Facies Interpretation Research Articles

The carbonate platform of the Upper Tibasosa Formation, Lower Cretaceous, Eastern Cordillera Basin, Firavitoba-Boyacá, Colombia

The Tibasosa Formation is the main source of limestones in Boyacá. This unit corresponds to a Valanginian-Albian age according to the fossil content in the Eastern Cordillera Basin, recording the first incursion of the Cretaceous sea in Firavitoba. Outcrop-based facies and stratigraphic analyzes of the ~12 m-thick siliciclastic-carbonate succession of the uppermost Tibasosa Formation indicate tidal and carbonate systems. Ten facies/microfacies are grouped into two facies associations (FAs): FA1, tidal flat deposits consist of laminated sandstones/siltstones and floatstones with a single organism dominance (bivalve shells); and FA2 comprises fossiliferous rudstones, floatstones, packstones, and wackstones, representing a carbonate platform. The petrographic description determined rock textures/genesis and the diagenetic sequence with features of the eodiagenesis, mesodiagenesis, and telodiagenesis suggesting a primary origin of these carbonates. The analysis using cathodoluminescence (CL), energy disperse spectrometry (EDS), and scanning electron microscopy (SEM) allowed identify compositional differences, cementation phases, and morphological features in different processes as micritization, neomorphism, porosity, pyritization, compaction, cementation, fracturing, and weathering. The interpretation of facies and microfacies indicated a deposition mainly in a shallow platform with variation in the hydraulic conditions, warm waters, and episodic events of storms/tsunamis that fragmented the bioclasts. A shallow marine system in the Eastern Cordillera Basin during Cretaceous indicates a large transgressive event that flooded hundreds of kilometers, being a link with the Pacific Ocean before the Andes uplift. The main diagenetic events correspond to micritization, cementation of calcite, and mechanical/chemical compaction as a result of microbial activity, dissolution, precipitation in the vadose/phreatic zone, and burial diagenesis. The diagenetic sequence events reveal the incidence of marine and meteoric process that reduced porosity and attest to the microbial activity in carbonate precipitated. This new interpretation allows the understanding of carbonate platforms in the Eastern Cordillera Basin for future correlations of the Cretaceous sea in Colombia.

Automatic seismic facies interpretation using supervised deep learning

Seismic facies interpretation supports subsurface geologic environment analyses and reservoir predictions. Traditional interpretation methods require much manual work, and they heavily depend on the experience and expertise of the interpreters. We have developed advanced algorithms from supervised deep learning to perform automatic seismic facies interpretations. In deep learning, conventional convolutional neural networks (CNN) and encoder-decoder architectures are widely used for image classification and segmentation problems, respectively. Based on these two architectures, we build a 3D conventional CNN and a conventional encoder-decoder, and then we apply an enhanced encoder-decoder (DeepLabv3+) that integrates superior structures to our research. To train the networks, we develop an effective scheme to automatically and diversely augment data by using well-labeled 2D seismic sections in which facies are divided into nine classes. We perform experiments on the Netherlands F3 data set by training diverse samples and tuning parameters, implement the trained networks on the whole data volume, and then quantitatively evaluate the results. The testing results of the encoder-decoders are more accurate and efficient than those of the conventional CNN, as well as being more consistent with the geologic background. The mean intersection-over-union values for the encoder-decoders are 87.8% (conventional) and 92.4% (enhanced), respectively, whereas for the conventional CNN, the value is 67.8%. Besides, the prediction of one seismic section takes less than 1.0 s for the encoder-decoders, whereas it takes 4.0 min for the conventional CNN.

Seismic facies, stratigraphy, geomorphology, and seismic modelling of a Lower Cretaceous carbonate platform

Abstract Globally, Lower Cretaceous carbonate platforms form important hydrocarbon reservoirs. An exceptional seismic dataset allowed us to examine controls on the stratigraphy, seismic geomorphology, facies architecture and along-strike variability of a Lower Cretaceous platform. Within the platform succession, a partitioning of facies is developed between Transgressive, Highstand and Forced Regressive seismic sequences. Spectacular seismic geomorphological images of the platform using spectral decomposition techniques reveal spatial organization within both depositional and diagenetic (i.e. palaeokarst) patterns. The study was undertaken in order to optimize a well location. Predrill seismic facies interpretations were interpreted with the aid of offset well data and drill cores. Core data encompass a range of slope, platform margin and platform interior facies with inferred palaeoenvironments that are matched to the seismic geomorphology of the platform. 2D seismic forward modelling was integrated in our workflow to investigate the extent of potential sealing lithologies and the reservoir potential of the individual seismic sequences. Nearby wells were used to calibrate a modified rock physics model for the different lithofacies. Multiple seismic model realizations were generated to assess reservoir quality in alternative well locations and the continuity and quality of sealing strata. Results of the predrill forward-modelled poro-perm prediction are presented, showing a good fit with the final well observations after drilling.

Microfauna- and sedimentology-based facies analysis for palaeolandscape reconstruction in the back-barrier area of Norderney (NW Germany)

AbstractPalaeolandscape reconstructions at the German North Sea coast are essential for the understanding of coastal changes and dynamic landscape-forming processes. This study contributes to reconstructing Holocene coastal changes in the back-barrier area of the East Frisian island of Norderney and draws conclusions on the local palaeogeography. Five sediment cores were analysed in terms of sedimentology (grain-size distribution), geochemistry (TOC, TIC, N, C/N), microfauna (foraminifers and ostracods) and 13 radiocarbon dates. In order to identify driving environmental factors and support the facies interpretation, multivariate statistics (PCA) were carried out. Additional cores from the surrounding area (WASA Project and ‘Landesamt für Bergbau, Energie und Geologie’ (LBEG) Hannover) enabled correlation of the investigated cores over a transect of ~6 km, showing six depositional environments, which can be used for landscape reconstruction. Deposition starts with periglacial (aeolian and glaciofluvial) Pleistocene sediments, with subsequent pedogenesis followed by swamp conditions that develop into a salt marsh. The overlying tidal-flat sediments are partially cut by (fossil and recent) channel deposits. A hiatus at the base of the tidal-flat deposits that spans some 3000 years hints at their reworking caused by a combination of antrophogenic coastal protection measures and the impact of storms. Furthermore, based on the profile correlation and the age data, a widespread salt-marsh area with a minimum age of ~4000 cal BP is defined for the ‘Hohes Riff’ in the southwestern back-barrier of Norderney Island.

Investigation of Groundwater In-rush Zone using Petrophysical Logs and Short-offset Transient Electromagnetic (SOTEM) Data

The water burst from the Ordovician limestone underlain by the Permo-Carboniferous coal seams have potential to trigger coalmine hazards in Northern China. Therefore, it is crucial to identify and accurately map the water enrichment zones and delineate coal seams using an integrated approach based on surface TEM and subsurface wireline log information to avoid water-inrush hazard and ensure safe production of coal. We inverted surface based TEM data using 1-D Occam inversion to identify the conductive anomaly and then further quantified the zone of interest by gamma and resistivity logs. 1-D Occam inversion results show conductive zone around 370 m while higher resistivity and lower gamma ray log signatures were observed against coal seams. Groundwater inrush zone falls within the mid-range gamma ray and resistivity interval as shown on the petrophysical logs. The distinct log signatures (low gamma-ray and high resistivity values) clearly indicated coal seams at depth of 410 and 470 m and subsequently the log trends were used to distinguish between coal units and more permeable sands. The magnitude and the variability of these parameters in the borehole are attributed to the subsurface stratigraphic heterogeneity. They can be key clues for interpretation of depositional facies of coal-bearing sequence and may also be used as a constraint in characterization of groundwater enrichment zone.

Integrated simulation to seismic and seismic reservoir characterization in a CO2 EOR monitoring application

Understanding the behavior of CO2 injected into a reservoir and delineating its spatial distribution are fundamentally important in enhanced oil recovery (EOR) and CO2 capture and sequestration activities. Interdisciplinary geoscience collaboration and well-defined workflows, from data acquisition to reservoir simulation, are needed to effectively handle the challenges of EOR fields and envisioned future commercial-scale sites for planned and incidental geologic CO2 storage. Success of operations depends on decisions that are based on good understanding of geologic formation heterogeneities and fluid and pressure movements in the reservoir over large areas over time. We present a series of workflow steps that optimize the use of available data to improve and integrate the interpretation of facies, injection, and production effects in an EOR application. First, we construct a simulation-to-seismic model supported by rock physics to model the seismic signal and signal quality needed for 4D monitoring of fluid and pressure changes. Then we use Bayesian techniques to invert the baseline and monitor seismic data sets for facies and impedances. To achieve a balance between prior understanding of the reservoir and the recorded time-lapse seismic data, we invert the seismic data sets by using multiple approaches. We first invert the seismic data sets independently, exploring sensible parameter scenarios. With the resulting realizations, we develop a shared prior model to link the reservoir facies geometry between seismic vintages upon inversion. Then we utilize multirealization analysis methods to quantify the uncertainties of our predictions. Next, we show how data may be more deeply interrogated by using the facies inversion method to invert prestack seismic differences directly for production effects. Finally, we show and discuss the feedback loop for updating the static and dynamic reservoir simulation model to highlight the integration of geophysical and engineering data within a single model.

Facies interpretation and geochronology of diverse Eocene floras and faunas, northwest Chubut Province, Patagonia, Argentina

Abstract The Eocene Huitrera Formation of northwestern Patagonia, Argentina, is renowned for its diverse, informative, and outstandingly preserved fossil biotas. In northwest Chubut Province, at the Laguna del Hunco locality, this unit includes one of the most diverse fossil floras known from the Eocene, as well as significant fossil insects and vertebrates. It also includes rich fossil vertebrate faunas at the Laguna Fría and La Barda localities. Previous studies of these important occurrences have provided relatively little sedimentological detail, and radioisotopic age constraints are relatively sparse and in some cases obsolete. Here, we describe five fossiliferous lithofacies deposited in four terrestrial depositional environments: lacustrine basin floor, subaerial pyroclastic plain, vegetated, waterlogged pyroclastic lake margin, and extracaldera incised valley. We also report several new 40Ar/39Ar age determinations. Among these, the uppermost unit of the caldera-forming Ignimbrita Barda Colorada yielded a 40Ar/39Ar age of 52.54 ± 0.17 Ma, ∼6 m.y. younger than previous estimates, which demonstrates that deposition of overlying fossiliferous lacustrine strata (previously constrained to older than 52.22 ± 0.22 Ma) must have begun almost immediately on the subsiding ignimbrite surface. A minimum age for Laguna del Hunco fossils is established by an overlying ignimbrite with an age of 49.19 ± 0.24 Ma, confirming that deposition took place during the early Eocene climatic optimum. The Laguna Fría mammalian fauna is younger, constrained between a valley-filling ignimbrite and a capping basalt with 40Ar/39Ar ages of 49.26 ± 0.30 Ma and 43.50 ± 1.14 Ma, respectively. The latter age is ∼4 m.y. younger than previously reported. These new ages more precisely define the age range of the Laguna Fría and La Barda faunas, allowing greatly improved understanding of their positions with respect to South American mammal evolution, climate change, and geographic isolation.

Sediment descriptions and geochemical analyses of radiocarbon-dated deposits from the vicinity of Göbekli Tepe-A dataset.

This dataset comprises the detailed descriptions and laboratory measurements of sediment profiles from the semi-arid environs of the Pre-Pottery Neolithic site Göbekli Tepe in southeastern Turkey—one of the oldest monumental structures of humankind dating to c. 11.5–10 ka BP. Focus of the descriptions are the architectural elements of the deposits allowing to conduct facies interpretations and the reconstruction of different depositional environments. This is supported by bulk geochemical sediment analyses (pH, electrical conductivity, magnetic susceptibility, and loss on ignition) and the determination of total and inorganic carbon contents and chemical element concentrations. The Late Holocene chronology is based on radiocarbon dating of charcoal pieces and bulk samples containing organic matter from buried organic-rich topsoil horizons and soil sediments. Lithic artifacts from the Pre-Pottery Neolithic provide additional age estimates. Nykamp et al. [1] provide the synthesis that is based on the presented datasets.

Late Holocene geomorphodynamics in the vicinity of Göbekli Tepe, SE Turkey

This study traces the geomorphological development in the environs of the Pre-Pottery Neolithic site Göbekli Tepe by means of radiocarbon dated sediment profiles from its close vicinity. Based on facies interpretation we identify different depositional environments and discuss the involved process dynamics. Our results show that the sediments from the foot slopes are characterized by soil creep and slope wash. Further downstream, in the proximal piedmont zone, fluvial deposition prevails forming a channel and an overbank facies. The sediments at the foot slopes were mainly deposited during Roman and Byzantine times, while those from the proximal piedmont zone cover the period from the Bronze Age to the Roman times. Phases of geomorphological activity and stability can be distinguished in the course of the later Holocene, where organic rich topsoils were buried at c. 4750, 4200, and 3650 cal. a BP documenting phases of landscape stability followed by enhanced geomorphodynamics. These phases fall into the Bronze Age in Anatolia and coincide with an increasing population, pronounced human impact, and climatic aridization that occurred in Turkey around 5.3–4.1 ka BP. Our findings provide among the first insights into the environmental development including the involved process dynamics in the vicinity of the UNESCO World Heritage site of Göbekli Tepe during the later Holocene, also allowing to further develop hypotheses for the period of its occupation.

A river-dominated to tide-dominated delta transition: A depositional system case study in the Orinoco heavy oil belt, Eastern Venezuelan Basin

The Orinoco heavy oil belt (OHOB), which has the most significant heavy oil reserve in the world, has shown various sedimentary patterns and different evolution processes within its different blocks. We selected two blocks, Junin in the west and Carabobo in the east, to analyze the depositional environment distinctions due to different transgression processes. Based on the interpretation of 3D seismic data and electrical well-logging facies and analysis of depositional phenomena using cores, we clarified diverse depositional associations and constructed a sedimentary evolution model of the depositional system in the study area. We suggest that the depositional system transitioned from a braided river delta to a tide-dominated delta in the Early Miocene and that two factors mainly controlled the transition: paleo-flow and paleo-geomorphology, which are related to tectonic uplift and transgression processes. Transgression increased gradually through tectonic activity, though transgression rates varied area to area, resulting in different depositional environment transitions and sand-body distribution patterns. In the Carabobo block (east), a gentle slope developed, indicating a fast transgression rate. The intense interaction between river and tide flow led to a large inter-distributary channel area with high-sinuosity- or tidal-channels (relative to the Junin block). In the Junin block (west), tectonic activity developed a large accommodation area providing space for the sediment produced, slowing the transgression rate, and contributing to a mainly fluvial delta environment. Due to the gradual intensive transgression, channel stack patterns transitioned from braided-to meandering-channel in the river dominated delta or tidal-channel in the tide-dominated delta.

Facies analysis relationships depositional environments of the subsurface stratigraphy of the Snake Cave Interval in the Bancannia Trough, western Darling Basin, New South Wales, SE Australia

Abstract This work presents the first detailed research on the subsurface stratigraphy of the sedimentary Snake Cave Interval (late Early to late Middle Devonian) in the Bancannia Trough, the westernmost component of the Darling Basin, in western New South Wales, Australia. The study is based on data from wireline-log responses (especially gamma-ray and sonic logs), and core and cuttings descriptions in three exploration wells that are used to develop a model for depositional environments in the Bancannia Trough. This study provides re-evaluation and re-interpretation of the positions of the top and bottom boundaries of the Snake Cave Interval using distinct patterns changes in gamma-ray and sonic log signatures in relation to lithological characteristics in the Bancannia South-1, Bancannia North-1 and Jupiter-1 wells. The log facies interpretation of the Snake Cave Interval section enabled the detailed facies description of four lithostratigraphic units (A, B, C and D, in ascending order) in the study area. The Snake Cave Interval displays units with ten distinct sedimentary facies identified from core and then tied to the gamma ray log characteristics, forming facies associations that are visible in both vertical and lateral sections. Five facies associations have been identified: FA-I, braided fluvial multistory channel belt complex deposits; FA-II, meandering fluvial distributary channel sandstone complex deposits; FA-III, sandy braided fluvial distributary channels deposits; FA-IV, meandering fluvial deposits; and FA-V, fluvial channel-fill association with fluvio-tidal transition zone complex deposits. Detailed comparison of lithologic logs with wireline-log suite signatures (mainly gamma-ray logs) that are dominantly braided fluvial and meandering fluvial deposits, with minor fluvio-tidal transition zone complex deposits in this trough. This article presents a new depositional model that will promote exploration and discovery of potential petroleum resources and stratigraphic-trap configurations in this trough and adjacent regions of the Darling Basin.

Interpreting the Subsurface Lithofacies at High Lithological Resolution by Integrating Information From Well‐Log Data and Rock‐Core Digital Images

AbstractSpectral facies interpretation and classification methods have been proposed to improve the sophistication of interpretation of the subsurface heterogeneity. In the spectral facies interpretations, the intensity values of the RGB spectrum and the local entropy from rock‐core digital images are used, and the results are compared to conventional electrofacies and expert petrophysical interpretations. During the classification, a practically applicable model that identifies the more detailed types of lithofacies is constructed by using a multilayer neural network model, with the interpreted spectral facies and well‐log data from the corresponding depths used as response and explanatory variables, respectively. Core digital images and five types of well‐log data from the Satyr 5 well in Western Australia are applied for the actual implementation. Through comparative interpretations, three spectral facies are identified as separable lithofacies (i.e., shale, shaly‐sandstone, and sandstone lithofacies), which is supported by detailed HyLogger mineralogy along the tested cores. On the other hand, two electrofacies (i.e., shale‐dominant and sand‐dominant facies) are identified by a conventional method. In the classification based on the spectral facies, the trained multilayer neural network model showed high prediction accuracy for all the lithofacies. Based on these observations, it is confirmed that more precise lithofacies interpretation and classification can be conducted with the developed methods. The developed methods have the potential to improve subsurface characterization when high lithological resolution is essential.

Reservoir Quality and Flow Unit Characterization of a Reservoir in X Field, Baram Delta

Reservoir stratigraphic continuity are uncertainties that may be due to lack of facies association definition in reservoirs. These uncertainties come into play where proper porosity–permeability (poroperm) evaluation is misrepresented, leading to volumetric estimation uncertainties. Most oil fields in the Baram Delta have been previously studied with the development of static models. The lack of sequence stratigraphic input in the study was due to constraints including fault shadowing and gas chimney presence which deterred the volume estimations. Earlier interpretation of facies distribution and depositional environment of a field, named X, was achieved mainly by using core descriptions and interpretations. In this study, a reinterpretation of the depositional environment and facies distribution were carried out in the R1 and R2 reservoirs. The analysis was done by incorporating the depositional environment and facies with newly interpreted facies comprising of sand, silty sand, sandy shale and shale facies, created using neural network programme. Utilising newly set facies definitions with additional inputs including porosity and permeability data, a better facies distribution for the reservoir is emplaced. With the facies definitions set for 3 wells, the reservoir quality was investigated through poroperm relationship, reservoir quality index (RQI) and fluid flow unit interpretation. The new definitions for reservoir facies consequently matched well to the core descriptions. The R1 reservoir facies-poroperm relationship were clustered well with respect to each facies type. The RQI was then evaluated from the permeability and porosity values for all the selected wells. The fluid flow units were estimated using depth interval difference, effective porosity and permeability data. The fluid flow regimes are different for all the wells, where the updip Well B displayed significantly better flow capacity than both Well C and Well A. However, Well C also displayed good fluid flow capability, indicated by high gradient flow capacity over storage capacity, although with presence of some layers of poor flow quality. Good communication for the downdip wells provides a potential for lateral fluid flow component which can influence the storage and flow capacity of fluid in the updip Well A, and thus creating an overall control and validation of fluid capacity in the reservoir.

Surface to subsurface correlation of the Middle-Upper Triassic Shublik Formation within a revised sequence stratigraphic framework

Recent work on cores and outcrops of the Middle-Upper Triassic Shublik Formation has facilitated surface to subsurface correlation of depositional sequences across the Alaska North Slope. Five transgressive-regressive depositional sequences have been defined within three large-scale stratigraphic units. Outcrop spectral gamma-ray (GR) profiles were used to correlate observed stacking patterns with nearby exploration wells, and GR logs from 161 exploration wells were used to correlate the three large-scale stratigraphic units across the North Slope and nearby offshore. Interpretations of depositional facies and sequence stratigraphy in cores from 26 wells were used to corroborate regional correlations. Isochore maps constructed for each of the three stratigraphic units illustrate the influence of accommodation on depositional patterns and suggest reactivation of several older tectonic elements during Shublik deposition. An isochore map of the richest, oil-prone interval of the Shublik Formation reveals a thick pod south of Harrison Bay, the eastern part of which lies beneath a recent giant Shublik-sourced oil discovery in the Cretaceous Nanushuk Formation. In addition, when integrated with thermal maturity, this isochore map may provide leads for areas that are optimal for unconventional resource exploration.

Provenance and Sediment Maturity as Controls on CO2 Mineral Sequestration Potential of the Gassum Formation in the Skagerrak

In order to meet the increasing demand to decarbonize the atmosphere, storage of CO2 in subsurface geological reservoirs is an effective measure. To maximize storage capacity, various types of saline aquifers should be considered including dynamic storage options with open or semi-open boundaries. In sloping aquifers, assessment of immobilization potential for CO2 through dissolution and mineralization along the flow path is a crucial part of risk evaluations. The Gassum Formation in Skagerrak is considered a nearshore CO2 storage option with layers shallowing northwards. In this study, petrographic data and provenance analysis provide the basis for estimating reactivity of the sandstones with respect to CO2 immobilization potential. These analyses are integrated with seismic interpretation, well-log analysis and sedimentological observations of sedimentary facies to estimate mineral distribution and corresponding reactivity in the proposed injection area. Here the Gassum Formation comprises south-prograding, shoreface-fluvial para-sequences, sourced from northern hinterlands. Pronounced differences in the mineralogical maturity in the studied area are identified and explained by the sediment transport distances and the type of sediment source. This is possible because the U-Pb ages of zircon grains in the sediments can be used to pinpoint the areas where they originate from in the Fennoscandian Shield, such as Telemarkia (gneissic) or Idefjorden (granitic) terranes. Of special importance are the most reactive mineral phases like albite and Fe-rich chlorite, of which the feldspar occurs in largest abundance and the grain-coating chlorite has largest surface area. Their distribution is partly controlled by provenance, so their abundance decreases basinwards with increasing sediment maturity. The abundance of fluvial sandstones presumably increases northwards in basal parts of para-sequences, while shoreface sandstones comprise the top part of sandy units. CO2 injected in the proposed area will migrate upwards within the reservoir and up-dip along the seal, towards more immature sediments (i.e. higher contents of albite and chlorite) and higher proportions of Telemarkian-derived sediment. Thus, the mineralization potential increases along the migration path, while kinetic reaction rates will decrease in shallower, lower temperature regions. Identifying these parameters is important to estimate the CO2 mineral sequestration potential and ensure safe storage of CO2.

Gradual Evolution from Fluvial Dominated to Tide Dominated Deltas and Channel Type Transformation: A Case Study of MPE3 Block in the Orinoco Heavy Oil Belt of the Eastern Venezuelan Basin

Based on the data of core description and sporopollen analysis, the gradual evolution of deltas in vertical direction and transition of channel types in the MPE3 block of the eastern Venezuela Basin have been surveyed by seismic phase and well logging facies interpretation. The results show that due to the great sea level rise, the sedimentary system of the Miocene Oficina Formation in the MPE3 block shifted from the distal‐source sandy braided river delta to tide‐affected delta, and eventually to tide‐dominated delta. Vertically, during the early stage of sedimentation of Oficina Formation, the distributary channels of the delta were dominated by braided river channels. While in the later stage, as the tidal effect was gradually intensified, the channel changed from braided channel to meandering channel. On plane, as a result of differential transgression, sedimentary framework and distribution of sand bodies vary across the study area. Compared with the eastern part, the western part has more braided channels, larger channel bars, less developments of distributary bay and higher ratio of sand to mud. Whereas the braided channels in the south are larger than those in the north. It is the first time we pointed out the impact of marine transgression differences on the sedimentary facies distribution and river type transition in the study area. Factors like the structural and paleogeomorphological change, sea level variation, supply of sediments have strong influence on the evolution of sedimentary system and distribution of sandbodies. It is predicted that the major sandbody is more developed in the central south, which can guide the subsequent horizontal well development.

Thickness prediction for high-resolution stratigraphic interpretation by fusing seismic attributes of target and neighboring zones with an SVR algorithm

Abstract Predicting the thickness of fluvial sandbodies is significant for hydrocarbon exploration and development programs. Owing to spatially dense sampling, the analysis of sand thickness based on 3D seismic data has become one of the most popular methods. However, in terms of high-resolution stratigraphic interpretations, the thickness range of the target zone is usually less than the seismic temporal resolution; so seismic responses in the target zone are significantly affected by the responses of the upper and lower zones (neighboring zones). Therefore, we developed a new method of sand thickness prediction to reduce the interferences of neighboring zones by fusing the seismic attributes of the target and neighboring zones based on machine learning with a support vector regression (SVR) algorithm. First, the sand thickness values interpreted from wells were set as supervised data, and seismic attributes (around the wells) in the target and neighboring zones were input as training data. Then, an SVR model was trained using both sets of input data. Finally, the attributes in the target and neighboring zones were inverted into the predicted sand thickness using the trained SVR model. To test the proposed method, a multi-thin-bed, 2D model was designed, and a complex, geologically realistic, 3D model was established based on well-log-based facies interpretation using an object-based modeling method. This sand-thickness prediction method was also applied to a real seismic dataset of Chengdao Oilfield in the Bohai Bay Basin of China. These applications demonstrate that the proposed method can significantly reduce the interference of neighboring zones and improve sand thickness prediction.

Depositional facies and the sequence stratigraphic control of a mixed‐process influenced clastic wedge in the Cretaceous Western Interior Seaway: The Gallup System, New Mexico, USA

AbstractDepositional facies have been hypothesized to be linked to sequence stratigraphic positions. Also, shoreline systems are built by mixed processes, including rivers, storms, fair‐weather waves and tides. Resolving the complexity of shoreline deposition requires detailed quantitative facies analysis with particular attention to heterolithic successions. In this study, 71 sections in a 130 km long outcrop belt of the Cretaceous Gallup Formation in the north‐west of the San Juan Basin were measured. Five major facies associations were identified using sedimentological and iconological interpretations, including offshore shelf, non‐deltaic shoreline sandstones, deltas, coastal bayline and fluvial. Each facies association also comprises subordinate facies. Depositional facies interpretations are placed in a high‐resolution sequence stratigraphic framework that allows for reconstructions of the palaeogeography of individual parasequence sets that demonstrate temporal and spatial evolution of facies associations and depositional processes. The results show that the Gallup is a mixed‐process‐controlled depositional system with fair‐weather and storm‐wave dominance, river influence and tide‐effect, contrasting with previous interpretations of a solely fair‐weather wave‐dominated environment. Depositional processes and the resultant facies change with sequence stratigraphic positions in response to relative sea‐level changes – particular facies are only deposited in certain systems tracts. Distinction and transition between non‐deltaic shorefaces and wave‐dominated deltas have also been documented in this study. Non‐deltaic shorefaces are characterized by homogeneous sandstones with a wide‐range bioturbation index and the absence of mudstones. Wave‐dominated deltas are subject to river influence and contain prodelta facies. This study shows the importance of detailed facies analysis with high‐resolution sequence stratigraphic control using outcrops for documenting sedimentary processes of shallow marine shoreline systems.

Value of Geologically Derived Features in Machine Learning Facies Classification

The aim of this work is to demonstrate how geologically interpretative features can improve machine learning facies classification with uncertainty assessment.Manual interpretation of lithofacies from wireline log data is traditionally performed by an expert, can be subject to biases, and is substantially laborious and time consuming for very large datasets. Characterizing the interpretational uncertainty in facies classification is quite difficult, but it can be very important for reservoir development decisions. Thus, automation of the facies classification process using machine learning is a potentially intuitive and efficient way to facilitate facies interpretation based on large-volume data. It can also enable more adequate quantification of the uncertainty in facies classification by ensuring that possible alternative lithological scenarios are not overlooked. An improvement of the performance of purely data-driven classifiers by integrating geological features and expert knowledge as additional inputs is proposed herein, with the aim of equipping the classifier with more geological insight and gaining interpretability by making it more explanatory. Support vector machine and random forest classifiers are compared to demonstrate the superiority of the latter. This study contrasts facies classification using only conventional wireline log inputs and using additional geological features. In the first experiment, geological rule-based constraints were implemented as an additional derived and constructed input. These account for key geological features that a petrophysics or geological expert would attribute to typical and identifiable wireline log responses. In the second experiment, geological interpretative features (i.e., grain size, pore size, and argillaceous content) were used as additional independent inputs to enhance the prediction accuracy and geological consistency of the classification outcomes. Input and output noise injection experiments demonstrated the robustness of the results towards systematic and random noise in the data. The aspiration of this study is to establish geological characteristics and knowledge to be considered as decisive data when used in machine learning facies classification.

The Ediacara Member, South Australia: Lithofacies and palaeoenvironments of the Ediacara biota

The Ediacara Member of the Rawnsley Quartzite in the Flinders Ranges (South Australia) has undergone considerable investigation due to its placement within the package of terminal Ediacaran sediments in the region and as the host sediments of the Ediacara biota fossils. A focus on palaeoenvironment reconstruction and taphonomy has seen a succession of lithofacies models presented. These have evolved with the expansion of recognised Ediacara biota localities and prevailing palaeontological methodologies. Much of the recent descriptive lithofacies work has focused on the Nilpena fossil site in the west of the Flinders Ranges. This location is particularly fossil-rich but does not represent a “typical” section through the Ediacara Member. The Ediacara Member elsewhere in the region contains up to six parasequences with total thicknesses varying from ten to 260 m. With the exclusion of the Ikara-Chace Range region, the majority of studied locations external to Nilpena do not show clear evidence for significant (canyon-scale), intra-member erosional features. In this study we review existing facies models for the Ediacara Member and compile a “best-fit” revised facies model by incorporating the modern facies interpretations (largely based at Nilpena) and previous basin-wide observations, models and stratigraphic sections. The revised model is assessed against a series of newly measured stratigraphic sections from across the basin. We propose the division of the wave-base facies into two facies, representative of the upper and lower storm wave-base environments respectively and the re-inclusion of a facies representative of a shoreface palaeoenvironment. Additional characters and identifiers for the facies have been incorporated to aid field identification, as the ability to identify facies of fossil-bearing isolated hand-specimens can allow fossils found on scree slopes to be traced back to source beds. Likewise, palaeoenvironmental interpretations are critical to the reconstruction of Ediacara biota habitat and preservational environments.