiopia imaged by time dependent elastic inversion of interferometric synthetic aperture radar data 1 interferometric synthetic aperture radar insar data spanning the time intervals separating thirteen dike intrusions in the manda hararo dabbahu rift afar ethiopia from 2005 to 2009 show that transient deformation occurs in the inter diking period this deformation can be explained by the presence of seven inflating or deflating pressure sources by combining the data acquired on four different insar tracks through time dependent elastic models we are able to track these deformation modes with a time resolution smaller than 1 month sustained deflation of a deep magma reservoir at dabbahu in the 6 months following the main rifting event of 2005 and slow decelerating post eruptive re inflation of two shallow magma reservoirs below dabbahu and gabho volcanoes are monitored a deflation signal of deep origin on the neighboring rift system is also detected possibly caused by outflow of material from a preexisting reservoir into the deep plate boundary in contrast rapidly evolving deformation is observed at the center of the manda hararo rift segment transient deformation events are monitored in the weeks months following the diking events with pulses of localized rift opening after the dike intrusions followed by an exponential like decay of opening rate this signal may be associated with the replenishment of the central magma reservoir involved in feeding the 2005 2009 dikes alternatively the predominantly horizontal mode of deformation suggests an interaction between the response of the lithosphere to tectonic strain accumulation and the process of hydraulic connectivity within the central magma plumbing system

methodology for predicting reservoir breakdown pressure and fracture opening pressure in low permeability reservoirs based on an in situ stress simulation abstract using numerical simulations of the paleostress field during the time of fracture formation we predict the occurrence of fractures in the reservoirs of the second member of the funing formation in the tongcheng fault zone subei basin east china we use sonic velocity measurements from rock cores and microseismic monitoring to determine the in situ stress which is combined with fracture data to calculate the magnitude of the in situ stress at the well site by determining the mechanical parameters of the rock we use the finite element method fem to develop a geomechanical model and conduct numerical simulations of the in situ stress field based on the occurrence of fractures and the numerical simulation results of the in situ stress field we predict the opening pressure and opening sequence of natural fractures in the reservoirs the results indicate that the maximum horizontal principal stress in the second member of the funing formation in the tongcheng fault zone is oriented ene during the injection process the ene trending fractures open first and the ese trending fractures open later the opening pressure of the fractures increases as the angle between the fracture strike and the maximum horizontal principal stress increases and the burial depth of the fractures also has a relatively positive correlation with the opening pressure at the structurally high site 1850 m 2350 m the opening pressure of the fractures is in the range of 25 mpa 50 mpa and at the structurally low site 3300 m 4000 m the opening pressure of the fractures is in the range of 45 mpa 75 mpa by calculating the actual fracture pressure of the reservoirs we propose using different injection pressures in different blocks to ensure the high and stable production of oil from wells

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

geochemical characterization and methane adsorption capacity of overmature organic rich lower cambrian shales in northeast guizhou region southwest china abstract the niutitang shale lower cambrian is another set of organic rich shale in addition to the lower silurian longmaxi shale in southwest china in this study methane adsorption capacities of both whole rock and organic matter were investigated based on adsorption isotherms measured at various temperatures 40 120 c and pressures up to 35 0 mpa for eleven niutitang shale samples collected from northeast guizhou province the investigated samples cover a wide range of toc contents varying from 1 8 to 11 3 with an average equivalent vitrinite reflectance eqvro value of approximately 4 0 their bet specific surface areas and micropore volumes range from 11 1 to 26 2 m2 g rock and between 4 3 and 11 2 cm3 kg rock respectively both of which are positively correlated to toc content model fitted methane maximum absolute adsorption capacities n range from 1 80 to 5 85 cm3 g rock at 60 c and are found to largely increase with increasing toc this suggests that the toc control on methane adsorption capacity obtained by other authors for other shales with relative low thermal maturity levels may be extended to a very high thermal maturity level e g eqvro 4 0 the methane adsorption capacity of organic matter om in our shale samples however is somehow reduced as compared to the lower silurian longmaxi shale and other shales that display eqvro values smaller than 3 0 indicating thermal maturity may adversely affect methane adsorption capacity of shales when it evolves to be eqvro 4 0 nevertheless this reduction in adsorption capacity may be compensated by the very enrichment of om in the niutitang shale in addition a higher thermal maturity level results in a lower langmuir pressure value which makes it more difficult for methane desorption at reservoirs conditions the temperature dependency of adsorption parameters was also investigated which could be used to predict the changes of methane adsorption with burial depth under geological conditions beyond experimental temperature and pressure ranges

a philosophy of rivers equilibrium states channel evolution teleomatic change and least action principle until recently no universal agreement as to a philosophical or scientific methodological framework has been proposed to guide the study of fluvial geomorphology an understanding of river form and process requires an understanding of the principles that govern the behaviour and evolution of alluvial rivers at the most fundamental level to date the investigations of such principles have followed four approaches develop qualitative unifying theories that are usually untested collect and examine data visually and statistically to define semi quantitative relationships among variables apply newtonian theoretical and empirical mechanics in a reductionist manner resolve the primary flow equations theoretically by assuming maximum or minimum outputs here we recommend not a fifth but an overarching philosophy to embrace all four clarifying and formalising an understanding of the evolution of river channels and iterative directional changes in the context of least action principle lap the theoretical basis of variational mechanics lap is exemplified in rivers in the form of maximum flow efficiency mfe a sophisticated understanding of evolution in its broadest sense is essential to understand how rivers adjust towards an optimum state rather than towards some other because rivers as dynamic contemporary systems flow in valleys that are commonly historical landforms and often tectonically determined we propose that most of the world s alluvial rivers are over powered for the work they must do to remain stable they commonly evolve to expend surplus energy via a variety of dynamic equilibrium forms that will further adjust where possible to maximise their stability as much less common mfe forms in stationary equilibrium this paper 1 shows that the theory of evolution is derived from and applicable to both the physical and biological sciences 2 focusses the development of theory in geomorphology on the development of equilibrium theory 3 proposes that river channels like organisms evolve teleomatically progression towards an end state by following natural laws and iteratively one stage forming the basis for the next towards an optimal end state 4 describes lap as the methodological basis for understanding the self adjustment alluvial channels towards mfe 5 acknowledges that whereas river channels that form within their unmodified alluvium evolve into optimal minimum energy systems exogenic variables such as riparian or aquatic vegetation can cause significant variations in resultant river styles we specifically attempt to address luna leopold s lament in 1994 that no clearly expressed philosophy explains the remarkable self adjustment of alluvial channels

response of bedrock channel width to tectonic forcing insights from a numerical model theoretical considerations and comparison with field data the morphology of bedrock river channels is controlled by climatic and tectonic conditions and substrate properties knowledge of tectonic controls remains scarce this is partly due to slow tectonic rates and long response times of natural channels and partly due to the difficulty in isolating and constraining tectonic forcing conditions in the field to study the effect of tectonic forcing on channel geometry we have developed a numerical model of the cross sectional evolution of a detachment limited channel its predictions are matched by an analytical model based on the assumption of the minimization of potential energy expenditure using these models we illustrate how local tectonics can alter the observed width discharge scaling and discuss published field data in light of our findings except for one case the models fail to correctly describe field observations of well constrained cases this implies that the shear stress stream power family of models is too simple to describe the behavior of natural channels additional complexities such as sediment effects and discharge variability exert a strong control on channel morphology and need to be taken into account in the modeling of channel dynamics and steady state

simulation of three dimensional tectonic stress fields and quantitative prediction of tectonic fracture within the damintun depression liaohe basin northeast china abstract tectonic fractures are important factors that influence oil and natural gas migration and accumulation within buried hill reservoirs to obtain a quantitative forecast of the development and distribution of reservoir fractures in the damintun depression we analyzed the characteristics of regional structural evolution and paleotectonic stress field setting a reasonable geological model of the research area was built based on an interpretation of the geological structure a test for rock mechanics and experiment on acoustic emission thereafter a three dimensional paleotectonic stress field during the yanshan movement was simulated by the finite element method rock failure criterion and comprehensive evaluation coefficient of fractures were used to determine the quantitative development of fractures and predict zones that are prone to fracture development under an intense yanshan movement high stress strength is distributed in the south and northeast parts of the study area where stress is extremely high the fracture development zones are mainly controlled by the tectonic stress field and typically located in the same areas as those of high maximum principal and shear stresses the predicted areas with developed fractures are consistent with the wells with high fracture linear density and in locations with high producing oil and gas wells

numerical study of multi period palaeotectonic stress fields in lower cambrian shale reservoirs and the prediction of fractures distribution a case study of the niutitang formation in feng gang no 3 block south china abstract fractures not only control the distribution of oil and gas reservoirs but also are key points in the research of oil and gas reservoir development programmes the tectonic fractures in the lower cambrian shale reservoirs in the feng gang no 3 block are effective reservoir spaces for hydrocarbon accumulation and these fractures are controlled by palaeotectonic stress fields therefore quantitatively predicting the development and distribution of tectonic fractures in the lower cambrian shale reservoir is important for the exploration and exploitation of shale gas in the feng gang no 3 block in the present study a reasonable geological mechanical and mathematical model of the study area was established based on the faults systems interpreted from seismic data fracture characteristics from drilling data uniaxial and triaxial compression tests and experiments on the acoustic emissions ae of rocks then a three dimensional 3 d finite element method is applied to simulate the palaeotectonic stress field with the superposition of the yanshan and himalayan movements and used to predict the fracture distribution the simulation results indicate that the maximum principal stress value within the study area ranged from 269 97 mpa to 281 18 mpa the minimum principal stress ranged from 58 29 mpa to 79 64 mpa and the shear stress value ranged from 91 05 mpa to 106 21 mpa the palaeotectonic stress field is controlled by the fault zone locations the fracture development zones are mainly controlled by the tectonic stress fields and are located around the faults at the end of the fault zones at the inflection point and at the intersection of the fault zones

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

incipient motion of sand particles on side slopes several criteria have been theoretically proposed for the critical shear stress of noncohesive sediment on side slopes however no laboratory work has ever been done on this problem a theoretical study of the incipient motion of sediment particles on side slopes is presented including the effects of viscous sublayer turbulence and lift force as a special case of level beds the theory describes the experimental values reported by several workers a specially designed rotary wind tunnel permits the evaluation of the critical shear stress on side slopes and the experiment supports the theory these works reveal that the lift force can be neglected in estimating the critical shear stress using the proposed theory if the averaged experimental values are concerned but inclusion of the lift force in the theory is recommended for safety and for describing the lower limit of the possibility of incipient motion