application of neural networks for the prediction of the unconfined compressive strength ucs from equotip hardness abstract this paper presents the application of a neural network for the prediction of the ucs from hardness tests on rock samples to investigate the suitability of this approach the results of the network are compared to predictions obtained by conventional statistical relations the network was trained to predict the ucs based on the hardness porosity density grain size and rock type information of a rock sample a dataset containing 194 rock sample records ranging from weak sandstones to very strong granodiorites was used to train the network with the levenberg marquardt training algorithm two sets each containing 17 rock samples were used to validate the generalization and prediction capabilities of the network

estimation of missing logs by regularized neural networks an approach based on regularized back propagation neural networks can be used to estimate the missing logs or parts of those logs in wells with incomplete log suites this is done by first analyzing the interdependence of the various log types in a training well that has a complete suite of logs and then applying the network to nearby wells whose log suites are incomplete to estimate the missing logs in these wells the accuracy of the method is evaluated by blind tests conducted on real well log data these tests indicate that the method produces accurate estimates that are close to the measured log values and the method can thus be an effective means of enhancing limited suites of wire line logs moreover this approach has several advantages over the ad hoc practice of manually patching the missing logs from the complete log suites of proximate wells because it is automatic objective completely data driven inherently nonlinear and does not suffer from the overfitting difficulties commonly associated with conventional back propagation networks additionally it seems that an accurate selection of the optimal input log types is not necessary because redundant input containing several logs yields reasonably accurate results as long as some of the logs in the input are sufficiently correlated with the missing log

the importance of overpressure timing and permeability evolution in fine grained sediments undergoing shear abstract we summarise new experimental data which clarify the hydrological behaviour of clayey sediments undergoing shear and which emphasise the importance of the relative timing of deformation and overpressure fluid flow in fine grained materials subjected to shear is strongly dependent on the previous stress history of the material underconsolidated sediments such as those that retain high porosities through retarded dewatering and consequent excess pore fluid pressure generation deform by bulk volume loss which reduces permeability the deformation fabrics are pervasive in style weakly developed and without a significant influence on hydrological properties in contrast sediment that has been consolidated and then subjected to excess pore fluid pressure deforms dilatively along discrete brittle shear zones which markedly affect the permeability moreover below a certain threshold of effective stress these localised zones prompt a markedly non linear increase in hydraulic conductivity a laboratory demonstration and quantification of the concept of fracture permeability

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

geologically constrained electrofacies classification of fluvial deposits an example from the cretaceous mesaverde group uinta and piceance basins statistical classification methods consisting of the k nearest neighbor algorithm k nn a probabilistic clustering procedure pcp and a novel method which incorporates outcrop based thickness criteria through the use of well log indicator flags are evaluated for their ability to distinguish fluvial architectural elements of the upper mesaverde group of the piceance and uinta basins as distinct electrofacies classes data utilized in training and testing of the classification methods come from paired cores and well logs consisting of 1626 wireline log curve samples each associated with a known architectural element classification as determined from detailed sedimentologic analysis of cores n 9 thickness criteria are derived from outcrop based architectural element measurements of the upper mesaverde group through an approach which integrates select classifier results with thickness criteria an overall accuracy number of correctly predicted samples total testing samples of 83 6 was achieved for a four class fluvial architectural element realization architectural elements were predicted with user s accuracies accuracy of an individual class of 0 891 0 376 0 735 and 0 985 for the floodplain crevasse splay single story channel body and multi story channel body classes respectively without the additional refinement by incorporation of thickness criteria the k nn and pcp classifiers produced similar results in both the k nn and pcp techniques the combination of gamma ray and bulk density wire line log curves proved to be the most useful assemblage tested

three levels of compartmentation within the overpressured interval of the anadarko basin deep basin pressure compartments can be classified on the basis of their size stratigraphy and pressure regimes detailed investigations of the geologic setting and pressure gradients of numerous reservoirs in the anadarko basin reveal the presence of three distinct levels of compartmentation level 1 is a basinwide feature known as the megacompartment complex mcc this complex is an overpressured volume of rocks that is completely enclosed by seals it is approximately 241 km 150 mi long 113 km 70 mi wide and has a maximum thickness in excess of 4877 m 16 000 ft gas reserves of the overpressured reservoirs within the mcc are speculated to be approximately 20 tcf the other two compartmentation levels are further subdivisions of the internal volume of the mcc level 2 compartmentation consists of multiple district or field sized configurations within a particular stratigraphic interval these compartments are 32 to 49 km 20 to 30 mi long 19 to 32 km 12 to 20 mi wide and 122 to 183 m 400 to 600 ft thick their reserve estimates can exceed 2 tcf examples of this type are the upper morrowan chert conglomerate reservoirs in the cheyenne reydon field area level 3 consists of a single small field or a particular reservoir nested within level 2 these compartments are generally 3 to 6 km 2 to 4 mi long the hierarchical classification of compartments has important implications for petroleum exploration and development recognizing the upper and lower boundaries of the mcc is essential to safe drilling practices the similar pressures within level 2 compartments allow the prediction of approximate reservoir pressures across trend size areas of the basin tens to

determination of lithology from well logs using a neural network we have developed a computer program to automatically determine lithologies from well logs using a back propagation neural network unlike a conventional serial computer a neural network is a computational system composed of nodes sometimes called neurons neurodes or units and the connections between these nodes neural computing attempts to emulate the functions of the mammalian brain thus mimicking thought processes the neural network approach differs from previous pattern recognition methods in its ability to learn from examples unlike conventional statistical methods this new approach does not require sophisticated mathematics and a large amount of statistical data this paper discusses the application of neural networks to a pattern recognition problem in eology the determination of lithology from well logs the neural network determined the lithologies limestone dolomite sandstone shale sandy and dolomitic limestones sandy dolomite and shale sandstone from selected well logs in a fraction of the time required by an experienced human log analyst

global crustal thickness from neural network inversion of surface wave data summary we present a neural network approach to invert surface wave data for a global model of crustal thickness with corresponding uncertainties we model the a posteriori probability distribution of moho depth as a mixture of gaussians and let the various parameters of the mixture model be given by the outputs of a conventional neural network we show how such a network can be trained on a set of random samples to give a continuous approximation to the inverse relation in a compact and computationally efficient form the trained networks are applied to real data consisting of fundamental mode love and rayleigh phase and group velocity maps for each inversion performed on a 2 2 grid globally we obtain the a posteriori probability distribution of moho depth from this distribution any desired statistic such as mean and variance can be computed the obtained results are compared with current knowledge of crustal structure generally our results are in good agreement with other crustal models however in certain regions such as central africa and the backarc of the rocky mountains we observe a thinner crust than the other models propose we also see evidence for thickening of oceanic crust with increasing age in applications characterized by repeated inversion of similar data the neural network approach proves to be very efficient in particular the speed of the individual inversions and the possibility of modelling the whole a posteriori probability distribution of the model parameters make neural networks a promising tool in seismic tomography

thickening the altiplano crust by gravity driven crustal channel flow 1 in the central andes crustal thickness is not well correlated to upper crustal shortening only little shortening is documented in the upper crust of the 60 65 km thick altiplano plateau whose thickening and uplift were delayed with respect to earlier and greater thickening in the adjacent western and eastern cordilleras because crustal thickness variations induce horizontal stress gradients and cause crustal flow a thickness dependent channel flow is modeled here and applied to the central andes in situ thickening is assumed for both cordilleras while the altiplano crustal thickening is generated by lateral flow from these overthickened adjacent domains a 8 1018 pa s viscosity channel is predicted for crustal thicknesses exceeding 45 50 km to match the estimated topographic evolution of the central andes thickening in the cordilleras was sufficient to generate a flow of 6 109 m3 per unit length toward the initially 30 35 km thick altiplano

megacompartment complex in the anadarko basin a completely sealed overpressured phenomenon integrated pore pressure potentiometric and geologic data in the anadarko basin demonstrate the existence of a basinwide completely sealed overpressured compartment called the megacompartment complex all reservoirs within this complex exhibit pressure gradients that exceed the normal gradient of 10 515 kpa m 0 465 psi ft these reservoirs have produced large quantities of natural gas particularly from the pennsylvanian red fork and morrowan sandstones this megacompartment complex is enclosed by top basal and lateral seals the top seal zone which is located between 2290 m and 3050 m 7500 and 10 000 ft below the surface is relatively horizontal dips slightly to the southwest and appears to cut across stratigraphy however the diagenetically enhanced basal seal is stratigraphically controlled and seems to coincide with the devonian woodford shale the complex is laterally sealed to the south by a vertical cementation zone associated with the frontal fault zone of the wichita mountain uplift and by the convergence of the top and basal seals along the eastern northern and western boundaries the interior of the complex is subdivided into a myriad of smaller compartments with distinct pressure gradients in addition local overpressured compartments are present outside the megacompartment complex in normally and near normally pressured regions

predicting permeability from porosity using artificial neural networks permeability values in a borehole are predicted by an artificial neural network from the porosity values at the same depths the network used in this study employs an architecture called backpropagation that is good at making predictions the traditional approach for permeability prediction is regression analysis in regression analysis the relationship between porosity and permeability is assumed to be known in reality the functional form of this relationship i e the model equation is unknown in contrast the neural network approach assumes no functional relationship six wells from big escambia creek jurassic smackover carbonate field in southern alabama were used to test predicting permeability from porosity using a neural network porosity and spatial data alone were used to predict permeability because these data are readily available from any hydrocarbon field three scenarios were performed in each one a subset of the six wells was used for a training set one well for calibration and one or two wells were used for prediction for each scenario simple linear regression was also used to predict permeability from porosity the neural net predicted permeability much better than did regression in one scenario in the other two scenarios the two methods performed equally well the neural net predicted permeability accurately using minimal da a but other kinds of information e g log or core derived lithologic information are easily incorporated if available in addition compartmentalization of carbonate reservoirs may be recognizable by this approach

the use of artificial neural network analysis and multiple regression for trap quality evaluation a case study of the northern kuqa depression of tarim basin in western china abstract artificial neural network analysis is found to be far superior to multiple regression when applied to the evaluation of trap quality in the northern kuqa depression a gas rich depression of tarim basin in western china this is because this technique can correlate the complex and non linear relationship between trap quality and related geological factors whereas multiple regression can only describe a linear relationship however multiple regression can work as an auxiliary tool as it is suited to high speed calculations and can indicate the degree of dependence between the trap quality and its related geological factors which artificial neural network analysis cannot for illustration we have investigated 30 traps in the northern kuqa depression for each of the traps the values of 14 selected geological factors were all known while geologists were also able to assign individual trap quality values to 27 traps they were less certain about the values for the other three traps multiple regression and artificial neural network analysis were therefore respectively used to ascertain these values data for the 27 traps were used as known sample data while the three traps were used as prediction candidates predictions from artificial neural network analysis are found to agree with exploration results where simulation predicted high trap quality commercial quality flows were afterwards found and where low trap quality is indicated no such discoveries have yet been made on the other hand multiple regression results indicate the order of dependence of the trap quality on geological factors which reconciles with what geologists have commonly recognized we can conclude therefore that the application of artificial neural network analysis with the aid of multiple regression to trap evaluation in the northern kuqa depression has been quite successful to ensure the precision of the above mentioned geological factors and their related parameters for each trap a study of the petroleum system in kuqa depression was conducted which included the partitioning and mechanisms of the kuqa petroleum system three migration models are presented

using neural networks to predict thermal conductivity from geophysical well logs summary we present a new approach based on neural networks to predict the thermal conductivity of sedimentary rocks from a set of geophysical well logs this method is calibrated on ocean drilling program odp data which provide several thousands of conductivity measurements combined with five geophysical well logs sonic density neutron porosity resistivity and gamma ray this data set is used to train multilayer perceptrons mlp and to find an empirical relationship between well logs mlp inputs and thermal conductivity mlp output validation tests suggest that mlp provide better estimates of thermal conductivity within 15 per cent confidence level than classical linear models and still give satisfying results with sets of only four well logs if neutron porosity is included in two odp sites 863b and 1109d mlp s predictions are compared to conventional mixing methods although this latter technique gives reliable results provided that rocks description is precise enough the mlp is more straightforward does not need any extra parameter and makes predictions in good agreement with the experimental trends this method will be useful in the estimation of heat flow from data acquired in scientific and industrial boreholes

neural network analyses of stress induced overpressures in the pannonian basin summary artificial neural networks can learn relationships between sediment characteristics burial depth composition coordinates and thickness of overlying quaternary deposits and overpressures from well data after which they can interpolate and extrapolate to areas and depths not covered by wells we analyse data from the south eastern part of the pannonian basin we use a neural network for analysing fluid overpressures because of the complex interaction of the key variables making it difficult to derive the functional relationships required for a statistical analysis the optimal topology of the network number of hidden layers and neurons is found by minimizing the network s training and testing errors the optimal design of the network resembles the interactions scheme of the key variables the pannonian basin originally formed in an extensional regime has been in a compressive state of stress since late pliocene causing anomalous subsidence patterns numerical forward modelling of compaction driven fluid overpressures shows that due to an increase in the level of compressive interplate stress the fluid overpressures in the deep subbasins have increased substantially since late pliocene giving rise to a very high overpressure up to 45mpa at present the neural network analyses provide an independent estimate of the current amount of overpressuring in this basin complementing the numerical forward modelling results the overpressure profiles obtained by the two modelling approaches are in excellent agreement showing the same magnitude of overpressures a reversal of the overpressure in the deepest parts of the subbasins and a general decrease of the overpressure from sw to ne

petrogenesis of a type granitoids from the alto moxoto and alto pajeu terranes of the borborema province ne brazil constraints from geochemistry and isotopic composition abstract a type granitoids 512 ma either intruded into paleoproterozoic gneiss of the alto moxoto terrane prata complex and serra da engabelada pluton or into early neoproterozoic metavolcanic metasedimentary sequence of the alto pajeu terrane serrote santo antonio pluton constitute a small proportion of brasiliano pan african granitoids in the central tectonic domain of the borborema province northeastern brazil the prata complex consists of syenogranites monzogranites mafic enclaves of diorites and norites the felsic and mafic members are not genetically related through fractionation mingling and mixing were extensive processes within the prata complex the granites evolution appears to have involved fractionation of alkali feldspar biotite apatite and sphene without significant wall rock assimilation the serra da engabelada and serrote santo antonio plutons consist of biotite syenogranites with rare mafic enclaves the studied granitoids are dominantly metaluminous characterized by fe rich biotite and fe hornblende high total alkalis y nb and ree and low cao mgo and sr abundances and high feo feo mgo ratios characterize these granitoids chondrite normalized ree patterns show enriched lree moderate to strong negative eu anomalies and more or less flat heavy ree the studied granitoids and diabase from dykes and enclaves show negative end 512ma values 14 to 10 high incompatible elements such as lile hfse and ree suggesting important contribution of paleoproterozoic crust the origin of the granites is thought to have involved partial melting of granodioritic or tonalitic lower crust such isotopic signature of the diabase from the dykes also reflects a paleoproterozoic enriched lithospheric mantle in the area the intrusion of the studied granitoids contemporary with sub volcanic bimodal magmatism and deposition of many cambrian pull apart basins in the north and central tectonic domain of the borborema province suggest intrusion during post tectonic relaxation of the brasiliano orogeny following the assembly of west gondwana

u pb dating of granites in the neoproterozoic sergipano belt ne brazil implications for the timing and duration of continental collision and extrusion tectonics in the borborema province abstract the sergipano belt is the outcome of collision between the pernambuco alagoas massif and the sao francisco craton during neoproterozoic assembly of west gondwana field relationships and u pb geochronology of granites intruded in garnet micaschists of the macurure domain are used to constrain the main collisional event d 2 in the belt the granites are divided into two groups the pre collisional granites pre to early d 2 and the syn collisional granites syn to tardi d 2 the latter were emplaced as sheets along the s 2 axial plane foliation or they were collected at the hinge zones of f 2 folds a u pb shrimp zircon age of 628 12 ma was obtained for the pre collisional camara tonalite two u pb tims titanite ages were obtained for the syn collisional granites 584 10 ma for the angico granite and 571 9 ma for the pedra furada granite and these ages are close to the garnet whole rock sm nd isochron of 570 ma found for the peak of metamorphism in the sergipano belt the ages of the camara tonalite 628 ma and the pedra furada granite 571 ma mark respectively the maximum age for beginning of the d 2 event and minimum age for the end in the macurure domain using these ages the main neoproterozoic d 2 collisional event has been in operation in the sergipano belt for at least 57 million years correlation with coeval granitoids farther north in the borborema province indicate that while in the sergipano belt the syn d 2 granites ca 590 570 ma were emplaced under compression in the borborema province they emplaced under extensional conditions related to regional strike slip shear zones these contrasting emplacement settings for contemporaneous neoproterozoic granitoids are explained by a combination of continent continent collision and extrusion tectonics

reworked old crust derived shoshonitic magma the guarany pluton northeastern brazil abstract the 572 ma guarany stock consists of magmatic epidote bearing hornblende monzodiorite to biotite granite that intruded paleoproterozoic orthogneisses about 10 km inland from the coast in northeastern brazil co magmatic diorite enclaves and dikes are abundant throughout the pluton the monzodiorite granite pluton and diorite enclaves are shoshonitic and display continuous trends in variation diagrams they display chemical and isotopic characteristics of crustal melts such as enrichment in incompatible elements high back calculated initial 87 sr 86 sr ratios avg 0 71253 negative end 0 57ga values avg 14 58 as well as high and variable 9 1 to 11 1 vsmow 18 o zircon values correlations between o isotope and whole rock silica contents as well as initial 87 sr 86 sr ratios with 1 sr concentrations suggest hybridization of a lower continental crustal melt with more felsic crustal rocks concomitant with fractional crystallization amphibole chemistry and whole rock zr tio 2 and p 2 o 5 contents suggest magma solidification at a pressure 7 kbar and near liquidus temperature 900 c the parental magma was likely formed by partial melting of old tdm 2 0 ga amphibolitic lower continental crustal rocks in a post collisional setting probably triggered by underplating of mantle derived mafic magma during the period of relaxation after collision

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

empirical prediction of porosity and permeability in sandstones current efforts to predict porosity and permeability in sandstones prior to drilling are focused on empirical and process oriented models empirical predictions are based on the correlation between porosity and permeability and a limited number of parameters obtained from calibration data sets or estimated from appropriate geologic models of these parameters the most important are detrital composition grain size sorting and temperature history or pressure history or both despite its limitations the empirical approach provides accurate predrill predictions of reservoir quality in many sandstones containing not only primary but also secondary porosity and permeability predictions of the average porosity and permeability of target sandstones are arbitrarily defined h re as accurate if they fall within 2 porosity of the mean measured porosity and within the same order of magnitude as the mean measured permeability in a sample population representing the interval of interest the effectiveness of the empirical predictive approach is illustrated by case studies from the taranaki basin new zealand and yacheng field people s republic of china these studies indicate that empirical predictions are basin specific or even play specific and require at least some understanding of fundamental processes affecting reservoir quality of a given sandstone target process oriented approaches attempting to model the effect of diagenesis on reservoir quality are hampered by inadequate quantitative understanding of the processes responsible for preserving primary porosity and generating secondary porosity and permeability until adequate quantification of the sandstone diagenesis processes is achieved empirical models have a distinct advantage over process oriented models in providing reliable predictions of reservoir quality in many sandstone intervals

using artificial neural networks to predict the presence of overpressured zones in the anadarko basin oklahoma many sedimentary basins throughout the world exhibit areas with abnormal pore fluid pressures higher or lower than normal or hydrostatic pressure predicting pore pressure and other parameters depth extension magnitude etc in such areas are challenging tasks the compressional acoustic sonic log dt is often used as a predictor because it responds to changes in porosity or compaction produced by abnormal pore fluid pressures unfortunately the sonic log is not commonly recorded in most oil and or gas wells we propose using an artificial neural network to synthesize sonic logs by identifying the mathematical dependency between dt and the commonly available logs such as normalized gamma ray gr and deep resistivity logs reid the artificial neural network process can be divided into three steps 1 supervised training of the neural network 2 confirmation and validation of the model by blind testing the results in wells that contain both the predictor gr reid and the target values dt used in the supervised training and 3 applying the predictive model to all wells containing the required predictor data and verifying the accuracy of the synthetic dt data by comparing the back predicted synthetic predictor curves grnn reidnn to the recorded predictor curves used in training gr reid artificial neural networks offer significant advantages over traditional deterministic methods they do not require a precise mathematical model equation that describes the dependency between the predictor values and the target values and unlike linear regression techniques neural network methods do not overpredict mean values and thereby preserve original data variability one of their most important advantages is that their predictions can be validated and confirmed through back prediction of the input data this procedure was applied to predict the presence of overpressured zones in the anadarko basin oklahoma the results are promising and encouraging

porosity and permeability prediction from wireline logs using artificial neural networks a north sea case study estimations of porosity and permeability from well logs are important yet difficult tasks encountered in geophysical formation evaluation and reservoir engineering motivated by recent results of artificial neural network ann modelling offshore eastern canada we have developed neural nets for converting well logs in the north sea to porosity and permeability we use two separate back propagation anns bp anns to model porosity and permeability the porosity ann is a simple three layer network using sonic density and resistivity logs for input the permeability ann is slightly more complex with four inputs density gamma ray neutron porosity and sonic and more neurons in the hidden layer to account for the increased complexity in the relationships the networks initially developed for basin scale problems perform sufficiently accurately to meet normal requirements in reservoir engineering when applied to jurassic reservoirs in the viking graben area the mean difference between the predicted porosity and helium porosity from core plugs is less than 0 01 fractional units for the permeability network a mean difference of approximately 400 md is mainly due to minor core log depth mismatch in the heterogeneous parts of the reservoir and lack of adequate overburden corrections to the core permeability a major advantage is that no a priori knowledge of the rock material and pore fluids is required real time conversion based on measurements while drilling mwd is thus an obvious application

ediacaran aguas belas pluton northeastern brazil evidence on age emplacement and magma sources during gondwana amalgamation abstract ediacaran syenogranites from the aguas belas pluton borborema province northeastern brazil were investigated in this work the studied granitoids show high sio2 fe feo feo mgo total alkalis k2o na2o and bao contents and medium sr and low nb contents they show gentle fractionated rare earth patterns with discrete eu negative anomalies major and trace element data point to chemical features of transitional high k calc alkaline to alkaline post collisional magmatism structural data coupled with geochronological data suggest that nne ssw trending sinistral movements at shear zones were initiated at ca 590 ma and have activated e w pre existing structures at the current crustal level the synchronism of these shear zones allowed the dilation to generate the necessary space for the emplacement of the aguas belas pluton u pb shrimp zircon data show a cluster of ages around 588 4 ma which is interpreted as the crystallization age some zircon grain cores yielded ages within 2060 1860 ma and 1670 1570 ma intervals oxygen isotope compositions of zircon grains with distinct ages were measured using shrimp techniques twenty three analyses in the same zircon spots previously analyzed for u pb show 18o values ranging from 5 79 to 10 30 smow this large range of values results from variations both between grains and within grains core mantle rim and is interpreted as the result of mixing of components with distinct oxygen isotope compositions the u pb zircon ages and the 18o values associated with paleoproterozoic nd tdm model ages suggest that the protolith of these granitoids involved a mantle component paleoproterozoic lithospheric mantle paleoproterozoic and mesoproterozoic igneous rocks interactions with mesoproterozoic or neoproterozoic supracrustal rocks may have occurred during the intrusion the resulting magma evolved through biotite and k feldspar fractionation

proterozoic links between the borborema province ne brazil and the central african fold belt the congo cc and the sao francisco sfc cratons were joined at about 2 05 ga northern parts of palaeoproterozoic basement subsequently underwent extension at about 1 ga forming intracratonic basins neoproterozoic metasedimentary rocks in these basins yield detrital zircons as young as 630 ma the brasiliano and pan african c 620 580 ma assembly of west gondwana extensively altered this system the sergipano domain occurs north of the sfc and the comparable yaoundedomain occurs north of the cc crust north of the sergipano domain com prises the pernambuco alagoas peal domain the ne sw striking tchollire banyo fault in cameroon may extend southwestwards between the peal and sergipano domains defining northern limits of abundant sfc cc basement the adamawa yadedomain in africa does not appear to extend into brazil the transverse domain of brazil is a collage of palaeoproterozoic crustal blocks the 1 0 ga cariris velhos orogen cvo late neoproterozoic basins and brasi liano granites the cvo extends ene for more than 700 km in brazil but eastern continuation into africa has not been identified north of the transverse domain contiguous c 2 15 ga gneisses comprise basement of rio grande do norte and cearadomains which continue eastwards into western nigeria and western sahara

abstract sequence stratigraphic framework of shu aiba formation shaybah field saudi arabia a basis for reservoir development of an aptian carbonate ramp complex

subduction margin assemblages in the proterozoic pinal and cochise blocks southeastern arizona protoliths of paleoproterozoic rocks broadly referred to as pinal schist in the johnny lyon hills and the dragoon and little dragoon mountains of cochise county arizona include intrusive and subaqueous extrusive mafic rocks turbiditic clastic rocks and highly deformed sedimentary rocks visually similar to phanerozoic melanges the combination of these lithologies and their present spatial distribution clastic rocks to the northwest separated by a region of melange from mafic igneous rocks to the southeast is suggestive of an assemblage formed at a subduction type continental margin protoliths of the mafic rock sequence about 700 m thick consist upward from its base of composite diabase dikes pillow lavas and pillow breccias and pelitic sedimentary rocks it may be an ophiolite fragment the clastic rocks though complexly deformed form a largely coherent mostly northwest younging sequence a fault bounded deformed belt present between the mafic and the clastic rocks includes pre metamorphic melange and broken formation the study area falls along or near previously suggested boundaries between lithotectonic assemblages within the precambrian rocks of southeastern arizona our results provide insight into the location and nature of the boundary and strongly suggest the presence of a suture zone juxtaposing predominantly metavolcanic rocks to the southeast against predominantly metasedimentary rocks to the northwest consistent with the terminology used by eisele and isachsen this issue we adopt the terms cochise block and pinal block for the regions to the southeast and northwest of the suture respectively

reservoir characterization modeling and evaluation of upper jurassic smackover microbial carbonate and associated facies in little cedar creek field southwest alabama eastern gulf coastal plain of the united states an integrated field study of the microbial carbonate and associated reservoirs at little cedar creek field in southwest alabama eastern gulf coastal plain of the united states provides an excellent opportunity to examine the spatial distribution of the sedimentary petrophysical and productivity trends in microbial reservoirs this study includes characterizing the sedimentary petrophysical and hydrocarbon productivity characteristics of microbialites developing a three dimensional geologic reservoir model and evaluating the hydrocarbon potential of these reservoirs the lower reservoir comprises subtidal thrombolitic boundstone associated with microbial buildups oriented in a southwest to northeast direction over an area that encompasses 32 mi2 83 km2 these buildups developed in clusters in the western central and northern parts of the field and attained thicknesses of 43 ft 13 m the clusters are separated by interbuildup areas of microbialites of 7 9 ft 2 3 m in thickness that are overlain by a thick section of nonreservoir microbially influenced lime mudstone and wackestone porosity in the microbial reservoirs includes depositional constructed void intraframe and diagenetic solution enhanced void and vuggy pore types this pore system provides for high permeability and connectivity in the reservoir beds permeability ranges to as much as 7953 md and porosity to as much as 20 the microbial boundstone beds have high potential as hydrocarbon flow units however the buildup areas are separated by interbuildup areas associated with a thick section of low permeability to nonreservoir beds that serve as potential baffles or barriers to flow much of the 17 2 million bbl oil produced from the field is from the microbial lithofacies the results from the little cedar creek field study have application in the design of improved development strategies for other fields producing from microbial carbonate reservoirs

late interseismic state of a continental plate bounding fault petrophysical results from dfdp 1 wireline logging and core analysis alpine fault new zealand 1 we present a geophysical characterization at 0 1 100 m scales of a major plate bounding continental fault in a late interseismic state the alpine fault produces mw 8 earthquakes every 200 400 years and last ruptured in 1717 ad wireline geophysical logs and rock cores extending from one side of the alpine fault to the other were acquired in two boreholes drilled in 2011 at gaunt creek during the first phase of the deep fault drilling project dfdp 1 these data document ambient conditions under which the next alpine fault earthquake will occur principal component analysis of the wireline logging data reveals that 80 of the variance is accounted for by electrical acoustic and natural gamma properties and preliminary multivariate classification enables the lithologies of sections of missing core to be reconstructed from geophysical measurements the fault zone exhibits systematic variations in properties consistent with common processes of progressive alteration and comminution near the principal slip zone superimposed on different protolith compositions our observations imply that the fault zone has the opposite sense of elastic asymmetry at 0 1 100 m scales to that of the crustal scale orogen imaged by remote geophysical methods on the basis of the fault zone scale asymmetry the bimaterial interface model of preferred earthquake rupture directions implies a northeastward direction of preferred alpine fault rupture on going characterization of the structural and hydraulic architecture of the alpine fault will improve our understanding of the relationship between in situ conditions earthquake rupture processes and the hazards posed by future earthquakes

application of artificial neural networks to paleoceanographic data abstract artificial neural networks are computer systems that have the ability to learn a set of output or target vectors from a set of input vectors learning is achieved by self adjustment of a set of parameters to minimize the error between a desired output and the actual network output we have explored the potential of this approach in paleoceanography by application of a neural network algorithm to a problem involving prediction of sea surface water temperatures from relative abundances of planktonic foraminifer species in the southern indian ocean we employed a backpropagation bp network to assess how well it was able to predict the actual summer and winter surface water temperatures we compared the results with those obtained from statistical methods previously used for temperature predictions imbrie kipp transfer functions the modern analog technique and soft independent modelling of class analogy the efficiency of predictions was tested using the leaving one out technique in which each of the observations in the data set is left out one at a time while the remaining observations are used to generate a predictor the accuracy of the predictor is then tested on the observation left out by comparison with its actual value a set of tests using 1 2 3 4 5 and 10 neurons processing elements in a 3 layer bp network showed that a network with 3 neurons gave the smallest errors of prediction for both summer and winter temperatures 0 71 and 0 76 respectively corresponding errors for the statistical pattern recognition techniques ranged between 1 01 and 1 26 for summer temperatures and 1 05 1 13 for winter temperatures hence predictions of paleotemperatures from new data on planktonic foraminifer relative abundances in the southern indian ocean may be made with a precision of 0 7 0 8 c using the bp network and 1 0 1 3 c using the statistical pattern recognition procedures the bp network was thus the most successful among the methods employed here for temperature predictions artificial neural networks may therefore be seen as a viable alternative to more conventional approaches to data analysis in paleoceanography

application of artificial neural networks to chemostratigraphy artificial neural networks a branch of artificial intelligence are computer systems formed by a number of simple highly interconnected processing units that have the ability to learn a set of target vectors from a set of associated input signals neural networks learn by self adjusting a set of parameters using some pertinent algorithm to minimize the error between the desired output and network output we explore the potential of this approach in solving a problem involving classification of geochemical data the data taken from the literature are derived from four late quaternary zones of volcanic ash of basaltic and rhyolithic origin from the norwegian sea these ash layers span the oxygen isotope zones 1 5 7 and 11 respectively last 420 000 years the data consist of nine geochemical variables oxides determined in each of 183 samples we employed a three layer back propagation neural network to assess its efficiency to optimally differentiate samples from the four ash zones on the basis of their geochemical composition for comparison three statistical pattern recognition techniques linear discriminant analysis the k nearest neighbor k nn technique and simca soft independent modeling of class analogy were applied to the same data all of these showed considerably higher error rates than the artificial neural network indicating that the back propagation network was indeed more powerful in correctly classifying the ash particles to the appropriate zone on the basis of their geochemical composition

artificial neural network modelling as an aid to source rock characterization abstract a data based approach is used to establish detailed and accurate geochemical characterization in oil source rock intervals using well logs and noisy information from cuttings the method starts by extracting examples from the intervals of interest using generalized relationships between total organic content toc and well log responses the examples were used to train an artificial neural network ann that extracted more detailed and accurate relationships between toc and well log responses specific to the study area a combination of the quickprop algorithm and dynamic node creation scheme was utilized to facilitate efficient training the trained ann is useful for mapping source rock intervals in the area of interest this method performs satisfactorily when applied to the egret source rock of the jeanne d arc basin offshore eastern canada

u pb geochronologic constraints on the age of thrusting crustal extension and peraluminous plutonism in the little rincon mountains southern arizona the little rincon thrust fault is a mylonitic shear zone that juxtaposes middle proterozoic continental granodiorite over metasedimentary rocks of proterozoic and early paleozoic age this fault is structurally beneath the san pedro detachment fault and associated ductile deformational fabrics which formed during early oligocene to early miocene time a syntectonic leucogranite sill within the little rincon shear zone yields a u pb concordia intercept age 66 plus minus 10 ma for zircon and a concordant age 51 plus minus 2 ma for fractions composed of monazite and xenotime this demonstrates that compressional deformation in the catalina and rincon mountains is generally coeval with laramide thrust faults that extend at least from southeastern california to southeastern arizona a peraluminous granite pluton that truncates the shear zone but displays extension related fabrics yields a lower intercept age 24 plus minus 12 ma for zircon and an age of 30 plus minus 6 ma for monazite this indicates that some peraluminous plutons in the region were emplaced during regional crustal extension

an effective bayesian model for lithofacies estimation using geophysical data 1 a bayesian model coupled with a fuzzy neural network bfnn is developed to enhance the use of geophysical data in lithofacies estimation prior estimates are inferred from borehole lithofacies measurements using indicator kriging and posterior estimates are obtained by updating the prior using geophysical data the novelty of this study lies in the use of the fuzzy neural network for the inference of the likelihood function this allows spatial correlation of lithofacies as well as nonlinear cross correlation between lithofacies and geophysical attributes to be incorporated into lithofacies estimation the effectiveness of bfnn is demonstrated using synthetic data emulating measurements at the lawrence livermore national laboratory llnl site

the umarizal igneous association borborema province ne brazil implications for the genesis of a type granites abstract the umarizal igneous association ne brazil consists of three a type plutons intruded over an interval of about 15 ma during the post collisional phase of the brasiliano orogeny all the plutons have sr isotopic compositions which indicate important or dominant crustal contributions crystallization of the umarizal sill formed of fayalite quartz syenite and syenogranite and of the lagoa stocks formed by mangerite and granite commenced under water undersaturated conditions at pressures around 700 800 mpa and temperatures around 900 c and continued during magma rise with the crystallization of hornblende at about 480 570 mpa crystallization of the acao stock which contains a rapakivi like facies commenced at similar temperatures and hornblende appeared at slightly less than 800 c and around 500 mpa different f o2 conditions controlled the compositions of the ferromagnesian phases and the nature of the oxide mineral assemblage simple fractional crystallization models from homogeneous parent magmas are insufficient to explain the chemical variation of the rocks suites

committee neural networks for porosity and permeability prediction from well logs neural computing has moved beyond simple demonstration to more significant applications encouraged by recent developments in artificial neural network ann modelling techniques we have developed committee machine cm networks for converting well logs to porosity and permeability and have applied the networks to real well data from the north sea simple three layer back propagation anns constitute the blocks of a modular system where the porosity ann uses sonic density and resistivity logs for input the permeability ann is slightly more complex with four inputs density gamma ray neutron porosity and sonic the optimum size of the hidden layer the number of training data required and alternative training techniques have been investigated using synthetic logs for both networks an optimal number of neurons in the hidden layer is in the range 8 10 with a lower number of hidden units the network fails to represent the problem and for higher complexity overfitting becomes a problem when data are noisy a sufficient number of training samples for the porosity ann is around 150 while the permeability ann requires twice as many in order to keep network errors well below the errors in core data for the porosity ann the overtraining strategy is the suitable technique for bias reduction and an unconstrained optimal linear combination olc is the best method of combining the cm output for permeability on the other hand the combination of overtraining and olc does not work error reduction by validation simple averaging combined with range splitting provides the required accuracy the accuracy of the resulting cm is restricted only by the accuracy of the real data the ann approach is shown to be superior to multiple linear regression techniques even with minor non linearity in the background model

permeability prediction with artificial neural network modeling in the venture gas field offshore eastern canada estimating permeability from well log information in uncored borehole intervals is an important yet difficult task encountered in many earth science disciplines most commonly permeability is estimated from various well log curves using either empirical relationships or some form of multiple linear regression mlr more sophisticated multiple nonlinear regression mnlr techniques are not as common because of difficulties associated with choosing an appropriate mathematical model and with analyzing the sensitivity of the chosen model to the various input variables however the recent development of a class of nonlinear optimization techniques known as artificial neural networks anns does much to overcome these difficulties we use a back propagation ann bp ann to model the interrelationships between spatial position six different well logs and permeability data from four wells in the venture gas field offshore eastern canada are organized into training and supervising data sets for bp ann modeling data from a fifth well in the same field are retained as an independent data set for testing when applied to this test data the trained bp ann produces permeability values that compare well with measured values in the cored intervals permeability profiles calculated with the trained bp ann exhibit numerous low permeability horizons that are correlatable between the wells at venture these horizons likely represent important intra reservoir barriers to fluid migration that are significant for future reservoir production plans at venture for discussion we also derive predictive equations using conventional statistical methods i e mlr and mnlr with the same data set used for bp ann modeling these examples highlight the efficacy of bp anns as a means of obtaining multivariate nonlinear models for difficult problems such as permeability estimation

two stage terrane assembly in western gondwana insights from structural geology and geophysical data of central borborema province ne brazil abstract combined geophysical and structural data from the transversal subprovince of the borborema province ne brazil highlight the internal structure of and interrelationships between the constituent terranes radiometric and magnetic maps show distinctive signatures for the archean paleoproterozoic alto moxoto and meso to neoproterozoic alto pajeu and pernambuco alagoas terranes mapped radiometric and first and second order magnetic lineaments associated with euler deconvolution enable correlation between geophysical data and major structures in addition to early related deformation of the alto moxoto terrane combined analysis of late transposition foliations lineations and kinematic criteria reveal a complex structural evolution marked by two distinct assembly stages the first phase is characterized by thrust tectonics with top to the south vergence resulting in the juxtaposition of the allochtonous alto pajeu terrane with the structurally underlying alto moxoto terrane the terrane boundary is delineated by the serra de jabitaca shear zone which is associated with low dipping collisional granitic sheets and ca 1 0 ga mafic ultramafic rocks interpreted as obtudcted ophiolite remnants later strike slip movements strongly folded and obliterated thrust related markers and the continental scale e w pernambuco lineament is interpreted as the result of lateral assembly between the composite alto pajeu alto moxoto terranes and the pernambuco alagoas terrane during the metamorphic peak of the brasiliano orogeny evolution of the borborema province reflects accretionary processes during the assembly of western gondwana

lithospheric gravitational potential energy and past orogenesis implications for conditions of initial basin and range and laramide deformation gravitational body forces i e buoyancy forces have come to be seen as critical to the evolution of orogens nevertheless constraining the role of body forces in specific geologic scenarios is made difficult by the substantial number of poorly constrained physical parameters needed to fully relate forces to deformation by separating the calculation of buoyancy forces from the calculation of the resulting deformation models based on relatively simple descriptions of the lithosphere can yield geologically useful constraints among these are the importance of paleoelevation in driving syn and postcontractional extension and in localizing contractional strain although such phenomena have been considered in more complex models of continental deformation the simpler analysis presented here clearly establishes first order limits on lithospheric structures and paleoelevations consistent with buoyancy driven deformation in the early cenozoic great basin of the western united states we show that the low elevations inferred in much of the geologic literature are inconsistent with a body force origin for observed extensional tectonism east of the colorado plateau localization of laramide deformation coincides with pre laramide subsidence of the western interior seaway this subsidence prestressed the lithosphere making the southern rocky mountains the weak link in responding to regional compressional stress

a fuzzy logic approach for the estimation of facies from wire line logs a method based on fuzzy logic inference can be used to identify lithological and depositional facies from wire line logs fuzzy logic is inherently well suited to characterizing vague and imperfectly defined knowledge a situation encountered in most geological data it can thus yield models that are simpler and more robust than those based on crisp logic the method is simple easy to comprehend and robust it also generates several confidence measures that can be used to assess the quality of the analysis several enhancements including static and dynamic constraints are discussed the technique is tested here by applying it to predict the depositional facies of a cored well in a marine carbonate environment and comparing the output with the facies derived from core analysis the two show considerable agreement which indicates that this method can be an effective means of predicting the facies of uncored wells from their logs the method has advantages when contrasted with other techniques that rely on multivariate statistics and neural networks compared to those techniques this method is simpler easier to retrain more reproducible noniterative and more computer efficient

pore facies of smackover carbonate reservoirs in southwest alabama abstract pore facies are rock units that are defined by certain proportions of pore types contain specific pore throat size distributions and exhibit certain consequent fluid flow properties pore facies may contain only one pore type but more typically are characterized by a combination of several pore types data used in this study consist of point counts of thin sections that are plotted on ternary diagrams whose apices are pore types ternary pore plots commercial porosity and permeability data from core analyses qualitative thin section descriptions and qualitative core descriptions two distinct but partially intergrading pore facies are recognized in the smackover of southwestern alabama these pore facies are defined based on the two most common pore types in the smackover particle moldic including secondary intraparticle and intercrystalline pores which together account for greater than 85 of total porosity in the smackover rocks assigned to the moldic pore facies exhibit similar depositional fabrics and experienced similar diagenetic processes for example this pore facies is most commonly composed of peloid and ooid grainstone some fabric selectively dolomitized modified by early cementation and particle dissolution by contrast in the intercrystalline pore facies destruction of primary fabrics by nonfabric selective dolomitization is almost the sole determinant of pore system characteristics the moldic pore facies dominates to the northwest choctaw western clarke washington counties the updip area and the intercrystalline pore facies is dominant to the south and east mobile monroe baldwin escambia and conecuh counties the downdip area pore facies distributions overlap in some areas e g western monroe county indicating that multiple pore facies occur in many smackover fields the two pore facies exhibit substantially different petrophysical characteristics the mean slope of regression lines of porosity on ln natural log permeability for the intercrystalline pore facies is 0 47 with a range of 0 19 to 0 90 the mean slope for the moldic pore facies is 0 22 with a range of 0 18 to 0 27 the higher slopes for the intercrystalline pore facies mean that permeability values may be more precisely predicted from porosity data in this pore facies the mean maximum permeability for the intercrystalline pore facies is 130 md the corresponding value is 91 md for the moldic pore facies high permeability fluid conduits are more common in the intercrystalline pore facies than in the moldic pore facies in addition all high permeability examples of the moldic pore facies contain substantial amounts of interparticle porosity and are found near the smackover subcrop the remainder of the moldic pore facies is characterized by permeability values substantially less than those of the intercrystalline pore facies porosity values are commonly higher in the moldic pore facies which has a range of mean porosity of 10 2 to 28 0 compared to 9 6 to 20 5 for the intercrystalline pore facies greater hydrocarbon volumes can be stored in reservoirs dominated by the moldic pore facies but connectivity is better in the intercrystalline pore facies mixtures between the two pore facies are moderately common mixed pore systems commonly resemble the intercrys talline pore facies in the slope of the regression line of porosity on ln permeability in strata with mixed pore systems isolated particle moldic pores are commonly connected by networks of intercrystalline pores which control transport of fluids out of particle moldic pores

cenozoic crustal extension in southeastern arizona and implications for models of core complex development abstract in conventional models of cordilleran style metamorphic core complex development initial extension occurs along a breakaway fault which subsequently is deformed into a synform and abandoned in response to isostatic rebound and new faults breaking forward in the dominant transport direction the catalina core complex and associated geology in southeastern arizona have been pointed to as a type example of this model from southwest to northeast the region is characterized by the nw se trending tucson basin the catalina core complex the san pedro trough and the galiuro mountains the catalina core complex is bounded by the top to the southwest catalina detachment fault along its southwestern flank and the low angle northeast dipping san pedro fault along its northeastern flank the galiuro mountains expose non mylonitic rocks and are separated from the san pedro trough to the southwest by a system of low to moderate angle southwest dipping normal faults this galiuro fault system is widely interpreted to be the breakaway zone for the catalina core complex it is inferred to be folded into a synform beneath the san pedro trough to resurface to the southwest as the san pedro fault and to have been abandoned during slip along the younger catalina detachment this study aimed to test this model through analysis of field relations and geochronological age constraints and reprocessing and interpretation of 2 d seismic reflection data from the catalina core complex and san pedro trough in contrast to predictions of the conventional breakaway zone model we raise the possibility of a moderate angle southwest dipping detachment fault beneath the san pedro trough that could extend to mid crustal depths beneath the eastern flank of the catalina mountains we present an alternative kinematic model in which extension was accommodated by a pair of top to the southwest normal fault systems the catalina and galiuro detachment faults with the only major difference between the two being the magnitude of displacement which was greater for the catalina detachment

estimation of reservoir properties from seismic data by smooth neural networks the performance of traditional back propagation networks for reservoir characterization in production settings has been inconsistent due to their nonmonotonous generalization which necessitates extensive tweaking of their parameters in order to achieve satisfactory results and avoid overfitting the data this makes the accuracy of these networks sensitive to the selection of the network parameters we present an approach to estimate the reservoir rock properties from seismic data through the use of regularized back propagation networks that have inherent smoothness characteristics this approach alleviates the nonmonotonous generalization problem associated with traditional networks and helps to avoid overfitting the data we apply the approach to a 3d seismic survey in the shedgum area of ghawar field saudi arabia to estimate the reservoir porosity distribution of the arab d zone and we contrast the accuracy of our approach with that of traditional back propagation networks through cross validation tests the results of these tests indicate that the accuracy of our approach remains consistent as the network parameters are varied whereas that of the traditional network deteriorates as soon as deviations from the optimal parameters occur the approach we present thus leads to more robust estimates of the reservoir properties and requires little or no tweaking of the network parameters to achieve optimal results

the role of mantle delamination in widespread late cretaceous extension and magmatism in the cordilleran orogen western united states extension during plate convergence and mountain building is widely recognized yet the causes of synconvergent extension remain controversial here we propose that delamination of lithospheric mantle aided by decoupling of the crust from the mantle via a reduction in the viscosity of the lower crust through heating incursion of fl uids and partial melting explains many enigmatic yet prevalent aspects of the metamorphic magmatic and kinematic history of the sevier laramide orogen of the western united states during the late cretaceous extension heating anatexis magmatism and perhaps rock uplift were widespread during a restricted time interval in the late cretaceous 75 67 ma along the axis of maximum crustal thickening within the mojave sector of the sevier orogen and to a lesser extent within the interior of the idaho utah wyoming sector to the north similar processes may have been active in the peninsular range sierran western mojave and salinian segments of the mesozoic cordilleran arc these processes are viewed as predictable consequences of the thermal rheological and dynamic state of the overlying crust following delamination of mantle lithosphere beneath isostatically compensated mountain belts the proposed delamination would have occurred immediately prior to eastward propagation of lowangle subduction of the farallon plate during the inception of the laramide orogeny following delamination extension and anatexis of the north american crust were aided locally by egress of slab derived fl uids from the low angle farallon slab we suggest that lithospheric delamination may have aided in the shallowing of the slab to achieve lowangle subduction geometry delamination has been proposed to be common in areas of thickened continental lithosphere in the terminal phase or late in orogenesis the late cretaceous delamination event proposed here for the sevier laramide orogen occurred during protracted plate convergence and was synchronous with and followed by continued shortening in the external part of the orogen

brasiliano pan african granitic magmatism in the pajeu paraiba belt northeast brazil an isotopic and geochronological approach the neoproterozoic brasiliano pan african orogeny in the borborema province bp ne brazil is characterized by intense granitic magmatism spatially associated with continental scale shear zones and metamorphism under high temperature conditions u pb zircon and rb sr whole rock data for 14 granite intrusions from the paje u parabelt have ages that suggest more than 100 ma of intrusive magmatism which can be divided in four events the oldest granites between 620 and 600 ma are medium to slightly high k calc alkaline i type granitoids intruded into metagreywackes and gneiss granites of 0 9 1 0 ga they are related to the peak of metamorphism and to the development of a flat lying foliation the youngest intrusions 540 520 ma have geochemical signature of a type post orogenic extension related granites and are associated with sub volcanic bimodal magmatism probably contemporaneous with deposition of small sedimentary basins in the north iara jaibaras graben and sa ori and central fatima bet ania and carnatectonic domains of the borborema province they reflect post tectonic relaxation of the brasiliano orogeny between these episodes two other intrusive events were identified 1 high k calc alkaline granitoids and shoshonitic granitoids associated with mafic syenites meladiorites and hornblende biotite diorites intruded between 590 and 581 ma associated with a transcurrent deformation event and 2 alkaline post collisional granitoids having u pb zircon ages of ca 570 ma marking the final stage of the brasiliano orogeny in the south domain of the borborema province migmatization took place between 610 and 600 ma although similar ages were not found in the granitoids of the central tectonic domain field evidence suggest that migmatization followed the intrusions of the oldest 620 600 ma granitoids 2004 elsevier b v all rights reserved

crustal evolution of the pernambuco alagoas complex borborema province ne brazil nd isotopic data from neoproterozoic granitoids the borborema province in northeast brazil forms the western part of a major 600 ma brasiliano pan african mobile belt that extends from brazil through central africa in a pre drift reconstruction of gondwanaland the pernambuco alagoas peal complex is a large area within the borborema province and consists of high grade migmatitic gneisses and granitic batholiths although the peal complex has previously been called a massif or terrane in reality it comprises many different types of protoliths or plutons the protoliths for many of the migmatitic gneisses are difficult to decipher due to the varied deformation and metamorphism during the cariris velhos and brasiliano orogenies nd isotopic data discriminate two major crustal domains in the peal complex the garanhuns and the agua branca domains rocks of the garanhuns domain have nd tdm in the range of 1 8 to 2 4 ga indicating that most of it is underlain by paleoproterozoic crust and does not include significant mesoproterozoic or neoproterozoic crustal additions the marimbondo correntes batholith is inside the garanhuns domain but includes younger tdm ages similar to those found in the agua branca domain this batholith includes contributions from younger sources and may intrude a block of younger allocthonous crust thrust over the older crust of the garanhuns domain rocks of the agua branca domain show tdm within the range of 0 90 to 2 10 ga with most nd model ages between 1 5 and 1 0 ga the pre brasiliano crust in this domain thus includes substantial amounts of mesoproterozoic to neoproterozoic additions the presence of some older model ages suggests that the aguas belas domain may have some vertical crustal zonation with paleoproterozoic and neoproterozoic crustal segments tectonically interleaved during successive accretional or collisional episodes including the ultimate brasiliano collision at 600 ma the mesoproterozoic nd model ages therefore represent mixing of different crustal and mantle sources rather than a discrete episode of mesoproterozoic crustal formation various metaluminous or peraluminous granitoids of brasiliano age from the buique paulo afonso aguas belas caninde and marimbondo correntes batholiths show tdm ranging from 0 90 ga to 1 10 ga suggesting that they either were wholly derived from juvenile material of the 1 0 ga cariris velhos orogeny or contain substantial contributions of juvenile material from the 0 6 ga brasiliano cycle some high k to shoshonitic granitoids from the aguas belas domain show mesoproterozoic 1 4 ga tdm model ages the model ages recorded in these plutons could suggest either that the magma was derived from enriched lithospheric mantle associated with the cariris velhos orogeny or that it was a mixture between enriched lower crust of transamazonian age and juvenile material from the cariris velhos or brasiliano orogenies

joint inversion of geochemical data and geophysical logs for lithology identification in ccsd main hole the chinese continental scientific drilling ccsd main hole is located in the sulu ultrahigh pressure metamorphic uhpm belt providing significant opportunities for studying the metamorphic strata structure kinetics process and tectonic evolution lithology identification is the primary and crucial stage for above geoscientific researches to release the burden of log analyst and improve the efficiency of lithology interpretation many algorithms have been developed to automate the process of lithology prediction while traditional statistical techniques such as discriminant analysis and k nearest neighbors classifier are incompetent in extracting nonlinear features of metamorphic rocks from complex geophysical log data artificial intelligence algorithms are capable of solving nonlinear problems but most of the algorithms suffer from tuning parameters to be global optimum to establish model rather than local optimum and also encounter challenges in making the balance between training accuracy and generalization ability optimization methods have been applied extensively in the inversion of reservoir parameters of sedimentary formations using well logs however it is difficult to obtain accurate solution from the logging response equations of optimization method because of the strong overlapping of nonstationary log signals when applied in metamorphic formations as oxide contents of each kinds of metamorphic rocks are relatively less overlapping this study explores an approach set in a metamorphic formation model and using the broyden fletcher goldfarb shanno bfgs optimization algorithm to identify lithology from oxide data we first incorporate 11 geophysical logs and lab collected geochemical data of 47 core samples to construct oxide profile of ccsd main hole by using backwards stepwise multiple regression method which eliminates irrelevant input logs step by step for higher statistical significance and accuracy then we establish oxide response equations in accordance with the metamorphic formation model and employ bfgs algorithm to minimize the objective function finally we identify lithology according to the composition content which accounts for the largest proportion the results show that lithology identified by the method of this paper is consistent with core description moreover this method demonstrates the benefits of using oxide content as an adhesive to connect logging data with lithology can make the metamorphic formation model more understandable and accurate and avoid selecting complex formation model and building nonlinear logging response equations

studies of the relationship between petrography and grindability for kentucky coals using artificial neural network abstract although there are several formulas available for predicting hardgrove grindability of coal most of them are linear and do not simultaneously take into consideration most of the relevant factors the artificial neural network is an information processing tool that is capable of establishing an input output relationship by extracting controlling features from a database presented to the network in this paper a neural network approach was proposed to deal with the grindability behavior of coal 195 sets of experimental data were evaluated with artificial neural network to predict the hgi of kentucky coals two different kinds of the trained artificial neural network were undertaken using the database created in this study it is shown from the examples that the artificial neural network adequately recognized the characteristics of the coal experimental data sets retaining a generality for further prediction it is believed that an artificial neural network based prediction procedure shown in this paper can be further employed for hardgrove grindability index prediction the influence of liptinite vitrinite ash and sulfur content on hgi was studied by a parametric study

an improved technique in porosity prediction a neural network approach genetic reservoir characterization is important in developing for a given petroleum reservoir an improved understanding of the total amount and fluid flow properties of hydrocarbon reserves application of genetic concepts involves the classification of well log data into different lithofacies groups followed by a facies by facies description of rock properties such as porosity and permeability this work contrasts the genetic and nongenetic approaches in predicting porosity values of an oil well using backpropagation neural network methods the performance of both methods are critically evaluated a systematic technique to optimise the network configuration using weight visualization curves is proposed thereby enabling the amount of training time to be significantly reduced in the example problem the genetic approach provides superior porosity estimates to that based on a nongenetic approach

inversion of nuclear well logging data using neural networks this work looks at the application of neural networks in geophysical well logging problems and specifically their utilization for inversion of nuclear downhole data simulated neutron and ray fluxes at a given detector location within a neutron logging tool were inverted to obtain formation properties such as porosity salinity and oil water saturation to achieve this the forward particle radiation transport problem was first solved for different energy groups 47 neutron groups and 20 ray groups using the multigroup code event a neural network for each of the neutron and ray energy groups was trained to re produce the detector fluxes using the forward modelling results from 504 scenarios the networks were subsequently tested on unseen data sets and the unseen input parameters formation properties were then predicted using a global search procedure the results obtained are very encouraging with formation properties being predicted to within 10 average relative error the examples presented show that neural networks can be applied successfully to nuclear well logging problems this enables the implementation of a fast inversion procedure yielding quick and reliable values for unknown subsurface properties such as porosity salinity and oil saturation

sediment classification using neural networks an example from the site u1344a of iodp expedition 323 in the bering sea abstract a novel approach based on the concept of bayesian neural network bnn has been implemented for classifying sediment boundaries using downhole log data obtained during integrated ocean drilling program iodp expedition 323 in the bering sea slope region the bayesian framework in conjunction with markov chain monte carlo mcmc hybrid monte carlo hmc learning paradigm has been applied to constrain the lithology boundaries using density density porosity gamma ray sonic p wave velocity and electrical resistivity at the hole u1344a we have demonstrated the effectiveness of our supervised classification methodology by comparing our findings with a conventional neural network and a bayesian neural network optimized by scaled conjugate gradient method scg and tested the robustness of the algorithm in the presence of red noise in the data the bayesian results based on the hmc algorithm bnn hmc resolve detailed finer structures at certain depths in addition to main lithology such as silty clay diatom clayey silt and sandy silt our method also recovers the lithology information from a depth ranging between 615 and 655 m wireline log matched depth below sea floor of no core recovery zone our analyses demonstrate that the bnn based approach renders robust means for the classification of complex lithology successions at the hole u1344a which could be very useful for other studies and understanding the oceanic crustal inhomogeneity and structural discontinuities

reconstruction of mid cenozoic extension in the rincon mountains area southeastern arizona usa and geodynamic implications nsf ear 1649254 u s geological survey national cooperative geologic mapping program under statemap grant 03hqag0114 statemap grant 06hqag0051 g09ac00199

oblique lineations in orthogneisses and supracrustal rocks vertical partitioning of strain in a hot crust eastern borborema province ne brazil detailed structural work conducted at the eastern area of the neoproterozoic brasiliano zpan african borborema province northeastern brazil has shown two orientations of stretching lineations with ese trend in supracrustal rocks and ne trend in underlying orthogneisses in the metasedimentary sequence numerous kinematic indicators showing a top to the northwest sense of shear denote a welldeveloped non coaxial deformation in the orthogneisses lineations formed dominantly during coaxial deformation although a component of ne directed shear is locally observed the two lineations were produced under similar high temperature metamorphic conditions and are interpreted as the result of a protracted nw se contractional strain regime where i subhorizontal non coaxial shear with superimposed flattening led to an initial phase of nw directed thrusting ii flattening strains mainly accumulated in the orthogneisses with progressive deformation leading to a lineation oblique to the transport direction iii the subhorizontal fabric in basement and cover rocks was refolded by overturned folds and then iv cross cut by conjugate ene striking dextral and nne striking sinistral shear zones contemporaneous with ne trending upright folds it is proposed that vertical partitioning of strain between basement and cover may explain the presence of oblique lineations in this orogenic belt that did not go through a final stage of extensional collapse q 2005 elsevier ltd all rights reserved

time frame of 753 680 ma juvenile accretion during the sao gabriel orogeny southern brazilian shield abstract the time frame of the three main geological events in the neoproterozoic cambai complex juvenile sao gabriel belt in the southern brazilian shield is established by integrating field mapping back scattered electron imaging and sensitive high resolution ion microprobe shrimp ii u pb dating of 96 zircon crystals from nine granitic and metasedimentary rock samples the three events are 1 voluminous flat lying paragneisses cambaizinho complex and orthogneisses vila nova gneisses between 735 and 718 ma 2 tonalite trondhjemite association lagoa da meia lua suite between 710 and 690 ma and 3 late granodiorite intrusions sanga do jobim suite at 680 ma an additional older volcanic event campestre formation was dated at 753 ma these results are most significant for the reconstruction of west gondwana

using constrained inversion of gravity and magnetic field to produce a 3d litho prediction model geologically constrained inversion of gravity and magnetic field data of the victoria property located in sudbury canada was undertaken in order to update the present three dimensional geological model the initial and reference model was constructed based on geological information from over 950 drillholes to constrain the inversion in addition downhole density and magnetic susceptibility measured in six holes were statistically analysed to derive lower and upper bounds on the physical properties attributed to the lithological units in the reference model constrained inversion of the ground gravity and the airborne magnetic data collected at the victoria property were performed using grav3d and mag3d respectively a neural network was trained to predict lithological units from the physical properties measured in six holes then the trained network was applied on the three dimensional distribution of physical properties derived from the inversion models to produce a three dimensional litho prediction model some of the features evident in the lithological model are remnants of the constraints where the data did not demand a significant change in the model from the initial constraining model e g the thin pair of diabase dykes however some important changes away from the initial model are evident for example a larger body was predicted for quartz diorite which may be related to the prospective offset dykes a new zone was predicted as sulfide which may represent potential mineralisation and a geophysical subcategory of metabasalt was identified with high magnetic susceptibility and high density the litho prediction model agrees with the geological expectation for the three dimensional structure at victoria and is consistent with the geophysical data which results in a more holistic understanding of the subsurface lithology

determination of the volcanostratigraphy of oceanic crust formed at superfast spreading ridge electrofacies analyses of odp iodp hole 1256d 1 the objective of this study is to construct a representative volcanostratigraphy of ocean drilling program hole 1256d the first complete penetration of intact upper oceanic crust formed at a superfast spreading rate an accurate knowledge of the volcanostratigraphy is vital to understand processes of crustal construction and submarine magmatism and to estimate chemical exchange with seawater but this is rarely achieved due to very low recovery rates in most basement holes we used two approaches to determine the rock types that form the wall rocks in the basement sections of hole 1256d 1 user guided interpretations of electrofacies acquired by imaging tools combined with other wireline tools and 2 the use of an artificial neutral network to objectively classify the responses of all available logging information great availability of formation microscanner fms images provided superior coverage of the borehole wall compared to previous attempts at core log integration this has resulted in more confident and detailed lithologic classifications such as with the distinction between pillows and different styles of breciation ten lithology types are suggested for a volcanostratigraphy model massive flows ponded lava fractured massive flows fragmented flows thin flows or thick pillows pillows breccias dikes in dike complex isolated dikes and gabbros three major lithology types in the extrusive section are massive flows both massive and fragmented massive flow 22 fragmented flows 32 and breccias 19 pillow lavas make up only 1 9 of the volcanic section and are confined to a 100 m interval below the extrusive section subvertical contacts interpreted to be dike margins are typically observed every 1 to 2 m with brecciated zones along the contacts the dikes dip steeply to the northeast indicating slight rotation away from the ridge axis we used an artificial neural network ann approach to determine a quantitative lithostratigraphy the ann is most strongly influenced by porosity and alteration degrees and the resulting stratigraphy most closely resembles the above classifications when clustered by fms texture as opposed to lithologic interpretation the ann thus provides a porosity based stratigraphy of the basement rather than the traditional lithology based stratigraphy

estimation of lithologies and depositional facies from wire line logs we approach the problem of identifying facies from well logs through the use of neural networks that perform vector quantization of input data by competitive learning the method can be used in either an unsupervised or supervised manner unsupervised analysis is used to segregate a well into distinct facies classes based on the log behavior supervised analysis is used to identify the facies types present in a certain well by making use of the facies identified from cores in a nearby well the method is suitable for analyzing lithologies and depositional facies of horizontal wells which are almost never cored especially if core data is available for nearby vertical wells both modes are implemented and used for the automatic facies analysis of horizontal wells in saudi arabia in addition to the identification of facies the method is also able to calculate for each analysis confidence measures that are indicative of how well the analysis procedure can identify those facies given uncertainties in the data moreover we can apply constraints derived from human experience and geologic principles to guide the inference process

neural network modelling and classification of lithofacies using well log data a case study from ktb borehole site summary a novel approach based on the concept of super self adapting back propagation ssabp neural network has been developed for classifying lithofacies boundaries from well log data the ssabp learning paradigm has been applied to constrain the lithofacies boundaries by parameterzing three sets of well log data that is density neutron porosity and gamma ray obtained from the german continental deep drilling project ktb a multilayer perceptron mlp neural networks model was generated in a supervised feed forward mode for training the published core sample data a total of 351 pairs of input and output examples were used for self adaptive network learning and weight and bias values were appropriately updated during each epoch according to the gradient descent momentum scheme the actual data analysis suggests that the ssabp network is able to emulate the pattern of all three sets of ktb data and identify lithofacies boundaries correctly the comparisons of the maximum likelihood geological sections with the available geological information and the existing geophysical findings over the ktb area suggest that in addition to the known main lithofacies boundaries units namely paragneisses metabasites and heterogeneous series containing partly calc silicate bearing paragneisses metabasites and alternations of former volcano sedimentary sequences the ssabp neural network technique resolves more detailed finer structures embedded in bigger units at certain depths over the ktb region which seems to be of some geological significance the efficacy of the method and stability of results was also tested in presence of different levels of coloured noise the test results suggest that the designed network topology is considerably unwavering for up to 20 per cent correlated noise however adding more noise 50 per cent or more degrades the results our analyses demonstrate that the ssabp based approach renders a robust means for the classification of complex lithofacies successions from the ktb borehole log data and thus may provide useful guide information for understanding the crustal inhomogeneity and structural discontinuity in many other regions

reinterpretation of lime peak thrust as a low angle normal fault implications for the tectonics of southeastern arizona normal separation of offset stratigraphic units across the lime peak fault mapped by cooper and silver as a thrust in the dragoon quadrangle of southern arizona indicates that the fault is actually a low angle normal fault reflecting crustal distension rather than crustal contraction the fault has been identified by drewes as one of the few exposed segments of the supposed hidalgo thrust of inferred subregional extent recognition that the structure is a low angle normal fault of probable mid tertiary age thus casts doubt on the concept that coherent subhorizontal thrust sheets of laramide age actually exist in southern arizona

inferring the lithology of borehole rocks by applying neural network classifiers to downhole logs an example from the ocean drilling program in boreholes with partial or no core recovery interpretations of lithology in the remainder of the hole are routinely attempted using data from downhole geophysical sensors we present a practical neural net based technique that greatly enhances lithological interpretation in holes with partial core recovery by using downhole data to train classifiers to give a global classification scheme for those parts of the borehole for which no core was retrieved we describe the system and its underlying methods of data exploration selection and classification and present a typical example of the system in use although the technique is equally applicable to oil industry boreholes we apply it here to an ocean drilling program odp borehole hole 792e izu bonin forearc a mixture of volcaniclastic sandstones conglomerates and claystones the quantitative benefits of quality control measures and different subsampling strategies are shown direct comparisons between a number of discriminant analysis methods and the use of neural networks with back propagation of error are presented the neural networks perform better than the discriminant analysis techniques both in terms of performance rates with test data sets 2 3 per cent better and in qualitative correlation with non depth matched core we illustrate with the hole 792e data how vital it is to have a system that permits the number and membership of training classes to be changed as analysis proceeds the initial classification for hole 792e evolved from a five class to a three class and then to a four class scheme with resultant classification performance rates for the back propagation neural network method of 83 84 and 93 per cent respectively

trans alkaline magmatism in the serrinha pedro velho complex borborema province ne brazil and its correlations with the magmatism in eastern nigeria abstract the sol nea complex 572 8 ma comprises various intrusions that total 200 km 2 it cuts palaeoproterozoic migmatized orthogneisses of the serrinha pedro velho complex which is part of the sao jose do campestre massif north tectonic domain of the borborema province ne brazil it is a post collisional intrusion constituted of coarse grained biotite amphibole monzogranites fine grained leucogranites and diorites major trace and rare earth elements data used to constrain the origin and nature of these rocks indicate that the monzogranites display chemical features of weakly peraluminous ferro potassic trans alkaline granitoids similar to coeval occurrences described in eastern nigerian sm nd data together with the whole rock geochemical data suggest that i the monzogranites were generated by partial melting of tonalitic gneiss from the lower crust leaving behind a granulitic residue ii the diorites originated by partial melting of an enriched lithospheric mantle iii the evolution of the sol nea complex involved magma mixing between the monzogranites and diorites k feldspar and amphibole fractionation appear to have occurred during the evolution of the monzogranites leucogranites constituting an elliptical shaped intrusion 80 km 2 the dona ines pluton are intruded to the north of the sol nea complex they also occur as small intrusions cross cutting the border of the sol nea complex geochemical and isotopic data suggest that the leucogranites were generated by melting of crustal palaeoproterozoic rocks rb sr data gave an age of 544 16 ma trans alkaline magmatism is associated with ductile brittle deformation in the serrinha pedro velho complex of the sao jose do campestre massif this event follows the peak of an extensional related high temperature metamorphism upper amphibolite to granulite facies with estimated age of 578 to 574 ma if a pre gondwana reconstruction is considered this event is seen to extend to the african side of gondwana in eastern nigeria

regional variation in microscopic and megascopic reservoir heterogeneity in the smackover formation southwest alabama abstract quantitative rank measures of microscopic and megascopic reservoir heterogeneity are used to characterize the distribution of reservoir heterogeneity in smackover hydrocarbon fields and wildcat wells in southwest alabama microscopic reservoir heterogeneity h is 0 25 meanlnk 1 5lnk 3 megascopic heterogeneity mh is of reservoir intervals of high k reservoir intervals of of reservoir intervals where reservoir rock is defined as exhibiting permeability values 0 1 md and high permeability reservoir rock exhibits permeability values 1 0 md both mh and h are determined from core data the dykstra parsons coefficient dp is a measure of microscopic heterogeneity that is partially independent of h r2 0 428 all three of these parameters are primarily measures of vertical heterogeneity although averaging of wells within a field incorporates lateral heterogeneity in h and dp h and mh are distributed in contrasting but related patterns h generally decreases from northwest to southeast with the highest values found in the vicinity of the choctaw ridge complex north of the mississippi interior salt basin misb moderately high values typify the manila embayment and the conecuh ridge complex to the south whereas lower values are found in the misb on the north flank of the wiggins arch and in the conecuh embayment h values are high in the moldic pore facies and low in the intercrystalline pore facies the distribution of mh is roughly opposite to that of h mh values are high on the north flank of the wiggins arch on the conecuh ridge complex and in the conecuh embayment mh values are low near the choctaw ridge complex the conecuh ridge is unique because it is characterized by high values of both h and mh also the low relief north south trending salt cored anticline in western washington county is characterized by relatively high values of mh reservoirs belonging to the moldic pore facies tend to be homogeneous with respect to mh whereas reservoirs assigned to the intercrystalline pore facies are characterized by relatively high values of mh mh and h vary congruently with pore system characteristics controlled by depositional patterns dissolution and dolomitization and regional structural and paleogeographic trends this suggests that reservoir heterogeneity characteristics are controlled by structural and paleogeographic setting by depositional fabric and by diagenesis however because contours of h and mh are approximately normal to structure contours but parallel to smackover thickness contours it appears that depositional setting or paleogeography influenced reservoir heterogeneity more than did structural evolution the distribution of dp values is not related to pore facies distribution thus we conclude that dp is less useful for regional heterogeneity studies than is mh or h

reservoir characterization of the giant hugoton gas field kansas hugoton field in kansas is the largest gas field in north america with cumulative production over 23 tcf infill and deep drilling activity over the last 10 yr have made it possible to build an extensive database of modern wireline log and core data such data formed the basis for a wide ranging reservoir characterization done to obtain critical information for optimum reservoir management of the field reservoir heterogeneity and formation evaluation problems made it difficult to characterize fluid distribution estimate gas in place and determine permeability from wireline log data but few of the problems in this reservoir characterization study are unique to hugoton the techniques described here may be applicable to other reservoirs technologies employed to solve the formation evaluation and lateral variability problems included artificial neural networks resistivity modeling geostatistics and three dimensional grid manipulation copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received april 29 1996 revised manuscript received october 21 1996 final acceptance june 10 1997 2amoco production co 1670 broadway denver colorado 80202 3amoco production co 501 westlake park blvd houston texas 77253 current address altura energy ltd p o box 4294 houston texas 77210 4amoco production co 501 westlake park blvd houston texas 77253 5amoco production co 4502 e 41st st tulsa oklahoma 74102 6amoco production co 501 westlake park blvd houston texas 77253 current address pgs reservoir 10550 richmond ave houston texas 77042 7amoco production co 1670 broadway denver colorado 80202 current address rocky mountain petrophysics p o box 470337 aurora colorado 80047 we thank the hugoton jomt of amoco production company for permission to publish this study we are grateful to mobil exploration and production u s especially w h jamieson jr for permission to use and publish additional core and log data we also thank david reese from amoco denver for his work on equations relating water saturation to permeability porosity and height in the gas column 3 d seismic interpretation by mike bahorich formerly with amoco currently with apache is appreciated thanks go to amoco operations and reservoir engineers too numerous to mention for teamwork and testing of the ideas herein ann pettit and stefan nowina provided invaluable technical support this paper benefited from constructive reviews by robert raynolds joyce budai n c wardlaw salman bloch and virginia riggert tcf trillion cubic feet gcf billion cubic feet