Facies Classification Research Articles

Basal ice facies: a review and unifying approach

Over the past ∼30 years numerous basal ice facies have been identified, named and classified. However, the resulting facies descriptions and names are inconsistent and no single scheme encompasses all of the different ice types that exist at different ice masses. In this paper, we review and critique existing basal ice facies names, descriptions and classification schemes, and propose a new, non-genetic approach that has the capacity to name and describe all basal ice types. We define six fundamental basal cryofacies and a further 12 composite cryofacies which can all be defined on the basis of a cursory evaluation of debris disposition and concentration. More detailed cryofacies description is based on characterizing three sets of ice properties that can also be estimated visually in the field: (a) the thickness of the basal ice facies and its constituent sub-layers, (b) the concentration and texture of debris included within any or all of those layers, and (c) the concentration and size of bubbles included within any or all of those layers. We also propose a shorthand method for the presentation of this descriptive information. Here, codes for the layer thicknesses are presented as standard text, and codes for the included debris characteristics and included bubble characteristics are presented as superscripts and subscripts respectively. Sub-layers are characterized similarly, but within a nested sequence of brackets. We evaluate the effectiveness of these two schemes by using them to rename and reclassify several existing basal ice facies. Results indicate that the schemes are robust and that they provide a coherent, non-genetic framework for the effective naming and description of basal cryofacies.

A visual data-mining methodology for seismic facies analysis: Part 2 — Application to 3D seismic data

A visual data-mining approach to unsupervised clustering analysis can be an effective tool for visualizing and understanding patterns inherent in seismic data (i.e., seismic facies). The unsupervised clustering analysis is completely data-driven, requiring no external information (e.g., well logs) to guide the seismic-trace classification. We demonstrate the application of the visual data-mining approach to seismic facies analysis on a real 3D seismic data volume. We select two stratigraphic intervals, the first including a Devonian pinnacle reef system and the second containing a Jurassic siliciclastic channel system. Both analyses show major stratigraphic features that can be defined in horizon slices or other types of visualization. However, the visual data-mining approach creates seismic facies maps with improved visual detail, distinguishing seismic trace-shape variability in the data. We also compare the facies maps with those obtained from a commercial package for seismic facies classification. Both approaches created similar facies maps, but the visual strategy better depicts subtle stratigraphic changes in the bodies being imaged, offering insight into the nature of these features.

Http://www.socgeol.it/368/58/products/a_simplified_scheme_for_the_description_of_textural_features_in_welded_ignimbrites_the_example_of_san_pietro_island_sardinia_italy.html

Welded ignimbrites show a large variability of welding intensity and of post-depositional crystallization. According to existing literature,a complete characterization of welded ignimbritic units involves: 1) a classification scheme which includes up to 5-6 categoriesof welding intensity; 2) the definition of the style of post depositional crystallization. This classification can be very time-consumingand well beyond the standards required for a general description of ignimbrite units for regional geological mapping purposes.During the geological survey of the San Pietro Island (Sardinia, Italy) in the framework of the new geological map of Italy on a scale1:50000 (CARG Project), a large number of samples from different ignimbritic units has been collected. The geology of the area is characterizedby Oligocene-Miocene volcanic deposits, which testify for the intense explosive activity with the deposition of many variablywelded ignimbritic units and, subordinately, local effusive activity, mainly characterized by the emplacement of lava coulees. All theproducts derive from the eruption of highly evolved magmas of both calc-alkaline and peralkaline affinity.We present here a new simplified scheme for the facies classification of these ignimbritic deposits. The scheme is based on threemain textural features: the aspect ratio of the fiammae, the degree of glass shards alignment and the style of crystallization of the matrix.All these features can be used to describe the ignimbrite units for the scope of their lithological characterization in mapping projects.We suggest that the scheme can have a general interest for the geological mapping of areas dominated by the presence of weldedignimbritic units.

Seismic Facies Identification and Classification Using Simple Statistics

Summary The identification and mapping of rock facies is important to reliable reservoir characterization. Traditionally, facies identification and mapping are based on inspection of core data and/or well-log signatures, a procedure that has subjective aspects because it is relies on samples from only a very small portion of the reservoir. Such identification is also difficult to perform at the onset of the exploration stage because of lack of sufficient well data. This paper demonstrates a simple practical approach to identify and classify facies from seismic-amplitude data using basic statistical concepts. Within a geologic facies, measured properties [in this case acoustic impedance (AI)] are assumed to differ mainly as a result of random additive events and are modeled by a normal distribution, as justified by the central-limit theorem. The facies are identified by estimating the combination of facies volume fractions and distribution parameters (means and standard deviations of the facies probability-density function) that best fit the population distribution of AI. A simple form of Bayes theorem is then used to compute the probability of occurrence of each of the facies at the measured locations. This generates a volume of facies probabilities corresponding to the seismic volume. Such a volume can be used to perform facies-specific petrophysical analysis or be a starting point to generate multiple realizations of petrophysical properties. The approach is simple and transparent to use, with no significant computational requirements even on large data sets. We describe an application of the procedure to a synthetic reference data set and a Gulf of Mexico AI data set. Mapped probabilities of the individual facies show the spatial continuity and geologic character of the underlying depositional environment. Property values within the mapped regions are substantially less variable than the original data across the entire region. The within-facies semivariograms exhibit much less spatial correlation than across all facies. Since the facies are mapped across an exhaustive data volume, this approach considerably reduces the need for the geostatistical construction of property distributions within them as long as a high correlation exists between the seismic attribute and petrophysical properties.

Turbidites and turbidity currents from Alpine ‘flysch’ to the exploration of continental margins

Turbidites and turbidity currents from Alpine ‘flysch’ to the exploration of continental margins

Irrigation agriculture and the sedimentary record in the Palpa Valley, southern Peru

Abstract Irrigation agriculture is an ancient and widespread feature in regions where allogenic rivers flow through arid landscapes. This paper reports the results of sedimentological–pedological investigations in the Palpa Valley in the coastal desert of southern Peru where sediment-laden river water is used for irrigation. An adapted facies classification is used to deduce a generalised stratigraphical sequence of the valley bottom sediments. Chronological constraints from radiocarbon dating and archaeological finds are used to reconstruct sedimentation rates for fossil to recent irragric anthrosols. Actualistic case studies are used to quantify present-day irrigation sedimentation. The investigations result in a clarification of the sedimentological and geomorphic history of this valley and a quantification of irrigation-related sedimentation. Irragric anthrosols date back more than 3500 years and provide direct evidence for the beginning of irrigation agriculture in this region. It is concluded that: (i) the up to approximately 4 m thick fine-grained sediments in the Palpa Valley bottom totaling a volume of 21.4 Mio. m3 are a result of long-lasting human impact and have to be considered as artefacts of prehistoric and historic irrigation agriculture in the hyperarid coastal desert; (ii) the fine-grained sediments represent a geoarchive which holds information on the history of irrigation agriculture as well as information on possible natural disturbance by extreme fluvial events; (iii) the identification of irragric anthrosols has implications for archaeological and paleoenvironmental reconstructions.

Genesis, classification, and evaluation method of diagenetic facies

Abstract Based on the controlling of diagenesis and diagenetic facies on reservoir development, this article discusses the formation, classification, and evaluation of diagenetic facies and its application and significance in petroleum exploration. For constructive diagenetic facies such as clastic rock, carbonate rock, and igneous rock, eight kinds of genetic mechanisms are developed, including dissolution of organic acid, dolomitization, and so on. Nine constructive diagenetic facies and seven destructive diagenetic facies are classified. A naming scheme for diagenetic facies is proposed reflecting lithology, diagenesis, porosity, and permeability, that is, “porosity and permeability level + rock type + diagenesis type”. Diagenetic facies are evaluated synthetically and quantitatively on the basis of sedimentary facies, log facies, seismic facies, rock cores, and thin sections, and “four steps” and “superposition of three charts” are put forward as the methods of evaluation and mapping. Favored reservoirs, “sweet spots”, and lithostratigraphic traps can be predicted according to the distribution of different types of diagenetic facies. The development of the study on diagenetic facies is also discussed in the article.

Well log facies classification for improved regional exploration

Well log and rock sample data from fourteen offshore petroleum exploration wells have been successfully up-scaled and integrated using facies classification. Over 100 rock samples were categorised into six petrofacies classes based on their composition and texture. Cluster analysis was used to classify well log data into five electrofacies units, after careful conditioning and selection of input logs. The result is a direct link between well logs and rock samples. Electrofacies profiles clearly illustrate stratigraphic information previously hidden in the well logs. In addition, well log acoustic rock property relationships based on the new electrofacies classes are found to be better constrained than lithology-based models.Previous facies studies either have been applied at a field scale or have had conventional core for petrofacies calibration. In this paper, I illustrate how facies analysis can be successfully applied at a regional scale with only sidewall sample calibration. Particular attention was given to conditioning the cluster analysis input logs by removing all effects of fluid fill and mechanical compaction, which varied significantly across the study area. A lesson learned from the project was that it is easy to generate misleading results with cluster analysis, so care was taken to select only the most appropriate input logs, and to thoroughly quality control the output electrofacies.

Interpreting shoreline sands using borehole images: A case study of the Cretaceous Ferron Sandstone Member in Utah

To establish borehole image interpretation guidelines in a siliciclastic shoreline environment, this study used unique data from the Ferron Sandstone Member in Utah, where several core holes were drilled next to the outcrop cliff and logged with electrical borehole images. The guidelines include three main components: (1) differentiating depositional elements based on borehole image textures, (2) multiwell stratigraphic correlation and depositional architectures, and (3) ambiguity and data limitations. The stratigraphic interpretation of the image logs is closely correlated with the cores and the outcrops to evaluate the interpretation methodology. The sandstones of upper shoreface, middle shoreface, and channels are differentiated in each well based on a list of depositional textures and sequence characteristics revealed by the images and open-hole logs. The coals, carbonaceous shales, bay fill, and transgression lag deposits are identified as important elements in building the stratigraphic framework. Channels eroding into the shoreface and shoreface pinch-out into delta plains are recognized based on the facies classification and stratigraphic framework. The shoreface progradation directions are drawn through multiwell sequence correlation, paleoflow, and seaward facies transition analysis. In the Muddy Canyon area, the progradation directions of the shoreface parasequences vary from north to east with dominance to the northeast. The complex channel systems with diverse flow directions amalgamated in the delta plains and eroded into the strand-plain shoreface sandstones in most of the regression cycles. In the northern study area, the latest borehole image data revealed the south- or southeastward-prograding Ferron shorelines and the cyclic Blue Gate Member shoreline sequences. The integrated study supports the regional V-shaped Ferron shoreline with oblique delta progradations within the regional eastward transportation into the Mancos Sea.

Diagnosis of the Upper Cretaceous palaeokarst and turbidite systems from the Iranian Persian Gulf using volume-based multiple seismic attribute analysis and pattern recognition

Depositional facies variability with a secondary overprint of Turonian palaeokarst controls the quality of the Cenomanian Mishrif reservoir, the main oil producer in the southeastern Persian Gulf. Subsequent drowning of the prominent area and successive deepening of the basin during the Coniacian and Santonian enabled the deposition of pelagic marls of the Coniacian Laffan Formation and the development of a carbonate turbidite system within the overlying Santonian Ilam Formation. The Ilam Formation occurs within slope and pelagic carbonates and consists of oil-bearing channel-reworked limestone facies. Although high-quality 3D seismic data exist over the Sirri C/D oil fields studied in this paper, it is a real challenge to map the palaeokarst and turbidite deposits in 3D space using conventional seismic interpretation procedures. This work describes a procedure using Paradigm's Seisfacies software for seismic facies classification and uses this to develop a volume-based interpretation of palaeokarst geobodies and sedimentary patterns of the carbonate turbidite. A hierarchical facies classification technique combined with principal component analysis (PCA) is used to analyse a set of seismic attribute volumes that capture the seismic stratigraphic patterns inherent in the data. PCA as a data reduction algorithm greatly optimized the analysis of the attribute volumes while preserving the essential features of seismic character. A hierarchical facies classifier recognized enough variability within the seismic data to reveal details of the associated geological features. This classification method uses multiple 3D volume attributes as input and generates a single 3D seismic facies volume (a synthesis of different attributes). Using this method, interpretative work can focus directly on geological features in 3D space. This study gives new insights into the internal variability of palaeokarst and carbonate turbidite systems in the Sirri C/D oil fields (SE Persian Gulf) that are essential for the estimation of reservoir volume, connectivity and variability.

Comparison of four approaches to a rock facies classification problem

In this study, seven classifiers based on four different approaches were tested in a rock facies classification problem: classical parametric methods using Bayes’ rule, and non-parametric methods using fuzzy logic, k-nearest neighbor, and feed forward-back propagating artificial neural network. Determining the most effective classifier for geologic facies prediction in wells without cores in the Panoma gas field, in Southwest Kansas, was the objective. Study data include 3600 samples with known rock facies class (from core) with each sample having either four or five measured properties (wire-line log curves), and two derived geologic properties (geologic constraining variables). The sample set was divided into two subsets, one for training and one for testing the ability of the trained classifier to correctly assign classes. Artificial neural networks clearly outperformed all other classifiers and are effective tools for this particular classification problem. Classical parametric models were inadequate due to the nature of the predictor variables (high dimensional and not linearly correlated), and feature space of the classes (overlapping). The other non-parametric methods tested, k-nearest neighbor and fuzzy logic, would need considerable improvement to match the neural network effectiveness, but further work, possibly combining certain aspects of the three non-parametric methods, may be justified.

Facies and depositional sequence of the Mesoproterozoic Rohtas Limestone: Eastern Son valley, Vindhyan basin

Paleogeography and process-related facies analysis of the shelf-originated Rohtas Limestone of early Mesoproterozoic age has been attempted. Lithology, structure, microfabric and TOC are the mainstay of facies classification. The Rohtas Limestone consists of seven facies; out of which the organic-rich black shale and the crinkle laminated limestone facies dominates the basal part, reveal distinctive fabric of microbial mat origin and represents outer shelf products. With gradual shoaling, the crinkle laminated limestone facies gains importance and locally turns into the nodular limestone facies through early diagenetic modification. The grey shale facies, poor in organic content, replaces them further upward. The other three facies, viz., the thinly laminated heterolithic facies, typified by close alternations between black shale and limestone, the planar laminated limestone facies and the wavy laminated limestone facies alternate with the grey shale facies, progressively dominating the top part of the succession. While the heterolithic facies records deposition across the paleochemocline, the planar laminated and the wavy laminated limestone facies document deposition in shallow agitated shelf. Confined between a condensed zone below and an unconformity above, the overall coarsening upward Rohtas Limestone records development of a HST.

Three-dimensional sedimentary architecture of Quaternary sand and gravel resources: a case study of economic sedimentology (SW Germany)

Quaternary sands and gravels form important, yet often highly heterogeneous economic deposits. Detailed 3-D analysis of the sedimentary structure and stratigraphy of these deposits allows for an accurate estimation of exploitable material. This paper presents a case study in SW Germany reconstructing the 3-D distribution of glacial sediments based on a high-resolution, process-orientated sedimentary facies classification and lithostratigraphy integrated within the geo-modelling package gOcad. Situated along the maximal ice-extent of the Rhine glacier during the last glaciation, the study area is characterised by a morphologically prominent terminal moraine and its associated sandur, which form the stratigraphically youngest sediments of a glacial basin, partially exposed in two gravel pits. These outcrops helped to reconstruct the complex sedimentary architecture of the northern part of the glacial basin. The regional analysis is based on core data, as well as geoelectric and geomagnetic surveys. All data were integrated into km-scale, high-resolution geological 3-D models, depicting the large-scale dynamics of multiple glacier advances and retreats during the Early to Late Pleistocene. These models allow quantifying the thickness and volume distribution of exploitable sandy gravel and help to evaluate the occurrence of non-exploitable interbedded diamicton horizons. The high quality and quantity of gravels particularly north of the terminal moraine classifies the investigated area as very prospective for raw materials exploitation in the future.

Innovative hybrid algorithm designed to enhance seismic characterization

Pascal Klein and Andy Peloso of Paradigm present a method for multi-disciplinary interpretation of rock and fluid properties by classifying data into seismic facies volumes, used to describe and characterize seismic heterogeneities and properties. Seismic facies analysis has been performed since the use of seismic data for E&P. The traditional method of seismic interpretation involves analyzing the seismic reflection patterns, including configurations (i.e. sigmoidal, hummocky, etc.) and their associated attributes (i.e. amplitude, frequency, continuity, etc.). These patterns and/or configurations were mapped to generate a seismic facies map. This technique, however, is painstakingly slow, very dependent on the interpreter’s skills, and limited to 2D. With the introduction of computer-aided seismic facies techniques, this process is automated and volume-based. These techniques classify all samples from a set of seismic attribute volumes over a user specified zone to produce a volume of classified samples. The multi-attribute seismic classification methodology performs a clustering of the samples of a set of input attributes. These techniques continue to grow and play a vital role in interpretation workflows within the industry. In recent years, there has been an explosion in the number of seismic attributes available for use in E&P. Use of these attributes helps analyze the subsurface and can reveal important features, from regional geology to detailed reservoir properties. To effectively understand the multitude of seismic attributes, Paradigm has developed classification techniques to support the quantitative assessment of exploration targets and to improve reservoir characterization within field development projects (Peloso et al., 2005). The objective of the facies classification process is to describe characteristics within the seismic data and relate these characteristics to the interpretation of rock and fluid properties and help identify quality hydrocarbon accumulations.

Multi-attribute seismic volume facies classification for predicting fractures in carbonate reservoirs

Poststack seismic attributes are beginning to be routinely utilized in the analysis of 3D seismic data for both reservoir development and exploration targets. In addition to conventional geologic and engineering data, seismic attributes can provide valuable insight into how carbonate reservoirs are fractured. Optimized oil production in one prolific Jurassic carbonate reservoir in Saudi Arabia can be affected by fracturing (Pham and Ali, 2003). Proper reservoir management considers that reservoir fluids move differentially along these natural migration pathways. The detailed and accurate mapping of the distribution and extent of these fractures is important for reservoir management. New types of seismic volumetric attributes and better integration of geophysical, geologic, borehole, and engineering data are being adopted to meet this challenge. Volumetric seismic attributes computed from 3D seismic data are being used to map and interpret small faults and fractures that may affect fluid flow. These fractu...

Upper Dalan Member and Kangan Formation between the Zagros Mountains and offshore Fars, Iran: depositional system, biostratigraphy and stratigraphic architecture

Upper Dalan Member and Kangan Formation between the Zagros Mountains and offshore Fars, Iran: depositional system, biostratigraphy and stratigraphic architecture

Enhanced detection of the coral Acropora cervicornis from satellite imagery using a textural operator

The strength of a texture-based classification lies in the fact that it detects spatial patterning as a function of spectral variation within a particular facies class, as opposed to spectral consistency which drives standard probability-driven image classifiers. Following this premise, the Moran's I spatial autocorrelation metric was proven to return values which differed significantly for areas characterised by dense interlocking thickets of the coral Acropora cervicornis versus areas populated by a sparse mixed coral assemblage dominated by Montastrea annularis. The different behaviour of the metric was sufficient to facilitate spatial discrimination of the two assemblages using a supervised classifier with accuracies that surpass the level of prediction offered by standard spectral-based methods. Discrimination was optimum when autocorrelation was evaluated within a moving window with side-lengths ranging between circa. 30–70 m. The discrimination ability is postulated to be linked to intrinsic differences in the spatial-patterning of the two assemblages at scales of tens of metres. The observed patterning can be further related to the growth form and architecture of the differing coral assemblages. The study demonstrates the potential of using kernel-based autocorrelation metrics in unison with satellite data and offers a pertinent tool for monitoring ecologically important coral assemblages that are statistically indistinct using traditional spectral methods.

Remote Sensing of Geomorphology and Facies Patterns on a Modern Carbonate Ramp (Arabian Gulf, Dubai, U.A.E.)

Abstract The occurrence of power law relationships in the spatial distribution of sedimentary lithotopes has been identified in both modern and ancient carbonate depositional bodies. In this study, facies patterns and their spatial relationships are investigated quantitatively in an Arabian Gulf shallow subtidal carbonate ramp setting, using a synergy of IKONOS satellite imagery and vessel-based acoustic bathymetry survey. Three-dimensional reconstruction of the facies distribution on the seabed enabled quantification of relationships between eight dominant facies classes and the association of particular lithotopes to water depth. Fractal behavior was investigated using a combination of boundary- and patch-based metrics, and the spatial distribution of early diagenetically cemented hardgrounds and unconsolidated carbonate sand were shown to display strong fractal properties. In contrast, we show that landscape-scale processes can be treated as essentially deterministic and facies neighborhood patterns are strongly probabilistic. Identifying that the heterogeneity of shallow subtidal carbonate facies scales with a power law within certain thresholds has the potential to serve as a tool in environmental reconstruction in the ancient, where information on the lateral persistence of facies units is difficult to obtain. The findings are relevant to the interpretation of stratigraphic sequences and paleo-depth analysis.

Facies identification within the playa-lakes of the Monegros desert, Spain, from field and satellite data

The Monegros desert and its saline wetlands, called saladas (literally translated as “the salties”), are a unique European landscape of great scientific and ecological value. The saladas (i.e., playa-lakes and other small saline depressions) are dynamic environments; changing their surface morphology on a seasonal–diurnal basis in response to both climate and groundwater fluxes. To depict changes in these natural systems, we have identified five surface facies classes which are detectable both in the field and from remote sensing data. These facies are crucial for describing and promoting the protection of these habitats. Remote sensing has provided worthwhile historical data and additional information that compensate for scarce field records. Combined field and satellite criteria are used to catalog these facies with a new conceptual integration that manages the asynchronism between the field and satellite data. The catalog of facies is intended to be helpful for monitoring these wetlands, and for understanding the current hydrological patterns and trends in the playa-lakes. This work will serve as a baseline for studying the future evolution of the saladas which may soon fall under manmade environmental forces such as increased water input from adjacent newly irrigated lands. It is hoped that identification of these facies will be useful, with minor adaptations, in using more advanced sensors or in studying similar habitats.

Tracking Tertiary delta sands (Urdaneta West, Lake Maracaibo, Venezuela)

This paper illustrates a novel approach (based on seismic facies classification and 3D visualization) for tracking deltaic sand systems in the Urdaneta West producing field, Lake Maracaibo, Venezuela. As part of a major field review (volume evaluation and well planning), the following oil-bearing reservoirs were studied: Among the geologic challenges associated with developing these reservoirs, the thinness of the sand layers and the lack of amplitude response of heavy oil-bearing sands were key. Consequently, a dedicated geophysical workflow was designed to address these issues. It comprises the following steps: This workflow integrated all available seismic attributes (including poststack attributes and impedance data), improved the seismic interpretation, and provided the means to predict sands (in a nonamplitude-supported play). The geophysical results have been compared with the geologic data (cores and logs) and have confirmed the depositional model established by the geologists. The Urdaneta West field is operated by Shell Venezuela on behalf of Petroleos de Venezuela SA (Pdvsa). Even though this field has been producing for nearly 40 years (with more than 100 well penetrations over the …