geologic evolution of the iraqi zagros and its influence on the distribution of hydrocarbons in the kurdistan region whereas the vast majority of discovered hydrocarbon reserves in iraq reside in cretaceous and cenozoic reservoirs numerous oil and gas fields have been discovered recently in deeper jurassic and triassic reservoirs in the kurdistan region of iraq this study presents a middle upper jurassic thermal maturity map for the kurdistan region of iraq and demonstrates that regional first order trends in jurassic source rock maturity show a close correlation to the spatial distribution of oil gravities within the overlying jurassic and cretaceous reservoirs this distribution is consistent with compartmentalization of the active source rock kitchens due to zagros folding resulting in relatively short distance migration and charge of the anticlinal structures from the adjacent synclinal lows the thermal maturity map confirms relatively low maturity over the mosul high where the cretaceous and cenozoic section overlying the source rock interval is relatively thin and increasing maturity to the southeast as the thickness of the cenozoic foredeep sediments increases toward the depocenter located in the southeastern iraqi zagros and the adjacent iranian zagros the correlative trend in oil gravities is exemplified by the recent jurassic discoveries low to medium gravity oils 14 27 api in shaikan and atrush to the northwest light oil 39 47 api in mirawa and bina bawi and gas condensate 55 api in miran west to the southeast understanding thermal maturity patterns and hydrocarbon fluid type distributions will help to guide risk assessment for remaining prospectivity and future exploration drilling within the kurdistan region of iraq

gas prospective areas in the zagros domain of iran and in the gulf iranian waters in the province of fars and in its offshore gas reserves in excess of 600tcf discovered in permo triassic carbonates well sealed by the anhydrite of the dashtak fm were originated from early llandoverian highly organic and radioactive shales the current distribution of this source rock was influenced by the pre permian erosion on a system of n s tilted blocks extensive geochemical modeling has shown that oil generation began in the middle jurassic in some areas while the onset of gas window was reached locally as early as middle cretaceous a suite of cumulative isopachs shows the evolution of the source rocks maturity through time it also provides a reliable image of the geometry of the reservoirs the long range migrations and the location of large size oil and gas accumulations on a few continuous regional highs prior to the zagros orogeny huge amounts of gas and limited amounts of light oil later re accumulated in the zagros folds formed during the late miocene and pliocene the characteristics of the dalan and kangan reservoirs and the areal extent of the dashtak fm which seals the system could be deduced from paleogeographic reconstruction distribution of facies and isopachs the distribution of the reservoirs seals surface oil and gas seepages and hydrocarbon related indications together with the location of the gas fields makes possible to select among the numerous permotriassic prospects those which are the most attractive some prospects may also contain light oil rings below gas the silurian source rocks in the zagros foothills of iran a variety of proterozoic rocks were uplifted by proterozoic salt diapirs hormuz fm but no source rocks were found in the few hormuz samples we analyzed no source rocks were found either in the cambro

thermal evolution of the kuh e asmari and sim anticlines in the zagros fold and thrust belt implications for hydrocarbon generation abstract mixed layer clay minerals vitrinite reflectance and geochemical data from rock eval pyrolysis were used to constrain the burial evolution of the mesozoic cenozoic successions exposed at the kuh e asmari dezful embayment and sim anticlines fars province in the zagros fold and thrust belt in both areas late cretaceous to pliocene rocks show low levels of thermal maturity in the immature stages of hydrocarbon generation and early diagenetic conditions r0 i s and ro values

palaeoclimate change recorded in upper cretaceous albian cenomanian kazhdumi formation borehole spectral gamma ray logs south pars gas field persian gulf abstract th u and th k data from spectral gamma ray logs obtained from outcrop successions have been used as a rapid and inexpensive proxy for determining possible episodes of humid arid palaeoclimate change such outcrop based measurements have never been tested using spectral gamma ray data obtained from wireline logs in subsurface boreholes th k and th u ratios have traditionally been used to decipher sequence stratigraphic patterns at outcrop and in borehole the possible influence of palaeoclimate on such ratio changes has yet to be proven especially from borehole data in this work we compare borehole derived th k and to a lesser extent th u to palaeoenvironmental changes inferred from palynology and deduce that both sea level and changing hinterland weathering regimes caused discrete fluctuations observed in the spectral gamma ray logs this is the first time such subsurface information has been used in this way interpretation of wireline logs in terms of palaeoclimate as well as sea level may now be considered and the use of such logs in palaeoclimate reconstruction is strengthened

hydrocarbon reserves of gachsaran oilfield sw iran geochemical characteristics and origin abstract biomarkers and carbon isotope data were used to depict geochemical properties and to delineate source of the crude oils from asmari and bangestan reservoirs of the giant gachsaran oilfield sw iran despite the distinct horizons of the reservoirs and severe petrophysical heterogeneity inside each reservoir all oil samples show an identical level of thermal maturity furthermore similar source related parameters reflect identical source rock for both reservoirs they indicate carbonate marl source deposited in a marine environment under anoxic suboxic conditions strong marine organic matter signatures of predominantly algal origin along with evidence of a terrigenous angiosperm plant contribution were detected geochemical evidence suggests that the gachsaran field asmari and bangestan oils being sourced from a mix of organic rich kazhdumi and pabdeh source rocks of albian and middle eocene early oligocene ages respectively carbon isotope composition and v ni ratio signatures indicate kazhdumi formation as the main source rock meanwhile significant presence of oleanane and less than unity values of c 29 c 30 hopanes ratio demonstrate a partial contribution of pabdeh formation this contradiction could be explained by two scenarios 1 incorporating very immature non expelled pabdeh oils into the mature kazhdumi oils during migration or 2 partial charge form low maturity pabdeh oils that is insufficient to impact a typical mixed signature over the geochemical fingerprint of the reservoired oils additionally geochemical similarities give rise to an assumption of reservoir and trap inter connection for this giant field

2d basin modeling study of the binak trough northwestern persian gulf iran abstract the northwestern part of the persian gulf is one of the most prominent hydrocarbon exploration and production areas oilfields are located in structural highs formed around the cenomanian depression known as binak trough to evaluate the highly variable source rock maturity timing of hydrocarbon generation as well as migration pattern and the remaining hydrocarbon potential of the early cretaceous source rocks burial and thermal histories were constructed for four production wells and one pseudo well in addition two cross sections covering the depression and the structural highs around the trough were investigated by 2d basin modeling to provide a better regional overview on basin evolution the modeling results indicate that whereas the cretaceous source rocks are immature or early mature at the location of oilfields they reached sufficient maturity to generate and expel considerable amounts of hydrocarbons in the binak depression the main phase of oil generation and expulsion from the cretaceous source rocks is relatively recent and thus highly favorable for the conservation of hydrocarbon accumulations trap charging occurred through the late miocene to pliocene after the zagros folding 2d models predict that the albian source rock still has significant hydrocarbon generation potential whereas the lower neocomian source rock has reached already a high transformation ratio within the deep kitchen area oil migration occurs in both lateral and vertical directions this migration pattern could explain the distribution of identified oil families in the northwestern part of the persian gulf

diagenesis of the maxon sandstone early cretaceous marathon region texas a diagenetic quartzarenite abstract environments of deposition climate detrital mineral composition and stratigraphic position within a thick sequence of carbonate rocks were major controls on the diagenesis of maxon sandstones fluvial deltaic sands which were subjected to calichification and other pedogenic processes lost all macroporosity prior to burial most sands underwent compaction average of 14 porosity loss minor cementation by quartz and kaolinite possibly during invasion of meteoric water introduced during a low stand of sea level followed by extensive cementation and grain replacement by calcite c and o isotopic values of calcite suggest that carbonate was introduced by formation waters derived from adjacent limestones mass balance calculations on the loss and gain of chemical components during diagenesis show there was a major loss of silica from loss of feldspars and major gains in cao and co2 in calcite cement the overlap of calcite cement on detrital quartz grains gives the impression in thin section that the replacement of quartz by calcite was extensive however thin section and sem views of samples leached in hc1 show that even partial replacement of quartz is rare and is limited largely to the edges of tiny quartz overgrowths ignoring intraformational clasts most maxon sandstones now are quartzarenites q86f1r3 however compensating conservatively for feldspar grains replaced by calcite sands originally were subarkoses q86f10r3

silica diagenesis ii general mechanisms abstract amorphous silica phases opal a precipitate in nature due to the formation of dense colloids in supersaturated alkaline aqueous solutions with low relative concentrations of other ions opal a dissolves and yields solutions of still relatively high silica content in pore waters containing abundant cations open framework polymers form which flocculate to yield opal ct opal ct becomes increasingly ordered primarily due to preferential growth of cristobalite relative to tridymite and crystal size increase opal ct dissolves to yield pore waters of low silica concentration which allows slow growth of quartz crystals from monomeric solution the quartz crystals then slowly increase in size and crystallinity carbonates appear to enhance opal ct formation possibly due to the activity of positively charged hydroxyl complexes hence polymerization in relatively pure systems is involved in opal a formation and polymerization in impure systems is involved in opal ct formation and slow growth from monomeric low silica concentration solutions is involved in precipitation of quartz in sedimentary realms

petrophysical characterization of low permeable carbonaceous rocks comparison of different experimental methods abstract pore structure and gas transport properties of fourteen samples from the jurassic sargelu and the cretaceous garau formations in lurestan province southwest iran were studied under the aspect of shale gas exploration and production porosity was determined by helium pycnometry and water saturation archimedes principle low pressure adsorption of n2 was used to determine total pore volumes specific surface areas and microporosity high pressure mercury intrusion porosimetry mip was applied to assess pore size distributions permeability measurements were performed with helium and methane at confining pressures of 40 to 10 mpa using steady state and non steady state methods permeability and porosity values determined by the different methods are in a good agreement for low permeable samples less than 1 microdarcy 10 18 m2 the constant downstream pressure technique is the most efficient method for slip flow evaluation klinkenberg plot yielding apparent permeability coefficients over a wide range of reciprocal mean pressures 1 pmean in one single run a positive correlation was found between toc content porosity and permeability coefficients samples displaying clear signs of recrystallization tend to exhibit higher permeability none of the parameters determined in this study however showed a correlation with mineralogy the relationship between klinkenberg corrected permeability coefficients and confining pressure could be expressed by an exponential decay function stress sensitivity was typically higher for low permeable samples samples containing highly recrystallized carbonates exhibited lower stress sensitivity indicating an increase in rigidity due to recrystallization no correlation was found between methane helium permeability ratios sorption capacity and toc contents thus gas transport properties of this sample set were not affected by sorption and or swelling of organic matter

variations in the sterane carbon number distributions of marine source rock derived crude oils through geological time abstract the analysis of the sterane data of a large set of crude oils 414 derivedfrom marine carbonate 27 and siliciclastic source rocks 14 where influences of terrestrial or lacustrine derived organic matter can reasonably be excluded shows that there are increases in the relative content of c28 steranes and decreases in the relative content of c29 steranes through geological time there are no consistent variations in the relative content of c27 steranes through time with one major exception a proterozoic oil from oman palaeozolic and older crude oils are thus generally characterised by strong predominances of c29 steranes and low relative concentrations of c28 steranes significantly higher proportions of c28 steranes and lower proportions of c29 steranes occur in oils derived from jurassic and upper cretaceous source rocks these changes through time do not appear to reflect the chemical evolution of the sterols of one particular variety of marine organism the increase in c28 steranes may be related to the increased diversification of phytoplantonic assemblages in the jurassic and cretaceous possible sources of the c28 sterols necessary for the observed changes in crude oil steranes includes diatoms coccolithophores and dinoflagellates although the technique does not give an accurate means of determining the age of the source rock of a crude oil it is possible to distinguish younger crudes derived from the upper cretaceous and tertiary from palaeozoic and older crudes

regional stratigraphy of the zagros fold thrust belt of iran and its proforeland evolution the latest neoproterozoic through phanerozoic stratigraphy of the zagros fold thrust belt of iran has been revised in the light of recent investigations the revised stratigraphy consists of four groups of rocks each composed of a number of unconformity bounded megasequences representing various tectonosedimentary settings in the lowest group ranging in age from latest precambrian to devonian the uppermost neoproterozoic to middle cambrian rocks constitute a megasequence of evaporites siliciclastic deposits and interlayered carbonates which were deposited in pull apart basins that developed by the najd strike slip fault system this megasequence is overlain by a second one middle to late cambrian in age which consists of shallow marine siliciclastic and carbonate rocks representing deposition in an epicontinental platform the overlying shales siltstones and partly volcanogenic sandstones of ordovician silurian and devonian age are local remnants of stratigraphic units that were extensively eroded during development of several major unconformities the second group consists of two megasequences one permian and the other triassic composed of widespread transgressive basal siliciclastic rocks and overlying evaporitic carbonates of an equatorial epi pangean very shallow platformal sea the third group is composed of four megasequences formed of shallow and deep water carbonates with some siliciclastic and evaporite deposits which accumulated on a neo tethyan continental shelf during earliest jurassic through late turonian time the fourth group comprises siliciclastic and carbonate deposits of a largely underfilled nw to se trending forward and backward migrating late cretaceous to recent proforeland basin which has evolved as an integral part of the zagros orogen this last group consists of three megasequences ix x and xi with distinctive lateral and vertical facies variations which reflect specific tectonic events megasequence ix comprises uppermost turonian to middle maastrichtian prograding and retrograding siliciclastic and carbonate deposits whose accumulations reflect emplacement obduction of ophiolite slivers and subsequent collisional events in the zagros orogen megasequence x consists of uppermost maastrichtian to upper eocene siliciclastic and carbonate rocks which deposited first progradationally in front of the zagros orogenic wedge with reduced contractional tectonic activity and then retrogradationally due to intensified thrust stacking in the interior parts of the orogen megasequence xi consists of oligocene and lower miocene carbonate strata deposited retrogradationally shortly after a period of intensified late eocene thrust faulting in the deformational wedge and an overlying succession of upward coarsening northeasterly derived siliciclastic deposits of lower miocene to recent age which are composed of erosional byproducts of the southwest vergent zagros thrust sheets

the bituminous mixtures of tall e abu chizan a vth millennium bc settlement in southwestern iran abstract various bituminous artifacts were excavated from the tall e abu chizan a late prehistoric middle susiana to middle uruk settlement on the middle of the curvy plain between the karun river and the ram hormoz plain all samples dated from the vth millennium bc and cover three periods 5000 4700 bc late middle susiana 4700 4200 bc late susiana 1 and 4200 3900 bc late susiana 2 the bitumens were studied using the techniques of petroleum geochemistry and were compared both to the unaltered crude oils produced from the main oil fields in the area and to the famous mamatain oil seeps all samples are very rich in bitumen average 46 wt which has been biodegraded and oxidized despite these alteration phenomena 13 c of asphaltenes occur within a narrow range of less than 1 pdb biodegradation affected the steranes terpanes dibenzothiophenes and mono and triaromatic steroids molecular characteristics of terpanes especially the occurrence of 18 h oleanane suggest that the bitumen from tall e abu chizan is a mixture generated from cretaceous kazdhumi and eocene pabdeh petroleum source rocks in that respect bitumens from tall e abu chizan belong to the same oil family as oil from the naft safid field which is in the vicinity of the archaeological site in fact the bitumen at tall e abu chizan likely originated from oil seepages at naft safid these oil seeps have not yet been sampled or analysed

the diagenesis of continental karoo tertiary siliciclastics from an east african rift valley rukwa tukuyu area tanzania abstract the diagenetic history of the karoo and jurassic tertiary beds of east african rift valleys is related to the tectonic activity and sedimentary evolution of the rift valley area in the karoo beds early diagenetic calcite and hematite formation are succeeded by mechanical compaction and minor quartz kaolinite and calcite precipitation renewed tectonic activity possible half graben formation and exposure of the karoo beds in jurassic tertiary time resulted in alluvial fan deposition the red sandstone group and associated fresh water flushing caliche formation and hematite precipitation late diagenetic precipitation of potash feldspar and feldspar leaching were the final controls on the porosity and permeability development of the sediments

geometry of propagating continental rifts reconstruction of past plate configurations through palinspastic restoration of continental margins1 4 requires a detailed knowledge of the geometries of horizontal continental extension extension is often restricted to discrete linear zones termed rifts5 6 and rift models that invoke propagating vertical dykes and cracks7 10 are useful for assessing the relative significance and timing of uplift subsidence and extension in the tectonic evolution of rift basins however many models do not adequately account for the observed asymmetry of rifts i describe here the general three dimensional character of young and aborted continental rifts which can be used to derive a structural model for the propagation of rifts in continental lithosphere the rifts become asymmetric as a consequence of the role played by low angle normal faults in the overall rift geometry

geochemical characteristics and genetic types of the crude oils from the iranian sector of the persian gulf abstract comprehensive geochemical study shows genetic relationships among 33 crude oils from iranian sector of the persian gulf and suggests the ages and paleoenvironments of their source rocks the samples were collected from jurassic to tertiary reservoirs of 17 developed oil fields where about 15 billion barrels of recoverable oil have been reserved the oil density varies in rather wide range between 12 2 and 39 2 api asphaltene contents ranged from 0 8 18 5 and the maltene fractions are dominated by saturated hcs 29 3 70 9 with subordinate proportions of aromatic hcs 22 30 38 30 and polar compounds 7 15 70 pristane to phytane pr ph ratios are variable 0 67 1 41 sulfur content in crude oil samples are highly variable 0 65 3 7 according to the tissot and welte s classification most of the oils can be classified as high sulfur oils statistical and geochemical results indicate that the studied oils belong to four main genetic groups group i oils jurassic to early cretaceous reservoirs of the dorood kharg aboozar and foroozan oil fields in the nw part of the persian gulf originated from jurassic or older carbonate rich source rocks deposited in an anoxic environment group ii oils jurassic to early cretaceous reservoirs of the salman resalat reshadat and balal oilfields in the eastern part of the persian gulf were sourced from jurassic or older carbonate source rocks deposited in a relatively oxic environment group iii oils late cretaceous to tertiary reservoirs of the aboozar bahregansar souroush nowrouz dorood and kharg oilfields in the north north west part of the persian gulf were probably sourced from middle cretaceous calcareous shales group iv oils late cretaceous reservoir of the sirri a sirri c sirri d sirri e resalat and reshadat oilfields in the eastern part of the persian gulf probably originated from mid to late cretaceous source rock

source rock distribution and maturation in the zagros orogenic belt provenance of the asmari and bangestan reservoir oil accumulations abstract the zagros orogenic belt of iran is one of the most prolific petroliferous areas accounting for approx 12 of proven global reserves correlation techniques reveal that a majority of the oils variously reservoired in asmari oligo miocene and bangestan group upper cretaceous anticlinal structures share a common provenance oils of the n e khuzestan fields are an exception showing a conspicuously different origin candidate source potential for the crucial central zagros embayment and contiguous areas was assessed on field survey and from well materials collected during the decade from 1968 onwards although varying locally in vertical and lateral distribution attractive sources occur throughout the section included were silurian shales the sargelu middle jurassic garau gadvan lower cretaceous kazhdumi albian gurpi upper cretaceous and pabdeh paleogene fms maturation of these source units was essentially controlled by the foredeep subsidence related to the zagros orogeny being a neogene event hydrocarbon generation and migration are very recent and essentially synorogenic consolidation of this information with the real distribution of candidate sources application of carbon isotope based source oil assignments and biomarker results successfully differentiated the provenance of the generic oil groupings over much of khuzestan the kazhdumi was recognised as the major contributor elsewhere the pabdeh fm yields isotopically distinctive oils in n e khuzestan evaluation of this basin allowed identification of prolific source rocks in low energy euxinic argillaceous lime mudstones similarly it provided an early application of pyrolysis techniques carbon isotopic correlations and subsidence history maturation migration modelling approaches now routinely employed in basin evaluation

the paleozoic petroleum geology of central arabia exploratory drilling in central saudi arabia has established significant paleozoic petroleum potential in this region in recent discoveries the permian interval of the unayzah formation has been identified as the primary oil and gas reservoir the unayzah formation consists of alluvial and fluvial to shallow marine siliciclastic sandstones and siltstones that were deposited on a major pre unayzah unconformity saudi arabian paleozoic oil is a high gravity 43 53 degrees api crude with low sulfur content usually less than 0 07 that is classified as arabian super light oil gas with condensate has also been discovered in the unayzah formation the identified paleozoic traps are moderate relief fault generated structures with generally 30 100 m of closure unayzah structural traps developed primarily during the triassic to early jurassic however an earlier phase of significant pre unayzah structural development is also indicated between the devonian and late carboniferous and is related to a hercynian structural event post triassic structure in central arabia is mainly regional and results principally from late cretaceous to tertiary development of the central arabian arch the established source rock is the basal qusaiba shale a widespread organic rich shale that was deposited following regional deglaciation in the early silurian migration occurred regionally updip through unayzah formation reservoirs from the underlying qusaiba shale subcrop and or vertically along fault bounded zones on the flanks of structures from the underlying qusaiba shale interbedded upper permian shales and evaporites provide a top seal for the unayzah and form the basal sequence of the overlying transgressive khuff carbonate pre qusaiba reservoir targets include the cambrian ordovician saq sandstone the ordovician qasim formation and upper ordovician to lower silurian periglacial clastics of the zarqa and sarah formations high gravity low sulfur oil has also been discovered in this pre qusaiba clastic section the reservoirs of the pre qusaiba structures are fault bounded and sources laterally by the down faulted qusaiba shale

late cretaceous to recent deformation related to inherited structures and subsequent compression within the persian gulf a 2d seismic case study abstract the persian gulf is part of an asymmetric foreland basin related to the zagros orogen few published studies of this basin and associated onshore areas include seismic reflection data we present a seismic stratigraphic interpretation based on marine 2d seismic data which reveals the presence of two types of compressional structures within the basin 1 faulted domes related to salt movement and the offshore trace of a nne ssw trending dextral basement fault the kazerun fault 2 long wavelength 16 km low amplitude 60 ms two way travel time folds relating to the advancing deformation front associated with the orogen thinning of age constrained stratal units across structures related to the offshore trace of the kazerun fault implies a distinct pulse of uplift on this fault during the maastrichtian the geometry of growth strata across other intra basin structures suggests a second later stage of deformation which began in the middle miocene thickening and folding of post middle miocene stratal units towards the ne i e towards the zagros orogen is interpreted to reflect rapid loading subsidence and compression related to southwestwards advance of the orogen the results of this study have implications for the interaction between pre existing structures and later compressional events both within the persian gulf and elsewhere

atmospheric circulation upwelling and organic rich rocks in the mesozoic and cenozoic eras abstract by using the basic principles of atmospheric circulation and analogies from present circulation patterns it is possible to construct qualitative atmospheric circulation models on paleogeographic maps the wind patterns predicted by these models then serve as the basis for predicting the locations of ancient upwelling zones atmospheric circulation and upwelling models for seven geologic stages in the mesozoic and cenozoic were constructed and the distribution of the upwelling zones compared with the distribution of organic rich rocks for all time periods together the correlation was statistically significant when the individual time periods were analyzed separately the following pattern emerged significant correspondence between upwelling zones and organic rich rocks in the triassic middle early cretaceous to late cretaceous and middle paleogene to neogene no significant correspondence was found for the intervening times upwelling does not account for all organic rich rocks so called anoxic oceanic events and transgressions play an important role in their deposition it is suggested that upwelling contributes significantly to the pattern of organic rich rock distribution and is important in determining organic facies

structural evolution of lake malaŵi africa over 2 000 km of seismic reflection profiles have been collected in lake mala i nyasa the southernmost of the east african rift lakes these studies reported here reveal a severely faulted lake floor bounded by rift structures of pliocene or greater age faults that penetrate the uppermost sedimentary units and numerous earthquakes1 attest to continuing activity in the rift inter basinal differences in fault spacing orientation and sedimentary thicknesses have led to a subdivision of lake mala i into four discrete structural provinces these provinces only now are linked by faults attributed to the most recent episodes of extension an evolutionary sequence of 1 initial block faulting and subsidence 2 fragmentation of fault blocks 3 uplift and 4 renewed subsidence and rotation of fault blocks is proposed for the central part of the mala i rift

meteoric burial diagenesis of pennsylvanian arkosic sandstones southwestern anadarko basin texas pennsylvanian arkosic sandstones at mobeetie field were deposited in fan deltas that prograded onto a shallow shelf in the southern anadarko basin the detrital minerals of the sandstones reflect the composition of the precambrian granites and granodiorites that were exposed in the nearby amarillo uplift distal margins of some fan delta lobes were reworked by marine processes and carbonate fossil fragments and oolites were mixed with terrigenous clastics the diagenetic history and hence reservoir quality of the distal marine reworked sandstones differ from those of the more proximal nonreworked sandstones the earliest diagenetic events formation of chlorite ooids and precipitation of fibrous submarine mg calcite cement took place in the depositional environment of the marine reworked sandstones on the basis of isotopic data the remainder of the diagenesis evidently occurred in fluids of meteoric origin shallow early meteoric diagenesis induced precipitation of iron poor calcite spar in reworked sandstones nonreworked sandstones lack calcite spar but contain early pore lining chlorite cement dissolution of aragonite by fresh meteoric ground water created moldic porosity within reworked sandstones as burial increased porosity in both the reworked and nonreworked fan delta sandstones was reduced by precipitation of authigenic quartz feldspar kaolinite fe calcite and ankerite oxygen isotope data suggest that these cements also precipitated from fluids of meteoric origin that became increasingly hot but remained relatively constant in isotopic composition the last diagenetic events were influenced by the overlying permian evaporites sodium rich fluids caused partial albitization of detrital plagioclase and sulfate derived from the evaporites precipitated as anhydrite and celestite

seismic reflection imaging of karst in the persian gulf implications for the characterization of carbonate reservoirs karstification positively and negatively affects the quality of carbonate reservoirs for example dissolution and brecciation can increase porosity and permeability whereas cavern collapse or cementation driven by postkarstification fluid flow may occlude porosity and reduce permeability karst may also pose challenges to drilling because of the unpredictable and highly variable porosity and permeability structure of the rock and the corresponding difficulty in predicting drilling mud weight when combined outcrop petrographic and geochemical data can constrain the style distribution and origin of seismic scale karst which may provide an improved understanding of carbonate reservoir architecture and allow development of safer drilling programs however relatively few studies have used seismic reflection data to characterize the regional development of seismic scale karst features in this study we use time migrated two dimensional seismic reflection data to determine the distribution scale and genesis of karst in a 3 km thick 9800 ft thick jurassic miocene carbonate dominated succession in the persian gulf we map 43 seismic scale karst features which are expressed as vertical pipe columns of chaotic reflections capped by downward deflected depressions that are onlapped by overlying strata the columns are up to 2 km 6500 ft tall spanning the upper jurassic to upper cretaceous succession and are up to 5 5 km 18 000 ft in diameter we interpret these pipes to have formed in response to hypogene karstification by fluids focused along preexisting faults with hypogene generated depressions enhanced by epigene processes during key intervals of exposure our study indicates that seismic reflection data can and should be used in conjunction with petrographic and geochemical techniques to determine the presence of hypogene karst plays and to help improve the characterization of carbonate reservoirs and associated drilling hazards

early silica cementation and subsequent diagenesis in arenites from four early proterozoic iron formations of north america abstract in four unmetamorphosed north american iron formations that display arenitic granular textures much of the chert and megaquartz occupies former intergranular pore space and exhibits textures typical of cements iron bearing phases are very rare in these cements excluding replacive crystals cracks and more irregular cavities that formed in these arenites soon after deposition probably via the shrinkage of gelatinous silica are filled with similar chert and megaquartz cements silica cemented intraclastic pebbles of arenite local occurrences of cross stratified cherty internal sediments resting on the cements and numerous zones where the abundance of cement equals the porosity of comparable modern sands indicate the cementation commenced near the sediment water interface opa ine silica fibrous silica polymorphs and megaquartz druses are inferred to have been the most voluminous initial precipitates and they are very inhomogeneously distributed silica concentrations in the pore waters of newly deposited iron formation sands must therefore have been high but variable the lack of evidence for subaerial desiccation or normal saline deposits renders an evaporative origin for either the cements or iron formations as a whole highly unlikely steeper geothermal gradients are suggested as a more likely cause of rapid silica cementation and silica cements from geothermal areas show very similar textures most of the cements in iron formation arenites were affected by neomorphism replacement mechanical compaction and or pressure solution regardless of their origin the cements are noteworthy for the following reasons they indicate that modern iron formations are enriched in silica relative to their precursor sediments they provide new evidence that iron formations are not replaced limestones or dolomites and the iron minerals they are associated with are probably the closest approaches to primary ferruginous phases in iron formation arenites early silica cements also appear to be widespread in lutitic or banded iron formations in the form of chert pods

oleanane or lupane reappraisal of the presence of oleanane in cretaceous tertiary oils and sediments nonpolar gc columns are normally used for gc ms analysis of saturate fractions from crude oils under these conditions lupane coelutes with oleananes and some minor c30 compounds of non terrigenous origin having lupane like mass spectra because any peak eluting fractionally earlier than 17 21 h hopane in the m z 191 mass chromatogram is routinely assigned to oleanane the presence of lupane may sometimes have been overlooked lupane and oleananes are easily separated using reverse phase hplc triterpane concentrates from 10 crude oils known to contain oleananes were hplc separated lupane was unambiguously identified in six of the oils by full scan gc ms analysis of fractions having the hplc retention time of authentic lupane gc separation of lupane and oleananes is possible using polar gc columns having a polyethylene glycol stationary phase organic geochemistry 23 1995 21 allowing estimation of the lupane lupane oleanane ratio high ratios were measured in the marraat oil west greenland 0 8 and the amauligak oil from the beaufort mackenzie delta 0 26 the results suggest that lupane may be more frequently occurring than previously thought and that this compound is preferably associated with high latitude samples high concentrations of 28 nor and 24 28 bisnortriterpanes oleananes lupanes and taraxastanes were detected in the marraat oil

structural style variation and its impact on hydrocarbon traps in central fars southern zagros folded belt iran abstract the fars area is the main target for permian gas exploration in the zagros fold belt it contains approximately 15 percent of the world s proven gas reserves the geometrical characteristics of the folded structures change dramatically across the n s trending gavbandi high we used seismic profiles well data magnetic survey information and field observations to show that thickness variation of the sedimentary pile inherited from basement geometry is the main reason behind structural style variation in this area which occurred during the zagros folding differences in thickness were more significant in early middle paleozoic time and decreased considerably upward in time the total thickness of the lower paleozoic succession in the eastern side of the gavbandi high is approximately 40 50 thicker than on the summit of this basement high sedimentary pinch outs through cretaceous and tertiary times indicate that the activity of the basement faults decreased but did not stop the impact on hydrocarbon traps of the pre folding basin architecture and the differences in the behavior of the sedimentary cover after miocene folding is discussed and documented

lower silurian hot shales in north africa and arabia regional distribution and depositional model abstract lowermost silurian organic rich hot shales are the origin of 80 90 of palaeozoic sourced hydrocarbons in north africa and also played a major role in petroleum generation on the arabian peninsula in most cases the shales were deposited directly above upper ordovician peri glacial sandstones during the initial early silurian transgression that was a result of the melting of the late ordovician icecap deposition of the main organic rich shale unit in the north african arabian region was restricted to the earliest silurian rhuddanian stage acuminatus atavus and probably early cyphus graptolite biozones during this short period 1 2 m y a favourable combination of factors existed which led to the development of exceptionally strong oxygen deficiency in the area in most countries of the study area the post rhuddanian silurian shales are organically lean and have not contributed to petroleum generation the distribution and thickness of the basal silurian hot shales have been mapped in detail for the whole north african region using logs from some 300 exploration wells in libya tunisia algeria and morocco in addition all relevant accessible published and unpublished surface and subsurface data of the lower silurian shales in north africa and arabia have been reviewed including sedimentological biostratigraphic and organic geochemical data the lowermost silurian hot shales of northern gondwana are laterally discontinuous and their distribution and thickness were controlled by the early silurian palaeorelief which was shaped mainly by glacial processes of the late ordovician ice age and by pan african and infracambrian compressional and extensional tectonism the thickest and areally most extensive basal silurian organic rich shales in north africa occur in algeria tunisia and western libya while on the arabian peninsula they are most prolific in saudi arabia oman jordan and iraq the hot shales were not deposited in egypt which was a large palaeohigh at that time the depositional model presented may help in better understanding the source potential of the basal silurian shales in less explored regions of north africa and arabia including morocco northern niger and the kufra basin in southeast libya

numerical methods in rock mechanics the purpose of this civilzone review paper is to present the techniques advances problems and likely future development directions in numerical modelling for rock mechanics and rock engineering

tectonic controls on residual oil saturation below the present day fluid contact level in reservoirs of the persian gulf abstract the presence of residual oil below the present day free water level fwl and oil water contact owc is common in many oil fields in the middle east particularly those in the persian gulf this residual oil is seen in both clastic and carbonate reservoirs prior to the start of production the characterisation and modelling of these fields is difficult in practice also these residual oils below the fwl and owc could become classified as reserves if ways to produce them could be found however the first step is to better understand their origin therefore the goal of this study was to investigate the role of geological events on the presence of the residual oil zone roz below the fwl and owc it has been suggested that the presence of residual oil below the present day fwl and owc is related to the geotectonic history of the region from the middle miocene reverse faulting and overfolding propagated over the zagros leading to the amplification of folds and the migration of the zagros orogeny towards its foreland basin persian gulf in response to this additional massive loading on the continental margin the forebulge amplitude was increased its location migrated towards the uplifted zagros mountains and consequently the persian gulf became narrower this exerted a north to north east downward tilting of the entire basin including all the structures and reservoirs previously filled by hydrocarbons this basin tilting changed the equilibrium of the structures and their fluid contents and resulted in the hydrocarbons and water attempting to find a new equilibrium under these conditions the early migrated and accumulated oil was flushed out by water imbibition and a roz was left below the present day fwl and owcs the angle of regional basin tilt has been calculated to be 0 836 based on seismic sections

tectonics versus eustatic control on supersequences of the zagros mountains of iran abstract at least 12 km of strata ranging in age from the latest precambrian to the recent are exposed in the zagros mountains of iran this sedimentary cover is characterized by distinct stratal packages separated by major unconformities forming twelve supersequences they are informally named as 1 late precambrian cambrian hakhamanesh supersequence 2 ordovician kourosh supersequence 3 silurian camboojiyeh supersequence 4 devonian darioush supersequence 5 mississippian pennsylvanian khashayar supersequence 6 permian triassic ashk supersequence 7 jurassic farhad supersequence 8 early cretaceous mehrdad supersequence 9 late cretaceous ardavan supersequence 10 paleocene oligocene sassan supersequence 11 oligocene miocene ardeshir supersequence and 12 miocene pleistocene shapour supersequence these supersequences and their correlatives in neighboring areas have been used to infer tectonic events the dominant interpretation has been that local or regional epeirogenic movements were responsible for the formation of these supersequences unconformities are considered as indications that epeirogenic movements associated with tectonic events affected the area the present investigation provides an alternative to the established view of the phanerozoic supersequences of the zagros mountains a good correlation exists between the lithofacies of supersequences in the zagros mountains and the second order eustatic sea level changes deposition of deep water marine shales occurred during periods of eustatic sea level rise platform wide unconformities coincided with eustatic sea level lows in fact supersequences of the zagros mountains are nearly identical to those described from the north american craton and the russian platform suggesting that these stratal packages are global these observations suggest that supersequences of the zagros mountains formed by second order eustatic sea level changes and not by local or regional epeirogenic movements although tectonic events did not produce supersequences of the zagros mountains they influenced regional lithofacies patterns through the formation of intrashelf depressions such as the hormoz salt basin during the precambrian and the dezful embayment and the lorestan basin during the mesozoic tectonic events also affected sedimentation during the tertiary collision of arabia and the central iran microplate through uplift erosion and the formation of the zagros foreland basin the results of this investigation necessitate a re evaluation of the role and the significance of pre tertiary tectonic events commonly used to interpret the geological evolution of the zagros mountains

geology and geophysics of the rukwa rift east africa exploration in the rukwa rift using gravity and seismic reflection surveys fieldwork and drilling has defined the structure and stratigraphy of the basin in greater detail than any other part of the western rift the stratigraphy comprises precambrian basement karroo sandstones shales and coals upper miocene red beds and miocene recent lacustrine and fluvial sediments during miocene recent rifting the greatest sediment input apparently came from axial fluvial systems flowing from the northwest and southeast the southwestern area experienced alternating shallow lacustrine and fluviodeltaic conditions during the miocene recent cenozoic age rift structures have a dominant nw se and a subordinate n s trend the nw se trend tends to follow a precambrian basement and later karroo structural trend ne sw seismic lines indicate up to 10 km extension of the tertiary section in a direction oblique to the probable e w regional extension direction in the southeastern portion of the basin both karroo and tertiary quaternary sediments expand into the lupa fault zone reaching thicknesses of up to 3 and 7 km respectively tertiary quaternary sediment thicknesses decrease northwestward accompanied by a decrease in the amount of extension and a broadening of the basin as extension is transferred to the lake tanganyika rift

impact of the late triassic dashtak intermediate detachment horizon on anticline geometry in the central frontal fars se zagros fold belt iran abstract integration of 2 d seismic lines well data and field studies allow us to determine the geometry variations of anticlines in the highly prolific central frontal fars region in the se zagros fold belt these variations are directly related to changes in thickness of the principal evaporitic intermediate detachment level located along the late triassic dashtak formation anticlines of short wavelength contain a significant over thickening of the evaporitic detachment level in their crestal domain that may reach 1900 m from an original thickness of 550 800 m folds containing thick dashtak evaporites show decoupling across the detachment level and thus a shift of the anticline crest in the underlying permo triassic carbonates of the dehram group which form the major gas reservoir in the central frontal fars four main parameters control the extent and distribution of the decoupled anticlines in the study area a original large thickness of the late triassic evaporitic basin b coinciding larger amounts of anhydrites with increasing total thickness of formation c parallel occurrences of abnormally high fluid pressures and d shortening variations across and along the strike of specific folds the present work relating the different parameters of the dashtak evaporites with the anticline geometry allows a better understanding of the fold geometry variations with depth which is applicable to oil and gas exploration in the se zagros and other similar hydrocarbon provinces characterised by intermediate detachment horizons

diagenetic k feldspar pseudomorphs in the triassic buntsandstein sandstones of the iberian range spain early diagenetic k feldspar in the triassic buntsandstein of the iberian range spain occurs as pseudomorphs after detrital k feldspar or 99 untwinned commonly heavily clouded by vacuoles and tiny inclusions dark luminescing and are composed of numerous fine euhedral crystals of k feldspar the latter property suggests that the pseudomorphs form via dissolution of detrital k feldspar and plagioclase and precipitation of authigenic k feldspar x ray diffraction analysis shows that the authigenic k feldspar is intermediate microcline

east african rift system offset age and tectonic significance of the tanganyika rukwa malawi intracontinental transcurrent fault zone abstract the 1000 200 km tanganyika rukwa malawi fractures area is shown to be a right lateral intracontinental transform zone belonging to the east african rift system using the results carried out from complementary techniques remote sensing field structural analysis and k ar isotopic dating it appears that tectonics in this area have acted at different times the oldest being at 2000 1400 m y the youngest being still active today and are mainly due to the reactivation of nw se structures the area consists mainly of large nw se en echelon dextral transcurrent faults along which the southern tanganyika rukwa and northern malawi troughs are opening ne sw transverse faults showing a curved horizontal shape end these troughs axially eocene to recent volcanic activity is associated with the intersection of the northeastern main nw se transcurrent fracture the livingstone fault

hydrocarbon habitat in main producing areas saudi arabia current hydrocarbon production in saudi arabia is from reservoirs of cretaceous and jurassic age geochemical studies of the sediments and oils suggest that the hydrocarbons were derived from two separate source rock provinces oil production from the large fields in the southern part of the area is from jurassic carbonate reservoirs most of these oils were derived from thermally mature thinly laminated organic rich carbonate rocks of jurassic age callovian oxfordian these source rocks were deposited in an intrashelf basin which is limited to the southern part of the main producing areas extensive vertical migration of oils originating in these sediments is prevented by superjacent evaporite seals deposited during the late jurassic fields in the northern producing areas appear to have derived their hydrocarbons from a source rock province on the north production from cretaceous clastic and carbonate reservoirs is limited to the northeastern part of the producing areas this distribution may be explained by limitation of thermally mature cretaceous source rocks to the northeastern areas or by the local lack of subjacent evaporite seals to separate these reservoirs from jurassic source rocks thermal maturation studies indicate that the hydrocarbons in mesozoic reservoirs migrated into the present traps during the early tertiary

authigenic k feldspar in the bromsgrove sandstone formation triassic of ccntral england abstract authigenic k feldspar is a ubiquitous feature of the bromsgrove sandstone formation triassic in central england it occurs mainly as partially to completely developed euhedral overgrowths on detrital k feldspar cores the authigenic k feldspar is virtually pure kalsi3o8 potassian low sanidine and occurs as optically continuous overgrowths on detrital sanidine and optically discontinuous overgrowths on detrital orthoclase differences in structure and al si disorder thus control the degree of optical continuity of the overgrowths an important feature is the presence of optically and compositionally zoned overgrowths due to minor fluctuations in the bao and na2o content the formation of the overgrowths was dependent upon intrastratal dissolution of detrital grains for a supply of potassium aluminum and silicon precipitation took place within the k2o na2o al2o3 sio2 h2o system and in association with other phases in this system the diagenetic sequence 1 illite 2 quartz 3 k feldspar 4 illite 5 kaolinite is consistent with a progressive increase in k h ratio or h4sio4 activity followed by a general decrease so that the later interstitial fluids were much depleted in k ions and kaolinite was the final phase to precipitate

organic geochemistry and petrography of kazhdumi albian cenomanian and pabdeh paleogene potential source rocks in southern part of the dezful embayment iran there are several source rock units in the zagros basin but the cretaceous kazhdumi and paleogene pabdeh formations probably have produced the majority of the commercial hydrocarbons in this area among the hydrocarbon provinces of iran the dezful embayment which is located southwest of zagros mountains is one of the most prolific regions in the middle east numerous studies have been made in the northern part of the dezful embayment but relatively few have been done in its southern part the present study focuses on organic matter characterization of two potential source rocks kazhdumi and pabdeh formations in southern part of the dezful embayment cuttings samples 114 were collected from 10 wells and evaluated using rock eval pyrolysis and organic petrography in order to characterize the content and type of organic matter and thermal maturity the results showed that the average total organic carbon toc content of kazhdumi and pabdeh formations are 2 48 and 1 62 wt respectively the highest toc contents for both formations are found in the northern compartment and decreased gradually toward the south pyrolysis data reveal that organic matter has a fair to very good hydrocarbon generation potential and are classified as type ii iii and type iii rock eval t max and vitrinite reflectance show that the majority of samples are in the early mature to mature stage of the oil generation window c 2012 elsevier ltd all rights reserved

neogene sediments and modern depositional environments of the zagros foreland basin system a sedimentological investigation of the neogene deposits of the zagros foreland basin in sw iran reveals a continuous and largely gradational passage from supratidal and sabkha sediments at the base represented by the gachsaran formation to carbonates and marine marls mishan formation with basal guri carbonate member followed by coastal plain and meandering river deposits agha jari formation and finally to braided river gravel sheets bakhtyari formation this vertical succession is interpreted to represent the southward migration of foreland basin depozones from distal foredeep and foredeep to distal wedge top and proximal wedge top respectively as the zagros fold thrust belt migrated progressively southward towards the arabian foreland this vertical succession bears a striking similarity to modern depositional environments and sedimentary deposits observed in the zagros region today where one passes from mainly braided rivers in the zagros mountains to meandering rivers close to the coast to shallow marine clastic sediments along the northern part of the persian gulf and finally to carbonate ramp and sabkha deposits along the southeastern coast of the persian gulf this link between the neogene succession and the modern day depositional environments strongly suggests that the major neogene formations of the zagros foreland basin are strongly diachronous as shown recently by others and have active modern day equivalents

calcareous nannofossils of the barremian aptian interval from the southeastern tethys zagros basin west iran and their paleoceanographic implications a record of oceanic anoxic event 1a abstract calcareous nannofossils and stable isotope data 13ccarb from a pelagic section of the zagros basin west iran were used for an integrated oceanographic analysis of the barremian aptian interval the study aims at analyzing various oceanographic shifts recorded from this period including the oceanic anoxic event 1a oae 1a in an expanded carbonate rich mudstone sequence of the eastern tethys the extreme thickness 510 m of the succession allows us to study the environmental changes known from the barremian and aptian interval in much more detail than previously done by looking at closely spaced samples it is possible to better understand the onset the course and the aftermath of the oae 1a event calcareous nannofossils suggest an early barremian nannofossil zone cc5 nc5c to late aptian age nannofossil zone cc7b nc7b for the studied sequence the biostratigraphic zonation is based on the last occurrence of calcicalathina oblongata the first occurrences of rucinolithus irregularis and eprolithus floralis and the last occurrence of micrantholithus hoschulzii a total of 98 species has been encountered in the studied interval with good to moderate in few cases poor preservation based on the calcareous nannofossil assemblages signals for a warming event in the mid barremian are characterized by high relative abundances of warm water specie e g rhagodiscus asper along with neritic taxa micrantholithus spp nannoconus spp the oae 1a was identified via calcareous nannofossil biostratigraphy in combination with the 13ccarb record for the oae 1a early aptian warm and eutroph conditions were likely as suggested by high relative abundances of r asper diazomatolithus lehmanii small zeugrhabdotus spp and lithraphidites carniolensis the late aptian is characterized by cool surface water conditions

occurrence of organic matter rich deposits middle jurassic to lower cretaceous from qalikuh locality zagros basin south west of iran a possible oil shale resource abstract organic rich deposits of qalikuh locality zagros basin southwest of iran are unconventional hydrocarbon resources considered as an oil shale which is hosted within a carbonate succession with the age range of middle jurassic to lower cretaceous leco carbon rock eval vi and modified fischer assay analysis were performed on some outcrop samples of these resources to investigate the occurrence of oil shale in the studied samples mean total organic carbon toc is 17 3 wt and the average of petroleum genetic potential s1 s2 is 98 kg hc t rock furthermore toc has direct relationship with petroleum genetic potential hydrogen index hi tmax diagram indicates that the organic matter corresponds to type ii kerogen of probable marine origin with high quality of oil generation according to rock eval data and bitumen reflectance brr the samples are thermally early mature based on the studied samples oil yield of the qalikuh oil shales ranges from 6 1 to 7 9 wt mean oil gas ratio is 2 7 and mean oil yield is 56 7 l t rock according to the observations the production value of qalikuh oil shale is more or less similar in the entire studied regions whereas the total production is below the expected values the produced oil is considerably lighter higher api than that of most other known oil shales

palynology and petroleum potential of the kazhdumi formation cretaceous albian cenomanian in the south pars field northern persian gulf abstract the kazhdumi formation of the bangestan group is a well known source rock that has produced abundant oil in most petroleum fields in the zagros basin which stretches from northwest to southwest iran over hundreds of kilometres the formation reaches a thickness of 230 m at the type section in northwest zagros but thins out to 40 50 m in wells studied from the south pars giant petroleum field where it comprises mainly grey shales with occasional intercalations of marls and sandstones south pars best known as the iranian part of the world s largest non associated gas field contains small quantities of oil above and below the kazhdumi formation palynology has been used to assess the age and palaeoenvironment of the kazhdumi formation and to evaluate its petroleum potential a total of 68 ditch cutting samples recovered from five wells of which four are oil prone have been analyzed an age between late albian and cenomanian is established for the formation based on dinoflagellate cyst biostratigraphy and four palynofacies types have been recognized using the relative proportions of terrestrial elements marine palynomorphs and amorphous organic matter aom the ratio of terrestrial to marine elements is high in most samples indicating a nearshore sedimentary environment twenty two samples from the four oil prone wells were also selected for geochemical analysis using rock eval pyrolysis results show that the kazhdumi formation at south pars in contrast to the zagros basin is gas prone predominantly type iii kerogen thermally immature and poor in terms of hydrocarbon generation it could not have produced the oil in those oil prone wells studied

organic geochemistry of crude oils and cretaceous source rocks in the iranian sector of the persian gulf an oil oil and oil source rock correlation study abstract the marls and argillaceous limestones of the cretaceous kazhdumi formation ahmadi member of the sarvak formation and gurpi formation are considered to be important source rock candidates in the persian gulf to evaluate their source rock characteristics 265 cutting samples of these rock units from 20 fields in offshore iran were analyzed using rock eval pyrolysis organic petrography stable carbon isotope composition and biomarker analysis 1d basin modeling was also applied to analyze the burial and thermal history of these source rock candidates based on the results the kazhdumi and gurpi formations which have fair source rock potential and the ahmadi member which has fair to good source rock characteristics were deposited in a marine reducing environment with marine organic matter as the main input different maturity indicators showed that the ahmadi member and kazhdumi formation are thermally immature to mature and the gurpi formation is immature to early mature in the study area the results of the modeling suggested that the kazhdumi formation and ahmadi member in the southeastern parts of the study area are within the main oil window and that the gurpi formation has just begun to generate hydrocarbons all three formations are thermally immature in the eastern parts in the western parts of the persian gulf the kazhdumi formation is early mature and the other formations are immature the biomarker and stable carbon isotope parameters of these rock units were compared with 20 crude oil samples in the southeastern persian gulf based on the hierarchical cluster analysis hca principal component analysis pca and carbon isotope composition the studied crude oils were divided into two groups group i oils from cretaceous reservoirs were probably derived from cretaceous source rocks while group ii oils from jurassic and cretaceous reservoirs with jurassic rocks as the expected source rocks the performed oil source rock correlation shows a positive correlation between the group i oils and the ahmadi member

engineering geological characterization and comparison of predicted and measured deformations of a cavern in the italian alps a detailed engineering geological characterization and performance monitoring were carried out at the site of an underground powerhouse cavern in the italian alps in the area of the hydroelectric project consisting of a 4 m diameter and 10 km long diversion tunnel and a powerhouse cavern 20 m wide 39 m long and 30 m high metamorphic anisotropic rocks are present a pervasive foliation whose trend describes an open fold at the cavern site characterizes the geological structure the studies include petrographic analyses and geo mechanical properties of the rocks in situ stress measurements and rock mass classifications for the cavern site as well as the surrounding area based on field investigations two numerical models fem and dem codes were used to investigate the overall stability of the excavation and to predict the expected deformation caused by each excavation phase the measurements of actual deformations by multi base extensometer data are reasonably close to those predicted through the numerical approaches

a classification of petroleum on the basis of the ratio of sulfur to nitrogen abstract examination of the ratio of organic sulfur to organic nitrogen s n in 455 petroleums shows that individual petroleum families selected geographically stratigraphically and by source exhibit distinctive limited ranges of the value of this ratio commonly observed values in petroleums are between 1 and 20 the coefficient of variation within a family is frequently 100

stable carbon isotope compositions of crude oils application to source depositional environments and petroleum alteration the carbon isotopic composition of the c15 saturate and aromatic hydrocarbon fractions and the gas chromatographs of the c15 saturate fraction of 339 oils were geochemically and statistically evaluated results of this study show that the average isotopic compositions of the c15 aromatic hydrocarbon fractions of oils sourced from terrigenous or marine organic matter are identical the average isotopic composition of the c15 saturate fraction of oils derived from terrigenous organic sources is slightly more negative 0 9 pmil than the average for marine oils but this difference is insufficient to be used as a reliable source indicator reports in the literature stating that marine oils are isotopically more positive than te rigenous oils and that the difference can be utilized to distinguish between the two are therefore not supported by this study the isotopic differences between oils sourced from terrigenous and marine organic matter do not manifest themselves in the range of absolute values of one oil fraction but rather in the isotopic relationship between the saturate and aromatic hydrocarbon fractions the isotopic relationship is the following oils of terrigenous organic source dgr13caro 1 12 dgr13csat 5 45 oils of marine organic source dgr13caro 1 10 dgr13csat 3 75 the difference between the two equations was evaluated statistically and a statistical parameter cv the canonical variable cv 2 53 dgr13csat 2 22 dgr13caro 11 65 was used to distinguish between marine and terrigenous oils cv values larger than 0 47 indicate predominantly a terrigenous organic source for the oil whereas cv values smaller than 0 47 indicate mostly a marine organic source thermal maturity differences in oils and isotopic variations in the source beds can cause as much as 2 pmil variations in the isotopic composition of one family of oils finally stable carbon isotopes can in some situations help correlate biodegraded oils to their nondegraded counterparts

petroleum system analysis of the northwestern part of the persian gulf iranian sector abstract geochemical geological and geophysical data were used to identify and update genetic oil families potential source rocks and hydrocarbon generation kitchen as well as probable migration pathways in the northwestern part of the persian gulf rock eval analysis was performed on 52 cutting samples of prospective cretaceous tertiary source rocks according to the results most of the samples have poor to fair potential for hydrocarbon generation except for the albian formation which possesses good to excellent source rock characteristics in the study area two genetic oil families were identified based on source and age related biomarkers as well as stable carbon isotope ratios for 23 crude oil samples family i occurs in upper jurassic lower cretaceous reservoirs mainly in the surmeh hith basin whereas family ii occurs in lower cretaceous tertiary reservoirs mainly in the garau gotnia basin all attempts to correlate the identified families to prospective source rocks failed due to substantial maturity differences between the oils and rock samples inversion correlation based on detailed isotopic and biomarker analyses however confirms that the carbonates and marls of the neocomian and albian formations are the main oil generating facies for families i and ii respectively the geographical extension and composition of the identified oil families are highly affected by source rock facies distribution and migration pathways 2d cross sections provided in the region indicate the dominance of lateral and vertical migration pathways from the binak depression as the main hydrocarbon generation kitchen toward the structural highs in the study area

new biostratigraphic age dates from the lake rukwa rift basin in western tanzania geologic note 1 the rukwa rift basin in western tanzania is a segment of the western branch of the east african rift system three major stratigraphic units have been recognized in the basin from oldest to youngest karroo supergroup the red sandstone and the lake beds these units have traditionally been assigned the following ages respectively based upon lithologic correlations permian triassic jurassic cretaceous and tertiary recently microfloral assemblages collected from sidewall cores and cuttings from two deep exploration wells drilled in the basin have provided new data on the age of these formations the biostratigraphic data suggest the formations should be assigned the following ages karroo supergroup late permian red sandstone neogene miocene late pliocene and the lake beds late pliocene holocene the new age dates indicate that the post karroo to pre miocene history of the basin is one of relative quiescence and the modern rift is a relatively young feature this interpretation is more consistent with the tectonic histories of the other basins of the western rift

the lower silurian qalibah formation of saudi arabia an important hydrocarbon source rock 1 the lower silurian qalibah formation represents a distinct lithostratigraphic time transgressive sequence it is disconformably bounded below by the upper ordovician to possibly lower silurian sarah formation and above by the continental to marginal marine lower devonian and possibly upper silurian tawil sandstone formation this paper redefines the qalibah formation within these boundaries in its reference section near the town of al qalibah in northwest saudi arabia the qalibah is 499 m thick whereas in a subsurface composite section it reaches 955 m the qalibah formation is a coarsening upward progradational sequence consisting of a lower qusaiba shale member and an upper sharawra sandstone member the basal hot shale of the qusaiba is a black euxinic bottomset shale up to 70 m thick which was deposited during the early silurian sea level rise following the deglaciation of gondwana this paleozoic shale is organic rich and the most likely source rock of the low sulfur high gravity oil condensate and gas discovered in recent years in the paleozoic rocks of central and eastern saudi arabia lithologically similar silurian sequences were deposited over most of the broad stable shelf of gondwana from the middle east to the african sahara

simulation of cracking near a large underground cavern in a discontinuous rock mass using the expanded distinct element method abstract the rock masses in a construction site of underground cavern are generally not continuous due to the presence of discontinuities such as bedding joints faults and fractures the performance of an underground cavern is principally ruled by the mechanical behaviors of the discontinuities in the vicinity of the cavern a number of experimental and numerical investigations have demonstrated the significant influences of discontinuities on the mechanical thermal and hydraulic behaviors of discontinuous rock masses indicating that the deformation mechanism and stability of rock structures in the discontinuous rock masses depend not only on the existing discontinuities but also on the new cracks generated and thereafter keep propagating due mainly to the stress redistribution induced by excavation in this study an expanded distinct element method edem was developed for simulating the crack generation and propagation due to the shear and tension failures in the matrix rock blocks using this method excavation simulations of deep underground caverns have been carried out on the models with differing depths of cavern and differing geometrical distributions of the existing discontinuities model experiments by using the base friction test apparatus were conducted to verify the proposed numerical approach furthermore the support effects of rock bolts on controlling the deformations of the rock mass surrounding a cavern and movements of key blocks were evaluated by means of the edem approach

burial history reconstruction and thermal maturity modeling for the middle cretaceous early miocene petroleum system southern dezful embayment sw iran abstract the middle cretaceous early miocene petroleum system is the most important hydrocarbon system in the zagros basin rock eval pyrolysis organic petrography and thermal 1d modeling were performed on wells located in the southern dezful embayment the results provide information on organic matter quantity and quality as well as burial and thermal histories of source rocks in the framework of the basin evolution a total of 98 cutting samples from bk 4 kk 1 si 4 and rs 2 wells were pyrolyzed by rock eval 6 also thermal maturity of organic matter derived from tmax of rock eval was interpreted in conjunction with vitrinite reflectance data 50 samples the toc values of the sequences mainly range from 0 5 to 2 5 wt the average values of tmax and vitrinite reflectance indicate that samples from the wells have reached maturities corresponding to early mid oil generation reconstruction of thermal history suggests that various steady heat flow values 62 54 50 and 56 mw m2 for bk 4 kk 1 si 4 and rs 2 wells respectively resulted in the best fit between the calculated and the observed vitrinite reflectance and bottom hole temperatures in our modeling thus values of heat flow decrease from 60 mw m2 in the southern basin margin to about 50 mw m2 along the ne of the dezful embayment and the zagros basin according to our modeling results the onset of oil generation from source rocks in the studied area occurs well after deposition of the seal rock and formation of traps ensuring entrapment and preservation of migrated hydrocarbons

the effect of joint constitutive laws on the modelling of an underground excavation and comparison with in situ measurements the paper discusses the results of a numerical study which examines the influence of joint constitutive models on the response of a specific jointed rock mass mane up of an anisotropic rock slate it presents a comparison between predicted convergences and displacements of rock mass surrounding a pilot gallery and those measured during field investigations to perform this analysis the two dimensional distinct element method code udec is used and three joint laws are compared based on field investigations for site characterisation two models are constructed according to fracture density model a and model b for each of them the influence of joint constitutive law on the stability of the gallery is examined and comparisons between the investigations and predictions are made examination of the results shows that there is no noticeable change in stress magnitudes between laws the displacement magnitudes depend on 1 the constitutive law 2 the input model parameters and 3 the fracture density a parametric study in the case of model a indicates that a relatively good march between predicted and measured displacements around the gallery can be observed in certain areas

evaluation of oil fingerprints similarity by a novel technique based on ftir spectroscopy of asphaltenes modified moving window correlation coefficient technique abstract investigation of oil fingerprints heterogeneities in different wells across the reservoir is a critical effort in various disciplines of geochemical studies exploring new trustworthy and straightforward techniques is an ongoing and interesting subject in the oil industry in this paper a novel procedure for oil fingerprints comparison by employing the structural characteristics of asphaltenes is suggested for the first time the modified version of the moving window correlation coefficient is proposed to resolve the drawbacks of the standard procedure and then implementing for comparison of oil fingerprints this procedure is based on peak ratios calculated from the second derivative ftir spectra of asphaltene samples the results of this technique are summarized in a matrix with green red and yellow cells based on the calculated values of the minimum correlation coefficient in all moving windows mmwr and the average of correlation coefficients in all moving windows amwr regarding defined thresholds to better visualization of fingerprint similarity or dissimilarity between studied samples the oil fingerprint similarities in the two case studies from the dezful embayment of southwest iran were investigated to demonstrate the usefulness of this technique ten samples from different wells in the qale nar oil field and eight samples from the shadegan oil field were studied results showed that crude oils in the asmari reservoir from the qale nar field have a similar fingerprint and are homogenous but crude oils in the asmari reservoir from the shadegan field involves several zones based on oil fingerprints similarity whole oil gas chromatography wogc was performed for checking purposes the proposed method based on ftir spectra of asphaltene samples and their comparison with the modified moving window correlation coefficient can be regarded as a novel reliable and straightforward technique for oil fingerprint similarity assessment

the diagenesis of continental karoo tertiary siliciclastics from an east african rift valley rukwa tukuyu area tanzania discussion

study of hydrocarbon generation and 1d 2d modeling of hydrocarbon migration at the karanj and parsi oilfields southern dezful embayment sw iran abstract this study is a 2d basin modeling to determine the petroleum system i e cretaceous neogene play of the karanj and parsi oilfields in the southern dezful embayment sw iran this system is characterized by occurrence of source rocks of middle cretaceous late cretaceous and paleocene to eocene kazhdumi pabdeh and gurpi formation reservoirs of upper cretaceous and late oligocene early miocene ilam sarvak and asmari formations and seals of paleocene and miocene pabdeh and gachsaran formation considering temperature transformation ratio and vitrinite reflectance the maturity of source rocks kazhdumi pabdeh and gurpi formation was investigated a maturity history analysis showed that the maturity of kazhdumi pabdeh and gurpi formation started during 70 60 and 4 ma respectively generation and expulsion of hydrocarbons started 16 ma in the kazhdumi formation and 3 ma in the pabdeh formation that continued up to the present the analysis of the transformation ratio indicates transformation of significant amounts of kazhdumi source rocks for generating hydrocarbons migration of hydrocarbons from the kazhdumi formation is mainly vertically upward from pabdeh formation migration is both vertically upward to the asmari reservoir and downwards to the ilam sarvak reservoir however some local traps have formed due to the hydrocarbon accumulation above the faults our results reveal that petroleum generation migration and entrapment occurred at proper timing which facilitated the migration of hydrocarbons and their accumulation in the reservoirs