Sedimentary Facies Characteristics Research Articles

An Ediacaran glacial deposit in southern margin of the North China Craton: The Luoquan Formation—sedimentology, geochronology and provenance

The end of the Neoproterozoic global ice age has promoted the evolution of the Earth's surface system and initiated the ‘Great Explosion of Life’. Glaciation deposits provide valuable insights into the extreme climate conditions. In the southern margin of the North China Craton (NCC), an Ediacaran glacial deposit named ‘Luoquan Formation’ has been recently described in Luonan County, Shaanxi Province. It has significant characteristics of dark grey and black glacial deposits. Through extensive research in sedimentology, geochemistry and geochronology, the glacial sedimentary evolution sequence of the Luoquan Formation has been established. This research also help to define the age of the formation and reveal its provenance and sedimentary environment. The study reveals that four lithofacies associations were identified in the Luoquan Formation: diamictites, carbonates, dropstone‐bearing rock and black shale. The Luoquan Formation has experienced three cycles of glacial advance–retreat. Sedimentological evidence suggests that the sedimentary environments of the Luoquan Formation evolved from subglacial (diamictite) to intertidal, then to intertidal lagoon, or from subglacial deposits to shoreface (inner shelf, subtidal), then to deep water basin and fine‐grained turbidite and ice‐rafting. The age of the Luoquan Formation is estimated to be 562–550 Ma constrained by indirect chronological and paleontological data, maybe representing an Upper Ediacaran glaciation that occurred later than the Gaskiers glaciation. The overall age profile of detrital zircons from the Luoquan Formation can be divided into six groups, ranging from 1.1 to 1.6, 1.85 to 1.95, ~2.1, ~2.3, ~2.5 and 2.65 to 2.9 Ga. These age groups are consistent with the Archean to Meso‐Neoproterozoic magmatic–tectonic events in the southern margin of NCC, indicating they are ascribed to an origination directly from the southern margin of NCC. The Luoquan Formation exhibits the characteristics of isochronous and different sedimentary facies, with the glacial front moving from north to south. The discovery of Luoquan Formation in Lianshuigou section not only reflects the important significance of the restoration and reconstruction of the Ediacaran ice age, paleoenvironment and palaeogeography of the NCC but also provides significant evidence to support the further subdivision and correlation within the Ediacaran glacial deposits globally.

An Ediacaran glacial deposit in southern margin of the North China Craton: The Luoquan Formation—sedimentology, geochronology and provenance

The end of the Neoproterozoic global ice age has promoted the evolution of the Earth's surface system and initiated the ‘Great Explosion of Life’. Glaciation deposits provide valuable insights into the extreme climate conditions. In the southern margin of the North China Craton (NCC), an Ediacaran glacial deposit named ‘Luoquan Formation’ has been recently described in Luonan County, Shaanxi Province. It has significant characteristics of dark grey and black glacial deposits. Through extensive research in sedimentology, geochemistry and geochronology, the glacial sedimentary evolution sequence of the Luoquan Formation has been established. This research also help to define the age of the formation and reveal its provenance and sedimentary environment. The study reveals that four lithofacies associations were identified in the Luoquan Formation: diamictites, carbonates, dropstone‐bearing rock and black shale. The Luoquan Formation has experienced three cycles of glacial advance–retreat. Sedimentological evidence suggests that the sedimentary environments of the Luoquan Formation evolved from subglacial (diamictite) to intertidal, then to intertidal lagoon, or from subglacial deposits to shoreface (inner shelf, subtidal), then to deep water basin and fine‐grained turbidite and ice‐rafting. The age of the Luoquan Formation is estimated to be 562–550 Ma constrained by indirect chronological and paleontological data, maybe representing an Upper Ediacaran glaciation that occurred later than the Gaskiers glaciation. The overall age profile of detrital zircons from the Luoquan Formation can be divided into six groups, ranging from 1.1 to 1.6, 1.85 to 1.95, ~2.1, ~2.3, ~2.5 and 2.65 to 2.9 Ga. These age groups are consistent with the Archean to Meso‐Neoproterozoic magmatic–tectonic events in the southern margin of NCC, indicating they are ascribed to an origination directly from the southern margin of NCC. The Luoquan Formation exhibits the characteristics of isochronous and different sedimentary facies, with the glacial front moving from north to south. The discovery of Luoquan Formation in Lianshuigou section not only reflects the important significance of the restoration and reconstruction of the Ediacaran ice age, paleoenvironment and palaeogeography of the NCC but also provides significant evidence to support the further subdivision and correlation within the Ediacaran glacial deposits globally.

A hybrid model based on unsupervised learning for seismic response feature extraction and gas-bearing reservoir prediction using longitudinal and transverse waves seismic data in low-degree exploration areas: A case study

Predicting gas-bearing reservoirs from seismic data is a major field of research. Recently, deep learning has been applied to achieve better results; however, challenges such as high sample demand remain. Drilling data are often insufficient, and gas-bearing sample data are difficult to acquire in large quantities, particularly for low-level (new) exploration areas, which limits gas-bearing reservoir prediction by supervised learning. Therefore, this study proposes a hybrid model using unsupervised learning to extract seismic response features and predict gas-bearing reservoir distribution. First, seismic attribute analysis was used to extract as many longitudinal and transverse waves seismic attributes as possible to provide richer information about gas-bearing reservoirs. However, abundant seismic attributes contain a large amount of redundant information, thereby increasing computation time. Thus, principal component analysis (PCA) was used to reduce the dimensions of the extracted multi-component seismic attributes, remove redundant information, and obtain the most important characteristics that are sensitive to gas-bearing reservoirs. The sensitive seismic attributes obtained after the PCA were fed into a self-organizing neural network (SOM) for unsupervised learning. Neurons in the SOM compete with each other to optimize their own features and extract reservoir-sensitive seismic response features for prediction. To evaluate the proposed method, it was applied to part of the Marmousi2 model and real seismic data for validation. The following results were obtained: (1)The results of the synthetic data test results not only proved the effectiveness of the proposed method, but also showed that the method has strong noise resistance capability and is suitable for predicting gas-bearing reservoirs with low signal-to-noise ratio seismic data; (2) Based on the drilling data and sedimentary facies characteristics in the test area, the actual 3D seismic data test results showed that there are four wells that match the predicted results, and the distribution boundaries of the gas-bearing reservoirs they depict are relatively clear; (3) In low exploration areas (areas with few or no wells), this method is important as a guide to hydrocarbon exploration.

Study on Sedimentary Facies and Reservoir in Taiyuan Formation in Qingshimao area

Recent exploration results show that there is an industrial airflow in Taiyuan Formation in Qingshimao area of Ordos Basin. The Marine quartz sandstone reservoir developed in Taiyuan Formation is the target reservoir after He 8 and Shan 1 Members in Qingshimao area. In order to study the sedimentary facies characteristics of Taiyuan Formation in Qingshimao area, this paper analyzed the well logging, single well facies and connected well facies on the basis of core observation. In addition, using the data of casting thin section, scanning electron microscope and cathode luminescence, the response relationship between sedimentary facies and well logging facies is established, thus the sedimentary facies in the study area is divided and the reservoir characteristic is studied. The results show that the Taiyuan Formation mainly developed barrier coastal sedimentary facies, which can be subdivided into four sub-facies: marsh, tidal flat, barrier island and lagoon. Lithic quartz sandstone is mainly developed in Taiyuan Formation, followed by quartz sandstone and lithic sandstone. The reservoir space types include intergranular pores, dissolved pores, intergranular pores and micro-fractures. Extra-ultra-low porosity and ultra-low permeability reservoir is developed in Taiyuan Formation in study area.

乌什城南剖面沉积相类型及特征

乌什城南剖面沉积相类型及特征

Sedimentary Facies, Paleogeography, and Depositional Models of the Middle–Late Permian in the Sichuan Basin, Southwest China

This study focuses on the analysis of the sedimentary facies of the Middle–Late Permian, including the Qixia, Maokou, Wujiaoping/Longtan, and Changxing/Dalong Formations, in the Sichuan Basin, southwest China. Integrating drilling data and field outcrop data, various sedimentary facies indicators were employed to define eight sedimentary facies types in the Sichuan Basin during the Middle–Late Permian, namely, mixed tidal flat, tidal flat, restricted platform, open platform, platform margin, slope, basin, and volcanic facies. Detailed facies analysis was conducted on selected well logs, and sedimentary facies distribution maps were compiled for different time intervals, establishing depositional models. During the Qixia to Maokou stages, an extensive open platform was developed in the Sichuan Basin, accompanied by shallow intra-platform shoals. Towards the west along the Dayi–Ya’an line, platform margins were developed, followed by slope facies and basin facies in a northwest direction. During the Changxing stage, the Kaijiang–Liangping fault block subsided, forming the “Kaijiang-Liangping” paleochannel, which controls reef–shoal deposition in the region. This study provides comprehensive insights into the sedimentary facies characteristics and depositional environments of the Middle–Late Permian in the Sichuan Basin, contributing to the understanding of the regional sedimentary history and geological evolution.

Intragranular fractures within tight sandstone reservoirs in the Hangjinqi area, northern Ordos Basin, China: Morphology, intensity and controlling factors

Microfractures play a critical role in the evaluation and exploitation of unconventional reservoirs. Tight sandstones of the He-1 Member in Shihezi Formation in Hangjinqi area are rich in intragranular fractures while morphology, intensity and factors controlling the development of these fractures are still unclear, which limits the exploration and development of tight gas in the study area. Therefore, thin sections observations, porosity and permeability measurements, minerals composition, along with intragranular fracture areal density of the target layer was carried out to obtain a comprehensive understanding of the formation. Based on this data, by considering effective pressure, mineral composition and grain size as main controlling factors, 16 synthetic cores were made and their fracture density was also documented. Integrating burial history and sedimentary facies as well as comparison between the natural cores with synthetic ones, showed that both natural and synthetic cores developed two types of fractures: simple and complex. Most fractures in natural cores are filled with clay minerals while in the synthetic cores fractures are open with a large aperture. Furthermore, average fracture density of natural and synthetic cores is found 5.27 × 10−3 μm/μm2 and 0.61 × 10−3 μm/μm2, respectively. Additionally, it was found that intragranular fractures are the result of intense compaction during eodiagenesis. Moreover, fracture density is positively correlated with grain size and effective pressure but negatively correlated with clay mineral content. The correlation between fracture density and effective pressure as well as clay minerals is almost logarithmic. Considering the characteristics of sedimentary facies, reservoirs developed in braided bar and channel should be rich in fractures and those in floodplain having fewer fractures. It was concluded that intragranular fractures are generally found in layers that subside quickly and have had low temperature gradient causing an indirect improvement of the porosity but directly enhancing the permeability. As a result, reservoirs should have better petrophysical properties in braided bar and channels. Collectively, this study enables us to illustrate the controlling factors on the development of intragranular fractures and their implication for tight reservoirs in the Ordos Basin and other basins with similar settings around the world.

Hydrocarbon potential assessment of the lacustrine fan delta reservoirs in the Lower Cretaceous syn-rift Xing’anling Formation in the Beier Sag, Hailar Basin, Northeast China

Efficient exploration and development of oil and gas resources in complex geological environments continue to pose significant challenges for the energy industry. The localization and extraction of reservoirs in basins with complex structures, developed faults, and scattered sedimentary sand bodies are topics of international interest. One such basin, the Hailar Basin in northeastern China, represents a complex geological environment with heterogeneous distributions of oil and gas reserves, along with variable reservoir conditions, leading to challenges in hydrocarbon exploration and extraction. The Sudeert oil field, situated within this basin, is known for its high productivity; nevertheless, the underlying factors responsible for its success are not yet fully comprehended. Based on seismic, logging, and core data from the Sudeert oil field, as well as previous research, this study comprehensively analyzed the sedimentary environment, sedimentary facies characteristics, sand body distribution patterns, vertical stacking relationships of sand bodies, and hydrocarbon accumulation potential of the oil reservoirs in the Lower Cretaceous Xing’anling Formation in the Sudeert oil field. The Xing’anling Formation I and II oil reservoirs are deposited in a fan-delta front sedimentary environment, and the sedimentary microfacies that are conducive to the development of reservoir sand bodies include underwater distributary channels, underwater natural levees, estuary dams, front silt beds, and turbidite sands. Among them, the underwater distributary channel microfacies is the main depositional facies for the development of reservoir sand bodies. Three major depositional patterns of fan lobes can be identified within this depositional system: 1) isolated, 2) contact, and 3) superimposed lobes. Different combinations of lobes developed in different blocks and resulted in different sand body depositional patterns. The isolated lobes mainly developed in the western oil-producing (B28 block) due to the scarcity of sand and slowly increasing accommodation space. The contact lobes mainly developed in the central oil-producing block (B14 block) due to sufficient sediment supply and steadily increasing accommodation space across a wide area. The superimposed lobes mainly developed in the southeast oil-producing block (B16 block) due to sufficient sediment input and steadily increasing accommodation space within a restricted area. In the whole study area, the superimposed lobe pattern is the most favorable depositional pattern and forms the highest-quality reservoirs because of the high degree of sand body connectivity. These results also highlight the utility of sedimentary patterns and sand body assemblage studies for the oil exploration and development of similar rifted basins.

Stratigraphical, microfacies, and ichnological characteristics and depositional environments of the Permo‒Carboniferous Aheimer Formation, western side of the Gulf of Suez, Egypt

The palaeoenvironments of the upper Palaeozoic succession in the eastern foot slopes of the Northern Galala Plateau, west of the Gulf of Suez, Egypt, are interpreted based on a detailed study of the sequence-stratigraphic framework, sedimentary facies and trace fossils. The upper Carboniferous–lower Permian Aheimer Formation has been studied in its type section exposed in Wadi Aheimer. Three unconformities bound four 3rd-order depositional sequences, including the upper Carboniferous DS NG 1, and the lower Permian DS NG 2‒4. These sequences are correlated with their counterparts on the North African and Arabian plates. The sedimentary facies characteristics indicate palaeoenvironments ranging from fluvial, estuarine, intertidal, shallow subtidal, shoreface to offshore transitional settings. The abundant and diverse ichno-assemblages are composed of horizontal, vertical and sub-vertical traces. At least 26 ichnotaxa have been identified, representing suites of the Glossifungites, proximal Cruziana, and proximal-archetypal Cruziana ichnofacies. Ichnofabric analysis revealed three distinct ichnofabrics: Tisoa, Schaubcylindrichnus and Zoophycos ichnofabrics. The trace and body fossil distribution and trophic structure of some of the recorded faunal assemblages confirm relatively stable and low-stress shallow-marine environments. In contrast, the trophic structure of some other assemblages indicates the influence of particular environmental parameters, including substrate consistency, bathymetry, water energy, productivity, rate of sedimentation, salinity and oxygen availability. The integrated results indicate that the sequences were formed during an interval dominated by different perturbations that resulted in a wide spectrum of depositional features. Moreover, evidence for Carboniferous–Permian glaciation is tentatively established in North Egypt but require further investigations.

Effect of Sedimentary Facies Characteristics on Deep Shale Gas Desserts: A Case from the Longmaxi Formation, South Sichuan Basin, China

Shale gas is one of the hot spots of energy development. Due to the strong heterogeneity and low physical properties of shale gas reservoirs, and the complex influencing factors of pore development, it is necessary to conduct a comprehensive analysis of the control factors of high-quality reservoirs. The sedimentary characteristics, mineral composition, pore structure and controlling factors of high quality reservoir development are studied on the basis of thin section, scanning electron microscopy (SEM) and QEMSCAN analysis, X-ray diffraction (XRD), total organic carbon (TOC), Nano-CT scanning and Low-pressure N2 adsorption (N2GA) analysis on shale samples from the Longmaxi Formation in South Sichuan Basin. The results show the following: (1) According to lithology, sedimentary structure, organic carbon content and mineral composition, six sedimentary microfacies can be divided. (2) Organic matter pores are developed in organic-rich siliceous shale and organic-rich silty shale at the bottom of the first member of the Longmaxi formation, with average porosity of more than 5% and permeability of more than 2 × 10−3 μm2, which is conducive to the formation of high-quality shale gas reservoirs. (3) The contents of siliceous and TOC are positively correlated with porosity and specific surface area, while the contents of carbonate and clay minerals are negatively correlated with reservoir quality. (4) In the first member of the Longmaxi formation, the sedimentary water depth becomes shallower from bottom to top, and the sedimentary environment changes from a reduction to an oxidation environment. The contents of siliceous and organic matter decrease, while the contents of clay minerals and carbonate minerals show the opposite trend. The difference in sedimentary microfacies affects the distribution of mineral and organic matter and controls the heterogeneity of the shale reservoir.

Geochemistry and heterogeneous accumulation of organic matter in lacustrine basins: A case study of the Eocene Liushagang Formation in the Fushan Depression, South China Sea

Determining the spatial distributions of organic-rich mudstones in hydrocarbon-bearing lacustrine basins is crucial for targeting exploration wells and discovering commercially viable petroleum accumulations. However, the strong heterogeneity of sedimentary systems and organic matter (OM) input and accumulations make it difficult to identify OM-rich mudstones in lacustrine deposits. This paper takes the Eocene Liushagang Formation, in the Fushan Depression, South China Sea, as an example to clarify the relationship between the geochemical characteristics of OM and sedimentary facies. A practical approach is proposed for predicting the spatial distribution of good-quality source rocks with high OM contents. The method used is a combination of logging-based surface fitting and the mudstone to stratum thickness ratio (M/S ratio) of different depositional systems. It was found that this approach improved TOC content prediction both vertically and laterally. The results suggest that semi-deep lacustrine mudstones with predominantly aquatic organism input, deposited in suboxic-anoxic saline stratified water, contain more preserved OM than other mudstones. Using this method, limited areas on the southern slope of the lower Liushagang sequence (SQls3), the central part of the Huangtong Sag in the middle Liushagang sequence (SQls2), and the northern part of the Huangtong Sag in the upper Liushagang sequence (SQls1) are determined to be the best-quality source rocks in the development area.

Sedimentary Characteristics of Denglouku third member in the south of Shuangcheng area, Songliao Basin

Based on sedimentary theory and high-resolution sequence stratigraphic theory, Denglouku third member in the south of Shuangcheng area is finely divided into a long-term reference surface cycle, 3 medium-term reference surface cycles and 20 short-term reference surface cycles. Denglouku third member is divided into three sand groups from top to bottom according to the medium-term reference surface cycles, and 6 layers, 6 layers, 8 layers in the groups respectively. Through fine observation of rock cores and data analysis of nearly one hundred wells, it is believed that alluvial fan facies, fluvial facies and delta facies are developed in the study area, which can be further divided into 6 subfacies and 12 microfacies. After the analysis to the plane distribution and vertical evolution characteristics of sedimentary facies, it is found that Denglouku third member in the south of Shuangcheng area shows a water-transgression sedimentary cycle from bottom to top which reflects the sedimentary process of water body gradually deepening.

Late Triassic–Early Jurassic paleogeomorphic characteristics and hydrocarbon potential of the Ordos Basin, China, a case of study of the Jiyuan area

Abstract Paleogeomorphology is the surface morphology formed by the deposition of strata in the basin in historical period, which is greatly affected by the regional tectonic movement; however, the effect of basin paleogeomorphology on reservoir has been underexplored. This study documents the basin paleogeomorphic terrain features and their implications for the depositional processes and oil migration and accumulation in the Jiyuan area of the Ordos Basin. Stratigraphic classification is achieved through well logging data analysis. A seismic fine interpretation of the Triassic–Jurassic paleogeomorphology is conducted. Typical drilling core observations were utilized in a well section analysis of the strata at the top of the Yanchang formation sedimentary facies characteristics. Studies have shown that the Chang 1 subsection on top of the Triassic Yanchang formation in the Jiyuan area was eroded by an ancient Jurassic river, and the residual strata are primarily distributed in the Dingbian and Jiyuan plateaus. The Chang 1 reservoir in the Jiyuan area is dominated by a delta distributary channel sand body. The reservoir is concentrated in a high reservoir sand body structure position, and is controlled by a combination of structural and rock characteristics. This study suggests that the Indosinian movement in the late Triassic caused the entire basin to uplift and denudate, and the strata at the top of the Yanchang formation suffered from weathering and river erosion. The residual strata in the upper part of the Yanchang formation are controlled by the late Triassic–early Jurassic paleogeomorphology.

Study on Sedimentary Characteristics of Chang 9 Member of Triassic in Ordos Basin

The Triassic Yanchang Formation in the Ordos Basin is one of the main exploration targets. Based on the detailed exploration of the outcrop at the southern margin of the Ordos Basin, combined with previous results, a systematic analysis of lithology, rock assemblage, sedimentary facies characteristics and temporal evolution is carried out. The results show that the Changchang 9 oil-bearing group on the southern margin of the Ordos Basin can be divided into 9 lithofacies types, and three types of sedimentary facies, meandering river, meandering river delta, and braided river delta are developed. The meandering river facies develops riverbed retention deposits, beaches, and There are four types of microfacies in natural dikes and rupture fans. There are five types of microfacies in meandering river deltas: underwater distributary channels, underwater natural dikes, divert bays, estuary dams, and remote sand dams. Braided river deltas develop underwater distributary channels, There are two kinds of microfacies between distributary channels; the Chang 9 oil-bearing group has a coarse-fine-coarse compound rhythm in the vertical direction; meandering river sand bodies and delta front sand bodies are the main places for oil and gas migration and accumulation.

Multiple Influences of Paleogeography, Sequence Stratigraphy, and Fold Structure on Coalbed Methane Accumulation in the Lopingian (Late Permian) of Junlian Coalfield, SW China

Junlian coalfield is one of the main targets for coalbed methane (CBM) exploration and development in the southwest China. Based on field geological survey, core observation, gas content statistics, coal maceral composition, vitrinite reflectance ( R O ), proximate analysis and trace element test, lithological types, lithofacies, sedimentary environment, and structural analysis, this research established the sequence stratigraphy frame, revealed the plane distribution characteristics of sedimentary facies, and defined CBM accumulation mode. The results show that six rock types were identified and further subdivided into twenty lithofacies types. Four types of sedimentary systems such as alluvial plains, delta, lagoon-tidal flat, and carbonate platform were summarized according to their combination characteristics. Additionally, 12-14 fourth-order sequences and three third-order sequences CSI, CSII, and CSIII were divided, and a sequence stratigraphic framework of the Lopingian coal-bearing series was established. Among them, the features of third-order sequence CSIII paleogeography from west to east are alluvial plains, deltas, lagoon-tidal flats, and limited carbonate platforms. Thick coal seams are mainly developed in the sedimentary environment of tidal flats, delta plains, and floodplains behind banks. Closely related to coal seam thickness, gas contents of Lopingian coal seams are generally higher than 8 m3/t, except the low level in northwest and partial denudation areas. CBM accumulation is significantly controlled by the fold structure, and the hydraulic plugging effect makes the syncline core favorable for CBM accumulation. Furthermore, favorable geostress conditions enable the secondary anticline to become a favorable area for CBM accumulation when the sealing conditions are better. This research will provide a theoretical guide for the exploration and development of CBM in the study area.

Sedimentary facies characteristics of Yan 9 oil-bearing formation of Yan’an Formation in D area of northern Shaanxi

In order to promote the exploration and development of oil reservoirs in northern Shaanxi, the study of sedimentary facies characteristics in D area was carried out. Using core, logging and logging data, the Yan 9 oil layer group in the D area is divided into two small layers, Yan 91+2 and Yan 93. Based on the core description, the analysis of single-well sedimentary facies, continuous-well sedimentary facies, and planar sedimentary facies is carried out. It is believed that the Yan 9 member of the study area is a delta plain deposit, which is mainly composed of distributary channels, natural embankment and inter-branch swamp microfacies. Vertically, the sand bodies in the Yan 9 oil-bearing group are discontinuous, with distributary channels and inter-branch swamps mainly developed. Horizontally, the channels of the Yan 9 oil layer group spread out in strips on the plane, extending in the northwest-south east direction. There are 6 main rivers in the study area of Yan93 stage and 7 main rivers in Yan91+2 stage. Channel deposits constitute the main body of the sand body skeleton and are also the main oil and gas enrichment area.

Analysis of sedimentary facies characteristics and source reservoir allocation of fault depressed Lake Basin—Taking Xu-Xi area of Songliao Basin as an example

At present, Xu-Xi area is in the primary stage of exploration, and its sedimentary characteristics and distribution law are not clear. In this study, based on the analysis of regional structural background, through core observation and description, grain size analysis, well logging and seismic and other technical means, the sedimentary facies types and spatial distribution characteristics of Shahezi Formation in Xu-Xi area are studied. It is believed that there are three types of sedimentary systems in Shahezi Formation in the study area: Fan Delta, braided river delta and lake. The fan delta is mainly developed in the steep slope belt in the west of Xu-Xi area, while the braided river delta is mainly developed in the gentle slope belt in the East and the axial belt in the north, and the lake facies is developed in the depression belt between them. On the whole, the sedimentary pattern shows the obvious characteristics of “North-South block, east-west belt”. From the West steep slope to the East gentle slope, the sedimentary facies type transits from fan delta to deep lake semi deep lake and then to Braided River Delta. Combined with the study of reservoir forming conditions, it is found that the sand bodies of fan delta front and braided river delta front have good reservoir physical properties and are often adjacent to large-scale high-quality source rocks in the upper and lower or lateral directions. The reservoir forming conditions are superior and are favorable for oil and gas accumulation facies belt.

Cretaceous Forearc Sedimentation and Contemporary Basin Tectonics in Northwestern Borneo: New Sedimentological Insights from Pedawan Formation, Kuching Zone, East Malaysia

Sedimentary successions developed at the destructive plate margin settings are extremely important as they bear valuable record of contemporary basin tectonics and consequent sedimentation. Intense deformation and metamorphism often obliterate the primary sedimentary texture and structures of the sedimentary successions formed at destructive plate margins. However, sedimentological analysis of young unmetamorphosed forearc successions provides rare opportunity to infer the interplay between tectonics and sedimentation. Therefore, a process-based sedimentological facies analysis and provenance studies of the Cretaceous Pedawan Formation in the Kuching Zone, Borneo, have been undertaken for the first time. The sandstones are compositionally and texturally immature. They are normally graded with sole marks and have erosional lower contacts with mudstones and generally have gradational upper contacts. The massive sandstones, parallel-laminated sandstones, and the combination of rippled sandstones with thin mudstones are interpreted as turbidites. The lack of wave-generated structures, including hummocky cross stratification, indicates that deposition took place below storm wave base, possibly in a shelf setting. The lower part of the Pedawan Formation is mudstone dominated, and the upper part progressively becomes sandstone dominated. The Pedawan Formation bears several penecontemporaneously deformed horizons sandwiched between laterally persistent undeformed beds. Deformation structures include folds with reclined to recumbent geometry and layer-confined normal and reverse faults. We have interpreted these deformed horizons as seismites. Modal analyses of the sandstones indicate recycled orogenic as well as arc provenance and thus indicate mixing of recycled orogenic sediments with arc-derived volcanic material. The sedimentary facies characteristics of the Pedawan Formation in combination with numerous penecontemporaneous deformation features at selected stratigraphic levels indicate that the turbidites formed in a seismically active deepwater depositional setting as part of a long-lived subduction complex in eastern Sundaland during which several crustal fragments were accreted to Borneo.

The Sedimentary Facies and Evolution Characteristics of the Middle and Deep Strata in the Nanpu No. 3 Structural Area

In this study, due to the inconsistencies in the understanding of the sedimentary types in the second section of the Dongying Formation (Ed2) and the third section of the Shahejie Formation (Es3) in the middle and deep strata of Nanpu No. 3 structural area, the depositional characteristics of the deep braided river delta, fan delta, deep-water slump turbidite fan, and coastal and shallow lake in the Nanpu No. 3 structural area were examined in-depth. The investigations were begun based on the descriptions and observations of core samples obtained from eight cored wells in the study area, in combination with seismic, well logging, and rock ore data. The results revealed that the sources of the material in the study area originated from the Shaleitian salient in the southwest direction. It was determined that the fan deltas and the shallow lake sedimentary system had developed during the SQ1 sequence and SQ2 sequence periods. The braided river deltas and the shallow lake and turbidite sedimentary system with multi-stage superposition had developed during the SQ3 to SQ7 sequence periods, and their distribution range had been controlled by the structural background of the gentle slope zone of the lake basin. On that basis, a sequence deposition filling model controlled by a slope break zone in the middle and deep strata of the Nanpu No. 3 structural area was established in this study starting from the typical seismic profile, in which such factors as the tectonic activity characteristics, lake basin boundary shape, water depths, and so on, were comprehensively considered. The goal of this research investigation was to provide beneficial information for oil and gas explorations in similar areas.

Analysis of physical properties of middle-deep reservoirs in the east of Jizhong Depression

The Jizhong Depression is one of the hot spots for oil and gas exploration in North China. As the Jizhong Depression has the largest area and richest oil and gas resources, the Raoyang Depression has good prospects for exploration. This paper takes the middle-deep reservoirs of the Shahejie Formation in the Raoyang Depression as the research object. Aiming at the problem of the unclear characteristics of the middle-deep reservoirs in the Raoyang Depression, using core description, thin section identification, and cathodoluminescence technology, the physical properties of the middle-deep reservoirs in Shahejie are clarified. The following points of understanding have been obtained: The rock types of Shahejie Formation in Raoyang area are mainly feldspar sandstone and detrital feldspar, followed by feldspar detrital sandstone and feldspar quartz sandstone. The main mineral content of different structural belts is different. The quartz content in Suning and Maxi areas is higher than that in Liuchu and Dawangzhuang areas. The feldspar content in Liuchu and Dawangzhuang areas is higher than that in Suning, Maxi and Liuxi areas. The Maxi area has the highest lithic content. There are 7 types of pores, including intergranular pores, intragranular pores, granular dissolved pores, mold pores, intergranular dissolved pores, intragranular dissolved pores, and intergranular pores. The porosity in Raoyang area is between 0.85% and 35.26 % with the average value of 12.05%. The permeability is 0.01mD-1312mD, and the average value is 12.75mD. It belongs to low porosity-low permeability reservoirs. Finally, combined with sedimentary facies characteristics and actual drilling and logging data, the reservoir division of the study area is completed, and 10 favorable areas are proposed. The research results provide a reference for the next step in the study of the physical characteristics of the middle and deep reservoirs in the eastern part of the Jizhong Depression.