Facies Groups Research Articles

An integrated approach to the substantiation of the boundary values and the assessment of the character of saturation in the deposits of the Tyumen formation

Background. The Tyumen formation is characterized by the complexity of the structure of deposits and consists of the sediments of different facies groups. To build hydrodynamic models, improve the development system and identify prospective zones, the conditions of sedimentation must be taken into account. Objective. Increasing the reliability of reservoir permeability assessment and clarifying critical resistivities when assessing the nature of saturation, which requires new approaches to petrophysical modeling. Materials and methods. The work uses the results of core studies and interpretation of well-logging data for the JV2 formation considering the facies. Results. The wettability of extracted and nonextracted samples is studied, the dependence of the saturation parameter on the water saturation coefficient is corrected taking into account the wettability of reservoirs, and the relative phase permeabilities are calculated for drainage conditions in the “oil–water” system. Conclusions. An integrated approach makes it possible to clarify the values of permeability, critical resistivities and oil and gas saturation of reservoirs, which can be used to identify prospecting zones when drilling new wells.

The growth and demise of a Middle Miocene carbonate platform in Central Luconia, offshore Malaysia

The evolution and facies distribution of relatively small carbonate platforms, ∼30 km2, are not well documented, even though they are common in ancient and modern carbonate systems. This study investigates depositional facies and evolution of a Miocene carbonate platform in Central Luconia, offshore Malaysia. An integrated approach, including core-described lithofacies, well-log correlation, and seismic analysis, allowed for the mapping of facies through time. The platform was divided into five stratigraphic zones (1 [top], 2 Upper, 2 Lower, 3 Upper, 3 Lower [bottom]) separated by low porosity intervals. Five depositional facies groups were recognized in core samples: (1) bioclastic wacke-packstone facies deposited in a platform interior, (2) bioclastic packstone facies deposited in backreef environments, (3) coral boundstone facies deposited at the reef margin, (4) interbedded shale and carbonate facies deposited on the slope, and (5) argillaceous carbonate facies deposited across the platform as flooding layers. Well D penetrated almost the entire platform, and facies in that well changed upward from mainly bioclastic wacke-packstone at the bottom to mainly bioclastic packstone in the middle to coral boundstone near the top before being covered by interbedded shale and carbonate. Six seismic facies were identified and combined with well data to map the five facies groups through time. The platform shows repeated backstepping of facies at flooding layers followed by aggradation of facies belts up to exposure surfaces, resulting in a long-term backstepping of depositional environments until the platform drowned. Sr-isotopes dating near the top of the platform yielded an age of approximately 12 Ma. This suggests that the platform drowned earlier than other carbonate platforms in Central Luconia (8–10 Ma). More tectonic subsidence in this area during the Middle Miocene is proposed as the main cause of the early demise of this carbonate platform compared to other Luconia platforms.

О ПАЛЕОЭКОЛОГИЧЕСКОЙ ЦЕННОСТИ КОЛЛЕКЦИЙ НИЖНЕФРАНСКИХ БЕСПОЗВОНОЧНЫХ ГЛАВНОГО ДЕВОНСКОГО ПОЛЯ В ФОНДАХ ГОРНОГО МУЗЕЯ

The article describes two groups of facies most widely represented in the collections of Lower Frasnian invertebrates of the Main Devonian Field in the Mining Museum (hardgrounds and pelecypod banks). The presence of three types of hardgrounds has been established, differing in the nature of the original bottom and the time of exposure of each hardground, and hence structural and textural features of rocks and systematic composition of oryctocenoses. The first type is crinoidal limestone with an extensive complex of sclerobionts and traces of bioerosion by Trypanites Mägdefrau, an uneven surface and a visually almost complete absence of impregnation. In hardgrounds of this type, three generations of sclerobionts are distinguished, namely: abiogenic substrates (first), incrustators of the remains of organisms of the first generation (second), and bioerosion organisms (third). The second type is micritic limestone with a smooth glass-type surface, a small complex of sclerobionts and traces of bioerosion by Trypanites Mägdefrau. The third type is pelecypod limestones with an uneven surface, isolated sclerobionts, numerous traces of bioerosion by Trypanites Mägdefrau and strong ferruginous impregnation. For the most widespread hardgrounds of the first type, the presence of specific taphofacies has been established, characterized by good preservation of organic remains of the first generation, an almost complete absence of organic remains of the second generation, and a complete absence of bioerodible organisms. The appearance of such taphofacies is due to the short exposure time of the hardground and the beginning of a rapid process of new accumulation immediately after the appearance of the first organisms of the second generation. The presence of such taphofacies emphasizes the importance of distinguishing taphofacies in certain paleofacies and certain types of oryctocenoses. In the oryctocenoses of pelecypod shells, three morphological and ethological types of cornulitids have been established. The most representative settlements of cornulithids were characteristic of calcareous clay soils with small areas of compacted bottom.

Petrographical and petrophysical characterization of pre-salt Aptian carbonate reservoirs from the Santos Basin, Brazil

Reservoir quality in carbonates is influenced by various factors such as the depositional environment, burial history and diagenesis processes. Understanding these geological heterogeneities is essential for successful petroleum exploration. This study characterizes Brazilian pre-salt reservoirs and aims to understand how their heterogeneity impacts reservoir quality. We analysed carbonate samples from the Barra Velha Formation (Santos Basin) through an integration of petrographical and core plug descriptions, petrographical facies characterization, porosity and permeability measurements, and image analysis to identify the principal controls on porosity and permeability, pore-size distribution, and groups with similar petrophysical properties using the hydraulic flow unit (HFU) concept. Five facies groups were recognized: Spherulitestone (F1); Shrubstone (F2); Intraclastic Grainstone (F3); Intraclastic Packstone, Spherulitestone with mud and Shrubstone with mud (F4); and Shrub–Spherulite Intercalations and Bioclastic Grainstone (F5). The analysis of porosity and permeability showed that their variations are associated with pore type and cementation rate. Greater contributions of inter-aggregate, interparticle and vugular porosity, combined with a reduced amount of cement, results in higher porosity and permeability but an increase in cement tends to reduce the porosity and permeability. Among the facies groups, F2 and F3 exhibited the best porosities and permeabilities, followed by F1, F4 and F5. From image analysis, small pores (1.5 × 10 −5 –0.01 mm 2 ) are the most common in all rocks. However, these small pores contributed significantly to total porosity only in F4 and some samples of F3. For F2 and F3, the large pores (from 0.01 mm 2 to a maximum of 19.62 mm 2 ) are the main contributors, while F5 has a homogeneous contribution. Finally, the data were grouped into five HFUs: HFU1 and HFU2 represent the zones with the best reservoir quality, primarily composed of F2 and F3.

Cyclicity of the Lower Buntsandstein in the eastern part of the Central European Basin: implications for Early Triassic palaeogeography and for geochronological calibration

Lower Buntsandstein small–scale cycles recognized in the Central European Basin (CEB) are readily used for astrochronological calibration of the Early Triassic time scales, although they are not well studied sedimentologically. Three borehole sections from the eastern part of the CEB, forming a south-north transect perpendicular to the basin axis, were studied in terms to better understand the depositional history of the Lower Buntsandstein developed as the Baltic Formation in the studied Polish part of the basin. Eleven sedimentary facies were recognized, based on lithological and sedimentological investigations of 655.7 m of drill cores from the Otyń IG 1, Gorzów Wielkopolski IG 1 and Kamień Pomorski IG 1 boreholes. The facies can be grouped according to a lithological criterion into facies of predominantly siliciclastic lithology (including 9 facies types) and facies of predominantly carbonate lithology (including 2 facies types). Facies analysis allowed to distinguish 8 facies associations of: 1) alluvial fan, 2) playa, 3) sandy-muddy coastal plain, 4) embayment and distal delta, 5) lagoon, 6) sand bars or shoals, 7) ooidal shoals or bars, and 8) offshore. Deepening-upward (DC) and shallowing-upward (SC) sedimentary cycles were recognized in parts of the Baltic Formation, with DCs dominating in the southernmost located Otyń IG 1, and SCs dominating in Gorzów Wielkopolski IG 1, located in the axial part of the basin. Symmetrical cycles are very rare. The statistical significance of the sedimentary cycles is relatively low according to Markov-chain analysis conducted with the phpSedistat software of Stanova et al. (2009). Analysis of small–scale cycles performed on well logs of investigated boreholes and additional boreholes in the vicinity of Otyń IG 1, implementing the earlier study of Becker (2005), showed that the correlation of well-log cycles (GR cycles) and sedimentary cycles is not obvious. GR cycles can be roughly correlated with lithological carbonate–siliciclastic cycles (c-s cycles), reflecting alternations of facies groups of predominantly carbonate and siliciclastic lithology. Calibration of GR cycles to earlier magnetostratigraphic results of Nawrocki (1997) and Becker and Nawrocki (2014) showed that neither the boundaries of GR cycles serve as reference horizons, nor the cycles document equal time periods. All existing depositional models of the Lower Buntsandstein were discussed, stressing the possible simultaneous interaction of allochthonous and autochthonous processes. Moreover, the tectonic overprint of the Central European Basin system during the Early Triassic should be taken into account. The presented results suggest that the Lower Buntsandstein cyclicity of the CEB cannot serve as a basis for astrochronological analysis.

Depositional Architecture and Reservoir Quality Assessment of Abu Roash (G) Dolomite, as a Low Resistivity Pay, Razzak Oilfield, Western Desert, Egypt.

Abu-Roash (G) dolomite (A/R-G) is considered one of the most prolific oil-bearing reservoirs in the Western desert. In this study, Razzak Oilfield was selected to investigate the geological and petrophysical findings of these successions that were assigned stratigraphically to the upper Cretaceous (Late Cenomanian), in the Alamein basin. Sedimentologically, three main facies groups have been recognized in the studied successions of A/R-G and include dolostone, limestone and mudstone facies; and depositional; are divided into three parts: A) Back-reef to reef crest (Reefal depositional setting) - dolostone facies group; graded to B) Inner-ramp of limestone / dolomitic limestone facies types; then C) mud-flat (intertidal setting) of calcareous mudstone facies type. Petrophysically, most of the recorded pore sizes in the dolomite zone are mesopores (≈1 micron), with scattered macropores (2-10 microns), as identified by MICP on some selected 1.5” core plugs. In general; A/R-G dolomite displays low resistivity pay (high conductivity) due to: A) The heterogeneity of moldic and vuggy pore size distributions (macropores); associated with the dominant intercrystalline-dolomite mesopores; and B) Fe-rich minerals that increase the conductivity; where most of the identified dolomite crystals are secondary, late-diagenetic stage ferroan dolomite; and confirmed that petrographically by thin-section analysis.

Determination of the conditions of sedimentation of the Jurassic deposits of the Karaton field based on a comparison of electrofacies and sedimentological description of the core

This paper presents the results of lithofacies analysis of log curves and sedimentological description of the core material of wells from the Karaton field to determine the environmental condition and determine the similarity of the behavior of log curves. The field is located in the Karaton-Tengiz zone of uplifts, which are characterized by a rather complicated environmental conditions. Based on typical models of facies groups and a description of the core material of the Jurassic deposits, it was possible to identify zones of development of sandy deposits and determine the main environmental condition. Keywords: lithology; sedimentology; facies; electrofacies; generic model; depositional environment.

Impacts of Depositional Facies and Diagenesis on Reservoir Quality: A Case Study from the Rudist‐bearing Sarvak Formation, Abadan Plain, SW Iran

AbstractAn integrated geological‐petrophysical analysis of the rudist‐bearing sequence of the Cretaceous Sarvak Formation is given one giant oilfield, and provides an improved understanding of this main reservoir in the Abadan Plain, in the Zagros Basin, SW Iran. The main objective of this study is to evaluate reservoir potential of the Sarvak Formation, and then to utilize the calibrated well log signature to correlate reservoir potential in un‐cored wells. Eight main facies are recognized and categorized in five facies groups: lagoon, shoal, rudist‐biostrome, slope, and shallow open marine, deposited on a shelf carbonate platform. Given the distribution of diagenetic products and their effects on pore systems, three diagenetic facies namely, (DF‐1) low dissolution and cementation; (DF‐2); high dissolution; and (DF‐3) high cementation are differentiated. The initial sedimentary characteristics in combination with distribution of diagenetic products play an important role in reservoir quality heterogeneity. The effect of diagenetic processes related to disconformities mainly depends on the facies nature below these surfaces. Grain‐dominated facies of shoal and rudist debris, observed below the Cenomanian–Turonian disconformity, are mostly characterized by high dissolution and interconnected pore systems. Finally, depositional and diagenetic facies in the studied wells are correlated by petrophysical well log data, leading to distribution of the reservoir zones. Data obtained can be utilized for efficient reservoir characterization of the Sarvak Formation and its equivalent units in the Arabian Plate.

Факторный анализ эффективности бурения боковых стволов с горизонтальным окончанием

Introduction. One of the ways to increase oil recovery at the late stages of development of mature fields is the drilling of lateral shafts with horizontal sections. Hard-to-recover residual oil reserves are mainly concentrated in the marginal zones of formations with small oil-saturated thicknesses and low permeability. The article studies the efficiency of drilling lateral horizontal shafts and the resulting additional oil production by multifactor analysis with account of geological heterogeneity and technological features. Materials and research methods. The effectiveness of the results obtained when drilling lateral horizontal shafts depends not only on the choice of a point on the map of the oil reservoir, but also on the structure of the residual hard-to-recover oil reserves and the filtration and reservoir properties of the reservoir. The article presents an analysis of the obtained results of drilled horizontal lateral shafts, the placement of which was worked out with account of the facies conditions of formation and geological heterogeneity. Research results and their discussion. The authors analyzed the operation of lateral horizontal shafts from the moment of their launch, which makes it possible to determine the dependence of the efficiency of their work on the joint or separate operation of the AB1 3 and AB2 layers, taking into account the geological features of sedimentation and differences in filtration and capacitance properties. To select prospective wells for cutting the lateral trunk, groups of facies of continental genesis were identified, with which sand bodies are associated. Conclusion. The dependency of technological parameters of the lateral second shafts on geological features is traced. On the basis of factor analysis directions for further approaches to the drilling of the UW are specified. Monitoring of the actual data determined the factors affecting the efficiency of the input technological indicators of the wells.

Classifying Facies in 3D Digital Rock Images Using Supervised and Unsupervised Approaches

Lithology is one of the critical parameters influencing drilling operations and reservoir production behavior. Well completion is another important area where facies type has a crucial influence on fracture propagation. Geological formations are highly heterogeneous systems that require extensive evaluation with sophisticated approaches. Classification of facies is a critical approach to characterizing different depositional systems. Image classification is implemented as a quick and easy method to detect different facies groups. Artificial intelligence (AI) algorithms are efficiently used to categorize geological formations in a large dataset. This study involves the classification of different facies with various supervised and unsupervised learning algorithms. The dataset for training and testing was retrieved from a digital rock database published in the data brief. The study showed that supervised algorithms provided more accurate results than unsupervised algorithms. In this study, the extreme gradient boosted tree regressor was found to be the best algorithm for facies classification for the synthetic digital rocks.

Reservoir characterization and multiphase flow property in the upper Minnelusa sandstone: Implication for geological carbon storage

This report summarizes the reservoir characterization [Wang et al., J. Hydrol., 2022] and multiphase flow property [Kou et al., J. Hydrol., 2021] in a target deep saline aquifer, upper Minnelusa sandstone in Wyoming. Multiscale petrophysical characterization and flow unit classification were carried out to identify two different facies groups: cross-bedded and massive sandstone. Based on the rock typing results, two representative core samples were selected accordingly to conduct coreflooding experiments. Results illustrate that the sub-core scale heterogeneity significantly affects CO2 -brine multiphase flow properties. As a result, the subcore scale heterogeneity should be considered during CO2 injection to reduce the uncertainties in storage and fluid flow. Cited as: Kou, Z., Wang, H., Alvarado, V. Reservoir characterization and multiphase flow property in the upper Minnelusa sandstone: Implication for geological carbon storage. Advances in Geo-Energy Research, 2022, 6(6): 535-536 . https://doi.org/10.46690/ager.2022.06.10

Effect of the depositional environment on the formation of tar-rich coal: A case study in the northeastern Ordos Basin, China

Tar yield, as a basic evaluation index of tar-rich coal, is unclear to be affected by the depositional environment. In this work, the vertical variations in tar yield, macerals, and major/trace elements were investigated for highly volatile bituminous coal in the Ordos Basin, China, to analyse the effect of the depositional environment on the tar-rich coal distribution. The results show that the tar yield more than 7% (tar-rich coal) accounts for 70% in this formation, which formed in a depositional environment with a stable supply of terrestrial sediments, a warm and humid climate, and weakly reducing to reducing conditions. For the coal facies, all samples were distributed into two groups of coal facies, with the first group containing limnic, dry forest swamp, wet forest swamp and another group contains bog, forest bog. Moreover, limnic and bog with less woody tissue and a higher water table contribute to the higher tar yield of coal. Correspondingly, the vitrinite content and the gelation index (GI) were positively correlated with tar yield, and the tissue preservation index (TPI) and vegetation index (VI) were negatively correlated with tar yield. The inorganic composition, the ash yield, which is mainly composed of SiO2 and Al2O3, reduced the tar yield. CaO and MgO in small proportions promote the tar yield of coal due to catalytic effects. The relationship between tar yield and the parameters Sr/Ba, Sr/Cu, Cu/Zn, (Cu + Mo)/Zn, U/Th, Ni/Co, δU, Ce/La, δCe, and δEu are also discussed here. It was concluded that the paleoclimate had little effect on the tar yield, while the paleoreduction conditions had an obvious influence on the tar yield. The depositional environment with higher reduction and lower salinity conditions was conducive to the increase in tar yield of coal. This work aims to accurately identify and predict tar-rich coal based on its depositional environment, which provides guidance for its exploration and development.

Application of Machine Learning for Lithofacies Prediction and Cluster Analysis Approach to Identify Rock Type

Nowadays, there are significant issues in the classification of lithofacies and the identification of rock types in particular. Zamzama gas field demonstrates the complex nature of lithofacies due to the heterogeneous nature of the reservoir formation, while it is quite challenging to identify the lithofacies. Using our machine learning approach and cluster analysis, we can not only resolve these difficulties, but also minimize their time-consuming aspects and provide an accurate result even when the user is inexperienced. To constrain accurate reservoir models, rock type identification is a critical step in reservoir characterization. Many empirical and statistical methodologies have been established based on the effect of rock type on reservoir performance. Only well-logged data are provided, and no cores are sampled. Given these circumstances, and the fact that traditional methods such as regression are intractable, we have chosen to apply three strategies: (1) using a self-organizing map (SOM) to arrange depth intervals with similar facies into clusters; (2) clustering to split various facies into specific zones; and (3) the cluster analysis technique is used to identify rock type. In the Zamzama gas field, SOM and cluster analysis techniques discovered four group of facies, each of which was internally comparable in petrophysical properties but distinct from the others. Gamma Ray (GR), Effective Porosity(eff), Permeability (Perm) and Water Saturation (Sw) are used to generate these results. The findings and behavior of four facies shows that facies-01 and facies-02 have good characteristics for acting as gas-bearing sediments, whereas facies-03 and facies-04 are non-reservoir sediments. The outcomes of this study stated that facies-01 is an excellent rock-type zone in the reservoir of the Zamzama gas field.

Conditions of sedimentation and distribution of organic matter in the Lower-Middle Jurassic complex of the South-Western part of the West Siberian oil and gas basin

The article is devoted to the variation of generation potential of the Lower-Middle Jurassic organic matter in the Karabash area (South-Western part of the West Siberian basin) depending on facies and sedimentary cyclisity. Based on geochemical and lithological core studies, specific geochemical features of organic matter established for main facies groups of Early-Middle Jurassic in the study area. The best generation potential inherent in deposits of swamps, swampy floodplains and tidal plains. These facies groups characterized by predominance of the continental organic matter and considered to gas source rocks. However, macerals composition, kinetic spectra and biomarker analysis show the presence also of marine organic matter. Some facies groups, such as flooded swamps and swampy floodplains has potential to generate hydrocarbons due to preservation of liptinites with high hydrogen index. Cyclic analysis with basics of sequence stratigraphy of the continental deposits allow tracing the correlation between generation potential and relative sea level changes.

Typification of the deposits of the Tyumen Formation according to the degree of hydrodynamic conditions of sedimentation to create a petrophysical model and differentiated interpretation of well log data

The article considers facies analysis and the application of its results for the typification of rocks of the Tyumen Formation. The aim of the article is to create algorithms for the differentiated interpretation of geophysical studies of well log data of the Tyumen formation based on a detailed study of the core. Based on core studies, as well as geological, geophysical data and field information on the Tyumen Formation of some deposits in Western Siberia, the main groups of facies were identified, reflecting the hydrodynamic activity of sedimentation conditions: group 1 – high-dynamic conditions, group 2 – transitional conditions, group 3 – low-dynamic conditions. On the basis of this typification, petrophysical models of the deposits of the Tyumen Formation were created: petrophysical functions were built with differentiation by facies zones, boundary values of petrophysical parameters were obtained to identify reservoirs of different sedimentation conditions, algorithms for differentiated interpretation of well log data were proposed, also based on test results and field geophysical survey, differences in field characteristics for different sedimentation conditions were revealed, linear oil reserves were calculated using a new petrophysical model. The development and implementation of an integrated approach to the interpretation of well log data, taking into account the conditions of sedimentation, make it possible to increase the reliability of determining the properties of the reservoirs of the Tyumen Formation, and the efficiency of calculating the oil reserves.

Testing rebound hardness for estimating rock properties from core and wireline logs in mudrocks

Rebound hardness (RHN) has become a widely applied rock mechanical parameter in the petroleum industry due to economic and convenient testing procedures. However, the RHN data can be under-utilized when lacking detailed integration with other rock properties. Targeting the unconventional “Mississippian Limestone”/STACK play in north-central Oklahoma, USA, and outcrops of the Vaca Muerta Formation in Argentina, this study aims to test the value of RHN in predicting rock properties. RHN data from the “Mississippian Limestone”/STACK cores show correlative trends with mineralogy and porosity. All the correlations show clusters by facies groups with overlaps being present among different clusters. Within these correlations, mineralogy and porosity show variable significance levels in affecting RHN among different facies groups. Leverage analysis suggests that bulk clay content and porosity exhibits the most significant control on RHN for the MISS/STACK data, with variabilities being present in different facies groups. These partitioning patterns of data by facies groups imply that facies variability affects the statistical pattern and that RHN can assist in rock typing, and hence, sample selection for detailed laboratory analyses. Forward regression analysis reveals that the confidence level of predicting porosity and sonic velocity can be enhanced using RHN. In addition to the correlative trends between RHN and rock properties, results from forward regression analysis indicate that RHN can help estimate these properties in a faster, cheaper, and non-destructive way relative to conventional laboratory analyses. Correlative trends are also observed in Vaca Muerta data, suggesting the value of RHN in characterizing similar types of mixed carbonate-siliciclastic reservoirs. • Rebound hardness (RHN) can help estimate bulk clay content, porosity, sonic velocity, and dynamic elastic parameters. • RHN may help estimate static rock mechanical properties, but more data are needed for further investigation. • RHN cluster by facies and thus can help design an integrated rock typing and sample selection scheme. • Multivariate methods indicate RHN is affected by multiple factors and can help apply RHN to predict rock properties. • A facies-based, integrated approach with a well-designed testing protocol is critical for using RHN in reservoir analysis.

Multiscale petrophysical characterization and flow unit classification of the Minnelusa eolian sandstones

Integration of petrophysical and geological information is critical to simulation of subsurface carbon storage (GCS). In this sense, two depositional facies were identified from the core description and well-log interpretation, namely massive (MS) and cross-bedded (CB) facies groups. Additionally, pore-scale characteristics were studied by a combination of techniques, e.g. Nuclear Magnetic Resonance (NMR) and mercury intrusion capillary pressure (MICP). Scanning electron microscope (SEM) and petrographic analyses show that the pore structure is dominantly controlled by the depositional environment and dolomite cementation. NMR-T2 distributions of MS and CB facies show triple and quadruple modes, respectively. In addition, MICP of high- and low-permeability MS facies samples, and their CB facies group mixtures were collected. The MS sample pore-throat size distribution is uni-modal, while the triple-modal characteristic of the mixtures indicates heterogeneous pore structures at the sub-core scale for CB facies. The reliably estimates of porosity and permeability for both facies groups via NMR techniques and the MLR (Multiple Linear Regression) approach demonstrate the applicability of these techniques to eolian sandstone. Moreover, irreducible water saturation via the T2-cutoff method correlates strongly with T2LM instead of porosity. Finally, the rock quality index and flow zone indicator were calculated based on Combinable Magnetic Resonance (CMR) log interpretations. This provides direct connection to properties measured in the well. Four flow units were classified for both facies groups. Results show that better reservoir quality with significant heterogeneities is observed in the CB facies. This study highlights the importance integrating multiscale petrophysical properties including facies, pore architecture and diagenesis analysis with core- to log-scale property characterization. The results herein validate our reservoir characterization and flow unit classification in eolian reservoirs.

Ландшафтообразующие процессы, факторы и ландшафтная структура юга Селенгинского среднегорья

The article studies the landscape structure of the territory of south the Selenga middle mountains. The introduction to the article defines the concepts of landscape structure, factor-dynamic system, and reveals the essence of the structural-dynamic approach to the study of geosystems. The section "Object and methods of research" describes the natural conditions of the south of the Selenga middle mountains and methods of landscape research. The results of the study present an analysis of the main landscape-forming processes, factor-dynamic series, and dynamic categories of geosystems, as well as a map of the landscape structure of the study area. A structural-dynamic (factor-dynamic) approach to the analysis of landscape structure was implemented using GIS technologies based on remote sensing data, field research materials, maps of various contents and literary information. The leading landscape-forming processes and the main factors that influence the formation of the landscape structure are shown. As a result of the conducted research, a landscape map of geosystems of the topological hierarchical level was constructed, which shows the types of geosystems (geomes, classes and groups of facies) reflecting the factor-dynamic structure of landscapes. For the mountains of the south of the Selenga Middle Mountains, the leading landscape-forming processes are gravity-slope, slope water-erosion, fluvial and aeolian processes that determine the formation of lithomorphic, alluvial-hydrolithomorphic and psammo-lithomorphic factorial-dynamic series of geosystems (facies classes). For plains, the leading landscape-forming processes are slope water-erosion, alluvial, lacustrine and aeolian, forming lithomorphic, alluvial-hydromorphic and psammomorphic series of facies.

Geosystems of the Primorsky ridge (Baikal region) — classification and mapping

In this article, the application of landscape approach for geosystem classification and mapping was discussed on the example of the landscapes of the Primorsky ridge (Baikal region). Authors of this study used the geosystem concept formulated by V. Sochava and method of factorial-dynamical series of facies developed by A. Krauklis for modeling landscape structure of study area. The basis for the development of a hierarchical classification of geosystems was the data of fieldwork at 70 plots. The ordination of the plots by three parameters (topographic wetness index, slope steepness and humus thickness) was carried out using the method of ternary plots to group geosystems into classes and determine their dynamic state. The landscape map was compiled at the local scale (1:50 000) based on fieldwork, DEM, and remote sensing data. As a result, 14 groups of facies were identified in the study area. They were represented by both climax and succession stages, as well as anthropogenic modifications. The main classes of facies formed under the influence of local environmental factors were revealed using factor-dynamic analysis. They are represented by the following dynamic series: sublithomorphic, subhydromorphic, and subxerolithomorphic. The 66 % of the study area is occupied by landscapes of the sublitomorphic series.

Classification and evaluation of tight sandstone reservoirs based on diagenetic facies: a case study on Chang 6 reservoir in the center-west Ordos Basin

AbstractTight sandstone reservoirs dominated by are developed in the Chang 6 oil layer group of the Yanchang Formation in the central-western part of the Ordos Basin. Featuring the lacustrine delta facies, Chang 6 formation in the center-west area of Ordos Basin shows an increasing petroleum reserve expectation. Its exploitation practice, however, has many problems caused by tight sandstone reservoir features. According to diagenetic and pore analysis, the diagenetic facies in the study area are grouped into four types: chlorite-film-intergranular-pore, feldspar-dissolution, clay-cemented-micropore, carbonate-cemented-tightness for their obvious differences in mineral feature and pore evolution. By introducing the comprehensive classification parameter synthesized from 9 other parameters, the reservoir quality is divided up into four levels: I(Feci > 1), II(3 ≤ Feci ≤ 7), III(-2 ≤ Feci ≤ 3), IV(Feci ≤ -2). The reservoir quality division matches well with the diagenetic facies group. To decide the diagenetic type and reservoir quality division in all wells, the logging data are utilized with the Fisher discriminant method, which has obtained a good performance. The method enables the reservoir quality analysis expanding to all wells from samples, which is helpful for exploitation of the study area.