rapid gravitational adjustment of horizontal shear flows the evolution of a horizontal shear layer in the presence of a horizontal density gradient is explored by three dimensional numerical simulations these flows exhibit characteristics of both free shear flows and gravity currents but have complex dynamics due to strong interactions between the turbulent features of each vertical vortices produced by horizontal shear are tilted and stretched by the gravitational adjustment rapidly enhancing vorticity shear intensification at frontal convergences produces high wavenumber vertical vorticity and the slumping of the density interface produces horizontal kelvin helmholtz vortices typical of a gravity current the interaction between these instabilities promotes a rapid transition to three dimensional turbulence the flow development depends on the relative time scales of shear instability and gravitational adjustment described by a parameter gamma where the limits gamma rightarrow infty and gamma rightarrow 0 represent a pure gravity current and a pure mixing layer respectively the growth rate of three dimensional instability and the mixing increase for smaller gamma when gamma is sufficiently small there are two distinct regimes an early period of during which the interface grows rapidly followed by horizontal diffusive growth numerical results are consistent with field observations of tidal separation flows in the haro strait farmer pawlowicz jiang dyn atmos oceans vol 36 2002 pp 43 58 including the magnitude of downwelling vertical currents horizontal scales of surface vortex features and mixing rate

modelling elastic properties of impure chalk from south arne field north sea in impure chalk the elastic moduli are not only controlled by porosity but also by contact cementation resulting in relatively large moduli for a given porosity and by admixtures of clay and fine silica which results in relatively small moduli for a given porosity based on a concept of solids suspended in pore fluids as well as composing the rock frame we model p wave and s wave moduli of dry and wet plug samples by an effective medium hashin shtrikman model using chemical mineralogical and textural input for a given porosity the elastic moduli correspond to a part of the solid the iso frame value forming the frame of an upper hashin shtrikman bound whereas the remaining solid is modelled as suspended in the pore fluid the iso frame model is thus a measure of the pore stiffness or degree of cementation of the chalk the textural and mineralogical data may be assessed from logging data on spectral gamma radiation density sonic velocity and water saturation in a hydrocarbon zone whereas the iso frame value of a chalk may be assessed from the density and acoustic p wave logs alone the iso frame concept may thus be directly used in conventional log analysis and is a way of incorporating sonic logging data the rigs 1 and rigs 2 wells in the south arne field penetrate the chalk at the same depth but differ in porosity and in water saturation although almost the entire chalk interval has irreducible water saturation our model combined with petrographic data indicates that the difference in porosity is caused by a higher degree of pore filling cementation in rigs 1 petrographic data indicate that the difference in water saturation is caused by a higher content of smectite in the pores of rigs 1 in both wells we find submicron size diagenetic quartz

lobe cleft instability in the buoyant gravity current generated by estuarine outflow gravity currents represent a broad class of geophysical flows including turbidity currents powder avalanches pyroclastic flows sea breeze fronts haboobs and river plumes a defining feature in many gravity currents is the formation of three dimensional lobes and clefts along the front and researchers have sought to understand these ubiquitous geophysical structures for decades the prevailing explanation is based largely on early laboratory and numerical model experiments at much smaller scales which concluded that lobes and clefts are generated due to hydrostatic instability exclusively in currents propagating over a nonslip boundary recent studies suggest that frontal dynamics change as the flow scale increases but no measurements have been made that sufficiently resolve the flow structure in full scale geophysical flows here we use thermal infrared and acoustic imaging of a river plume to reveal the three dimensional structure of lobes and clefts formed in a geophysical gravity current front the observed lobes and clefts are generated at the front in the absence of a nonslip boundary contradicting the prevailing explanation the observed flow structure is consistent with an alternative formation mechanism which predicts that the lobe scale is inherited from subsurface vortex structures

how burial diagenesis of chalk sediments controls sonic velocity and porosity based on p wave velocity and density data a new elastic model for chalk sediments is established the model allows the construction of a series of isoframe if curves each representing a constant part of the mineral phase contributing to the solid frame the if curves can be related to the progress of burial diagenesis of chalk which is revised as follows newly deposited carbonate ooze and mixed sediments range in porosity from 60 to 80 depending on the prevalence of hollow microfossils despite the high porosity these sediments are not in suspension as reflected in ifs of 0 1 or higher upon burial the sediments lose porosity by mechanical compaction and concurrently the calcite particles recrystallize into progressively more equant shapes high compaction rates may keep the particles in relative motion whereas low compaction rates allow the formation of contact cement whereby if increases and chalk forms rock mechanical tests show that when compaction requires more than in situ stress porosity reduction is arrested during subsequent burial crystals and pores grow in size as a consequence of the continuing recrystallization the lack of porosity loss during this process testifies to the absence of chemical compaction by calcite calcite pressure dissolution as well as to the porosity preserving effect of contact cementation at sufficient burial stress the presence of stylolites indicates that pressure dissolution takes place between calcite and silicates and depending on pore water chemistry and temperature pore filling cementation may occur over a relatively short depth interval limestone and mixed sedimentary rock form and porosity may be reduced to less than 20 isoframe increases to more than 0 6 in hydrocarbon reservoirs in north sea chalk relatively high porosity and high ifs are found the reason may be that recrystallization and porosity preserving contact cementation progress whereas pore filling cementation is small probably because pressure dissolution along stylolites is arrested pressure dissolution may be arrested for two reasons 1 the introduction of hydrocarbons causes a fall in effective burial stress and 2 adsorption of polar hydrocarbons on the silicates may shield calcite from the silicates

elastic and nonelastic deformation of greensand analysis of greensand reservoirs all over the world has challenged geologists engineers and petrophysicsts one challenge is to identify from core data the degree to which deformation of the reservoir rock affects hydrocarbon production in the central part of the north sea massive allochtonous paleocene greensands form reservoirs for oil we study the deformation of one oil zone sample from one of these reservoirs by sonic measurements uniaxial compression testing and image analysis of backscatter electron micrographs before and after testing

practical aspects of avo modeling avo amplitude variation with offset modeling contributes significantly in seismic data acquisition design and prestack seismic data processing and interpretation it has become a common practice in prestack seismic analysis it is also used for verifying and developing avo theories conducting avo modeling is by nature an exercise of multidiscipline integration it thus enhances reservoir characterization and reduces the risk in hydrocarbon exploration

principles of avo crossplotting hydrocarbon related avo anomalies may show increasing or decreasing amplitude variation with offset conversely brine saturated background rocks may show increasing or decreasing avo

model based shear wave velocity estimation versus empirical regressions modelling of avo signatures for reservoir characterization requires v s estimation from other available logs when shear wave data are not available we tested various models for predicting v s from p wave velocity porosity and shale volume measured in well logs effective medium models which characterize the pore space in terms of ellipsoidal inclusions were compared with statistical v p v s regressions the inclusion models were calibrated by non linear minimization of the difference between model predicted velocities and actual measured velocities the quality of the v s prediction was quantified in terms of the rms error by comparison with shear wave data in wells where both v p and v s were measured the linear regressions were found to be more robust and the rms error in the prediction was comparable to effective medium model based predictions

estimation of net to gross from p and s impedance in deepwater turbidites the limitations of using low frequency 3 d seismic data for detailed reservoir characterization are well recognized nonetheless these data are very well suited for quantitative estimates of the net to gross n g which is a reservoir scale property critical in deepwater turbidite reservoir characterization and development projects the acoustic impedance inversion of 3 d seismic has been routinely used with varying success to estimate n g in many clastic reservoirs indeed when the shale baseline impedance can be estimated the departure from this trend can be argued to represent a certain measure of the hydrocarbon saturated sand volume on the reservoir scale we take this technique a step further by using both acoustic and shear impedance ai and si and applying them to horn mountain deepwater reservoirs gulf of mexico gom where six appraisal wells were available for calibration

controls on hydrocarbon accumulation in glauconitic sandstone suffield heavy oil sands southern alberta hydrocarbon distribution in the lower cretaceous glauconitic sandstone in the suffield area of southeastern alberta is controlled by three factors sedimentology structure and mineralogy the glauconitic sandstone consists of six lithological facies interpreted to represent the lower middle shoreface middle shoreface upper shoreface foreshore backshore marsh and lagoonal zones of a progradational barrier island system sediment deposited in the foreshore zone laminated sandstone facies has the best reservoir qualities good porosity low clay content and good lateral continuity the bioturbated argillaceous sandstone deposited in the backshore zone has poor reservoir qualities low porosity and high clay content with only isolated porous zones tidal inlet a d or later stage fluvial channel deposits cutting through the sandstone trend form discontinuities in the reservoir the hydrocarbon trapping mechanism is stratigraphic but with some structural influence deep faults active during the deposition of upper mannville sediments caused differential subsidence and local thickening of sediment this activity resulted in the apparent lateral juxtaposition of different facies parts of the glauconitic sandstone form an exceptionally thick beach shoreface sequence up to 45 m or 148 ft thick faulting of sub cretaceous units may have controlled the rate of subsidence and the amount of sediment accumulation during deposition of the glauconitic sandstone the abundance of clay mostly kaolinite largely controls reservoir quality argillaceous backshore sandstones which contain abundant detrital kaolinite are poor reservoirs clean foreshore deposits are good reservoirs porosity and permeability are only slightly reduced in the clean sandstone by formation of diagenetic phases such as kaolinite and quartz during the wet forward combustion recovery process migration of kaolinite and dissolution reprecipitation of silica could cause formation damage

rock physics model of glauconitic greensand from the north sea the objective of this study was to establish a rock physics model of north sea paleogene greensand the hertz mindlin contact model is widely used to calculate elastic velocities of sandstone as well as to calculate the initial sand pack modulus of the soft sand stiff sand and intermediate stiff sand models when mixed minerals in rock are quite different e g mixtures of quartz and glauconite in greensand the hertz mindlin contact model of single type of grain may not be enough to predict elastic velocity our approach is first to develop a hertz mindlin contact model for a mixture of quartz and glauconite next we use this hertz mindlin contact model of two types of grains as the initial modulus for a soft sand model and a stiff sand model by using these rock physics models we examine the relationship between elastic modulus and porosity in laboratory and logging data and link rock physics properties to greensand diagenesis calculated velocity for mixtures of quartz and glauconite from the hert

a note on the structure of the head of an intrusive gravity current the head of an intrusive flow advancing along the interface between two fluids is studied experimentally when the two layers are of equal depth and the density of the intrusion is the mean of the two densities the dependence of the flow on the interface thickness and the depth of the intrusion is determined when the interface is very thin the flow is similar to the nominally inviscid gravity currents observed by britter simpson 1978

a new velocity model for clay sand mixtu res1 none of the standard porosity velocity models e g the time average equation raymer s equations is satisfactory for interpreting well logging data over a broad depth range clays in the section are the usual source of the difficulty through the bias and scatter that they introduce into the relationship between porosity and p wave transit time because clays are composed of fine sheet like particles they normally form pores with much smaller aspect ratios than those associated with sand grains this difference in pore geometry provides the key to obtaining more consistent resistivity and sonic log interpretations a velocity model for clay sand mixtures has been developed in terms of the kuster and toksoz effective medium and gassmann theories in this model the total pore space is assumed to consist of two parts 1 pores associated with sand grains and 2 pores associated with clays including bound water the essential feature of the model is the assumption that the geometry of pores associated with sand grains is significantly different from that associated with clays because of this porosity in shales affects elastic compliance differently from porosity in sand stones the predictive power of the model is demonstrated by the agreement between its predictions and laboratory measurements and by its ability to predict sonic logs from other logs over large depth intervals where formations vary from unconsolidated to consolidated sandstones and shales

comparison of avo indicators a modeling study a worldwide collection of 25 sets of velocity and density measurements from adjacent shales brine sands and gas sands was acquired with full waveform sonic dipole sonic and conventional well logging devices and or in the laboratory these data provide theoretical shale over brine sand and shale over gas sand p wave and s wave normal incidence reflection coefficients r p and r s avo intercepts a avo gradients b the avo indicators r p r s reflection coefficient difference and a b avo product the reflection coefficient difference is found to be a more universal indicator than the avo product in clastic stratigraphic intervals for shale over brine sand re flections the average r p r s tends to be near zero and relatively invariant with depth irrespective of gas sand impedance r p r s is always negative for shale over reservoir quality gas sand reflections and more negative than for the corresponding brine sand reflections in comparison the avo product may be positive near zero or negative for gas sands depend ing on the impedance contrast with the overlying shale these measurements also verify that r p r s is well approximated by a simple linear combination of a and b

inside the head and tail of a turbulent gravity current gravity currents are an important buoyancy driven flow in environmental geophysical and industrial settings turbulence and mixing is commonplace in these flows but is typically overlooked in theoretical models and predictions sher woods j fluid mech vol 784 2015 pp 130 162 have quantified the velocity and density structure in turbulent gravity currents by combining high quality experimental data with new theory their insights are set to stimulate significant advances in the area

predictive permeability variations in a hermod sand reservoir stine segments siri field danish north sea abstract the hermod sand of the stine segments siri field danish north sea displays large permeability variations 1 600 md these permeability variations represent horizontal layering in the reservoir largely formed by diagenetic processes they have a significant impact on reservoir performance because horizontal producers in fairly thin reservoirs 30 m are protected against bottom water influx and can produce water free for long periods of time this paper presents the results of a detailed multidisciplinary study where the observed variation in permeability can be explained by two main diagenetic phases silica as opal cement and microquartz and berthierine a serpentine mineral that is closely related to chlorite opal microquartz and berthierine cements dominate in separate parts of the reservoir bodies opal microquartz cemented sands have high permeability typically 500 600 md berthierine cement has a different growth pattern in the oil and water zones resulting in intermediate permeability in the oil zone typically 50 100 md and very low permeability in the water zone typically 1 10 md

analysis and direct numerical simulation of the flow at a gravity current head part 1 flow topology and front speed for slip and no slip boundaries direct numerical simulations are performed of gravity current fronts in the lock exchange configuration the case of small density differences is considered where the boussinesq approximations can be adopted the key objective of the investigation is a detailed analysis of the flow structure at the foremost part of the front where no previous high resolution data were available for the simulations high order numerical methods are used based on spectral and spectral element discretizations and compact finite differences a three dimensional simulation is conducted of a front spreading along a no slip boundary at a reynolds number of about 750 the simulation exhibits all features typically observed in experimental flows near the gravity current head including the lobe and cleft structure at the leading edge the results reveal that the flow topology at the head differs from what has been assumed previously in that the foremost point is not a stagnation point in a translating system rather the stagnation point is located below and slightly behind the foremost point in the vicinity of the wall the relevance of this finding for the mechanism behind the lobe and cleft instability is discussed in order to explore the high reynolds number regime and to assess potential reynolds number effects two dimensional simulations are conducted for reynolds numbers up to about 30 000 for both no slip and slip i e shear stress free boundaries it is shown that although quantitative reynolds number effects persist over the whole range examined no qualitative changes in the flow structure at the head can be observed a comparison of the two dimensional results with laboratory data and the three dimensional simulation provides evidence that a two dimensional model is able to capture essential features of the flow at the head the simulations also show that for the free slip case the shape of the head agrees closely with the classical inviscid theory of benjamin

vp vs relationship and amplitude variation with offset modelling of glauconitic greensand the relationship between vp and vs may be used to predict vs where only vp is known vp vs is also used to identify pore fluids from seismic data and amplitude variation with offset analysis theoretical physical as well as statistical empirical vp vs relationships have been proposed for reservoir characterization when shear wave data are not available in published work the focus is primarily on the vp vs relationship of quartzitic sandstone in order to broaden the picture we present vp vs relationships of greensand composed of quartz and glauconite by using data from the paleocene greensand nini oil field in the north sea a vp vs relationship derived from modelling is compared with empirical vp vs regressions from laboratory data as well as from log data the accuracy of vs prediction is quantified in terms of root mean square error we find that the vp vs relationship derived from modelling works well for greensand shear wave velocity prediction we model the seismic response of glauconitic greensand by using laboratory data from the nini field our studies here reveal that brine saturated glauconitic greensand can have a similar seismic response to that from oil saturated quartzitic sandstone and that oil saturated strongly cemented greensand can have a similar amplitude variation with offset response to that from brine saturated weakly cemented greensand

a physical model for shear wave velocity prediction the clay sand mixture model of xu and white is shown to simulate observed relationships between s wave velocity or transit time porosity and clay content in general neither s wave velocity nor s wave transit time is a linear function of porosity and clay content for practical purposes clay content is approximated by shale volume in well log applications in principle the model can predict s wave velocity from lithology and any pair of p wave velocity porosity and shale volume although the predictions should be the same if all measurements are error free comparison of predictions with laboratory and logging measurements show that predictions using p wave velocity are the most reliable the robust relationship between s and p wave velocities is due to the fact that both are similarly affected by porosity clay content and lithology moreover errors in the measured p wave velocity are normally smaller than those in porosity and shale volume both of which are subject to errors introduced by imperfect models and imperfect parameters when estimated from logs because the model evaluates the bulk and shear moduli of the dry rock frame by a combination of kuster and toksoz theory and differential effective medium theory using pore aspect ratios to characterize the compliances of the sand and clay components the relationship between p and s wave velocities is explicit and consistent consequently the model sidesteps problems and assumptions that arise from the lack of knowledge of these moduli when applying gassmann s theory to this relationship making it a very flexible tool for investigating how the v p v s relationship is affected by lithology porosity clay content and water saturation numerical results from the model are confirmed by laboratory and logging data and demonstrate for example how the presence of gas has a more pronounced effect on p wave velocity in shaly sands than in less compliant cleaner sandstones

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

shear wave velocity estimation in porous rocks theoretical formulation preliminary verification and applications shear wave velocity logs are useful for various seismic interpretation applications including bright spot analyses amplitude versus offset analyses and multicomponent seismic interpretations measured shear wave velocity logs are however often unavailable we developed a general method to predict shear wave velocity in porous rocks if reliable compressional wave velocity lithology porosity and water saturation data are available the precision and accuracy of shear wave velocity prediction are 9 and 3 respectively the success of our method depends on 1 robust relationships between compressional and shear wave velocities for water saturated pure porous lithologies 2 nearly linear mixing laws for solid rock constituents 3 first order applicability of the biot gassmann theory to real rocks we verified these concepts with laboratory measurements and full waveform sonic logs shear wave velocities estimated by our method can improve formation evaluation our method has been successfully tested with data from several locations

intrusive gravity currents from finite length locks in a uniformly stratified fluid gravity currents intruding into a uniformly stratified ambient are examined in a series of finite volume full depth lock release laboratory experiments and in numerical simulations previous studies have focused on gravity currents which are denser than fluid at the bottom of the ambient or on symmetric cases in which the intrusion is the average of the ambient density here we vary the density of the intrusion between these two extremes after an initial adjustment the intrusions and the internal waves they generate travel at a constant speed for small departures from symmetry the intrusion speed depends weakly upon density relative to the ambient fluid density however the internal wave speed approximately doubles as the waves change from having a mode 2 structure when generated by symmetric intrusions to having a mode 1 structure when generated by intrusions propagating near the bottom in the latter circumstance the interactions between the intrusion and internal waves reflected from the lock end of the tank are sufficiently strong and so the intrusion stops propagating before reaching the end of the tank these observations are corroborated by the analysis of two dimensional numerical simulations of the experimental conditions these reveal a significant transfer of available potential energy to the ambient in asymmetric circumstances

diagenesis of the safaniya sandstone member mid cretaceous in saudi arabia abstract safaniya member of the mid cretaceous wasia formation was deposited as fluvio marine deltaic sediments in northeastern saudi arabia and the northwestern arabian gulf after its deposition and initial burial the mid cretaceous sequence was uplifted during late cretaceous structural movements structural traps in the region also started forming at this time but structural growth continued during the eocene and new structures developed during the plio pleistocene the diagenetic mineral assemblage in the safaniya sandstones includes kaolinite illite glauconite pyrite quartz and carbonate cements kaolinite and illite occur both as authigenic and detrital minerals authigenic kaolinite exists as skeletal and euhedral plates forming vermicules and aggregates of booklets infilling the pore spaces authigenic illite occurs as overgrowths of projecting laths quartz cement is present as syntaxial overgrowths and as microcrystalline quartz carbonates occur as patches and show replacement textures early diagenetic events include the formation of calcite siderite glauconite and pyrite at or close to the sediment water interface vermicular kaolinite and microcrystalline quartz probably formed by meteoric water diagenesis during the late cretaceous uplift quartz overgrowths and the bulk of the euhedral kaolinite may have formed during the late cretaceous early tertiary burial illite and ankerite were precipitated during deep burial probably from fluids expelled from the basinal kazhdumi shales to the east and northeast the precipitation of authigenic minerals in the clean quartz sandstones has reduced the primary interparticle porosity by an average of about 9 of the rocks because the clays occur mainly as pore filling cements their precipitation has caused only a small reduction in the permeability of these rocks

framework for avo gradient and intercept interpretation amplitude variation with offset avo interpretation may be facilitated by crossplotting the avo intercept a and gradient b under a variety of reasonable petrophysical assumptions brine saturated sandstones and shales follow a well defined background trend in the a b plane generally a and b are negatively correlated for background rocks but they may be positively correlated at very high vp vs ratios such as may occur in very soft shallow sediments thus even fully brine saturated shallow events with large reflection coefficients may exhibit large increases in avo deviations from the background trend may be indicative of hydrocarbons or lithologies with anomalous elastic properties however in contrast to the common assumptions that gas sand amplitude increases with offset or that the reflection coefficient becomes more negative with increasing offset gas sands may exhibit a variety of avo behaviors a classification of gas sands based on location in the a b plane rather than on normal

the intrusion of fluid mechanics into geology during the last few years a number of fluid dynamicists often in collaboration with geologists have been investigating problems suggested by geology and creating the new field of geological fluid mechanics the research has uncovered many new fluid mechanical phenomena and the studies have ranged widely over theoretical contributions laboratory experiments and confirmatory field observations this paper presents an overview of part of the field with a strong emphasis on the novel fluid mechanical concepts the presentation includes discussion of some of the effects of cooling and crystallization and the resulting convective motions the flow of gravity currents at both high and low reynolds number and the erosion of solid retaining walls by hot turbulent flows

shale rock physics and implications for avo analysis a north sea demonstration shales normally constitute more than 80 of sediments and sedimentary rocks in siliciclastic environments shales are important both in controlling the overburden seismic wave propagation as well as the reflectivity contrast between cap rocks and reservoir rocks in prestack seismic data therefore during avo analysis it is crucial to understand the seismic properties of shales as a function of mineralogy and compaction in this study we derive the local shale trend for a north sea gas and oil field by integrating rock physics modeling with well log and seismic data analysis

shelf sheet sand reservoir of the lower cretaceous greensand north celtic sea basin offshore ireland core and log data show that the marine early to middle albian a sand of the aptian to lower cenomanian greensand gault interval north celtic sea basin offshore ireland was deposited as an approximately tabular sand body in shelf water depths the a sand is the major reservoir interval at kinsale head and ballycotton gas fields the reservoir sandstone is bioturbated variably glauconitic shell rich and least muddy toward its provenance in a local area of the irish massif and finer grained southeastward into the basin thickness and coarseness of the a sand are related in part to distance from a narrow area of the paleoshore bathymetric control of sand thickness was superimposed on proximal distal trends specifically thick intervals are inferred to have be n deposited in shelf lows and thin zones were deposited over bathymetric highs the a sand was not deposited as a ridge sand and positive relief on the depositional sand body appears to have been minor deposition of the greensand occurred during thermal subsidence of the north celtic sea basin following early cretaceous rifting overall late early cretaceous to late cretaceous transgression was interrupted by progradation of the a sand probably caused by a relative drop in sea level forced regression the a sand sheet consists of several units within the central depositional basin three slightly coarsening upward units up to 15 m thick probably are the consequence of high frequency fluctuations in sea level during progradation the top of the a sand consists of a several m ter thick very glauconitic muddy sandstone to sandy mudstone the upper unit accumulated in deepening water following the maximum lowstand

fracture detection using crosswell and single well surveys we recorded high resolution 1 to 10 khz crosswell and single well seismic data in a shallow 15 to 35 m water saturated fractured limestone sequence at conoco s borehole test facility near newkirk oklahoma our objective was to develop seismic methodologies for imaging gas filled fractures in naturally fractured gas reservoirs the crosswell 1 4 m receiver spacing 50 to 100 m well separation surveys used a piezoelectric source and hydrophones before during and after an air injection that we designed to displace water from a fracture zone our intent was to increase the visibility of the fracture zone to seismic imaging and to confirm previous hydrologic data that indicated a preferred pathway for the single well seismic imaging a piezoelectric source and an eight element hydrophone array at 1 4 m spacing we also recorded data before and after the air injection the crosswell results indicate that the air did follow a preferred pathway that was predicted by hydrologic modeling in addition

relationships between compressional wave and shear wave velocities in clastic silicate rocks new velocity data in addition to literature data derived from sonic log seismic and laboratory measurements are analyzed for clastic silicate rocks these data demonstrate simple systematic relationships between compressional and shear wave velocities for water saturated clastic silicate rocks shear wave veloci ty is approximately linearly related to compressional wave velocity and the compressional to shear velocity ratio decreases with increasing compressional velocity laboratory data for dry sandstones indicate a nearly constant compressional to shear velocity ratio with rigidity approximately equal to bulk modulus ideal models for regular packings of spheres and cracked solids exhibit behavior similar to the observed water saturated and dry trends for dry rigidity equal to dry bulk modulus gassmann s equations predict velocities in close agreement with data from the water saturated

tail structure and bed friction velocity distribution of gravity currents propagating over an array of obstacles the bed friction velocity distribution and sediment entrainment potential of boussinesq compositional gravity currents propagating over a series of obstacles and over a smooth surface respectively are analysed based on high resolution three dimensional large eddy simulations the investigation focuses on the parameter regime for which currents with a high volume of release go through an extended slumping phase with approximately constant front velocity tokyay constantinescu meiburg j fluid mech vol 672 2011 570 605 under these conditions a quasi steady regime is reached between consecutive obstacles that is similar to the steady regime observed for constant density channel flows over bottom obstacles at a given location this quasi steady regime is reached in the tail of the current after the passage of the front and the associated hydraulic jumps reflected from the first few downstream obstacles a double averaging procedure is employed to characterize the global changes in the structure of the tail region between currents with a high volume of release propagating over smooth surfaces and over obstacles reynolds number induced scale effects on the flow and turbulence structure within the tail region are discussed in some detail the presence of this quasi steady regime is significant since the simulations with obstacles show that most of the sediment is entrained by the tail of the current rather than by its front a detailed analysis of the effects of the obstacle shape on the quasi steady mean flow and turbulence structure is presented which provides insight into why gravity currents over dunes can entrain more sediment than gravity currents over ribs of comparable size finally the bed friction velocity distributions and the potential to entrain sediment are compared for a compositional current with a high volume of release during the slumping phase and a current with a low volume of release for which transition to the buoyancy inertia phase occurs a short time after the release of the lock gate

petrography diagenesis and facies controls on porosity in shannon sandstone hartzog draw field wyoming on the basis of lithology and sedimentary structures six sedimentary facies a f were distinguished in cores of shannon sandstone in hartzog draw field campbell county wyoming core porosities and permeabilities are highest in facies a average 15 and 16 md moderately high in facies b average 13 and 11 md low in facies c average 11 3 and 3 5 md and very low in facies d and e average 9 10 and 1 2 md dispersed detrital clay is a primary control on porosity but in cross bedded sandstones of facies a and b the main productive interval dispersed detrital clay is sparse and variations in porosity are due mainly to diagenesis microporosity does not contribute to permeability it is low in facies a and b high in facies c e and is associated mainly with detrital clay as microporosity increases water saturation increases the paragenetic sequence inferred is 1 siderite cementation 2 formation of a brown grain coating clay possibly illite smectite 3 quartz cementation 4 calcite and dolomite cementation 5 dissolution of carbonate cements and some framework grains 6 a second generation of quartz cementation along with some chlorite and interlayered illite smectite formation and 7 oil emplacement

effect of glauconite on the elastic properties porosity and permeability of reservoir rocks glauconite is an iron rich variety of clay that can be found as individual pellets composite grains and intergranular cement its density ranges between 2 4 g cm3 and 2 95 g cm3 averaging 2 67 g cm3 it has a moh s scale hardness of 2 authigenic glauconite is formed under a limited range of geologic and geochemical conditions it typically develops on the outer margins of continental shelves in areas of low sediment input odin 1980 and its presence is valuable as an indicator of transgressive sequences identifying glauconite in the subsurface is important for depositional environment interpretation stratigraphic correlation dating tracing of unconformities and geochemical exploration for source and reservoir rocks srivastava 1986 a number of commercial hydrocarbon reservoirs are glauconitic sandstones for example in colombia ecuador peru venezuela australia eastern china north sea united states canada saudi arabia and ireland although glauconite tends to exist as grains and as such is part of the rock framework under moderate overburden pressure these grains are easily compacted figure 1 and may form a pseudomatrix that occludes the original primary porosity this behavior is in contrast to that observed in clay minerals this problem and the fact that there are no published studies about the elastic properties of glauconite and glauconitic sandstones motivated this research to understand their rock physics properties we present analyses of data from five lithologies containing varying amounts of glauconite and identify the best seismic attributes to evaluate its presence and the reservoir quality figure 1 optical image of a glauconitic sandstone made at 20x magnification showing formation of a pseudomatrix that occludes the original primary porosity glauconite green quartz white the samples in this study come from caballos formation in putumayo and upper magdalena basins colombia figure 2 which is described as a marine transgressive blanket sandstone deposited in a shallow

coalbed methane cook inlet south central alaska a potential giant gas resource cook inlet basin of south central alaska is a forearc basin containing voluminous tertiary coal deposits with sufficient methane content to suggest a major coalbed gas resource coals ranging in thickness from 2 to 50 ft 0 6 to 15 m and in gas content from 50 to 250 scf ton 1 6 to 7 8 cm2 g occur in miocene oligocene fluvial deposits of the kenai group these coals have been identified as the probable source of more than 8 tcf gas that has been produced from conventional sandstone reservoirs in the basin cook inlet coals can be divided into two main groups 1 those of bituminous rank in the tyonek formation that contain mainly thermogenic methane and are confined to the northeastern part of the basin matanuska valley and to deep levels elsewhere and 2 subbituminous coals at shallow depths 5000 ft 1524 m in the tyonek and overlying beluga formations which contain mainly biogenic methane and cover most of the central and southern basin based on core and corrected cuttings desorption analyses gas contents average 230 scf ton 7 2 cm2 g for bituminous coals and 80 scf ton 2 5 cm2 g for subbituminous coals isotherms constructed for samples of both coal ranks suggest that bituminous coals are saturated with respect to methane whereas subbituminous coals at shallow depths along the eroded west central basin margin are locally unsaturated a preliminary estimate of 140 tcf gas in place is derived for the basin