prediction of lithofacies and reservoir quality using well logs late cretaceous williams fork formation mamm creek field piceance basin colorado understanding the controls and distribution of reservoir quality is important for the economic success of tight gas reservoirs in which diagenesis interacts with primary depositional variations in environment and texture to exert a strong control on pore networks rock mechanical properties and natural fractures in the upper cretaceous williams fork formation of the piceance basin framework grain composition is a major control on compaction and the occurrence of authigenic phases alteration of volcanic grains in the upper williams fork led to grain coating clay precipitation ferroan dolomite cement is found only in the deeper marine influenced intervals in which dolostone fragments are present this study shows that careful petrographic assessment of lithofacies heterogeneity can be upscaled by correlation with log properties to yield tools for field scale reservoir quality prediction twelve lithofacies are identified based on sand grain populations cement types and clay matrix content sandstones of the highest reservoir quality are those with grain coating clays that inhibit quartz cementation these sandstones can be identified based on high density porosity log values sandstones with the poorest reservoir qualities are tightly cemented with carbonate and quartz cement or are rich in clay matrix carbonate cemented intervals are identified by low density porosity clay matrix rich samples have high gamma ray and low density porosity values the presence of abundant potassium feldspar in the upper intervals results in high gamma ray readings even in the clean clay matrix free sandstone

the coupling mechanism of basin and orogen in the western ordos basin and adjacent regions of china abstract during the late triassic and jurassic three structural belts developed in the western ordos basin and adjacent regions of china the alxa compressive wedge the helanshan structural belt and the liupanshan fold and thrust belt three types of basin also developed a late triassic composite basin with a northwestern ordos rift sub basin and a southwestern ordos foreland sub basin an early middle jurassic intracratonic basin and a late jurassic foreland type molasse wedge it is suggested that these basins resulted from late triassic unconstrained lateral extrusion and jurassic constrained lateral extrusion the alxa region is interpreted as an extrusional wedge bounded by strike slip deformation which escaped laterally from the indentation of the liupanshan thrust belt from the south during the late triassic the sino korean block to the east of helanshan was controlled by a stress state with nearly e w trending extension at this stage extrusion was unconstrained the helanshan developed as a rift sub basin due to transtensional tectonics at the lateral margin of the wedge at this time a foreland sub basin was formed in front of the liupanshan thrust belt during the jurassic the sino korean block to the east of the helanshan was gradually compressed westwards and the extrusion structure became constrained the early middle jurassic shows a transitional stage from unconstrained to constrained extrusion and the ordos basin developed as an intracratonic basin from the latest middle jurassic to the late jurassic intense lateral escape and opposite compression led to the formation of the helanshan fold and thrust belt and its frontal foreland molasse wedge at the same time another foreland molasse wedge was developed in front of the liupanshan thrust belt the switch from rifting to thrusting in the helanshan is a result of the changing stress field at the circum pacific plate boundary the clockwise rotation of the sino korean block to the east of the helanshan and the anticlockwise rotation of the alxa block

quantitative characterization of connectivity and conductivity of sandstone carriers during secondary petroleum migration applied to the third member of eocene shahejie formation dongying depression eastern china abstract studies on migration pathways remain qualitative albeit extensive quantification of migration forcing in this study hydrocarbon carriers are defined as carrier units and their corresponding carrier beds for the third member of eocene shahejie formation in the dongying depression bohai bay basin eastern china on the basis of their lithofacies and physical properties spatial relationships and data availability secondary migration conduits are then quantified a carrier unit is defined as a stratigraphic unit that contains microscopically porous and permeable carrier beds and is covered by regional seals the carrier beds are macroscopically and physically connected to each other within a carrier unit and are hydrodynamically connected during secondary migration a method of quantifying sandstone carrier units using common physical properties is developed first a carrier unit containing potential carrier beds is identified on the basis of lithofacies and their lateral changes second physical connectivity of sandstone carrier beds is assessed on the basis of percolation theory third the hydrodynamic connectivity of a sandstone carrier unit is analyzed using effective parameters that may reflect the hydraulic circulation in the carrier unit last the conductivity of a sandstone carrier bed is quantitatively characterized using appropriate physical property parameters the results for sandstone carrier units in the third member of the shahejie formation are used in numerical models addressing pleistocene secondary migration the model results explain the discovered accumulation and hydrocarbon shows well and the model predictions on exploration targets have been confirmed by drilling

sandstone diagenesis and reservoir quality prediction models myths and reality models and concepts of sandstone diagenesis developed over the past two decades are currently employed with variable success to predict reservoir quality in hydrocarbon exploration not all of these are equally supported by quantitative data observations and rigorous hypothesis testing simple plots of sandstone porosity versus extrinsic parameters such as current subsurface depth or temperature are commonly extrapolated but rarely yield accurate predictions for lithified sandstones calibrated numerical models that simulate compaction and quartz cementation when linked to basin models have proven successful in predicting sandstone porosity and permeability where sufficient analog information regarding sandstone texture composition and quartz surface area is available analysis of global regional and local data sets indicates the following regarding contemporary diagenetic models used to predict reservoir quality 1 the effectiveness of grain coatings on quartz grains e g chlorite microquartz as an inhibitor of quartz cementation is supported by abundant empirical data and recent experimental results 2 vertical effective stress although a fundamental factor in compaction cannot be used alone as an accurate predictor of porosity for lithified sandstones 3 secondary porosity related to dissolution of framework grains and or cements is most commonly volumetrically minor 2 exceptions are rare and not easily predicted with current models 4 the hypothesis and widely held belief that hydrocarbon pore fluids suppress porosity loss due to quartz cementation is not supported by detailed data and does not represent a viable predictive model 5 heat flow perturbations associated with allochthonous salt bodies can result in suppressed thermal exposure thereby slowing the rate of quartz cementation in some subsalt sands

ephemeral fluvial deposits integrated outcrop and simulation studies reveal complexity ephemeral fluvial sandstones form the main reservoirs in many oil and gas fields production histories and development difficulties suggest these deposits are more complex than is commonly supposed in the petroleum industry there is inadequate published information to account for this observation relevant sedimentological literature on such deposits is qualitative and unsuitable for detailed reservoir characterization studies therefore integrated sedimentological petrophysical and fluid flow simulation studies have been conducted on outcrop analogs in the southwestern united states our key objectives were to define flow units and to find areas of sensitivity inherent both in the sediments and in the analytical and statistical procedures used to describe and model s ch systems we report results of integrated studies on the lower jurassic kayenta formation in southeastern utah the kayenta formation is a relatively proximal sand rich succession dominated by channel fill sandstones sedimentological analysis identified eight main genetic units in contrast reservoir simulations based on probe permeameter data collected at outcrop show that six of the main genetic units have uniform flow behavior intraformational mudclast conglomerates are the dominant permeability barriers both because of the clasts themselves and because they act as sites of preferential cementation stochastic permeability models conditioned to the outcrop data produce results little different from models based on averaged values for each facies the most sensitive feature of the mode s concerns the assumptions made about the mudclast conglomerates the model results show that only by integrating analytical approaches can we understand the full character of an outcrop analog in such a way that we can use it predictively

petrofacies and provenance of a late cretaceous suture zone thrust top basin cantwell basin central alaska range abstract the lower cantwell formation in the cantwell basin provides an excellent opportunity to study the petrofacies and provenance of siliciclastic deposits from an ancient thrust top basin the late cretaceous cantwell basin formed on a series of thrust sheets along a suture zone between the allochthonous wrangellia composite terrane and the north american continental margin i e the yukon tanana terrane analysis of the lower cantwell formation provides an understanding of sediment transport in the interior of an ancient suture zone sandstone and conglomerate compositional data indicate two main source areas for the lower cantwell formation 1 uplifted thrust sheets located south of the basin associated with development of the suture zone and 2 a regional anticlinorium locat d north of the basin along the north american continental margin in the northwestern cantwell basin petrofacies southward paleocurrent directions and alluvial lithofacies record reactivation of a regional anticlinorium located in the metamorphic yukon tanana terrane lithic types in this part of the basin are dominated by quartz mica tectonite mica schist metamorphic chert and other quartz rich metamorphic and sedimentary varieties q48f2l50 lv0lm54ls46 in the northeastern and southern parts of the basin sediment was derived from volcanic and sedimentary strata exposed in the hanging walls of thrust faults that define the southern margin of the basin source diagnostic conglomerate clasts spatial variations in sandstone detrital modes northward paleocurrent indicators and progressively rotated strata record syndepositional uplift of local thrust sheets along the suture zone the dominant sandstone grain types in these parts of the basin are plagioclase grains and lithic fragments of argillite radiolarian bearing mudstone and metabasalt q44f28l28 lv2lm23ls75 sandstone compositions documented for the cantwell basin may be typical of thrust top basins that form along suture zones the two main petrofacies of the lower cantwell formation consist of a petrofacies rich in sedimentary and volcanic detritus associated with uplifted oceanic rocks along areas of the basin proximal to the suture zone and a petrofacies characterized by quartz rich metamorphic and sedimentary detritus along areas of the basin proximal to the deformed continental margin compositional data from this study combined with previous petrologic studies of similar basins show that sandstones from suture zone thrust top basins are more feldspathic than sandstones from typical foreland basins these compositional differences reflect a complex assemblage of accreted terran s which include relict volcanic arcs batholiths oceanic sedimentary deposits and ophiolitic melanges that are accreted to continental margins along suture zones in collisional accretionary orogenic belts

diagenetic heterogeneity and reservoir quality fluvial deltaic and turbiditic sandstone reservoirs potiguar and reconcavo rift basins brazil fluvial and lacustrine deltaic and turbiditic sandstones are major hydrocarbon reservoirs in the onshore lower cretaceous potiguar and reconcavo rift basins in northeastern brazil diagenetic elements including mechanically infiltrated mi clay calcite dolomite and chlorite show distinct distribution patterns at interwell and field wide reservoir scales such distributions and thereby diagenetic heterogeneity have been modeled based on thin section core well log and petrophysical data at the interwell scale relationships between sandstone body geometry and the distribution of diagenetic elements are a critical aspect of reservoir heterogeneity at this level 1 mi clay concentrations occur in fluvial reservoirs following the orientation of paleochannels generating strong compartmentalization of the reservoirs 2 calcite cement appears either concentrated near sand shale contacts peripheral distribution or dispersed in the interior of the sandstone layers scattered distribution 3 dolomite cement may appear concentrated along laminations in cross stratified sandstones causing a decrease of one order of magnitude in the effective horizontal permeability and 4 authigenic chlorite is observed to reduce more significantly the permeability in fine grained sandstones than in coarse grained sandstones an effect that may cause important modifications in the permeability structure of the reservoirs at the field wide scale diagenetic heterogeneity includes 1 stratigraphic zonation of diagenetic properties in fluvial reservoirs 2 increasing carbonate cementation toward the border of the hydrocarbon accumulations in deltaic reservoirs and 3 distinct patterns of carbonate cementation observed in channel fills and lobes in turbiditic reservoirs incorporating the distribution and effects of diagenetic elements into the interwell and field wide geological modeling is essential to achieve a realistic reservoir representation such incorporation is performed by the integration of diagenetic properties with other geological attributes including nature and distribution of depositional facies structural elements and stratigraphic framework this procedure improves reservoir quality evaluation and leads to more precise prediction of reservoir performance

sandstone reservoir quality prediction the state of the art joanna ajdukiewicz joined exxon production research company in 1980 she was reservoir quality assessment and prediction team lead there from 1991 to 1995 and at imperial oil research centre in calgary from 1995 to 1997 subsequently she has worked a variety of exploration company assignments in the north sea gulf of mexico and middle east her current interests are in predicting the distribution of early diagenetic controls on deep reservoir quality rob lander develops diagenetic models for geocosm llc he obtained his ph d in geology from the university of illinois in 1991 was a research geologist at exxon production research from 1991 to 1993 and worked for rogaland research and geologica as from 1993 to 2000 he is also a research fellow at the bureau of economic geology to guess is cheap to guess wrongly is expensive chinese proverb reservoir quality predictive models will be a useful element of risk analysis until remote sensing tools are invented that accurately measure effective porosity and permeability ahead of the bit this issue of the aapg bulletin highlights recent advances in a new generation of reservoir quality models that have successfully predicted porosity and permeability in diverse siliclastic reservoirs under many different burial conditions most previous attempts at predrill reservoir quality prediction have relied on empirical correlations or on first principle geochemical simulations that incorporate laboratory derived input parameters wood and byrnes 1994 the new reservoir quality models differ from previous approaches in that although incorporating theory inspired algorithms they include terms with values that are explicitly designed to be calibrated by and tested against data sets of high quality petrographic analyses that are linked to thermal and effective stress histories petrographic observations therefore provide essential constraints in these models on the types timing and rates of key geologic processes affecting sandstone pore systems this approach avoids the pitfalls inherent

continuous hydrocarbon accumulation over a large area as a distinguishing characteristic of unconventional petroleum the ordos basin north central china abstract global petroleum exploration is currently undergoing a strategic shift from conventional to unconventional hydrocarbon resources unconventional hydrocarbons in tight reservoirs show characteristics distinct from those of conventional hydrocarbon sources hosted in structural and stratigraphic traps the characteristic features include the following a hydrocarbon source and reservoir coexist porosity and permeability are ultra low nano pore throats are widely distributed hydrocarbon bearing reservoir bodies are continuously distributed there is no obvious trap boundary buoyancy and hydrodynamics have only a minor effect and darcy s law does not apply phase separation is poor there is no uniform oil gas water interface or pressure system and oil or gas saturation varies examples of unconventional hydrocarbon accumulations are the mesozoic tight sandstone oil province and the upper paleozoic tight sandstone gas province in the ordos basin north central china generally continuous hydrocarbon accumulation over a large area is a distinguishing characteristic of unconventional hydrocarbon sources because of the great potential of unconventional petroleum resources it is believed that research on such resources will be at the forefront of the future development of petroleum geology

carbonate cementation patterns and diagenetic reservoir facies in the campos basin cretaceous turbidites offshore eastern brazil massive turbidite arkoses contain more than 80 of the oil reserves of the campos basin the main petroleum province of brazil the porosity and permeability distribution in the namorado albian cenomanian and carapebus turonian santonian sandstones is

mesozoic contractional deformation in the middle of the asian tectonic collage the intraplate western ordos fold thrust belt china abstract intraplate deformation can occur at great distances from synchronous plate boundaries and is most likely the result of strain concentrations into weak zones these weak zones may be pre existing crustal heterogeneities such as faults thermally weakened zones due to magmatism and or the effects of a thick sedimentary cover or mechanical contrasts between adjacent crustal blocks intraplate deformation is not exclusively related to continent continent collision it can be the result of a change in subduction dynamics or the interaction of two convergent plate boundaries asia has many examples of active intraplate deformation that are thought to be related to the cenozoic indo asian collision although much attention is placed on active examples discerning controls on pre cenozoic asian intraplate deformation will lead to not only a better understanding of the processes involved in intraplate orogens but also the tectonic evolution of asia situated on either side of the yellow river along the western margin of the ordos plateau the intraplate western ordos fold thrust belt involves units as old as archean basement and as young as late jurassic the fold thrust belt is spectacularly exposed in two ranges the helan shan and the zhuozi shan cross sections drawn through the north trending fold thrust belt suggest 30 minimum shortening a paleocurrent reversal within the lower middle jurassic section is interpreted to mark the onset of contraction and mountain building a late jurassic synorogenic boulder conglomerate records the final deformation in the fold thrust belt synchronous with contraction and cutting across the fold thrust belt is an e w striking strike slip fault that displays right lateral drag and sub horizontal striae we interpret this fault as an accommodation structure in the thrust belt following e w contraction the thrust belt was dismembered by an n15 w trending left lateral strike slip fault the left lateral fault displaces the frontal portion of the thrust belt the zhuozi shan 62 km to the north relative to a more internal portion the helan shan we propose that the anomalous orientation and intraplate location of the western ordos fold thrust belt is a function of mechanical contrasts between a previously deformed area and a stable crustal block ordos to the east pre existing crustal weakness or anisotropy along the western margin of the ordos block is most likely related to either a late proterozoic early paleozoic aulacogen a triassic fault system or to both although its intraplate location and the complexities of mesozoic asian plate interactions make it difficult to relate deformation in the western ordos fold thrust belt to a specific contemporaneous plate boundary its n s trend may suggest a link with paleo pacific subduction along the eastern margin of asia

cooling dynamics of spatter fed phonolite obsidian flows on tenerife canary islands abstract relaxation geospeedometry has been applied to two series of clastogenic obsidian flows on tenerife to determine their thermal history across the glass transition the phonolite flows investigated were both generated by lava fountaining activity followed by rheomorphism of the deposits the detailed sampling resolution within the two series enabled an accurate quantification of their thermal history cooling rates within the investigated spatter fed flows vary over more than two orders of magnitude the highest cooling rates of 0 39 k min were modeled for the central vesiculated part of one flow the dense basal obsidian layers of both flows were cooled at substantially lower rates of 0 0042 and 0 0028 k min respectively there appears to be an influence of in situ vesiculation processes on the thermal budget of the investigated flows in addition the slow cooling rates for the basal portions of both flows seem to be associated with a stage of thermal buffering continual advective heat transport of hot material along a basal shear plane may sustain elevated temperatures associated with quasi isothermal annealing within this decollement numerical simulations based on conductive heat loss concepts fail to resolve the cooling history quantified through relaxation geospeedometry for the investigated flows the effects of vesiculation and thermal annealing on the cooling behavior of the clastogenic flows across the glass transition are discussed in the light of these new data in addition viscometric data on these phonolites are used to correlate the known cooling rates to viscosities at the glass transition

diagenesis of a tight gas sand reservoir upper cretaceous mesaverde group piceance basin colorado abstract the upper cretaceous mesaverde group in the piceance basin western colorado contains thick sections of low porosity low permeability sandstones that are reservoirs for large accumulations of hydrocarbon gas the mesaverde sandstones are lithic arkoses and feldspathic litharenites containing quartz plagioclase variable k feldspar chert and volcanic rock fragments important diagenetic processes that have affected the sandstones include compaction dissolution of feldspar and or alteration to clay precipitation of carbonate and quartz cements precipitation of illite and alteration of detrital clays mixed layer illite smectite porosity is relatively constant a decrease in primary porosity downward is approximately balanced by an increase in secondary porosity with significant microporosity in authigenic and diagenetic clays k feldspar is almost completely absent below 5500 feet 1675 m fibrous illite is relatively abundant above this depth and variable in abundance below the k ar ages of the clays increase with depth from 40 m y at the top of the sampled section to 55 m y at the base indicating illitization of a precursor smectite at approximately the 100 c isotherm samples with abundant fibrous illite have relatively smaller age values mass balance calculations indicate that dissolution of k feldspar illitization of smectite and precipitation of fibrous illite were coupled these reactions suggest the transport of dissolved potassium upward hundreds of feet 100 300 m in the section possibly associated with water driven vertically by the migration of gas

petrofacies prediction and 3 d geological model in tight gas sandstone reservoirs by integration of well logs and geostatistical modeling abstract these effective reservoir rocks that can have sufficient porosity and permeability and hydrocarbon accumulations determine economic reserves and high yield of tight oil and gas understanding the origin and distribution of these effective reservoir rocks is important for sorting out sweet spots in tight reservoirs multiple scale analyses from the microscopic via drill core to single wellbore have been conducted to examine reservoir heterogeneity of the upper paleozoic shanxi formation in the southeastern ordos basin five sandstone petrofacies have been defined in terms of texture and framework composition detrital matrix diagenesis and pore types quartz arenite tuffaceous quartz arenite ductile lithic lean sub litharenite ductile lithic rich sandstone and tightly carbonate cemented sandstone the various petrofacies show fundamentally different pathways of diagenetic and reservoir quality evolutions due to the complexity of texture and detrital composition in the shanxi formation directly related to the provenance and depositional environment quartz arenites and ductile grain lean sub litharenites both form effective reservoir rocks by translating petrofacies to well log signatures corrected from petrographic and core analysis data a model based on factor analysis has been built to predict petrofacies at the well scale for investigating the distribution of each petrofacies at the field scale sequential indicator simulation method has been used to construct a 3 d petrofacies model with facies conditioning the isopach maps of quartz arenites and ductile lithic lean sub litharenites have been made from the 3 d petrofacies model to quantify their areal distributions and to define the sweet spots by combining isopach maps of these effective reservoir rocks and gas production data from well tests the concept of reservoir petrofacies is an important tool for the characterization of tight sandstone reservoirs

pore throat sizes in sandstones tight sandstones and shales pore throat sizes in siliciclastic rocks form a continuum from the submillimeter to the nanometer scale that continuum is documented in this article using previously published data on the pore and pore throat sizes of conventional reservoir rocks tight gas sandstones and shales for measures of central tendency mean mode median pore throatsizes diameters are generally greater than2 mm in conventionalreservoir rocks range from about 2 to 0 03 mm in tight gas sandstones and rangefrom0 1to0 005 mminshales hydrocarbonmolecules asphaltenes ring structures paraffins and methane form another continuum ranging from 100 a 0 01 mm for asphaltenes to 3 8 a 0 00038 mm for methane the pore throat size continuum provides a useful perspective for considering 1 the emplacement of petroleum in consolidated siliciclastics and 2 fluid flow through fine grained source rocks now being exploited as reservoirs

facies architecture and heterogeneity of the fluvial aeolian reservoirs of the sergi formation upper jurassic reconcavo basin ne brazil abstract the sergi formation upper jurassic represents the main hydrocarbon reservoir of the reconcavo basin brazil the basal vertical facies succession of the sergi formation comprises reservoirs formed by a complex fluvio aeolian lacustrine interaction facies architecture and detailed petrophysical analysis of these reservoirs have enhanced the understanding of heterogeneity at a variety of scales and has allowed the development of predictive models that describes the range of styles of mixed fluvial aeolian reservoirs at megascopic scale the reservoirs are predominantly composed of sand bodies deposited by fluvial channel and aeolian facies associations regional flooding surfaces and sequence boundaries are their main flow barriers the regional flooding surfaces are composed of fine grained sediments deposited by lacustrine facies associations and the sequence boundaries act as flow barriers due to mechanically infiltrated clays based on its geometrical relations reservoirs linked to fluvial aeolian lacustrine interaction formed two types of reservoirs at macroscopic scale i with good lateral continuity of aeolian packages and relatively simple stratigraphic correlation and ii of highly compartmentalized aeolian packages with complex stratigraphic correlation and truncation by fluvial deposits mesoscopic heterogeneity reflects lithofacies sedimentary structures and lamina scale variability within aeolian and fluvial facies associations

provenance environmental and paleogeographic controls on sandstone composition in an incised valley system the eocene la meseta formation seymour island antarctica abstract the eocene la meseta formation is the youngest exposed unit of the back arc james ross basin antarctic peninsula cropping out in seymour marambio island the formation comprises 720 m of clastic sedimentary rocks of deltaic estuarine and shallow marine origin it was subdivided into six unconformity based units valle de las focas acantilados campamento cucullaea i cucullaea ii and submeseta allomembers grouped into three main facies associations facies association i represents valley confined deposition in a progradational aggradational tide dominated and wave influenced delta front delta plain environment facies association ii includes tidal channels mixed tidal flats tidal inlets and deltas washover and beach environments facies association iii represents nonconfined tide and storm influenced nearshore environments la meseta formation sandstones are quartzofeldspathic with some hybrid arenites glauconite and carbonate bioclasts rich sandstone detrital modes are subdivided into two distinctive petrofacies the low quartz petrofacies petrofacies i q 12 interpreted to retain the original provenance signal and the high quartz petrofacies petrofacies ii q 55 and l 1 4 is clearly dominated by volcanic derived clasts it developed at times of high sea level and or during later stages of the valley fill when an energy fence at the shoreline prevented delivery of sediment from the antarctic peninsula thus enhancing the relative participation of local volcanic sources

basin centered gas systems basin centered gas systems bcgss are potentially one of the more economically important unconventional gas systems in the world in the united states they contribute as much as 15 of the total annual gas production these regionally pervasive gas accumula tions are different from conventionally trapped accumulations in several respects the basin centered gas accumulations bcgas associated with bcgss are typically characterized by regionally pervasive accumulations that are gas saturated abnormally pres sured commonly lack a downdip water contact and have low permeability reservoirs the accumulations range from single isolated reservoirs a few feet thick to multiple stacked reservoirs several thousand feet thick two types of bcgss are recognized a direct type characterized by having gas prone source rocks and an indirect type characterized by having liquid prone source rocks during the burial and thermal histories of these systems the source rock differences between the two types of bcgss result in strikingly different characteristics that impact exploration strategies the majority of known bcgas are the direct type exploration activity for bcgas is in the early stages and thus far has been focused in north america in other parts of the world concepts of basin centered gas systems are poorly known and exploration activity focused on basin centered gas accumulations is minimal

diagenetic heterogeneity in sandstone at the outcrop scale breathitt formation pennsylvanian eastern kentucky twenty seven samples of feldspathic phyllarenite were obtained from three 1 m grids in a large homogeneous distributary bar sand stone body with the goal of elucidating bed scale diagenetic het erogeneity significant variability in the content of both detrital and diagenetic components is present in the sample set this variation is within the range of values predicted from comparison with a large regional data set from the same formation but nonetheless it is large enough to preclude successful prediction of diagenetic prop erties from consideration of average composition and thermal his tory alone grain size is one important local control on the overall abundances of cement and porosity grain size operates to control the overall degree of cementation in these particular rocks indi rectly through its influence on lithic grain content and hence on compaction relatively minor carbonate cement is an exception to this trend and appears to be distributed somewhat randomly with out regard to the size or composition of the detrital components diagenetic heterogeneity of the magnitude documented in this example is correlated to differences in porosity and permeability and therefore has implications for reservoir simulation and explo ration risk assessment prediction of rock properties through dia genetic modeling is more successful if the textural controls on dia genetic heterogeneity are considered

modeling vertical and horizontal diffusivities with the sigma coordinate system abstract the use of diffusive terms in numerical ocean models is examined relative to different coordinate systems the conventional model for horizontal diffusion is found to be incorrect when bottom topographical slopes are large a new formulation is suggested which is simpler than the conventional formulation when transformed to a sigma coordinate system and makes it possible to model realistically both surface ekman and bottom boundary layers

organic rich marcellus shale lithofacies modeling and distribution pattern analysis in the appalachian basin the marcellus shale is considered to be the largest unconventional shale gas resource in the united states two critical factors for unconventional shale reservoirs are the response of a unit to hydraulic fracture stimulation and gas content the fracture attributes reflect the geomechanical properties of the rocks which are partly related to rock mineralogy the natural gas content of a shale reservoir rock is strongly linked to organic matter content measured by total organic carbon toc a mudstone lithofacies is a vertically and laterally continuous zone with similar mineral composition rock geomechanical properties and toc content core log and seismic data were used to build a three dimensional 3 d mudrock lithofacies model from core to wells and finally to regional scale an artificial neural network was used for lithofacies prediction eight petrophysical parameters derived from conventional logs were determined as critical inputs advanced logs such as pulsed neutron spectroscopy with log determined mineral composition and toc data were used to improve and confirm the quantitative relationship between conventional logs and lithofacies sequential indicator simulation performed well for 3 d modeling of marcellus shale lithofacies the interplay of dilution by terrigenous detritus organic matter productivity and organic matter preservation and decomposition affected the distribution of marcellus shale lithofacies distribution which may be attributed to water depth and the distance to shoreline the trend of normalized average gas production rate from horizontal wells supported our approach to modeling marcellus shale lithofacies the proposed 3 d modeling approach may be helpful for optimizing the design of horizontal well trajectories and hydraulic fracture stimulation strategies

best practice stochastic facies modeling from a channel fill turbidite sandstone analog the quarry outcrop eocene ainsa basin northeast spain using data from an outcrop characterization of a sandstone rich turbidite channel fill the so called quarry outcrop in the ainsa basin several stochastic facies models were constructed at bed scale resolution cells 2 5 m 8 ft wide and 0 05 m 2 in thick several industry standard reservoir modeling algorithms were employed truncated gaussian simulation sequential indicator simulation multiple point geostatistics and object based methods with varying degrees of complexity the degree of similarity i e realism between realizations and the outcrop characterization was quantified through the use of several responses 1 static connectivity 2 effective permeability and 3 recovery efficiency from waterflood simulations differences in the responses measured from the outcrop and facies models were observed these are mostly algorithm related instead of caused by soft data or different stochastic realizations differences increase greatly when the permeability of the heterolithic packages and mudstone beds ht m decreases and reflect the methods ability to model the inclined and undulating ht m packages and beds that occur in the outcrop these packages and beds can drape scours and sandstone beds with depositional topography and pinch outs producing sandstone thinning and dead ends object based methods capable of introducing highly undulating ht m beds provided the most realistic models variogram based and simple object based methods failed to capture and reproduce the whole length of undulating beds multiple point geostatistics provided realizations with responses intermediate between variogram based and simple object based methods and the more successful advanced object based methods the conditioning to hard data capabilities of multiple point geostatistics are higher than those of the object based methods which give them an added advantage

resource assessment perspectives for unconventional gas systems concepts are described for assessing those unconventional gas sys tems that can also be defined as continuous accumulations contin uous gas accumulations exist more or less independently of the wa ter column and do not owe their existence directly to the buoyancy of gas in water they cannot be represented in terms of individual countable fields or pools delineated by downdip water contacts for these reasons traditional resource assessment methods based on es timating the sizes and numbers of undiscovered discrete fields can not be applied to continuous accumulations specialized assessment methods are required unconventional gas systems that are also continuous accumu lations include coalbed methane basin centered gas so called tight gas fractured shale and chalk gas and gas hydrates deep basin and bacterial gas systems may or may not be continuous accumu lations depending on their geologic setting two basic resource assessment approaches have been em ployed for continuous accumulations the first approach is based on estimates of gas in place a volumetric estimate of total gas in place is commonly coupled with an overall recovery factor to nar row the assessment scope from a treatment of gas volumes residing in sedimentary strata to a prediction of potential additions to re serves the second approach is based on the production perfor mance of continuous gas reservoirs as shown empirically by wells and reservoir simulation models in these methods production characteristics as opposed to gas in place are the foundation for forecasts of potential additions to reserves

increasing the predictive power of geostatistical reservoir models by integration of geological constraints from stratigraphic forward modeling current static reservoir models are created by quantitative integration of interpreted well and seismic data through geostatistical tools in these models equiprobable realizations of structural settings and property distributions can be generated by stochastic simulation techniques the integration of regional or basin scale knowledge in reservoir models is typically performed qualitatively or semi quantitatively for example through the definition of regional property trends or main channel belt orientations this limited use of regional information does not allow an assessment of the impact of the uncertainties associated with the regional knowledge on the overall uncertainty of the reservoir model a novel approach is proposed in this study which allows us to consistently integrate basin scale information into reservoir models a new type of data related to the distribution of the potential hydrocarbon bearing volumes at basin scale was obtained from a 2 dh process based stratigraphic forward model sfm and integrated as a soft constraint in the geostatistical reservoir modeling as a consequence reservoir models are quantitatively consistent with the large scale geological setting defined by the sfm output furthermore the uncertainty associated with each sfm parameter can be propagated to reserve estimation thus the partitioning of the overall uncertainty affecting a reservoir model into the contributions of the uncertainties at the basin and reservoir scales can be quantitatively assessed several synthetic case studies were carried out with and without conditioning to sfm output which verified the effectiveness of the method a logical next step is to apply the proposed methodology to a real world case

effects of carrier bed heterogeneity on hydrocarbon migration abstract reservoir carrier bed heterogeneity is a common geological phenomenon this study applied a hydrocarbon migration model based on the invasion percolation theory to simulate the formation of hydrocarbon migration pathways in heterogeneous carrier beds the results indicate that the pathways and hydrocarbon accumulations in reservoirs may differ from conventional models when continuous low permeability layers occur as networks within reservoirs such low permeability layers may have formed through depositional or diagenetic processes within reservoir rocks at variable scales oil bearing reservoir in donghe sandstone in hadexun oilfield in northern tarim basin china was analyzed to demonstrate the forming mechanisms of substantial tilting of oil water contact donghe sandstone is a quartz sandstone deposited in an open marine shoreface shelf environment during a major transgression in early carboniferous major diagenetic products are abundant tabular concretions along bedding planes and cross laminae the low permeability concretions serve as fluid flow barriers which compartmentalize the donghe sandstone reservoir as a result the oil water contacts and the saturation of oil in the reservoir appear irregular and tilted in hadexun oilfield and neighboring regions

effects of diagenesis on enhanced resolution bulk density logs in tertiary gulf coast sandstones an example from the lower vicksburg formation mcallen ranch field south texas diagenetic heterogeneity strongly influences porosity and permeability distribution in sandstone reservoirs of the lower vicksburg formation enhanced resolution bulk density logs which use a 3 cm 1 2 in rather than the standard 15 cm 6 in sampling increment offer important new information in understanding diagenetically complex sandstones in the subsurface detailed petrographic mapping and sedimentologic description of core from the oligocene lower vicksburg formation of mcallen ranch field south texas have identified cement variations that result in diagenetic zones ranging in thickness from 0 1 cm 0 04 in to 0 9 m 3 ft the petrographic and petrophysical properties of these diagenetic zones define three diagenetic facies that can be correlated with log esponse from the enhanced resolution bulk density log 1 the quartz cemented facies averaging 13 porosity and 0 342 md permeability and having a recorded density greater than or equal to 2 43 g cm3 but less than 2 48 g cm3 2 the chlorite cemented facies averaging 16 7 porosity and 0 193 md permeability and having a recorded density less than 2 43 g cm3 and 3 the calcite or transitional cemented facies averaging 9 4 porosity and 0 04 md permeability and having a recorded density greater than or equal to 2 48 g cm3 intervals cemented with different minerals are identified by the enhanced resolution bulk density log based on the ranges in density that define each diagenetic facies this identification of diagenetic facies not only influences the accurate determination of the net sandstone thickness and porosity of reservoirs within the lower vicksburg formation but also directly controls permeability calculations for example classification of cement intervals from lower vicksburg gas reservoirs using enhanced resolution bulk density logs and porosity and permeability regressions for each of the diagenetic facies results in estimated permeability thicknesses as much as 50 greater than those calculated using standard log analysis because standard log analysis ignores the effects of diagenetic eterogeneity the use of the enhanced resolution bulk density log provides significant information that leads to more accurate reservoir and field evaluations in diagenetically complex sandstones

the impact of diagenesis on the heterogeneity of sandstone reservoirs a review of the role of depositional facies and sequence stratigraphy diagenesis exerts a strong control on the quality and heterogeneity of most clastic reservoirs variations in the distribution of diagenetic alterations usually accentuate the variations in depositional porosity and permeability linking the types and distribution of diagenetic processes to the depositional facies and sequence stratigraphic framework of clastic successions provides a powerful tool to predict the distribution of diagenetic alterations controlling quality and heterogeneity the heterogeneity patterns of sandstone reservoirs which determine the volumes flow rates and recovery of hydrocarbons are controlled by geometry and internal structures of sand bodies grain size sorting degree of bioturbation provenance and by the types volumes and distribution of diagenetic alterations variations in the pathways of diagenetic evolution are linked to 1 depositional facies hence pore water chemistry depositional porosity and permeability types and amounts of intrabasinal grains and extent of bioturbation 2 detrital sand composition 3 rate of deposition controlling residence time of sediments at specific near surface geochemical conditions and 4 burial thermal history of the basin the amounts and types of intrabasinal grains are also controlled by changes in the relative sea level and therefore can be predicted in the context of sequence stratigraphy particularly in paralic and shallow marine environments changes in the relative sea level exert significant control on the types and extent of near surface shallow burial diagenetic alterations which in turn influence the pathways of burial diagenetic and reservoir quality evolution of clastic reservoirs carbonate cementation is more extensive in transgressive systems tract tst sandstones particularly below parasequence boundaries transgressive surface and maximum flooding surface because of the abundance of carbonate bioclasts and organic matter bioturbation and prolonged residence time of the sediments at and immediately below the sea floor caused by low sedimentation rates which also enhance the formation of glaucony eogenetic grain coating berthierine odinite and smectite formed mostly in tst and early highstand systems tract deltaic and estuarine sandstones are transformed into ferrous chlorite during mesodiagenesis helping preserve reservoir quality through the inhibition of quartz cementation the infiltration of grain coating smectitic clays is more extensive in braided than in meandering fluvial sandstones forming flow barriers in braided amalgamated reservoirs and may either help preserve porosity during burial because of quartz overgrowth inhibition or reduce it by enhancing intergranular pressure dissolution diagenetic modifications along sequence boundaries are characterized by considerable dissolution and kaolinization of feldspars micas and mud intraclasts under wet and warm climates whereas a semiarid climate may lead to the formation of calcrete dolocrete cemented layers turbidite sandstones are typically cemented by carbonate along the contacts with interbedded mudrocks or carbonate mudstones and marls as well as along layers of concentration of carbonate bioclasts and intraclasts commonly hybrid carbonate turbidite arenites are pervasively cemented proximal massive turbidites normally show only scattered spherical or ovoid carbonate concretions improved geologic models based on the connections among diagenesis depositional facies and sequence stratigraphic surfaces and intervals may not only contribute to optimized production through the design of appropriate simulation models for improved or enhanced oil recovery strategies as well as for co2 geologic sequestration but also support more effective hydrocarbon exploration through reservoir quality prediction

outcrop architecture of a fluvio lacustrine succession upper triassic yanchang formation ordos basin china abstract although several studies have considered the sedimentary facies of the upper triassic yanchang formation in terms of their hydrocarbon potential in the petroliferous ordos basin such studies have mostly interpreted subsurface data and few have systematically examined the detailed outcrop based anatomy of this succession this study characterizes a series of well exposed outcrop sections along an 80 km long e w oriented series of road cuttings in the southeast ordos basin to reconstruct the sedimentary architecture of a fluvio lacustrine succession and determine the principal controls that governed the style of accumulation and preservation the yanchang formation is divided into 10 depositional units chang 10 base to chang 1 top that record the sedimentary evolution of a series of large scale fluvial systems that constructed delta front and pro delta bodies as they entered a large interior draining lake detailed analysis of the internal architectures of the delta front bodies records the mechanism of growth of a large scale shallow water delta succession lacustrine subaqueous distributary channels are composed of 3 15 m thick sandstone fills such channelized bodies are highly elongate and many can be traced several kilometres such bodies can be shown to be commonly associated with thin bedded mouth bar and subaqueous interdistributary bay deposition the progradational architecture of the delta front elements is difficult to recognize on outcrop scale deposits of the chang 10 to 1 units record 4 major lacustrine transgressive regressive cycles during the late triassic transgressive events are signified by the widespread occurrence of 10 20 m thick oil shale prone intervals regressive events are signified by the progradational stacking towards the basin centre of sandstone prone facies associations mainly accumulated in fluvial channel delta plain and upper delta front environments the uppermost chang 1 interval records late stage filling of the lacustrine basin the transgressive regressive cycles equate to sequences that can be correlated across the region development of which was controlled by a combination of changes in the rate of tectonic subsidence the rate of sediment delivery from the basin margin hinterland and climate factors that were themselves influenced by intracontinental growth of the neighbouring qinling orogen

calcite cement distribution and its effect on fluid flow in a deltaic sandstone frontier formation wyoming precipitation of extensive calcite cement during burial diagenesis can strongly modify the depositional permeability of a sandstone reservoir and affect fluid flow during production to predict subsurface flow through cemented reservoirs permeability distributions used in fluid flow models must reflect this diagenetic overprint calcite cements in sandstones commonly occur as irregularly distributed concretions which makes it difficult to predict diagenetic permeability modifications in the subsurface from typically spaced wells outcrops can provide a continuous image of heterogeneity produced by concretionary calcite cements the size and distribution of calcite concretions were mapped in outcrops of the frewens sandstone frontier formation in central wyoming large tabular calcite concretions in this deltaic sandstone generally follow basinward inclined bedding median thickness of the concretions is 0 6 m length is 4 2 m and width is 5 3 m the highest cement fraction is in the high permeability facies at the top of the sandstone body concretion centers are approximately poisson distributed within the sandstone the upward increasing cement fraction is caused by upward increasing concretion size lateral variation in the fraction of the sandstone cemented by calcite has a normal distribution with a mean of 12 s 5 spatial distribution of calcite cement in the frewens sandstone was modeled using indicator geostatistics variograms were inferred from outcrop maps of cement indicator semivariograms of cement have a range of 30 m horizontally and 2 5 m vertically dimensions that correspond approximately to the size of the largest concretions stochastic images of cement were created using indicator simulation with vertically varying cement proportion flow models indicate that concretions make flow paths more tortuous and retard flow in the coarser facies near the top of the sandstone the fastest path through the sandstone is in the lightly cemented high net to gross center of the sandstone body because the cement mainly occurs within the highest permeability facies in the sandstone body a model based on depositional facies alone would overestimate upscaled permeability of the frewens sandstone

architectural units and heterogeneity of channel reservoirs in the karamay formation outcrop area of karamay oil field junggar basin northwest china reservoirs of the karamay formation occur as oil sandstones in outcrop in the karamay oil field two types of high quality reservoirs are present in this field low sinuosity channel sandstones and distributary channel sandstones each having different sediments bounding surfaces and architectural units the low sinuosity channel has coarse grained sediments a smaller scale and relatively simple architectural units composed of intrachannel units and lithofacies that occur in a vertically stacked pattern the distributary channel has fine grained sediments a larger scale and relatively complex architectural units which are reflected in the following three ways 1 the distributary channels have three multiorder architectural units an intrachannel unit a macroform accretion unit and a lithofacies unit 2 isolated barrier beds whose permeability is lower occur near third order and fifth order surfaces 3 the evolution of the distributary channels has two stages in the flooding stage the sediments were coarse grained and the intrachannel units were in a vertically stacked pattern in the waning stage the sediments were fine grained and the intrachannel units were in a laterally stacked pattern reservoir heterogeneity of distributary channel sandstones is revealed in the following three scales 1 in a microscale range the growth of pores is associated directly with lithofacies the pore diameter and the throat width both increase with the coarsening of the grain size in the sediments the anisotropic pore structure is reflected in the variation of permeability the horizontal permeability parallel to the paleocurrent is the largest the horizontal permeability perpendicular to the paleocurrent is intermediate and the vertical permeability is the smallest 2 at a channel scale the fluid flow units are demarcated according to the isolated barrier bed and porosity and permeability inside the distributary channel the fluid flow unit distributed mainly in the middle lower interval of the distributary channel or the intrachannel unit is associated closely with third order or fifth order surfaces the porosity and permeability inside the fluid flow unit decrease gradually from its center to the margin and upper interval depending on the spatial distribution of lithofacies in this kind of lithofacies which is characterized by a low matrix content and by coarse grained sediments with large trough cross beds high porosity and permeability are commonly found 3 in a lacustrine delta system the distributary channel sandstone has the best porosity and permeability and is the best reservoir

facies to sandbody scale heterogeneity in a tight gas fluvial reservoir analog blackhawk formation wasatch plateau utah usa abstract using photomosaics and measured sections this outcrop study characterizes facies to sandbody scale heterogeneity in the fluvial and coastal plain deposits of the blackhawk formation of the wasatch plateau utah usa as an outcrop analog for the fluvial tight gas reservoirs of the adjacent greater western rocky mountain basins as well as for conventional fluvial reservoirs elsewhere analysis on eight contiguous vertical cliff faces comprising both depositional dip and strike oriented segments provides field validation and calibration of the entire range of fluvial heterogeneity where 1 large scale heterogeneity 10 s of m vertically and 100 s of m laterally is associated with stacking of channelized fluvial sandbodies encased within coastal plain fines 2 intermediate scale heterogeneity 1 s of m vertically and 10 s of m laterally is related to type and distribution of architectural elements like bar accretion and crevasse splay units within individual sandbodies and 3 small scale heterogeneity 10 s of cm vertically and 1 s of m laterally is attributed to facies spatial variability within individual architectural elements at a reservoir scale 6 km strike transect impact of these heterogeneities has resulted in potential stratigraphic compartmentalization in varied patterns and scales within and among three zones which have similar lateral extents distinct vertical or lateral compartmentalization contrasting net to gross pattern width constraint by either large or intermediate scale heterogeneity disparity in communication between principal reservoir compartments by intermediate scale heterogeneity and reservoir quality segregation to barrier styles rendered by small scale heterogeneity are documented in an array of trends these intriguing trends are challenging to correlate across the reservoir scale dataset contributing to multiple analogous exploration and production uncertainties for improved tight gas exploration and production strategy of the western rocky mountain basins study results were also used in developing potential predictive tools 1 thickness threshold of individual channelized sandbody favoring multiple well intersection 2 aspect ratio in performing probabilistic sandbody width estimation and 3 prediction of sandbody amalgamation using underlying coal thickness