in situ gas hydrate hydrate saturation estimated from various well logs at the mount elbert gas hydrate stratigraphic test well alaska north slope abstract in 2006 the u s geological survey usgs completed detailed analysis and interpretation of available 2 d and 3 d seismic data and proposed a viable method for identifying sub permafrost gas hydrate prospects within the gas hydrate stability zone in the milne point area of northern alaska to validate the predictions of the usgs and to acquire critical reservoir data needed to develop a long term production testing program a well was drilled at the mount elbert prospect in february 2007 numerous well log data and cores were acquired to estimate in situ gas hydrate saturations and reservoir properties gas hydrate saturations were estimated from various well logs such as nuclear magnetic resonance nmr p and s wave velocity and electrical resistivity logs along with pore water salinity gas hydrate saturations from the nmr log agree well with those estimated from p and s wave velocity data because of the low salinity of the connate water and the low formation temperature the resistivity of connate water is comparable to that of shale therefore the effect of clay should be accounted for to accurately estimate gas hydrate saturations from the resistivity data two highly gas hydrate saturated intervals are identified an upper 43 ft zone with an average gas hydrate saturation of 54 and a lower 53 ft zone with an average gas hydrate saturation of 50 both zones reach a maximum of about 75 saturation

dating reservoir filling a case history from the north sea abstract secondary petroleum inclusions in reservoir sandstones in the froy field and the rind discovery are used in combination with burial history modelling reservoir oils and core extracts to shed light on how and when these structures received their hydrocarbon charges analysis of normal alkane and biomarker distributions in these three data sets fluid inclusions core extracts and drill stem tests dsts provide information on the changes in organic facies and maturity of petroleum in the various reservoir strata over time the geochemistry of core extracts and dst oils in rind and froy reveal that the maturity of the rind petroleum system is higher and also of slightly less anoxic facies compared to the oil present in the froy system biodegraded oil is found today in a small sub compartment of the froy field using the burial history of the froy and the assumption that biodegradation effectively comes to a halt at 70 80 c we tentatively conclude that the filling of this sub compartment and the biodegradation of the oil must have occurred earlier than 30 40 m y b p and before oil from the upper jurassic draupne shales more recently homogeneously filled the main froy structure at 30 40 m y b p the froy structure was at a depth of 1 5 2 km compared to the present depth of 3 5 4 km and it is more than likely that neither the heather nor the draupne formations were mature in the paleo drainage area of the field at this time still the stratigraphically deeper dunlin formation could have been mature and the geochemical signatures of the now biodegraded oil correlates with known signatures from the dunlin formation in this region in the rind discovery no fluorescent petroleum inclusions are observed in k feldspar overgrowths however the number of inclusions in quartz and plagioclase is larger than that observed in the shallower froy field from the mean homogenization temperatures of the petroleum inclusions which are close to the present reservoir temperature filling of the froy field and main rind structure is suggested to have been a recent event a presently dry compartment penetrated by well 25 2 15r2 in the rind discovery contains high residual oil saturations indicating loss of oil from this structure either by direct cap rock leakage or displacement of oil by gas and subsequent cap rock leakage numerous petroleum and coexisting water inclusions were found in the presently dry overpressured structure and it is clear from measurements of homogenization temperatures that the water and the petroleum inclusions are not both saturated with respect to gas due to the lower solubility of hydrocarbon gas in water compared to in oil it is more likely that water inclusions are closer to saturation than are the petroleum inclusions using the difference in homogenization temperatures in these two systems and the burial history we tentatively suggest that the cap rock leakage occurred later than 10 m y b p such information on time for reservoir filling and seal failure when used to calibrate basin modelling should facilitate better models for understanding movement of hydrocarbon fluids in basins

sand spit rhythmic development a potential record of wave climate variations arcay spit western coast of france abstract this study aims at showing the sedimentary and geomorphological records of wave climate variations by spits the studied spit arcay spit is located on the french atlantic coast and has displayed a rapid elongation since the beginning of the 19th century that potentially represents a two century long wave climate record wave climate and spit growth relationships are studied from two complementary methods 1 numerical modelling of wave and longshore transport temporal and spatial variabilities and 2 morphological monitoring based on the analysis of 4 historical maps 1811 1945 8 aerial photographs 1945 2000 and 17 satellite spot images 1987 2005 results at seasonal to interannual time scales show that the sand spit area gain variations are the result of variations in longshore transport themselves modulated mainly by wave height moreover energetic swells seem to cause massive sand accumulation and spit elongation whereas less energetic swells appear to be responsible for small sand accumulation and spit curvature at longer time scale decades to centuries increasing spit growth phases are also synchronised with periods of energetic swells or high storm surge frequency these results suggest that wave climate variations are the main factor controlling spit morphological evolutions

relationship between diagenesis and reservoir quality in sandstones of the garn formation haltenbanken mid norwegian continental shelf a quantitative model is proposed for the dependence of porosity and permeability on diagenesis in subarkosic arenites of the middle jurassic garn formation porosity variation is controlled by the combined effects of compaction and quartz cementation in general more porosity has been lost by compaction than by quartz cementation but compactional porosity loss appears to have occurred relatively early in the burial history before burial below 2 km below the sea floor thus progressive reduction of the total porosity with increasing burial below 2 km results mainly from quartz cementation permeability is a function of the abundance of intergranular macroporosity which is interpreted to be a measure of effective porosity at depths less than 3 5 km below the sea fl or intergranular macroporosity generally comprises more than 50 percent of the total porosity but at greater depth as total porosity decreases below about 16 percent the ratio of effective to ineffective porosity drops below one this depth corresponds to the onset of extensive illitization and grain dissolution which results in major reorganization of the pore system generation of secondary porosity by feldspar dissolution appears not to have been beneficial to reservoir quality in the garn formation but it is regarded as an intrinsic part of the overall process of porosity destruction with increasing diagenesis

synthetic fluid inclusions vii re equilibration of fluid inclusions in quartz during laboratory simulated metamorphic burial and uplift p t conditions inferred from fluid inclusions in metamorphic rocks often disagree with the values predicted from mineral equilibria calculations these observations suggest that inclusions formed during early stages of regional metamorphism continue to re equilibrate during burial and subsequent uplift in response to differential pressure p t conditions accompanying burial and uplift were experimentally simulated by initially forming pure h2o inclusions in quartz at elevated temperatures and pressures and then re equilibrating the inclusions in the presence of a 20 wt nacl solution such that final confining pressures ranged from 5 kbar above to 4 kbar below the initial internal pressure of the inclusions at the temperature of re equilibration in all samples re equilibrated at confining pressures below the internal pressure some inclusions were formed that had compositions of 20 wt nacl and densities in accord with the final p t conditions additionally some inclusions were observed to contain fluids of intermediate salinities between 0 and 20 wt nacl densities of these inclusions were also consistent with formation at the re equilibration p t conditions the remainder of the fluid inclusions observed in these samples contained pure h2o and their homogenization temperatures corresponded to densities intermediate between the initial and final p t conditions in short term experiments 7 days where the initial internal overpressure exceeded 1 kbar no inclusions were found that contained the original density and none were found to have totally re equilibrated instead most h2o inclusions re equilibrated until their internal pressures were between 750 and 1500 bars above the confining pressure regardless of the initial pressure differential in a long term experiment 52 days inclusions re equilibrated at a lower confining pressure than the initial internal pressure displayed homogenization temperatures corresponding to a range in final internal pressures between 0 kbar i e total re equilibration and 1 2 kbar above the confining pressure in experiments where the confining pressure during re equilibration exceeded the initial internal pressure densities of pure h2o inclusions increased to values intermediate between the initial and final p t conditions additionally these inclusions were generally surrounded by a three dimensional halo of smaller inclusions also of intermediate density resulting in a texture similar to that previously ascribed to decrepitation from internal overpressure in extreme cases where confining pressures were 4 5 kbar above the initial pressure the parent inclusion almost completely closed leaving only the three dimensional array of small 5 m inclusions the outline of which may be several times the volume of the original inclusion groups of such inclusions closely resemble textures commonly observed in medium to high grade metamorphic rocks inclusions containing 10 and 42 wt nacl solutions trapped at 600 c and 3 kbar were re equilibrated at 600 c and 1 kbar for 5 days in dry argon to evaluate the importance of h2o diffusion as a mechanism of lowering the inclusion bulk density salinities of re equilibrated inclusions obtained from freezing point depressions and halite dissolution temperatures indicate that original compositions were preserved density changes similar to those previously described were noted in these experiments in inclusions showing no visible microfractures therefore density variations observed in inclusions in this study re equilibrated under rapid deformation conditions are considered to result from a change in the inclusion volume without significant loss of contents by diffusion or leakage

the structure of methane gas hydrate bearing sediments from the krishna godavari basin as seen from micro ct scanning abstract the indian national gas hydrate program nghp expedition 1 of 2006 cored through several methane gas hydrate deposits on the continental shelf around the coast of india the pressure coring techniques utilized during the expedition hyacinth and pcs enabled recovery of gas hydrate bearing fine grained sediment cores to the surface after initial characterization core sections were rapidly depressurized and submerged in liquid nitrogen preserving the structure and form of the hydrate within the host sediment once on shore high resolution x ray ct scanning was employed to obtain detailed three dimensional images of the internal structure of the gas hydrate using a resolution of 80 m the detailed structure of the hydrate veins present in each core could be observed and allowed for an in depth analysis of orientation width and persistence of each vein hydrate saturation estimates could also be made and saturations of 20 30 were found to be the average across the core section with some portions showing highs of almost 60 saturation the majority of hydrate veins in each core section were found to be orientated between 50 and 80 to the horizontal analysis of the strikes of the veins suggested a slight preferential orientation in individual sample sections although correlation between individual sections was not possible due to the initial orientation of the sections being lost during the sampling stage the preferred vein orientation within sample sections coupled with several geometric features identified in individual veins suggest that hydraulic fracturing by upward advecting pore fluids is the main formation mechanism for the veined hydrate deposits in the k g basin

an integrated thermal and isotopic study of the diagenesis of the brent group alwyn south u k north sea abstract the petrography fluid inclusion thermometry and isotope geochemistry of diagenetic cements are used to reconstruct the pore fluid history of the middle jurassic brent group reservoir sandstones in the alwyn south area of the u k north sea the study focuses on a relatively limited area of three adjacent reservoir compartments at successively higher structural levels the cement assemblage of kaolinite quartz and illite has resulted in severe deterioration of otherwise good reservoir quality early precipitation of vermiform and late blocky kaolinite was succeeded by a period of relatively intense illite precipitation temperature estimates for kaolinite precipitation of 80 c and 18o of 15 3 suggest co existing fluids of 18o 3 quartz cementation overlapped both kaolinite and illite formation fluid inclusion data indicate that quartz cementation took place at temperatures of 109 7 c pore fluid salinities were 4 wt nacl with a h2o o isotopic composition of 1 o 0 5 smow the fluids which precipitated coexisting illite were compositionally homogeneous with equilibrium 18o water compositions of 0 5 smow illite sd values range from 33 to 50 smow these fluid inclusion and isotopic data suggest that both quartz and illite were precipitated from pore waters with a uniform marine signature this is consistent with the predominantly marine to paralic depositional context of the brent group in alywn south illite precipitation was followed by hydrocarbon emplacement between the middle eocene and lower oligocene

nourishing the shoreface observations and hindcasting of the egmond case the netherlands abstract although beach nourishment policy in the netherlands is generally successful in maintaining the 1990 shoreline the efficiency of nourishments at several locations along the north sea coast is unacceptably low these locations are identified as erosion hotspots egmond aan zee is such a hotspot the bathymetric longshore irregularities make this coastal stretch highly susceptible to rip currents and horizontal circulations which transport large volumes of nourished sand to the sea in 1999 an alternative nourishment design was implemented this consisted of a shoreface nourishment at the outer bar at 7 5 m depth combined with a nourishment of the beach behind it high resolution bathymetric surveys carried out with the wesp revealed that the shoreface nourishment resulted in a significant shoreward migration of the outer bar during 1999 2001 after 2 years the system started to return to its natural dynamic equilibrium and lost the positive influence of the shoreface nourishment area shoreward movement of bars and increase of bar height which forms the first defense line of the mainland against the sea and positive contribution to the sand budget which increased as a result of the nourishment after 3 years may 1999 to april 2002 the sediment volume still had an increase of 477 500 m3 45 of the applied sand relative to may 1999 the shoreface nourishment area did not have a direct effect on the beach the shoreface nourishment area probably will have to be maintained to retain the sediment on the beach in the long run in egmond the shoreface nourishment started to disappear before the sediment could reach the beach the time scale of sediment feed to the beach zone probably is of the order of 5 10 years the shoreface nourishment seems to function as a reef creating a lee side effect that influences both cross shore and longshore sediment transport resulting in two main hypotheses firstly the longshore effect in which large waves break at the shoreface nourishment cause a calmer wave climate shoreward of the shoreface nourishment area and a reduction of the longshore current the shoreface nourishment partially blocks the wave driven longshore current secondly the cross shore effect in which shoaling waves generate onshore transport these hypotheses are supported by generated model results with both a process based profile model unibest tc and a process based coastal area model delft3d mor the unibest tc model was able to predict the detachment of the outer bar from the shoreface nourishment and to some extent the shoreward bar movements in the lee of the shoreface nourishment area the model found an increase in sediment confirming the shielding effect of the shoreface nourishment area the delft3d model found as a result of the shoreface nourishment area a decrease of the flow velocity and the wave height just shoreward of the shoreface nourishment area the model was able to predict the similar trend in sedimentation erosion pattern although the intensities were smaller in the lee of the shoreface nourishment area a clear sedimentation was found erosion was found south and seaward of the shoreface nourishment area the modeled profiles did not follow the measured profile changes the separation of the shoreface nourishment from the outer bar and the shoreward migration of the bars could not be accurately modeled because the cross shore transport caused by wave asymmetry is not taken into account in the standard version of delft3d these results were in line with the expectations

mount elbert gas hydrate stratigraphic test well alaska north slope coring operations core sedimentology and lithostratigraphy abstract in february 2007 bp exploration alaska the u s department of energy and the u s geological survey completed the bpxa doe usgs mount elbert gas hydrate stratigraphic test well mount elbert well in the milne point unit on the alaska north slope the program achieved its primary goals of validating the pre drill estimates of gas hydrate occurrence and thickness based on 3 d seismic interpretations and wireline log correlations and collecting a comprehensive suite of logging coring and pressure testing data the upper section of the mount elbert well was drilled through the base of ice bearing permafrost to a casing point of 594 m 1950 ft approximately 15 m 50 ft above the top of the targeted reservoir interval the lower portion of the well was continuously cored from 606 m 1987 ft to 760 m 2494 ft and drilled to a total depth of 914 m ice bearing permafrost extends to a depth of roughly 536 m and the base of gas hydrate stability is interpreted to extend to a depth of 870 m coring through the targeted gas hydrate bearing reservoirs was completed using a wireline retrievable system the coring program achieved 85 recovery of 7 6 cm 3 in diameter core through 154 m 504 ft of the hole an onsite team processed the cores collecting and preserving approximately 250 sub samples for analyses of pore water geochemistry microbiology gas chemistry petrophysical analysis and thermal and physical properties eleven samples were immediately transferred to either methane charged pressure vessels or liquid nitrogen for future study of the preserved gas hydrate additional offsite sampling analyses and detailed description of the cores were also conducted based on this work one lithostratigraphic unit with eight subunits was identified across the cored interval subunits ii and va comprise the majority of the reservoir facies and are dominantly very fine to fine moderately sorted quartz feldspar and lithic fragment bearing to rich sands lithostratigraphic and palynologic data indicate that this section is most likely early eocene to late paleocene in age the examined units contain evidence for both marine and non marine lithofacies and indications that the depositional environment for the reservoir facies may have been shallower marine than originally interpreted based on pre drill wireline log interpretations there is also evidence of reduced salinity marine conditions during deposition that may be related to the paleo climate and depositional conditions during the early eocene

physical properties and rock physics models of sediment containing natural and laboratory formed methane gas hydrate this paper presents results of shear strength and acoustic velocity p wave measurements performed on 1 samples containing natural gas hydrate from the mallik 2l 38 well mackenzie delta northwest territories 2 reconstituted ottawa sand samples containing methane gas hydrate formed in the laboratory and 3 ice bearing sands these measurements show that hydrate increases shear strength and p wave velocity in natural and reconstituted samples the proportion of this increase depends on 1 the amount and distribution of hydrate present 2 differences in sediment properties and 3 differences in test conditions stress strain curves from the mallik samples suggest that natural gas hydrate does not cement sediment grains however stress strain curves from the ottawa sand containing laboratory formed gas hydrate do imply cementation is present acoustically rock physics modeling shows that gas hydrate does not cement grains of natural mackenzie delta sediment natural gas hydrates are best modeled as part of the sediment frame this finding is in contrast with direct observations and results of ottawa sand containing laboratory formed hydrate which was found to cement grains waite et al 2004 it therefore appears that the microscopic distribution of gas hydrates in sediment and hence the effect of gas hydrate on sediment physical properties differs between natural deposits and laboratory formed samples this difference may possibly be caused by the location of water molecules that are available to form hydrate models that use laboratory derived properties to predict behavior of natural gas hydrate must account for these differences

a reevaluation of using laboratory shear tests the expression for the average undrained shear strength mobilized on a slip surface in the field resulted from in situ vane and oedometer data combined with a correction factor obtained from the computed factor of safety of unstable embankments footings and excavations it is shown here that the same expression for mobilized undrained strength of soft clays is also obtained from laboratory shear tests by taking into account anisotropy and time effects this result is highly significant since the laboratory undrained shear strength data as well as the correction factor for the time effect are completely unrelated to the in situ data that previously resulted in the expression for field mobilized undrained shear strength key words mobilized undrained shear strength in situ vane test laboratory shear tests

protecting natural landforms and habitats by nourishing an eroding estuarine beach an important issue facing coastal managers is how natural coastal habitats can be protected against wave erosion by human action an assessment is made of attempts to protect a rare maritime forest on the bay side of a barrier island at fire island new york usa using artificial beach fill the sediment deficit is caused by human attempts to stabilize the island by restricting inlet formation overwash and dune migration and it is exacerbated by a nearby marina bulkhead a total of 1099 m3 of sand dredged from the navigation channel was placed near the bulkhead loss of fill was 5 54 7 87 m3 m 1 in the first 6 months the fill was gone 18 months after placement sediment moving out of the fill area caused almost 4 m of shoreline advance 40 m downdrift after 6 months gain of 3 28 m3 m 1 followed by retreat of about 5 m at that location over the next 12 months loss of 5 51 m3 m 1 these results reveal how small changes in volume of microtidal estuarine beaches can cause great shoreline displacement rates the amount of fill from maintenance dredging is insufficient to replenish erosion losses placing additional fill sediment on the bayside to create artificial washover fans can mimic natural landforms and overcome loss of sediment inputs caused by stabilizing the ocean shore mechanical placement may be preferable to natural processes which would deliver sediment across the island and through pre existing stable habitat eliminating some of the features that take long to form

multi measurement approach for establishing the base of gas hydrate occurrence in the krishna godavari basin for sites cored during expedition nghp 02 in the offshore of india abstract the 2015 national gas hydrate program of india s second expedition nghp 02 acquired logging and coring datasets for constraining the base of the gas hydrate occurrence zone deepest gh and the theoretical base of gas hydrate stability zone bghs these data are used here for two primary goals to constrain the deepest occurrence of gas hydrate relative to predicted stability limits and the observed bsr and to characterize the nature of the contact between gas hydrate bearing sediment and the underlying gas hydrate free sediment a consensus depth for the deepest gh is derived for each nghp 02 coring site from downhole indicators of gas hydrate occurrence obtained from well log electrical resistivity and acoustic data pressure core compressional wave velocity measurements and conventional core measurements of anomalously low temperatures to establish the theoretical bghs models of gas hydrate phase stability with depth are compared with downhole temperature profiles derived from 1 assuming a constant geothermal gradient consistent with downhole temperature measurements and 2 assuming constant heat flow using a geotherm through the downhole temperature measurements and incorporating thermal conductivity calculated from borehole logging data although the deepest nghp 02 gh occurrences are controlled at several sites by a lithologic boundary most sites have deepest gh occurrences within a single coarse grained lithology cutoffs within a single coarse grained lithology which occur for the primary nghp 02 area b gas hydrate reservoir will inhibit pore pressure drawdowns used to extract methane from gas hydrate as an energy resource

extent of gas hydrate filled fracture planes implications for in situ methanogenesis and resource potential 1 high angle gas hydrate filled fracture planes were identified along a 31 m interval in logging while drilling images in two holes located 11 m apart drilled during the indian national gas hydrate program expedition 01 offshore india using monte carlo simulations to account for uncertainty in hole location hole deviation strike and dip we assert with 95 confidence that the fracture planes in the two holes are not the same the gas hydrate filled fracture planes likely only extend a few meters laterally from each borehole and occur in an isolated interval in the middle of the gas hydrate stability zone this suggests gas generated microbially within in the gas hydrate stability zone may have supplied the gas hydrate filled fracture interval production of methane from these reservoirs using conventional methods may be quite challenging

effective medium modeling of gas hydrate filled fractures using the sonic log in the krishna godavari basin offshore eastern india 1 indian national gas hydrate program expedition 01 has established that clay rich marine sediment from the krishna godavari kg basin in the eastern indian margin hosts one of the richest gas hydrate deposits in the world resistivity at bit images and pressure cores reveal that the gas hydrate morphology in clay rich sediment varies from complex vein structures grain displacing to invisible pore filling existing rock physics models which relate acoustic data to in situ gas hydrate concentrations generally assume isotropic pore filling gas hydrate which yields misleading concentration estimates for fractured fine grained sediments the anisotropic kg basin sediment presents additional complications here we apply differential effective medium theory to incorporate grain displacing morphologies by which gas hydrate is included as vertical ellipsoids with aspect ratios ranging from those of thin veins up to those of nodules in an elastic anisotropic background we have estimated gas hydrate concentrations from sonic velocities at hole 10d in the kg basin considering three basic gas hydrate morphologies i pore filling ii grain displacing and iii a combination of grain displacing and pore filling average gas hydrate saturations for these three cases are 35 42 27 30 and 33 41 of the total porosity respectively in the depth range 60 140 m below seafloor mbsf saturation is highest at 67 mbsf for any morphology but the values differ between morphologies for the pore filling morphology the maximum gas hydrate saturation of 56 is 18 22 higher than the grain displacing morphology and 2 9 higher than the combined morphology estimates differ by 6 of the sediment volume with rotations of gas hydrate veins from vertical to horizontal

comparison of the physical and geotechnical properties of gas hydrate bearing sediments from offshore india and other gas hydrate reservoir systems abstract the sediment characteristics of hydrate bearing reservoirs profoundly affect the formation distribution and morphology of gas hydrate the presence and type of gas porewater chemistry fluid migration and subbottom temperature may govern the hydrate formation process but it is the host sediment that commonly dictates final hydrate habit and whether hydrate may be economically developed in this paper the physical properties of hydrate bearing regions offshore eastern india krishna godavari and mahanadi basins and the andaman islands determined from expedition nghp 01 cores are compared to each other well logs and published results of other hydrate reservoirs properties from the hydrate free kerala konkan basin off the west coast of india are also presented coarser grained reservoirs permafrost related and marine may contain high gas hydrate pore saturations while finer grained reservoirs may contain low saturation disseminated or more complex gas hydrates including nodules layers and high angle planar and rotational veins however even in these fine grained sediments gas hydrate preferentially forms in coarser sediment or fractures when present the presence of hydrate in conjunction with other geologic processes may be responsible for sediment porosity being nearly uniform for almost 500 m off the andaman islands properties of individual nghp 01 wells and regional trends are discussed in detail however comparison of marine and permafrost related arctic reservoirs provides insight into the inter relationships and common traits between physical properties and the morphology of gas hydrate reservoirs regardless of location extrapolation of properties from one location to another also enhances our understanding of gas hydrate reservoir systems grain size and porosity effects on permeability are critical both locally to trap gas and regionally to provide fluid flow to hydrate reservoirs index properties corroborate more advanced consolidation and triaxial strength test results and can be used for predicting behavior in other nghp 01 regions pseudo overconsolidation is present near the seafloor and is underlain by underconsolidation at depth at some nghp 01 locations

a video based technique for mapping intertidal beach bathymetry abstract measuring the location of the shoreline and monitoring foreshore changes through time are core tasks carried out by coastal engineers for a wide range of research monitoring and design applications with the advent of digital imaging technology shore based video systems provide continuous and automated data collection encompassing a much greater range of time and spatial scales than were previously possible using field survey methods a new video based technique is presented that utilises full colour image information which overcomes problems associated with previous grey scale methods which work well at steep reflective sites but are less successful at flatter dissipative sites identification of the shoreline feature is achieved by the automated clustering of sub aqueous and sub aerial pixels in hue saturation value hsv colour space and applying an objective discriminator function to define their boundary i e shoreline within a time series of consecutive geo referenced images the elevation corresponding to the detected shoreline features is calculated on the basis of concurrent tide and wave information which is incorporated in a model that combines the effects of wave set up and swash at both incident and infragravity frequencies validation of the technique is achieved by comparison with dgps survey results to assess the accuracy of the detection and elevation methods both separately and together the uncertainties associated with the two sub components of the model tend to compensate for each other the mean difference between image based and surveyed shoreline elevations was less than 15 cm along 85 of the 2 km study region which corresponded to an horizontal offset of 6 m the application of the intertidal bathymetry mapping technique in support of czm objectives is briefly illustrated at two sites in the netherlands and australia

hydrate morphology physical properties of sands with patchy hydrate saturation 1 the physical properties of gas hydrate bearing sediments depend on the volume fraction and spatial distribution of the hydrate phase the host sediment grain size and the state of effective stress determine the hydrate morphology in sediments this information can be used to significantly constrain estimates of the physical properties of hydrate bearing sediments including the coarse grained sands subjected to high effective stress that are of interest as potential energy resources reported data and physical analyses suggest hydrate bearing sands contain a heterogeneous patchy hydrate distribution whereby zones with 100 pore space hydrate saturation are embedded in hydrate free sand accounting for patchy rather than homogeneous hydrate distribution yields more tightly constrained estimates of physical properties in hydrate bearing sands and captures observed physical property dependencies on hydrate saturation for example numerical modeling results of sands with patchy saturation agree with experimental observation showing a transition in stiffness starting near the series bound at low hydrate saturations but moving toward the parallel bound at high hydrate saturations the hydrate patch size itself impacts the physical properties of hydrate bearing sediments for example at constant hydrate saturation we find that conductivity electrical hydraulic and thermal increases as the number of hydrate saturated patches increases this increase reflects the larger number of conductive flow paths that exist in specimens with many small hydrate saturated patches in comparison to specimens in which a few large hydrate saturated patches can block flow over a significant cross section of the specimen

evidence for resetting of fluid inclusion temperatures from quartz cements in oilfields abstract quartz is a major pore occluding cement in north sea oilfield reservoir sandstones fluid inclusions yield homogenization temperatures t h which have been thought to represent growth temperatures for the host quartz however early diagenetic inclusions from the detrital grain overgrowth boundary yield excessively high palaeotemperatures which do not match the growth temperatures calculated from the depth of cementation the temperatures of these inclusions increase with present day depth of burial and approach present day reservoir temperatures this suggests that the inclusions have begun to reset towards present day pressure temperature conditions the t h of the inclusions hence represent burial temperatures rather than growth temperatures for the quartz experimental studies indicate that the amount of resetting undergone by an inclusion varies depending on its size shape and fluid composition a relationship between inclusion t h and these variables has been observed in inclusions from deeply buried quartz cements in the north sea

beach nourishments at coolangatta bay over the period 1987 2005 impacts and lessons abstract erosion of the southern gold coast beaches se queensland australia was exacerbated after the extension of the tweed river training walls in the early 1960s to achieve the objective of restoring and maintaining beach amenity significant nourishment works have been undertaken in coolangatta bay over the past 30 years particularly under the tweed river entrance sand bypassing project tresbp since 1995 a number of nourishment campaigns and the implementation of a permanent sand bypass system in 2001 have resulted in significant changes of coolangatta bay morphology the present case study investigates the influence of both wave climate and nourishment works on the area extending from the updrift snapper rocks area to downdrift kirra beach swan spectral wave model is implemented at coolangatta bay area and forced by the global wave model ww3 to estimate wave forcing and the potential natural longshore drift entering in coolangatta specific transects extracted from accurate bathymetric surveys are used to investigate and quantify coolangatta bay sedimentation for the period 1987 2005 a network of argus video stations provides high sample rate information on the shoreline evolution results show that over the past 10 years coolangatta bay has infilled rapidly sedimentation reached up to 6 m in some areas between 1995 and 2005 with beach width increasing by 200 m at kirra beach rapid seaward shoreline migration is consistent with the intense over pumping of sand relative to the natural potential to move sand alongshore the nourishment strategy used during this project has successfully delivered large amounts of sand to the southern gold coast embayment although it has been up to now controversial from many community perspectives the artificial sand bypassing process proved to be much more efficient than depositing the dredged sand in the nearshore area which requires a significant period of low energy condition in order for the deposited sediment to migrate shoreward and weld to the shore this case study confirms that when carefully undertaken sand bypassing is a sustainable and flexible soft engineering approach which can work in concert with natural processes

gas hydrate saturations estimated from fractured reservoir at site nghp 01 10 krishna godavari basin india 1 during the indian national gas hydrate program expedition 01 nghp 01 one of the richest marine gas hydrate accumulations was discovered at site nghp 01 10 in the krishna godavari basin the occurrence of concentrated gas hydrate at this site is primarily controlled by the presence of fractures assuming the resistivity of gas hydrate bearing sediments is isotropic the conventional archie analysis using the logging while drilling resistivity log yields gas hydrate saturations greater than 50 as high as 80 of the pore space for the depth interval between 25 and 160 m below seafloor on the other hand gas hydrate saturations estimated from pressure cores from nearby wells were less than 26 of the pore space although intrasite variability may contribute to the difference the primary cause of the saturation difference is attributed to the anisotropic nature of the reservoir due to gas hydrate in high angle fractures archie s law can be used to estimate gas hydrate saturations in anisotropic reservoir with additional information such as elastic velocities to constrain archie cementation parameters m and the saturation exponent n theory indicates that m and n depend on the direction of the measurement relative to fracture orientation as well as depending on gas hydrate saturation by using higher values of m and n in the resistivity analysis for fractured reservoirs the difference between saturation estimates is significantly reduced although a sizable difference remains to better understand the nature of fractured reservoirs wireline p and s wave velocities were also incorporated into the analysis

physical properties of fine grained sediments with segregated hydrate lenses abstract the physical properties of natural gas hydrate bearing sediments are critical for the analysis of natural systems and for the design of gas production strategies this work explores the properties of fine grained sediments containing segregated hydrate lenses our analyses show that hydrate formation is grain displacive when the product of the effective stress and the grain radius is r

grain scale imaging and compositional characterization of cryo preserved india nghp 01 gas hydrate bearing cores abstract we report on grain scale characteristics and gas analyses of gas hydrate bearing samples retrieved by nghp expedition 01 as part of a large scale effort to study gas hydrate occurrences off the eastern indian peninsula and along the andaman convergent margin using cryogenic scanning electron microscopy x ray spectroscopy and gas chromatography we investigated gas hydrate grain morphology and distribution within sediments gas hydrate composition and methane isotopic composition of samples from krishna godavari kg basin and andaman back arc basin borehole sites from depths ranging 26 to 525 mbsf gas hydrate in kg basin samples commonly occurs as nodules or coarse veins with typical hydrate grain size of 30 80 m as small pods or thin veins 50 to several hundred microns in width or disseminated in sediment nodules contain abundant and commonly isolated macropores in some places suggesting the original presence of a free gas phase gas hydrate also occurs as faceted crystals lining the interiors of cavities while these vug like structures constitute a relatively minor mode of gas hydrate occurrence they were observed in near seafloor kg basin samples as well as in those of deeper origin 100 mbsf and may be original formation features other samples exhibit gas hydrate grains rimmed by nacl bearing material presumably produced by salt exclusion during original hydrate formation well preserved microfossil and other biogenic detritus are also found within several samples most abundantly in andaman core material where gas hydrate fills microfossil crevices the range of gas hydrate modes of occurrence observed in the full suite of samples suggests a range of formation processes were involved as influenced by local in situ conditions the hydrate forming gas is predominantly methane with trace quantities of higher molecular weight hydrocarbons of primarily microbial origin the composition indicates the gas hydrate is structure i

synthetic fluid inclusions vi quantitative evaluation of the decrepitation behaviour of fluid inclusions in quartz at one atmosphere confining pressure the decrepitation behaviour of fluid inclusions in quartz at one atmosphere confining pressure has been evaluated using pure h2o synthetic inclusions formed by healing fractures in natural quartz three different modes of non elastic deformation referred to as stretching leakage or partial decrepitation and total decrepitation have been observed the internal pressure required to initiate non elastic deformation is inversely related to inclusion size according to the equation internal pressure kbar 4 26 d 0 423 where d is the inclusion diameter in microns regularly shaped inclusions require a higher internal pressure to initiate non elastic deformation than do irregularly shaped inclusions of similar size heating inclusions through the quartz inversion results in mechanical instability in the quartz crystal and leads to mass decrepitation of inclusions owing to structural mismatches generated by pressure gradients in the quartz around each inclusion long term heating experiments 2 years suggest that the internal pressure required to initiate non elastic deformation does not decrease significantly with time and indicates that short lived thermal fluctuations in natural systems should not alter the inclusion density and homogenization temperature inclusions that do exhibit decreased density higher homogenization temperature are however always accompanied by a change in shape from irregular to that of a negative crystal observations of this study are consistent with elasticity theory related to fracture generation and propagation around inclusions in minerals these results indicate that an inclusion will not be influenced by a neighbouring inclusion or other defect in the host phase as long as the distance between the two is 2 4 diameters of the larger of the two inclusions

gas hydrate saturation in the krishna godavari basin from p wave velocity and electrical resistivity logs abstract during the indian national gas hydrate program nghp expedition 01 a series of well logs were acquired at several sites across the krishna godavari kg basin electrical resistivity logs were used for gas hydrate saturation estimates using archie s method the measured in situ pore water salinity seafloor temperature and geothermal gradients were used to determine the baseline pore water resistivity in the absence of core data arp s law was used to estimate in situ pore water resistivity uncertainties in the archie s approach are related to the calibration of archie coefficient a cementation factor m and saturation exponent n values we also have estimated gas hydrate saturation from sonic p wave velocity logs considering the gas hydrate in frame effective medium rock physics model uncertainties in the effective medium modeling stem from the choice of mineral assemblage used in the model in both methods we assume that gas hydrate forms in sediment pore space combined observations from these analyses show that gas hydrate saturations are relatively low s h 15 20 in two zones between 168 and 198 mbsf site nghp 01 05 s h 35 38 in two discrete zone between 70 and 90 mbsf and site nghp 01 07 shows the gas hydrate saturation more than 25 in two zones between 75 and 155 mbsf a total of 10 drill sites and associated log data regional occurrences of bottom simulating reflectors from 2d and 3d seismic data and thermal modeling of the gas hydrate stability zone were used to estimate the total amount of gas hydrate within the kg basin average gas hydrate saturations for the entire gas hydrate stability zone seafloor to base of gas hydrate stability sediment porosities and statistically derived extreme values for these parameters were defined from the logs the total area considered based on the bsr seismic data covers 720 km 2 using the statistical ranges in all parameters involved in the calculation the total amount of gas from gas hydrate in the kg basin study area varies from a minimum of 5 7 trillion cubic feet tcf to 32 1 tcf

a fluid inclusion study of quartz cemented sandstones from offshore mid norway possible evidence for continued quartz cementation during oil emplacement abstract jurassic sandstones from the oil zone in a well from the haltenbanken area offshore mid norway contain both aqueous and hydrocarbon fluid inclusions within quartz overgrowths homogenization temperatures for the inclusions range from 92 c up to the present formation temperature of approximately 118 c since the inclusions mostly are located at the boundaries between quartz clasts and quartz overgrowths the homogenization temperatures indicate that quartz cementation started at temperatures slightly below 92 c poikilotopic ferroan calcite cement usually predates formation of quartz overgrowths and most calcite cement must be precipitated at temperatures below 90 c although in one calcite cemented zone ferroan calcite encloses quartz overgrowths with inclusions trapped at temperatures of up to 105 c none of the examined hydrocarbon inclusions homogenized below 102 c and this suggests that oil started entering the reservoir at temperatures of around 100 c the burial history of the examined sandstones indicates that temperatures of 100 c were not reached before the late pliocene and that filling of the reservoir has taken place during the last few million years homogenization temperatures approximately equal to present formation temperature suggest that quartz cementation may still be in progress and that emplacement of oil did not necessarily stop precipitation of quartz cement possible continued quartz cementation after oil filled the reservoir could be explained by dissolution of quartz at stylolites and grain contacts as transport of dissolved quartz from these sources might possibly take place by diffusion through irreducible water

a unified contact cementation theory for gas hydrate morphology detection and saturation estimation from elastic wave velocities abstract good knowledge of hydrate morphology and accurate quantification of hydrate saturation are significant for reservoir characterization resource exploitation and geohazards assessment although many of empirical or theoretical models have been developed to detect hydrate morphology and predict hydrate saturation from elastic wave velocities they either fail to hold true for complex morphologies or cannot provide accurate hydrate saturation estimate in this study we propose a unified contact cementation theory by applying the modified hashin shtrikman upper and lower bounds to an extended cementation theory by merging the cementation theory and effective medium theory it can be used to account for four types of hydrate morphologies numerical modeling results provide some new insights into effects of normalized thickness of hydrate layer friction coefficient and effective pressure on elastic wave velocities for different morphologies which will be helpful for analyzing the borehole stability and determining optimum production related strategies in addition we propose a hydrate morphology based inversion method by introducing the ratio of multiple hydrate morphologies from statistical analyses and apply it to the acoustic logs from the mallik 5l 38 permafrost related gas hydrate research well in mackenzie delta and other three marine wells in nankai trough and hikurangi margin the velocity based gas hydrate saturation estimations are in good agreement with those predicted from resistivity log and nuclear magnetic resonance measurement as well as core data confirming feasibility and applicability of our theory and inversion method and indicating its potential in seismic characterization of gas hydrate reservoirs

physical properties of sediments from the ulleung basin east sea results from second ulleung basin gas hydrate drilling expedition east sea korea abstract physical properties including basic index properties undrained shear strength and thermal conductivities were measured on conventional cores retrieved from the ulleung basin during the second ulleung basin gas hydrate expedition ubgh2 the ubgh2 logged 13 sites and cored 10 sites to locate potential sites for an offshore test production a total of 211 conventional cores were recovered undrained shear strength thermal conductivity and index properties including porosity and grain density were measured onboard mineral composition analyses and grain size analyses were completed onshore after the expedition the averaged porosity at each site ranges from 65 to 71 the averaged grain density at each site ranges from 2 57 to 2 66 g cm3 and the mean grain size mostly lies between 4 m and 25 m with sparsely scattered coarse grained intervals the relatively high porosity and low grain density are due to the large portion of diatomaceous sediments the thermal conductivities average around 0 8 w mk and the low porosity and the abundance of clay mineral and oapl a may have caused the relatively low thermal conductivity in the ulleung basin the geomechanical analyses revealed a few relevant findings important for sediment physical behaviors during gas hydrate production the particle migration in coarse grained layers during production necessitates proper measure for sand productions while fine grained layers are mostly self filtering the vertical deformation estimated from the compression index suggested that the subsidence induced by the pore pressure change from the depressurization is much higher than those induced by the lost of gas hydrate particles from dissociation massive vertical deformation in fine grained layers has been predicted to occur due to the pore pressure change from depressurization induced gas hydrate production the drilling mud weight induced pressure window is mostly determined by the water depth in deep sea drilling but caution should be taken in determination of fracture pressures in hydrate bearing sediments because gas hydrate saturations alter poisson s ratio

multigrain sedimentation erosion model based on cross shore equilibrium sediment distribution application to nourishment design abstract in the light of global warming and sea level rise there are many coastal beaches that suffer from erosion beach nourishment has become a common practice to maintain the sediment balance on a shore face in this paper a three dimensional numerical model for evaluating long term impact of beach nourishment projects has been developed the model addresses the longstanding complex issue of coastal morphology and sediment grain size distribution from an unconventional angle which exploits the strong links between grain size distribution and the prevailing transport direction of each sediment constituent under average wave and storm action the present model predicts the redistribution of nourished sediment according to the subtle clues implied by equilibrium distribution curves and latest coastal wave transformation theories after verification against recent field observations in terschelling the netherlands the model was used to predict long term effects of different beach nourishment strategies it was found that a given the source sediment available in terschelling the tactics of large volume and less frequent implementation are better than otherwise and b from a pure engineering point of view waterline nourishment outperforms offshore trough nourishment the model offers an additional tool for coastal engineers to evaluate the feasibility effectiveness and the optimization of dumping locations for beach nourishment projects it is also a useful tool for stratigraphic modelling of shallow marine sedimentation in conjunction with sea level changes

origin of reservoir fractures in little knife field north dakota thin vertical planar fractures observed in the mission canyon formation at the little knife field are naturally occurring and appear to be extension fractures the predominant east west trend of the fractures measured in oriented core from six wells parallels the contemporary maximum horizontal compressive stress in the williston basin the fractures occur only in carbonate units but within the carbonates their occurrence is not lithology dependent fracture density measured in cores of the reservoir carbonates averages 1 ft 3 m of fracture per 2 3 ft 7 m of core the formation and mineralization of reservoir fractures were the most recent diagenetic events in the mission canyon formation at little knife study of aqueous and hydrocarbon fluid inclusions associated with the fractures reveals 1 fractures formed after the strata were buried to at least their present depth of 9 800 ft 2 987 m which indicates their age is post mesozoic 2 the pore fluid pressure gradient was normal hydrostatic immediately after if not during fracture system development 3 formation water salinity has remained fairly constant since fracture initiation 4 migration of hydrocarbons into the reservoir probably preceded fracture genesis and 5 methane concentration may have decreased since fracture initiation

mount elbert gas hydrate stratigraphic test well alaska north slope overview of scientific and technical program abstract the mount elbert gas hydrate stratigraphic test well was drilled within the alaska north slope ans milne point unit mpu from february 3 to 19 2007 the well was conducted as part of a cooperative research agreement cra project co sponsored since 2001 by bp exploration alaska inc bpxa and the u s department of energy doe in collaboration with the u s geological survey usgs to help determine whether ans gas hydrate can become a technically and commercially viable gas resource early in the effort regional reservoir characterization and reservoir simulation modeling studies indicated that up to 0 34 trillion cubic meters tcm 12 trillion cubic feet tcf gas may be technically recoverable from 0 92 tcm 33 tcf gas in place within the eileen gas hydrate accumulation near industry infrastructure within ans mpu prudhoe bay unit pbu and kuparuk river unit kru areas to further constrain these estimates and to enable the selection of a test site for further data acquisition the usgs reprocessed and interpreted mpu 3d seismic data provided by bpxa to delineate 14 prospects containing significant highly saturated gas hydrate bearing sand reservoirs the mount elbert site was selected to drill a stratigraphic test well to acquire a full suite of wireline log core and formation pressure test data drilling results and data interpretation confirmed pre drill predictions and thus increased confidence in both the prospect interpretation methods and in the wider ans gas hydrate resource estimates the interpreted data from the mount elbert well provide insight into and reduce uncertainty of key gas hydrate bearing reservoir properties enable further refinement and validation of the numerical simulation of the production potential of both mpu and broader ans gas hydrate resources and help determine viability of potential field sites for future extended term production testing drilling and data acquisition operations demonstrated that gas hydrate scientific research programs can be safely effectively and efficiently conducted within ans infrastructure the program success resulted in a technical team recommendation to project management to drill and complete a long term production test within the area of existing ans infrastructure if approved by stakeholders this long term test would build on prior arctic research efforts to better constrain the potential gas rates and volumes that could be produced from gas hydrate bearing sand reservoirs

electrical anisotropy due to gas hydrate filled fractures in 2006 the indian national gas hydrate program expedition01 ornghp 01 discoveredgashydrateasfillinnearvertical fractures in unconsolidated sediments at several drillingsitesontheindiancontinentalmargins thesegashydrate filled fractures were identified on logging while drilling resistivity images the gas hydrate filled fracture intervals coincide with high measured resistivity at the nghp 01 sites high measured resistivity translates into high hydrate saturationsviaarchie sequation however thesehighsaturations contradict lower gas hydrate saturations determined from pressure core and chlorinity measurements also in intervalswithnear verticalgashydrate filledfractures thereis considerable separation between phase shift and attenuation resistivity logs with 2 mhz resistivity measurements being significantly higher than 400 khz resistivity measurements we modeled the sensitivity of the propagation resistivity measurements in the gas hydrate filled fracture intervals at nghp 01 sites 5 and 10 near vertical hydrate filled fracturescancausetheabnormallyhighresistivitymeasurements in vertical holes due to electrical anisotropy the model suggests the gas hydrate saturations in situ are usually significantlylowerthanthosecalculatedfromarchie sequation in addition these modeled gas hydrate saturations generally agree with the lower gas hydrate saturations obtained from pressure core and chlorinity measurements at nghp 01 sites5and10

permafrost associated natural gas hydrate occurrences on the alaska north slope abstract in the 1960s russian scientists made what was then a bold assertion that gas hydrates should occur in abundance in nature since this early start the scientific foundation has been built for the realization that gas hydrates are a global phenomenon occurring in permafrost regions of the arctic and in deep water portions of most continental margins worldwide in 1995 the u s geological survey made the first systematic assessment of the in place natural gas hydrate resources of the united states that study suggested that the amount of gas in the gas hydrate accumulations of northern alaska probably exceeds the volume of known conventional gas resources on the north slope researchers have long speculated that gas hydrates could eventually become a producible energy resource yet technical and economic hurdles have historically made gas hydrate development a distant goal this view began to change in recent years with the realization that this unconventional resource could be developed with existing conventional oil and gas production technology one of the most significant developments was the completion of the bpxa doe usgs mount elbert gas hydrate stratigraphic test well on the alaska north slope which along with the mallik project in canada have for the first time allowed the rational assessment of gas hydrate production technology and concepts almost 40 years of gas hydrate research in northern alaska has confirmed the occurrence of at least two large gas hydrate accumulations on the north slope we have also seen in alaska the first ever assessment of how much gas could be technically recovered from gas hydrates however significant technical concerns need to be further resolved in order to assess the ultimate impact of gas hydrate energy resource development in northern alaska

methane migration within the submarine gas hydrate stability zone under deep water conditions abstract possible pathways of methane migration and associated gas hydrate accumulation are considered gas hydrates precipitate in water filtration routes when the methane concentration in water exceeds its solubility which significantly decreases within the hydrate stability zone towards the sea floor in the vicinity of the ascending free gas flows gas hydrates are formed within a diffusion aureole resulting from the difference between chemical potentials of gaseous and water dissolved methane the role of diffusion is also essential in the vicinity of gas saturated water flows as well as within and above the sections where biochemical methane is intensively generated a chemical potential gradient of dissolved methane which is a necessary condition for gas hydrate accumulation is created due to inhomogeneity of the geological medium manifested as temperature and water salinity gradients or changes of permeability the thermobaric gas hydrate stability zone is a geochemical barrier for hydrocarbon gas emigrating from sediments into the water column however methane is not completely preserved in a hydrate state it is unknown yet which fraction of migrating methane is detained on this barrier

physical properties of sediment from the mount elbert gas hydrate stratigraphic test well alaska north slope this study characterizes cored and logged sedimentary strata from the february 2007 bp exploration alaska department of energy u s geological survey bpxa doe usgs mount elbert gas hydrate stratigraphic test well on the alaska north slope ans the physical properties program analyzed core samples recovered from the well and in conjunction with downhole geophysical logs produced an extensive dataset including grain size water content porosity grain density bulk density permeability x ray diffraction xrd mineralogy nuclear magnetic resonance nmr and petrography this study documents the physical property interrelationships in the well and demonstrates their correlation with the occurrence of gas hydrate gas hydrate gh occurs in three unconsolidated coarse silt to fine sand intervals within the paleocene and eocene beds of the sagavanirktok formation unit d gh 614 4 m 627 9 m unit c gh1 649 8 m 660 8 m and unit c gh2 663 2 m 666 3 m these intervals are overlain by fine to coarse silt intervals with greater clay content a deeper interval unit b is similar lithologically to the gas hydrate bearing strata however it is water saturated and contains no hydrate in this system it appears that high sediment permeability k is critical to the formation of concentrated hydrate deposits intervals d gh and c gh1 have average plug intrinsic permeability to nitrogen values of 1700 md and 675 md respectively these values are in strong contrast with those of the overlying gas hydrate free sediments which have k values of 5 7 md and 49 md respectively and thus would have provided effective seals to trap free gas the relation between permeability and porosity critically influences the occurrence of gh for example an average increase of 4 in porosity increases permeability by an order of magnitude but the presence of a second fluid e g methane from dissociating gas hydrate in the reservoir reduces permeability by more than an order of magnitude published by elsevier ltd

physical property characteristics of gas hydrate bearing reservoir and associated seal sediments collected during nghp 02 in the krishna godavari basin in the offshore of india abstract india s national gas hydrate program expedition 02 nghp 02 was conducted to better understand geologic controls on gas hydrate occurrence and morphology targeting coarse grained sediments along the lower continental slope offshore eastern india this study combines seismic logging while drilling data and a petroleum system approach to provide a regional geologic and lithologic context for 1 gas hydrate morphology and distribution and 2 effects of fine grained sediments clays and other grains smaller than 63 m on gas production in nghp 02 area b in the krishna godavari basin area b seismic data show a buried anticline syncline structure with strong reflectors r1 and r2 that delineate two of the five lithologic units unit i shallowest ii r1 iii iv r2 and v below the bas of gas hydrate stability throughout area b gas hydrate morphology depends on its placement within these units specifically core and grain scale measurements indicate fines content exerts a primary control on the gas hydrate distribution and morphology units i ii and iii are generally fine grained on the anticline crest these units host primarily grain displacing gas hydrate veins linked to pore occupying gas hydrate in thin localized coarser grained deposits diatoms in unit iii increase porosity with depth reaching 70 where it contacts unit iv the gas hydrate reservoir associated with reflector r2 the unit iii lithology and porosity allow fluid and dissolved phase methane to escape unit iv and form gas hydrate in the fine grained overburden within unit iv fine grained layers are interbedded with coarser grained gas hydrate reservoir sands and the fines content even in the sands is high enough to impact hydraulic and mechanical properties during gas production fluid motion during gas production can mobilize fines which can then clog pore throats limiting production rates pore water freshening during gas hydrate dissociation can increase fines mobilization particularly given the smectite identified in the fine grained interbeds

gas hydrate destabilization enhanced dewatering benthic material turnover and large methane plumes at the cascadia convergent margin mixed methane sulfide hydrates and carbonates are exposed as a pavement at the seafloor along the crest of one of the accretionary ridges of the cascadia convergent margin vent fields from which methane charged low salinity fluids containing sulfide ammonia 4he and isotopically light co2 escape are associated with these exposures they characterize a newly recognized mechanism of dewatering at convergent margins where freshening of pore waters from hydrate destabilization at depth and free gas drives fluids upward this process augments the convergence generated overpressure and leads to local dewatering rates that are much higher than at other margins in the absence of hydrate discharge of fluids stimulates benthic oxygen consumption which is orders of magnitude higher than is normally found at comparable ocean depths the enhanced turnover results from the oxidation of methane hydrogen sulfide and ammonia by vent biota the injection of hydrate methane from the ridge generates a plume hundreds of meters high and several kilometers wide a large fraction of the methane is oxidized within the water column and generates 13c anomalies of the dissolved inorganic carbon pool

seismic imaging of a fractured gas hydrate system in the krishna godavari basin offshore india gas hydrate was discovered in the krishna godavari kg basin during the india national gas hydrate program nghp expedition 1 at site nghp 01 10 within a fractured clay dominated sedimentary system logging while drilling lwd coring and wire line logging confirmed gas hydrate dominantly in fractures at four borehole sites spanning a 500 m transect three dimensional 3d seismic data were subsequently used to image the fractured system and explain the occurrence of gas hydrate associated with the fractures a system of two fault sets was identified part of a typical passive margin tectonic setting the lwd derived fracture network at hole nghp 01 10a is to some extent seen in the seismic data and was mapped using seismic coherency attributes the fractured system around site nghp 01 10 extends over a triangular shaped area of 2 5 km2 defined using seismic attributes of the seafloor reflection as well as seismic sweetness at the base of the gas hydrate occurrence zone the triangular shaped area is also showing a polygonal nearly hexagonal fault pattern distinct from other more rectangular fault patterns observed in the study area the occurrence of gas hydrate at site nghp 01 10 is the result of a specific combination of tectonic fault orientations and the abundance of free gas migration from a deeper gas source the triangular shaped area of enriched gas hydrate occurrence is bound by two faults acting as migration conduits additionally the fault associated sediment deformation provides a possible migration pathway for the free gas from the deeper gas source into the gas hydrate stability zone it is proposed that there are additional locations in the kg basin with possible gas hydrate accumulation of similar tectonic conditions and one such location was identified from the 3d seismic data 6 km nw of site nghp 01 10

video monitoring of sandbar shoreline response to an offshore submerged structure at a microtidal beach abstract in early 2013 an 800 m long and 12 m wide submerged breakwater with its crest in 2 m depth was implemented at the wave dominated barred beach of sete se france to fight against erosion and submersion hazards daily video images from april 2011 to april 2016 covering an alongshore distance of 3 5 km are used to analyse the response of both the sandbar s and the shoreline to the structure implementation results show that the breakwater had a profound impact on the nearshore system both shoreward of the structure and well away from it alongshore a progressive rotation and linearisation of the sandbar was observed shoreward of the submerged breakwater this resulted in the splitting of the sandbar adjacent to the structure during a net offshore sandbar migration event driven by a severe storm in december 2013 the typical formation of a salient or tombolo was not observed instead shoreline coupled to the sandbar geometry which resulted in a slight seaward migration of the shoreline in front of the structure overall this study highlights that the role of the sandbar is critical to shoreline response to the implementation of breakwaters on barred beaches

wave climate and morphosedimentary characteristics of the kenitra bouknadel sandy coast morocco the bouknadel kenitra 20 km sandy coastline is of strong interest from the perspectives of beach amenity tourism and erosion issues this section of the moroccan coastline has only received little attention in the literature so far and morphosedimentary characteristics as well as wave climate are poorly understood the present paper provides the first extensive description of both wave climate and alongshore variability in the morphosedimentary behavior of these wave dominated beaches combined with accurate topographic surveys 9 year long global wave model output time series and subsequently driven empirical longshore drift formula and shoreline change measurements from aerial photographs results show that the coast is mainly exposed to high energy low steepness nw waves mostly during the october march period generated in the north atlantic by eastward traveling low pressure systems given the shoreline orientation northward and southward longshore drift components generated by this wave regime nearly balance in contrast the lower energy higher steepness n nw wave regime april september period contributes to an overall quantity of sand being transported southward similar to the yearly averaged net longshore drift beaches are mostly of the double barred intermediate type the southern beaches exhibit persistent rhythmic sandbars and rather steep beachface while the northern beaches are close to the dissipative state despite all the beaches are exposed to the same wave regimes beach states predicted using the dean s number roughly match these observations while previous studies elsewhere had shown that inherited geological factors may overwhelm contemporary dynamics in the determination of beach states here differences are attributed to coastal protection works that appear to be important additional determinants of beach morphology

nourishment evolution and impacts at four southern california beaches a sand volume analysis abstract four southern california beaches were nourished with offshore sand placed as subaerial pads several meters thick 50 m wide and spanning between 500 and 1500 m alongshore three nourishments constructed with coarser than native sand placed in 2012 at imperial cardiff and solana beaches elevated subaerial sand volumes for several years even when exposed to the energetic winter waves of the 2015 16 el nino followed by a stormy 2016 17 winter as these relatively resilient pads were overwashed landward tilted subaerial profiles accretionary crowns formed at the eroding front face of the originally flat topped pads and pooling occurred in the backbeach at imperial beach nourishment sand helped prevent waves from directly impacting riprap fronting houses while groundwater flooding behind the pad was observed at a location where the pad was elevated 1 6 m above the street as the nourishments retreated alongshore oriented spits grew downdrift from the eroding face the alongshore displacement of the subaerial center of mass of the 2012 nourishments is positively correlated with the seasonally varying s x y the alongshore radiation stress component after four years the net southward drift of the imperial beach nourishment contributed to the winter 2016 closure of the tijuana river mouth and the associated hyper polluted and anoxic estuary conditions nourishment impacts on sand levels on rocky reefs were not unambiguously detectable in the background of natural variability over several years gains or losses in the total sand volume integrated from the back beach to 8 m depth over the few km alongshore survey spans are sometimes comparable to nourishment volumes suggesting relatively large interannual sediment fluxes across the control volume boundaries the clearest trend in total volume is at torrey pines during 16 years since the 2001 nourishment about 300 000 m3 of sand has been lost if the trend continues the thinning veneer of sand will be removed more often from the subaerial winter beach exposing rocks and cobbles

quantification of gas hydrate saturation and morphology based on a generalized effective medium model abstract numerous models have been developed for prediction of gas hydrate saturation based on the microstructural relationship between gas hydrates and sediment grains however quantification of hydrate saturation and morphology from elastic properties has been hindered by failing to account for complex hydrate distributions here we develop a generalized effective medium model by applying the modified hashin shtrikman bounds to a newly developed cementation theory this model is validated by experimental data for synthetic methane and tetrahydrofuran hydrates good comparison of model predictions with experimental measurements not only reveals its ability to merge the results of contact cementation theory and effective medium theory but also indicates its feasibility for characterizing complex morphologies moreover the results of inverting acoustic measurements quantitatively confirm that for synthetic samples in excess gas condition gas hydrates mainly occur as a hybrid cementing morphology with a low percentage of pore filling morphology whereas for pressure core hydrate bearing sediments in natural environments they exist as matrix supporting and pore filling morphologies with a very low percentage of hybrid cementing morphology the hydrate saturations estimated from sonic and density logs in several regions including northern cascadia margin integrated ocean drilling program expedition 311 hole u1326d and hole u1327e alaska north slope mount elbert test well and mackenzie delta mallik 5l 38 are comparable to the referenced hydrate saturations derived from core data and resistivity and or nuclear magnetic resonance log data confirming validity and applicability of our model furthermore our results indicate that 8 hybrid cementing 33 matrix supporting and 59 pore filling hydrates may coexist in the fine grained and clay rich marine sediments on the northern cascadia margin whereas 10 hybrid cementing 54 matrix supporting and 36 pore filling hydrates may coexist in the coarse grained and sand dominated terrestrial sediments of the alaska north slope and mackenzie delta

selected problems of sediment transport and morphodynamics of a multi bar nearshore zone the paper reviews recent progress in the investigations of nearshore litho and morphodynamics at the institute of hydroengineering of the polish acad of sci ibw pan it features both advanced physical modelling and data driven analyses of nearshore processes aimed at better understanding of mechanisms driving the evolution of a wave dominated coastal zone with multiple longshore sandbars it reveals the synergy both methodologies jointly possess to achieve such a goal

a mechanism for the formation of methane hydrate and seafloor bottom simulating reflectors by vertical fluid expulsion bottom simulating reflectors bsr are observed commonly at a depth of several hundred meters below the seafloor in continental margin sedimentary sections that have undergone recent tectonic consolidation or rapid accumulation they are believed to correspond to the deepest level at which methane hydrate clathrate is stable we present a model in which bsr hydrate layers are formed through the removal of methane from upward moving pore fluids as they pass into the hydrate stability field in this model most of the methane is generated below the level of hydrate stability but not at depths sufficient for significant thermogenic production the methane is primarily biogenic in origin the model requires either a mechanism to remove dissolved methane from the pore fluids or disseminated free gas carried upward with the pore fluid the model accounts for the evidence that the hydrate is concentrated in a layer at the base of the stability field for the source of the large amount of methane contained in the hydrate and for bsrs being common only in special environments strong upward fluid expulsion into the hydrate stability field does not occur in normal sediment depositional regimes so bsrs are uncommon upward fluid expulsion does occur as a result of tectonic thickening and loading in subduction zone accretionary wedges and in areas where rapid deposition results in initial undercconsolidation in these areas hydrate bsrs are common the most poorly quantified aspect of the model is the efficiency with which methane is removed and hydrate is formed as pore fluids pass into the hydrate stability field the critical boundary in the phase diagram between the fluid plus hydrate and fluid only fields is not well constrained however the amount of methane required to form the hydrate and limited data on methane concentrations in pore fluids from deep sea boreholes suggest very efficient removal of methane from rising fluid that may contain less than the amount required for free gas production in most fluid expulsion regimes the quantity of fluid moved upward to the seafloor is great enough to continually remove the excess chloride and the residue of isotope fractionation resulting from hydrate formation thus as observed in borehole data there are no large chloride or isotope anomalies remaining in the local pore fluids the differences in the concentration of methane and probably of co2 in the pore fluid above and below the base of the stability field may have a significant influence on early sediment diagenetic reactions

initial spreading of a mega feeder nourishment observations of the sand engine pilot project sand nourishments are a widely applied technique to increase beach width for recreation or coastal safety as the size of these nourishments increases new questions arise on the adaptation of the coastal system after such large unnatural shapes have been implemented this paper presents the initial morphological evolution after implementation of a mega nourishment project at the dutch coast intended to feed the surrounding beaches in total 21 5 million m3 dredged material was used for two shoreface nourishments and a large sandy peninsula the sand engine peninsula a highly concentrated nourishment of 17 million m3 of sand in the shape of a sandy hook and protruding 1 km from shore was measured intensively on a monthly scale in the first 18 months after completion we examine the rapid bathymetric evolution with concurrent offshore wave forcing to investigate the feeding behaviour of the nourishment to the adjacent coast our observations show a large shoreline retreat of o 150 m along the outer perimeter of the peninsula with locally up to 300 m retreat the majority 72 of the volumetric losses in sediment on the peninsula 1 8 million m3 were compensated by accretion on adjacent coastal sections and dunes confirming the feeding property of the mega nourishment further analyses show that the morphological changes were most pronounced in the first 6 months while the planform curvature reduced and the surf zone slope flattened to pre nourishment values in the following 12 months the changes were more moderate overall the feeding property was strongly correlated to incident wave forcing such that months with high incoming waves resulted in more alongshore spreading months with small wave heights resulted in minimal change in sediment distribution alongshore and mostly cross shore movement of sediment

energy resource potential of natural gas hydrates the discovery of large gas hydrate accumulations in terrestrial per mafrost regions of the arctic and beneath the sea along the outer continental margins of the world s oceans has heightened interest in gas hydrates as a possible energy resource however significant to potentially insurmountable technical issues must be resolved be fore gas hydrates can be considered a viable option for affordable supplies of natural gas the combined information from arctic gas hydrate studies shows that in permafrost regions gas hydrates may exist at subsurface depths ranging from about 130 to 2000 m the presence of gas hydrates in offshore continental margins has been inferred mainly from anomalous seismic reflectors known as bottom simulating reflectors that have been mapped at depths below the sea floor ranging from about 100 to 1100 m current estimates of the amount of gas in the world s marine and permafrost gas hydrate accumulations are in rough accord at about 20 000 trillion m3 disagreements over fundamental issues such as the volume of gas stored within delineated gas hydrate accumulations and the concentration of gas hydrates within hydrate bearing strata have demonstrated that we know little about gas hydrates recently however several countries including japan india and the united states have launched ambitious national projects to further examine the resource potential of gas hydrates these projects may help answer key questions dealing with the properties of gas hydrate reservoirs the design of production systems and most important the costs and economics of gas hydrate production

basin scale evolution of formation waters a diagenetic and formation water study of the triassic chaunoy formation paris basin abstract formation waters and their movements within basins are commonly attributed with responsibility for patterns of cementation and porosity loss within reservoirs and aquifers it is thus important to understand when and how waters move in the subsurface we have studied the evolution and movement of formation water in the triassic chaunoy formation of the paris basin nw europe to define the way in which the water has evolved and to interpret water movement patterns using mineral isotope and fluid inclusion data in conjunction with detailed formation water analyses the chaunoy formation is cemented with different types of dolomite calcite and quartz cement we have studied the evolution of waters in terms of oxygen carbon and strontium isotopes and salinity connate waters were meteoric in origin but strongly influenced by the proximity of a playa lake input of palaeo meteoric water which entered the chaunoy via eastern halite bodies resulted in highly saline formation water for the majority of the chaunoy formation from about 100 ma until and for some time after maximum burial saline waters spread into the aquifer initially taking a west north west trajectory and then switching to a west south west pattern in the eocene following the alpine orogeny and localised uplift of the basin margin the southern portion of chaunoy received fresh low salinity meteoric water it is likely that formation water was lost from the chaunoy in a more central part of the basin via sub vertical cross formational flow to the mid jurassic dogger formation to accommodate the influx of fresh water

the effect of oil emplacement on quartz cementation in a deeply buried sandstone reservoir quartz is an important porosity occluding cement in sandstone reservoirs that have been subjected to elevated temperature 80 c to 100 c for a substantial period of time the effect of oil emplacement on quartz cementation in reservoir sandstones is controversial some studies have concluded that early oil emplacement can inhibit quartz cementation leading to the preservation of porosity whereas other studies have concluded that quartz cementation appears largely unaffected by oil emplacement here we have studied shallow marine upper jurassic sandstones from ula field norwegian north sea with reservoir temperatures of approximately 150 c to determine whether oil emplacement had a significant impact on diagenesis with particular attention to quartz cementation following sedimentological description of cores samples above and below the oil water contact have been collected adjacent to core analysis plug points these samples then underwent a series of studies including petrographic point counting with a transmitted light microscope scanning electron microscopy sem backscattered electron microscopy sem cathodoluminescence microscopy and fluid inclusion studies these data were integrated with routine core analysis and petrophysical log data density and resistivity log data have been used to determine the precise oil saturation of each sample studied the distributions of all potential controls on porosity and permeability such as grain size sorting matrix clay content and degree of bioturbation the presence of grain coatings and dolomite cement and the amount of quartz cement have been assessed the presence of primary oil inclusions within quartz cement shows that oil ingress into the ula reservoir commenced prior to the onset of quartz cementation very fine grained matrix rich bioturbated microquartz cemented sandstones have uniformly low quartz cement contents irrespective of oil saturation medium grained graded matrix poor microquartz poor sandstones have quartz cement ranging from 1 to greater than 17 associated with core porosities of approximately 22 and 7 respectively higher oil saturations equate to higher porosities and permeabilities in the medium grained graded matrix poor microquartz poor sandstones which cannot be explained by any control other than the amount of quartz cement as a function of pore fluid type oil emplacement therefore appears to have inhibited quartz cementation at high oil saturations and can be viewed as an important control on reservoir quality the significance of this study is that the presence of oil in a sandstone reservoir at the time that quartz cement was growing can have a considerable impact on reservoir quality models that seek to predict quartz cement and reservoir quality in sandstones need to account for the timing of oil emplacement compared with other diagenetic processes

diagenesis and its impact on the reservoir quality of miocene sandstones surma group from the bengal basin bangladesh abstract rapid supply and deposition of 1000 s of meters of miocene and pliocene sediment tend to lead to a different set of controls on reservoir quality than older more slowly buried sandstones here we have studied miocene fluvial deltaic bhuban formation sandstones from the surma group bengal basin buried to 3 000 m and 110 c using a combination of petrographic geochemical and petrophysical methods in order to understand the controls on miocene sandstone reservoir quality to facilitate improved prediction of porosity and permeability the main conclusions of the study are that mechanical compaction processes are the dominant control on porosity loss although early calcite growth has led to locally negligible porosity in some sandstones mechanical compaction occurred by grain rearrangement ductile grain compaction and brittle grain fracturing calcite cement occupying up to 41 intergranular volume was derived from a combination of dissolved and recrystallized bioclasts an influx of organic derived carbon dioxide and plagioclase alteration clay minerals present include smectite illite kaolinite and chlorite the smectitic clay was probably restricted to low energy depositional environments and it locally diminishes permeability disproportionate to the degree of porosity loss kaolinite is probably the result of feldspar alteration resulting from the influx of organic derived carbon dioxide quartz cement is present in small amounts despite the relatively high temperature due to a combination of limited time available in these young sandstones grain coating chlorite and low water saturations in these gas bearing reservoir sandstones reservoir quality can now be predicted by considering primary sediment supply and primary depositional environment the magnitude of the detrital bioclast fraction and the influx of organic derived carbon dioxide

thermal conductivity of methane hydrate bearing ulleung basin marine sediments laboratory testing and numerical evaluation the thermal conductivity of gas hydrate bearing sediments is a key parameter used to evaluate the heat transfer process relevant to phase transformation during gas hydrate production and to assess heat flux properties within the hydrate stability zone relatively few thermal conductivity values for in situ hydrate bearing sediments and laboratory hydrate bearing sediments have been reported for under saturated conditions with vertical effective stress in this study we used sandy sediments obtained during the ulleung basin gas hydrate expedition 2 ubgh2 expedition in korea to synthesize methane hydrate bearing sediments with saline pore fluid the transient plane source method was implemented to measure the thermal conductivity of specimens with variable gas hydrate saturations the measured thermal conductivity was 1 47 w m k and was independent of hydrate saturation results from additional tests of ice and water unsaturated sediments were also compared to our findings both geometric mean and 3d thermal network models corroborated the experimentally measured thermal conductivities assuming expected physical properties

physical property changes in hydrate bearing sediment due to depressurization and subsequent repressurization physical property changes in hydrate bearing sediment due to depressurization and subsequent repressurization w f waite 1 t j kneafsey 2 w j winters 1 d h mason 1 u s geological survey 384 woods hole road woods hole ma 02543 usa lawrence berkeley national laboratory 1 cyclotron rd ms 90r1116 berkeley ca 94720 usa