Distributary Mouth Research Articles

COMPOUND CLINOFORM MODEL FOR TIDAL-INFLUENCED DELTAS IN THE MIXED SILICICLASTIC-CARBONATE CISCO GROUP, VIRGILIAN (GZHELIAN), EASTERN SHELF OF THE PERMIAN BASIN, U.S.A.

Deltas in the Cisco Group contain significant volumes of potential reservoir sandstones in the Late Pennsylvanian (Virgilian/Gzhelian) mixed siliciclastic-carbonate succession in the Eastern Shelf of the Permian Basin. While early studies predominantly supported a river-dominated model for these deltas, our findings establish the presence of tide-influenced deltas characterized by the following features: (i) predominant heterolithic lithology; (ii) diagnostic structures such as flaser bedding, bidirectional ripple cross-lamination, or double-mud drapes; (iii) an abundance of interpreted fluid muds; and (iv) elongated bars on the subaqueous platform. Through analysis of 290.2 m of core, we identify six (6) facies associations related to tide-influenced deltaic systems in highstand and falling-stage intervals of the proximal Eastern Shelf: lower-delta-plain/embayed tidal flat, distributary channel and distributary mouth bar/delta front deposits on the subaerial delta; subaqueous delta platform, subaqueou s delta foreset, and prodelta deposits on the subaqueous delta. Moreover, two (2) additional facies associations, transgressive shelf deposits, and subtidal shallow-water carbonates, record continuous episodic transgressions within the deltaic packages. Well-log cross sections reveal repetitive stacking of deltas, typical of icehouse systems, and sandstone mapping suggests elongated tidal bars forming the interpreted subaqueous delta platforms. These features suggest a compound clinoform morphology of the Cisco Group deltas akin to modern tide-influenced deltas that have carbonate banks such as the Gulf of Papua. This compound clinoform morphology has implications for the elongate geometry and isolation of sandstone reservoirs, impacting fluid migration and storage. Moreover, these insights extend beyond the Cisco Group to other Pennsylvanian and Permian levels on the Eastern Shelf, as well as to other deltas in mixed siliciclastic-carbonate systems in icehouse conditions.

Organic geochemical, petrographic and palynological characterization of claystones of the Palaeogene Toraja Formation, and oil seeps in the Enrekang Sub-basin, south Sulawesi, Indonesia: Implications for hydrocarbon source rock potential

An organic geochemical, petrographical, and palynological evaluation was conducted on 30 claystone outcrop samples of the Toraja Formation, along with a geochemical analysis of an oil seep in the Enrekang Sub-basin. The aim of the study was to determine the correlation between oil and source rock in terms of age, depositional environment, organic material sources, and maturity level. The total organic carbon content of the claystone samples varies from 0.03 to 4.52 wt%, which are classified as poor to excellent. The claystones are immature to post-mature with a mixture of Type Ⅱ and Ⅲ kerogen. Their vitrinite reflectance values range from 0.47 to 4.52 %Ro. The samples of Toraja Formation rock and the oil seep source rock might have a similar depositional environment, a deltaic marine depositional setting with high oxidizing conditions. Organic material sources for rock and oil samples are dominated by terrestrial input. The oil is inferred to have originated from the Paleogene source rocks, which correlates in age with the Toraja Formation. The recovered palynomorphs from the studied rock samples suggest a late Eocene to Oligocene age with a strong terrestrial influence of shallow marine depositional setting. The biomarker analysis shows that the rock samples have a more substantial contribution from the terrigenous higher plants, while the oil sample indicates a higher degree of marine influence. The maturity levels are also different between the oil (peak mature) and the analyzed rock samples (immature). It is inferred that the oil seep source rock is equivalent to the analyzed rock sample but more mature, having been deposited under more marine conditions. The oil seep source rock is not exposed and is located in the deeper part of the basin. A deeper marine facies (i.e. distal delta front and prodelta facies) in front of the distributary mouth bar within a delta is interpreted as the source rock of the oil seep sample.

Detecting the magical yellow-blue demarcation off the Yellow River Estuary from the space

River deltas rank among the most ecologically and socio-economically valuable environments on the planet. The Yellow River Delta in China is not only home to young wetland ecosystem, but also to world-renowned tourism resources. One of these was the unique yellow-blue demarcation line (YBDL), formed in the Yellow River Estuary (YRE) as a result of the meeting of terrestrial sediment-laden river water and clear sea water, which had developed into a famous attraction and generated significant tourism revenues. Moreover, its distribution was of vital ecological and geomorphological importance due to association with the dynamics of estuarine turbidity plume. However, little is yet known about the dynamics and influencing factors of YBDL. In this study, we proposed an integrated method for extracting YBDL from satellite imagery and investigated the spatiotemporal distributions of YBDL during the flood season (June-October) from 2016 to 2022 using multi-source satellite imageries. The average relative error of our algorithm reached 10.53%. The results indicated that the YBDL started to frequently occur after 2018, mainly distributed within 10 km off the YRE, with two types of short straight and long curved shapes. July was the period with the highest frequency and most widespread distribution of YBDL. The riverine water and sediment discharge controlled 45.9% of the variations in YBDL length, and the extreme flooding, as well as the implementation of Water-Sediment Regulation Scheme, significantly increased the distribution extent of the YBDL. The morphology of river distributary mouths dominated the changes in the YBDL distribution centres, and the north distributary mouth experienced dramatic evolution in the last three years, with an increased YBDL distribution. Tidal currents could promote the development of YBDL at the front of the river mouth plumes while inhibiting the YBDL on the other side. This study is the first systematic investigation of the spatiotemporal evolutions and driving mechanisms of YBDL in the YRE, which could provide a reference for tourism planning and YRE National Park construction.

Paleoproterozoic (Huronian) valley-controlled deglacial-fluvial sedimentation, northern Cobalt Basin, Ontario, Canada

Detailed sedimentological and stratigraphic analysis of pre-vegetation sedimentary systems that deposited across global-scale climate change episodes is key to fully understanding past feedback responses in Earth surface systems and the details of their paleoenvironments. The Cobalt Basin, recording the upper Huronian Supergroup, captures a transition from glacial (Gowganda Formation) to post-glacial (Lorrain Formation) deposystems in parallel with Earth's Great Oxidation Event and is ideal for sedimentological/stratigraphic analysis due to its limited post-depositional deformation. Stratigraphic measurements and correlations from the northern Cobalt Basin reveal that the Gowganda and Lorrain formations are preserved within a paleovalley, interpreted as a fjord. Sub-glacial deposits of the Coleman Member (lower Gowganda Formation) are preserved at the base of the paleovalley, unconformably above Archean volcanic and granitic rocks of the Abitibi subprovince. Subsequently, the fjord was filled by glaciomarine strata sourced from a grounded tidewater icesheet prior to climate warming. Above the glaciomarine deposits, deltaic deposits of the Firstbrook Member (upper Gowganda Formation) represent a transition to nonglaciogenic deposition under a warm and humid climate. The deltaic deposits comprise three facies associations: (1) delta front/slope strata dominated by horizontally stratified siltstone; (2) interdistributary bay deposits composed of symmetrically rippled and thinly laminated siltstone; (3) distributary mouth bar deposits dominated by very fine-grained arenite. Delta front/slope deposits occur directly above glaciomarine strata, while interdistributary bay and distributary mouth bar deposits occur above delta front/slope strata and are laterally discontinuous across the study area. Prodelta deposits are not preserved in the study area, although they are reported elsewhere in the basin. At the flanks of the paleovalley, alluvial fan deposits, confined by Archean rocks, interfinger with deltaic strata. Alluvial fan sedimentation, triggered by enhanced weathering in an unvegetated warm and humid setting, led to flashy sheetflood deposition due to significant topographic variations at the flanks of the valley setting. In some instances, sandstone beds of the overlying Lorrain Formation, comparable to distal to medial reaches of the modern South Saskatchewan River, cut down through delta strata. Up-section, the braidplain strata coarsen to gravel-rich facies representing Donjek River-type deposits. Overall, the stratigraphic succession in the northern Cobalt basin study area represents a single progradation from glaciomarine through deltaic deposition, into fluvial braidplain deposition. The succession is preserved at the cratonward limit of a passive margin, suggesting that progradation was likely influenced by relative sea-level fall linked to glacio-isostatic uplift, similar to fjord-filled sedimentary successions that have developed since the Last (Pleistocene) Glacial Period.

ANALYSIS OF DEPOSITIONAL ENVIRONMENTS OF UK FIELD RESERVOIR SANDS IN NIGER DELTA BASIN, NIGERIA

The environments of deposition play a vital role during hydrocarbon formation, migration, trapping and storage. Since the reservoir rocks are a function of their depositional environments, the successful tapping of hydrocarbon from its host rock when wells are drilled depends largely on the petrophysical characteristics of the reservoir rocks which in turn originated from and are influenced by their depositional environment. The reservoir facies in Niger Delta shows a broad range of characteristic sedimentological complexities that gave rise to subsurface geological, drilling and production problems occurring in UK Field. The problems include inaccurate determination of environments of deposition, imperfect stratigraphic correlations and reservoir top uncertainty across the UK Field which are targeted by this research in other to help resolve these challenges facing oil and gas industries in the Niger Delta basin of Nigeria. The research findings will assist in the evaluation of depositional environments and well-to-well lithologic correlation within the UK Field and Niger Delta Basin at large. It will also help to unravel major causes of reservoir top uncertainty in UK Field. Also, it will help in future planning and drilling of new wells within UK Field. The determination of the depositional environments of UK Field reservoir sands were carried out to determine the depositional environment of reservoir sand bodies based on data from seven (7) wells. The determination of depositional environments of sand facies penetrated by wells UK1, UK2, UK3, UK4, UK5, UK6 and UK8 was achieved through a side-by-side comparison of their log suites to standard log motifs. Results of facies analysis showed that the reservoir sands belong to mostly (i) fluvial channel, (ii) barrier bar, (iii) lower-middle shoreface, (iv) distributary mouth bar, (v) distributary channel, (vi) point bar and (vii) tidal channel environments that belonged to parts of a deltaic system. Lithologic correlation result reveals the existence of good correlation among all wells in UK Field due to good geological similarities except well UK8 that failed to correlate perfectly with others thereby establishing the existence of reservoir top uncertainty within UK Field. Therefore, reservoir top uncertainty within UK Field is geologically controlled.

Deposition of sandstone (early Cambrian) above the Great Unconformity in the Sino-Korean Block, Gondwana: Control of antecedent topography

The global transition between the Precambrian and Phanerozoic eons in concert with rise in eustatic sea-level caused an important change in paleoenvironments, represented by sedimentary records above the Great Unconformity. In the Sino-Korean Block, Gondwana, the unconformity has been recognized by a boundary between various basement rocks and the overlying distinctive suite of sandstone (including conglomerate, conglomeratic sandstone, and mudstone) of the early Cambrian age. A plate tectonic reconstruction of the Cambrian-Ordovician succession in the northeast Asian continent reveals that the sandstone deposited largely in the eastern part of the platform (North China Platform), including the Taebaeksan and Pyeongnam basins. In the western part of the platform, the basal sandstone is correlated to basal carbonate rocks of middle Cambrian age, forming a time-transgressive or diachronous unconformity. The disparity in sedimentary facies of the basal deposits overlying the Great Unconformity was primarily due to antecedent topography of the bounding continent: in the eastern platform, the drainage area comprised high-relief Precambrian massifs, whereas in the western part, it comprised low-relief massifs. During the initial stage of sea-level rise, the eastern part of the platform formed progressively open shoreface and foreshore environments with localized embayments in which relatively coarse-grained gravelly sandstone deposited in fan-delta and tide-dominated environments. In the western platform, however, the supply of siliciclastic sediments was limited and the sandstone formed a relatively narrow linear belt of delta and distributary mouth bars and foreshore deposits. In the rest of the platform farther west, accommodation created by subsequent sea-level rise was filled with carbonate sediments. This study demonstrates that antecedent topography of the unsubmerged drainage area played a major role for the deposition of sandstone in the initial transgression stage, forming the Great Unconformity.

Fiber-Optic Sensors Evaluate Well Performance in Polymerflooding Pilot

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 199023, “Evaluation of Well Performance Using Data From Fiber-Optic Sensors in Wells of a Pilot Polymerflooding Test, Orinoco Basin, Venezuela,” by Andres Ramirez, Edgar Vasquez, and Luis Quevedo, PDVSA, et al. The paper has not been peer reviewed. The complete paper describes a pilot test using polymerflooding in which evaluating the performance of injector wells was a main priority. The authors chose to complete the wells using a distributed temperature sensor. The paper describes how a better understanding of the connection between the well and the reservoir can improve reservoir simulation models, the decision-making process, and well-performance evaluation. The authors also stress the importance of determining the possibility of unswept areas in the reservoir, which could result in low volumetric sweep efficiency and, consequently, low recovery factor. Introduction The field is in the Orinoco Belt, mainly unconsolidated Miocene sandstone, and has produced heavy oil since 1999. At the time of writing, more than 711 producing wells have been drilled since the beginning of the exploitation of the field. After reaching a production plateau of 200,000 B/D, enhanced-oil-recovery technologies have been considered. One of these is polymerflooding. A pilot test was conducted in an area of the field in which conditions did not indicate application of any thermal recovery technique. The reservoir pressure at project startup was 315 psia, with a reservoir temperature of 115.5°F. Average porosity was 0.32, reservoir absolute permeability was estimated to be between 25 and 15 darcies, and reservoir thickness was 25 ft. Oil mobility was very low because of high viscosity. The pilot test began in 2016. Polymer at a concentration of 900 ppm was injected in a deltaic sedimentary environment composed of distributary channel fills and mouth bars. Polymer was injected through three injector wells. The objective of the test is to provide rapid answers to questions about injection performance, polymer stability, and the effect of heterogeneities. The results will determine if the technology represents a feasible opportunity for future development of the field. The objectives of the control plan in this phase include the following: - Establish how much of the horizontal section contributes to the well injectivity - Estimate an injection profile distribution - Determine if important changes occur during injection

Origin and distribution of grain-coating and pore-filling chlorite in deltaic sandstones for reservoir quality assessment

Grain-coating chlorite preserves porosity and permeability through the inhibition of quartz cement whereas pore-filling chlorite blocks pore-throats and diminishes reservoir quality. The aim of this study is to determine the origin and principal mechanisms which govern the distribution of grain-coating and pore-filling chlorite in Jurassic deltaic sandstones (Tilje Formation, Smørbukk field, Mid Norwegian Shelf). The study focussed on very high-density sampling for petrographic analysis, from three sections of sandstone core from the same well with contrasting reservoir quality, rather than the low-density sampling approach typically employed. The aim was to gain new understanding of specific controls on porosity and permeability based on core description, core analysis measurements and a suite of petrographic techniques. Results of this study show grain-coating chlorite originated from the thermally-driven recrystallisation of detrital clay coats and/or clay mineral precursors. Pore-filling chlorite has principally derived from the ductile deformation of chlorite-rich Fe-ooids, that were possibly reworked from a proximal evaporitic setting. The distribution of chlorite precursor material, detrital clay coats, and subsequently the distribution of grain-coating and pore-filling chlorite, were controlled by the relative dominance of tidal and fluvial processes active during sediment deposition. Optimum grain-coating chlorite is found in tidal-fluvial sandstones with moderate fluvial influence. Pore-filling chlorite is pervasive in tidal-fluvial channel sandstones deposited during periods of high fluvial discharge, or proximal to the central turbidity maximum zone; marked by an abundance of fluid mud. Tidal channel sandstones with no fluvial influence are pervasively quartz cemented due to an absence of grain-coating chlorite. Grain-coating chlorite and good reservoir quality occurs in heterolithic distributary mouth bar sandstones, however mixing of mud- and sand-prone facies due to intense bioturbation has reduced permeability. Results from this study can be used to predict reservoir quality in the Smørbukk field and in analogous shallow-marine sandstones worldwide.

Sedimentary system and sand bodies distribution of the second member of the Xujiahe Formation in the Xinchang area, Western Sichuan Depression, China

The Xujiahe Formation of the Late Triassic in the Western Sichuan Depression contains abundant gas reservoirs. Influenced by the thrust tectonic movement of the foreland basin, the fluvial-delta sedimentary system supplied by multiple provenances formed the Xu2 Formation of the Xinchang area. We used detailed description of drilling wells and cores to define the sequence stratigraphic framework and sand body types. We used stratal slices through the seismic texture model regression (TMR) attribute volume to map the evolution of the sedimentary system and the sand body distribution. Our results indicate that the Xu2 Formation exhibits a complete long-term base-level cycle and that there are six sand body deposit types: distributary channel, interchannel, subaqueous distributary channel, interdistributary bay, mouth bar, and sheet sand. Stratal slices through the seismic TMR attribute volume at different levels map the spatial variation of sand and mudstone, which we use to construct a sedimentary filling evolution model. This model indicates that during the time of deposition of the lower submember, the main provenance supply came from the northwest direction, resulting in the sand bodies mainly being deposited in the west. During the time of deposition of the central submember, the sediment supply was large and came from the northwest and northeast directions, resulting in large, laterally extensive, thick sands. During the time of deposition of the upper submember, the sediment supply was from the northeast direction, with the sand bodies more developed in the east. The flow direction of the (subaqueous-) distributary channels indicate that they migrated from northwest to northeast. There are significant differences in the channel energy, sedimentary characteristics, and reservoir physical properties in the three submembers, which cause differences in oil and gas productivity in the reservoir of the Xu2 Formation. We believe that detailed mapping of the spatial distribution of sedimentary systems can provide critical guidance not only to explore but also to develop in high-quality oil and gas reservoirs such as the Xu2 Formation.

Core-based sedimentological and sequence stratigraphic analysis of shale-dominated gas plays: An example of the early to middle permian Roseneath-Epsilon-Murteree strata in the Cooper basin, Australia

The early to middle Permian Roseneath-Epsilon-Murteree (REM) strata of the Cooper Basin are considered the most feasible shale gas play in Australia. The sedimentary evolution of the fluvial-lacustrine REM strata is complex and previous studies on the facies architecture have been very few and rough in nature. A systematic, core-based sedimentological and sequence stratigraphic analysis from this study reveals a range of complex features and sheds new light on the depositional process. More than 1400-m cores from nine wells penetrating the REM strata have been described in detail to study the lithofacies, facies associations, and associated stacking patterns. Twelve lithofacies are identified and further categorized into eight facies associations: (1) open lacustrine, (2) lacustrine shoreface, (3) flood plain/interdistributary bay/channel fill, (4) distributary channel/fluvial channel, (5) crevasse channel/splay/natural levee, (6) distributary mouth bar, (7) prodelta, and (8) mire/swamp. The Roseneath and Murteree Shales were deposited in a widespread lake with dominant rhythmites and claystones whereas the Epsilon Formation was formed in a transitional environment with a mixture of fluvial, deltaic, shoreface and mire deposits. Sequence stratigraphic analysis of cores and wireline logs reveals that the REM strata were deposited within two 1st-order Transgressive-Regressive (T-R) cycles and can be further separated into four sequence units. Lower-order T-R cycles are also observed among these 1st-order cycles. This study provides a good analogue and/or a case for comparison with other shale-dominated gas plays around the world and a similar approach should help clarify their depositional process.

A Core Logging, Machine Learning and Geostatistical Modeling Interactive Approach for Subsurface Imaging of Lenticular Geobodies in a Clastic Depositional System, SE Pakistan

Facies models are essential tools for imaging subsurface geobodies and for reducing exploration and development risks efficiently. The Lower Goru Formation is one of the principal formations in the Lower Indus Basin, Pakistan. Its substantial hydrocarbon potential is unexplored, as most of the wells within the Sawan gas field are facing relatively low production yields. This study aimed to delineate subsurface geobodies by developing a facies model to study the depositional processes and facies distributions that have been neglected previously. The interactive approaches used in this research consisted of petrophysical, mineral composition, well-log facies, and horizon attribute analyses, as well as an unsupervised vector quantizer artificial neural network (UVQ–ANN) and sequential indicator simulation (SIS) modeling. A series of E–W-oriented lenticular geobodies were delineated. These geobodies had variable thicknesses, and they pinch out to the NW and prograde to the NE. The results of the SIS, UVQ–ANN, petrographic analysis, and attribute analysis show a fluvial fan-delta sedimentary system. The reservoir sands were deposited in distributary mouth bars and deltaic channels in proximal delta front settings. The coarse- to very fine-grained reservoir sands prograde toward the NE. Thinly laminated beds of fine-grained black shales and lime muddy siltstones were deposited under low-energy conditions in mid-shelf marine settings. The adopted methodology for the generated facies model can be extended to different basins within Pakistan with the same geological settings, and it can be used for prospect evaluation, future drilling, and development plans within the Sawan gas field in the Lower Indus Basin.

Correlation of the lithostratigraphic facies relationships and depositional environments of the uppermost Silurian through Lower Devonian strata across the central Darling Basin, western New South Wales, SE Australia

This paper is focused on the detailed lithostratigraphic facies characterisation of the paleo-environments of the uppermost Silurian through Lower Devonian Winduck Interval strata from the Bancannia South 1, Pondie Range 1 and Booligal Creek 1 and 2 wells, across the central Darling Basin of western New South Wales. Based on data from both wireline logs and drill cores and cuttings, an interpretation of paleo-environments and evolution of the depositional facies is presented. Our approach involves two key interpretations. The first outcome was the delineation of the Winduck Interval section (maximum observed thickness of approximately 1475 m) and formal subdivision into lower and upper Winduck Intervals, based on well data from the central Bancannia Trough, southern Pondie Range Sub-basin and northwestern flank of the Blantyre Sub-basin. The second outcome is based on the internal lithostratigraphy of the Winduck Interval represented by 11 sedimentary lithofacies organised into three lithofacies associations (LFAs). LFA-X1 is interpreted as distributary-channel sandstone complex deposits, LFA-X2 is interpreted as distributary mouth bar with small-scale braided delta plain complex deposits and LFA-X3 is interpreted as tidal channel sands with proximal delta front complex deposits. Subsurface lithostratigraphic facies analysis relationships and depositional environments of the Winduck Interval section have implications for evaluating the hydrocarbon potential and may assist future exploration efforts in the central Darling Basin, especially the Bancannia Trough and Pondie Range Sub-basin. KEY POINTS A detailed lithostratigraphic facies characterisation of the paleo-environments of the uppermost Silurian–Lower Devonian Winduck Interval strata in the central Darling Basin is presented. Evaluation and interpretation of the Winduck Interval section in study area was subdivided into two informal stratigraphic units, a lower Winduck Interval and an upper Winduck Interval. Eleven distinct sedimentary lithofacies codes (LFs), which have been recognised in the internal lithostratigraphy of the Winduck Interval from the Bancannia South 1, Pondie Range 1 and Booligal Creek 1 and 2 wells, have been grouped into three lithofacies associations (LFAs). Lithostratigraphic facies analysis relationships and depositional environments of the Winduck Interval section has implications for evaluating the hydrocarbon potential and may assist future exploration in the Bancannia Trough and Pondie Range Sub-basin.

Sustained growth of river-mouth bars in the vulnerable Changjiang Delta

Based on 345 satellite images from 1991 to 2018, we examine the height, area and morphological changes of two large newborn river-mouth bars in the vulnerable Changjiang Delta as well as their influencing factors. The growth of inaccessible river-mouth bars is less affected by human estuarine activities, therefore, studying their growth shows particular promise in revealing the effects of relative sea level rise and human activities upstream of the river basin. We find the morphologic changes of the river-mouth bars in the Changjiang Delta are seriously affected by waves, tides and runoff, but their height and area growth depends on whether there is sufficient river sediment supply, and the impact of relative sea level rise is relatively small. The river-mouth bar located in the active distributary mouth has maintained rapid growth in the past three decades, although the Three Gorges Dam has trapped most of the upstream sediment. We believe it is the sediment scoured from the main channel downstream of the dam substantially supplements the sediment discharged to the sea, contributing to the rapid growth of the river-mouth bar. Our finding inspires a reassessment of the effects of dam construction on delta evolution when sediment reserves downstream of the dam are large and the runoff is ample. Under the current circumstances of rapid sea level rise and intensified human activities, the rapid growth of river-mouth bars mainly due to the sediment supply from the river channels allows precious buffer time to protect the vulnerable Changjiang Delta, and it also brings hope for and new perspectives on the protection of other major deltas in the world.

Seismic Stratigraphy and Reservoir Characterization of ‘E’ Field Sediments: Inferences from South-Eastern Late Miocene - Pliocene Records, Offshore Niger Delta

Studies of Late Miocene – Pliocene continental shelf and slopes sediments on the south-eastern continental margin, Niger Delta (a broad region from the shelf – slope break extending to the ultra-deep waters: > 1500m), have revealed markedly different responses to sea level fluctuations. Significant features of the stratigraphy include siliciclastic-dominated facies consisting principally of one or more of the following genetic types: deltaic distributary mouth bars, channel and shoreface sands, barrier beach, shelf and offshore turbidites. These sands are Late Miocene – Early Pliocene in age and were deposited in deep water settings on the slope of the ‘Y’ field by a range of depositional processes that include slumps, debris flows and turbidity currents. Most of these sands could be interpreted to relate to periods of base level fall, if not Global Eustatic lowstands. Working within a sequence stratigraphic framework, eight (8) sequences have been delineated on the basis of reflection termination patterns. The major sequences were related to sea level fall during which the shelf was exposed to erosion. A cross section of the stratigraphic correlation drawn showed that the horizons are laterally continuous. However, pinch-out channel sands and lenticular sandbodies are evident. The recognition of depositional surfaces on the stratigraphic cross-sections allows subdivision of the stratigraphy into systems tracts: HST, FSST, TST and LST. On the seismic package, three (3) main seismic surfaces with distinct chronostratigraphic expressions are evident. They include non-marine, marine and fault plane surfaces. In addition, clinoform strata in the basin-margin setting of this field have relatively flat topsets and sloping clinoforms. On the shelf settings, a composite surface exists consisting of the merged sequence boundary, otherwise marked and interpreted as 4.2 Ma sequence boundary, transgressive surface (TS) and maximum flooding surface (MFS), unless separated by an incised valley fill (IVF). In the ‘Y’ field, failure, slumping and re-sedimentation processes that cause base-of-slope thickening in response to gravity and geotropic flows modify the slope. Furthermore, within the same basinal setting, affected by the same sea level rise, the facies boundaries are diachronous. Keywords: Seismic stratigraphy, Petrophysics, Sea level change, South-eastern, Miocene – Pliocene Sedimentation, Offshore Niger Delta DOI: 10.7176/JNSR/11-14-04 Publication date: July 31 st 2020

Sedimentary characteristics of early Miocene platform deposits in the Neogene Adana Basin, southern Turkey

We report a detailed description of the sedimentological characteristics of the Early Miocene platform deposits to contribute towards the understanding of the evolution of the Neogene Adana Basin southern Anatolia . Several detailed sedimentological logs were measured and interpreted from the platform deposits Kaplankaya, Karaisali, and turbiditic Cingoz formations of the Adana Basin. The depositional evolution of the Adana Basin began during the Early Miocene as a foreland basin. The basin fill is both marine and nonmarine in character, which shows a gradual transition at the northern margin of the basin from one into another. Formation of the basin commenced by a major marine transgression during the Early Miocene. The pre-Miocene sedimentation area was a large platform with an adjacent depression area, which greatly affected the development of Miocene sedimentation after the Aquitanian-Burdigalian transgression. Prior to this transgression, the paleotopography was filled by terrestrial Gildirli deposits, and after transgression, shallow platform sediments of Kaplankaya-Karaisali formations, and Cingoz and Guvenc formations were deposited in the slightly deeper parts of the basin. The Early Miocene Kaplankaya and Karaisali formations conformably overlie the Gildirli Formation. However, both formations are seen resting with angular unconformity on the tilted Oligocene age Karsanti Basin sediments. Early Miocene sediments were developed due to the transgression towards the north. In the areas close to the shore, the northerly sourced littoral-brackish and deltaic Kaplankaya Formation and the more marine reefal Karaisali Formation were deposited. Stratigraphical, sedimentological, and paleontological evidence has proven that the platform sediments of the basin were deposited during the Aquitanian-Burdigalian. While the Karaisali Formation is represented by reef sediments, the base of Kaplankaya is characterized by alluvial fan and distributary mouth bar deposits with intermittent fluvial and marine conditions. These pass upward into prodelta clayey facies that consist of shallow marine fossils. The Burdigalian-Serravalian turbiditic Cingoz Formation cuts the Kaplankaya Formation with a channelized erosive contact.

The facies analysis of a fan delta by integrating multiple discipline data — A case study of the KL-A oilfield, Bohai Bay Basin, China

The third member of the Shahejie Formation (Es3) is the main hydrocarbon exploration target in the KL-A oilfield, Bohai Bay Basin, East China. The facies classification is an essential step in mapping the depositional system of Es3 within the Bohai Bay Basin. The facies model is important for identifying the “sweet” lithology within the reservoirs. We characterize the facies of Es3 by integrating cores, well logs, and seismic data. The analysis indicates that the Es3 consists of fan delta deposits. The analysis using well logs and cores indicates that there are five different lithofacies for the Es3 Formation: massive sandstone, horizontally bedded sandstone, trough cross-bedded sandstone, ripple cross-laminated sandstone, and massive mud. The microfacies of Es3 include distributary channel, distributary mouth bar, interdistributary bay, and lacustrine mudstone deposits. The sweet lithologies for hydrocarbon accumulation within the KL-A oilfield include the coarse- and fine-grained sand developed within the channels and distributary mouth bar. We use seismic rms amplitude strata slices to determine the horizontal distribution of facies of the fan delta. The correlation between rms amplitude and well logs indicates that relatively low rms amplitude anomalies on the strata slices can be used as an indicator for sandstone within the KL-A oilfield.

Stratigraphy and Depositional Model of Palaeogene Dongying Braided-River Delta Sandstones, L Field, Bohai Bay Basin, Offshore Eastern China

Fluid production of L field, Bohai Bay Basin, offshore eastern China is mainly from the Palaeogene Dongying D interval. The stratigraphy framework and depositional model of the braided-river delta system within the D interval are investigated using seismic, well log, core data and production response. The D interval is interpreted as having been deposited in a lowstand system tract. And two progradational successions are recognized, including in ascending order the D2 and D1. The younger sandstone in the D1 interval is of greater thickness and larger distribution area than the elder sandstone in the D2 interval. Six core facies and five log patterns are recognized and interpreted to be underwater distributary channels, levees, overbank splays, mouth bars, sheet sand and shalier interchannel deposits. Channel deposits occur along the trend of thickest D2 and D1 sandstones. The sandstones that flank each side of the channel deposits are interpreted to be levee and overbank splay deposits. The sandstones that develop at terminal distributary channel mouth are interpreted to be mouth bar and sheet sand deposits. Channel-flank deposits can form good-quality reservoir sandstones, but they contain interbedded siltstones and thus have lower porosity and permeability than do channel deposits. The facies distributions predicted for the D interval match trends of the daily total fluid production. Knowledge gained from study of the L field has application to the development of other fields with similar depositional and diagenetic histories.

Lithogeomorphological facies analysis of Upper Miocene coal-prone fluviodeltaic reservoirs, Northern Malay Basin

The Group E stratigraphic unit is a significant gas producer in the Northern Malay Basin. However, due to the thinly bedded nature of the sandstone reservoirs, thick shale, and abundant coal beds, accurate seismic attributes interpretation of lithology and fluid prediction has been a daunting task. To address this problem, we have conducted an integrated seismic sedimentology workflow using spectral decomposition, color blending, waveform classification, prestack seismic inversion, and stratal slicing to characterize the lithogeomorphological facies of the coal-bearing reservoirs. On spectral decomposition and waveform classification maps, we clearly identified depositional elements such as the distributary channel, distributary mouth bar, subaqueous levee, and interdistributary fill. We computed the elastic properties through prestack seismic inversion to obtain good lithology discrimination between coal and gas-charged sandstone. Both lithologies are characterized by low acoustic impedance, but the compressional to shear velocity ratio ([Formula: see text]) of coal is high compared to gas-charged sandstone. The current interpretation indicated that the Group E interval was deposited in a delta plain setting. The varying flow directions of the distributary channels in the area support the hypothesis that describes the Malay Basin during Miocene time as a narrow gulf, connected to an open sea to the south and flanked by deltas and fan deltas.

Flow unit characteristics of fan delta front deposits and its influence on reservoir development - Taking yulou oil bearing sets in some experimental area in west depression in Liaohe Basin in China as an example

Taking some steam flooding experimental area in the western depression of the Liaohe Basin in China as an example, it quantitatively evaluates the flow units of the sedimentary facies in fan delta front and analyzes the influences of the flow units on the development of the oilfields. Comprehensive analysis of multifarious data such as geology, core analysis and well logs indicates that porosity, permeability and FZI are key parameters for classification and evaluation of the reservoir flow units. Then using SPSS cluster analysis software platform, cluster analysis are conducted on reservoir physical properties of cored wells, and based on which discriminant analysis are performed to obtain the discriminant formula. The discriminant analysis of reservoir physical properties of the wells without core data is based on fine interpretation of well logging data. Combined with the results of cored wells, the classification and evaluation of the flow units has been completed in the target layer of ​​the whole study area. Finally the flow units are divided into four classes, namely, Class A, Class B, Class C and Class D. Classes A and B flow units represent high-quality reservoirs. The flow units are mainly controlled by sedimentation. Classes A and B are mainly sedimentary microfacies of underwater distributary channel and distributary mouth sand bar. The paper proposes five principles of judging the rationality of flow units, describes the development characteristics of different classes of flow units on section and plane, analyzes the influence of flow units on oilfield development and suggests countermeasures. Specially, in the process of steam flooding, target injection layers should be optimized and steam injection pressure should be effectively controlled to prevent steam channeling; when planning infill wells, injection and production wells should be deployed in the same class of flow unit to ensure good connectivity; the development of remaining oil should focus on Classes A and B flow units, and meanwhile pay more attention to the fine interpretation results of well logging data.

Contribution of deltaic wetland food sources to coastal macrobenthic consumers (Po River Delta, north Adriatic Sea)

Estuaries are known to export huge quantities of terrigenous/riverine organic matter and nutrients to coastal areas, subsidizing food sources to their communities; however, this process is seldom investigated in complex multichannel delta-prodelta systems. Stable isotope analysis was used to investigate the contribution of organic sources originated from the Po River Delta, one of the widest deltaic wetlands in the northern Mediterranean Sea, to the diet of the nearby coastal macrobenthic consumers, and their influence on invertebrates' trophic structure and biomass. Following intense river flood events, macrofauna samples were collected in the prodelta area at increasing distance from the main river distributary mouth. Potential primary resources were collected within the delta and the prodelta areas. A terrestrial signal in the primary consumers' diet was evident as a shift in their δ13C, being this more 13C depleted near the main river distributary. The Bayesian mixing models indicated an important contribution of deltaic sources, in particular C4-grass detritus (25–57%), to primary consumers' diet, confirming a strong energetic link between delta and prodelta areas. Overall, most of the consumers' biomass were concentrated at sites close to the main distributary mouth, mainly as suspension and surface deposit feeders. A simplification of the macrobenthic community structure, accompanied by narrower transfer pathways was also evident at sites more distant from the main river distributary, in relation to changes in the quality of resources. Our data, although limited to winter season, suggest that during periods of low in situ productivity but high river flow energy, invertebrates are able to efficiently exploit terrigenous food sources, restraining the detrimental effect of increased turbidity and sedimentation. We conclude that riparian/wetland vegetation associated with river deltas can provide important food sources to marine primary consumers. These results furthermore highlight the need for integrated management and protection strategies of connected land-sea ecosystems.