influence of pore pressure on the event size distribution of induced earthquakes 1 during an enhanced geothermal system egs experiment fluid is injected at high pressure into crystalline rock to enhance its permeability and thus create a reservoir from which geothermal heat can be extracted the fracturing of the basement caused by these high pore pressures is associated with microseismicity however the relationship between the magnitudes of these induced seismic events and the applied fluid injection rates and thus pore pressure is unknown here we show how pore pressure can be linked to the seismic frequency magnitude distribution described by its slope theb value we evaluate the dataset of an egs in basel switzerland and compare the observed event size distribution with the outcome of a minimalistic model of pore pressure evolution that relates event sizes to the differential stress d we observe that the decrease of b values with increasing distance of the injection point is likely caused by a decrease in pore pressure this leads to an increase of the probability of a large magnitude event with distance and time

statistical analysis of the induced basel 2006 earthquake sequence introducing a probability based monitoring approach for enhanced geothermal systems summary geothermal energy is becoming an important clean energy source however the stimulation of a reservoir for an enhanced geothermal system egs is associated with seismic risk due to induced seismicity seismicity occurring due to the water injection at depth have to be well recorded and monitored to mitigate the seismic risk of a damaging event an appropriate alarm system needs to be in place for each individual experiment in recent experiments the so called traffic light alarm system based on public response local magnitude and peak ground velocity was used we aim to improve the pre defined alarm system by introducing a probability based approach we retrospectively model the ongoing seismicity in real time with multiple statistical forecast models and then translate the forecast to seismic hazard in terms of probabilities of exceeding a ground motion intensity level one class of models accounts for the water injection rate the main parameter that can be controlled by the operators during an experiment by translating the models into time varying probabilities of exceeding various intensity levels we provide tools which are well understood by the decision makers and can be used to determine thresholds non exceedance during a reservoir stimulation this however remains an entrepreneurial or political decision of the responsible project coordinators we introduce forecast models based on the data set of an egs experiment in the city of basel between 2006 december 2 and 8 approximately 11500 m 3 of water was injected into a 5km deep well at high pressures a six sensor borehole array was installed by the company geothermal explorers limited gel at depths between 300 and 2700 m around the well to monitor the induced seismicity the network recorded approximately 11200 events during the injection phase more than 3500 of which were located with the traffic light system actions where implemented after an ml 2 7 event the water injection was reduced and then stopped after another ml 2 5 event a few hours later an earthquake with ml 3 4 felt within the city occurred which led to bleed off of the well a risk study was later issued with the outcome that the experiment could not be resumed we analyse the statistical features of the sequence and show that the sequence is well modelled with the omori utsu law following the termination of water injection based on this model the sequence will last 31 29 14 years to reach the background level we introduce statistical models based on reasenberg and jones and epidemic type aftershock sequence etas models commonly used to model aftershock sequences we compare and test different model setups to simulate the sequences varying the number of fixed and free parameters for one class of the etas models we account for the flow rate at the injection borehole we test the models against the observed data with standard likelihood tests and find the etas model accounting for the on flow rate to perform best such a model may in future serve as a valuable tool for designing probabilistic alarm systems for egs experiments

investigation of permeability change in ultradeep coal seams using time lapse pressure transient analysis a pilot project in the cooper basin australia very limited literature is available relating to gas production from ultradeep 9000 ft 2700 m coal seams this paper investigates permeability enhancement in ultradeep coal seams of the late carboniferous and early permian to late triassic cooper basin in central australia using a time lapse pressure transient analysis pta approach for a pilot well the gas production history and three extended shut in periods are used to construct the time lapse pta for the study well a new approach is introduced to construct a permeability ratio function this function allows the calculation of permeability change resulting from competition between the compaction and coal matrix shrinkage effects pressure transient analysis indicates that gas flow is dominated by a bilinear flow regime in all extended pressure buildup tests hence reservoir depletion is restricted to the stimulated area near the hydraulic fracture this implies that well completion practices that create a large contact area with reservoirs such as multistage hydraulically fractured horizontal wells may be required for achieving economic success in these extremely low permeability reservoirs the permeability ratio is constructed using the slope of the straight lines in bilinear flow analysis because of uncertainty in average reservoir pressure probabilistic analysis is used and a monte carlo simulation is performed to generate a set of possible permeability ratio values the permeability ratio values indicate that coal permeability has increased during the production life of the wellbore because of the coal matrix shrinkage effect permeability enhancement in this ultradeep coal reservoir has offset the effect of permeability reduction caused by compaction which is beneficial to gas production

the importance of earthquake interactions for injection induced seismicity retrospective modeling of the basel enhanced geothermal system author s catalli f rinaldi ap gischig v nespoli m wiemer s abstract 2016 american geophysical union all rights reserved we explore the role of earthquake interactions during an injection induced seismic sequence we propose a model which considers both a transient pressure and static stress redistribution due to event interactions as triggering mechanisms by calibrating the model against observations at the enhanced geothermal system of basel switzerland we are able to reproduce the time behavior of the seismicity rate we observe that considering earthquake interactions in the modeling leads to a larger number of expected seismic events 24 more if compared to a pressure induced seismicity only the increase of the number of events is particularly evident after the end of the injection we conclude that implementing a model for estimating the static stress changes due to mutual event interactions increases significantly the understanding of the process and the behavior of induced seismicity

cross formational flow of water into coalbed methane reservoirs controls on relative permeability curve shape and production profile coalbed methane cbm wells tend to produce large volumes of water especially when there is hydraulic connectivity between coalbed and nearby formations cross formational flow between producing coal and adjacent formations can have significant production and environmental implications affecting economic viability of production from these shallow reservoirs such flows can also affect how much gas can be removed from a coalbed prior to mining and thus can have implications for methane control in mining as well the aim of this paper is to investigate the impact of water flow from an external source into coalbed on production performance and also on reservoir variables including cleat porosity and relative permeability curves derived from production data analysis a reservoir model is constructed to investigate the production performance of a cbm well when cross formational flow is present between the coalbed and the overlying formation results show that cleat porosity calculated by analysis of production data can be more than one order of magnitude higher than actual cleat porosity due to hydraulic connectivity water saturation within coalbed does not considerably change for a period of time and hence the peak of gas production is delayed upon depletion of the overlying formation water saturation in coalbed quickly decreases rapid decline of water saturation in the coalbed corresponds to a sharp increase in gas production as an important consequence when cross flow is present gas and water relative permeability curves derived from simulated production data have distinctive features compared to the initial relative permeability curves in the case of cross flow signatures of relative permeability curves are concave downward and low gas permeability for a range of water saturation followed by rapid increase afterward for water and gas respectively the results and analyses presented in this work can help to assess the impact of cross formational flow on reservoir variables derived from production data analysis and can also contribute to identifying hydraulic connectivity between coalbed and adjacent formations

a numerical model for fluid injection induced seismicity at soultz sous forets abstract during fluid injection experiments at the geothermal site of soultz sous forets france more than 114 000 induced seismic events with magnitudes between 2 0 and 2 9 were detected by a local downhole monitoring network of these 35 039 events are sufficiently constrained to be located hypocenters align along a sub vertical planar structure with the apparent width being dominated by data scattering indicating that seismic activity predominantly occurs along a pre existing larger scale fault structure for this scenario we present a numerical model to simulate hydraulic overpressures and induced seismicity during hydraulic injection the numerical model is based on the physical processes of fluid pressure and stress diffusion with triggering of the induced seismicity being controlled by coulomb friction even in its simplest form of a fault zone without any structural heterogeneity the numerical model reproduces typical observations at soultz sous forets such as number and magnitude of induced events hypocenter locations including the kaiser effect occurrence of post injection seismicity and the largest magnitude event occurring several days after shut in

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

relative permeability of cbm reservoirs controls on curve shape abstract relative permeability to gas and water for 2 phase flow coalbed methane cbm reservoirs has long been known to exhibit a strong control on gas and water production profile characteristics despite its important control on both primary and enhanced recovery of cbm for coal seams that have not been fully dewatered relative permeability in coal has received little attention in the literature in the past decade there are few published laboratory derived curves these studies and their resulting data represent a small subset of the commercial cbm reservoirs and do not allow for a systematic investigation of the physical controls on relative permeability curve shape other methods for estimation of relative permeability curves include derivation from simulation history matching and production data analysis both of these methods will yield pseudo relative permeability curves whose shapes could be affected by several dynamic cbm reservoir and operating characteristics the purpose of the current work is to perform a systematic investigation of the controls on cbm relative permeability curve shape including non static fracture permeability and porosity multi layer effects and transient flow to derive the relative permeability curves effective permeability to gas and water are obtained from flow equations flow rates and pressure data simulated cases are analyzed so that derived and input curves may be compared allowing for investigation of cbm reservoir properties on curve shape one set of relative permeability curves that were input into the simulator were obtained from pore scale modeling field cases from two basins are also examined and controls on derived relative permeability curve shape inferred the results of this work should be useful for future cbm development and greenhouse gas sequestration studies and it is hoped that it will spark additional research of this critical cbm flow property

inter event times of fluid induced earthquakes suggest their poisson nature 1 we analyze the inter event time distribution of fluid injection induced earthquakes for six catalogs collected at geothermal injection sites at soultz sous forets and basel we find that the distribution of waiting times during phases of constant seismicity rate coincides with the exponential distribution of the homogeneous poisson process hpp we analyze the waiting times for the complete event catalogs and find that as for naturally occurring earthquakes injection induced earthquakes are distributed according to a non homogeneous poisson process in time moreover the process of event occurrence in the injection volume domain is a hpp these results indicate that fluid injection induced earthquakes are directly triggered by the loading induced by the fluid injection we also consider the spatial distance between events and perform a nearest neighbor analysis in the time space magnitude domain our analysis including a comparison to a synthetic catalog created according to the etas model reveals no signs of causal relationships between events therefore coupling effects between events are very weak the poisson model seems to be a very good approximation of fluid induced seismicity

gas and water relative permeability in different coals model match and new insights abstract a recently derived relative permeability model for coal reservoirs has been applied to fit the published gas water relative permeability data for different coals from europe china australia and the u s which exhibit a myriad of shapes and curvatures the two parameter model is shown to be capable of describing a total of 32 sets of data including those history matched from field production and laboratory core flooding tests as well as laboratory measured ones the fitted values of the two model parameters namely cleat tortuosity parameter and cleat size distribution index fall in the range between 0 and 2 and 0 3 and 8 8 respectively for the european and chinese coals whose rank information is available there is tentative evidence that a u shape correlation between and coal rank exists whereas no discernible trend is observed for this u shape dependency on coal rank has also been reported for some other coal properties such as total porosity

the role of triggering by static stress transfer during geothermal reservoir stimulation 1 during creation of an enhanced geothermal system massive fluid injections are conducted to induce fracture shear which generates reservoir permeability in this study we analyze coseismic static stress transfer caused by induced seismic events during a stimulation at the european research project at soultz sous forets alsace france for this purpose we developed an efficient method to calculate coseismic static stress changes from an elliptical slip distribution on a circular fracture using superposition of rectangular sources which enables us to apply an analytical solution for fast computation this method is applied on a data set of 715 focal mechanisms derived from seismic recordings of the stimulation of the well gpk2 to calculate temporal evolution of static stress transfer we find that the resulting structure of coseismic stress changes can be divided into three parts a quiet zone where no spreading of seismicity occurs an active zone within the created reservoir with ongoing fracturing and a process zone where the growth of the reservoir occurs static stress changes in the active zone are of the order of 1 mpa both positive and negative but may exceed this value considerably on a local scale analysis of stress changes from a cluster of events that occurred after shut in lets us conclude that triggering by coseismic static stress changes is possible for some events our analysis shows that triggering by static stress transfer plays a minor role for injection induced seismicity in a volumetric reservoir whereas it can be quite effective for rupture propagation along single large fault zones

relative permeabilities of gas and water for different rank coals characteristics of gas water two phase flow through coal seams play crucial roles in water depletion and gas production associated with coalbed methane cbm recovery one of the most important characteristic is the relative permeability of gas and water which is largely dependent on gas water saturations in coal varying with coal ranks for better understanding of the seepage mechanism of the gas water flow in coal the relative permeabilities of gas and water in different rank coals selected from south qinshui basin have been investigated under various gas water saturations through water replacement with methane using an unsteady state method the results have shown that the ratio of effective methane permeability and absolute permeability is obviously increasing with rank implying that the gas slippage of high rank coal has more significant effect than the low rank coal a series of relative permeability curves for selected coals have been obtained all of these curves show that the selected coals are featured by smaller methane permeabilities and narrow spans of two phase flow regions and lower relative permeability and have low methane permeabilities under irreducible water condition as well the experiments also revealed that the selected coals exhibit high residual water saturation with low relative permeabilities of gas and water with increasing of the maximal vitrinite reflectance the irreducible water saturation exhibits a u shaped tendency whereas the methane permeability under the irreducible water condition generally increases the irreducible water saturation slightly increases with increasing of vitrinite and weakly decreases as inertinite increases while the methane permeability under irreducible water condition is negatively related with vitrinite and positively related to inertinite to some extent the experimental data were further parameterized to correlate the relative permeabilities of methane and water to gas saturation showing that a correlation of power function can fit the experiments well as a result a permeability model incorporated with coal rank and maceral compositions with gas saturation was developed to predict the relative permeabilities of gas methane and water in coals

an improved relative permeability model for coal reservoirs abstract in this work the conventional relative permeability model for two phase flow in porous media is improved to describe the relative permeability for coal the fracture geometry is considered through applying the matchstick model instead of the bundle of capillary tubes model which is often used as the conceptual model for conventional porous media to derive the relative permeability model the effect of porosity change on relative permeability for coal is taken into account by introducing a residual phase saturation model and a shape factor as functions of permeability ratio in the improved model the relative permeability is dependent on both the phase saturation and the porosity or permeability change this improved model shows a strong capability to match the experimental data for different coal relative permeability measurements furthermore we evaluate the relative permeability models as a unary function of wetting phase saturation and as a binary function of wetting phase saturation and permeability ratio in a coupled numerical model for water gas flow in coal seams the results illustrate that the relative permeability change due to the porosity change can significantly affect the evolution of wetting phase saturation and the gas production rate

on the stress dependence of the earthquake b value laboratory experiments have shown that the b value in the size distribution of acoustic emission events decreases linearly with differential stress there have been a number of observations that indicate that this relation may also hold for earthquakes here using a simple frictional strength model for stresses in the continental lithosphere combined with earthquake b values measured as a function of depth in a wide variety of tectonic regions we verify and calibrate that relation finding b 1 23 0 06 0 0012 0 0003 1 3 where the stress difference 1 3 is in megapascal for subduction zones we find that b value correlates linearly with the slab pull force and with the net reduction of plate interface normal force both of which also indicate a negative linear relation between b value and differential stress

identification of potential locations for well placement in developed coalbed methane reservoirs abstract this study investigates well placement in developed coalbed methane cbm reservoirs a workflow is developed to find potential locations for well placement within the reservoir it consists of a reservoir simulator and statistical analysis the application of this workflow is to reduce the need to perform computationally expensive simulations in large reservoirs to obtain potential locations for drilling an additional well the workflow is also used to study the role of dominant reservoir properties in finding potential locations for well placement the effects of permeability anisotropy gas and water relative permeabilities sorption time and water content in well placement are discussed results demonstrate that permeability anisotropy results in the formation of elliptical drainage areas around the wells when drainage patterns are orthogonal to the direction of placement of wells the drainage area of the reservoir is large and penetrated into distant locations this leads to a non uniform drainage area and extends well placement options to distant locations comparison between well placement in two scenarios with different gas and water relative permeabilities shows that potential locations tend to be on a border region between existing wells and virgin area when water mobility is restricted by water relative permeabilities this region has the advantage of having higher pressure and gas content compared to locations among existing wells in this study changing the sorption time does not affect the well placement within the reservoir except at very early times gas production from presented reservoir models is mainly controlled by darcy flow in cleat system permeability dominated rather than diffusion process in coal matrix

variations in earthquake size distribution across different stress regimes the earthquake size distribution follows in most instances a power law1 2 with the slope of this power law the b value commonly used to describe the relative occurrence of large and small events a high b value indicates a larger proportion of small earthquakes and vice versa statistically significant variations of b values have been measured in laboratory experiments mines and various tectonic regimes such as subducting slabs near magma chambers along fault zones and in aftershock zones3 however it has remained uncertain whether these differences are due to differing stress regimes as it was questionable that samples in small volumes such as in laboratory specimens mines and the shallow earth s crust are representative of earthquakes in general given the lack of physical understanding of these differences the observation that b values approach the constant 1 if large volumes are sampled4 was interpreted to indicate that b 1 is a universal constant for earthquakes in general5 here we show that the b value varies systematically for different styles of faulting we find that normal faulting events have the highest b values thrust events the lowest and strike slip events intermediate values given that thrust faults tend to be under higher stress than normal faults we infer that the b value acts as a stress meter that depends inversely on differential stress

integration of vertical and in seam horizontal well production analyses with stochastic geostatistical algorithms to estimate pre mining methane drainage efficiency from coal seams blue creek seam alabama coal seam degasification and its efficiency are directly related to the safety of coal mining degasification activities in the black warrior basin started in the early 1980s by using vertical boreholes although the blue creek seam which is part of the mary lee coal group has been the main seam of interest for coal mining vertical wellbores have also been completed in the pratt mary lee and black creek coal groups of the upper pottsville formation to degasify multiple seams currently the blue creek seam is further degasified 2 3 years in advance of mining using in seam horizontal boreholes to ensure safe mining the studied location in this work is located between tuscaloosa and jefferson counties in alabama and was degasified using 81 vertical boreholes some of which are still active when the current long mine expanded its operation into this area in 2009 horizontal boreholes were also drilled in advance of mining for further degasification of only the blue creek seam to ensure a safe and a productive operation this paper presents an integrated study and a methodology to combine history matching results from vertical boreholes with production modeling of horizontal boreholes using geostatistical simulation to evaluate spatial effectiveness of in seam boreholes in reducing gas in place gip results in this study showed that in seam wells boreholes had an estimated effective drainage area of 2050 acres with cumulative production of 604 mmscf methane during 2 years of operation with horizontal borehole production gip in the blue creek seam decreased from an average of 1 52 mmscf to 1 23 mmscf per acre it was also shown that effective gas flow capacity which was independently modeled using vertical borehole data affected horizontal borehole production gip and effective gas flow capacity of coal seam gas were also used to predict remaining gas potential for the blue creek seam

a case study of nonmesocyclone tornado development in northeast colorado similarities to waterspout formation abstract the evolution of the 26 july 1985 erie colorado tornado is described using data from ncar s cp 2 doppler radar this tornado develops within 20 km of the radar site under weakly forced synoptic conditions and weak tropospheric flow and is not accompanied by a mesocyclone the initial circulation forms near the surface at the intersection of two mesoscale boundaries and develops vertically intensifying into an fl tornado when it becomes collocated with the intense updrafts of a rapidly developing cumulonimbus this tornado appears to be the land equivalent of a waterspout and comparisons between the two vortices are made it is speculated that florida and portions of the western high plains may be prone to nonmesocyclone tornado development and that vortex intensification processes associated with nonmesoscyclone tornadoes may be important in mesocyclone tornadogenesis suggestions on how to better forecast these tornadoes are also presented

the role of coulomb stress changes for injection induced seismicity the basel enhanced geothermal system 1 we estimate coulomb stress variations cfs by considering interactions among 163 earthquakes ml 3 4 that occurred during the hydraulic stimulation of the enhanced geothermal system in basel switzerland in 2006 we observe that overall 75 of event locations are consistent with positive cfs the performance of the model increases with time and distance from injection accordingly with the presumed less dominant role of the pore pressure further from the injection well and after shut in we analyze the sensitivity of results to location and focal mechanism uncertainties the fault plane ambiguity and the friction coefficient we find that cfs are highly sensitive to location accuracy but robust with regard to uncertainties of the other parameters our results suggest that i the coulomb model may complement conventional pore pressure triggering models and ii implementing it for time dependent seismic hazard assessment during fluid injection may improve the forecasting ability but will require highly accurate hypocenter estimates

balancing reservoir creation and seismic hazard in enhanced geothermal systems summary fractureshear dilatancyisanessentialprocessforenhancingthepermeabilityofdeepgeothermal reservoirs and is usually accompanied by the radiation of seismic waves however the hazard and risk perspective of induced seismicity research typically focuses only on the question of how to reduce the occurrence of induced earthquakes here we present a quantitative analysisofseismichazardasafunctionofthetwokeyfactorsdefininganenhancedgeothermal system the permeability enhancement and the size of the stimulated reservoir our model has two coupled components 1 a pressure diffusion model and 2 a stochastic seismicity model permeability is increased in the source area of each induced earthquake depending on the amount of slip which is determined by the magnitude we show that the few largest earthquakes i e 5 10 events with m 1 5 contribute more than half of the total reservoir stimulation the results further indicate that planning and controlling of reservoir engineering operations may be compromised by the considerable variability of maximum observed magnitude reservoir size the gutenberg richter b value and shapiro s seismogenic index i e a measure of seismic reactivity of a reservoir that arises from the intrinsic stochastic nature of induced seismicity we also find that injection volume has a large impact on both reservoir size and seismic hazard injection rate and injection scheme have a negligible effect the impact of site specific parameters on seismicity and reservoir properties is greater than that of the injected volume in particular conditions that lead to high b values possibly a low differential stress level have a high impact on seismic hazard but also reduce the efficiency of the stimulation in terms of permeability enhancement under such conditions target reservoir permeability can still be achieved without reaching an unacceptable level of seismic hazard if either the initial reservoir permeability is high or if several fractures are stimulated the proposed methodology is a first step towards including induced seismic hazard analysis into the design of reservoir stimulation in a quantitative and robust manner

the numerical simulation of nonsupercell tornadogenesis part ii evolution of a family of tornadoes along a weak outflow boundary abstract nonsupercell tornadogenesis along a weak outflow boundary has been simulated using a three dimensional moist convective cloud model thermodynamic conditions similar to those observed for nonsupercell tornado nst events of the high plains were utilized in the model initialization as the ensemble system of storm outflow boundary and leading edge vortices evolve six distinct life cycle stages for the development and decay of nsts are documented that span a period of about 35 min consistent with the results of part i of this numerical study vortex sheet dynamics exert considerable control over the outflow leading edge the progression of pretornadic life cycle stages serves to concentrate vertical vorticity effectively along the outflow boundary in discrete misocyclone circulations aligned in a 3 km wavelength pattern the organization of larger scale misocyclones and ultimate intensification to initial tornadic intensity occurs coincident with the rapid development of deep convection overhe

injection induced seismicity poroelastic and earthquake nucleation effects the standard model of injection induced seismicity considers changes in coulomb strength due solely to changes in pore pressure we consider two additional effects full poroelastic coupling of stress and pore pressure and time dependent earthquake nucleation we model stress and pore pressure due to specified injection rate in a homogeneous poroelastic medium stress and pore pressure are used to compute seismicity rate through the dieterich 1994 model for constant injection rate the time to reach a critical seismicity rate scales with t r2 cfc where r is distance from the injector c is hydraulic diffusivity and fc is a factor that depends on mechanical properties and weakly on r the seismicity rate decays following a peak consistent with some observations during injection poroelastic coupling may increase or decrease the seismicity rate depending on the orientation of the faults relative to the injector if injection induced stresses inhibit slip abrupt shut in can lead to locally sharp increases in seismicity rate tapering the flux mitigates this effect the maximum magnitude event has been observed to occur postinjection we suggest the seismicity rate at a given magnitude depends on the nucleation rate the size distribution of fault segments and if the background shear stress is low the time varying volume of perturbed crust this leads to a rollover in frequency magnitude distribution for larger events with a corner that increases with time larger events are absent at short times but approach the background frequency with time larger events occurring post shut in are thus not unexpected

stress drop variations of induced earthquakes at the basel geothermal site 1 we determine stress drops from p wave spectra of about 1000 earthquakes induced by hydraulic stimulation in crystalline rock for a deep heat mining project in basel switzerland we observe an increase in stress drop by about a factor of five with radial distance from 10 m to 300 m which suggests that stress drop correlates with pore pressure perturbations due to the injection we test this hypothesis by calculating the injection related pore pressure perturbation based on a simple linear pore pressure diffusion model and find a good correlation of the expected pore pressure perturbation with the estimated stress drops

non supercell tornadoes abstract analyses of tornadoes that are not associated with supercells are presented the database for this study was collected during cinde convention initiation and downburst experiment a field project operated during the summer of 1987 in colorado a total of 27 visual vortices were studied they appeared to form as shear instabilities along radar detected convergence lines the circulations initiated at low levels generally in the absence of precipitation echo subsequently as these vortices propagated along the convergence line they appeared to strengthen to tornadic intensity when they became colocated with the updraft of a rapidly developing storm it is hypothesized that vortex stretching is responsible for intensifying the initial rotation although these tornadoes were weaker than those accompanied by strong midlevel mesocyclones estimates of their strength suggest damage capability as high as f2 the implications for operational radars to detect these types of phenomena were identified the

kinematic observations of misocyclones along boundaries during ihop during the international h2o project mobile radars collected high resolution data of several 0 5 2 kmwide vertically oriented vortices or misocyclones along at least five mesoscale airmass boundaries this study analyzes the properties of the misocyclones in three of these datasets 3 10 and 19 june 2002 to verify findings from finescale numerical models and other past observations of misocyclones and to further the understanding of the role that they play in the initiation of deep moist convection and nonsupercell tornadoes misocyclones inflect or disjoint the swath of low level convergence along each boundary to varying degrees depending on the size of their circulations when several relatively large misocyclones are next to each other the shape of low level convergence along each boundary is arranged into a staircase pattern mergers of misocyclones are an important process in the evolution of the vorticity field as a population of small vortices consolidates into a smaller number of larger ones additionally merging misocyclones may affect the mixing of thermodynamic fields in their vicinity when the merger axis is perpendicular to the boundary misocyclones interact with linear and cellular structures in the planetary boundary layers pbls of the air masses adjacent to each boundary cyclonic low level vertical vorticity generated by both types of structures makes contact with each boundary and sometimes is incorporated into preexisting misocyclones intersections of either type of pbl structure with the boundary result in strengthened pockets of low level convergence and typically strengthened misocyclones

unsteady state diffusion modeling of gas in coal matrix for horizontal well production in this work an unsteady state diffusion model was developed to describe gas transport in coal structures for horizontal well production the model assumes unsteady state diffusion of gas through the matrix according to fick s law darcy flow through the cleat network natural fractures and that gas adsorption can be described by the langmuir equation then the model using laplace integral transformation was solved using the new model dimensionless type curves for pressure transient and rate decline analyses were used to analyze transient transport characteristics the differences for unsteady state diffusion between horizontal and vertical well models and the differences for horizontal well production between unsteady state diffusion and pseudosteady state diffusion were specifically analyzed several scenarios confronting real coal beds were studied and discussed fully through simulating well production under different conditions the research results showed that the unsteady state diffusion model would be another choice with which to analyze well tests

modeling transient flow behavior of a horizontal well in a coal seam abstract cbm is an important unconventional energy resource with continuing interest in research and development based on langmuir adsorption isotherm and pseudo steady diffusion in matrix and darcy flow in the network of cleats and treating the media directly connected with horizontal wellbore as the network of cleats we established a model of cbm horizontal well production and the partial differential equations were solved by the method of laplace transform later in the paper we obtained the standard log log type curves of pressure transient and rate decline analysis using numerical simulation and analyzed the transient transport behavior thoroughly the numerical simulation results showed that the type curves are the typical response of cbm horizontal well production we also showed that type curves characteristics are affected by external boundary conditions transfer coefficient storage coefficient and adsorption coefficient etc at the end we showed the differences of our cbm horizontal well model with the cbm vertical well model and the dual porosity non coal reservoir models the research results show that our model would be a good semi analytical model to make well test interpretations in real case studies

a funnel cloud in a convective cloud line to the rear of a surface cold front abstract this brief case study describes the unusually benign environment in which a funnel cloud formed along a line of convective towers during the summer in kansas the parent cloud line was solitary and very narrow yet organized on the mesoscale the cloud line appeared to be best correlated with a zone of horizontal temperature gradient to the northwest of cool evaporatively produced outflow from an area of precipitation located just to the rear of a cold front implications for forecasting such an event are noted

forecasting implications of the 26 july 1985 northeastern colorado tornadic thunderstorm case abstract the case of a tornadic thunderstorm on 26 july 1985 in northeastern colorado is described from the synoptic to the thunderstorm scale utilizing a number of datasets some of which will become operational in the 1990s the available data included profilers doppler radar surface mesonet satellite and special soundings although the synoptic environment did not favor tornadic thunderstorms strong thunderstorms formed in localized area during a 2 h period in the afternoon and produced an 18 min tornado a number of events took place to produce the stronger then anticipated development including interaction among mesoscale outflow and stationary boundaries of particular importance was the change in the local environment along a stationary boundary known as the denver convergence vorticity zone special soundings taken near the stationary boundary revealed a deepening moist layer over time in association with the convergent wind field additional forcing from the collision of this boundary with o