geologic framework of the mississippian barnett shale barnett paleozoic total petroleum system bend arch fort worth basin texas this article describes the primary geologic characteristics and criteria of the barnett shale and barnett paleozoic total petroleum system tps of the fort worth basin used to define two geographic areas of the barnett shale for petroleum resource assessment from these two areas referred to as assessment units the u s geological survey estimated a mean volume of about 26 tcf of undiscovered technically recoverable hydrocarbon gas in the barnett shale the mississippian barnett shale is the primary source rock for oil and gas produced from paleozoic reservoir rocks in the bend arch fort worth basin area and is also one of the most significant gas producing formations in texas subsurface mapping from well logs and commercial databases and petroleum geochemistry demonstrate that the barnett shale is organic rich and thermally mature for hydrocarbon generation over most of the bend arch fort worth basin area in the northeastern and structurally deepest part of the fort worth basin adjacent to the muenster arch the formation is more than 1000 ft 305 m thick and interbedded with thick limestone units westward it thins rapidly over the mississippian chappel shelf to only a few tens of feet the barnett paleozoic tps is identified where thermally mature barnett shale has generated large volumes of hydrocarbons and is 1 contained within the barnett shale unconventional continuous accumulation and 2 expelled and distributed among numerous conventional clastic and carbonate rock reservoirs of paleozoic age vitrinite reflectance ro measurements show little correlation with present day burial depth contours of equal ro values measured from barnett shale and typing of produced hydrocarbons indicate significant uplift and erosion furthermore the thermal history of the formation was enhanced by hydrothermal events along the ouachita thrust front and mineral wells newark east fault system stratigraphy and thermal maturity define two gas producing assessment units for the barnett shale 1 a greater newark east fracture barrier continuous barnett shale gas assessment unit encompassing an area of optimal gas production where dense impermeable limestones enclose thick 300 ft 91 m barnett shale that is within the gas generation window ro 1 1 and 2 an extended continuous barnett shale gas assessment unit covering an area where the barnett shale is within the gas generation window but is less than 300 ft 91 m thick and either one or both of the overlying and underlying limestone barriers are absent

maps of titan s surface from 1 to 2 5 μm abstract we have acquired resolved images of titan with the adaptive optics systems pueo kir at the cfht hawaii and naos conica at the vlt chile we report here on images and maps when data at several orbital phases are available of titan s surface from observations taken during the last 4 years 2001 2004 in all the methane windows between 1 and 2 5 m namely at 1 08 1 28 1 6 and 2 m we present the only complete maps of titan currently available at 1 3 m a spectral window where titan appears particularly bright in spectroscopy with a resolution of about 200 km at best on the ground our surface maps show the bright and dark regions sharing titan s landscape with as much detail as possible from the ground and with high contrast in most cases from the information gathered by comparing the maps at different wavelengths we derive constraints on the ground s composition our results could complete optimize the return of the cassini huygens mission

titan s surface composition and atmospheric transmission with solar occultation measurements by cassini vims abstract solar occultation measurements by the cassini visual and infrared mapping spectrometer vims reveal the near infrared transmission of titan s atmosphere down to an altitude of 40 km by combining these observations with vims reflectance measurements of titan s surface and knowledge of haze and gas opacity profiles from the huygens probe we constrain a simple model for the transfer of radiation in titan s atmosphere in order to derive surface reflectance in the methane windows used for compositional analysis the advantages of this model are twofold 1 it is accurate enough to yield useful results yet simple enough to be implemented in just a few lines of code and 2 the model parameters are directly constrained by the vims occultation and on planet measurements we focus on the 2 0 2 7 2 8 and 5 0 m windows where haze opacity is minimized and diagnostic vibrational bands exist for water ice and other candidate surface species a particularly important result is the strong atmospheric attenuation at 2 7 m compared to 2 8 m resulting in a reversal of apparent spectral slope in a compositionally diagnostic wavelength range these results show that titan s surface reflectance is much bluer and more closely matched by water ice than the uncorrected spectra would indicate although the majority of titan s surface has a spectrum consistent with mixtures either intimate or areal of water ice and haze particles precipitated from the atmosphere compositions of geologic units can be accurately modeled as mixtures ranging from predominantly water ice sinlap crater ejecta and margins of dark equatorial terrain to predominantly organic rich tui regio and hotei regio with particles in the size range 10 20 m in distinguishing between hypothesized formation mechanisms for tui and hotei regio their organic rich composition favors a process that concentrates precipitated haze particles such as playa lake evaporite deposition barnes j w bow j schwartz j brown r h soderblom j m hayes a g vixie g le mouelic s rodriguez s sotin c jaumann r stephan k soderblom l a clark r n buratti b j baines k h nicholson p d 2011 icarus 216 136 140 in other places kilometer scale exposures of nearly pure water ice bedrock on titan s surface indicate relatively locally rapid erosion compared to rates of accumulation of solid hydrocarbons precipitated from the atmosphere somewhat surprisingly titan s vast equatorial dune fields appear slightly enriched in water ice compared to the surrounding bright regions but the spectrum of the dune material itself may nonetheless be consistent with a predominantly organic haze derived composition

lake charles louisiana earthquake of 16 october 1983 on 16 october 1983 at 19 40 utc a magnitude 3 8 earthquake occurred near lake charles in southwestern louisiana the earthquake was felt over an area of 2600 km2 and had a maximum modified mercalli intensity of v this was the first significant louisiana gulf coast earthquake to be recorded and located by nearby microseismic networks one possible foreshock and three aftershocks also were recorded and located using a velocity model developed for this study the focal mechanism of the earthquake was determined based on p wave first motions from 22 local and regional stations the solution indicates a predominantly east west trending southeast dipping normal fault with a small strike slip component the depth of this event 14 km provides the first significant evidence that normal faulting within the crystalline basement may control shallower growth faults along the gulf coast

radar evidence for liquid surfaces on titan arecibo radar observations of titan at 13 centimeter wavelength indicate that most of the echo power is in a diffusely scattered component but that a small specular component is present for about 75 of the subearth locations observed these specular echoes have properties consistent with those expected for areas of liquid hydrocarbons knowledge of the areal extent and depth of any deposits of liquid hydrocarbons could strongly constrain the history of titan s atmosphere and surface

evidence for the exposure of water ice on titan s surface the smoggy stratosphere of saturn9s largest moon titan veils its surface from view except at narrow wavelengths centered at 0 83 0 94 1 07 1 28 1 58 2 0 2 9 and 5 0 micrometers we derived a spectrum of titan9s surface within these windows and detected features characteristic of water ice therefore despite the hundreds of meters of organic liquids and solids hypothesized to exist on titan9s surface its icy bedrock lies extensively exposed

characteristics of loose rough boundary streams at near threshold laboratory experimental results on the turbulent flow characteristics measured by an acoustic doppler velocimeter over loose rough boundaries at the near threshold of motion are reported the primary endeavor was to investigate the response of the turbulent flow field having zero pressure gradient to the uniform gravel beds at the near threshold of motion with reasonably wide range of relative roughness e h 0 02 e h 0 15 where e nikuradse s equivalent roughness and h flow depth five uniform gravel sizes ranging from 4 1 to 14 25 mm were used in the experiments the vertical distributions of time averaged velocity turbulence intensities and the reynolds stress were measured and analyzed the variation of the mixing length is considerably linear with the depth within the inner layer whose thickness is 0 23 times the boundary layer thickness and the von karman constant is obtained as 0 35 the boundary shear stresses were determined by three independent methods such as using the logarith

induced microearthquake patterns in hydrocarbon and geothermal reservoirs six case studies the injection or production of fluids can induce microseismic events in hydrocarbon and geothermal reservoirs by deploying sensors downhole data sets have been collected that consist of a few hundred to well over 10 000 induced events we find that most induced events cluster into well defined geometrical patterns in many cases we must apply high precision relative location techniques to observe these patterns at three sedimentary sites thin horizontal strands of activity are commonly found within the location patterns we believe this reflects fracture containment between stratigraphic layers of differing mechanical properties or states of stress at a massive carbonate and two crystalline sites combinations of linear and planar features indicate networks of intersecting fractures and allow us to infer positions of aseismic fractures through their influence on the location patterns in addition the fine scale seismicity patterns often evolve systematically with time at sedimentary sites migration of seismicity toward the injection point has been observed and may result from slip induced stress along fractures that initially have little resolved shear in such cases triggering events may be critical to generate high levels of seismic activity at one crystalline site the early occurrence of linear features that traverse planes of activity indicate permeable zones and possible flow paths within fractures we hope the continued development of microseismic techniques and refinement of conceptual models will further increase our understanding of fluid behavior and lead to improved resource management in fractured reservoirs

depth averaged shear stress and velocity in open channel flows turbulent momentum and velocity always have the greatest gradient along wall normal direction in straight channel flows this has led to the hypothesis that surplus energy within any control volume in a three dimensional flow will be transferred toward its nearest boundary to dissipate starting from this the boundary shear stress the reynolds shear stress and the velocity profiles along normal lines of smooth boundary may be determined this paper is a continuous effort to investigate depth average shear stress and velocity in rough channels equations of the depth averaged shear stress in typical open channels have been derived based on a theoretical relation between the depth averaged shear stress and boundary shear stress equation of depth mean velocity in a rough channel is also obtained and the effects of water surface or dip phenomenon and roughness are included experimental data available in the literature have been used for verification that shows that the model reasonably agrees with the measured data

titan s 2 μm surface albedo and haze optical depth in 1996 2004 1 we observed titan in 1996 2004 with high resolution 2 m speckle and adaptive optics imaging at the w m keck observatory by observing in a 2 m broadband filter we obtain images that have contributions from both titan s surface and atmosphere we have modeled titan s atmosphere using a plane parallel radiative transfer code that has been corrected to agree with 3 d monte carlo predictions we find that titan s surface albedo ranges from 0 02 in the darkest equatorial region of the trailing hemisphere to 0 1 in the brightest areas of the leading hemisphere over the past quarter of a saturnian year haze optical depth in titan s southern hemisphere has decreased substantially from a value of 0 48 in 1996 down to 0 18 in 2004 while the northern haze has been increasing over the past few years as a result of these changes in 2004 the north south haze asymmetry at k band has disappeared

near infrared spectral mapping of titan s mountains and channels 1 we investigate the spectral reflectance properties of channels and mountain ranges on titan using data from cassini s visual and infrared mapping spectrometer vims obtained during the t9 encounter 26 december 2005 we identify the location of channels and mountains using synthetic aperture radar maps obtained from cassini s radar instrument during the t13 30 april 2006 flyby channels are evident even in vims imaging with spatial resolution coarser than the channel size the channels share spectral characteristics with titan s dark blue terrain e g the huygens landing site that is consistent with an enhancement in water ice content relative to the rest of titan we use this fact to measure widths of 1 km for the largest channels comparison of the data sets shows that in our study area within the equatorial bright spectral unit east of xanadu mountains are darker and bluer than surrounding smooth terrain these results are consistent with the equatorial bright terrain possessing a veneer of material that is thinner in the regions where there are mountains and streambeds that have likely undergone more recent and extensive erosion we suggest a model for the geographic relationship of the dark blue dark brown and equatorial bright spectral units based on our findings

potential field evidence for a volcanic rifted margin along the texas gulf coast potential fi eld data along the texas portion of the gulf of mexico indicate a large amplitude coast parallel magnetic maximum and a smaller bouguer gravity high models constrained by seismic refraction data indicate that these maxima manifest a deeply buried volcanic rifted passive margin or other magnetic high in the outer transitional crust buried 12 15 km the source is 220 km wide similar to the voring plateau in norway and the u s east coast this margin which formed during the opening of the gulf of mexico differs in origin from the transform boundary of the northeast mexico margin tehuantepec transform and we infer a jurassic triple junction related to the borderland rift system which is traceable as far as southeast california

scaling of seismicity induced by nonlinear fluid rock interaction 1 fluid injections into geothermal systems sometimes can produce significant seismic events with magnitudes of up to 4 however in the case of hydraulic fracturing of hydrocarbon reservoirs such events occur extremely seldom in the last case in contrast to the former one the structure of rocks is being actively destroyed e g opening of tensile fractures and the fluid rock interaction is strongly nonlinear e g a strong increase of permeability what is the role of this nonlinearity we consider nonlinear pore pressure diffusion to explain features of seismicity we formulate seismicity triggering front its propagation is sensitive to a grade of nonlinearity to spatial dimension of diffusion and to the injection rate we show that a probability of an event with a magnitude larger than a given one increases proportionally to the injected mass an increase of this probability with time is insensitive to the nonlinearity we compare different borehole experiments in some cases the injection produces clearly nonlinear impact on rocks in others this impact is approximately linear we find a well agreement with our theory we observe an insensitivity of temporal increments of magnitude probability to the grade of nonlinearity these increments are controlled by injection rate increments in contrast nonlinear fluid rock interactions are characterized by a strong dominance of small earthquakes defects activated by a nonlinear diffusion possibly obey gutenberg richter statistics with anomalous high b values in the case of a linear diffusion magnitude distributions of events are probably inherited from pre existing fracture systems

fluvial architecture and reservoir compartmentalization in the oligocene middle frio formation south texas abstract seeligson stratton and agua dulce fields south texas are being studied as part of a gas research institute department of energy state of texas cosponsored program designed to develop and test methodologies and technologies for gas reserve growth in conventional reservoirs in mature gas fields over the last five decades each field has produced approximately 2 tcf of gas from middle frio reservoirs alone recent drilling old well workover results and reservoir pressure data however point to the possibility of additional reserves within these fields the middle frio oligocene is composed of sand rich channel fill and splay deposits interstratified with floodplain mudstones all forming part of the gueydan fluvial system channel fill deposits are 30 ft 9 m thick and 2 500 ft 76 m wide splay deposits are as much as 20 ft 6 m thick proximal to channels and extend as much as 2 mi 3 km from channels channel fill and associated splay sandstones are reservoir facies porosity 20 percent permeability 10 s to 100 s md floodplain mudstones and levee sandy mudstones impede or obstruct flow and separate individual reservoirs and compartments both vertically and laterally deposition on an aggrading coastal plain resulted in a continuum of fluvial architectural styles that has important implications for reservoir compartmentalization relatively slow aggradation resulted in laterally stacked channel systems whereas more rapid aggradation resulted in vertically stacked channel systems in seeligson field laterally stacked architecture alternates with vertically stacked architecture through the 2 000 ft 610 m thick middle frio section in stratton and agua dulce fields the same general alternation in architectural modes exists through the 2 500 ft 763 m thick middle frio section in stratton and agua dulce however the reservoir zones composed of laterally stacked architecture are not laterally continuous instead the laterally stacked architecture locally changes into a vertically stacked architecture because laterally stacked sandstone bodies lead to separate but potentially leaky reservoir compartments and vertically stacked sandstone bodies favor more isolated reservoir compartments a high potential for reserve growth through the identification of untapped poorly drained and bypassed gas reservoir compartments exists in each of these fields differences in reservoir architecture also must be taken into account as part of exploitation strategies

reservoir heterogeneity in the middle frio formation case studies in stratton and agua dulce fields nueces county texas abstract selected middle frio oligocene reservoirs of stratton field and the contiguous agua dulce field are being studied as part of a gas research institute department of energy state of texas cosponsored program designed to improve reserve growth in mature gas fields during the past four decades stratton has produced 1 8 tcf of gas from 110 middle frio reservoirs and agua dulce has produced 1 6 tcf from 120 reservoirs recent drilling and workover activities however suggest the presence of additional untapped or bypassed middle frio reservoirs the middle frio is composed of sand rich channel fill and splay deposits interstratified with floodplain mudstones all forming part of the gueydan fluvial system channel fill deposits are 30 ft 9 m thick and 2 500 ft 76 m wide splay deposits are as much as 20 ft 6 m thick proximal to channels and extend as much as 2 mi 3 km from channels channel fill and associated splay sandstones are reservoir facies porosity 20 percent permeability tens to hundreds of millidarcys floodplain mudstones and levee sandy mudstones impede or obstruct flow and separate individual reservoirs and compartments both vertically and laterally the e31 6100 and e25 6050 reservoirs are examples of vertically stacked channel systems reflecting higher rates of coastal plain aggradation pressure tests strongly suggest that bypassed compartments have only recently been contacted or are still present for exploitation vertically stacked architectures are considered to be more favorable for isolated compartments and therefore are better candidates for infield reserve growth

global scale surface spectral variations on titan seen from cassini vims we present global scale maps of titan from the visual and infrared mapping spectrometer vims instrument on cassini we map at 64 near infrared wavelengths simultaneously covering the atmospheric windows at 0 94 1 08 1 28 1 6 2 0 2 8 and 5 m with a typical resolution of 50 km pixel or a typical total integration time of 1 s our maps have five to ten times the resolution of ground based maps better spectral resolution across most windows coverage in multiple atmospheric windows and represent the first spatially resolved maps of titan at 5 m the vims maps provide context and surface spectral information in support of other cassini instruments we note a strong latitudinal dependence in the spectral character of titan s surface and partition the surface into 9 spectral units that we describe in terms of spectral and spatial characteristics

spatially resolved images of titan by means of adaptive optics abstract images of titan were acquired with the adonis adaptive optics system installed at the eso 3 6 m telescope in la silla chile the near infrared range from 1 2 5 m was covered in 1994 and 1995 in the methane atmospheric windows at 1 3 1 6 and 2 0 m with narrow band filters and cvf diffraction limited images were obtained 0 14 arcsec at 2 m thus allowing us to resolve the titan disk we have corrected the images for systematic effects removed center to limb variation and applied deconvolution processes to our data the contrast on the images is on the order of 30 both the leading and trailing hemispheres were observed the 2 m images presented in this paper show a broad bright feature on the surface of titan s leading hemisphere near 114 lcm which is in agreement with the hst images and with spectroscopy performed at these longitudes from the ground that show a higher geometric albedo on titan s leading side high quality flat fielding of our data has highlighted the presence of at least two main bright spots within the equatorial region the trailing hemisphere of titan s surface is not completely dark but shows brightness near the poles with some north to south asymmetry the northern latitudes are uniformly brighter than the lower equatorial and southern latitudes factor of about 2 our results bring new constraints on the models of the satellite s surface

dallas fort worth earthquakes coincident with activity associated with natural gas production on 31 october 2008 and the following day numerous dallas fort worth dfw residents called 911 to report experiencing several small earthquakes accompanied by loud booming noises and the shaking of walls and furniture using data recorded by regional seismic stations the usgs national earthquake information center neic located nine earthquakes with magnitudes between 2 5 and 3 0 on 16 may 2009 this scenario repeated itself as local residents felt three earthquakes and the neic located four largest magnitude 3 3 a third sequence of felt events began on 2 june 2009 approximately 65 km southwest near the city of cleburne texas but has not yet been studied in detail figure 1

faulting induced by forced fluid injection and fluid flow forced by faulting an interpretation of hydraulic fracture microseismicity carthage cotton valley gas field texas we analyzed precisely located microearthquake data detected during five hydraulic fracture treatments in the carthage gas field of east texas the treat ments were conducted in two adjacent boreholes within interbedded sands and shales of the upper cotton valley formation the microearthquakes were induced within narrow horizontal bands that correspond to the targeted sandstone layers events throughout all the treatments show strike slip faulting occurring uniformly along vertical fractures trending close to maximum horizontal stress direction these events are consistent with the reservoir s prevalent natural fractures known to be isolated within the sands and trending subparallel to the expected hydraulic fracture orien tation when this uniform fracture system was activated exclusively the detected shear deformation measured as the moment release per unit volume of fluid injected was constant independent of various fluid viscosities and flow rates used within the base of the upper cotton valley formation anomalous event counts and moment release occurred within dense clusters that delineate bends or jogs in the fracture zones the mechanisms are also strike slip but the fault planes are more favorably oriented for failure the dense clusters show location patterns diverging in time suggesting the expulsion of fluids from compressive fault jogs fluid flow forced by the adjacent slip induced loading appears to initially extend the treatments but the loading also tends to lock up and concentrate stress at the jogs as evident by fewer but larger events populating the structures as treatments progress as a result effec tive drainage lengths from the boreholes may be shorter than would be inferred from the seismicity extending past the jogs these high moment asperities are similar to dense patches of seismicity observed along creeping sections of the san andreas fault where they have been attributed to localized zones of strength or stress con centration surrounded by larger regions undergoing stable aseismic slip this sim ilarity plus large moment deficits in terms of volume injected suggests a large component of aseismic slip is induced by the cotton valley treatments

momentum balance method and estimation of boundary shear stress distribution abstractdetermination of local boundary shear stress is an important topic in hydraulic engineering when attempting to determine this from a very thin boundary region it is a difficult one because it requires special skills and instruments to treat the measured data with the advent of new equipment like the acoustic doppler velocity profilers advp all the velocity profiles in the primary flow region can be simultaneously measured and it is necessary to develop a new method to estimate the boundary shear stress using the primary flow data this paper presents such a method called the momentum balance method mbm a theoretical relationship between the boundary shear stress and parameters of the primary flow region has been established the results obtained from mbm agree reasonably well with other methods indicating that the new method is workable in closed duct flows and possibly its applicability can be extended to a wide range of boundary conditions

moderate to large seismicity induced by hydrocarbon production it is well known that various human activities have the potential to generate seismic activity examples range from subsurface waste injection and reservoir impoundment in the vicinity of large dams to the development of mining geothermal or hydrocarbon resources recently induced seismicity in connection to geologic carbon sequestration projects has emerged as a new field of interest this review discusses seismicity induced by hydrocarbon production in particular i focus on published cases for which earthquakes of moderate to large magnitudes in other words earthquakes that can be felt on the surface have been reported i also discuss current theoretical approaches to model this phenomenon the emphasis on moderate to large magnitudes is intended to complement the other contributions in this issue which focus primarily on microseismicity evidently it is important to understand the conditions under which hydrocarbon production may induce seismic activity in order to ensure that field operations can

reynolds stress and bed shear in nonuniform unsteady open channel flow expressions for the reynolds stress and bed shear stress are developed for nonuniform unsteady flow in open channels with streamwise sloping beds assuming universal logarithmic velocity distribution law and using the reynolds and continuity equations of two dimensional open channel flow the computed reynolds stress distributions are in agreement with experimental data

a large cloud outburst at titan s south pole images of titan acquired over five nights in october 2004 using the adaptive optics system at the keck observatory show dramatic increases in tropospheric cloud activity at the south pole compared with all other images of titan clouds to date during this time titan s south polar clouds brightened to more than 18 times their typical values the cassini ta flyby of titan occurred as this storm was rapidly dissipating we find that the brightness of this cloud outburst is consistent with the dramatic transient brightening of titan observed in atmospheric windows on two nights in 1995 by griffith et al griffith c a owen t miller g a geballe t 1998 nature 395 6702 575 578 if we scale the brightness of the cloud by projecting it onto the equator while apparently infrequent the fact that large cloud events have been observed in different seasons of titan s year indicates that these large storms might be a year round phenomenon on titan we propose possible mechanisms to explain these occasional short term increases in titan s cloud activity

estimating local bed shear stress from velocity observations replicate velocity observations using conventional equipment under typical field conditions are used to evaluate the precision of different methods for estimating local boundary shear stress from velocity measurements the bed shear velocity u can be estimated within 3 using the depth averaged velocity in the vertically averaged logarithmic velocity profile to be accurate this method is limited to relatively simple flow geometries which may be expected to have the appropriate velocity structure estimates of u made using a single near bed velocity observation are less precise by a factor of 3 because of the larger uncertainty associated with a single observation accuracy of this method requires appropriate flow conditions only near the bed so it may be applied in a wider range of flow conditions including spatially variable flow estimates of u from the slope of the near bed velocity profile are the least precise and require the most restrictive flow conditions for accuracy but offer the advantage that they may be made without independent knowledge of the bed roughness different methods for estimating roe should be useful in judging the precision of estimates made under similar conditions these estimates of precision together with considerations of convenience and model accuracy provide the basis for select ing the most appropriate or advantageous method for different conditions and purposes

the vicksburg formation of texas depositional systems distribution sequence stratigraphy and petroleum geology the lower oligocene vicksburg formation of the gulf coastal plain contains major petroleum reservoirs in the rio grande embayment and is an economically viable target in other areas of texas knowledge of the distribution of vicksburg depositional systems is essential to understanding sandstone concentrations and therefore is fundamental to effective exploration and production of the vicksburg section the depositional setting of the vicksburg reservoirs their position in a sequence stratigraphic framework and the influence these factors have on the petroleum geology of the vicksburg are the focus of this paper surface and subsurface geological and geophysical data provided the framework for an analysis of the depositional systems and the petroleum geology of the vic sburg the two primary texas vicksburg depocenters the rio grande embayment and the houston embayment are separated by the san marcos arch a deep rooted structural nose within the embayments sand rich deltaic complexes merged along strike with barrier strand plains contemporaneous growth faulting controlled depositional patterns of shelf edge deltas in the rio grande embayment but had only a minor effect on the configuration of the shelfal deltas in the houston embayment smaller wave dominated shelf delta complexes interspersed with barrier strand plains extended across the san marcos arch updip of these sandy paralic depocenters fluvial systems traversed mud rich coastal plain units seaward of the paralic systems sand and mud deposits prograded across and built up over the r lict jackson shelf and shelf margin shales these depositional complexes are contained in the systems tracts of one eustatic exxon sequence vicksburg production from each of the three structural regions of texas is characterized by reservoirs from different systems tracts and of distinct different depositional origins

deep injection and closely monitored induced seismicity at paradox valley colorado the u s bureau of reclamation s paradox valley unit pvu extracts aquifer brine from nine shallow wells along the dolores river paradox valley in southwestern colorado and after treating high pressure injects the brine 4 3 4 8 km below the surface pvu injects at rates between 800 and 1300 l min since 1991 pvu has emplaced over 4 106 m3 of fluid and induced more than 4000 surface recorded seismic events the events are recorded on the local 15 station paradox valley seismic network the induced seismicity at paradox separates into two distinct source zones a principle zone 95 of the events asymmetrically surrounding the injection well to a maximum radial distance of 3 km and a secondary ellipsoidal zone 2 5 km long and centered 8 km northwest of the injection well the expansion of these zones has stabilized since mid 1999 about three years after the onset of continuous injection within the principal zone hypocenters align in distinct linear patterns showing at depth stratigraphy and the local wray mesa fracture and fault system the primary faults of the wray mesa system are aseismic striking subparallel to the inferred maximum principal stress direction with one or more faults probably acting as fluid conduits to the secondary seismic zone individual seismic events in both zones do not discernibly correlate with short term injection parameters however a 0 5 km2 region immediately northwest of the injection well responds to long term large scale changes in injection rate and the surpassing of a threshold injection pressure focal mechanisms of the induced events are consistent with simple double couple strike slip moments and subhorizontal extension to the northeast in addition the fault planes are consistent with principal stress directions determined from borehole breakouts more than 99 9 of the pvu seismicity is below human detection m 2 5 however approximately 15 events have been felt locally with the largest being a magnitude m 4 3 because of the m 4 3 and two earlier felt m 3 5 events and injection economics pvu changed injection strategies three times since 1996 these changes reduced seismicity from 1100 events year to as low as 60 events year

titan s surface composition and variability from the near infrared albedo abstract we report observations of titan covering the 1 075 1 28 1 6 and 2 0 m windows which show variations with the orbital phase implying variability of the satellite s geometric albedo as found earlier by other authors the observations cover the region 4400 to 9600 cm 1 and were taken in june 1991 august 1993 and september 1994 using the fourier transform spectrometer at the cfh telescope hawaii the resolving power was 10000 1000 and 300 for the 1991 1993 and 1994 spectra respectively the data sets cover titan s greatest western elongation and opposite conjunctions we find titan s geometric albedo to be about the same 0 29 at 1 28 and 1 075 m on the other hand our observations of uranus show the 1 28 m albedo to be lower by 30 than that in the 1 075 m window the geometric albedos in the 1 6 and 2 0 m methane windows on titan are clearly lower 0 20 and 0 16 respectively at the four wavelengths a noticeable decrease in geometric albedo is observed near greatest western elongation with respect to inferior and superior conjunctions the sum of the existing titan data point to a bright leading side and a darker trailing one with a maximum brightness near 120 20 orbital longitude and a minimum near 230 20 despite important uncertainties in the value of the ch 4 absorption coefficients in the window regions modeling titan s observed albedos strongly suggests the existence of a surface material with a comparable albedo at 1 075 and 1 28 m 0 4 0 5 but much darker at 1 6 and 2 0 m about 0 2 titan s surface spectrum appears consistent with that of hyperion and we suggest that this behavior may be due to the dominant presence of water ice on titan s surface the inhomogeneity of the surface implies that some other material e g hydrocarbon lakes is mixed with water ice in variable proportions

the dallas fort worth earthquake sequence october 2008 through may 2009 this paper describes a sequence of small earthquakes m b 3 3 that occurred at the dallas fort worth airport texas between 30 october 2008 and 31 may 2009 analysis of records at regional station wmok identified more than 180 earthquakes in the sequence about 90 percent occurred in four clusters on 30 october 1 november 20 november 26 december and 15 17 may after the sequence began a six station temporary local network obtained high quality three component records for 11 earthquakes occurring between 20 november and 1 december analysis of these data demonstrated that all 11 earthquakes originated from a focus near 32 855 n 97 051 w with an estimated depth 4 4 km this location is less than 0 5 km from a well completed in august 2008 that extends to a depth of 4 2 km drilled to dispose of brines collected during flowback of hydraulic fracturing fluids associated with the production of natural gas brine disposal commenced at the well on 12 september 2008 seismograms and s p intervals for the earthquakes are similar though not identical and relative locations indicate they occurred along a north northeast south southwest trend with horizontal and vertical dimensions of 1 1 km and 0 2 km respectively this trend is approximately coincident with that of a mapped normal fault in the subsurface and consistent with the maximum horizontal in situ stress direction because of the absence of previous historical earthquakes the proximity of the brine disposal well and the similarity with other documented cases of induced seismicity it seems likely that fluid injection induced the 2008 2009 sequence

mississippian barnett shale fort worth basin north central texas gas shale play with multi trillion cubic foot potential the mississippian barnett shale serves as source seal and reservoir to a world class unconventional natural gas accumulation in the fort worth basin of north central texas the formation is a lithologically complex interval of low permeability that requires artificial stimulation to produce at present production is mainly confined to a limited portion of the northern basin where the barnett shale is relatively thick 300 ft 92 m organic rich presentday total organic carbon 3 0 thermally mature vitrinite reflectance 1 1 and enclosed by dense limestone units able to contain induced fractures the most actively drilled area is newark east field currently the largest gas field in texas newark east is 400 mi 2 1036 km 2 in extent with more than 2340 producing wells and about 2 7 tcf of booked gas reserves cumulative gas production from barnett shale wells through 2003 was about 0 8 tcf wells in newark east field typically produce from depths of 7500 ft 2285 m at rates ranging from 0 5 to more than 4 mmcf day estimated ultimate recoveries per well range from 0 75 to as high as 7 0 bcf efforts to extend the current barnett play beyond the field limits have encountered several challenges including westward and northward increases in oil saturation and the absence of lithologic barriers to induced fracture growth patterns of oil and gas occurrence in the barnett in conjunction with maturation and burial history data indicate a complex multiphased thermal evolution with episodic expulsion of hydrocarbons and secondary cracking of primary oils to gas

two year survey of earthquakes and injection production wells in the eagle ford shale texas prior to the mw4 8 20 october 2011 earthquake abstract between november 2009 and september 2011 the earthscope usarray program deployed 25 temporary seismograph stations on a 70 km grid in south central texas between 27 n 31 n and 96 w 101 w this area includes the eagle ford shale for decades this geographic region has produced gas and oil from other strata using conventional methods but recent developments in hydrofracturing technology has allowed extensive development of natural gas resources from within the eagle ford our study surveys small magnitude seismic events and evaluates their correlation with fluid extraction and injection in the eagle ford identifying and locating 62 probable earthquakes including 58 not reported by the u s geological survey the 62 probable earthquakes occur singly or in clusters at 14 foci of these foci two were situated near wells injecting recently increased volumes of water eight were situated near wells extracting recently increased volumes of oil and or water and four were not situated near wells reporting significant injection extraction increases thus in this region while the majority of small earthquakes may be triggered induced by human activity they are more often associated with fluid extraction than with injection we also investigated the m w 4 8 20 october 2011 fashing earthquake the largest historically reported earthquake in south central texas that occurred two weeks after the removal of the temporary usarray stations a field study indicated that the highest intensity mmi vi region was about 10 km south of 2010 2011 foreshock activity and that there were no high volume injection wells within 20 km of the mmi v vi region or the foreshocks however the 20 october 2011 earthquake did coincide with a significant increase in oil water extraction volumes at wells within the mmi v vi region and this was also true for previous earthquakes felt at fashing in 1973 and 1983 in contrast our study found significant increases in injection prior to an mblg3 6 20 july 1991 earthquake near falls city texas thus the eagle ford geographic region with seismic activity associated both with extraction and injection appears to be more complex than the barnett shale of northeast texas where a similar survey found possible correlations only with fluid injection

the evolution of seismic barriers and asperities caused by the depressuring of fault planes in oil and gas fields of south texas fluid pressures within some oil and gas fields of south texas have dropped to less than 20 per cent of their original values producing earthquakes with magnitudes up to 3 9 in recent years differential compaction of the depressurized region may be sufficient to result in the number and size of earthquakes generated or the faults may have been creeping prior to depressurization in either model the depressuring of fluids strengthens a fault and at first produces a barrier to slip as strain accumulates due to compaction or the continued aseismic slip of nearby portions of the fault stress builds up along the locked portions eventually forming high stress regions or asperities the asperities ultimately fail and earthquakes occur the process is repeated as long as the faults are active as the fluid pressures continue to decrease the barriers and subsequent asperities may increase in size and strength resulting in increasingly large and frequent earthquakes

hydrodynamic forces generated on a spherical sediment particle during entrainment the objective of this research is to study the relationship between the coherent flow structures and the hydrodynamic forces leading to entrainment of a spherical bed sediment particle for a rough bed uniform turbulent flow two types of experiments namely movable and fixed balls were conducted using spherical roughness element beds with particle image velocimetry to measure the instantaneous flow velocity field miniature piezoelectric pressure sensors were used to capture the instantaneous pressure on the surface of the sphere movable ball experiments reveal the predominance of large sweep structures at the instant of entrainment fixed ball experiments carried out at entrainment conditions show the importance of both vertical and horizontal pressure gradients on the ball leading to entrainment probability distribution function plots of pressures based on quadrant analysis of velocities also reveal the higher probability of occurrence of high magnitude force induced by sweep q4 events

the spectral nature of titan s major geomorphological units constraints on surface composition we investigate titan s low and mid latitude surface using spectro imaging near infrared data from cassini vims we use a radiative transfer code to first evaluate atmospheric contributions and then extract the haze and the surface albedo values of major geomorphological units identified in cassini synthetic aperture radar data which exhibit quite similar spectral response to the vims data we have identified three main categories of albedo values and spectral shapes indicating significant differences in the composition among the various areas we compare with linear mixtures of three components water ice tholin like and a dark material at different grain sizes due to the limited spectral information available we use a simplified model with which we find that each albedo category of regions of interest can be approximately fitted with simulations composed essentially by one of the three surface candidates our fits of the data are overall successful except in some cases at 0 94 2 03 and 2 79 m indicative of the limitations of our simplistic compositional model and the need for additional components to reproduce titan s complex surface our results show a latitudinal dependence of titan s surface composition with water ice being the major constituent at latitudes beyond 30 n and 30 s while titan s equatorial region appears to be dominated partly by a tholin like or by a very dark unknown material the albedo differences and similarities among the various geomorphological units give insights on the geological processes affecting titan s surface and by implication its interior we discuss our results in terms of origin and evolution theories

surface albedo spectral properties of geologically interesting areas on titan we investigate the nature and possible formation processes of three areas on titan s surface which have been suggested as geologically interesting hotei regio tui regio and sotra patera we also reanalyze the spectral characteristics of the huygens landing site we apply a statistical principal component analysis pca and a radiative transfer rt method on the visual and infrared mapping spectrometer datacubes in order to retrieve the surface albedo of distinct spectral units in the near infrared we have been able to exploit only a subset of the currently available hotei regio data which are in general not optimal in terms of geometry for an analysis with a plane parallel rt code our inferred surface albedos present generally higher values from 1 to 2 m and lower ones at 0 94 and in the 2 6 5 m region the regions of interest rois within hotei regio tui regio and sotra patera are always significantly brighter than the surrounding areas the largest variations are found longward of 2 m and mainly at 5 m this higher surface albedo with respect to the surrounding area and in general the fact that the spectral behavior is different for each of these areas is probably indicative of diverse chemical compositions and origins we compare the spectral albedos with some suggested surface candidates on titan such as h2o co2 and ch4 ices as well as tholin and discuss possible chemical composition variations as well as other interpretations

reprint of two year survey of earthquakes and injection production wells in the eagle ford shale texas prior to the mw4 8 20 october 2011 earthquake abstract between november 2009 and september 2011 the earthscope usarray program deployed 25 temporary seismograph stations on a 70 km grid in south central texas between 27 n 31 n and 96 w 101 w this area includes the eagle ford shale for decades this geographic region has produced gas and oil from other strata using conventional methods but recent developments in hydrofracturing technology has allowed extensive development of natural gas resources from within the eagle ford our study surveys small magnitude seismic events and evaluates their correlation with fluid extraction and injection in the eagle ford identifying and locating 62 probable earthquakes including 58 not reported by the u s geological survey the 62 probable earthquakes occur singly or in clusters at 14 foci of these foci two were situated near wells injecting recently increased volumes of water eight were situated near wells extracting recently increased volumes of oil and or water and four were not situated near wells reporting significant injection extraction increases thus in this region while the majority of small earthquakes may be triggered induced by human activity they are more often associated with fluid extraction than with injection we also investigated the m w 4 8 20 october 2011 fashing earthquake the largest historically reported earthquake in south central texas that occurred two weeks after the removal of the temporary usarray stations a field study indicated that the highest intensity mmi vi region was about 10 km south of 2010 2011 foreshock activity and that there were no high volume injection wells within 20 km of the mmi v vi region or the foreshocks however the 20 october 2011 earthquake did coincide with a significant increase in oil water extraction volumes at wells within the mmi v vi region and this was also true for previous earthquakes felt at fashing in 1973 and 1983 in contrast our study found significant increases in injection prior to an m blg 3 6 20 july 1991 earthquake near falls city texas thus the eagle ford geographic region with seismic activity associated both with extraction and injection appears to be more complex than the barnett shale of northeast texas where a similar survey found possible correlations only with fluid injection

titan s surface and atmosphere from cassini vims data with updated methane opacity abstract we present an analysis of titan data acquired by the cassini visual and infrared mapping spectrometer vims making use of recent improvements in methane spectroscopic parameters in the region 1 3 5 2 m we first analyzed vims spectra covering a 8 10 km2 area near the huygens landing site in order to constrain the single scattering albedo 0 of the aerosols over all of the vims spectral range our aerosol model agrees with that derived from huygens probe descent imager spectral radiometer disr in situ measurements below 1 6 m at longer wavelengths 0 steadily decreases from 0 92 at 1 6 m to about 0 70 at 2 5 m and abruptly drops to about 0 50 near 2 6 m a spectral variation that differs from that of khare et al s khare b n sagan c arakawa e t suits f callcott t a williams m w 1984 icarus 60 127 137 laboratory tholins our analysis shows that the far wings of the strong methane bands on both sides of the transparency windows provide a significant source of opacity in these windows and that their unknown sub lorentzian behavior limits our ability to determine precisely the surface albedos below 1 6 m the retrieved surface albedos agree with those derived from huygens disr the vims spectrum at 2 0 m indicates a surface albedo of 0 11 0 01 larger than derived in previous studies and inconsistent with the signature of water ice a series of vims data taken from 2004 to 2010 between 40 s and 40 n were then analyzed to monitor the latitudinal and temporal evolution of the atmospheric aerosol content in the 2004 2008 period the haze extinction is larger at northern mid latitudes by 20 with respect to the huygens site whereas southern mid latitudes are depleted by 15 20 in 2009 2010 a progressive decline of the haze content in the northern hemisphere is observed but no reversal of the north to south asymmetry is seen till mid 2010 finally data from five regions in tui regio and fensal that show markedly different spectral behaviors and morphologies were analyzed to investigate the wavelength dependence of their surface albedo the difference between bright and dark regions can be explained by different contents of small sized tholins at the surface brighter regions being more tholin rich than dark regions including the huygens landing site on the other hand the albedo spectrum of the so called blue regions either dark or bright can be explained by an excess of water ice particles compared with the huygens landing site the spectrum of a 5 m bright region in tui regio indicates a large excess of small sized tholins relative to the huygens site but does not point to any particular surface composition

the 9 april 1993 earthquake in south central texas was it induced by fluid withdrawal an earthquake that occurred 9 april 1993 about 80 km south of san antonio is the largest earthquake known mblg 4 3 in south central texas in historic times the earthquake was felt over a 4000 km2 area and modified mercalli intensities were as high as vi at a gas production facility near fashing texas similar smaller events have occurred since 1973 at three sites near fashing pleasanton and falls city texas we propose a list of nine yes no questions to assess whether a sequence of earthquakes may have been induced by fluid withdrawal the criteria suggest that at least two sites fashing and pleasanton had earthquakes that were induced by fluid withdrawal related to ongoing oil and gas production an alternative possibility is that these events are the southwesternmost examples in a band of weak natural seismic activity between 135 and 240 km from the coast of the gulf of mexico and extending from this region east to the texas louisiana border in addition some injection occurs at all three sites although the volumes of fluid injected at fashing and pleasanton are low enough as to make injection an unlikely cause

geological evolution of titan s equatorial regions possible nature and origin of the dune material in 13 years infrared observations from the visual and infrared mapping spectrometer onboard cassini provided significant hints about the spectral and geological diversity of titan s surface the analysis of the infrared ir signature of spectral units enables constraining the surface composition which is crucial for understanding possible interactions between titan s interior surface and atmosphere here we investigate a selection of areas in the equatorial regions imaged by cassini s instruments which exhibit an apparent transition from the visual and infrared mapping spectrometer ir bright to the ir blue and ir brown units from false color composites using red 1 57 1 27 m green 2 01 1 27 m and blue 1 27 1 08 m by applying an updated radiative transfer model we extract the surface albedo of ir units identified in these regions then we compare them with synthetic mixtures of two expected components on titan s surface namely water ice and laboratory tholins this allows us to reconnect the derived composition and grain size information to the geomorphology observed from radio detection and ranging instrument radar synthetic aperture radar images we interpret ir bright units as hills and plains coated by organic material and incised by fluvial networks erosion products are transported downstream to areas where ir blue units are seen near the ir bright units these units enriched in water ice are most likely outwash plains hosting debris from fluvial erosion farther away from the ir bright units the ir brown units are dominantly made of organics with varied grain sizes ranging from dust to sand sized particles that form the dune fields the transition areas therefore exhibit trends in water ice content and grain size supported by geomorphological observations

speckle imaging of titan at 2 microns surface albedo haze optical depth and tropospheric clouds 1996 1998 we present results from 14 nights of observations of titan in 1996 1998 using near infrared centered at 2 1 microns speckle imaging at the 10 meter w m keck telescope the observations have a spatial resolution of 0 06 arcseconds we detect bright clouds on three days in october 1998 with a brightness about 0 5 of the brightness of titan using a 16 stream radiative transfer model disort to model the central equatorial longitude of each image we construct a suite of surface albedo models parameterized by the optical depth of titan s hydrocarbon haze layer from this we conclude that titan s equatorial surface albedo has plausible values in the range of 0 0 20 titan s minimum haze optical depth cannot be constrained from this modeling but an upper limit of 0 3 at this wavelength range is found more accurate determination of titan s surface albedo and haze optical depth especially at higher latitudes will require a model that fully considers the 3 dimensional nature of titan s atmosphere

location and felt reports for the 25 april 2010 mblg 3 9 earthquake near alice texas was it induced by petroleum production abstract this study examines seismograms and felt reports for the 25 april 2010 alice texas earthquake and explores its possible relationship with gas and oil production in the stratton field we identified p arrivals at seven broadband stations situated within 100 km of the epicentral region and determined a location of 27 72 n 97 95 w about 11 km east of the location reported by the national earthquake information center but coincident with the region of highest intensity modified mercalli intensity v vi felt reports we compare arrivals for observed secondary p and s arrivals with predictions from a published gulf coast velocity model at nearby stations the secondary arrivals are much stronger than primary arrivals the arrival times and the presence of high amplitude phases traveling at the love wave velocity of the uppermost model layer suggest the focal depth was shallow 3 km or less this places the 2010 hypocenter approximately along the mapped trace of the vicksburg fault zone and at the depth of the frio formation the principal productive member in the stratton field which has produced at least 2 7 trillion cubic feet of gas and about 100 million barrels of oil since production commenced in 1938 we conclude it is plausible although not proven definitively that production in the stratton field contributed to the occurrence of the 2010 alice earthquake and an earlier similar earthquake that occurred on 24 march 1997

probing titan s atmosphere with the 1995 august stellar occultation abstract on 1995 august 21 saturn s moon titan occulted the 13th magnitude star gsc5254 00997 the predawn event was observed at 2 3 m with the nasa 3 0 m infrared telescope facility we measured the average atmospheric scale height between latitudes 50 s and 67 s by fitting isothermal models to the immersion portion of the occultation lightcurve within the altitude range of 300 to 500 km we find an isothermal scale height of titan s sunset atmosphere of 55 9 km our derived temperature of 180 30 k is consistent with modeled temperature profiles derived from voyager 1 iris observations a coustenis and b bezard 1995 icarus 115 126 140 and the 28 sagittarii occultation event w b hubbard et al 1993 astron astrophys 269 541 563 the atmospheric albedo asymmetry due to low level haze caldwell et al 1992 icarus 96 1 9 is inferred from the difference in titan s center of light determined from precise astrometric measurements of images of titan and the star before and after the occultation and the actual center of titan determined from the occultation analysis we find the southern hemisphere to be brighter than the northern hemisphere a result consistent with combes et al 1997 icarus 129 482 497 gibbard et al 1999 icarus 139 189 201 and smith et al 1996 icarus 119 336 349

induced seismic deformation in the cogdell oil field of west texas a sequence of induced earthquakes occurred at the cogdell oil field in west texas from about 1974 to 1982 the earthquakes occurred within an array of injecting wells which surrounded the perimeter of the field and which decreased in radius during the life of the injection project we examine this sequence of earthquakes in terms of two failure models in the first model seismic failure occurs when and where fluid pressures exceed some critical value in the second model earthquakes occur at the edges of low fluid pressure areas where stresses have been transferred as a result of aseismic deformation in adjacent high fluid pressure regions we calculate the history of fluid pressures in the cogdell field using the theis equation for fluid flow in an areally infinite aquifer the calculations show that the earthquakes occur in a region of relatively low pressure surrounded by regions of higher fluid pressure the cogdell earthquakes may occur on pre existing faults however fluid pressures are sufficiently high in surrounding portions of the field to also produce failure a long time delay between the start of injection and the onset of seismicity may correspond to the time required for fluid pressures on a pre existing fault to reach critical values or may be the result of an evolving injection pattern whereby the inward migration of injecting wells produces aseismic failure which loads stress onto stronger regions within the center of the field injection of fluids for secondary recovery occurs at over three thousand sites in the state of texas many of these sites are geographically near cogdell and many have higher injection pressures and volumes of injected fluid than cogdell however they do not exhibit any seismicity a failure model which incorporates stress loading suggests that the perimeter injection pattern is responsible for the onset of seismicity a consequence of this interpretation is that many other injection fields may be undergoing large amounts of aseismic deformation