Academic literature on the topic 'Bedded clastic facies'

Ngrayong sandstone composes a siliciclastic reservoir that produces oil for more than a century in North East Java Basin of Indonesia. Clean sand facies makes the best reservoir in western part of the basin, onshore East Java Island. Meanwhile, sand quality decreases eastward to Madura Island. In Madura, rock gradually changes to be more calcareous and shaly, due to the change of depositional environment. In offshore of Madura, the depositional environment is still questionable. This study is aimed to reveal differences between onshore and offshore facies of Ngrayong sandstone in Madura as their distribution is not well known and oil potential of Madura Strait is not well identified. Study methods consisted of geological field work, well correlation, and petrophysical analysis from several well data. The results show that Ngrayong sandstone was deposited during Middle Miocene, composed by interbedding of thickly bedded sandstone and alternating thinly bedded sandstoneshale. The succession is commonly intercalated by mudstone and thinly bedded limestone. At Madura Island, Ngrayong sandstone overlies the Early-Middle Miocene Tawun Formation, which both represent the Megasequence (MS) 3 interval. Due to regional subsidence and transgression during Late Miocene, Ngrayong sandstone and other equivalent rocks were overlain by monotonous mudstone and calcareous sandstone of Wonocolo Formation. The Ngrayong sandstone is evenly distributed in whole surface area of Madura Island and it spreads further 25-50 Km to the south and 100-125 Km to eastern part of offshore Madura Strait. Sandstone distribution is roughly depleted from the gross thickness hundreds of meters in northern part to only few centimeters in southeast part of study area. The facies changes to be more calcareous to the east, while the southward facies is shaly due to a deeper depositional environment. Despite of facies changing into shales or carbonate facies, Ngrayong sandstone potential in offshore Madura Strait needs to be considered as upside potential due to its distribution is wider than initial estimation, and its petrology and petrophysic data support it as a clastic reservoir.

In Zhengxiangbaiqi, the Sanmianjing Formation of Middle Permian exposes most completely. The Lithology is mainly clastic rocks, in the lower part of the section, there are 60m gray middle-thick-bedded limestone. Based on detailed measurement of the Elitu Pasture Ⅱ, indoor research, identifications with microscope, paleontology and sequence stratigraphy studies, explored sedimtentary facies and sedimentary paleoenvironment of the Sanmianjing formation. The lower part and the upper part of Sanmianjing formation might be deposited in a shore setting with a high energy, and the middle part might be formed in an epicontinental sea with a relative low-energy. Fossils and sedimentary facies further enrich the biological face of the section, and prove new informations for contrasting between different stratigraphic and plaeoenvironment. This study proved principal geological data for further research on palaeogeography, oil and gas exploration.

AbstractThe Lower Cambrian Fucoid Beds of northwest Scotland are a 20 m thick mixed clastic-carbonate sequence of thinly bedded storm beds deposited on the western margin of the Iapetus Ocean. Proximal facies display plane beds, current ripple laminations and wave ripple laminations and were deposited under the influence of combined steady andoscillatory currents. The steady component of flow appears to have expanded in an offshore direction and weakened during the final stages of storm deposition with respect to the oscillatory component, producing less asymmetrical ripples with less evidence of a preferred migration direction. Distal facies are represented by thin ‘graded rhythmites’. The palaeocurrent data suggest a wide spread of sediment transport directions, but with a north to northeasterly mode which may reflect a geostrophic component of flow. Following storms these beds were burrowed and echinoderms colonized the sea floor, although the limited extent of these processes and the presence of abundant collophane suggests that the fairweather Fucoid Beds shelf was generally quiescent and possibly dysaerobic.

This study reports the first accurate record of the Messinian Resedimented Gypsum in the forearc and back-arc basins connected to the Calabrian-Peloritan orogen. A multidisciplinary approach has been used to investigate a gypsum deposit located in the Benestare’s area (Calabria, Southern Italy). Such deposit is made of bedded gypsrudites displaying clastic selenite with chaotical textures. On the top, the gypsrudites are interspersed with gypsum lenses belonging to the branching-like facies. Despite these two facies seem different macroscopically, they show petrographic features, fluid inclusions, organic matter and Strontium isotopic values very similar to each other. On the other hand, both facies show fractured and folded crystals. Crystals are only locally corroded and preserve primary structure relict as well as allochthonous (organic debris) and autochthonous putative microbial remains. All crystals are rich in fluid inclusions but these are visibly affected by stretching and leaking (re-equilibration processes) suggesting a moderate plastic deformation during re-sedimentation and subsequent burial. Minimal transport of the deposit is testified by subangular shapes of the gypsum crystals. The gypsrudite and branching-like facies reveal an 87Sr/86Sr average value of 0.709045 and 0.709082, respectively. These values suggest a strong connection with the global Ocean and reduced freshwater input. The Benestare’s deposit originated from the partial to complete dismantling of selenite crystals related to the first stage (5.97–5.60 Ma) of the Messinian Salinity Crisis through gravitational collapse due to local controlling factors.

ABSTRACTGlaciotectonic features studied in the siliciclastic deposits of Cabeças Formation, Upper Devonian, represent the first evidence of Famennian glaciation in Southeastern Parnaíba Basin, Brazil. Outcrop-based stratigraphic and facies analyses combined with geometric-structural studies of these deposits allowed defining three facies association (FA). They represent the advance-retreat cycle of a glacier. There are: delta front facies association (FA1) composed of massive mudstone, sigmoidal, medium-grained sandstone with cross-bedding and massive conglomerate organized in coarsening- and thickening-upward cycles; subglacial facies association (FA2) with massive, pebbly diamictite (sandstone, mudstone and volcanic pebbles) and deformational features, such as intraformational breccia, clastic dikes and sills of diamictite, folds, thrust and normal faults, sandstone pods and detachment surface; and melt-out delta front facies associations (FA3), which include massive or bedded (sigmoidal cross-bedding or parallel bedding) sandstones. Three depositional phases can be indicated to Cabeças Formation: installation of a delta system (FA1) supplied by uplifted areas in the Southeastern border of the basin; coastal glacier advance causing tangential substrate shearing and erosion (FA1) in the subglacial zone (FA2), thus developing detachment surface, disruption and rotation of sand beds or pods immersed in a diamicton; and retreat of glaciers accompanied by relative sea level-rise, installation of a high-energy melt-out delta (FA3) and unloading due to ice retreat that generates normal faults, mass landslide, folding and injection dykes and sills. The continuous sea-level rise led to the deposition of fine-grained strata of Longá Formation in the offshore/shoreface transition in the Early Carboniferous.

The Miocene rocks of the Marádah Formation have been stratigraphically investigated from four stratigraphical sections around the Marádah Oasis in the Central Sirt Basin of Libya. The field investigations led to the identification of two members, the lower Qarat Jahannam Member and the upper Ar Ráhlah Member. Fourteen sedimentary facies at the outcrop-scale representing a gradual development of sedimentation from a continental clastic witness in the southwestern outcrops to transitional estuarine, lagoonal, and beaches to the proximal offshore in the northern outcrops, were recognized. The results indicates that the accumulation of the Marádah Formation is transgressive in nature and corresponding to two phases of deposition which have been mentioned in the earlier studies. The first phase is continental-dominated facies in which cross-bedded sandstones and calcareous sands comprise most of the depositional sequence of the lower Qarat Jahannam Member at the southwestern outcrops. This phase, however, is characterized by extremely bioturbated laminated-shale conquered by Skolithos ichnofacies in the lower part of the upper Ar Ráhlah Member at the northern outcrops. This phase is providing further evidence that the contact between the two members is diachronous everywhere in the study area. The clastic-phase has thought to be deposited in the Lower Miocene (Aquitanian-Burdigalian) since the lower Qarat Jahannam Member rests on an erosional surface of submarine origin in the southwestern outcrops above a 0.5 m. thick of a nummulitic unit of the Oligocene Bu Hashish Formation. The second phase is marine-dominated facies in which a bioclastic limestone unit rich in thick and disarticulated oysters, including Crassostrea gryphoides (Schlottheim), characterizes the sediments of the Ar Ráhlah Member at the southwestern outcrops. This phase also includes the upper part of the latter member at the northern outcrops in which a detrital limestone unit rich in turritelline gastropods is overlying by thick-bedded calcarenites rich in disarticulated oysters, gastropods, irregular echinoids (notably, Clypeaster and Echinolampas), bryozoans, and celestite corals. The upper part of the Ar Ráhlah Member at the northern outcrops, nevertheless, is terminated by a quite hard dolomitic limestone and by a pretty soft dolomitic marly limestone. Both lithologies, however, are combined with medium-sized oysters, including Ostrea digitalina Fuchs, and pectinid bivalves. The second phase, however, is interpreted to be deposited in the Middle Miocene (Langhian and Serravallian) based on the total-stratigraphic range of the larger benthic foraminifera Borelis melo melo (Fichtel & Moll), which recovered from the studied washed residues, and the associated microfacies.

A three‐dimensional (3‐D) 100 MHz ground‐penetrating radar (GPR) data volume is the basis of in‐situ characterization of a fluvial reservoir analog in the Ferron Sandstone of east‐central Utah. We use the GPR reflection times to image the bounding surfaces via 3‐D velocity estimation and depth migration, and we use the 3‐D amplitude distribution to generate a geostatistical model of the dimensions, orientations, and geometries of the internal structures from the surface down to ∼12 m depth. Each sedimentological element is assigned a realistic fluid permeability distribution by kriging with the 3‐D correlation structures derived from the GPR data and which are constrained by the permeabilities measured in cores and in plugs extracted from the adjacent cliff face. The 3‐D GPR image shows that GPR facies changes can be interpreted to locate sedimentological bounding surfaces, even when the surfaces do not correspond to strong GPR reflections. The site contains two main sedimentary regimes. The upper ∼5 m contain trough cross‐bedded sandstone with average permeability of ∼40 md and maximum correlation lengths [Formula: see text]. The lower ∼7 m contain scour and fill fluvial deposits with average permeability varying from ∼30 md to ∼15 md as clay content increases, and maximum correlation lengths [Formula: see text]. These representations are suitable for input to fluid flow modeling.

The Lower to Middle Jurassic Hazelton Group represents the final stage of magmatic arc activity in the intraoceanic Stikine terrane, which was followed by accretion within the Cordilleran terrane collage. The Hazelton Group is exposed in the following areas: (i) on the periphery of the Bowser Basin, where arc and back-arc strata are overlain by mainly sedimentary strata of the upper Hazelton Group and then by the clastic basin fill of the Bowser Lake Group; and (ii) within a 300 km long rift system, the Eskay rift, west of the Bowser basin, where a predominantly bimodal volcanic succession contains significant mineral deposits. Examination of representative stratigraphic sections throughout the regional extent of the upper Hazelton Group has suggested significant revisions and clarification of its stratigraphy and include the following: (i) informal division of the Hazelton Group into upper and lower parts and recognition of a diachronous unconformity or unconformities at the boundary between them; (ii) establishment of a type section for the sandstone-dominated Smithers Formation; (iii) establishment of separate Quock and revised Spatsizi formations in the north and extension of the Quock Formation to include all lithostratigraphically equivalent units of blocky, thinly bedded siliceous mudstone and tuff around the periphery of the Bowser basin; and (iv) introduction of the Iskut River Formation for rift-related and volcanic facies in the Eskay rift area. Two independent rifting events occurred during deposition of the Hazelton Group: a Late Sinemurian to Early Pliensbachian phase in the northwest-trending Hazelton trough and a more restricted Aalenian to Bajocian extensional event in the Eskay rift.

The Archean La Bruère Formation, which forms part of the Timiskaming Group of the Abitibi greenstone belt of Rouyn–Noranda, comprises a conglomerate–sandstone assemblage at least 360 m thick. The upward variations in grain size and con glomerate/sandstone ratio permit subdivision of the formation into three conglomeratic and two sandy members. Member 1 is composed essentially of conglomerate; members 2 and 4 consist of stacked composite beds of conglomerate and sandstone; member 3 is a sequence of cross-bedded sandstone. The formation is capped by a turbidite sequence (member 5).Three bed types (facies) were identified in the La Bruère Formation: two are restricted to the conglomerate; the third, to the upper member. Facies A, is characterized by matrix-supported, poorly sorted gravel beds, massive or reversely graded. In facies B, generally restricted to member 4, the conglomerate is commonly clast supported and transitional with the overlying sandstone bed, forming couplets that show primary structure sequences consisting, from base to top, of (i) normally graded gravel, (ii) plane-bedded sandstone, and (iii) cross-bedded sandstone. These sequences are similar to, although coarser and thicker than, some sequences found in turbidites. Facies C, observed only in member 5, is characterized by classic turbidites.In the conglomerate members of the formation, beds of facies A show no correlation between bed thickness and maximum grain size, whereas those of facies B show a fairly good correlation. The absence of correlation could result from accumulation in a channel rather than on an alluvial fan, but it may also be due to the nature of the flows responsible for the deposit and (or) the grain availability at the source.The characteristics of the three facies suggest that the La Bruère gravel accumulated from laminar and turbulent mass flows in a subaqueous channel, below storm wavebase and therefore in a relatively deep basin.

The Olympic Dam Cu-U-Au-Ag deposit in the Olympic Cu-Au Province (Gawler Craton, South Australia) is unique in the iron oxide-copper-gold (IOCG) deposit class for its polymetallic tenor and size; it is one of the largest economic accumulations of metals in the world. The deposit is hosted within the Olympic Dam Breccia Complex (ODBC) within the Roxby Downs Granite. The breccia complex also contains clasts and domains of other lithologies, including surficial lithologies (bedded clastic facies and felsic volcanic rocks). The Olympic Dam deposit, along with the other deposits and prospects in the Olympic Province, was originally suggested to have developed entirely within a geologically brief magmatic-hydrothermal event at ca. 1590 Ma. However, recent work has suggested Olympic Dam has been episodically modified after 1590 Ma. This thesis aims to clarify aspects of the architecture and timing of events at Olympic Dam as well as the nearby Olympic Province primarily through application of geochronology as well as mineral chemistry and textural analyses. This aim is addressed through: (1) determining the timing and relationships of the surficial lithologies in the ODBC with the Roxby Downs Granite, (2) demonstrating that Olympic Dam was originally overlain by the U-prospective Pandurra Formation and (3) exploring the complex history of hydrothermal mineralisation in the nearby Acropolis prospect. New high-precision CA-TIMS geochronology has constrained the Roxby Downs Granite (1593.87 ± 0.21 Ma) to be slightly younger than felsic volcanic clasts (Gawler Range Volcanics -1594.73 ± 0.30 Ma) in the ODBC. The absence of older country rock fragments in the ODBC and shallow emplacement textures in the Roxby Downs Granite suggest the granite intruded already-present Gawler Range Volcanics. The age of tuffaceous mudstone intervals (1590.97 ± 0.58 Ma) in the bedded clastic facies indicates a basin was present at Olympic Dam and the bedded clastic facies were being deposited ca. 3 myr after emplacement of the Roxby Downs Granite. The provenance of the bedded clastic facies is suggested to have changed from initially volcanic-dominated to granitoid-dominated as Hiltaba Suite granitoids within the vicinity of Olympic Dam were unroofed. The onset of formation of the breccia complex and the hydrothermal system is therefore constrained by the age of the Roxby Downs Granite; the breccia complex and the hydrothermal system were active after deposition of the bedded clastic facies. These age constraints and data from other workers are used to propose a model for the deposition and incorporation of the bedded clastic facies involving faults being responsible for their segmentation and entrainment into the breccia complex. A quartz-rich sandstone facies association recently discovered in the ODBC is entirely brecciated and has characteristics distinct from, and is not interbedded with, the other facies associations of the bedded clastic facies. In addition to the ca. 1590 Ma detrital zircon population present in all of the bedded clastic facies, the quartz-rich sandstone contains significant Palaeoproterozoic and Archaean age detrital zircon populations. The detrital and cement mineralogy, sedimentary textures, diagenetic age, and detrital zircon age populations match most closely sandstones of the ca. 1440 Ma Pandurra Formation which was originally deposited in the regionally extensive intracratonic Cariewerloo Basin. This correlation indicates the Cariewerloo Basin originally extended over the ODBC and that it was incorporated by tectonic activity at least 150 myr after the breccia complex first formed at ca. 1590 Ma. The Cariewerloo Basin is also speculated to have been a source of or conduit for oxidised U-bearing fluids that may have interacted with, and possibly added to, the Olympic Dam U resource long after 1590 Ma. Further evidence of post-1590 Ma events affecting the Olympic Province was obtained from a study of apatite in the hydrothermal mineral assemblage (comprising an initial magnetite-apatite assemblage and a later hematite-dominated assemblage) of the nearby Acropolis prospect. The prospect is structurally simpler and less brecciated than Olympic Dam, and the initial magnetite-dominated assemblage is well preserved. The apatite grains contain zones with abundant inclusions of REE-phosphate minerals (xenotime and monazite) as well as inclusion-free zones. The inclusion-rich zones are interpreted to have formed from the fluid-aided recrystallisation of original, inclusion-free apatite, resulting in the remobilisation of REE, U and Th from apatite into REE-phosphate inclusions. U-Th-Pb geochronology of apatite, xenotime and monazite revealed multiple ages; both inclusion-free and inclusion-rich zones of apatite yield ages coincident with the age of the host volcanic units (ca. 1590 Ma). The xenotime and monazite inclusions have ages that indicate alteration events at ca. 1370 Ma and possibly at ca. 500 Ma. Although the ca. 500 Ma age corresponds to the Delamerian Orogeny in the Adelaide Fold Belt adjacent to the Gawler Craton, the ca. 1370 Ma age does not correspond to any known event in or near the Gawler Craton but instead corresponds best with an event in Laurentia. Challenges in the interpretation of the monazite data imply xenotime is a more robust geochronometer in this setting. This thesis establishes a precise geochronological framework for the setting of significant lithologies at Olympic Dam and constrains the maximum age of the ODBC and the Olympic Dam deposit. Furthermore, the presence of the significantly younger Pandurra Formation in the ODBC implies that tectonic activity affected Olympic Dam long after 1590 Ma and has raised the potential for a late contribution of U to the deposit resource. The identification of multiple post-1590 Ma tectonothermal events affecting the Acropolis prospect suggests the wider Olympic Province has also experienced episodic modification. These findings contribute to the theory that the endowment of the Olympic Dam deposit and the Olympic Province did not occur within a single geologically brief event and may be due to episodic modification. The formation of such well-endowed deposits and metallogenic provinces may, in fact, require prolonged or episodic processes and offers the potential to assist in future exploration targeting for large IOCG deposits (i.e. in regions with a complex and long-lived geological history).

The goal of the field itinerary is to illustrate the facies and architecture of a Triassic high-relief carbonate platform (lithostratigraphically known as Esino Limestone; Lombardy, N Italy), similar in age and evolution to the more renowned coeval carbonate platforms of the Dolomites (NE Italy) and the coeval basinal facies. In the central Southern Alps dolomitization is less pervasive with respect to the Dolomites, so that the facies preservation is spectacular, allowing for the observation of detailed depositional and diagenetic features. Furthermore, the visited platform outcrops provide the unique opportunity to observe the sedimentological record of its demise, freezing the architecture of a platform that lasted for about 5 Myr (from close to the Anisian-Ladinian boundary to the Ladinian-Carnian boundary), from the platform top to the basin. The complete section of this Ladinian-Carnian (Middle-Upper Triassic) high-relief carbonate platform is exposed along the Brembana Valley, north of the city of Bergamo. Facies types can be observed in selected outcrops during the field trip, whereas seismic scale geometric and stratigraphic relationships (from the platform top to the slope and basinal setting), can be observed from selected viewpoints. The carbonate platform system reaches a thickness of up to 800 m, with a platform-basin relief of more than 600 m at the end of its evolution. The field itinerary crosses the entire system, from the inner platform to the basin, of one of the best-preserved Triassic carbonate platforms of the Southern Alps of Italy. Inner platform (subtidal to peritidal cycles consisting of oncoidal-bioclastic packstone to grainstone capped by stromatolitic beds), reef (mostly microbial boundstone), slope (clast-supported, early-cemented poorly-selected breccias produced by collapses of the reef-upper slope belt) and basinal facies (dark, well-bedded limestone) facies are exposed in the visited outcrops. During a ‘geological dive’, from the platform top to the basin floor, the diverse subenvironments of the carbonate system can be observed, appreciating the variability of facies along the depositional profile. Each observation is framed in the seismic-scale geometry of the platform that can be appreciated from easily accessible viewpoints. The exceptionally well-preserved facies, as the facies-destructive dolomitization that heavily affects the spectacular coeval platforms of the Dolomites is here rare, permit to document in detail the depositional, early and late diagenetic events. The visited high-relief carbonate system is characterised by a rapid demise, recorded by changes in the facies associations that are exposed in some of the stops representative of different depositional environments: platform top, reef and slope. The abrupt demise of this carbonate system is marked by a major (probably earliest Carnian) sea-level fall associated with a climate change recorded in the different parts of the depositional system by major facies changes. On the platform top the demise is marked by regressive carbonate facies that have different sedimentological characteristics and thickness in the inner platform and in the reef belt. In the basin and on the slope the demise of the carbonate platform is associated with the abrupt input of clay in the basinal setting facing the progradational platform: the seismic-scale onlap relationships between the last prograding clinoform of the Esino Limestone (clast-supported breccias) and the overlying basinal clay can be observed in a spectacular outcrop along the platform slope.

Cibulakan Formation as one of the prolific hydrocarbon-bearing intervals has become an interesting study object for many researchers. The continuous outcrop of the Cibulakan Formation in the Cipamingkis River comprises claystone, sandstone, and subordinate limestone of grainstone, packstone, and wackestone facies. The outcrop should be able to give a clearer vertical and spatial variation of sandstone and limestone geometry compared to the conventional core alone. Field observations followed by measuring the section is conducted to distinguish lithofacies and to create a stratigraphic profile from the chosen interval. Samples and thin sections from sandstone and limestone lithofacies are observed further to determine fragment type variation, matrix, cement, texture, and porosity types qualitatively. Fourteen (14) lithofacies have been recognized from the observation, i.e., Slumped Sandstone (A1), Claystone (A2), Slightly-bioturbated Sandstone (B1), Cross-laminated Sandstone (B2), Parallel-laminated Siltstone (B3), Calcareous Claystone (B4), Moderately-bioturbated Sandstone (C1), Hummocky Cross-stratified Sandstone (C2), Skeletal – Coral clast Wackestone (C3), Skeletal-clast Packstone (C4), Coralline Foraminiferal Boundstone (C5), Low-angle Planar Cross-bedded Sandstone (D1), Intensely-bioturbated Sandstone (D2), and Trough Cross-bedded Sandstone (D3). There are four architectural facies in the research interval and each of them is composed of different and specific lithofacies. An ideal parasequence is composed of all Architectural Facies namely : (A) Offshore-Transition (B) Lower Shoreface (C) Upper Shoreface with the whole thickness range between 15 to 25 m and the parasequence shows thickening upward succession. The detailed information about the lithofacies and architectural facies hopefully will provide a better understanding of the facies modelling of the mixed carbonate-siliciclastic depositional setting, new insights for parasequence recognition in clastic shoreline depositional environment and become a reference for other areas lacking in core data and/or outcrop analogue.

The Talang Akar Formation is one of the hydrocarbon-producing reservoirs of the South Sumatra Basin. This basin is filled from two different sources in the Eastern part and Western part paleo-high. The bottom Talang Akar consists of coarse-grained sandstone, and the upper part constrains intercalation of sandstone and shale, known as low resistivity low contrast zone (LRLC). The Talang Akar Formation from Air Batu and Sukomoro confers an excellent probability to observe and define LRLC zones over systematic approaches. This paper will provide an analogue of the LRLC reservoir zone by analyzing the relation between facies distribution and reservoir properties, including detailed shale structure. Facies distribution was obtained from the outcrop stratigraphic profile. The reservoir properties are identified by the Thomas Stieber plot and the petrographic section. Seven facies of Talang Akar Formation had been identified, which are: 1) planar cross-bedded sandstone (PCBS), 2) trough cross-bedded sandstone (TCBSS), 3) laminated sandstone (LSS), 4) heterolytic sandstone (HSS), 5) clay-rich sandstone (CSS), 6) mudstone (MS), 7) scour conglomeratic sandstone (SCSS). There are several types of shale distribution: structural shale, dispersed shale, and laminar shale. The laminar and dispersed shale consists of most of the reservoir and fills the pore. The clay structure deduces the disparity in the facies-porosity correlation. The finding of this study revealed that the LRLC zones are caused by lamination structures, thin intercalation layers, heterolytic and clay minerals.

Log-facies classification aims to predict a vertical profile of facies at well location with log readings or rock properties calculated in the formation evaluation and/or rock-physics modeling analysis as input. Various classification approaches are described in the literature and new ones continue to appear based on emerging Machine Learning techniques. However, most of the available classification methods assume that the inputs are accurate and their inherent uncertainty, related to measurement errors and interpretation steps, is usually neglected. Accounting for facies uncertainty is not a mere exercise in style, rather it is fundamental for the purpose of understanding the reliability of the classification results, and it also represents a critical information for 3D reservoir modeling and/or seismic characterization processes. This is particularly true in wells characterized by high vertical heterogeneity of rock properties or thinly bedded stratigraphy. Among classification methods, probabilistic classifiers, which relies on the principle of Bayes decision theory, offer an intuitive way to model and propagate measurements/rock properties uncertainty into the classification process. In this work, the Bayesian classifier is enhanced such that the most likely classification of facies is expressed by maximizing the integral product between three probability functions. The latters describe: (1) the a-priori information on facies proportion (2) the likelihood of a set of measurements/rock properties to belong to a certain facies-class and (3) the uncertainty of the inputs to the classifier (log data or rock properties derived from them). Reliability of the classification outcome is therefore improved by accounting for both the global uncertainty, related to facies classes overlap in the classification model, and the depth-dependent uncertainty related to log data. As derived in this work, the most interesting feature of the proposed formulation, although generally valid for any type of probability functions, is that it can be analytically solved by representing the input distributions as a Gaussian mixture model and their related uncertainty as an additive white Gaussian noise. This gives a robust, straightforward and fast approach that can be effortlessly integrated in existing classification workflows. The proposed classifier is tested in various well-log characterization studies on clastic depositional environments where Monte-Carlo realizations of rock properties curves, output of a statistical formation evaluation analysis, are used to infer rock properties distributions. Uncertainty on rock properties, modeled as an additive white Gaussian noise, are then statistically estimated (independently at each depth along the well profile) from the ensemble of Monte-Carlo realizations. At the same time, a classifier, based on a Gaussian mixture model, is parametrically inferred from the pointwise mean of the Monte Carlo realizations given an a-priori reference profile of facies. Classification results, given by the a-posteriori facies proportion and the maximum a-posteriori prediction profiles, are finally computed. The classification outcomes clearly highlight that neglecting uncertainty leads to an erroneous final interpretation, especially at the transition zone between different facies. As mentioned, this become particularly remarkable in complex environments and highly heterogeneous scenarios.

Abstract Developing new interpretation methods in line with new technology measurements to improve reservoir characterization becomes a must to overcome the challenges that petrophysicists are facing on a daily basis, among others, thinly bedded reservoirs. The standard acoustic logs vertical resolution (VR) is oftentimes insufficient to resolve the Formation features. In the case of laminated thin beds (LTB), conventional petrophysical characterization has often delivered results, such as hydrocarbon saturation, affected by uncertainties. The main objective of this work is to develop a methodology, and to reliably integrate high-resolution acoustic processing outputs into the Formation evaluation (FE) routines, including the quality controls to identify and remove artifacts and ultimately enhance the accuracy of reservoir characterization. The approach used in this study is based on the high-resolution acoustic slowness analysis. The measurement standard VR of the acoustic array measurement is determined by the array aperture (the length of the receiver’s array section; generally 3.5 ft), which tends to obscure features that are thinner than the aperture length. The configuration of the highest resolution is 0.5 ft aperture subarray combination, which considers only two receiver levels in the subarray, i.e., single Rx-Rx spacing. The processing has limitations, inherent to physics; one of them is the "Validity condition". The high-resolution acoustic slowness methodology cannot be applied to acoustic waveform arrivals with very long wavelengths. The subarray aperture should be greater than a quarter wavelength of the wave being used. In addition, as increasing the resolution goes hand in hand with decreasing the number of waveforms, the signal-to-noise ratio decreases. There are several quality control and consistency check workflows to be introduced in this study, which will help in differentiating between the real high-resolution acoustic slowness data and any encountered processing artifacts. These analyses will enable the right evaluation strategy that will enhance the accuracy of FE. Examples highlighting the value of high-resolution acoustic processing/analysis for both carbonate and clastic reservoirs evaluation are provided in the paper. Finally, this approach will evaluate the potential added value to the FE of the heterogeneous reservoirs. We propose workflows in various Formations and borehole settings to demonstrate that with the aid of enhanced VR acoustic data, the log interpretation becomes more representative of the actual subsurface. The resulting sonic profiles show better consistency with other log responses of similar resolution. These workflows then can be used on a more regular basis, especially in complex situations.

Abstract The biggest clastic reservoir based in Kuwait has been facing evaluation challenges over the thick intervals of highly laminated thin hydrocarbon layers. Conventional wireline tools have a limitation on resolution when it comes to addressing these thin beds. Therefore, the reserves are usually underestimated, and thin pays are often overlooked. This paper presents the integration of a variety of advanced Wireline tools in order to correctly evaluate and compute reserves from these thin pay zones. Acquisition of the triaxial induction tool enabled the study of resistivity anisotropy and the identification of thin pay zones through the distinct reading of the resistivity of the thin sand reservoir. The thin layers have also been further validated using high resolution advanced thin bed analysis from image logs. Advanced spectroscopy and NMR data were used to quantitively define the sand and shale fractions within the thin beds. These measurements were critical to input to improve the resistivity interpretation followed by a reliable estimate of the saturation. High resolution dielectric measurements provided resistivity-independent saturation information enhancing the NMR interpretation using water-filled porosity which was a key input into the identification of the heavy oil presence in Burgan. The newly identified thin pay zones have been further validated using the fluid sampling confirming presence of hydrocarbons with greater understanding of its properties and uniquely quantifying the mobile fluid fractions. The additional available reserves can only be properly determined by combining data from multiple sources to achieve a comprehensive evaluation. Resistivity anisotropy was observed based on the separation of vertical and horizontal resistivities and was therefore investigated to understand its root-cause over different zones. By integrating the results from the dielectric dispersion measurements, the diffusion-based NMR data, spectroscopy data, borehole image interpretation and high-resolution sand count delineation of different lithologic units at a finer scale, we were able to identify thin bedded sand-shale intervals in addition to pin-pointing the heavy oil intervals. Hydrocarbon saturations of individual sand layers showed improvement in hydrocarbon volumes, improvement in permeabilities across the studied zones and increased net pay estimations by 12%. Results from the fluid sampling performed across the newly identified thin pays have validated the advanced logging interpretation results and the presence of hydrocarbons. These intervals were overlooked by the standard basic evaluation and the reservoir potential has been revisited following the latest integrated advanced results. By combining the results of all these advanced wireline answer products, we were able to properly identify and quantify the additional available reserves and therefore change the classification of these reservoirs from poor to excellent with new development plan in place. The paper demonstrates the value solution of the high vertical resolutions taking advantage of the latest advanced technologies to enhance the characterization of laminated thin beds. The integrated advanced solution has enabled improved reservoir potential by the identification of new pay zones initially overlooked by the standard basic measurements.