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

controls on reservoir quality of lower cretaceous tight sandstones in the laiyang sag jiaolai basin eastern china integrated sedimentologic diagenetic and microfracturing data abstract the jiaolai basin fig 1 is an under explored rift basin that has produced minor oil from lower cretaceous lacustrine deltaic sandstones the reservoir quality is highly heterogeneous and is an important exploratory unknown in the basin this study investigates how reservoir porosity and permeability vary with diagenetic minerals and burial history particularly the effects of fracturing on the diagenesis and reservoir deliverability the laiyang sandstones are tight reservoirs with low porosity and permeability

reply to the comment on bonneville basin shoreline records of large lake intervals during marine isotope stage 3 and the last glacial maximum by s nishizawa d r currey a brunelle d sack palaeogeography palaeoclimatology palaeoecology 386 2013 374 391 abstract in their comment oviatt et al this issue criticize and dismiss our recent paper nishizawa et al 2013 by arguing that it contains misinterpretations and unreliable radiocarbon ages and therefore that our findings will confuse many people trying to understand the lacustrine chronology of the bonneville basin their comment however does not present evidence to substantiate their criticisms against our paper oviatt et al attribute statements to the paper that are not found in it and their attempt to re graph the radiocarbon ages omits 13 of our data numeric ages that oviatt et al contend are conflicting either are not or are not as problematic as those commenters claim comparisons of our lake interval interpretations with sediment core data likewise do not show the contradictions that oviatt et al claim in essence oviatt et al seem to advocate complete dismissal of all of our numeric ages and lake size interpretations regarding mis 3 on the basis of one tufa age the following sections identify the incorrect information presented in the comment by oviatt et al review the complete set of numeric ages for the contested intervals and respond to the implication that our late colleague mentor and coauthor donald r currey did not actively participate in this research

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

reservoir quality natural fractures and gas productivity of upper triassic xujiahe tight gas sandstones in western sichuan basin china abstract the main target for hydrocarbon exploration in the western sichuan basin in china is the tight gas sandstone reservoir of the upper triassic xujiahe formation sandstones of the xujiahe formation are characterized as tight with ultralow porosity ultralow permeability and intensive heterogeneity in this study various techniques such as scanning electron microscopy x ray diffraction cathodoluminescence microscopy casting thin section and fluid inclusion thermometry were employed to investigate the composition sedimentary facies diagenesis history diagenetic intensity natural fracture characteristics and their impact on reservoir quality the results showed that subaqueous distributary channels and mouth bars with low rock fragment content are favorable for pore preservation and secondary pore development except for the medium to strong dissolution intensity chlorite rim growth is also important for the development of high quality reservoirs intraformational shear fractures and horizontal shear fractures associated with tectonic movement increase pore space and improve the capability of transmitting fluids differences in gas productivity could be attributed to differences in reservoir quality which were controlled by the sedimentary environment diagenetic intensity and fracture characteristics a significantly positive correlation was found between total porosity and gas productivity of the tight sandstones the high density fracture distribution was found owing to the fault system and structural deformation zone which resulted in high gas productivity the research results were successfully applied to improve production efficiency in the xujiahe tight gas sandstones and could be applicable to other similar fields involving tight gas

diagenetic alterations and reservoir heterogeneity within the depositional facies a case study from distributary channel belt sandstone of upper triassic yanchang formation reservoirs ordos basin china abstract diagenesis is of decisive significance for the reservoir heterogeneity of most clastic reservoirs linking the distribution of diagenetic processes to the depositional facies and sequence stratigraphy has in recent years been discipline for predicting the distribution of diagenetic alterations and reservoir heterogeneity of clastic reservoirs this study constructs a model of distribution of diagenetic alterations and reservoir heterogeneity within the depositional facies by linking diagenesis to lithofacies sandstone architecture and porewater chemistry during burial this would help to promote better understanding of the distribution of reservoir quality evolution and the intense heterogeneity of reservoirs based on an analogue of deltaic distributary channel belt sandstone in upper triassic yanchang formation 83 sandstone plug samples were taken from 13 wells located along this channel belt an integration of scanning electron microscopy thin sections electron microprobe analyses rate controlled porosimetry rcp gas flow measurements of porosity and permeability and nuclear magnetic resonance nmr experiments together with published data were analysed for the distribution mineralogical and geochemical characteristics of detrital and diagenetic components and the distribution of reservoir quality within the distributary channel belt distribution of diagenetic alterations and reservoir heterogeneity within the distributary channel belt sandstones include i formation of high quality chlorite rims in the middle part of thick sandstones with coarser grain sizes and a lower content of ductile components resulted from the greater compaction resistance of these sandstones providing larger pore spaces for chlorite growth leading to formation of the intergranular pore wide sheet like throat and intergranular pore intragranular pore wide sheet like throat 15 k 1md in the middle part of thick sandstones ii formation of thinner chlorite rims in the middle part of thinner sandstones is associated with the intergranular pore intragranular pore narrow sheet like throat 9 18 o vpdb 23 4 to 16 6 13 c vpdb 4 0 to 2 3 favoured in the top and bottom of the channel sandstone which near the sandstone mudstone bouding surface destroying pore space

diagenetic history of the surma group sandstones miocene in the surma basin bangladesh abstract this study examines the various diagenetic controls of the miocene surma group sandstones encountered in petroleum exploration wells from the surma basin which is situated in the northeastern part of the bengal basin bangladesh the principal diagenetic minerals cements in the surma group sandstones are fe carbonates with fe calcite dominating quartz overgrowths and authigenic clays predominantly chlorite illite smectite and minor kaolin the isotopic composition of the carbonate cement revealed a narrow range of 18o values 10 3 to 12 4 and a wide range of 13c value 1 4 to 23 1 the 13c vpdb and 18o vpdb values of the carbonate cements reveal that carbon was most likely derived from the thermal maturation of organic matter during burial as well as from the dissolution of isolated carbonate clasts and precipitated from mixed marine meteoric pore waters the relationship between the intergranular volume igv versus cement volume indicates that compaction played a more significant role than cementation in destroying the primary porosity however cementation also played a major role in drastically reducing porosity and permeability in sandstones with poikilotopic pore filling blocky cements formed in early to intermediate and deep burial areas in addition to fe carbonate cements various clay minerals including illite smectite and chlorite occur as pore filling and pore lining authigenic phases significant secondary porosity has been generated at depths from 2500 m to 4728 m the best reservoir rocks found at depths of 2500 3300 m are well sorted relatively coarse grained more loosely packed and better rounded sandstones having good porosities 20 30 and high permeabilities 12 6000 md these good quality reservoir rocks are however not uniformly distributed and can be considered to be compartmentalized as a result of interbedding with sandstone layers of low to moderate porosities low permeabilities owing to poor sorting and extensive compaction and cementation

diagenetic controls on evolution of porosity and permeability in lower tertiary wilcox sandstones from shallow to ultradeep 200 6700 m burial gulf of mexico basin u s a abstract reservoir quality is a critical risk factor in deep to ultradeep reservoirs at depths 4 5 km analysis of paleogene wilcox sandstones on the upper texas gulf coast provides insight into the evolution of reservoir quality during shallow to ultradeep burial diagenesis reduction of porosity and permeability with burial in wilcox sandstones was evaluated using subsurface samples from 200 to 6700 m at temperatures of 25 230 c diagenesis and petrophysical properties were interpreted from petrographic data and core analyses wilcox sandstones are mostly lithic arkoses and feldspathic litharenites having an average composition of q59f22r19 provenance did not change significantly during wilcox deposition in this area nor does average sandstone composition vary among lower middle and upper wilcox sandstones however composition does vary with sequence stratigraphic position lowstand slope fan deposits contain more rock fragments than do deposits from highstand or transgressive systems tracts given observations from this onshore dataset wilcox sandstones deposited in deepwater environments in the gulf of mexico are likely to contain more rock fragments than their linked highstand equivalents pore types in wilcox sandstones change from a mix of primary and secondary pores and micropores at shallower depths to predominantly secondary pores and micropores in deeper sandstones wilcox sandstones show steady porosity reduction from an average of 33 at 38 c to 12 at 132 c with little additional loss at higher temperatures by 132 c most primary pores have been lost by mechanical compaction or occluded by quartz cementation volume of secondary pores remains nearly constant despite dissolution of 3 5 average potassium feldspar during deep burial volume of this late dissolution of potassium feldspar is offset by precipitation of ankerite albite illite and minor quartz in secondary pores the proportion of microporosity which occurs in authigenic clays altered grains and matrix increases in the deepest sandstones change in proportion of pore types and reduction in total porosity with increasing temperature changes porosity permeability transforms because most deep to ultradeep wilcox sandstones are dominated by secondary pores and micropores porosity permeability transforms have lower slopes than those for shallower sandstones

the coastal depositional system of a small mountainous river a perspective from grain size distributions abstract tseng wen river is a small mountainous river on a wave dominated coast of taiwan the spatial distribution patterns of 17 individual grain sizes offshore near the river mouth show strong morpho textural relationships with the bathymetry which also vary considerably according to the grain size the influence of seven hypothetical factors that could affect the observed grain size patterns were examined individually by using a methodology that combines filtering concept and a multivariate analysis technique eof these factors include the sediments discharged by the river offshore palimpsest sediments sediments eroded from a submarine sand ridge and the remnant river delta the effect of wave sorting and the northward and southward littoral drift the study results indicate that the tseng wen river is the most important source for modern sediments in the study area the reworking of offshore palimpsest sediments is also an important sediment source the agitation by waves is an important sorting mechanism in the study area and the net sediment transport in the study area is northward the findings based on grain sizes are also corroborated by short term observations of the near bed sediment dynamics and transport during the flood season of the tseng wen river

petrographic constraints on models of intergranular pressure solution in quartzose sandstones abstract petrographic and sem observations on 478 samples of six quartzose sandstones provide a data base that can be used to evaluate the role of intergranular pressure solution ips in sandstone diagenesis and to constrain predictive models of the pressure solution process sem examination of grain contacts that have experienced pressure solution suggests that ips occurs at the interior portions of contacts where the greatest stress is concentrated and that granulation of quartz grains at points of contact may contribute to the process the chemical compaction fabrics that result from ips suggest that the process is most commonly induced by effective lithostatic stress and that the resulting strain is uniaxial numerous geological variables influence ips grain size exerts a fundamental influence with finer grained samples experiencing more ips than coarser grained samples on both local and regional scales ips is inhibited by poor sorting an abundance of ductile grains the presence of shallow cement slow rates of shallow burial and overpressured conditions in contrast ips is enhanced by the presence of illite grain coatings increased maximum burial depth rapid rates of shallow burial longer times spent at great depths higher temperatures and high volumes and rates of fluid flow silica budgets indicate that some of the analyzed sandstones approximate mass balance whereas others have exported silica calculations of fluid flow requirements indicate that advanced stages of ips are favored by high volume high velocity fluid flow such flow can occur as a result of uplift of basin margins which is typical of foreland and intractonic basins

depositional and diagenetic controls on deeply buried eocene sublacustrine fan reservoirs in the dongying depression bohai bay basin china abstract this paper investigates the reservoir potential of deeply buried eocene sublacustrine fan sandstones in the bohai bay basin china by evaluating the link between depositional lithofacies that controlled primary sediment compositions and diagenetic processes that involved dissolution precipitation and transformation of minerals this petrographic mineralogical and geochemical study recognizes a complex diagenetic history which reflects both the depositional and burial history of the sandstones eogenetic alterations of the sandstones include 1 mechanical compaction and 2 partial to extensive non ferroan carbonate and gypsum cementation typical mesogenetic alterations include 1 dissolution of feldspar non ferroan carbonate cements gypsum and anhydrite 2 precipitation of quartz kaolinite and ferroan carbonate cements 3 transformation of smectite and kaolinite to illite and conversion of gypsum to anhydrite this study demonstrates that 1 depositional lithofacies critically influenced diagenesis which resulted in good reservoir quality of the better sorted middle fan but poor reservoir quality in the inner and outer fan lithofacies 2 formation of secondary porosity was spatially associated with other mineral reactions that caused precipitation of cements within sandstone reservoirs and did not greatly enhance reservoir quality and 3 oil emplacement during early mesodiagenesis temperatures 70 c protected reservoirs from cementation and compaction

spatial variability in depositional reservoir quality of deep water channel fill and lobe deposits abstract initial porosity and permeability in deep water systems are controlled by primary sedimentary texture and mineralogy therefore understanding the sedimentary processes that control changes in primary texture is critical for improved reservoir quality predictions a well constrained exhumed submarine lobe in the jaca basin and a submarine channel fill element in the ainsa basin northern spain were studied to characterize the depositional reservoir quality in axial to marginal fringe positions construction of architectural panels and strategic sampling enabled analysis of the spatial changes in textural properties and their relationship to reservoir quality distribution samples were analyzed in thin section to establish how depositional processes inferred from outcrop observations affect textural properties results show that high density turbidites are concentrated in lobe and channel axis positions and exhibit good depositional reservoir quality lobe off axis deposits contain high and low density turbidites and have moderate depositional reservoir quality conversely low density turbidites dominate lobe fringe and channel margin positions and have relatively poor depositional reservoir quality there is a sharp decrease in depositional reservoir quality between the lobe off axis and lobe fringe due to 1 an abrupt increase in matrix content 2 an abrupt decrease in sandstone amalgamation and 3 a decrease in grain size there is an abrupt increase in depositional reservoir quality from channel margin to channel axis corresponding to 1 an increase in total sandstone thickness and amalgamation 2 an increase in grain size 3 a decrease in matrix content rates of change of key properties are up to two orders of magnitude greater between channel fill sub environments compared to lobe sub environments spatial variability in properties of discrete architectural elements and rates of changes provides input to reservoir models during exploration appraisal and development phases of hydrocarbon fields

discussiondiscussion in response to knut bjorlykke regarding jmpg_1376 open system chemical behavior in deep wilcox group mudstones texas gulf coast usa

an investigation into pore structure and petrophysical property in tight sandstones a case of the yanchang formation in the southern ordos basin china abstract the complex and heterogeneous pore structures caused by complex diagenesis and sediment properties such as rock compositions and grain size play a critical role in macroscopic evaluating tight sandstone reservoir performance in order to gain insight into the genetic mechanism of the pore structure and evaluate reservoir quality in tight sandstone reservoirs this study investigated the impacts of diagenesis and sediment properties on pore structures and the relationship between microscopic pore structure parameters and macroscopic petrophysical performance based on the analysis of pore structure features including the morphology pore throat types sizes combinations distribution of combinations and pore connectivity sedimentary and diagenetic features and petrophysical properties samples from tight sandstones of the yanchang formation in southern ordos basin in china were evaluated by integrating scanning electron microscopy sem thin sections mercury injection porosimetry mip nuclear magnetic resonance nmr and gas n2 he porosity and permeability measurements three pore throat combinations were identified which represent the full range distribution of pores mp micropores dominanted pore throat combination iap intragranular pores dominanted pore throat combination and iep intergranular pores dominanted pore throat combinations the type and intensity of diagenesis and sediment properties grain size and ductile component content were found to result in differences in pore throat size and the distribution of pore throat combinations sandstones with coarser grain size and lower concentrations of ductile components have experienced weak compaction thick chlorite rim and minor kaolinite carbonate cementation were found to retain large iep pore space and wide strip shaped throat formed the intergranular pore throat inter t and intergranular pore intragranular pore throat inter intra t the intra intst t intragranular pore group of interstitial cement pores throat sandstones were characterized by intense dissolution and kaolinite cementation which resulted in small iep pore space and large mp iap pore space the intst t group of interstitial cement pores throat sandstones were characterized by intense compaction and kaolinite carbonate cementation compaction and cements destroyed iep pore space and formed mp pore space effectively connected pore space volume of iep and throat radius were positively correlated to porosity and permeability four pore structures are distinguished according to the proportion of effectively connected pore space and the radii of strip shaped throats the macroscopic behaviors and the geological genesis of the four pore structures are investigated

classification and sedimentary characteristics of lacustrine hyperpycnal channels triassic outcrops in the south ordos basin central china abstract subaquatic channels are known as active conduits for the delivery of terrigenous sediments into related marine and lacustrine basins as well as important targets for hydrocarbon exploration compared to submarine channels lacustrine subaqueous channels created by hyperpycnal flows are understudied using well exposed outcrops collected from three different locations in the southern ordos basin central china morphologies and architecture of a channelized hyperpycnal system were studied and classified six facies associations represent sedimentary processes from strong erosion by bedload dominated hyperpycnal flows to transitional deposition jointly controlled by bedload and suspended load dominated hyperpycnal flows finally to deposition from suspended load dominated hyperpycnal flows on the basis of channel morphologies infilling sediments and sedimentary processes the documented channels can be classified into four main categories which are erosional bedload dominated suspended load dominated and depositional channels in very proximal and very distal locations erosional channels and depositional channels serve as two end members while in middle areas bedload dominated channels and suspended load dominated channels are transitional types erosional channels as a response to strong erosion from bedload dominated hyperpycnal flows on upper slope were mainly filled by mud interbedded with thin sand beds as flow energy decreases bedload dominated channels develop on middle slopes which are characterized mainly by under to balanced sediment infillings with cross bedded sandstones and or minor massive sandstones compared to bedload dominated channels suspended load dominated channels mainly develop in deeper water and were filled mainly by massive or planar laminated sandstones depositional channels as a response to suspended load dominated hyperpycnal flows in deep water areas are characterized by thin medium bed classical turbidites with bouma sequences and thin to thick massive sandstones such evolution patterns of hyperpycnal channel systems are ascribed to the progressive decrease in flow capacity of hyperpycnal flows and provide an adequate explanation for the basinward channelization behavior of hyperpycnal systems

diagenesis and reservoir quality evolution of palaeocene deep water marine sandstones the shetland faroes basin british continental shelf abstract the palaeocene deep water marine sandstones recovered from six wells in the shetland faroes basin represent lowstand transgressive and highstand systems tract turbiditic sediments mineralogic petrographic and geochemical analyses of these siliciclastics are used to decipher and discuss the diagenetic alterations and subsequent reservoir quality evolution the middle upper palaeocene sandstones subarkoses to arkoses from the shetland faroes basin british continental shelf are submarine turbiditic deposits that are cemented predominantly by carbonates quartz and clay minerals carbonate cements intergranular and grain replacive calcite siderite ferroan dolomite and ankerite are of eogenetic and mesogenetic origins the eogenetic alterations have been mediated by marine meteoric and mixed marine meteoric porewaters and resulted mainly in the precipitation of calcite 18 o v pdb 10 9 and 3 8 trace amounts of non ferroan dolomite siderite 18 o v pdb 14 4 to 0 6 as well as smectite and kaolinite in the lowstand systems tract lst and highstand systems tract hst turbiditic sandstone below the sequence boundary minor eogenetic siderite has precipitated between expanded and kaolinitized micas primarily biotite the mesogenetic alterations are interpreted to have been mediated by evolved marine porewaters and resulted in the precipitation of calcite 18 o v pdb 12 9 to 7 8 and fe dolomite ankerite 18 o v pdb 12 1 to 6 3 at temperatures of 50 140 and 60 140 c respectively quartz overgrowths and outgrowth which post and pre date the mesogenetic carbonate cements is more common in the lst and tst of distal turbiditic sandstone discrete quartz cement which is closely associated with illite and chlorite is the final diagenetic phase the clay minerals include intergranular and grain replacive eogenetic kaolinite smectite and mesogenetic illite and chlorite kaolinite has been subjected to mesogenetic replacement by dickite the k feldspar and plagioclase grains have been albitized dissolution of calcite cement and of framework grain feldspar volcanic fragments and mud intraclasts has resulted in a considerable enhancement of reservoir quality

distribution and characteristics of lacustrine tight oil reservoirs in china abstract lacustrine tight oil resources in china are significant exploration targets similar to the marine tight oil resources in north america while there are clear differences in terms of the forming environment as well as reservoir properties of these two systems in this study the geological characteristics of lacustrine tight rocks are discussed including the distribution petrology storage space and movable fluid saturation the tight rocks are consisted of tight sandstone tight carbonate rock tight peperite and tight sedimentary tuff in which intergranular pores and dissolved pores with the dimensions of 30 900 nm are mainly dominated by the storage space the oil saturation typically exceeds 50 and the oil mobility is basically controlled by pore throats with diameter less than 1 m these four types of reservoirs show different potentials for tight oil in which tight sandstone plays in the ordos basin and the songliao basin are taken as the preferred targets into account for exploration and development although the distribution area physical properties and mobility of lacustrine tight oil in china are not as good as those of tight oil in north america the lacustrine reservoirs are often stacked in multiple layers resulting in a great thickness and possess relatively high oil saturation making them producible and commercially viable fluid properties are critical to effectively recovery of tight oil and more comprehensive geological evaluation on fluid mobility should be undertaken

genesis and distribution pattern of carbonate cements in lacustrine deep water gravity flow sandstone reservoirs in the third member of the shahejie formation in the dongying sag jiyang depression eastern china abstract the lacustrine deep water gravity flow sandstone reservoirs in the third member of the shahejie formation are the main exploration target for hydrocarbons in the dongying sag eastern china carbonate cementation is responsible for much of the porosity and permeability reduction in the lacustrine deep water gravity flow sandstone reservoirs the sandstones are mainly lithic arkose with an average framework composition of q43f33l24 the carbonate cements are dominated by calcite ferroan calcite ankerite and a small amount of dolomite the calcite and ferroan calcite are mainly poikilotopic blocky crystals while the dolomite and ankerite are mainly euhedral rhombohedra crystals filling intergranular and intragranular pores the relatively positive 13c values 2 to 3 9 of the carbonate cements in the sandstone reflect a mainly inorganically sourced carbon from 32 ma to 25 ma the pore water was rich in bicarbonate and ca2 due to carbonate dissolution in mudstone and which were transported with the pore water from mudstone to sandstone via advection and precipitated calcite cementation in thinly bedded sandstones and some high permeability zones in the middle of medium to thick sandstone beds from 12 ma to present abundant ca2 fe3 fe2 mg2 and bicarbonate had been transported from mudstone to sandstone via diffusion to form tight ferroan calcite cementation in the upper and lower parts of the medium to thick bedded sandstones ankerite is mainly distributed in the reservoirs associated with oil migration or charge because change of fe3 to fe2 from oil charge may supply sufficient fe2 for ankerite precipitation the center of sandstone beds 0 6 m is with potential of high quality reservoirs in the research area carbonate cementation appears to be an important factor that controls the accumulation of oil in deep water gravity flow sandstone reservoirs in the study area

measuring sandstone compaction from modal analyses of thin sections how to do it and what the results mean abstract calculation of compactional porosity loss from modal analyses of thin sections is a useful technique for characterizing the diagenesis and porosity evolution of sandstone reservoirs to obtain meaningful results however it is essential to assume an appropriate value for the original porosity and to use point counting categories that clearly distinguish between grains and intergranular materials because of the latter requirement it is commonly not appropriate to make calculations of compactional porosity loss from modal analyses that were not performed for the specific objective of measuring intergranular volume suites of modal analyses from deeply buried sandstone units typically show wide variations in the relative importance of compaction versus quartz cementation this heter geneity must reflect subtle variations in depositional sand characteristics in particular the distribution of detrital intergranular clays that tend to promote both mechanical grain rearrangement and stylolitic grain dissolution as well as locally inhibiting quartz cement growth despite wide variation in the mechanism of porosity loss total helium porosity tends to be relatively constant at individual well locations suggesting a close interdependence between compaction and quartz cementation with total porosity loss dependent mainly upon thermal exposure either maximum temperature or time temperature integral

open system chemical behavior in deep wilcox group mudstones texas gulf coast usa abstract wilcox group mudstones have been mechanically and geochemically transformed over a temperature range of 20 200 c our research controlled for provenance and age by sampling from five wells parallel to the paleodepositional axis all within the houston delta system across the sampled depths mudstone porosity has been reduced from 25 to

the origin and fate of silt sized carbonate in subsurface miocene oligocene mudstones south texas gulf coast combined petrographic and geochemical data document several kinds of detrital carbonate in subsurface miocene oligocene mudstones of the texas gulf coast in the extreme south of texas in muddy sediments deposited by ancient precursors to the modern rio grande mudstone carbonate is dominated by extrabasinal detritus derived from cretaceous limestones of the edwards plateau further north oligocene mudstones contain carbonate that is mostly syndepositional skeletal material minor amounts of authigenic carbonate are found as replacements of silt sized feldspars in all the mudstones depth related shifts in 18ocalcite and 13ocalcite suggest that small amounts of authigenic carbonate also form by replacement of detrital carbonate recrystallization although this cannot be demonstrated petrographically pervasive carbonate cementation in primary pores in mudstones is not generally observed textural evidence of carbonate loss through pressure dissolution is widespread providing a mechanism for the depth related decline in carbonate content observed in many gulf coast wells carbonate dissolution in mudstones and export of the caco3 implies a massive acid source probably resulting from silicate reactions within the mudstones during burial diagenesis

controls of diagenetic alteration on the reservoir quality of tight sandstone reservoirs in the triassic yanchang formation of the ordos basin china abstract the ordos basin is rich in tight oil resources and the upper triassic yanchang formation tight oil reservoir is one of the most important exploration targets in the study area the chang 63 tight sandstone reservoir exhibits lacustrine deep water lobe shaped delta deposits with low porosity low permeability and a complex diagenetic alteration history the reservoir quality is extremely heterogeneous because of the heterogeneity of the depositional lithofacies and diagenetic alterations this research integrates multiple techniques to investigate the depositional lithofacies the characteristics and distributions of various diagenetic alterations and their controls on reservoir quality four lithofacies are identified and the various lithofacies have different diagenetic characteristics and diverse reservoir qualities the chang 63 tight sandstone reservoir has experienced significant diagenetic alteration mechanical compaction and authigenic illite are the most important causes of the decrease in reservoir quality carbonate cementation preferentially occurs in sandstones of lithofacies i and ii near the mudstone sandstone contact surfaces sandstones within 1 m of adjacent mudstone sandstone contact surfaces are usually tightly cemented by carbonate cement illite can be divided into two types according to its morphology both types of illite lead to a decrease in reservoir quality ultimately by combining the relationship between depositional facies and lithofacies with the distribution of different diagenetic processes five evolutionary patterns are identified for reservoir quality in the lacustrine deep water lobe shaped delta deposits can be summarized by ratings of best moderate relatively poor poor and worst

open or closed geochemical systems during diagenesis in sedimentary basins constraints on mass transfer during diagenesis and the prediction of porosity in sandstone and carbonate reservoirs descriptions of mineralogy and textural relationships in sandstones and limestones have been used to establish a sequence of diagenetic events epigenesis involving mineral dissolution and precipitation which have been interpreted to have occurred during the burial history published epigenetic sequences commonly imply a geochemically open system with very significant changes in the bulk chemical composition of the sediments during burial near surface diagenetic reactions may be open involving significant changes in the sediment composition and formation of secondary porosity caused by high pore water flow rates of meteoric water or reactions with sea water near the sea floor calculations show that the bulk chemical composition of the sediments below the reach of high pore water flow rates of meteoric water or hydrothermal convection should remain nearly constant during progressive burial because of limited pore water flow mass transport between shales and sandstones is also limited because the pore water is in most cases buffered by the same minerals so that the concentration gradients are low recent studies show that silica released from clay mineral reactions in mudstones has been precipitated locally as small quartz crystals and not exported to adjacent sandstones if the geochemical constraints for mass transfer during burial diagenetic reactions are accepted the chemical reactions involved in diagenesis can be written as balanced equations this offers the possibility to make predictions about reservoir quality based on assumptions about primary sediment composition related to facies and provenance large scale changes in the bulk composition of sandstones and mudstones during burial diagenesis have been suggested but because such changes cannot be explained chemically and physically no predictions can be made burial diagenetic processes are in most cases not episodic but occur as slow adjustments to increased stress and temperature driving the sediments toward increased mechanical and thermodynamic stability as a result the porosity of a single lithology must decrease during progressive burial but each lithology has a different porosity curve this article discusses quantitative calculations and estimates that show clearly that burial diagenesis must represent geochemically nearly closed systems where mineral dissolution and precipitation must be balanced this provides a theoretical basis for the modeling and prediction of reservoir quality

quartz types and origins in the paleozoic wufeng longmaxi formations eastern sichuan basin china implications for porosity preservation in shale reservoirs abstract quartz in shales has been demonstrated to exert a significant effect on shale gas production by influencing rock mechanical behavior and reservoir porosity however quartz types and origins in shales are complicated and challenging to study due to their fine grained nature in this study we propose combining thin section images scanning electron microscopy sem images energy dispersive spectroscopy eds maps cathodoluminescence cl images and geochemical data to investigate quartz types and origins in shale formations shale samples from the ordovician wufeng silurian longmaxi formations eastern sichuan basin china were used to study quartz types origins and the effect of quartz cementation on porosity development samples from the wufeng longmaxi formations have toc contents in the range of 0 5 4 7 wt averaging 2 7 wt and are currently in the thermally overmature stage five types of quartz including silt size detrital quartz siliceous skeletal fragments quartz overgrowth clay matrix dispersed microquartz and aggregates of euhedral quartz were identified the ternary diagram of fe al mn the cross plot of sio2 versus zr and the cross plot of si versus al suggest that the dissolution and reprecipitation of siliceous skeletons may provide the major source of silica for quartz cementation in the lower part of the wufeng longmaxi formations and released silica as a result of smectite to illite transformation is also important for authigenic quartz formation in the upper part of the wufeng longmaxi formations our sem images suggest that the rigid framework formed by quartz cementation not only prevents primary interparticle pores from compaction but also favors the generation of organic matter associated pores

sandstone porosity loss a big picture view of the importance of compaction proper assessment of the relative importance of porosity loss by compaction and cementation is important to the prediction of porosity in sandstones studies of mass transport during diagenesis and the modeling of basin fluid flow quantitative estimation of the amounts of porosity loss by compaction and cementation can be made from standard point count data on cement and pore space abundance this method is discussed and its sources of error are evaluated error in the method arises mainly from uncertainty in initial sandstone porosities and the amount of local grain dissolution during burial data on the porosity of modern sands indicate that assumed initial porosities of 40 to 45 will produce small average errors in the calculation of compactional porosity loss for clean sandstones grain dissolution whether resulting in local porosity enhancement by export in solution of former grain mass or local precipitation of authigenic cement will cause an underestimation of the significance of compaction a large database of point count data from diverse sandstones is used to provide a broad perspective on the importance of compaction and cementation to sandstone porosity loss it is shown that the global importance of compactional porosity loss has generally been under appreciated in fact compaction mechanical and chemical is probably the dominant mechanism of porosity loss in most sandstones the extent of compactional porosity loss is related to sand grain composition and basin thermal structure

effect of pore structure on the producibility of tight gas sandstones the estimated ultimate recovery eur is one of the most significant properties of tight gas sandstone reservoirs but it remains difficult to predict estimated ultimate recovery is dependent on the success of stimulation by hydraulic fracturing the existence and connectivity of natural fractures and as illustrated in this article the pore structure of the matrix here we analyze the lab measurements that are indicative of the pore structure and then we predict the effect of pore structure on producibility we develop a relationship between the eur of tight gas sandstones and their petrophysical properties measured by drainage and imbibition tests mercury intrusion withdrawal and porous plate and by resistivity analyses we use the ratio of residual mercury saturation after mercury withdrawal s gr to initial mercury saturation s gi which is the saturation at the start of withdrawal as a measure of gas likely to be trapped in the matrix during production and hence a proxy for eur a multitype pore space model is required to explain mercury intrusion capillary pressures in these rocks implications of this model are supported by other available laboratory measurements the model comprises a conventional network model and a treelike pore structure an acyclic network that mimic the intergranular and intragranular void spaces respectively the notion of the treelike pore structure is introduced here for the first time in the context of tight gas sandstones applying the multitype model to porous plate data we classify the pore spaces of rocks into intergranular dominant intermediate and intragranular dominant this pore space classification is topological and is not based on scale or size these classes have progressively less drainage and imbibition hysteresis which leads to the prediction that significantly more hydrocarbon is recoverable from intragranular porosity than intergranular porosity available field data production logs corroborate the higher producibility of intervals with intragranular porosity although the data are not sufficient to eliminate the possible contribution of other factors such as size and shape of the volume contacted by hydraulic fractures or the presence and attributes of natural fractures the superior recovery of hydrocarbon from intragranular dominant pore structures is despite its inferior initial production rate

calcite cement in permian deep water sandstones delaware basin west texas origin distribution and effect on reservoir properties calcite cement is the dominant control on reservoir quality in turbidite sandstones of the upper permian bell canyon formation delaware basin these well sorted very fine grained arkoses were deposited in a basin floor setting by channel levee systems terminating in broad lobes calcite cement distribution in the east ford and geraldine ford fields was mapped using core log and thin section data calcite is concentrated in tightly cemented zones that are mostly less than 1 ft 0 3 m thick areas that have high percentages of calcite cemented sandstone 20 occur along the margins of the sandstone bodies in overbank and lobe deposits where sandstone pinches out into siltstone areas that have the lowest percentage of calcite cemented sandstone 10 occur where the sandstone is thickest in the channel facies isotopic composition of the calcite 13c 1 8 to 3 0 relative to the peedee belemnite pdb 18o 4 6 to 6 3 pdb is consistent with the source of calcium carbonate being from dissolution of detrital carbonate rock fragments and marine skeletal debris because internal sources of calcite were apparently insufficient to account for the cement volume cement components are interpreted as having been transported into the sandstones from organic rich basinal siltstones and limestones feldspars buffered acidic formation waters near where they entered the sandstone resulting in calcite concentrated near the sandstone margins the calcite formed near maximum burial depths of 4800 ft 1 5 km and temperatures of 104f 40c from marine pore waters with 18o of approximately 0 relative to standard mean ocean water most of the calcite cemented zones are interpreted as being concretions that extend no more than a few meters laterally production data and geophysical log correlations suggest that some cemented zones are laterally continuous at least 1000 ft 300 m and cause vertical reservoir compartmentalization laterally extensive calcite layers may be associated with the base of turbidite deposits

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

diagenetic history and reservoir quality of tight sandstones a case study from shiqianfeng sandstones in upper permian of dongpu depression bohai bay basin eastern china abstract the upper permian shiqianfeng sandstones located in the dongpu depression bohai bay basin china are fluvio lacustrine deposits and have high content of pore filling volcanic dust average 7 93 vol this study focuses on diagenetic processes and reservoir quality of the tight sandstones based on different lithofacies an integrated approach such as core observation x ray diffraction scanning electron microscopy cathode luminescence stable isotope analysis of carbon and oxygen compositions electron microprobe analysis and fluid inclusion analysis were utilized the tight sandstones consist of subarkose and lithic subarkose and have undergone significant diagenetic events including compaction quartz cementation carbonate cementation mainly calcite and ferrocalcite and formation of authigenic clay minerals i e chlorite rims kaolinite and mixed layer illite smectite the volcanic dust altered with increase of burial depth resulting in the production of abundant silicic materials and depletion of metallic ions i e fe 2 mg 2 ca 2 and mn 2 this process formed subhedral micro quartz pore filling authigenic quartz smectite and chlorite rims during the early diagenetic stage early phase carbonate cements calcite ferrocalcite occurred in several samples they were also influenced by volcanic dust alteration resulting in intrusive of fe 2 and high contents of mn 2 average 12 5 mol further alteration of volcanic dust at the mesogenetic stage can result in cementation of kaolinite and euhedral micro quartz quartz overgrowth developed because of smectite to illite reactions and the alteration of volcanic dust late phase carbonate cements dolomite and ankerite are rare the present low porosity average 6 17 vol and permeability average 0 198 md of the shiqianfeng sandstones mainly resulted from intense compaction diverse cementation and pore filling of volcanic dust as strong hydrodynamic conditions of pore water modification of reservoir quality in the conglomeratic sandstone and gritstone lithofacies mainly distribute in braided channel occurred by alteration of volcanic dust thick braided channel at the high structural position should be the focal point for the future exploration

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

diagenesis and reservoir quality of the sherwood sandstone triassic corrib field slyne basin west of ireland abstract the triassic sherwood sandstone in the corrib field slyne basin west of ireland on the european continental margin is a dry gas reservoir with a mercia mudstone top seal petrographic analysis combined with x ray diffraction stable isotope fluid inclusion and core analysis have been used to assess timing of growth and origin of mineral cements whether sandstone diagenesis involved mass flux the controls on reservoir quality and how reservoir quality is likely to vary in more deeply buried sections depositional and early diagenetic characteristics of the sherwood in corrib are typical of a semi arid fluvial environment containing groundwater of meteoric origin early diagenesis included the development of copious dolomite cement in the form of dolocrete as well as the formation of abundant clay while less volumetrically important grain coating haematite and k feldspar cement also grew burial diagenesis witnessed the initial growth of minor chlorite and albite quartz overgrowths and ankerite followed and are the most important burial cements growing over a temperature interval between 100 and 1165 c albite commenced growth at about 90 c quartz cement at 100 c and ankerite at 110 c these cements reached the zenith of their development at 105 110 c for albite 125 130 c for quartz and 135 145 c for ankerite siderite and anhydrite are relatively minor late stage cements the formation water has been consistently highly saline during burial and in terms of mineral cement derived oxygen stable isotope values is likely to be a diagenetically evolved version of the initial depositional water suggesting long term stagnation of the pore fluids the diagenetic reactions that formed burial cements all seem to be essentially isochemical including the ankerite that has carbon isotope characteristics of the cannibalisation of dolocrete reservoir quality is mainly controlled by early diagenetic dolomite and clay although grain size is also important because only sandstones with 200 m grain size have 50 md permeability both shallower and deeper sections than corrib may have similar porosity and permeability since temperature dependent diagenetic controls on reservoir quality e g quartz and illite cement are peripheral

diagenetic alteration and its control on reservoir quality of tight sandstones in lacustrine deep water gravity ﬂow deposits a case study of the yanchang formation southern ordos basin china abstract the tight oil sandstone reservoir of the upper triassic yanchang formation is one of the main targets for hydrocarbon exploration in the ordos basin china sandstones of the upper triassic yanchang formation within lacustrine deep water gravity ow deposits are characterized by ultralow porosity ultralow permeability and complex diagenetic alterations and sedimentary lithofacies however the diagenetic alterations and their controls on the reservoir quality of the chang 6 tight sandstones remain poorly understood this study integrated a variety of techniques such as casting thin section analysis scanning electron microscopy sem back scattered electron imagery bse x ray diffraction xrd cathodoluminescence cl microscopy and fluid inclusion to investigate the lithofacies diagenetic history and diagenetic intensity and also evaluate their controls on reservoir quality the research results indicated that the chang 6 sandstones exhibit variable intensity of diagenetic alterations among the various lithofacies which leads to variable reservoir quality mechanical compaction was the most important factor reducing primary porosity sandstones of the ss lithofacies siltstone to very fine grained sandstones with graded bedding or ripple laminations showed the highest loss of primary porosity carbonate cements were commonly present in sandstones of the sc fine grained and cross bedded sandstones and sm fine grained and massive sandstones lithofacies near the sandstone mudstone bounding surface sandstones with more authigenic illite rims were able to resist compaction to some extent and were favorable to the preservation of porosity however abundant pore filling illite aggregates commonly bridged pore throats causing a significant reduction in reservoir quality feldspar dissolution porosity leads to a slight enhancement in reservoir quality intergranular pores and feldspar dissolution pores are most abundant in the sandstones away from the sandstone mudstone bounding surface of the sc lithofacies resulting in the best reservoir quality which is followed by sandstones of the sm lithofacies ultimately four evolution patterns of diagenetic alterations that formed best moderate or poor reservoir quality were summarized by linking diagenetic alterations to lithofacies the research results are conducive to the evaluation of reservoir quality and to understanding the genetic mechanisms of tight sandstones so they should facilitate hydrocarbon exploration and production in similar lacustrine deep water gravity ow reservoirs

reservoir characterization of a tight oil reservoir the middle jurassic upper shaunavon member in the whitemud and eastbrook pools sw saskatchewan abstract new horizontal drilling and multi stage fracture completion technology have proven successful in unlocking hydrocarbons from previously uneconomic reservoirs in this paper we investigate the application of this new technology to a medium gravity oil sandstone reservoir to enhance the poor oil recovery within the pool but also to evaluate if the pool boundaries can be expanded petrophysical well logs were integrated with detailed core descriptions thin sections and core analysis data to provide insight to the reservoir characteristics and factors controlling production reservoir distribution depositional environments and lateral extent of depositional fairways for the reservoirs the middle jurassic upper shaunavon b sandstone is the main reservoir in the studied whitemud and eastbrook pools in southwest saskatchewan the reservoirs are composed of mixed siliciclastic carbonate shallow marine shoreface deposits which have a strike trend northeast southwest although the pools were discovered in 1953 and 1966 and have cumulative production of 3 3 mmbbls of medium gravity 22 api oil estimated oil recovery is less than 4 the upper shaunavon b sandstone has two main reservoir facies shoreface sandstones with permeabilities in the 0 1 10 md range and relatively thin but high permeability 10 1000 md coquina beds until recently wells targeted mainly the high permeability coquina for its higher production rates and as a means to drain the associated thick lower permeability shoreface sandstone reservoir this study evaluates the upper shaunavon b shoreface sandstone reservoir quality by examining the reservoir properties heterogeneity connectivity and pore volume of the flow units based on core and petrophysical data comparison of production data from wells intersecting both facies of the upper shaunavon b versus wells where the underlying high permeability coquina facies is absent allows a perspective on the impact that the coquina has on the recovery factor in both reservoir types integration of petrophysical well logs detailed core descriptions thin sections and core analysis data provide insight to the facies interpretation reservoir distribution and lateral extent of depositional fairways for both units reservoir characterization of the lower permeability siliciclastic facies at the whitemud and eastbrook pools coupled with recent advances in horizontal drilling and completion technology show that additional drilling opportunities exist within the pools to improve oil recovery but also that oil saturated sandstone reservoirs exist outside the boundaries of the pools recent successes with multi stage fracturing of horizontal wells have confirmed the findings of this study

diagenetic constraints on heterogeneous reservoir quality assessment a triassic outcrop analog of meandering fluvial reservoirs reliable modeling of meandering fluvial reservoirs is challenging because of the heterogeneity in magnitude and pattern of porosity and permeability related to depositional and diagenetic features early mechanical and chemical alterations proceed along different pathways directly related to depositionally governed differences in textural and compositional parameters in a well constrained sedimentological framework and with relatively homogeneous conditions of detrital composition this study aims to determine the effect of depositional fabric on early diagenetic processes and their collective effect on petrophysical properties pore size distribution open porosity and permeability a high resolution qualitative and quantitative petrographic analysis is conducted on 22 fine to very fine grained sandstones from the main meandering fluvial facies of the channel center and margin point bar lower middle and upper scroll bar and chute channel of a triassic outcrop analog the occurrence of small scale internal heterogeneity associated with detrital matrix and suspension settling laminae favors the compaction process and hinders early pore filling cement precipitation that helps the preservation of primary porosity multivariate statistical treatment of data demonstrates that large 1 m and well connected primary intergranular pores are the main contributors to permeability in the more heterogeneous samples the distribution of the finer grained sediment fraction is strongly facies related as a result of hydraulic sorting better understanding of linkages between depositionally predictable features and diagenetically induced heterogeneity may lead to realistic reservoir models and enhanced effectiveness of exploitation and bypassed oil recovery strategies