a model for fibrous illite nucleation and growth in sandstones we have developed a model for the formation of fibrous illite in sandstones where kaolinite is a primary reactant and potassium is derived from in situ k feldspar grain dissolution or imported into the model reference frame illite fiber nucleation and growth are modeled using arrhenius expressions that consider saturation state in addition to temperature and time nucleation occurs on pore walls and muscovite and detrital illite may be defined as energetically favorable substrates the model is integrated with other touchstone models to account for the influence of other diagenetic processes on surface area and reactant volumes and to provide input for permeability simulations we evaluated the illite model performance on two data sets 1 jurassic quartzose samples from offshore mid norway with maximum temperatures ranging from 108 to 173c 226 to 343f and 2 miocene lithic samples from offshore southeast asia that have maximum temperatures ranging from 157 to 182c 315 to 360f the model matches measured abundances of illite kaolinite and k feldspar in both data sets using identical kinetic parameters predicted k ar ages are consistent with available data given uncertainties associated with detrital contaminants although no illite particle size data are available from the analyzed samples modeled crystallite thicknesses from the norway data set are comparable to published measurements of 0 004 to 0 012 m from north sea samples with similar temperature histories

kinetic constraints on illitization reactions and the effects of organic diagenesis in sandstone shale sequences abstract based on water rock interaction modelling and kinetic considerations the present study is aimed at testing the impact of organic matter maturation on two kinds of diagenetic reactions leading to the alteration of the petrophysical properties of sandstones 1 clay mineral conversion to illite with k feldspar being a local potential source of k and 2 dissolution precipitation processes produced in sandstones by the action of water soluble organic species derived from adjacent shales assuming firstly that the chemical reactions take place in closed systems the nature and timing of diagenetic reactions in marine sandstone shale formations were modelled for a 50 120 c temperature range in order to improve understanding of the factors that control the illitization reaction with k feldspar coexisting with aluminous clay illite is modelled here as a muscovite type mineral we tested the effects of an energy barrier on illite growth by allowing or preventing the muscovite illite precipitation reaction to occur while using several illitization reaction rates we also compared the stable mineral parageneses predicted for organic material free systems with those predicted in the case of organic diagenesis release of co 2 ch 4 acetic and oxalic acids similarities and discrepancies between numerical results and natural mineral assemblages suggest that the illitization reaction depends on the nature of the reacting clays kaolinite conversion to end member illite involves high energy conditions 2 kcal mol 1 which are not met when the pore water equilibrates with the mineral matrix from undersaturated conditions in a closed system to overcome this barrier the fluid should be oversaturated with respect to k feldspar an external source of k or a ph increase in an open system is necessary for this reaction no particular effect of organic diagenesis on this reaction was found in the present study on the other hand smectite to illite conversion involves a lower energy barrier and can operate in closed systems where k feldspars are the source of k the maturation of organic matter may speed up the smectite to illite conversion rate by increasing the gibbs free energy of illite growth interactions between sandstone and shale were examined by modelling the transfer of aqueous species of organic origin from shale to sandstone fluid expulsion from shale had little or no effect on diagenesis in adjacent sandstones during each flushing cycle mainly because organic protons and ligands were neutralized in the source rock however the diffusion of shale derived cations through sandstone as organometallic complexes mg ca fe al appears to be an efficient process during carbonate cementation in sandstones where oxidizing conditions enhance the decomposition of such complexes

making diagenesis obey thermodynamics and kinetics the case of quartz cementation in sandstones from offshore mid norway calculation of the quantity and distribution of quartz cement as a function of time and temperature depth in quartzose sandstones is performed using a coupled dissolution diffusional transport precipitation model this model is based on the assumptions that the source of the silica cement is quartz surfaces adjoining mica and or clay grains at stylolite interfaces within the sandstones and the quantity of silica transport into and out of the sandstone by advecting fluids is negligible integration of the coupled mass transfer transport equations over geologically relevant time frames is performed using the quasi stationary state approximation results of calculations performed using quartz dissolution rate constants and aqueous diffusion coefficients generated from laboratory data are in close agreement with both the overall porosity and the distribution of quartz cement in the middle jurassic garn formation only after optimizing the product of the effective surface area and quartz precipitation rate constants with the field data when quartz precipitation rate constants are fixed to equal corresponding dissolution rate constants the effective surface area required to match field data depends on the choice of laboratory generated quartz rate constant algorithm and ranges from 0 008 cm 1 to 0 34 cm 1 in either case these reactive surface areas are 2 to 4 orders of magnitude lower than that computed using geometric models

authigenic potassium feldspar a tracer for the timing of palaeofluid flow in carbonate rocks northern calcareous alps austria

wide angle seismic constraints on the internal structure of tenerife canary islands abstract we have used wide angle seismic data to constrain the internal structure of tenerife canary islands the experiment was designed as a seismic fan profile to detect azimuthal variations in the seismic structure of the volcanic edifice and its flanks seismic energy was generated using a 75 l airgun array on board the rrs charles darwin fired every 40 s along a quasi circular profile around the island of tenerife centered on teide volcano we present the results obtained from the data recorded by five portable land stations distributed on the island the travel times indicate that the averaged p wave velocity within the volcanic edifice is greater than 6 km s the observed travel times were reduced to residual travel times by removing the effects of variations in the bathymetry along the profile variations in the shot receiver distance and from local heterogeneities negative residual travel times up to 0 8 s in amplitude indicate that the southwestern part of tenerife is characterized by a high p wave velocity zone coincident with a gravity maximum that was previously modeled as a high density body forming the core of an old large mafic volcano we estimate velocities greater than 7 3 km s within the anomalous body suggesting that it represents an intrusive plutonic complex this high velocity high density body may have played an important role in the evolution of tenerife buttressing las canadas edifice and preventing the occurrence of landslides in the southern and western areas of tenerife the bathymetric high between tenerife and la gomera is associated with travel time delays up to 0 4 s suggesting that it may be composed of large deposits of lava flows and volcaniclastic materials probably erupted from the shield massifs of teno roque del conde and la gomera the post shield volcanic zones of santiago and dorsal rifts also seem to be characterized by moderate high p wave velocities

chemistry of oil field brines in relation to diagenesis of reservoirs 1 use of mineral stability fields to reconstruct in situ water composition example of the mahakam basin abstract during mineral diagenesis the chemical composition of pore water can be strongly influenced by mineral reactions especially under geological conditions where water rock ratios are low to model and eventually to predict diagenesis it is important to have an understanding of formation water composition however available water analyses in many basins are not complete enough for this purpose in most cases reliable values for ph dissolved silica and aluminium are lacking such data can be reconstructed using various relations developed herein these data are constrained by petrographic observations because of their well preserved or authigenic character some alumino silicates are considered as relatively stable and can be thought of as effectively saturated with respect to them the saturation state of the other minerals of the matrix can be discussed according to these constraints the sub arkosic series of the mahakam basin resevoirs mio pliocene are used as a reference example to perfect a method capable of reconstructing consistent compositions of diagenetic waters suitable for input into diagenetic modelling

origin and rate of pedogenic carbonate accumulation in saskatchewan soils canada abstract limited information is available about inorganic carbon stocks in the boreal regions the objective of this study was to determine the amount and accumulation rate of pedogenic carbonate pc in soils of the boreal grassland and forest regions of saskatchewan canada the storage of pedogenic carbonate increases from 134 kg m 2 in semiarid grassland brown soils in the southwest to 165 kg m 2 in the northeast under forest gray soils within the time decreasing from 17 000 years in the southwest to 11 500 years in the northeast the rate of pedogenic carbonate accumulation likewise increases from 8 3 to 14 3 g m 2 year 1 in the same direction the results show that the soils of the prairies and forests have sequestered 1 4 times more c in the form of pedogenic carbonates than as organic matter stable carbon isotope values of pedogenic carbonate decreases from southwest to northeast this is consistent with decreasing representation of c4 plants in the vegetation in the same direction the rate of pedogenic carbonate accumulation increases with increasing annual precipitation this suggests that the rate limiting factor to precipitate with co2 is ca in the boreal region of canada silicate weathering is more significant in luvisols alfisols suggesting that they may be most effective in truly sequestering additional amount of c in the soil

near surface k feldspar precipitation in cretaceous sandstones from the potiguar basin northeastern brazil abstract the cretaceous fluvial sandstones of the acu formation potiguar basin northeastern brazil contain abundant very early authigenic k feldspar overgrowths around detrital orthoclase and microcline grains detailed optical and cathodoluminescence petrography scanning electron microscopy and electron microprobe analyses provided information about the conditions and timing of precipitation of these overgrowths as well as of the associated diagenetic phases the overgrowths are optically discontinuous with the detrital grains untwined nonluminescing and were formed clear on grain surfaces under phreatic conditions the overgrowths commonly show a rhombohedral sanidine habit range in thickness from about 0 4 to 1 0 mm are chemically pure kalsi3o8 and constitute up to 6 of the whole rock the extremely early origin of the k feldspar overgrowths is indicated by their coating of mechanically infiltrated smectitic clays authigenic smectite rims booklet and vermicular aggregates of kaolinit

postorogenic origin of the stratiform cu mineralization at lufukwe lufilian foreland democratic republic of congo the central african copperbelt which stretches across the border between zambia and the democratic republic of congo is one of the largest sediment hosted stratiform cu co provinces in the world the triangular shaped lufilian foreland is located to the northeast of the copperbelt recently sediment hosted stratiform copper occurrences have been explored in the foreland including the kinkumbi prospect in the lufukwe anticline although the stratiform copper mineralization in the copperbelt is mainly concentrated in the roan group sedimentary rocks where it is commonly associated with cobalt the lufilian foreland copper mineralization occurs in sedimentary rock units of the nguba and kundelungu groups where it is mainly associated with silver this paper examines the metallogenesis of the stratiform copper mineralization at lufukwe the lufukwe anticline is situated in the eastern part of the lufilian foreland and is composed of neoproterozoic sedimentary rocks belonging to the katanga supergroup the kinkumbi prospect a sediment hosted stratiform copper silver occurrence is located in the northern part of the western flank of the anticline this part of the anticline is characterized by disseminated copper silver mineralization hosted in the lower 10 to 15 m of the monwezi sandstone nguba group a comparison between the location of high copper grades in surface samples and boreholes and the location of structural lineaments visible on aster images indicates that the mineralization is spatially related to northeast southwest to east northeast west southwest strike slip faults these faults are nearly perpendicular to the strike of the host rock and postdate both the lufilian folding and deposition of the entire katanga supergroup the monwezi sandstone was subjected to strong compaction and silica cementation authigenic quartz overgrowths followed by intense feldspar dissolution which resulted in a well developed secondary porosity represented by dissolution cavities copper sulfides are mainly concentrated in these cavities and partially replace the detrital grains the copper mineralization is both hypogene chalcopyrite bornite and chalcocite and supergene digenite covellite and minor native copper with malachite and chrysocolla as the main oxidation products point counting and grain size measurements demonstrate that the sandstone horizons with high copper content 1 25 cu are those with a detrital grain size larger than 175 m more than 35 percent altered feldspars and little or no fine grained matrix microthermometry of fluid inclusions indicates that the authigenic quartz overgrowths precipitated from a moderate temperature 80 130 c high salinity 18 8 23 4 wt cacl2 equiv h2o nacl cacl2 fluid the hypogene copper silver mineralization was deposited from a hot 120 180 c and low to moderate salinity 1 9 7 7 wt nacl equiv h2o nacl fluid with a general trend of increasing homogenization temperatures with increasing salinities the interpretation of the available structural stratigraphic petrographic and fluid inclusion microthermometric data constrain the timing of the mineralization to a time after the lufilian folding and deposition of the entire katanga supergroup the data presented support a postorogenic fluid mixing model in which the mineralization is related to the mixing of a copper rich mineralizing fluid with a temperature 180 c and salinity 7 7 wt percent nacl equiv likely migrating upward along northeast southwest to east northeast west southwest oriented strike slip faults with a colder low salinity reducing fluid in the monwezi sandstone the location and distance between the northeast southwest to east northeast west southwest faults strongly influenced the spatial distribution of the copper mineralization in the anticline and the variability in grain size and composition of the monwezi sandstone caused the preferential lateral migration of the mineralizing fluid through the lower 10 to 15 m copper precipitation was possibly induced by reduction by preexisting noncopper sulfides pyrite and arsenopyrite and hydrocarbons and by the drop in fluid temperature and salinity based on this research the areas with dominant northeast southwest to east northeast west southwest structural lineaments are considered favorable sites for further copper exploration in the lufilian foreland especially where these lineaments cut previously deformed katanga sediments coarse grained sandstones with no fine matrix that underwent intense feldspar dissolution are the most promising host rocks for the late disseminated stratiform copper mineralization in the lufilian foreland airborne gamma ray spectrometric surveys could be used as a powerful exploration tool for targeting ore related k depleted zones in these sandstones

volcanic evolution of the island of tenerife canary islands in the light of new k ar data new age determinations from tenerife together with those previously published 93 in all provide a fairly comprehensive picture of the volcanic evolution of the island the oldest volcanic series with ages starting in the late miocene are formed mainly by basalts with some trachytes and phonolites which appear in anaga teno and roque del conde massifs in anaga ne three volcanic cycles occurred one older than 6 5 ma a second one between 6 5 and 4 5 ma with a possible gap between 5 4 and 4 8 ma and a late cycle around 3 6 ma in teno nw after some undated units the activity took place between 6 7 and 4 5 ma with two main series separated by a possible pause between 6 2 and 5 6 ma in the zone of roque del conde s the ages are scattered between 11 6 and 3 5 ma between 3 3 and 1 9 ma the whole island underwent a period of volcanic quiescence and erosion the large canadas volcano made up of basalts trachytes and phonolites was built essentially between 1 9 and 0 2 ma to the ne of this central volcano linking it with anaga is a chain of basaltic emission centers with a peak of activity around 0 8 ma the canadas caldera had several collapse phases associated with large ignimbrite emissions there were at least an older phase more than 1 ma old on the western part of the volcano and a younger one less than 0 6 ma old in the eastern side the two large valleys of guimar and la orotava were formed by large landslides less than 0 8 ma ago and probably before 0 6 ma ago the present canadas caldera was formed by another landslide less than 0 2 ma ago this caldera was later filled by the huge teide volcano which has been active even in historic times during the same period a series of small volcanoes erupted at scattered locations throughout the island the average eruptive rate in tenerife was 0 3 km3 ka with relatively small variations for the different eruptive periods this island and la gomera represent a model of growth by discontinuous pulses of volcanic activity separated by gaps often coinciding with episodes of destruction of the edifices and sometimes extended for several million years the neighbouring gran canaria on the other hand had an initial rapid shield building phase during which more than 90 of the island was built and a series of smaller pulses at a much later period a comparison between these three central islands indicates that the previously postulated westward displacement in time of a gap in the volcanic activity is valid only as a first approximation several gaps are present on each island overlapping in time and not clearly supporting either of the models proposed to explain the evolution of the canaries

diagenetic evolution and its impact on reservoir quality of tight sandstones a case study of the triassic chang 6 member ordos basin northwest china abstract the triassic chang 6 member sandstones are important oil reservoirs in the ordos basin of north western china and are actually considered to be typical tight sandstone reservoirs diagenetic alterations play a prominent role in considerably impacting the reservoir quality in this study an integrated approach of thin sections scanning electron microscopy sem x ray diffraction xrd cathodoluminescence cl fluid inclusions laser raman spectrographic analysis and stable isotope analysis was applied to examine the diagenetic history recorded in the chang 6 tight sandstones and investigate the influences of diagenesis on reservoir quality the sandstones consist of fine grained moderated to well sorted arkoses q48 5f40 9r10 6 and lithic arkoses q54 3f29 1r16 6 with an average porosity and permeability of 9 10 and 0 39 md respectively the sandstones have undergone complex diagenetic processes dominant eogenetic features include mechanical compaction leaching of feldspar in meteoric water chlorite coats originating from the transformation of precursor clays and precipitating directly from interstitial water calcites filling intergranular pores as poikilotopic cements and quartz and albite overgrowths on surfaces of grains subsequent mesogenetic events include ankerite cements filling porosity and replacing framework grains extensive dissolution of feldspars and precipitation of kaolinites due to emplacement of organic acids and secondary quartz overgrowths in the late period of mesogenesis early calcite is characterized by 13c 13cpdb ranging from 3 45 to 0 30 mean 2 00 and 18o 18opdb varying from 16 70 to 5 80 mean 10 50 while late ankerite is rich in 12c 13cpdb ranging from 10 71 to 0 80 mean 3 58 and 16o 18opdb varying from 24 30 to 15 80 mean 19 93 moreover calcite hosts single liquid fluid inclusions two phase fluid inclusions are contained in ankerite cements with mean homogenization temperature th of 96 0 c and salinity estimates from 11 47 to 18 96 eq wt nacl these data indicate that the calcite originated from meteoric water and the ankerite was associated with organic matter and recrystallization of the early calcite cements furthermore the metallic ions such as fe2 mg2 and ca2 required for ankerite precipitation were produced through alterations of volcanic fragments feldspars and biotites in comparison compaction has more important role than cementation in the loss of original porosity although cementation exerts enormous influence on reducing porosity quantitatively the compactional porosity loss reaches 54 9 while the cementation porosity loss accounts for up to 42 8 carbonate cements and the other authigenic products quartz and albite overgrowth and kaolinite mostly fill intergranular pores thus reduce porosity chlorite coats have effects in inhibiting compaction and restraining the development of quartz overgrowth thereby protect the intergranular porosity to some extent early secondary porosity was enhanced by leaching and dissolution of feldspar in the eogenetic period however these processes did not increase the net porosity in the mesogenetic stage

deep burial dissolution of k feldspars in a fluvial sandstone pentland formation uk central north sea the pentland formation of the uk central north sea is a quartzite in a sequence of more arkosic sandstones provenance sensitive heavy mineral indices are interpreted to indicate that it was probably derived by erosion of arkosic sediments which also supplied the arkosic marine sandstones of the contemporaneous fulmar formation a lack of apatite within the pentland formation suggests that the feldspars could have dissolved during exposure to groundwaters during very shallow burial however petrographic and geochemical evidence supports survival of at least some of the feldspar to burial depths in excess of at least 2 km when the sandstones had been stabilized against compaction by quartz cements or overpressure abundant kaolin which has not reacted to form illite is preserved at burial depths in excess of 4000 m suggesting an unusual lack of available potassium there is a strong contrast in diagenetic pathways with the overlying marine fulmar formation which most probably had the same initial composition but in which kaolin is absent and fibrous illite is present it is suggested that a lower concentration of potassium and aluminium within the pentland formation compared with the probable source and the comparably sourced fulmar formation represents export of k from the sands on a metre scale

natural restoration of soils on mine heaps with similar technogenic parent material a case study of long term soil evolution in silesian krakow upland poland abstract the study focused on the variability in properties and pedogenesis of soils located at post mining sites in the old industrial area in the silesian krakow upland southern poland the investigated sites were comparable in terms of zn pb mining history soil texture and climate but differed in duration of pedogenesis which started after the waste materials were accumulated and covered 30 70 100 and about 400 years of self restoration a wide spectrum of soil parameters including zn pb and cd contents dehydrogenase activity pores space and aggregate formation organic matter decomposition were studied by chemical and micromorphological image analyses with the aim of tracing the evolution of soils and checking if the results of image analysis could be integrated with results obtained by chemical and biological determinations stepwise progressive regression equations were obtained to establish the parameters that varied over time zn pb and cd contents exceeded several times permissible values in all soils studied the evolution of these soils was significantly different from each other during the process of self restoration of the soil the contents of organic carbon and total nitrogen available potassium and phosphorus including dehydrogenase activity increased with increasing age of soils pedogenesis resulted also in the increasing amounts of aggregates of small sizes which were set close to one another together with narrow pores which was able to store water a synchronisation between soil properties obtained by chemical biological and micromorphological analyses indicating their usefulness for the demonstration of temporal changes

features of crustal structure under the canary islands abstract the data and interpretation of a seismic refraction project carried out in the canary islands in 1977 and 1979 are presented the moho is reached at about 15 km under fuerteventura gran canaria and tenerife whereas under lanzarote a value of 11 km has been found the velocity at the surface varies even within one island from 2 8 to 4 4 km s there are variations in the velocity of the main crustal layer under the volcanic deposits a continuous velocity depth function seems to be more appropriate for the island of tenerife contrary to fuerteventura lanzarote and gran canaria which seem to have a layered structure there is evidence for pronounced structural differences between lanzarote and fuerteventura the mantle velocity has a value of about 8 0 km s under the western islands whereas a very low value of 7 4 km s has been found under lanzarote and fuerteventura despite the clear structural differences between the islands our results leave little doubt about the oceanic character of all the islands the differences between the eastern and western group may be due to the islands being situated close to the african continental margin the seismic velocities under the volcanic deposits do not support the idea of a common basement for all the islands they rather suggest independent volcanic edifices finally a comparison of the structure of the crust under the canary islands with that under other volcanic islands reveals remarkable similarities

amendments with organic and industrial wastes stimulate soil formation in mine tailings as revealed by micromorphology abstract mine tailings are inhospitable to plants and soil organisms because of low ph and poor soil organic matter contents vegetation establishment requires a soil system capable of supporting the nutrient and water requirements of plants and associated organisms the objective of this study was to understand the influence of added organic and industrial wastes to the formation of soils in degraded landscapes left behind by past mining activities specifically we stimulated the build up of soil organic matter som and the accumulation of calcite in mine tailing deposits we amended field experimental plots with pig manure pm sewage sludge ss in combination with blanket application of marble wastes mw soil samples were collected for physical and chemical analyses two years after the addition of industrial wastes three years after amendments we took undisturbed samples for micromorphological analysis soil ph increased from 2 7 to 7 4 due to dissolution of calcite from mw amendment the acidity in tailings and low rainfall in the study area precipitated the secondary calcite as infillings within the 0 4 cm layer total organic carbon toc increased from 0 86 to 2 5 g toc kg 1 soil after 24 months since the application of amendments the build up of som resulted to stable som calcite complex as dense incomplete infillings mixed with secondary calcite and cappings on calcite particles from mw addition these som cappings provide water and nutrient to support initial seedling establishment in mine tailings we attribute the granular structure of amended materials to soil organisms e g earthworm activity involved in the decomposition of plant materials we suggest that any organic matter amendments to acidic mine tailing deposits must be combined with calcium carbonate rich materials to accelerate the build up of som to accelerate the establishment of functional ecosystem characterized by among others the presence of healthy soils with granular microstructure

reservoir architecture and diagenesis in downthrown fault block plays the lowlander prospect of block 14 20b witch ground graben outer moray firth uk north sea

a diagenetic study of intrabasaltic siliciclastics sandstones from the rosebank field abstract the rosebank field contains producible hydrocarbons from paleocene eocene intrabasaltic fluvial and shallow marine siliciclastic sandstone reservoirs despite close proximity to volcanic lithologies the siliciclastic sandstones display very good reservoirs properties with permeability in the darcy range and porosity values ranging from 19 to 23 preservation of high quality reservoir properties is the result of low quantities of volcanic minerals in the siliciclastic sandstones and limited element diffusion e g fe and mg from adjacent basalts into siliciclastic reservoir sandstones the low content of volcanic derived detritus is most likely a result of the main sediment source being situated outside the volcanic terrain the effect is that formation of clay minerals smectites and or chlorites reducing permeability and porosity is low in contrast to the siliciclastic sandstones the pore space of the volcaniclastics is occupied by authigenic clays chlorite smectite and carbonates calcite and mg calcite resulting in poor reservoir quality this paper demonstrates that high quality reservoirs can be found in intrabasaltic siliciclastic reservoirs in depth analyses of core samples show that authigenic phases formed during progressive burial with temperatures up to 120 c the suite of diagenetic phases in siliciclastic sandstones between wells and the different colsay units vary and are interpreted to result from differences in pore water chemistry and or detrital mineralogy laumontite was formed as a late stage authigenic mineral restricted to cored colsay 1 and 3 units in well 213 26 1z and has not been observed in the neighbouring 213 27 2 core which may be explained by differences in pore water ph or co2 partial pressure the occurrence of laumontite is often associated with poor reservoir quality but due to the patchy distribution of this mineral in the rosebank reservoir sands it appears not to have affected reservoir quality

the potassic sedimentary rocks in gale crater mars as seen by chemcam on board curiosity key points mean k2o abundance in sedimentary rocks 5 times higher than that of the average martian crust presence of alkali feldspars and k phyllosilicates in basaltic sedimentary rocks along the traverse the k bearing minerals likely have a detrital origin

diagenetic study on the neogene sedimentary basin as paleoenvironmental proxy data for an offshore co2 storage project in pohang basin south korea abstract as the importance of reducing greenhouse gas emissions has attracted much attention pohang basin has been identified as a co2 geological sequestration test site in korea this study aims to provide a better understanding of the diagenetic history of pohang basin through mineralogical and microstructural analyses with a focus on tectonic evolution in the reservoirs offshore of the pohang basin during the east sea sea of japan opening in the miocene we focused on two sections in the core that are considered to be target layers for co2 storage samples were analyzed for texture observation and chemical analysis the major mineral components include quartz feldspar illite chlorite kaolinite and calcite and the minor mineral components include pyrite siderite iron oxide and titanium oxide the detrital grains are composed of quartz and feldspar and the primary pore is cemented with kaolinite i calcite pyrite and chlorite the analyzed chlorites are differentiated into five types by their textural characteristics such as pore filling pf pore filling with kaolinite pf k pore lining pl replaced rd and detrital da chlorites and they were all categorized as either brunsvigite diabantite or ripidolite generally the dissolution of feldspar is observed for all samples the diagenetic temperature is estimated by chlorite geothermometry to be 170 c on average which is higher than the present temperature of pohang basin 55 60 c considering all results together the target layers have undergone diagenetic processes from early diagenesis eogenesis to late diagenesis mesogenesis and uplift related diagenesis telogenesis after sedimentation of the pohang basin kaolinite i calcite and pyrite were cemented in the pore and detrital mica was replaced with chlorite as the burial depth increased the dissolution of feldspar advanced the high temperature resulting from the chlorite geothermometry could be influenced by the burial heat as source also the neogene volcanism and related tectonics known as eoil orogeny could become a heat source capable of high temperatures and a high geothermal gradient and tectonically compressional environment may have influenced fluid flow after the uplift kaolinite ii was precipitated in both an intergranular pore and intragranular pore as a result of dissolution the effects of diagenesis such as cementation and dissolution in co2 reservoir rocks could be an important factor in assessing the appropriacy of predicting potential charge after injection in carbon capture and storage project

pore pressure and reservoir quality evolution in the deep taranaki basin new zealand abstract the palaeocene fluvial to shallow marine sandstones of the farewell formation are an important proven hydrocarbon reservoir in the taranaki basin new zealand the kapuni deep 1 well was drilled to target farewell formation sandstones in the deeper overpressured 5000 m 3000 psi 21 mpa sections of the onshore manaia graben of the taranaki basin however the farewell formation sandstones display anomalously low measured helium porosities 1 4 5 and intergranular volumes 6 11 even for their present day close to maximum burial depth c 5000 m one dimensional burial history modelling demonstrates initial rapid burial leading to significant porosity reduction via mechanical compaction enhanced by poor sorting angular grain morphology and the presence of ductile grains which allowed efficient packing and plastic deformation low intergranular volume igv anhedral nature of quartz overgrowths a general lack of fluid inclusions and poor crystalline clay mineral content indicate that early burial compactional processes significantly influenced reservoir quality the lack of mudstone to siltstone grade lithologies within the overlying eocene section inhibited the early or shallow onset of overpressure in the farewell formation one dimensional basin modelling has shown that rapid pliocene subsidence related to exceptionally high sedimentation rates generated overpressure through disequilibrium compaction in the overlying oligocene to early miocene section during the past 6 ma however the late and deep 3000 m onset of overpressure had no effect on arresting porosity loss in the farewell formation continued compaction of farewell formation sandstones after dissolution of early carbonate cements of co2 rich fluids creates zones of extremely low permeability which have the potential to act with interbedded shales to form pressure seals as seen in the kapuni field

the influence of variations in illite morphology on the permeability of middle jurassic brent group sandstones cormorant field uk north sea abstract sem examination of core samples from brent group sandstones in the cormorant field reveals that critical point drying preserves delicate illite morphologies that are damaged during air drying this damage may lead to an increase in permeability as defined by the drying effect air permeability air dried air permeability critical point dried the cormorant reservoir sandstones contain four illite morphologies early diagenetic pore lining illite formed before hydrocarbon emplacement and occurs ubiquitously pore bridging illite blooming illite and illite that replaces kaolinite all formed later and occur preferentially at or below the oil water contact damage to these late illites causes an average drying effect of 3 5 and explains why measured permeabilities predict higher water injection rates than occur in the field comparison with data from other reservoirs reveals that the drying effect is influenced by variations in illite particle dimensions as well as illite morphology tem shadowing techniques reveal that illite particle sizes describe a trend from small particles in reservoirs with large drying effects to large particles in reservoirs with small drying effects these size variations probably reflect differing illite growth rates permeability in illite bearing sandstones thus reflects not only the amount of illite present but also the size of the individual particles and their morphology

clay cutans and the origin of illite rim cement an example from the siliciclastic rotliegend sandstone in the dutch southern permian basin

palaeo climate controlled diagenesis of the westphalian c d fluvial sandstones in the campine basin north east belgium the westphalian c and d fluvial sandstones in the campine basin north east belgium are potential reservoirs for the sequestration of co2 and interesting analogues of the hydrocarbon reservoirs in the southern north sea although these sandstones were deposited in a relatively short period of time their reservoir properties and mineralogical compositions are very different a petrographic study complemented with stable isotope analyses fluid inclusion microthermometry and x ray diffraction analyses of the clay fractions of the sandstones which were sampled from deep boreholes 1000 m in the campine basin revealed that these differences are related mainly to the climate at the time of deposition the most important eogenetic processes affecting the westphalian sandstones were the generation of a pseudomatrix by physical compaction of al silicates and lithic fragments that were strongly altered by extensive meteoric leaching kaolinitization of unstable silicates and precipitation of siderite these processes had a detrimental influence on the reservoir properties of westphalian c sandstones but their impact on the westphalian d sandstones was minimal the difference is assumed to be related to the climate at the time of deposition which changed from tropical humid in the westphalian c to semi arid arid during the late westphalian d both the westphalian c and d sandstones were affected by similar mesogenetic processes mesogenetic quartz cementation resulted from chemical compaction and illitization of kaolinite k feldspar and smectitic clays illitization of kaolinite was controlled by the available quantities of co existing kaolinite and k feldspar and mainly affected the westphalian d sandstones illitization of k feldspar was controlled by the k feldspar content it had a much larger impact on the reservoir properties of the westphalian d as in these sandstones k feldspar was less affected by eogenetic alteration the illitization of smectitic clays resulted in illite quartz and ankerite cementation in both reservoirs this process had a more important impact on the westphalian c reservoir since cementation here also resulted from smectite to illite conversion in the interbedded and underlying shales the effect of mesogenetic alterations on the reservoir properties was much less drastic than the impact of eodiagenesis mesogenetic alterations do exert a significant control on the properties of the westphalian d the vast impact of eodiagenesis on the westphalian c sandstones made them less susceptible to mesogenetic alteration the effect of telogenetic processes on the porosity and permeability of the westphalian sandstones was small and restricted to the top reservoir intervals that directly underlie the cimmerian unconformity no significant telogenetic alterations related to the variscan unconformity were observed

an isochemical model for formation of authigenic kaolinite k feldspar and illite in sediments abstract although thermodynamic calculations indicate a narrow range of conditions for coprecipitation of kaolinite and k feldspar coexistence of authigenic kaolinite and k feldspar is common in jurassic sandstones of the north sea this paper shows that the coexistence of authigenic k feldspar and kaolinite may indicate that this narrow range of conditions did prevail and that the system behaved as a closed system these conditions are presence of muscovite in the sediment pore waters supersaturated with respect to quartz and temperatures lower than 50 c at higher temperatures the authigenic kaolinite and authigenic k feldspar may react and form authigenic illite muscovite and quartz cement the direction of the isochemical reaction is thermodynamically determined by the degree of supersaturation with respect to quartz in the formation water published data on the degree of supersaturation with respect to quartz in formation waters suggest that the illitization of kaolinite may take place at temperatures as low as 50 c much lower than previously believed

pre requisites processes and prediction of chlorite grain coatings in petroleum reservoirs a review of subsurface examples abstract deeply buried reservoirs containing chlorite coated quartz sand grains commonly have higher than expected porosity and permeability although prediction of such positive anomalies still remains elusive a total of 54 published examples based on information and data from 62 scientific papers was collated quantification of some of the most common parameters including depositional environment age and latitude of sand deposition effect on reservoir quality and chemical composition of chlorite is presented the dataset indicates that chlorite coats are found in sandstones deposited in a range of depositional environments but most commonly occur in delta related environments 44 with fluvial environments the second most common 19 age relationships indicate that there is an overall exploration bias in published examples with chlorite coats becoming increasingly common through time the latitude at the time of deposition of sands with chlorite coats is wide 60 n 60 s and indicates that temperate and tropical climates are important for the generation of this clay mineral chlorite can have a variable effect on reservoir quality but is typically positive iron rich chlorites occur overwhelmingly in coastal environments while mixed iron and magnesium rich chlorites are principally found in marine and terrestrial sandstones analysis of these factors suggests that hinterland geology basinal soil development and geochemical weathering and proximity to river systems are essential to the formation of chlorite precursor phases these characteristics have been combined to define situations where chlorite coats were more likely or more unlikely to form these parameters will provide insights into the formation of chlorite and to further refine predictive models for the presence or absence of chlorite coated sandstones

illite distribution and morphology explaining basinal variations in reservoir properties of upper jurassic sandstones danish north sea abstract growth of fibrous illite may destroy an otherwise promising sandstone reservoir even sandstones characterized by microquartz coatings therefore detailed petrographical and diagenetic investigations were performed in order to understand the factors that control illite precipitation and other factors affecting the reservoir properties in the upper jurassic heno formation the heno formation is encountered in large parts of the danish central graben where its lower part the gert member was mainly deposited in back barrier environments and its upper part the ravn member was deposited in a shoreface environment in total 215 core samples from 15 wells were investigated petrographically by optical and scanning electron microscopy this was supplemented by plug porosity and permeability measurements and x ray diffraction of bulk and clay fraction the investigations show among other things that microquartz coatings may help to preserve porosity and permeability whereas the permeability is reduced when microquartz occurs combined with fibrous illite illite precipitation is largely governed by the amounts of k feldspar present during burial consequently the initial abundance of k feldspar in the sediment source area and its alteration during and immediately after deposition in particular during subaerial exposure at sequence boundaries has a major influence on the final reservoir properties of the sandstones the risk of illite precipitation can largely be predicted from the available sediment source material depositional environment and burial depth

reconstructing fluid flow events in lower triassic sandstones of the eastern paris basin by elemental tracing and isotopic dating of nanometric illite crystals lower to middle triassic sandstones from eastern paris basin were buried to a maximum depth of 2500 m at a paleo temperature of about 100 c they contain extensive amounts of authigenic platy and filamentous illite particles similar to those reported in reservoirs generally buried at 3000 to 5000 m and subjected to temperatures of 120 to 150 c to evaluate this unexpected occurrence such sandstones were collected from drill cores between 1825 and 2000 m depth and nanometric sized sub fractions were separated the illite crystals were identified by xrd observed by sem and tem analyzed for their major trace rare earth elements and oxygen isotope compositions and dated by k ar and rb sr illite particles display varied growth features in the rock pore space and on authigenic quartz and adularia that they postdate tem eds crystal chemical in situ data show that the illite lath fiber and platelet morphologies correspond at least to two populations with varied interlayer charges between 0 7 and 0 9 in the former and between 0 8 and 1 0 in the latter the fe fe mg ratio being higher in the platelets except for the deeper conglomerate the paas normalized ree patterns of the illite crystals are bell shaped enriched in middle rees ca carbonates and ca phosphates were detected together with illite in the separates these soluble components yield 87sr 86sr ratios that are not strictly in chemical equilibrium with the illite crystals suggesting successive fluids flows with different chemical compositions the k ar data of finer 0 05 m illite separates confirm two crystallization events at 179 4 4 5 and 149 4 2 5 ma during the early and late jurassic the slightly coarser fractions contain also earlier crystallized or detrital k bearing minerals characterized by lower 18o values the 18o of the finest authigenic illite separates tends to decrease slightly with depth from 18 2 0 2 to 16 3 0 2 suggesting different but contemporaneous crystallization conditions deeper in the section the illite platelets and filaments crystallized in changing physical chemical crystallization conditions induced by fluids flows through the host rock pore system these flow events were probably driven by repetitive rifting episodes of the north atlantic ocean although located several hundreds kilometers away from eastern paris basin and or by fracturing events in the nearby basement of the vosges massif complex relationships between geodynamical events thermal anomalies and advective fluids confirm that remote tectonic activities can impact quiescent basins even if located far from tectono thermal activities by discrete and long distance fluid flows

microgravimetric survey in the caldera of teide tenerife canary islands abstract in this study the first results obtained in a gravimetric exploration in the caldera of teide tenerife canary islands are presented the gravimetric anomalies observed permit us to deduce the existence of a double vault with an important mass deficit centered in the southeast base of the volcano teide that seems to support the hypothesis of a caldera collapse at least for an important part of the present depression

fibrous illite in oilfield sandstones a nucleation kinetic theory of growth fibrous illite is one of the most important cements that grows within sandstones during burial and the only one which is commonly dated using the k ar age technique a small quantity of illite can dramatically reduce porefluid flow rates within a sandstone thus making oil recovery uneconomic illite ages potentially correspond to geological events such as hydrocarbon filling of a sandstone reservoir providing calibration to basin models yet the fundamental processes controlling fibrous illite growth are not understood this contribution presents a new theory for illite growth within sandstones that explains the fibrous morphology of illite the restricted range of illite k ar age dates compared to the age of the host sandstones and the lack of 0 myr old illite reported the growth of fibrous illite as an authigenic cement may be controlled by nucleation kinetics and not by thermodynamic or growth kinetic considerations as has been previously assumed

influence of parent material and grain size on carbonate coatings in gravelly soils palo duro wash new mexico abstract close examination of carbonate coatings found on the bottoms of pebbles from gravelly soils indicates that soil hydraulic conductivity and respiration rate have a strong influence on the carbonate morphology of aridic soils clast size and lithology strongly correlate with coating thickness because of the nature of unsaturated flow within macropores of gravelly soils thicker coatings are found at the bottom of larger clasts coatings are thickest on limestone pebbles that commonly display dissolution features at their tops model values for soil co 2 based on gas diffusion predict soil atmospheric condition where soil water can remain undersaturated with respect to calcite and dissolve calcareous pebbles throughout the depth of the soil profile this coupled with soil hydrology creates a microenvironmental condition where the largest limestone clasts have the thickest coating a second phenomenon that is apparent from close observation of coatings is that soils containing abundant fines and translocated dust in the matrix have continuous coatings continuous coatings are absent however in soils that do not neighbor a dust source or do not have sufficient fines in the matrix in these soils coatings are almost completely absent from sand and granule size particles suggesting that zones of preferential flow in the soil inhibit carbonate precipitation in parts of the soil profile these inconstancies in the continuity and thickness of coatings suggest that stage iii morphology may not develop at the same rate even locally

geochemical constraints from formation water analyses from the north sea and the gulf coast basins on quartz feldspar and illite precipitation in reservoir rocks

diagenesis and pore water evolution in permian sandstones gharif formation sultanate of oman abstract shallow marine coastal plain and fluvial sediments of the lower permian gharif formation in the interior oman sedimentary basin presently range in depth from outcrop in the huqf haushi area to almost 5000 m in the northwest this large depth range results from a varied subsidence history with only minor uplift during the late triassic to early jurassic the degree of diagenetic overprint varies depending on burial history sandstone at shallow depth 2600 m is highly compacted and tightly cemented by quartz carbonate and sulfate minerals this varied diagenesis is caused by increasing temperature with burial by surface water infiltration during the late triassic to early jurassic basin inversion and uplift in the late cretaceous along the southeastern basin margin and obduction of the oman mountains in the late cretaceous depositional pore water was initially of low salinity 50 g l with 18osmow values of 0 5 to 1 5o oo in the marine lower gharif and 2o oo in the arid middle and upper gharif during shallow burial late triassic to early jurassic pore water in the three gharif members changed to high salinity brines 180 g l with 18osmow values of 4 to 7o oo highly saline deep burial pore water with a heavy 18o signature 0 5 5o oo is the result of rock water interactions in a rock dominated system present pore water compositions mainly reflect subsurface dissolution of ara group evaporites precipitation of late diagenetic carbonates and sulfates and recharge of surface water along the uplifted southeastern basin margin

chemistry of oil field brines in relation to diagenesis of reservoirs 2 reconstruction of palaeo water composition for modelling illite diagenesis in the greater alwyn area north sea abstract input data for water composition are required in order to numerically simulate diagenetic episodes in rock dominated closed system modelling the composition of water initially present in the pores has at most only a minor influence on the stability of the system and is controlled by the mineral composition in open system modelling the composition of infiltrating water can play an important role brent water salinities of the greater alwyn area exhibit a regional trend from the north to the south the k cl ratio of these waters varies along two trends it is higher in the north than in the south alkalinity and published pco2 values are used to calculate ph under subsurface conditions very few silica measurements are available aluminium analyses of pore water are not available some reservoirs of the greater alwyn area experienced a major reduction in permeability due to illite and quartz precipitation coeval with kaolinite and k feldspar dissolution saturation of present day brent waters with respect to these minerals is examined the method proposed in part 1 is applied to reconstruct a range of possible compositions for ancient waters in brent reservoirs between several extreme conditions one of these extremes is provided by buffering water with a set of minerals chosen from petrographic considerations the other extremes correspond to reasonable states of over saturation with respect to particular minerals e g quartz and concern the values of dissolved si and al which are the least well characterised concentrations from the routine analyses of formation waters

integration of petroleum engineering studies of producing brent group fields to predict reservoir properties in the pelican field uk north sea abstract diagenetic models and the results of laboratory experiments on cores from producing brent group fields cormorant and tern have been combined to aid prediction of reservoir properties in a deeply buried prospect pelican in cormorant and tern illite particles are thin 20 40 a lath shaped and liable to damage during drying before air permeability measurement leading to erroneously high permeabilities the magnitude of this drying effect k air conventional drying k air critical point drying varies with illite morphology and the timing of hydrocarbon emplacement in tern pore filling illites occur above and below the oil water contact and there is no significant difference in drying effect in cormorant the drying effect is higher below the oil water contact where a diversity of late diagenetic pore filling illite morphologies occur injectivity tests on cores from cormorant indicate that sea water injection will not lead to impairment of reservoir quality as a result of clay dispersal or other rock related phenomena impairment occurred when flooding cores with produced water and was avoided by introducing divalent cations saline brines or approximating in situ equilibrium conditions ph 6 4 this equilibrium point is strongly influenced by the surface chemistry of feldspar and illite rather than the more abundant kaolinite and quartz burial diagenetic replacement of kaolinite by illite will increase this equilibrium towards ph 7 but should not cause impairment during sea water injection into deeper reservoirs pelican contains abundant pore filling illite k ar age dates 44 25 ma suggest illite growth started after burial to over 8000 ft and palaeoburial temperatures of over 80 90 c compared with nearby reservoirs variations in the nature and abundance of illite result from illitisation being arrested by hydrocarbon charge at different times optimal reservoir and aquifer properties occur in shallower structures charged from more deeply buried source rocks good reservoir properties occur with charge after short lived illite growth although later burial may reduce aquifer properties the more prolonged illite growth experienced by deeply buried reservoirs such as pelican charged late in the tertiary has resulted in poor reservoir properties and poor aquifer permeabilities may be expected

mineralogical signature of hydrocarbon circulation in cretaceous red beds of the barda gonzalez area neuquen basin argentina the portezuelo formation is part of a red bed sequence in the neuquen basin assigned to the neuquen group lower cenomanian middle campanian in outcrops of the portezuelo formation in the barda gonzalez region iron oxide and hydroxide cements are only preserved in the less permeable claystone layers paleomigration of hydrocarbons and formation waters along the most permeable layers bleached the rocks due to partial to total dissolution of cements and grains and formation of several authigenic minerals 1 montmorillonite and pyrite in the medium to fine grained sandstones and mudstones and 2 multistage calcite and pyrite in the coarse grained sandstones and conglomerates the canyon diablo troilite of 24 4 to 60 values in pyrite point to microbial reduction of a sulfate precursor the oxidation of hydrocarbons and fluctuations in ph and carbon dioxide pressure caused by organic acids resulted in multiple stages of dissolution and precipitation of calcite calcite crystals host hydrocarbon bearing fluid inclusions pyrite with variable fluorescence color indicating that hydrocarbon composition changed with time the intermediate peedee belemnite 8 11 to 8 52 and 9 76 to 9 83 isotope composition of calcites may have resulted from mixtures of rich after the dissolution of local calcrete with poor from oxidizing hydrocarbons this contribution provides for the first time key information to predict the distribution of authigenic minerals in reservoir rocks in the basin and improves understanding of the diagenetic history of the portezuelo formation

climatic depositional and burial controls on diagenesis of appalachian carboniferous sandstones qualitative and quantitative methods abstract carboniferous quartz lithic and feldspar rich sandstones from different stratigraphic intervals within the central appalachian basin contain evidence for eogenetic and mesogenetic diagenesis important eogenetic products include fe oxide oxyhydroxide siderite kaolinite chlorite and calcite whereas quartz albite illite sericite fe carbonate and secondary porosity are the most important mesogenetic components correspondence and detrended correspondence analysis of the framework grain and diagenetic mineral data set has guided diagenetic interpretations and leads to two major conclusions first minerals that formed early appear to have been influenced by stratigraphic position the distribution of siderite and iron oxide oxyhydroxide is considered to reflect a second order paleoclimatic signature recognized throughout the carboniferous where siderite formed during everwet periods and iron oxide oxyhydroxide during semi arid conditions reflecting differences in redox second framework grain composition controlled the distribution of diagenetic products in the burial environment lithic arenites are deficient in authigenic quartz yet have undergone various degrees of illitization quartz deficiency is attributed to compaction related loss of primary porosity relatively early which inhibited sufficient fluid flow to account for much higher concentrations of quartz cement in the more competent quartz rich sandstones