imaging permeability structure within the highly permeable carbonate earth inverse theory and experiment in most oil reservoir rocks the squirt flow characteristic frequency fsq range of 10 100 khz is much less than the biot characteristic frequency f0 range of 1 mhz 1 ghz in contrast carbonate aquifers have very high permeability 10 3000 d and the two characteristic frequencies are reversed f0 from 10 hz to 10 khz and fsq from 1 mhz to 100 mhz the principal objective of this paper is to develop a pilot inverse method for robust imaging of the high permeability structure within carbonate aquifers an analytical approximate model called the super k model is developed the super k model coincides numerically with the combined biot and squirt flow mechanism model when permeability is higher than 100 md and the frequency is lower than 100 khz the super k regime in the super k regime the pore fluid is always relaxed so that the attenuation due to the biot mechanism is roughly four times larger than that of the biot model also empirical equations are developed that relate the stiffness and rigidit

petrography and reservoir physics ii relating thin section porosity to capillary pressure the association between pore types and throat size porosity in reservoir rocks is configured into a few types of pores whose size and shape are controlled by depositional fabric and postdepositional processes the size shape and abundance of each pore type can be objectively determined from thin section using image analysis and pattern recognition procedures each pore type tends to be associated with a limited range of throat sizes the association between pore type and throat size can be determined using regression procedures linking pore type data obtained from thin section with capillary pressure data to do so a set of samples is required wherein the association between pore type and throat size is fixed but where pore type proportions vary between samples this condition is met by a sample suite representing res rvoir facies from a single core or in many cases from a single field the relationship between pore type and throat size is an effective means to relate reservoirs in terms of the efficiency of the porous microstructure to multiphase flow parameters derived from the relationship can be used to construct accurate physical models that subdivide physical response in terms of the contributions of each pore type

impact of pore structure and fractal characteristics on the sealing capacity of ordovician carbonate cap rock in the tarim basin china abstract evaluating the heterogeneity and sealing capacity of carbonate cap rocks is of great significance for hydrocarbon production however the main controls on pore size distribution in carbonate cap rocks are not well constrained in this contribution we analyze drill core samples of carbonate cap rocks from the ordovician yingshan formation tarim basin to study their pore properties and investigate the controls of pore throat structure and fractal dimension on the sealing capacity of the cap rock results from petrography and a combination of mercury injection capillary pressure and nitrogen gas adsorption tests reveal that there are four lithological cap rock types with micrite being the most prevalent one followed by calcarenite six types of pore throat structures and fractal dimensions from d1 to d6 are classified based on the pore size distributions including macropore i macropore ii mesopore i mesopore ii transitional pore i and transitional pore ii the fractal dimensions show that there is a decreasing trend from d1 to d6 with decreasing pore size diameter suggesting that the macropore and mesopore types present more complex pore throat structures than the transitional type the total fractal dimension dtotal indicates that the pore throat structures are complex and heterogeneous the sealing heights of the gas column have a positive correlation with cement content in calcarenite and a negative correlation with microfracture density mesopore ii and transitional pore types make a significant contribution to enhancing the breakthrough pressure the fractal variations mainly result from macropores and mesopores while transitional pores and micropores weaken the impact of the whole pore system on the dtotal value the heterogeneity and anisotropy of macropores is the main control on the sealing capacity of the cap rock the increasing of d1 considerably contributes to the pore shape heterogeneity and enhances the capillary resistance force to hydrocarbon migration therefore the fractal dimension is an effective approach for investigating the pore throat structure and sealing capacity of carbonate cap rocks

geologic exploration of a molybdenum rich porphyry copper deposit at mocoa colombia concealed porphyry copper molybdenum target high grade mineralization drilling to date has delineated 260 million metric tons of hypogene ore averaging a little more than 1 percent cu equivalent the deposit is associated with a partly unroofed stock of biotite dacite porphyry which was emplaced into broadly cogenetic andesitic and dacitic volcanic rocks during the jurassic a composite batholith of intermediate composition is located only 1 7 km from the deposit but was emplaced 30 to 40 m y earlier the cylindrical orebody contains chalcopyrite molybdenite and local traces of bornite the orebody is largely overlain by an essentially barren quartz sericite pyrite lithocap up to several hundred meters thick high grade copper molybdenum ore is hosted by multiple hydrothermal breccias although the mocoa porphyry system is overlain by a jarositic zone of partial leaching up to 260 m thick rapid erosion during the late cenozoic precluded generation of a significant zone of supergene chalcocite enrichment the high precipitation caused nearly complete removal of abundant hypogene anhydrite and supergene gypsum to depths of at least 900 m modified journal abstract

subgrain scale decoupling of re and 187os and assessment of laser ablation icp ms spot dating in molybdenite abstract reproducibility of re os molybdenite ages depends on sample size and homogeneity suggesting that re and os are decoupled within individual molybdenite crystals and do not remain spatially linked over time in order to investigate the re os systematics of molybdenite at the subgrain micron scale we report la icp ms re os ages for an archean molybdenite crystal from aittojarvi finland analyzed in situ in a white aplite matrix a related aittojarvi molybdenite a996d in the form of a very fine grained mineral separate is used as one of our in house ntims standards and thus its age of 2760 9 ma is well established measurements of 187 re 187 os 185 re on micron scale spots along 200 m traverses across the crystal yield a wide range of ages demonstrating that in this case microsampling of molybdenite does not produce geologically meaningful ages experimentation with mineral separations and sample size over a 7 yr period predicted that this would be the outcome we suggest that 187 os is more likely to be the mobile species based on its charge and ionic radius and that 187 os becomes decoupled from parent 187 re with time on the micron and larger scale incompatible charge and ionic radius for os ions formed during reduction of molybdenite forming fluids may explain the widely observed absence of common initial os in molybdenite geologically accurate ages for molybdenite can only be obtained for fully homogenized crystals or crystal aggregates so that any post crystallization 187 re 187 os decoupling is overcome a growing number of geologically accurate id ntims 187 re 187 os ages for homogenized molybdenite suggest that postcrystallization mobility of radiogenic 187 os must be limited to within the molybdenite mineral phase we suggest that radiogenic 187 os may be stored in micron scale dislocations kink bands and delamination cracks produced by deformation and that the unusual structure and deformation response of molybdenite results in an increased chemical stability in this mineral migration of 187 os into adjacent silicate phases is highly unlikely but other contacting sulfides may take in os in an example from a proterozoic skarn deposit at pitkaranta western russia we demonstrate minor loss of radiogenic 187 os from molybdenite and a corresponding gain in adjacent chalcopyrite such that the molybdenite age is not perceptibly disturbed whereas the resulting chalcopyrite ages are impossibly old therefore it is unadvisable to perform re os analytical work on any sulfide in contact or intimate association with molybdenite in addition to large errors in the age if the isochron method is employed initial 187 os 188 os ratios could be erroneously high leading to seriously errant genetic interpretations

effect of carbonate pore structure on dynamic shear moduli elastic shear moduli from ultrasonic measurements of carbonate rocks show an increase or decrease when saturated from the dry state with brine the induced changes on the moduli have been attributed to several rock fluid interaction effects including viscous coupling reduction in free surface energy and dispersion caused by local flow with a subsequent effect on acoustic velocities as many studies have recognized that acoustic velocity in carbonate rocks is dependent on pore structure a relationship between the pore structure and observed changes must to a certain extent exist we make use of quantitative digital image analysis parameters such as dominant pore size and perimeter over area to demonstrate how changes in dynamic shear moduli upon saturation relate to the geologic make up of the rock samples with a small dominant pore size and large perimeter over area show abnormal decrease in shear moduli with saturation from the dry state this is attributed to the large surface area available for matrix fluid interaction samples with large dominant pore size and small perimeter over area show an increase in shear moduli with saturation this may be a dispersion effect as high frequency and high permeability may cause the fluid in the saturated samples to move out of phase with the solid during propagation of the acoustic wave and thus cause a stiffening effect

quantitative characterization of carbonate pore systems by digital image analysis a new method of digital image analysis can quantify pore parameters over more than three orders of magnitude from a submicron to a millimeter scale this porosity characterization does not require knowledge of lithology age burial depth or diagenesis of the sample the method is based on digital analyses of images from thin sections at variable magnifications taken under an optical microscope om and under an environmental scanning electron microscope esem the results help explain variations in permeability for carbonate samples with a variety of complex pore structures the analyses however can be done on any thin sections of other rock types the om images provide macroporosity information whereas the esem images yield information on microporosity the boundary between macroporosity and microporosity is defined at a pore area of 500 m2 which translates to a pore length of approximately 20 m which is roughly the thickness of a thin section and thus the resolution of the om the digitized thin section images are binarized into a macropore and a matrix phase om or a micropore and a solid phase esem a standard digital image analysis program is used to detect all individual pores and to measure pore area and pore perimeter based on these analyses one can calculate for each sample the amount of macroporosity the amount of microporosity within the matrix intrinsic microporosity the shapes of the macropores perimeter over area and the pore size distribution comparison of total porosity determined from plugs indicates that macroporosity and microporosity values based on this methodology match the plug data confirming the validity of the method the combination of macroporosity and microporosity data yields pore size distribution and pore shape information that can explain the distribution of physical properties in particular permeability in parameter sensitivity analyses using neural networks permeability appears to be mainly controlled by the macropore shape in high permeability samples and by the amount of intrinsic microporosity in the low permeability samples

controls on sonic velocity in carbonates compressional and shear wave velocities v p and v s of 210 minicores of carbonates from different areas and ages were measured under variable confining and pore fluid pressures the lithologies of the samples range from unconsolidated carbonate mud to completely lithified limestones the velocity measurements enable us to relate velocity variations in carbonates to factors such as mineralogy porosity pore types and density and to quantify the velocity effects of compaction and other diagenetic alterations

an autochthonous geological model for the eastern andes of ecuador abstract we describe a traverse across the cordillera real and sub andean zone of ecuador poorly known areas with very little detailed mapping and very little age control the spine of the cordillera comprises deeply eroded triassic and jurassic plutons the roots of a major arc emplaced into probable palaeozoic pelites and metamorphosed volcanic rocks the w flank comprises a jurassic submarine basaltic andesitic volcanic sequence which grades up into mixed jurassic cretaceous volcanic and sedimentary rocks of the inter andean valley the sub andean zone on the e flank of the cordillera comprises a newly recognized cretaceous basin of cleaved mudrocks quartz arenites and limestones east of the syndepositional cosanga fault the cretaceous basin thins into a condensed sequence that is indistinguishable from the rocks of the adjacent hydrocarbon bearing oriente basin the principal penetrative deformation of the cordillera real was probably latest cretaceous palaeocene it telescoped the magmatic belts but shortening was largely partitioned into the pelites between plutons the plutons suffered inhomogenous deformation some portions completely escaped tectonism the pelites conserve two foliations the earliest comprises slaty cleavage formed under low or sub greenschist conditions the later is a strong schistosity defined by new mica growth it largely transposed and obliterated the first both foliations may have developed during a single progressive deformation we find inappropriate recent terrane models for the cordillera real and sub andean zone of ecuador instead we find remarkable similarities from one side of the cordillera to the other including a common structural history in place of sutures we find mostly intrusive contacts between major plutons and pelites triassic to cretaceous events occurred on the autochthonous western edge of the archaean guyana shield the latest cretaceous paleocene deformation is interpreted as the progressive collision of an oceanic terrane s with the south american continent young fault movements have subsequently juxtaposed different structural levels through the cordillera real orogen

the remarkable re os chronometer in molybdenite how and why it works the re os rhenium osmium chronometer applied to molybdenite mos2 is now demonstrated to be remarkably robust surviving intense deformation and high grade thermal metamorphism successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite unique to each sample such that recognized spatial decoupling of 187re parent and 187os daughter within individual molybdenite crystals is overcome highly precise accurate and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry id ntims spatial decoupling of parent daughter precludes use of the laser ablation icp ms microanalytical technique for re os dating of molybdenite the use of a reference or control sample is necessary to establish laboratory credibility and for interlaboratory comparisons the rb sr k ar and 40ar 39ar chronometers are susceptible to chemical and thermal disturbance particularly in terranes that have experienced subsequent episodes of hydrothermal magmatic activity and therefore should not be used as a basis for establishing accuracy in re os dating of molybdenite as has been done in the past re os ages for molybdenite are almost always in agreement with observed geological relationships and when available with zircon and titanite u pb ages for terranes experiencing multiple episodes of metamorphism and deformation molybdenite is not complicated by overgrowths as is common for some minerals used in u pb dating e g zircon monazite xenotime nor are re and os mobilized beyond the margins of individual crystals during solid state recrystallization moreover inheritance of older molybdenite cores incorporation of common os and radiogenic os loss are exceedingly rare whereas inheritance common pb and pb loss are common complications in u pb dating techniques therefore molybdenite ages may serve as point in time markers for age comparisons

heterogeneity of intergranular intraparticle and organic pores in longmaxi shale in sichuan basin south china evidence from sem digital images and fractal and multifractal geometries abstract previous studies have determined many types of pores in shale such as organic pores inorganic pores and microfractures in this study pores are classified as intergranular intraparticle and organic pores based on the location of their occurrence the heterogeneities of the three pore types and their effects on the occurrence of shale gas which is of utmost practical importance for shale gas exploration and development are discussed in this study the three types of pores are quantitatively characterized using fractal and multifractal methods the mean fractal dimension and mean width of the multifractal spectrum of these pores are found to be different i e 1 5985 and 1 665 for intraparticle pores 1 5869 and 1 475 for intergranular pores and 1 6 and 1 3725 for organic pores intraparticle pores have the highest heterogeneity intergranular pores have intermediate heterogeneity and organic pores have the lowest heterogeneity sem images show that organic pores have good connectivity homogeneous distribution and small range of aperture change but have the lowest heterogeneity even where pores are abundant thus they provide the largest shale gas occurrence space in contrast intergranular pores are less abundant have lower connectivity and have higher heterogeneity than organic pores thereby providing a relatively smaller shale gas occurrence space finally intraparticle pores are the least abundant and possess the poorest connectivity largest range of aperture change and highest heterogeneity of the three pore types thereby providing the smallest shale gas occurrence space we conclude that organic pores are crucial to the occurrence of shale gas and can provide a new index for the evaluation of shale gas exploration and development

permeability estimation based on thin section image analysis and 2d flow modeling in grain dominated carbonates abstract permeability estimation based on image analysis is a good alternative when an intact core plug is not available for laboratory measurement while there is much research on permeability estimation from 2d and 3d images or models accurately estimating permeability for carbonates a type of rock with substantial heterogeneity is still challenging in this study a method for permeability estimation based on thin section image analysis and 2d permeability simulation is developed for grain dominated carbonates based on semi theoretical analysis of 2d and 3d permeability k2d and k3d relationship the mathematical expression of the k2d k3d is examined and validated with a grainstone carbonate sample for which both k2d and k3d were obtained through permeability simulation based on micro ct images the method was applied to 24 grain dominated carbonate samples collected from different locations with a large variation in rock textures and fabrics and a broad range of permeability from 0 1 md to 3200 md representativeness of the thin section and the correct determination of the effective pores are the key for accurate estimation the estimated permeability was compared to the measured value and 92 of the results are within a factor of 5 and 46 are with a factor of 2 potential sources of systematic error are discussed both qualitatively and quantitatively

novel microscopic imager instrument for rock and fluid imaging core analysis from reservoir rock plays an important role in oil and gas exploration as it can provide a large number of rock properties some of these rock properties can be extracted by image analysis of microscopic rock images in the visible light range such properties include the size shape and distribution of pores and grains or more generally the texture mineral distribution and so on a novel laboratory instrument and method allows for easy and reliable core imaging this method is applicable even when the core sample is in poor shape the capabilities of this technique can be verified by core images image interpretation and dynamic measurements of rock samples during flooding a microscopic imager instrument is operated in video acquisition mode and can measure additional properties such as fluid mobility by detecting the emergence of injected fluids across the core sample

lateral moisture flow beneath a sandy hillslope without an apparent impeding layer part of a small drainage basin on the sevilleta national wildlife refuge about 25 km north of socorro nm was intensively instrumented with soil monitoring equipment to estimate natural ground water recharge soil moisture data were analysed with special attention to characterizing the influence of topography on the direction of vadose water flow paths in fine to medium aeolian sand moisture content data were obtained by the neutron scattering technique and hydraulic head data were obtained using tensiometers in addition tracer experiments were conducted on a sandy hillslope to delineate the flow paths of vadose water the results indicate that there is a strong lateral component to unsaturated flow on a hillslope even in the absence of apparent sublayers of much lower permeability darcian calculations estimate the long term steady deep flux beneath a concave location to be about 4 per cent of an assumed mean annual precipitation of 20 cm the deep soil water flux downward varied by several orders of magnitude during the 17 month period of record

re os dating of low level highly radiogenic llhr sulfides the harnas gold deposit southwest sweden records continental scale tectonic events to obtain geologically meaningful and precise results on low level sulfides that are highly radiogenic blank corrections that account for the extreme difference in the os isotope composition of sample and blank are necessary and the resulting data is best plotted in 187 re 187 os space much like the approach used for molybdenites we here introduce the acronym llhr as a means of characterizing low level and highly radiogenic sulfides use of the traditional 187 re 188 os vs 187 os 188 os plot for llhr sulfides leads to large analytical uncertainties and highly correlated errors as 188 os is poorly determined and can generally be accounted for by the blank we now recognize that llhr sulfides such as those encountered at the harnas au deposit are a common occurrence and characteristic of many crustally affiliated ore systems the harnas au deposit in southwest sweden is located in the mjosa vanern mineral belt that transects from northwest to southeast the prominent geologic fabric of the sveconorwegian province including the mylonite zone the deposit is hosted in a strongly sheared and locally brecciated sulfide bearing quartz vein that crosscuts the foliation of orthogneisses belonging to the 1600 maa mal granitoid suite a 187 re 187 os isochron of 973 34 ma 2 for samples of pyrite and chalcopyrite from outcrops of the harnas alma and silvergruvan veins was obtained the harnas and subsidiary alma veins are au bearing whereas the silvergruvan 2 5 km to the southeast is not of the au bearing type four replicate analyses of an additional pyrite sample from the harnas vein yield a model age of 616 40 ma 95 c l in all samples re and 187 os concentrations are extremely low 0 35 to 7 1 and 0 005 to 0 074 ppb respectively and total common os 0 002 0 028 ppb is less than half the calculated radiogenic 187 os two samples of galena from the harnas vein yielded blank level re and os neither the 973 nor 616 ma time of mineralization is related to development of the mylonite zone at 920 ma or intrusion of the anorogenic bohus blomskog granites at 920 to 900 ma previously proposed sources for generating mjosa vanern mineral belt ore fluids an age of 973 ma for harnas alma silvergruvan suggests that sulfide deposition was associated with the waning stages 0 97 0 90 ga of the sveconorwegian grenvillian orogeny 1 15 0 90 ga postdating metamorphism and deformation that produced a regionally overthickened crust in the northern part of the sveconorwegian province the vein systems for these and numerous other small deposits in the mjosa vanern mineral belt could have resulted from regional exhumation in the late sveconorwegian with associated extension and the development of fracture systems at cooler middle to upper crustal levels in the southern part of the sveconorwegian province dominated by granulitic facies rocks no mineralization is present perhaps due only to increased exhumation and erosion that has exposed deeper crustal levels the late sveconorwegian age 973 ma records the main period of sulfide deposition for the harnas alma silvergruvan vein systems and indicates the robustness of the chronometer within tectonically complex terranes the late neoproterozoic age 616 ma records a later time of pyrite deposition probably associated with shearing and reopening of the harnas vein system because the au mineralization at harnas has been described as associated with shearing and occurring in fracture fillings in early pyrite we suggest that part or all of the au mineralization could have been introduced at 616 ma during reactivation of the vein system the 616 ma age for pyrite suggests a previously unrecognized and much younger mineralizing episode in the harnas region most likely reflecting continental scale extension and the late neoproterozoic opening of the iapetus ocean

effect of groundwater recharge on configuration of the water table beneath sand dunes and on seepage in lakes in the sandhills of nebraska u s a comment

genesis and magmatic hydrothermal evolution of the yangla skarn cu deposit southwest china the yangla skarn cu deposit 150 mt at 1 03 cu is located in the central segment of the jinshajiang metallogenic belt within the sanjiang three rivers region southwest china skarn orebodies are mainly developed between different units of devonian carbonate and quartz sandstone rocks with stratiform like shapes or within the contact zone between granitoids and marbles re os dating of molybdenite intergrowth with chalcopyrite yielded a well constrained 187re 187os isochron age of 232 0 1 5 ma with a weighted average age of 231 8 1 3 ma both coeval with the related intrusions 233 1 1 4 and 231 0 1 6 ma at 2 by zircon u pb dating from our previously published work field and textural relationships indicate three hydrothermal stages characterized by assemblages of prograde skarn pre ore stage retrograde skarn and cu fe mo bi sulfides main ore stage and pb zn sulfides associated with calcite and quartz late ore stage as well as one supergene stage marked by secondary cu mineralization malachite and azurite skarns contain garnets with andraditic compositions ad96 gr2 3py0 1 and clinopyroxene two series hd6di94 and hd86di13jo1 with low mn fe ratios 0 1 typical of cu skarn deposits worldwide three stages of fluid evolution were observed by a detailed fluid inclusion study 1 early fluids were trapped under two phase conditions as evidenced by the coexistence of brine homogenization temperatures 560 600 c average salinity 49 4 1 7 wt nacl equiv n 33 and vapor rich inclusions in pre ore stage andradite and diopside trapped at 600 bars or a depth of approximately 2 km assuming lithostatic pressure conditions 2 main ore stage fluid inclusions in quartz were also trapped under two phase conditions boiling as identified by the coexistence of vapor and liquid rich fluid inclusions liquid rich inclusions homogenized between 312 and 389 c average 350 24 7 c n 20 with salinities of 2 4 to 5 6 wt nacl equiv average 4 2 0 9 wt nacl equiv n 13 and a depth of 2 km 200 bars hydrostatic pressure conditions 3 late ore stage fluids are represented by inclusions in calcite characterized by homogenization temperatures ranging from 220 to 290 c average 249 27 c n 14 and salinities between 2 1 and 8 0 wt nacl equiv average 4 6 1 5 wt nacl equiv n 11 sulfur isotope compositions of sulfide minerals pyrite chalcopyrite pyrrhotite and molybdenite from the main and late ore stage have a narrow range of 34s values from 1 9 to 2 6 consistent with a magmatic origin calcite in the late ore stage has 13c values ranging from 3 2 to 5 9 and 18o from 7 2 to 18 0 distinct from the host rock marble compositions 13c 1 2 4 3 18o 10 8 23 9 when corrected for temperature 250 c estimated from fluid inclusion analysis in calcites these calcite data correspond to ore fluid 13cfluid values of 2 0 to 4 6 and 18ofluid values of 0 5 to 11 2 clustering at 10 which are consistent with a magmatic origin lead isotope compositions of sulfides 206pb 204pb 18 273 18 369 207pb 204pb 15 627 15 677 and 208pb 204pb 38 445 39 611 are similar to those of the granitic intrusions and sedimentary wall rocks but distinct from those of basalts 206pb 204pb 18 282 19 133 207pb 204pb 15 564 15 665 and 208pb 204pb 38 367 38 942 in the mining area taken together these geologic geochemical and isotopic data confirm that yangla is a typical cu skarn deposit

rock fabric controls on pore evolution and porosity permeability trends in oolitic grainstone reservoirs and reservoir analogs although the general influence of rock fabric on porosity and permeability k within carbonates is well documented if and how pore evolution and k scatter quantitatively relate to depositional fabric remains poorly constrained this project empirically explores this uncertainty within oolitic grainstones from a range of geologic ages and diagenetic histories to understand depositional sediment pore relationships and how they can evolve with lithification integrating data from point counting digital image analysis nuclear magnetic resonance and core analysis of holocene pleistocene pennsylvanian and mississippian oolitic grainstones reveals quantitative relations among rock fabric pores and petrophysical parameters oolitic grainstones of similar sedimentology taken from distinct diagenetic scenarios display a unique combination of pore size shape spatial distribution and k character within each scenario pore attributes and k are correlated more closely with grain size sorting and type than with cementation and compaction collectively these results are interpreted to suggest that sedimentology controls the trends or variability within an oolitic succession but that diagenesis defines the absolute values of pore attributes and petrophysical parameters these findings suggest that petrophysical variability within oolitic reservoirs may closely follow sedimentologic trends which may be predictable within a stratigraphic framework

geology mineralization and geochronological constraints of the mirador cu au porphyry district southeast ecuador the mirador porphyry cu au district is located in the southernmost sector of the northern andean cordillera in zamora chinchipe province southeastern ecuador the district contains two significant porphyry cu au ag mo deposits mirador and mirador norte and an interconnected series of narrow mineralized structures known collectively as chancho the principal mineralization in the porphyries is disseminated to blebby chalcopyrite developed primarily in potassic alteration with overlying chalcocite supergene enrichment zones prior to radiometric dating presented in this study these deposits were considered late jurassic based on close similarity and therefore assumed age equivalence with the well dated panantza san carlos and sutzu porphyry copper deposits located 40 km to the north new u pb zircon ages confirm a middle jurassic age for granodiorite of the zamora batholith at this location 163 8 1 9 ma and late jurassic ages for subvolcanic intrusions 156 2 1 0 and 153 1 1 3 ma re os molybdenite ages average 156 1 0 ma and indicate coeval mineralization between mirador and mirador norte mineralization and related sub volcanic igneous activity are closely associated at mirador and represent the same temporal event recorded at panantza san carlos and sutzu as well as coeval porphyry skarn and epithermal au mineralization extending at least 80 km south defining a north south cu au metallogenic belt spanning over 120 km

influence of depositional setting and sedimentary fabric on mechanical layer evolution in carbonate aquifers abstract carbonate aquifers in fold thrust belt settings often have low matrix porosity and permeability and thus groundwater flow pathways depend on high porosity and permeability fracture and fault zones methods from sedimentology and structural geology are combined to understand the evolution of fracture controlled flow pathways and determine their spatial distribution through this process bed parallel pressure solution surfaces ps1 are identified as a fracture type which influences fragmentation in peritidal and basinal carbonate and upon shearing provides a major flow pathway in fold thrust belt carbonate aquifers through stratigraphic analysis and fracture mapping depositional setting is determined to play a critical role in ps1 localization and spacing where peritidal strata have closer spaced and less laterally continuous ps1 than basinal strata in the peritidal platform facies units with planar lamination have bed parallel pressure solution seams along mudstone laminae in contrast burrowed units of peritidal strata have solution seams with irregular and anastamosing geometries laminated units with closely spaced bed parallel solution seams are more fragmented than bioturbated units with anastamosing solution seams in the deeper water depositional environment pelagic settling and turbidity currents are the dominant sedimentation processes resulting in laterally continuous deposits relative to the peritidal platform environment to quantify the fracture patterns in the basinal environment mechanical layer thickness values were measured from regions of low to high bed dip the results define a trend in which mechanical layer thickness decreases as layer dip increases a conceptual model is presented that emphasizes the link between sedimentary and structural fabric for the peritidal and basinal environments where solution seams localize in mud rich intervals and the resulting pressure solution surface geometry is influenced by sedimentary geometry i e stacked fining upward cycles burrows planar laminations in both facies types laterally continuous ps1 can behave as mechanical layer boundaries as layer parallel slip increases to accommodate shear strain in the fold thrust belt more ps1 behave as mechanical layer boundaries

electrical and fluid flow properties of carbonate microporosity types from multiscale digital image analysis and mercury injection electrical and fluid flow properties of porous media are directly related to the morphology of pores and the connectivity of the pore network both are closely linked to the amount and type of intrinsic microporosity in carbonate rocks which is not resolved by conventional techniques broad ion beam bib milling produces high quality true two dimensional cross sections for scanning electron microscopy sem and enables accurate quantification of carbonate microporosity for the first time the combination of bib sem mosaics with optical micrographs yields a multiscale digital image analysis msdia spanning six orders of magnitude in this paper the pore structures of 12 different carbonate rock samples from various rock types are quantified using msdia mercury injection capillary pressure measurements are used to assess pore throat properties the quantified pore structure parameters are correlated with plug measurements of electrical resistivity and permeability results indicate that petrophysical properties are closely linked to the type of microporosity which is distinctive for a certain rock type rock types with crystalline microporosity such as mudstone and dolomite generally show good connectivity in which the size of the pore network determines if the rock favors either hydraulic or electric flow rock types with intercement or micromoldic microporosity such as bindstone and travertine show variations in connectivity due to layering and moldic micropores of biological origin furthermore pore size distributions psd follow a power law in all samples despite their depositional and diagenetic differences the slope of the psd correlates with the electric properties in which samples with a steeper slope show lower cementation factors the linearity of the power law distribution enables predictions of pore populations outside the investigated length scales

pore structure and fractal characteristics of ordovician majiagou carbonate reservoirs in ordos basin china fractal analysis was performed on carbonate core plug samples from the ordovician majiagou carbonate reservoirs in the ordos basin using mercury intrusion capillary pressure micp nuclear magnetic resonance nmr and the x ray computed tomography ct measurements to improve our understanding of the pore structure characteristics the relationships between pore structure parameters and the fractal dimensions were investigated the pore systems are dominated by secondary intercrystalline pores and enlarged dissolution pores as well as microfractures the fractal curves from micp analysis break into two segments at the swanson s parameter the small pore throat systems can be described by the fractal theory whereas pores connected by relatively large throats greater than the pore throat radius at the pittman s hyperbola s apex are not cylindrical in shape cannot be described by a capillary tube model and tend to have apparent fractal dimensions larger than 3 0 the fact that the entirety of the capillary curve cannot be fit by a single fractal dimension implies that there are multiple pore systems present with different fractal dimensions the ct analysis shows that the pores are dispersed in the three dimensional spaces mainly with elliptical shapes the nmr measurements are sensitive to pore body size and micp probes pore throat dimensions the latter being complementary to the pore body size distribution none of the ct micp and nmr techniques provide right or wrong answers to the pore throat systems but they probe different aspects of the pore systems this study assumes the pore shapes to be spherical in general and then the fractal dimension is calculated from the nmr transverse relaxation time t2 spectrum the fractal dimensions of all the samples are calculated and the accuracy of the fractal model is verified by the high regression coefficients almost all the pore systems can be described by fractal theory and the fractal dimensions are strongly correlated with the t2 values separating the immovable fluid and the free fluid microfractures may bias t2 toward larger values making it hard to derive fractal dimensions from nmr measurements the coexistence of small pores pore radius 50 m results in a heterogeneous pore distribution and a high fractal dimension reservoir quality increases with the complexity degree of the microscopic pore structure conversely samples that are dominated by small pore systems tend to have a lower fractal dimension and a less complex pore structure

laboratory measurements of the acoustic and transport properties of carbonate rocks and their link with the amount of microcrystalline matrix laboratory data and computer tomography ct scan image analysis of carbonate rocks were combined demonstrating a quantitative link between acoustic and transport properties the fraction of microcrystalline calcite micrite in the matrix and the grain to micrite matrix ratio samples from the monte acuto formation gargano italy a transgressive system tract tst whose microstructure ranges from basal pelagic mudstones to coarse calciturbidites were analyzed results indicate that high micrite rocks with low grain to micrite matrix ratios typical of low energy depositional settings are relatively stiffer and more impermeable in contrast lower amounts of micrite due to high energy depositional settings or its removal from intergranular macropores by progressive leaching of the matrix leads to high grain to micrite matrix ratios this process will increase porosity and reduce rock stiffness both of which reduce velocity decreasing micrite content correlates well with increasing macroporosity

magmatic dominated fluid evolution in the jurassic nambija gold skarn deposits southeastern ecuador the jurassic approximately 145 ma nambija oxidized gold skarns are hosted by the triassic volcanosedimentary piuntza unit in the sub andean zone of southeastern ecuador the skarns consist dominantly of granditic garnet ad20 98 with subordinate pyroxene di46 92hd17 42jo0 19 and epidote and are spatially associated with porphyritic quartz diorite to granodiorite intrusions endoskarn is developed at the intrusion margins and grades inwards into a potassic alteration zone exoskarn has an outer k and na enriched zone in the volcanosedimentary unit gold mineralization is associated with the weakly developed retrograde alteration of the exoskarn and occurs mainly in sulfide poor vugs and milky quartz veins and veinlets in association with hematite fluid inclusion data for the main part of the prograde stage indicate the coexistence of high temperature 500 c to 600 c high salinity up to 65 wt eq nacl and moderate to low salinity aqueous carbonic fluids interpreted to have been trapped at pressures around 100 120 mpa corresponding to about 4 km depth lower temperature 510 300 c and moderate to low salinity 23 2 wt eq nacl aqueous fluids are recorded in garnet and epidote of the end of the prograde stage the microthermometric data th from 513 c to 318 c and salinity from 1 0 to 23 wt eq nacl and 18o values between 6 2 and 11 5 for gold bearing milky quartz from the retrograde stage suggest that the ore forming fluid was dominantly magmatic pressures during the early retrograde stage were in the range of 50 100 mpa in line with the evidence for co2 effervescence and probable local boiling the dominance of magmatic low saline to moderately saline oxidizing fluids during the retrograde stage is consistent with the depth of the skarn system which could have delayed the ingression of external fluids until relatively low temperatures were reached the resulting low water to rock ratios explain the weak retrograde alteration and the compositional variability of chlorite essentially controlled by host rock compositions gold was precipitated at this stage as a result of cooling and ph increase related to co2 effervescence which both result in destabilization of gold bearing chloride complexes significant ingression of external fluids took place after gold deposition only as recorded by 18o values of 0 4 to 6 2 for fluids depositing quartz below 350 c in sulfide rich barren veins low temperature 300 c meteoric fluids 18owater between 10 0 and 2 0 are responsible for the precipitation of late comb quartz and calcite in cavities and veins and indicate mixing with cooler fluids of higher salinities about 100 c and 25 wt eq nacl the latter are similar to low temperature fluids 202 74 5 c with 18o values of 0 5 to 3 1 and salinities in the range of 21 1 to 17 3 wt eq cacl2 trapped in calcite of late veins and interpreted as basinal brines nambija represents a deep equivalent of the oxidized gold skarn class the presence of co2 in the fluids being partly a consequence of the relatively deep setting at about 4 km depth as in other au bearing skarn deposits not only the prograde stage but also the gold precipitating retrograde stage is dominated by fluids of magmatic origin

discovery geology and origin of the fruta del norte epithermal gold silver deposit southeastern ecuador fruta del norte is a completely concealed and extraordinarily well preserved epithermal gold silver deposit located in the remote cordillera del condor mountain ranges of southeastern ecuador currently defined resources in a single steep relatively small body displaying exceptional grade continuity contain 9 81 million ounces moz of gold and 15 0 moz of silver with an indicated resource grade of 9 59 g t au and 12 9 g t ag the deposit was discovered in early 2006 during a greenfields program conducted by aurelian resources a canadian junior explorer discovery resulted from systematic drill testing of a conceptual geologic model which predicted that auriferous veins would be present in andesitic volcanic rocks inferred to underlie a steep silicified rib cutting a fluvial conglomerate sequence the rib is highly anomalous in arsenic antimony and mercury but contains low order gold values the second drill test the discovery hole intersected 230 m of ore grade gold silver mineralization beneath 200 m of the barren conglomerate cover the host andesitic volcanic rocks crosscutting feldspar porphyry and associated phreatic breccias are assigned to the piuntza unit of the santiago formation which along with the zamora batholith and a series of porphyry copper stocks was generated in a continental margin magmatic arc during the middle to late jurassic the deposit is located near the northeastern extremity of the 10 km long suarez pull apart basin where it is linked to the steep west and central faults part of the regionally extensive las penas strike slip fault zone the pull apart basin was progressively filled by fluviatile conglomerate dacitic ignimbrite flows finer grained siliciclastic sedimentary rocks and finally andesite flows all assigned to the chapiza formation the fruta del norte deposit consists of a 1 3 km long and up to 300 m wide vein stockwork associated with quartz illite pyrite alteration the deposit comprises two principal vein types one in the south dominated by quartz manganoan carbonates and abundant base metal sulfides and the other in the north dominated by manganese and base metal poor quartz and calcite adularia is a minor main stage gangue mineral in each both types are abruptly transitional upward and westward to a third ore type marked by intense silicification and chalcedony veining with disseminated and veinlet marcasite pyrite the uppermost part of this silicic zone is sulfide deficient probably the result of a short lived supergene oxidation event prior to initial conglomerate deposition the deposit is notable for the widespread occurrence of fine to coarse visible gold which gives rise to bonanza grades and is closely associated with quartz chalcedony carbonate and sulfide gangue the sulfide free silicic zone is overlain by an extensive silica sinter horizon which may either directly overlie the piuntza volcanic rocks and or occur as interbeds in the basal 20 m of the conglomerate which are invariably silicified and marcasite bearing otherwise the conglomerate above the orebody lacks silicification with one critical exception the steeply inclined zone that is exposed as the silicified rib that led to discovery the sinter horizon containing localized mud pool deposits and hydrothermal eruption breccias is in unusual proximity to the underlying gold silver orebody the northern and southern parts of the fruta del norte deposit possess characteristics that are usually considered typical of low and intermediate sulfidation epithermal deposits respectively they may have required two discrete mineralizing fluids both of which are suspected to have ascended via the west and central faults the upward change to the silicified zone is attributed to cooling of the ascendant fluid on approach to the paleosurface sinter progressive burial of the deposit beneath the suarez basin fill may have contributed to the suppression and eventual extinction of the epithermal system with gold mineralization of the conglomerate being inhibited by rheologic and chemical factors formation of the fruta del norte deposit and complete filling of the suarez basin took place in 3 to 6 m y during the late jurassic 157 154 ma

highly siderophile and strongly chalcophile elements in magmatic ore deposits an ore deposit by definition must be economically viable that is to say it must contain sufficient material at high enough grade to make it possible to mine and process it at a profit bates and jackson 1987 this requires the elements to be collected and concentrated by some phase and for them to be deposited close to the surface of the earth at the oxygen fugacities found in the crust native fe is not normally stable and thus the highly siderophile elements defined as ru rh pd re os ir pt and au cannot behave as siderophile elements except in rare cases such as on disko island klock et al 1986 where the magma is sufficiently reduced for native fe to be present however if mafic magmas become saturated in a base metal sulfide liquid the highly siderophile elements behave as highly chalcophile elements table 1 thus these elements are generally found in association with base metal sulfide minerals which crystallized from a magmatic sulfide liquid namely pyrrhotite pentlandite chalcopyrite cubanite pyrite an exception to this is au although au is strongly chalcophile and is produced as a by product from many platinum group element pge deposits table 2 most primary au deposits consist of native au groves et al 1998 these will not be discussed in this chapter there are many pge deposits i e accumulations of pge minerals and base metal sulfides containing pge bates and jackson 1987 around the world but most of these do not constitute pge ore deposits because they are either too small or their grade is too low or other political or infrastructure factors prevent the economic exploitation of the deposit bates and jackson 1987 for the purpose of this work we have defined pge ore deposits as those which have significant production 2 of the annual world

pore networks in holocene carbonate sediments abstract permeabilities of holocene carbonate sediments from florida and the bahamas determined for 74 samples by water flow rates in a variable head permeameter range from 0 6 to 57 000 millidarcies porosities range from 40 to 78 percent these parameters are related to depositional texture as follows table the muddiest sediments i e the finest grained have the highest porosities but lowest permeabilities this negative correlation between porosity and permeability is the reverse of the situation found in carbonate rocks even as young as pleistocene high porosity and low permeability in sediments show a strong correlation with percentage of fines 62 m from capillary pressure curves it is inferred that many of the pore throats of muddy carbonate sediments are less than 1 m in diameter at least after drying measured permeabilities are used to calculate cementation rates for simple models of upper phreatic zone cementation the calculated rates would require excessive time to produce the degree of cementation seen in late pleistocene rocks of florida and the bahamas the amounts of rainfall and evaporation are the most important factors in the degree of cementation

modifications of chalk microporosity geometry during burial an application of mathematical morphology abstract the diagenetic evolution of chalk during burial has previously been established and can be summarized as follows 1 ooze deposition and dewatering burial 1000 m moreover chalk particles tend to increase in size as a result of diagenesis i e recrystallization or cementation as a result of compaction and cementation the shape size and connectivity of chalk microporosity evolve during burial however if the evolution of bulk porosity during burial is well quantified actual modifications of pore space topology are less understood quantifying pore space properties such as pore and throat sizes aspect ratio and spatial distribution usually require costly instruments as well as long and complex experimental procedures instead this study documents the application of mathematical morphology to investigate chalk microporosity from two dimensional 2d scanning electron microscope sem chalk samples n 105 have been collected from onshore quarries and offshore oil and gas reservoirs six chalk lithotypes are defined based on their mineralogical composition i e clay and silica content as well as the average size of chalk particles and their apparent diagenetic impact which appears strongly related to the mean grain size the latter is used as a proxy for the diagenetic overprint while the burial diagenetic model offers a framework for the different lithotypes and their respective pore space properties during intermediate burial 1000 m pressure solution and cementation become pervasive and produce large clusters of coalescent calcite crystals 3 10 m mean 5 13 m total porosity is strongly reduced as a result 6 11 while pore body and throat dimensions drop to 1 58 and 0 03 m respectively a high aspect ratio 88 1 and lower proportion of rough porosity relative to total image porosity suggest that throats are proportionally more affected than pore bodies cementation leads to less dendritic more globular and isolated pores where processes such as overpressure and oil charge have helped preserve porosity during deep burial 20 30 pore and throat dimensions were locked to moderately high values 2 0 and 0 1 m respectively even in silica and clay rich chalk since the geometry of microporosity exerts a major control on fluid flow reservoir modelling and recovery predictions could benefit from a better understanding on the geological controls on chalk microporosity not only can mathematical morphology quantify pore space properties that are fundamental in pore network and flow modelling but by being applicable on large datasets it could provide a new insight into the geological modifications of chalk microporosity during burial

u pb re os and 40ar 39ar geochronology of the nambija au skarn and pangui porphyry cu deposits ecuador implications for the jurassic metallogenic belt of the northern andes new u pb re os and 40ar 39ar dates are presented for magmatic and hydrothermal mineral phases in skarn and porphyry related ores from the nambija and pangui districts of the subandean zone southeastern ecuador nambija has been one of the main gold producing centers of ecuador since the 1980s due to exceptionally high grade ores average 15 g t but frequently up to 300 g t au pangui is a recently discovered porphyry cu mo district the geology of the subandean zone in southeastern ecuador is dominated by the i type subduction related jurassic zamora batholith which intrudes triassic volcanosedimentary rocks the zamora batholith is in turn cut by porphyritic stocks which are commonly associated with skarn formation and or porphyry style mineralization high precision u pb and re os ages for porphyritic stocks u pb zircon associated prograde skarn u pb hydrothermal titanite and retrograde stage skarn re os molybdenite from veins postdating gold deposition of the nambija district are all indistinguishable from each other within error 145 ma and indicate a late jurassic age for the gold mineralization previously gold mineralization at nambija was considered to be early tertiary based on k ar ages obtained on various hydrothermal minerals the new jurassic age for the nambija district is slightly younger than the 40ar 39ar and re os ages for magmatic hydrothermal minerals from the pangui district which range between 157 and 152 ma mineralization at nambija and pangui is associated with porphyritic stocks that represent the last known episodes of a long lived jurassic arc magmatism 190 to 145 ma a jurassic age for mineralization at nambija and pangui suggests that the northern andean jurassic metallogenic belt which starts in colombia at 3 n extends down to 5 s in ecuador it also adds a new mineralization style au skarn to the metal endowment of this belt

low rhenium molybdenite by metamorphism in northern sweden recognition genesis and global implications abstract re os dating of molybdenite is an accurate means to date intrusions and intrusion related ore deposits using the model age or isochron approach but molybdenite has a new niche in the greenschist to granulite facies metamorphic environment re os ages for metamorphic molybdenite may be used to construct regional metamorphic histories age significance and accuracy are established by analyzing multiple molybdenite separates extracted from single petrographically characterized molybdenite occurrences in this study twelve geologically distinct molybdenite bearing samples from two small mo districts in northern sweden trace a 150 m y paleoproterozoic svecofennian metamorphic history from 1900 to 1750 ma these data reveal a little known widespread and protracted late svecofennian anatexis in northern sweden the kataberget mo cu f deposit is located in the moskosel granite batholith north of the economically renown skellefte district four different molybdenite samples from outcrop at kataberget indicate an intrusion age of 1895 6 ma with the formation of later pegmatite aplite at 1875 6 ma the allebuoda bjorntjarn and munka mo w deposits in the rappen district are represented by three outcrop and five drill core samples of molybdenite bearing aplite pegmatite granite these two deposits were previously described as intrusion related climax type mo mineralization re os ages for molybdenites from these deposits range from 1865 to 1750 ma and significantly re concentrations are markedly low extending to the sub ppm level age agreement within the deposits is conspicuously lacking whereas with one exception age agreement within any single sample geologic occurrence as established by analysis of additional molybdenite separates is very good these data together with fundamental geologic observations discussed in this paper suggest that mo w mineralization in northern sweden is not intrusion related but the local product of episodic melting of archean paleoproterozoic supracrustal gneisses related to the svecofennian orogeny petrographic traverses across the boundary between widespread foliation parallel units of aplitic to pegmatitic pink granite and hosting biotite gneiss directly capture the process of ore formation dehydration breakdown of zircon rich biotite aligned with the foliation in the gneiss is accompanied by formation of new pristine post deformational biotite plus sulfides oxides hydrothermal zircon and fluorite all associated with microcline dominant leucosomes this process has profound implication for the traditional leucogranite intrusion related genesis attributed to the broad classification of mo w sn base and precious metal mineralization e g south mountain batholith nova scotia okiep namaqualand south africa mactung yukon pogo liese tintina alaska carajas and goias rio tocantins brazil new england batholith nsw australia bergslagen sweden nevoria western australia alpeinerscharte austria erzgebirge germany sardinia corsica batholith in addition to biotite metallogenic contributions e g mo w sn u bi cu pb zn fe ni co au ag te as sb ree in various combinations may also be controlled by breakdown of amphibole in effect the trace element composition of dehydrating or recrystallizing components in a gneissic rock essentially defines the local and district metallogenic suite in the absence of focusing structures e g shear zones sheeted vein development this process will generally form small and disconnected subeconomic deposits with erratic and unpredictable grades low re content in associated molybdenite is a key indicator for a subeconomic origin by local melting of biotite gneiss mo w or muscovite schist sn w

experimental determination of noble gases and sf6 as tracers of co2 flow through porous sandstone abstract in order to label the co2 injected underground for geological storage and allow it to be differentiated from natural sources a panoply of additive chemical tracers have been proposed yet the transport of these tracers relative to co2 in pore space is currently poorly constrained this leads to uncertainty as to whether tracers will act as an early warning of co2 arrival or be preferentially retained in the pore space making them ineffective here we present the factors affecting transport of noble gases and sf6 relative to co2 in a porous rock using a porous sandstone core each of the tracers were loaded into a sample loop and injected as discrete gas pulses into a co2 carrier stream at five different experiment pressures 10 50 kpag upstream to ambient pressure downstream tracer arrival profiles were measured using a quadrupole mass spectrometer significantly our results show that peak arrival times of helium were slower than the other noble gases at each pressure gradient the differences in peak arrival times between helium and other noble gases increased as the pressure gradient along the system decreased and the curve profiles for each noble gas differ significantly the heavier noble gases kr and xe along with sf6 show an earlier arrival time and a wider curve profile compared to he and ne curves through the co2 carrier gas stream this shows that kr and xe could be substituted for sf6 a potent greenhouse gas in tracer applications for comparison co2 pulses were passed through a n2 carrier gas resulting in significantly slower peak arrival times compared to those of noble gases and sf6 hence all investigated tracers when co injected with co2 could potentially act as early warning tracers of co2 arrival though we find that kr xe and sf6 will provide the most robust advance warning analysis of our experimental results shows that they cannot be explained by a simple one dimensional flow model through a porous medium we outline a conceptual model that incorporates different preferential flow paths depending on flow velocities of individual gas streams this model can explain the observed dataset and shows that the flow of noble gases and sf6 tracers is influenced by pore scale heterogeneity

geodynamic evolution of the northern and central andes during early to middle mesozoic times a tethyan model the early to middle mesozoic sedimentary and magmatic history of the northern and central andes i e the nne trending colombian ecuadorian segment and the nw trending peruvian segment exhibits a spatially contrasted evolution involving several successive tectonic and geodynamic settings the late triassic to late liassic period began with a widespread marine transgression from the latest triassic the colombian marine shelf was progressively destroyed by southward propagating extensional tectonic activity but marine sedimentation continued in peru during this time no significant magmatic activity is recorded except in the emerging colombian area this period is interpreted as the result of rifting of a tethyan oceanic arm which separated the colombian and palaeo mexican margins from latest liassic an important calc alkaline magmatic arc developed along the emergent colombian segment further south the north peruvian shelf probably emerged but marine sedimentation continued in southern peru during middle and early late jurassic times the colombian segment was characterized by important magmatic activity and by coarse clastic continental sedimentation along the peruvian segment a turbiditic trough emergent areas and continental basins were created and the scarcity of calc alkaline magmatism suggests that only very local subduction took place this period is regarded as one of the southeastward subduction beneath the colombian segment and of tethyan oceanic crust originating in the newly formed colombian oceanic arm this pattern would have induced a chiefly left lateral transform motion along the peruvian segment by kimmeridgian tithonian times the palaeogeographic framework had drastically changed along the colombian segment magmatic activity ceased and continental accretions occurred along dextral strike slip sutures in peru tectonic activity was recorded by the creation of a new turbiditic trough and by the resumption of detrital sedimentation in the coastal area arc related volcanism indicated that subduction took place beneath this segment this geodynamic change is interpreted as the result of a sharp decrease in the spreading activity of the tethyan ridges and replacement by pacific spreading centres inducing a roughly northeastward convergence direction

influence of pore system characteristics on limestone vulnerability a laboratory study hyblean limestone of oligo miocene age was widely used as a construction material in the architectural heritage of eastern sicily italy among them the so called pietra bianca di melilli melilli limestone and calcare di siracusa syracuse limestone were prized for their attractive appearance ease of quarrying and workability syracuse limestone shows general weathering whereas melilli limestone is better preserved and only differential erosion or superficial exfoliation can be detected in monuments the cause of the different behavior of these two limestones was investigated from the petrographic and petrophysical points of view the saturation coefficient is higher in melilli limestone and ultrasound measurements indicate that it is less compact than syracuse limestone so that melilli limestone could deteriorate more easily than syracuse limestone however pore interconnections and the size of very small pores play the main role in the durability of both materials the irregularity of the syracuse pore system and its greater number of micropores hinder water flow through the exterior promote stress in pore structure and favor the development of scaling as confirmed by salt crystallization tests in melilli limestone the low concentration of micropores and fast water evaporation allow solutions to reach the surface more easily resulting in less damaging efflorescence

testing and evaluation of 2d 3d digital image analysis methods and inclusion theory for microporosity and s wave prediction in carbonates abstract three digital image analysis dia methods are proposed to evaluate the geometric properties of the pore system in 2d 3d and identify the macro and mesopores 1 optical microscopy of thin sections computed by fiji imagej software 2 ct data volume decomposition using 2d slices and fiji imagej and 3 application of geodict 2015 software and poreshape geolab routines to compute the 3d pores microporosity is characterized using assumptions based on the difference between helium gas and the image porosity and the classification system by anselmetti et al and rock physics modeling of the differential effective medium theory is applied to estimate the micropore aspect ratio via vp supplying a calibrated method to predict vs for similar rocks according to the results the 2d processing methods 1 and 2 are more realistic and theoretically consistent for estimating 2d dia parameters the approximation of the detected 3d pores to 2d in method 3 results in poor representativeness of the pore texture limiting the potential usefulness of the ct data although the same resolution is inherent to the ct data volume and is applied in methods 2 and 3 the use of ct data from 2d slices method 2 was evaluated as the best method for computing the 2d dia parameters and the optical thin sections used in method 1 were limited by differences in the resolution and the low representativeness of the micrograph quantity in correlating the texture complexities this work generates a valuable outcrop dataset and original discussions of dia at different image scales for input modeling to match ultrasonic and elastic properties with the lithological characteristics of oman samples

petrophysical heterogeneity in a lower cretaceous limestone reservoir onshore abu dhabi united arab emirates the upper zone of the lower cretaceous kharaib formation 151 177 ft 46 54 m thick in the studied wells is a major oil reservoir in several giant oil fields wide variations in porosity and permeability of this zone have been shown to result from both the inhibition of burial cementation by oil in the crest of each field and localized cementation adjacent to stylolites combined with the more subtle influence of widely varying depositional mud content and grain size the present study examines these relationships in closer detail using core and petrographic observations from two wells on the oil filled crest and two wells on the water filled flanks of a giant domal oil field although porosities are higher overall in the crestal cores each well shows wide variations within each of seven main groupings of the samples by depositional texture this heterogeneity results mainly from the distribution of clay which is concentrated along depositional laminations and causes widely varying porosity losses in all textures by promoting stylolite development and associated calcite cementation higher clay abundance and lower porosity within the upper and lower 12 17 ft 4 5 m of the reservoir reflects increased influx of siliciclastic fines across the epeiric barremian carbonate platform immediately following and preceding respectively third order falls in global sea level most 95 of porosity permeability data from the studied wells lie within lucia rock fabric class 3 showing distinct but relatively subtle differences between texture groups whereas a subordinate part of the data from the upper relatively mud poor third of the reservoir plot at higher permeabilities development of a predictive model for the petrophysical heterogeneity of this example requires a combination of the following 1 a diagenetic model for porosity controls 2 the use of a modestly higher porosity permeability transform upper class 3 in the upper part of the reservoir than in the lower reservoir lower class 3 and 3 a recognition of the scattered and widely varying occurrences of exceptionally high permeabilities in the upper reservoir

effect of ground water recharge on configuration of the water table beneath sand dunes and on seepage in lakes in the sandhills of nebraska u s a abstract analysis of water level fluctuations in about 30 observation wells and 5 lakes in the crescent lake national wildlife refuge in the sandhills of nebraska indicates water table configuration beneath sand dunes in this area varies considerably depending on the configuration of the topography of the dunes if the topography of an interlake dunal area is hummocky ground water recharge is focused at topographic lows causing formation of water table mounds these mounds prevent ground water movement from topographically high lakes to adjacent lower lakes if a dune ridge is sharp the opportunity for focused recharge does not exist resulting in water table troughs between lakes lakes aligned in descending altitudes parallel to the principal direction of regional ground water movement generally have seepage from higher lakes toward lower lakes

variations in petrophysical properties along a mixed siliciclastic carbonate ramp upper jurassic ricla ne spain abstract a multi scale petrophysical study was performed on an upper jurassic siliciclastic carbonate ramp system near the village of ricla spain a combination of textural field observations thin section and grain size analysis chemical mineralogical thermo gravimetric analysis and physical porosity gamma ray and velocity measurements properties was used to capture the heterogeneity of this mixed sedimentary system subsequently synthetic seismic sections with varying resolution were created to show the characteristics of the internal ramp structures the translation from the measured petrophysical properties to a synthetic seismic section helps to better understand subsurface seismic although upscaling problems are a recurring issue the homogeneity of the samples and the continuity of the outcrop and facies reduce the number of uncertainties acoustic properties are generally controlled by the amount and type of pore spaces due to the low porosities the ramp geometry is characterized by an overall lateral homogeneity and vertical heterogeneity textural sedimentological and stratigraphic transitions in the outcrop are related to the defined facies each has its own unique mineralogical signature amplitude variations in the synthetic seismic profile are primarily caused by changes in mineral composition thus facies transitions

factors controlling elastic properties in carbonate sediments and rocks carbonate sediments are prone to rapid and pervasive diagenetic alterations that change the mineralogy and pore structure within carbonate rocks in particular cementation and dissolution processes continuously modify the pore structure to create or destroy porosity in extreme cases these modifications can completely change the mineralogy from aragonite calcite to dolomite or reverse the pore distribution whereby original grains are dissolved to produce pores as the original pore space is filled with cement to form the rock figure 1 all these modifications alter the elastic properties of the rock and therefore the sonic velocity the result is a dynamic relationship among diagenesis porosity pore type and sonic velocity the result is a wide range of sonic velocity in carbonates in which compressional wave velocity vp ranges from 1700 to 6600 m s and shear wave velocity vs from 600 to 3500 m s

the geology and mesozoic collisional history of the cordillera real ecuador abstract the geology of the metamorphic rocks of the cordillera real of ecuador is described in terms of five informal lithotectonic divisions we deduce that during the mesozoic repeated accretionary events occurred and that dextral transpression has been of fundamental importance in determining the tectonic evolution of this part of the northern andes the oldest event recognised of probable late triassic age may be related to the break up of western gondwana and generated a regional belt of s type plutons during the jurassic major calc alkaline batholiths were intruded following this in latest jurassic to early cretaceous time a volcano sedimentary terrane of possible oceanic or marginal basin origin the alao division and the most westerly gneissic chaucha arenillas terrane were accreted to continental south america the accretion of the oceanic western cordillera took place in latest cretaceous to earliest tertiary time this latter event coincided with widespread thermal disturbance as evidenced by the large number of young k ar mineral ages recorded from the cordillera real

mineral zoning and gold occurrence in the fortuna skarn mine nambija district ecuador the fortuna oxidized gold skarn deposit is located in the northern part of the nambija gold district southern ecuador it has been subdivided into four mineralized sites covering a distance of 1 km which are named from north to south cuerpo 3 mine 1 mine 2 and southern sector massive skarn bodies occur in k na metasomatized volcanic and volcaniclastic rocks of the triassic piuntza unit they appear to result from selective replacement of volcaniclastic rocks very minor presence of bioclast relicts suggests the presence of subordinate limestone endoskarn type alteration with development of na rich plagioclase k feldspar epidote actinolite anhedral pyroxene and titanite affects a quartz diorite porphyritic intrusion which crops out below the skarn bodies in mine 2 and the southern sector endoskarn alteration in the intrusion grades into a k feldspar biotite magnetite assemblage k alteration suggesting that skarn formation is directly related to the quartz diorite porphyritic intrusion the latter being probably emplaced between 141 and 146 ma the massive skarn bodies were subdivided into a dominant brown garnet skarn a distal green pyroxene epidote skarn and two quartz rich varieties a blue green garnet skarn and light green pyroxene garnet skarn which occur as patches and small bodies within the former skarn types the proximal massive brown garnet skarn zone is centered on two 060 trending faults in mine 2 where the highest gold grades 5 10 g t were observed it grades into a distal green pyroxene epidote skarn zone to the north cuerpo 3 granditic garnet shows iron enrichment from the proximal to the distal zone diopsidic pyroxene exhibits iron and manganese enrichment from proximal to distal zones the retrograde stage is weakly developed and consists mainly of mineral phases filling centimeter wide veins vugs and interstices between garnet and pyroxene grains the main filling mineral is quartz followed by k feldspar epidote calcite and chlorite with minor sericite apatite titanite hematite pyrite chalcopyrite and gold metal and sulfur contents are low at fortuna and the highest gold grades coincide with high hematite abundance which suggests that retrograde stage and gold deposition took place under oxidizing conditions fluid inclusions from pyroxene indicate precipitation from high temperature high to moderate salinity fluids 400 to 460 c and 54 to 13 wt eq nacl which result probably from boiling of a moderately saline 8 wt eq nacl magmatic fluid later cooler 180 to 475 c and moderate to low saline fluids 1 to 20 wt eq nacl were trapped in garnet epidote and quartz and are interpreted to be responsible for gold deposition chlorite analysis indicates temperature of formation between 300 and 340 c in accordance with fluid inclusion data it appears thus that gold was transported as chloride complexes under oxidizing conditions and was deposited at temperatures around 300 c when transport of chloride complexes as gold carriers is not efficient

porosity permeability relationships in miocene carbonate platforms and slopes seaward of the great barrier reef australia odp leg 194 marion plateau this paper reports a series of 700 porosity permeability analyses and supporting petrographic and sedimentologic descriptions from early to late miocene carbonate strata cored on the marion plateau offshore from north eastern australia during ocean drilling program odp leg 194 the samples analysed are not only mainly coarse bioclastic limestones and dolomitized equivalents from platform top facies but also include 79 plugs from deeper water slope to hemipelagic drift facies outstanding characteristics of this data set are the wide ranges of porosity and permeability in both limestones and dolostones the large degree of short range heterogeneity typical of these strata and the better porosity permeability correlation of dolostones than limestones the platforms have experienced widely varying calcite cementation dolomitization and dissolution but show little clear evidence of meteoric diagenesis suggesting that subaerial exposure may have played little role in porosity permeability evolution permeability for given porosity is controlled by grain size and calcite cement content in grainstones and by occurrence of larger shelter pores and vugs in mud rich samples dolomitization tends to reduce the variation of permeability for given porosity by recrystallizing mud matrix to form intercrystalline macroporosity that connects vugs and moulds to become integrated with the effective pore system as a result there are no differences in permeability porosity trends for different dolostone textures whether dominated by intercrystalline vuggy or preserved intergranular pore types two platform top sites separated by only 5 km display a major lateral variation in dolostone porosity permeability characteristics within the youngest dolostone units this difference is interpreted as reflecting a relatively windward current facing setting of the site with the overall higher permeability for given porosity site 1199 that led to less muddy depositional facies greater cementation and lesser grain dissolution pore geometry parameters measured by petrographic image analysis confirm that the windward dolostones have pores that are both larger and less intricate than dolostones comprising the more current protected location

meteoric calcite cementation diagenetic response to relative fall in sea level and effect on porosity and permeability las negras area southeastern spain abstract a dolomitized upper miocene carbonate system in southeast spain contains extensive upper and lower zones of calcite cementation that cut across the stratigraphy cement textures including isopachous and circumgranular which are consistent with phreatic zone cementation cements in the upper cemented zone are non luminescent whereas those in the lower cemented zone exhibit multiple bands of luminescent and non luminescent cements in the upper cemented zone isotopic data show two meteoric calcite lines mcl with mean 18 o at 5 1 and 5 8 vpdb whereas no clear mcl is defined in the lower cemented zone where mean 18 o for calcite cement is at 6 7 vpdb 13 c values in both cement zones are predominantly negative ranging from 10 to 2 vpdb suggestive of carbon from soil gas or decayed organics measurements of tm ice in primary fluid inclusions yield a mode of 0 0 c in both zones indicating calcite cementation from fresh water these two zones define the positions of two different paleo water tables that formed during a relative sea level fall and erosional downcutting during the plio pleistocene the upper cemented zone pre dated the lower cemented zone on the basis of known relative sea level history meteoric calcite cementation reduced porosity and permeability but measured values are inconsistent with simple filling of open pore space each texture boundstone grainstone packstone wackestone produces a different relationship between percent calcite cement and porosity permeability distribution of cements may be predictable on the basis of known sea level history and the effect of the cementation can be incorporated into subsurface geomodels by defining surfaces of rock boundaries that separate cemented zones from uncemented zones and applying texture specific relationships among cementation porosity and permeability

fractal and multifractal analysis of carbonate pore scale digital images of petroleum reservoirs the petrophysical evaluation of the reservoir capacity is of great importance in predicting the reserves and productivity of petroleum fields which may directly affect petroleum exploration in the past such kind of evaluation was mainly based on the experimental measurements of the petrophysical porosity and permeability of reservoir rock samples assessing quantitatively the microstructures of carbonates including irregularities of pore shapes and frequency distributions of pore sizes is becoming one of the most challenging efforts in pore scale analysis based on the digital analyses of the two dimensional images from thin sections taken under the environmental scanning electron microscope esem at various magnification scales the current paper tries to quantify the pore spaces of carbonate samples by fractal and multifractal methods which have been demonstrated to be effective the study area is located in the western hubei and eastern sichuan china as many as 25 carbonate samples from various members in five formations of the permian triassic periods and 132 esem images were chosen in this study all individual pores had been recognized and their areas and perimeters had been calculated as well the box counting fractal dimensions and four major multifractal parameters associated with the multifractal spectra are used the results show that the values of the petrophysical porosity and permeability are closely related to the box counting dimensions and the multifractal parameters which demonstrates that the textural arrangements of the pores control the porosity and permeability to a certain extent there is also a link between the reservoiring capabilities of different formations and the fractal and multifractal parameters the reservoiring capability assessment result is in agreement with the field research analysis

characterizing the pore structure of low permeability eocene liushagang formation reservoir rocks from beibuwan basin in northern south china sea abstract the hydrocarbon exploration from low permeability 50 nm mainly contribute to the total pore spaces for most samples with lower shale content mesopores 2 50 nm dominate the pore spaces of samples with higher shale content which leads to the relatively large surface area of these samples permeability of these low permeability rocks is positively related with average pore throat radius and negatively related with relative sorting coefficient while no such a close relationship exists between permeability and porosity fractal dimension has a negative relationship with average pore throat radius and permeability in summary this work comprehensively investigates the pore structure characteristics of low permeability liushagang formation reservoir rocks from beibuwan basin using multiple complementary approaches which helps to further understand the hydrocarbon migration and accumulation mechanism of these low permeability reservoirs

three dimensional pore connectivity evaluation in a holocene and jurassic microbialite buildup microbial carbonates have complex pore networks formed by their biological growth framework which later may be modified by diagenetic alteration a proper evaluation of the porous media characteristics and their evolution is essential to better characterize microbial carbonate reservoirs however conventional methods of fundamental rock characteristic description are insufficient to elucidate the heterogeneity of pore networks and textural shifts x ray computed tomography allows a better evaluation of these fundamental characteristics which when integrated with stratigraphic analysis enhances the understanding of the volume and connectivity of pore networks in different microbial textures a three dimensional evaluation of a holocene microbialite from brazil provides insights about how the primary pore network is related to the textural changes in microbialite successions which in ancient deposits may be reduced or enhanced by diagenesis conventional methods such as petrography carbon and oxygen stable isotope analysis and laboratory measurements for porosity and permeability were integrated with computed tomography images and three dimensional rendering to provide a high resolution history of the evolution of porosity and permeability within this microbialite the pore network differences are related to microbial textural evolution driven by environmental changes the depositional textures control petrophysical properties based on fundamental rock characteristics such as structure size structure packing and framework fabric those fundamental characteristics influence the pore volume and number of pore throats large structures open packing and chaotic framework fabric result in a better connected pore network whereas small structures tight packing and organized fabric result in less connected pore networks comparative pore geometry analysis of the upper jurassic smackover formation thrombolites shows that their depositional textures also had high primary porosity values if the microbial textures and petrophysical properties are environmentally controlled their prediction in the subsurface is made possible by refined depositional models

quantification of depositional changes and paleo seismic activities from laminated sediments using outcrop data abstract measurements of laminations from marine and limnic sediments are commonly a time consuming procedure however the resulting quantitative proxies are of importance for the interpretation of both climate changes and paleo seismic activities digital image analysis accelerates the generation and interpretation of large data sets from laminated sediments based on contrasting grey values of dark and light laminae statistical transformation and correlation of the grey value signals reflect high frequency cycles due to changing mean laminae thicknesses and thus provide data monitoring climate change perturbations e g slumping structures seismites and tsunamites of the commonly continuous laminae record seismic activities and obtain proxies for paleo earthquake frequency using outcrop data from i the pleistocene lisan formation of jordan dead sea basin and ii the carboniferous permian copacabana formation of bolivia lake titicaca we present a two step approach to gain high resolution time series based on field data for both purposes from unconsolidated and lithified outcrops step 1 concerns the construction of a continuous digital phototransect and step 2 covers the creation of a grey density curve based on digital photos along a line transect using image analysis the applied automated image analysis technique provides a continuous digital record of the studied sections and therefore serves as useful tool for the evaluation of further proxy data analysing the obtained grey signal of the light and dark laminae of varves using phototransects we discuss the potential and limitations of the proposed technique

impact of sedimentology diagenesis and solid bitumen on the development of a tight gas grainstone reservoir in the feixianguan formation jiannan area china implications for gas exploration in tight carbonate reservoirs abstract tight gas grainstone reservoirs in the third member of the feixianguan formation jiannan area evolved from a paleo oil accumulation as evidenced from abundant solid reservoir bitumen porosity evolution of the grainstones was studied by evaluating relative influences of sedimentology diagenesis and solid bitumen formed during cracking of accumulated oils grainstones exhibited regional distinct effectiveness for paleo oil and present gas accumulations during oil window and subsequent gas window diagenesis in the southern zone where grainstones were not subjected to subaerial exposure and meteoric diagenesis in the early diagenetic stage paleoporosity at the time of oil charge was mainly controlled by sedimentologic factors e g grain size sorting and grain type and paleo oil reservoirs only occurred in the ooid dominated grainstones with good sorting and coarse grain size in contrast in the northern zone meteoric diagenesis was responsible for paleoporosity preservation due to the early mineral stabilization of grains and meteoric calcite cementation which caused grainstones greater resistance to compaction hence most of the grainstones in the northern zone regardless of textural variables formed effective reservoirs for paleo oil accumulation as the oil cracked to gas with increasing depth and temperature during the late oil window and initial gas window solid bitumen occluded reservoir pores to varying degrees and caused paleo oil reservoirs to be significantly heterogeneous or completely ineffective for gas accumulation in contrast most grainstones that were once ineffective oil reservoirs transformed into effective gas reservoirs due to no or minor influence of solid bitumen precipitation the model of reservoir transformation development of tight grainstones provides a plausible explanation for key observations concerning the diagenetic and distribution differences between paleo oil and present gas reservoirs it is useful in predicting the distribution of potential reservoirs in carbonate strata in future exploration

tectonic configuration of the apuseni banat timok srednogorie belt balkans south carpathians constrained by high precision r e o s molybdenite ages the apuseni banat timok srednogorie magmatic metallogenic belt abts belt forms a substantial metallogenic province in the balkan south carpathian system in southeastern europe the belt hosts porphyry skarn and epithermal deposits mined since pre roman times generally the deposits prospects and occurrences within the belt are linked to magmatic centers of calc alkaline affinity fifty one rhenium osmium re os ages and re concentration data for molybdenites define systematic geochronologic trends and constrain the geochemical metallogenic evolution of the belt in space and time from these data and additional existing geologic geochemical data a general tectonic history for the belt is proposed mineralization ages in apuseni banat timok and panagyurishte the central district of the larger e w srednogorie zone range from 72 83 81 88 and 87 92 ma respectively and clearly document increasing age from the northwestern districts to the southeastern districts further re os ages suggest rapidly migrating pulses of late cretaceous magmatic hydrothermal activity with construction of deposits in 1 m y districts in 10 m y and the entire 1 500 km belt in 20 m y ages in both timok and panagyurishte show systematic younging while deposit ages in banat and apuseni are less systematic reflecting a restricted evolution of the tectonic system systematic differences are also observed for molybdenite re concentrations on the belt scale re concentrations generally range from hundreds to thousands of parts per million typical of subduction related cu au mo pge porphyry systems associated with the generation of juvenile crust the geochronologic and geochemical trends are compatible with proposed steepening of subducting oceanic slab and relaxation of upper continental plate compression resulting influx of sub continental mantle lithosphere scml and asthenosphere provide a fertile metal source and heat while the subducting slab contributes connate and mineral dehydration fluids which facilitate partial melting and metal leaching of scml and asthenosphere cu au mo pge porphyry deposits may develop where melts are trapped at shallow crustal levels often with associated volcanism and epithermal style deposits south banat timok and panagyurishte mo fe pb zn skarn deposits may develop where felsic melts are trapped adjacent to mesozoic limestones at moderate crustal levels north banat and apuseni systematic spatial variations in deposit style commodity enrichment re os ages and re concentrations support specific tectonic processes that led to ore formation in a post collisional setting subduction of vardar oceanic crust may have stalled causing slab steepening and rollback the slab rollback relaxes compression facilitating and enhancing orogenic collapse of previously thickened balkan south carpathian crust the progression of coupled rollback orogenic collapse is evidenced by the width of late cretaceous extensional basins and northward younging of re os ages from panagyurishte 60 km 92 87 ma to timok 20 km 88 81 ma to apuseni banat 5 km 83 72 ma generation of a well endowed mineral belt such as the abts requires a temporally and spatially restricted window of magmatic hydrothermal activity this window is quickly opened as upper plate compression relaxes thereby inducing melt generation and ingress of melt to higher crustal levels the window is just as quickly closed as upper plate compression is reinstated the transient tectonic state responsible for economic mineralization in the abts belt may be a paleo analogue to transient intervals in the present subduction tectonics of se asia where much mineral wealth has been created in the last few million years

porosity permeability relationships in interlayered limestone dolostone reservoirs porosity and permeability data from five carbonate platform successions of different settings ages and burial depths are examined to identify overall similarities and differences in the reservoir quality of interlayered limestones and dolostones each succession consists mainly of limestone and dolostone with subordinate proportions of intermediate partly dolomitized compositions in the three deeply buried platforms the key features are that limestones have much lower average porosity than associated dolostones and that limestones and dolostones show little difference in average permeability for given porosity in contrast the shallowly buried platforms show little difference in average porosity between limestones and dolostones and also display higher average permeability for given porosity in dolostones than limestones these data suggest the following general guidelines for depositional and diagenetic controls on reservoir architecture in carbonates consisting of interlayered limestone and dolostone 1 reservoir compartmentalization by the formation of tight limestone barriers is largely a burial diagenetic process involving calcite cementation locally produced by chemical compaction 2 both the pattern of early dolomitization and the distribution of clay minerals because they influence the localization of chemical compaction are key factors that determine the distribution of tight limestone barriers separating flow units thus the pattern of eventual burial compartmentalization follows a template that is hardwired into the stratigraphic architecture by depositional mineralogy and early diagenesis 3 after burial 2 3 km 1 2 1 8 mi dolostones should not be expected to have higher permeability for given porosity than associated limestones these rules assume dolomitization to occur early relative to chemical compaction which will commonly be the case because of combined hydrologic and mass balance constraints dolomitization and concentration of clay appear linked to cycle and sequence architecture in the present examples and thus may have a useful degree of predictability at least in terms of statistical parameters such as net gross and probability of flow unit thickness distribution

quantifying flow in variably wet microporous carbonates using object based geological modeling and both lattice boltzmann and pore network fluid flow simulations abstract micropores can constitute up to 100 of the total porosity within carbonate hosted hydrocarbon reservoirs usually existing within micritic fabrics here three dimensional computational representations of end point micritic fabrics are produced using a flexible object based algorithm to further our understanding of the contribution that micropores make to flow by methodically altering model parameters we explore the state space of microporous carbonates quantifying single and multiphase flow using lattice boltzmann and network models in purely micritic fabrics average pore radius ranging from 0 26 to 0 44 m was found to have a positive correlation with single phase permeability 1 7 to 2 7 md respectively similarly increasing average pore size resulted in decreasing residual oil saturation under both water wet and 50 fractionally oil wet states permeability was found to increase by an order of magnitude from 0 6 to 7 5 md within fabrics of varying total matrix porosity from 18 to 35 because of increasing pore size 0 37 to 0 56 m respectively but minimal effect on multiphase flow was observed increased pore size due to micrite rounding notably increases permeability in comparison with original rhombic fabrics with the same porosity but multiphase flow properties are unaffected finally when moldic mesopores are added to a micritic matrix they impact flow when directly connected otherwise micropores control single phase permeability magnitude importantly recovery is dependent on both wetting scenario and pore network homogeneity under water wet imbibition increasing proportions of microporosity yield lower residual oil saturations together these results quantify the importance of micropores in contributing to or controlling overall flow and sweep characteristics in such fabrics

geochronological control for the main tectonic magmatic events of ecuador abstract a chronological outline of the principal tectonic magmatic events of ecuador is presented based upon approximately 100 k ar and rb sr age determinations eight magmatic episodes are recognized in southwestern ecuador evidence of plutonic and metamorphic activity in the late precambrian and in the middle to late triassic is found large granitic batholiths of middle to late jurassic age associated with widespread acidic volcanism are traceable along the eastern flank of the andes into colombia early cretaceous volcanism and plutonism is recognized only in southern ecuador although apparently equivalent units continue southwards into the coastal cordillera of peru a great orogenic belt characterized by metamorphism plutonism and volcanism was established in the late cretaceous and continued through the paleogene it is traceable into peru and colombia the macuchi fm of the western cordillera along with the pin on fm and associated sediments of the coastal zone represent the remnants of an island arc and the adjacent oceanic floor respectively that collided with the south american plate during the eocene feininger 1981 in the neogene quartz dioritic intrusions were emplaced in the western cordillera as well as in the cordillera de muelleturo although apparently at different times in the late oligocene and miocene acidic volcanism is noted in the southern ecuadorian andes but not in the north in the quaternary andesitic volcanism and large stratovolcanoes characterize the northern andes while widespread rhyolitic ashflow activity is noted in the southern andes in ecuador the post triassic magmatic episodes show a westerly migration similar to that found in colombia but opposite to that noted in peru

quantification of pore structure and its effect on sonic velocity and permeability in carbonates carbonate rocks commonly contain a variety of pore types that can vary in size over several orders of magnitude traditional pore type classifications describe these pore structures but are inadequate for correlations to the rock s physical properties we introduce a digital image analysis dia method that produces quantitative pore space parameters which can be linked to physical properties in carbonates in particular sonic velocity and permeability the dia parameters derived from thin sections capture two dimensional pore size domsize roundness aspect ratio ar and pore network complexity poa comparing these dia parameters to porosity permeability and p wave velocity shows that in addition to porosity the combined effect of microporosity the pore network complexity and pore size of the macropores is most influential for the acoustic behavior combining these parameters with porosity improves the coefficient of determination r2 velocity estimates from 0 542 to 0 840 the analysis shows that samples with large simple pores and a small amount of microporosity display higher acoustic velocity at a given porosity than samples with small complicated pores estimates of permeability from porosity alone are very ineffective r2 0 143 but can be improved when pore geometry information poa r2 0 415 and domsize r2 0 383 are incorporated furthermore results from the correlation of dia parameters to acoustic data reveal that 1 intergrain and or intercrystalline and separate vug porosity cannot always be separated using sonic logs 2 p wave velocity is not solely controlled by the percentage of spherical porosity and 3 quantitative pore geometry characteristics can be estimated from acoustic data and used to improve permeability estimates

geometry and petrophysical parameters of a calcarenitic turbidite lobe barremian aptian pas de la cluse france abstract several bioclastic resedimentation systems late barremian to early aptian in age outcrop in southeastern france the upslope portion of a calcarenitic turbidite lobe outcrops as a cliff 2 3 km wide and up to 45 m high oriented roughly perpendicular to the direction of palaeoflow it has been studied through 31 sections the studied body is point sourced and corresponds to a channel lobe transition located at the toe of slope of a urgonian carbonate platform on the western edge of the vocontian trough french subalpine chains the internal geometry of the lobe is the result of repeated erosion and filling of channels creating well defined stacked units filling phases result in lobe shaped morphology units evolve from base to top in an ordered way first the sediments exported from the platform and deposited in the basin are represented by decimetre thick sheet like and fine grained bouma a e and ab e sequences in this first unit erosion is limited and represented by shallow and symmetrical channels this initial phase of deposition corresponds to the formation of a lobe with a positive morphology the next phase of system development is more erosional and this is dominated by migrating sinuous channels several metres deep filled with coarse grained poorly graded turbidites these channels are first filled through lateral accretion and then sediment spills over to create a sub lobe the mixture of channel and lobe features could be considered as a carbonate equivalent of the channel levee system of siliciclastic deposits finally the system ends with the deposition of a flat based unit this unit extends for more than 2 km and is composed of the southwards lateral accretion of hundreds of metres wide sequences each composed of a debris flow deposit capped by a coarse grained calcarenite bed these sigmoidal bodies could be the ultimate forms of a spreading out phenomenon of the lobe overall the pas de la cluse system is a coarsening upward body as the grain size is related to the nature of the material this coarsening upward implies either an evolution in the nature of the carbonate material produced on the platform from grainy to bioconstructed a displacement of the source sediment from inner platform to margin or a displacement of the channel head through time from distal to proximal the upward evolution from classic turbidites to debris flow deposits can be explained either by the way the platform facies evolved with time in a depositional sequence or through retrogressive erosion by successive slope failures that cut deeper and deeper into the platform slope although its present day porosity is low the size of the system and the fact that it is encased in marls make it an interesting outcrop analogue for hydrocarbon exploration

permeability and acoustic velocity controlling factors determined from x ray tomography images of carbonate rocks carbonate reservoir rocks exhibit a great variability in texture that directly impacts petrophysical parameters many exhibit bi and multimodal pore networks with pores ranging from less than 1 m to several millimeters in diameter furthermore many pore systems are too large to be captured by routine core analysis and well logs average total porosity over different volumes consequently prediction of carbonate properties from seismic data and log interpretation is still a challenge in particular amplitude versus offset classification systems developed for clastic rocks which are dominated by connected intergranular unimodal pore networks are not applicable to carbonate rocks pore geometrical parameters derived from digital image analysis dia of thin sections were recently used to improve the coefficient of determination of velocity and permeability versus porosity although this substantially improved the coefficient of determination no spatial information of the pore space was considered because dia parameters were obtained from two dimensional analyses here we propose a methodology to link local and global pore space parameters obtained from three dimensional 3 d images to experimental physical properties of carbonate rocks to improve p wave velocity and permeability predictions results show that applying a combination of porosity microporosity and 3 d geometrical parameters to p wave velocity significantly improves the adjusted coefficient of determination from 0 490 to 0 962 a substantial improvement is also observed in permeability prediction from 0 668 to 0 948 both results can be interpreted to reflect a pore geometrical control and pore size control on p wave velocity and permeability

petrography and reservoir physics i objective classification of reservoir porosity porosity observed in thin section can be objectively classified using a combination of digital acquisition procedures and pattern recognition algorithms pore types are derived from the frequency distributions of sizes and shapes of patches of porosity exposed in thin section each pore type is represented by a characteristic distribution of sizes and shapes found in thin section most sandstone reservoirs contain fewer than six pore types much of the intersample variability in reservoir physics is associated with changes in pore type abundance the advantages of this approach to porosity classification are 1 the criteria for classification are objectively defined 2 classification procedure is rapid accurate and precise 3 pore types are understood easily in ter s of conventional genetic classification schemes and 4 pore type data are related strongly to petrophysical properties

sedimentologic and diagenetic controls on pore network characteristics of oligocene miocene ramp carbonates majella mountain central italy this article addresses the controls exerted by sedimentologic and diagenetic factors on the preservation and modification of pore network characteristics porosity pore types sizes shapes and distribution of carbonates belonging to the bolognano formation this formation exposed at the majella mountain italy is composed of oligocene miocene carbonates deposited in middle to outer ramp settings the carbonates consist of 1 grainstones predominantly composed of either larger benthic foraminifera especially lepidocyclina or bryozoans 2 grainstones to packstones with abundant echinoid plates and spines and 3 marly wackestones to mudstones with planktonic foraminifera the results of this field and laboratory based study are consistent with skeletal grain assemblages grain sizes sorting and shapes all representing the sedimentologic factors responsible for high values of connected primary macroporosity in grainstones deposited on the high energy middle to proximal outer ramp cementation responsible for porosity reduction and overall macropore shape and distribution in grainstones to packstones deposited on the intermediate outer ramp was mainly dependent on the following factors 1 amount of echinoid plates and spines 2 grain size 3 grain sorting and shapes and 4 clay amount differently in the wackestones to mudstones laid down on the low energy distal outer ramp matrix is the key sedimentologic factor responsible for low values of scattered macroporosity and dominance of microporosity the aforementioned results may be useful to improve the prediction of reservoir quality by means of mapping simulating and assessing individual carbonate facies with peculiar pore network characteristics

setting characteristics and age of the andean porphyry copper belt in colombia three distinct porphyry copper subbelts are defined in the colombian andes 1 a western subbelt emplaced during the early to middle eocene in an oceanic domain underlain by ophiolitic basement along the western side of the western cordillera 2 a composite eastern subbelt generated during the middle jurassic to earliest cretaceous in a continental domain underlain by elements of the guyana shield along the eastern side of the central cordillera and the western side of the eastern cordillera and between the two 3 a central subbelt formed in the early to late miocene at the contact of the oceanic and continental domains along the cauca patia depression and its flanks k ar geochronometry undertaken as part of this study provided preferred minimum ages of 54 7 or 1 3 m y for murindo 48 1 or 1 0 m y for acandi and 42 7 or 0 9 m y for pantanos pegadorcito in the western subbelt 166 or 4 m y for mocoa 166 or 4 m y for dolores 144 or 3 m y for california and 131 or 2 m y for infierno chili in the eastern subbelt and 17 4 or 0 4 m y for piedrasentada in the central subbelt the porphyry copper prospects are associated with dacite to tonalire porphyry stocks which in the western and eastern subbelts intruded batholiths emplaced perhaps 15 to 30 m y earlier but which in the central subbelt are isolated within metamorphic or sedimentary host rocks the porphyry copper systems exhibit a variety of alteration patterns with potassium silicate and sericitic alteration important in the highest grade prospects and propylitization predominant in low grade occurrences none of the prospects displays significant supergene enrichment although porphyry coppers in the continental domain tend to be more molybdenum rich than those in the oceanic domain gold rich prospects occur in both settings as do major lode gold deposits the jurassic and miocene subbelts are interpreted to have been emplaced during eastward subduction at andean type continental margins whereas the western eocene subbelt could have been generated in either a modified andean type setting or in an intraoceanic island arc prior to its accretion to the continental edge

statistical correlation between geophysical logs and extracted core the precise correlation of extracted core to geophysical borehole logs is often problematic in intervals in which no sufficiently large or distinctive features span the gap between the outer core surface and the borehole wall this impairs our ability to use techniques that require accurate correlation as a prerequisite e g to develop field based upscaling and downscaling relationships of porosity distributions at or below log resolution we propose a new method for such situations in which we correlate a cascade of statistics of core features with those of image logs taken from the borehole wall each statistic is used individually to calculate a likelihood function of possible correlation locations these results are combined using a joint likelihood function and with other prior information using bayesian techniques to bring all available information to apply to the final correlation solution the technique is demonstrated with computerized tomography for a core section and image log data extrac