Fan-delta Deposits Research Articles

Facies Analysis and Sequence Stratigraphy of Plio-Pleistocene Fan Delta Deposits in the East Arm Sulawesi, a case study of Biak Formation, Luwuk, Banggai

Abstract Fan delta deposits were found widespread in the east arm of Sulawesi as the area experienced tectonic uplift during Plio-Pleistocene continental collision, known as Bongka Formation in the western part and Biak Formation in the eastern part. One of key outcrops for Biak Formation was observed in Biak Village, North Luwuk District, Banggai Regency, thus served as the lithotype location for the Biak Formation. The outcrop was a roadcut and had a 50 m long and 25 m high. In general it shows a coarse-grained heterolithic inclined strata dipping southward and overlain by horizontal strata of similar facies. Its sequence stratigraphy was analyzed by examine its facies, facies association, petrography, and paleontology, along a 1:100 scaled measured section. Six lithofacies were identified, namely conglomeratic coralline limestone, conglomeratic coralline limestone, parallel bedding – gradation conglomerate-sandstone, gravely sandstone, conglomerate-sandstone – conglomeratic corraline limestone and gradation conglomerate-sandstone with horizontal bedding. Their lithofacies deposited during Late Pliocene in a transition – inner neritic environment. Their facies association made several depositional system tracts, showing a complete cycle of Highstand System Tract (HST), Sequence Boundary/Correlative Conformity (SB/CC), Lowstand System Tract (LST), Transgressive System Tract (TST), Transgressive Surface (TS) later capped by younger HST and LST. Result of this study suggesting repetitive cyclic depositiona tracts dictated by sea-level eustacy and tectonic uplift. This location served as an ideal outcrop as a textbook example to study sequence stratigraphy in an outcrop scale.

Facies of Quaternary Sediments In Bunga Village, North Luwuk District, Banggai Regency, Central Sulawesi

Abstract The distribution of Quaternary sedimentary rock deposits in Indonesia is quite extensive, and one of them is in the Quaternary coral reef units, which are evenly distributed along the eastern arm of Sulawesi. The research was conducted in Bunga Village, North Luwuk District, Banggai Regency, Central Sulawesi Province. This research was motivated by the lack of geological data, so the topic of developed facies became an interesting topic to be researched. Data was collected from a cliff at the coordinates 0053′57,57.1″N-122054′43′6″E. Stratigraphic measurements aim to determine the facies, depositional environment, and sedimentation mechanisms developed in the study area. The research was conducted using the method of field data collection and laboratory analysis. Collecting field data was carried out with measured stratigraphic with a 1:100 scale and taking several rock samples. Laboratory analysis was carried out in paleontological and petrographic analysis, which was carried out to determine the composition of the constituent rock and fossil identification, especially foraminifera in thin sections of rock that were selected. Based on the study’s results, the total rock layers measured in the study area were 15 m. Facies found in the stratigraphic path of the study area are floatstone facies, rudstone facies, allochemic sandstone facies, polymict conglomerate facies. The type of deposition environment of limestone and allochemic sandstone in the study area is on the foreslope, while the conglomerate facies is included in the fan delta deposition environment. Overall, the sedimentation dynamics in this area are in a high energy environment, indicating that the facies that developed were deposited with a sediment gravity flow mechanism.The results of the analysis of fossils found Cyclammina cancellata sp., Orbulina universa sp., Globigerina bulloides sp., and Trilobatus immaturus sp., which indicates the limestone in the study area was deposited in the Late Pleistocene to early Holocene.

Formation mechanism of high-quality Palaeogene “compositional mixing” reservoirs in lacustrine rift basins: A case from the offshore Bohai Bay Basin, China

Mixed siliciclastic-carbonate reservoirs are currently considered a unique type of reservoir for hydrocarbon exploration. However, to date, research on “compositional mixing”, an important type of mixed sediment, remains relatively scarce. In recent years, significant breakthroughs in hydrocarbon exploration have been achieved in compositional mixing deposits, which are found within a lacustrine setting of the offshore Bohai Bay Basin in China. Despite the lack of systematic studies on their formation mechanisms, these discoveries are insightful case for understanding compositional mixing reservoirs (CMRs). In this study, an interdisciplinary approach that integrates petrographic analysis, cathodoluminescence analysis, reservoir characterization, and high-pressure mercury injection tests from drilled wells, cores, and thin sections, is employed to elucidate the characteristics of CMRs and the factors controlling reservoir modifications. Our findings reveal that compositional mixing deposits predominantly occurred with fan delta systems adjacent to uplifts. Two distinct reservoir types, namely, mixed slide deposits and mixed sandy debris flow deposits, were formed by coexistence of fan delta front siliciclastics with shallow-water biota (carbonate components). A comparative analysis of reservoir properties suggests that CMRs are of equivalent or superior quality to fan delta systems, challenging existing paradigms. This superiority is attributed to two primary factors: (1) the unique internal texture of compositional variations significantly influences subsequent diagenesis, leading to the extensive development of selective dissolution porosity and a reduction of clay cementation; and (2) distinctive early diagenetic events, including micrite envelopes and early dolomitization, markedly enhance the reservoirs’ resistance to compaction. In contrast, fan delta deposits lacking carbonate components do not undergo selective dissolution and their siliciclastic composition facilitates clay cementation. This study offers novel insights and a model for understanding the formation mechanism of CMRs, providing implications for future global petroleum exploration in mixed sediment reservoirs.

The depositional evolution and associated controls on the reservoir property in the Permian Upper Urho Formation, southern Zhongguai Rise, Junggar Basin, northwest China

The Permian strata in southern Zhongguai Rise are famous for their abundant petroleum reservoirs. The depositional evolution of the Upper Urho Formation has been studied by analyzing the interactions between the sedimentary environments and the diagenetic evolution based on the comprehensive analysis of geologic and geophysical data sets. The obtained results have shown that fan delta deposits, overlain by lacustrine deposits, are deposited. Proceeding upward, the fan delta succession is characterized by retrogradational patterns, such as sandstone facies and conglomeratic facies. These facies have shown different clay mineralogic compositions, porosity, and physical properties. The sandstone facies indicate well-sorted and well-rounded sedimentological textures with good physical properties. In contrast, the conglomeratic facies indicate poorly sorted and poorly rounded sedimentological textures with poor physical properties. All of these characteristics lead to reservoir heterogeneity resulting from sedimentary facies and diagenesis.

Mixed siliciclastic-carbonate-tuffaceous sedimentation in a rift lacustrine basin: A case study of the Lower Cretaceous Jiufotang Formation in the Luxi sag, Songliao basin

The Lower Cretaceous Jiufotang Formation lacustrine successions in the rift Luxi sag, Songliao Basin are characterized by mixed siliciclastic-carbonate-tuffaceous and organic-rich deposits. Ten facies were recognized and were formed in fan delta, delta, littoral-sublittoral lacustrine and deep lacustrine environments. A depositional sequence characterized by significant changes in facies and lake regime has been defined, and is divided into lowstand systems tract (LST), transgressive systems tract (TST), and highstand systems tract (HST) that are separated by sequence boundaries, initial flooding surfaces, and maximum flooding surfaces, respectively. During the LST, the delta and fan delta deposits covered the marginal area and extended into littoral-sublittoral lacustrine and deep lacustrine environments, respectively. During the TST, the areas of delta and fan delta decreased and lake areas increased, and the carbonate-dominated shoals and mixed siliciclastic-carbonate shorelines occupied the edge of the Majiapu highland belt. During the HST, the lake areas further expanded, and the fan delta deposits extended into deep lacustrine environments and formed deposits of underflows and turbidites. A depositional model in the rift lacustrine Luxi sag is proposed, incorporating the effects of tectonics and sediment supply, climate and carbonate production, hydrodynamic conditions, and lake-level fluctuations. During the LST, the active tectonic movement, high input of siliciclastic sediments, and subaerial volcanic eruptions resulted in the wide distribution of mixed siliciclastic-tuffaceous sedimentation. During the TST, the brackish lake water controlled by periodic dry and hot climate facilitated the carbonate deposition in shallow water, and tractional currents onto the lake shore carried sediments to form the mixed siliciclastic-carbonate-tuffaceous facies. During the HST, more humid climate and increased runoff allowed formation of widely distributed, mostly oil shale-rich deposits, and the gravity flows carried the sediments into the deeper part of basin to form the mixed siliciclastic-carbonate-tuffaceous facies. The depositional model of mixed deposits in this rift lacustrine basin has been proposed here in order to encourage comparison with other similar basins.

A prospect analysis of the Upper Oligocene sandstone reservoirs of the Wenchang 9 block, Pearl River Mouth Basin, northern South China Sea margin

Faults can act as a migration pathway and/or a lateral seal in structural traps in the Wenchang 9 block (WC9B) oil field, affecting the potential for enhanced hydrocarbon recovery in the field. In this study, three-dimensional (3D) seismic survey and well data are used to characterize Upper Oligocene fan delta - tidal flat heterogeneous reservoirs and investigate fault seal potential in two new structural traps interpreted in the WC9B oil field. Five lithofacies are identified in the Upper Oligocene Zhuhai Formation based on the well log analysis and core description. The fan delta front and sand-rich tidal flat sandstone of facies F1 in reservoir unit A of the middle Zhuhai member is characterized by the best porosity and permeability. The RMS amplitude attribute analysis and facies modeling help to predict gradual upward progression of the F1 fan delta deposits from the proximity of the Shenhu Uplift to the NW into the basin for ∼ 7–8 km during accumulation of the middle member. The NE-dipping conjugate normal faults of lower throw in the hanging wall of the NW-dipping main normal basement faults contributed to the formation of hydrocarbon-bearing structural traps and side seals. Two new structural traps in the middle member of Zhuhai Formation interpreted in the WC9B oil field. The traps are 3-way dip closure bounded by the NE-dipping normal faults of the conjugate set that are characterized by good sealing potential in the interval of the middle member. The results of this study contribute to the optimization of the enhanced hydrocarbon recovery of the WC9B oil field.

Tonian basins record rifting of Kalahari from Rodinia and no evidence of a pre-Sturtian Kaigas glaciation

Neoproterozoic strata record evidence for two Snowball Earth glaciations during which ice extended to the equator. Geochronological data have confirmed the multi-million year duration, synchroneity, and global extent of the Cryogenian Sturtian and Marinoan glaciations between 717 and 635 Ma. It has been proposed that an earlier ca. 750 Ma glaciation, referred to as the Kaigas glaciation, included glaciomarine deposits that formed at low-latitude. Here we evaluate this hypothesis at the eponymous location with detailed stratigraphy and geochronology through the Kaigas, Rosh Pinah, and Numees formations on the western margin of the Kalahari craton in southern Namibia. We find that glacial deposits previously assigned to the Kaigas Formation are instead ca. 717–661 Ma diamictites of the Sturtian Numees Formation. Pre-Numees strata, including the Kaigas Formation, host facies associations diagnostic of fan delta deposition along an active normal fault. Interbedded volcanic rocks in the Rosh Pinah Formation overlying the Kaigas Formation were dated with U-Pb CA-ID-TIMS on zircon at ca. 752 Ma. These Tonian deposits are interpreted to have been deposited in an active rift basin without evidence for glaciation. Rosh Pinah magmatism could be broadly correlative with the Mount Rogers Complex in Virginia, USA, consistent with a scenario of the Kalahari craton actively rifting from Laurentia and associated terranes within 20° of the equator at the time. We conclude that, at least in marine settings, evidence for low-latitude glaciation is limited to the 717–635 Ma Cryogenian Period.

Variable Ophiomorpha ichnofabric: Improving the understanding of mouth bar environments in fan-delta complex depositional settings from the Upper Cretaceous of NW South America

Fan-delta deposits, an important sedimentary component of fan-delta complexes, are scarcely described in the ancient record because it is very difficult to distinguish them from other types of coarse-grained deposits (e.g., alluvial, fluvial, or deep marine deposits). This obstacle is overcome when a well-record of physical/biogenic sedimentary structures or fossils unambiguously marks the influence of the receiving basin. However, this is usually not the case. Here, we present the Ophiomorpha ichnofabric record as a key proxy of marine influence within a generally fluvial-dominated system for improving the paleoenvironmental understanding and reconstructing animal-substrate interplay during the evolution of a fan-delta complex. The ichnological record, together with detailed sedimentological analysis, allows us to define three ichnofabric types, distributed in four levels. The stratigraphic distribution of these features points to distal alluvial environments towards the base, dominated by debris and sheet flows deposits and locally shallow braided channels; they evolve upward into well-developed braided fluvial system whose facies arrangement is related to channel fills, locally influenced by debris flows. Subsequently, a basinward migration of the sedimentary system is recorded through the occurrence of the first level with Ophiomorpha ichnofabric A, and then ichnofabrics A and B in levels 2 and 3, respectively, suggesting marine-influenced mouth bar settings. Toward the top, another steep basinward migration is evidenced by Ophiomorpha ichnofabric C in level 4, indicating wave-dominated processes in distal mouth bars environments. The record of marine-influenced and dominated levels may indicate relative sea-level fluctuations related to local or autogenic processes at the basin scale. Furthermore, the present study demonstrates the ability of Ophiomorpha tracemaker to colonize challenging sedimentary environments.

Depositional cycles in a rift lacustrine basin linked with tectonics, climate, and source rocks and reservoirs development: Lower Cretaceous in Naiman sag, Songliao Basin, Inner Monglia, Northeast China

In order to improve understanding of the depositional evolution processes in rift lacustrine basins in Northeast China under Early Cretaceous greenhouse climate fluctuations, the roles of tectonics and climate along with the development of source rocks and reservoirs in the evolution of continental rift lacustrine basins in Naiman sag, Songliao Basin, Inner Monglia, were studied. Based on the detailed facies analysis of the subsurface boreholes, eight facies were identified in the Lower Cretaceous strata of Naiman sag and were grouped into three facies associations, namely fan delta, littoral to sublittoral lacustrine, and deep lacustrine. Based on the depositional characteristics, in combination with lacustrine evaporites and carbonate deposition, organic matter preservation, and lake depth, the Lower Cretaceous strata of the Naiman sag was further subdivided into four lake stages, namely initial formation of lake (Stage 1), sediment-fill shallow lake (Stage 2), rising to a high lake (Stage 3), and lake closure (Stage 4), respectively. The lake evolution in the Naiman sag was driven by both tectonics and climate changes. Fault-driven subsidence was likely contributed to episodic changes in accommodation and lake formation (Stage 1), expansion (Stage 3) and shrinkage (Stage 4). A combination of regional and global climate overprint controlled the sedimentary characteristics, depositional trends, and sediment and water supply. The global climate of ocean anoxic events 1a and 1b (OAE1a and OAE1b) may have effects on anoxic conditions of Stages 1 and 3, respectively. During regional climate changes between arid, hot and humid, seasonal climate tended to form evaporite deposits and multiple layers of oil shale deposits in Stage 1. During the more humid regional climate, steady runoff tended to form fan delta deposits prograding into the lake basin in Stages 2 and 4 and thick-bedded oil shale deposits in Stage 3. The development of source rocks is linked with lake formation and expansion stages (Stages 1 and 3), and the source rocks are mainly preserved in the deep lacustrine and littoral to sublittoral lacustrine environment. The development of reservoirs is associated with lake formation, sediment-fill, and shrinkage stages (Stages 1, 2, and 4), and the reservoirs are mainly preserved in the fan delta environment.

OLIGOCENE FAN-DELTA DEPOSITS IN NORTHERN ITALY: A SUMMARY

Lungo le colline e le basse montagne al limite tra Piemonte e Liguria affiora un'unità oligocenica, prevalentemente conglomeratica, nota come Formazione di Molare o come Conglomerati di Savignone. Questa formazione si estende per più di 100 km, con direzione ENE-OSO, dai dintorni di Genova fin quasi a Cuneo. I conglo­merati che la costituiscono rappresentano, per la maggior parte, conoidi alluvionali oligoceniche depostesi al limite tra la terraferma ed un bacino marino (« fan-deltas »). Lo studio sedimentologico ha consentito l'individuazione di diciotto principali litofacies e la loro interpretazione.

Sedimentary Characteristics and Their Controlling Factors of Lower Cretaceous Fan Deltas in Saidong Sub-Sag of Saihantala Sag, Erlian Basin, Northeastern China

Fan deltas of the Lower Cretaceous area in Saihantala sag, Erlian Basin have been identified as major petroleum exploration opportunities. The sedimentary evolution is, however, still debatable, which hinders insights into its controlling factors. This research employed new core observations, thin section observations, and grain size analyses of 28 wells in the Saidong sub-sag, together with numerous borehole and seismic data points, to explore lithofacies types, subfacies, and microfacies characteristics, thus leading to a further investigation of the sedimentary facies evolution of the sag and its controlling factors. The findings showed there are 3 categories, 12 sub-categories, and 20 fine lithofacies types in the Saidong sub-sag. Additionally, various sand-conglomerate lithofacies were characterized by lower composition and texture maturity. With dentate-shaped, box-bell-shaped, and other morphological well-logging responses, fan deltas were mostly developed in the A’ershan Formation and the Tengge’er Formation, which could be subdivided into three subfacies and eight microfacies. Given the sedimentary features and lithofacies characteristics of each microfacies, it can be determined that three main stages occurred in formations from the A’ershan to the Tengge’er: the water transgression, the water oscillation, and the water regression. Moreover, fan delta deposits were regulated primarily by semi-arid hygrothermal and semi-arid paleoclimate and paleotectonic factors.

Evaluating the sedimentological and diagenetic impacts on terrestrial lacustrine fan delta sandy conglomerates reservoir quality: Insights from the Triassic Baikouquan Formation in the Mahu sag, Junggar Basin, Western China

The terrestrial lacustrine fan delta conglomerate reservoirs in the Triassic Baikouquan Formation (BF) are the primary hydrocarbon exploration targets in the Mahu sag, Junggar Basin, Western China. However, the varying lithofacies and complex diagenesis controlling the reservoir quality remain poorly understood. For the sake of revealing how reservoir quality is associated with sedimentary processes and diagenetic alterations, we used integrated approaches like petrographical analysis, cores description, wireline, X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury intrusion capillary pressure (MICP) and measured petrophysical properties. The results showed that sedimentary processes have considerable control over facies distribution, grain size, and clay content, causing spatial variation of reservoir quality within the fan delta deposits. The coarser grain and high clay content fraction at the base of gravity flow will first settle in the fan delta plain near provenance, whereas the finer grains at the top of flows progressively deposit in the fan delta front areas. From proximal to distal fan delta, a progressive conversion from cohesive muddy debris flow into traction current can be inferred from the variations of lithofacies associations. A total of 8 types of microfacies were identified where the conglomerates of the BF were deposited. The grayish-green fine-grained conglomerates concentrated in the subaqueous distributary channels provide the best reservoir performance, whereas debris flow deposits dominated primarily by muddy debrites occupy the worst reservoir quality because of their highest clay content and coarsest grain size.The dominant diagenetic events include mechanical compaction that continued throughout the entire burial, two phases of quartz cementation, dissolution of unstable components, early and late carbonate cementation, precipitation of authigenic clay minerals, and two phases of hydrocarbon charging. It is unveiled that compaction is the predominant mechanism negatively affecting reservoir quality in the fan delta complex, while the effect of cementation on pore reduction of the conglomerate reservoir is weaker than compaction. Simultaneously, a complex relationship exists between reservoir petrophysical properties within different clay minerals. Dissolution does not significantly improve the permeability of the reservoir because of the partial dissolution which primarily generated intragranular pores with strong heterogeneity and poor connectivity. The most favorable reservoirs occur primarily in the subaqueous distributary channels in the fan delta front, which comprise well-sorted fine-grained conglomerates with well-developed residual intergranular pores and secondary dissolution pores and have undergone two phases of oil charge. This work may provide a useful reference for hydrocarbon exploration of the fan delta systems and regions which have encountered similar sedimentary and diagenetic processes.

Assessing the expansion of the Cambrian Agronomic Revolution into fan-delta environments

The intensity, extent, and ecosystem-level impact of bioturbation (i.e. Agronomic Revolution) at the dawn of the Phanerozoic is a hotly debated issue. Middle Cambrian fan-delta deposits in southwestern Saskatchewan provide insights into the paleoenvironmental extent of the Agronomic Revolution into marginal-marine environments. The studied deposits reveal that several environmental stressors had direct impact on trace-fossil distribution and bioturbation intensities in Cambrian fan deltas. Basal and proximal subaerial deposits are characterized by very coarse grain size and absence of bioturbation. Mid-fan and fan-toe deposits were formed under subaqueous conditions and are characterized by rapid bioturbation events in between sedimentation episodes when environmental stressors were ameliorated, providing evidence of a significant landward expansion of the Agronomic Revolution. Transgressive marine deposits accumulated after the abandonment of the fan-delta system display high levels of bioturbation intensity, reflecting stable environmental conditions that favored endobenthic colonization. The presence of intense bioturbation in both subaqueous fan delta and transgressive deposits provides further support to the view that Cambrian levels of biogenic mixing were high, provided that stable environmental conditions were reached. Our study underscores the importance of evaluating sedimentary facies changes to assess the impact of environmental factors prior to making evolutionary inferences.

Subtle reservoirs and implications for hydrocarbon exploration in terrestrial lacustrine fan-delta deposits: Insights from the Triassic Baikouquan Formation, Mahu Sag, Junggar Basin, western China

Petroleum reserves are abundant in the large-scale lacustrine fan delta reservoirs containing mixed oil in the Baikouquan Formation (MA131 Block, Junggar Basin). However, detecting such subtle reservoirs in the lacustrine foreland basins is challenging. High-resolution sequence stratigraphy, sedimentary basin evolution, and reservoir models are established by integrating the results obtained via wireline log data, cores, thin sections, and seismic data. A fifth-order sequence stratigraphic framework for the Baikouquan Formation is established, which enables the reconstruction of the sedimentary basin evolution and further detailing of the reservoir model, such that the correlation to multistage progradation and retrogradation of the fan delta complex can be determined. The study of core samples led to the identification of eight microfacies, of which sandy debris flows and distributary channels dominate approximately 80% of the depositional system. Stratal slices enable the characterization of the northern Xiazijie and eastern Madong fan-delta systems. The northern Xiazijie fan delta is widely distributed throughout sequences SSQ1–SSQ6, whereas the Xiazijie fan delta underwent, in general, gradual retrogradation during the formation of sequences SSQ6 and SSQ7. The eastern Madong gravity flow fan-delta system only developed during the formation of sequences SSQ1–SSQ5 at the location of an abrupt slope break. There are nine categories of reservoir models in the study area based on the source rocks, faults, and reservoirs. Geomorphology and climate are crucial in controlling the sedimentary infill. Deep faults and an unconformity between the Permian and the Triassic of the Mahu Sag played a decisive role in controlling the hydrocarbon migration pathways. The faults, source rocks, and microfacies together exert considerable control on hydrocarbon accumulation. Within the nearshore fan-delta front, variable reservoir quality can be observed. Crucial factors in improving reservoir quality are fine-grain size and relatively low clay content. This study may facilitate subtle reservoir characterization in other basins.

Reservoir characteristics and controlling factors of the Lower paleogene sandstones in the southeast part of Jiyang Sag, BohaiBay Basin, China

With the continuous improvement of exploration degree in Bohai Bay Basin, the red beds in Jiyang Sag has become a hot exploration spot in recent years, the red beds is buried deep, and the distribution of favorable reservoirs has become a key factor restricting oil and gas exploration. This paper combines logging, core and seismic data, mainly introduces the sandstone reservoir characteristics of red beds in the southeast of Jiyang depression, and analyzes the influence of sedimentary environment and diagenesis on its reservoir characteristics respectively. The results showed that the red bed sandstone is mainly composed of arkose, quartz-feldspar and feldspar-quartz graywackes, with good porosity and permeability. Under the control of the original sedimentary environment, three types of reservoir sand bodies are mainly developed in the study area: proluvial fan, fan delta and beach bar deposits, among them, fan delta deposits have better storage performance. The diagenetic environment was early alkaline and late acidic, compaction and cementation greatly reduced primary pores and a large number of secondary pores are produced due to minerals dissolution. Under the combined influence of sedimentary environment and diagenesis, the red-bed reservoirs have various types of reservoir spaces, with obvious differences in porosity and permeability.

Lithofacies paleogeography restoration and its significance of Jurassic to Lower Cretaceous in southern margin of Junggar Basin, NW China

In view of the difficulties in the study of lithofacies paleogeography and the low reliability of the distribution range of sedimentary sand bodies in the prototype basin caused by less deep drilling, complex seismic imaging and low degree of exploration in the southern margin of Junggar Basin, NW China. A new method based on the source to sink idea was used to restore lithofacies paleogeography and predict glutenite distribution. In the restoration, apatite fission track age was used to define range and uplift time of macro-provenance; the range of provenance area and the migration process of lake shoreline were restored based on the quantitative relationship between gravel diameter and transportation distance, tectonic shortening and other geological parameters; drilling cores and field outcrop sedimentary structures were analyzed, and a series of maps of lithofacies paleogeographic evolution and distribution range of glutenite bodies were compiled. It is concluded that from Early Jurassic to Early Cretaceous, in the southern margin of Junggar Basin, the provenance area gradually expanded from south to north, the lake basin expanded, shrunk and expanded, and the paleoclimate changed from humid to drought to humid. The western section always had proximal fan delta deposits from the southern ancient Tianshan provenance developed, and in the middle and eastern sections, the provenance areas evolved from far source to near source, mainly river-delta, braided delta, fan delta and other sediments developed. The boundary between provenance areas of the western and middle sections is speculated to be Hongche fault zone. In an angle open to the northwest with the current basin edge line, the restored ancient lake shoreline controlled the heterogeneity of reservoirs in the delta plain belt and delta front belt on its both sides. The ancient lake shoreline, current stratigraphic denudation line and current basin margin line limit the types and scope of favorable reservoirs. This understanding provides an important geological basis for oil and gas exploration in the deep lower source-reservoir assemblage at the southern margin of Junggar Basin.

Scoresbysund Composite Tectono-Sedimentary Element, East Greenland Rifted Margin, Denmark Strait

Abstract The little explored central East Greenland margin contains thick sedimentary accumulations confined within the Scoresbysund Basin. The geological evolution of the area distinguishes it from other parts of East Greenland. Even so, resemblances with the prospective basins onshore and offshore further north probably exist, and the margin may hold real petroleum potential. The Scoresbysund Composite Tectono-Sedimentary Element (CTSE) delineates the oldest part of the Scoresbysund Basin. It formed through multiple phases of rifting, volcanism, uplift and thermal subsidence between Devonian and Miocene times. The development of the CTSE concluded with the latest Oligocene or early Miocene continental break-up of the Jan Mayen microcontinent and East Greenland. The Scoresbysund CTSE contains approximately 4 km of Eocene–lower Miocene fan-delta deposits that accumulated during downfaulting along the East Greenland Escarpment and which further seawards intercalate with basalts. The fan-delta deposits rest on Paleocene basalts that most probably cover Paleozoic–Mesozoic strata. Equivalent to onshore, the deeply buried section probably includes source rock and reservoir intervals of Carboniferous, Permian and Mesozoic age. Together with the major fault structures existing in the western part of the area, this may form the basis for a working petroleum system.

Study on Pore Structure and Seepage Characteristics in Huhenuoren Oilfield

Pore structure and seepage characteristics have been studied in view of the problem of watercut rose rapidly in Nantun formation of huhenuoren oilfield of Hailar basin. Fan delta deposition with characteristics of close resource, rapidly accumulation results in pore distribution does not uniform, communication are weak. Throat distribution takes on dual peak. Left peak corresponds to smaller throat, which is invalid throat; Right peak corresponds to bigger throat, which is valid throat and seepage channel. There exists big difference in pore structure. Microanisotropy is very strong. Movable oil saturation is relatively low. Water relative permeability takes on convex shape. Strong water sensitivity and big Jamin effect brought about that injection water hard to displace oil below 1μm throat radius. The oil production above 1μm throat radius is about 77% of total oil production by NMR test. Throats above 1μm radius are preferred path of injection water, are the main reason for watercut rising rapidly.

Depositional models and sequence stratigraphy of the middle Miocene clastic/carbonate deposits in the Esh El-Mellaha range, southwest Gulf of Suez rift basin, Egypt

The Langhian was a time of clastic/carbonate deposition over many fault blocks in the Gulf of Suez due to rising eustatic sea level coupled with a warming trend. These deposits are of great interest as they are important hydrocarbon reservoirs. A detailed study on facies organization, depositional geometries and internal architecture of surface analogues helps to realize the reservoir heterogeneity. A good example is preserved in the Mellaha block that represents 80–100 m thick clastic/carbonate deposits. It comprises three facies associations indicating simultaneous accumulation in subaqueous fan-delta, nearshore lagoon and carbonate platform depending on whether they occur in footwall or hangingwall sites. The associations and environments are depicted in two depositional models that display clear insights into their characteristics. The Abu Gerfan facies association, dominated by conglomerate, denotes deposition in a footwall-derived coarse-grained fan-delta built into a shallow hangingwall basin closely adjacent to the eastern Mellaha faults (Depositional model I). The architecture of the fan-delta deposits is strictly linked to the relative movement across the fault system and the sea-level rise in the hangingwall basin. The fan-delta conglomerate grades distally and upward to limestone of the Gharamul facies association that implies deposition in a coastal lagoon. The Abu Shaar facies association is characterized by carbonates dominated by corals, microbialites and rhodoliths. It marks a reef-rimmed carbonate platform developed on a submerged footwall high at the southern end of the block due to its double asymmetry (Depositional model II). This platform is characterized by sigmoidal-bedded fringing reefs initiated on the block crest that pass westward into horizontally-bedded lagoon facies with scattered patch reefs, and eastward into inclined-bedded reef talus. Synsedimentary block tilting, eustatic sea-level rise and global warming have imposed major controls on the growth of the Abu Shaar platform. The facies associations are attributed to three rift tectonic events that record two sequences with a dominance of transgressive and highstand stratal units. These sequences are consistent with globally defined Langhian sequences, which indicate that sediment accumulation was largely controlled by eustasy with a strong overprint of rift tectonics. This result allows better regional correlations, particularly with the Miocene Mediterranean carbonate platforms.

Gravel roundness quantitative analysis for sedimentary microfacies of fan delta deposition, Baikouquan Formation, Mahu Depression, Northwestern China

AbstractGravel roundness is one of the simple but crucial parameters in particle shape, which is related to the transportation and deposition of sediments. Based on the digital images of underground drilling cores, this study attempted to characterize and distinguish sedimentary microfacies by quantitatively test gravel roundness trends in the fan delta deposition of the Early Triassic Baikouquan Formation in Mahu Depression, Juggar Basin of China. By the new proposed de-flat roundness measurement, two major parameters are recorded to manifest the rounding degree, which is de-flat roundness value (Rdn) and the corresponding variance value. In the case study, roundness characteristics of four microfacies in the fan delta deposits are displayed and compared. Results show that braided channels and submerged distributary channels are characterized by better rounding (Rdn0.379 to 0.603, and 0.366 to 0.591, respectively) and smaller variance, while debris flow and submerged debris flow are characterized by worse rounding (Rdn0.333 to 0.405 and 0.256 to 0.391, respectively) and larger variance. In vertical of the roundness curves, channels deposits and gravity flow deposits reveal notable distinction in terms of the numeric ranges, fluctuation amplitude, and fluctuate frequency. It is interpreted to represent the different sedimentary processes during particle transport and deposit, as well as new clastics mixed in from other sources. Therefore, roundness could be a useful complementary data to provide quantitative sedimentological evidence and theoretical support for the study of coarse clastic depositional system.