Stratal Slices Research Articles

Seismic-informed carbonate shelf-to-basin transition in deeply buried Cambrian strata, Tarim Basin, China

We develop an enhanced interpretation workflow to improve facies interpretation in ultradeep (5000–8000 m), high-velocity (6000–7000 m/s) carbonate rocks using low-frequency (as low as 18 Hz) seismic data. Our study area includes two seismic surveys north and south of the Cambrian platform margin that extends more than 500 km in strike direction. Relative impedance (−90° data) and frequency fusion are applied to predict impedance and lithology in carbonate platform-basin architecture. Outcrop seismic modeling clarifies the facies architecture of subtle subseismic clinoforms. Stratal slices are made for seismic geomorphology. We recognized eight seismic sequences and seven seismic facies in 1200-m prograding sediments. As a strongly prograding accretionary margin, the stratal relationships and transitions from platform interior to shelf margin to slope and basin are consistent throughout the basin. Platform interior is characterized by intertidal, supratidal, and salt flat facies; the shelf margin develops microbial reef and shoal facies; the slope and basin facies are dominantly gravity flow and deepwater sediments. The northern and southern areas of the margin, however, are characterized by different slope-to-basin geomorphology and environments. In the north, the shelf edge was cemented, with little reworking of shallow-water sediments to the slope and basin. Gravity failure–related facies, such as gullies and slump aprons, dominate in the slope. No turbidite fans are found in the sediment-starved deep basin. In the south, a series of submarine channels transported shallow sediments long distance to form slope fans and basin-floor fans. Turbidite sediments contain a significant amount of low-impedance sediments from the shelf edge. The syndepositional tectonic trench faults, by initiating channels, are hypothesized to be a new mechanism for sediment transport in a deepwater environment. Such a mechanism provides a clue to help researchers recognize and map deepwater reservoir facies in the basin.

Application of seismic sedimentology in a fluvial reservoir: A case study of the Guantao Formation in Dagang Oilfield, Bohai Bay Basin, China

A seismic sedimentology study was performed to analyse the complex fluvial reservoirs in the Neogene Guantao Formation in Kongdian Oilfield, Huanghua Depression. Three facies associations were identified by core and logging data, including bedload channel, mixload channel, and floodplain. Widely developed floodplain deposits beds were selected as the relatively reliable reference time surfaces. Stratal slices were generated applying the stratal‐slicing principle on two isochronous reference seismic events in Kongdian Oilfield. These stratal slices were used to analyse the distribution of sediments in a relative geologic‐time domain. The variety of sediment distribution observed on the stratal slices indicated that the fluvial channel systems of study interval had evolved from straight channel, sandy‐braided channel to combined channel. Sediment dispersal patterns were controlled by the change of accommodation (A) and sediment supply (S) rate. Setting with a low A/S ratio favours the development of fluvial environment and high A/S ratio favours the development of floodplain. Braided channel sandstones formed in a low A/S ratio depositional environment were generally thought to be excellent reservoirs. However, the muddy plug could damage the lateral continuity of sandbody, impede the fluid flow, and reduce the water‐injection efficiency.

Evolution of a Late Miocene Deep-Water Depositional System in the Southern Taranaki Basin, New Zealand

A long-standing problem in the understanding of deep-water turbidite reservoirs relates to how the three-dimensional evolution of deep-water channel systems evolve in response to channel filling on spatiotemporal scales, and how depositional environments affect channel architecture. The 3-D structure and temporal evolution of late Miocene deep-water channel complexes in the southern Taranaki Basin, New Zealand is investigated, and the geometry, distribution, and stacking patterns of the channel complexes are analyzed. Two recently acquired 3-D seismic datasets, the Pipeline-3D (proximal) and Hector-3D (distal) are analyzed. These surveys provide detailed imaging of late Miocene deep-water channel systems, allowing for the assessment of the intricate geometry and seismic geomorphology of the systems. Seismic attributes resolve the channel bodies and the associated architectural elements. Spectral decomposition, amplitude curvature, and coherence attributes reveal NW-trending straight to low-sinuosity channels and less prominent NE-trending high-sinuosity feeder channels. Stratal slices across the seismic datasets better characterize the architectural elements. The mapped turbidite systems transition from low-sinuosity to meandering high-sinuosity patterns, likely caused by a change in the shelf-slope gradient due to localized structural relief. Stacking facies patterns within the channel systems reveal the temporal variation from a depositional environment characterized by sediment bypass to vertically aggrading channel systems.

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.

Multi-disciplinary approach to sedimentary facies analysis of Messinian Salinity Crisis tectono-sequences (South-Mansoura Area, Nile Delta): Incised-valley fill geological model reconstruction and petroleum geology–reservoir element delineation

The quality of a hydrocarbon reservoir is strongly controlled by the depositional and diagenetic facies nature of the given rock. Therefore, building a precise geological/depositional model of the reservoir rock is critical to reducing risks while exploring for petroleum. Ultimate reservoir characterization for constructing an adequate geological model is still challenging due to the in general insufficiency of data; particularly integrating them through combined approaches. In this paper, we integrated seismic geomorphology, sequence stratigraphy, and sedimentology, to efficiently characterize the Upper Miocene, incised-valley fill, Abu Madi Formation at South Mansoura Area (Onshore Nile Delta, Egypt). Abu Madi Formation, in the study area, is a SW-NE trending reservoir fairway consisting of alternative sequences of shales and channel-fill sandstones, of the Messinian age, that were built as a result of the River Nile sediment supply upon the Messinian Salinity Crisis. Hence, it comprises a range of continental to coastal depositional facies. We utilized dataset including seismic data, complete set of well logs, and core samples. We performed seismic attribute analysis, particularly spectral decomposition, over stratal slices to outline the geometry of the incised-valley fill. Moreover, well log analysis was done to distinguish different facies and lithofacies associations, and define their paleo-depositional environments; a preceding further look was given to the well log-based sequence stratigraphic setting as well. Furthermore, mineralogical composition and post-depositional diagenesis were identified performing petrographical analysis of some thin sections adopted from the core samples. A linkage between such approaches, performed in this study, and their impact on reservoir quality determination was aimed to shed light on a successful integrated reservoir characterization, capable of giving a robust insight into the depositional facies, and the associated petroleum potential. The results show that MSC Abu Madi Formation constitutes a third-order depositional sequence of fluvial to estuarine units, infilling the Eonile-canyon, with five sedimentary facies associations; overbank mud, fluvial channel complex, estuarine mud, tidal channels, and tidal bars; trending SW-NE with a Y-shape channel geometry. The fluvial facies association (zone 1 and 3) enriches coarse-grained sandstones, deposited in subaerial setting, with significantly higher reservoir quality, acting as the best reservoir facies of the area. Although the dissolution of detrital components, mainly feldspars, enhanced a secondary porosity, improving reservoir quality of MSC Abu Madi sediments, continental fluvial channel facies represent the main fluid flow conduits, where marine influence is limited.

Application of seismic sedimentology to the western slope of northern Songliao basin

During the sedimentary period of Saertu reservoir on the western slope of the northern Songliao basin, delta front and shore-shallow lake subfacies are mainly developed, which have the characteristics of few sandstone layers and thin single layer thickness. The lithology of thin layer or thin interlayer can not be distinguished clearly by seismic response on conventional seismic section, and it is difficult to identify them. Geophysical response characteristics of channel sand bodies are defined by well-seismic combination. Under the guidance of seismic sedimentology, the qualitative and quantitative prediction of channel sand bodies is carried out by using 90°-phase conversion, stratal slicing and waveform indication inversion techniques. The results show that the seismic reflection axis is symmetrical with respect to the top and bottom surface of sandstone, and the channel sand body has obvious characteristics and completely corresponds to wave peak reflection. The channel bodies of S1 and S23 reservoir formation are separated respectively into two stages by using the amplitude attributes of stratal slices, and the coincidence rate of reservoir prediction to wells is 78%~84%, with an average of 79.7%. The waveform indicator inversion technique is used to predict the channel sand body thickness of the four stages, and the error of sand body thickness to well is 0~1.6m, with an average of 0.32m.

Quantitative prediction of fluvial sandbodies by combining seismic attributes of neighboring zones

The geological and geophysical characterization of hydrocarbon-bearing sandstones of fluvial origin is a challenging task. Channel sandbodies occurring at different stratigraphic levels (i.e., in a reservoir interval of interest as well as in overlying and underlying stratigraphic intervals) but overlapping in planview usually cause significant seismic interference due to limitations in seismic resolution: this can produce significant error in the prediction of sand location and thickness using seismic attributes. To mitigate the effect of seismic interferences by zones neighboring a target reservoir interval, a new method is proposed that combines multiple seismic attributes of the target interval and of its interfering neighboring zones, implemented by a supervised machine learning algorithm using support vector regression (SVR). Since the thickness of neighboring intervals causing seismic interference has a constant value of a quarter of a wavelength (1/4 λ), the stratal slice corresponding with the top horizon of the target interval is taken as the base of a window of 1/4 λ to calculate seismic attributes for the overlying zone; similarly, the stratal slice corresponding with the bottom horizon is taken as the top of a window of 1/4 λ to calculate seismic attributes for the underlying zone. The proposed method was applied to a subsurface dataset (including a 3D seismic dataset and 255 wells) of the Chengdao oilfield, in the Bohai Bay Basin (China). The interval of interest is located in the Neogene Guantao Formation, whose successions are interpreted as fluvial in origin. This application demonstrates how the proposed method results in remarkably improved sandstone thickness prediction, and how consideration of multiple attributes further improves the accuracy of predicted values of sandstone thickness.

Architectural analysis of subsurface meander-belt sandstones: A case study of a densely drilled oil field, Zhanhua sag, east of Bohai Bay Basin

The Gudong oil field offers a unique opportunity to characterize thin meander-belt sandstones in an area with a dense network of wells (100 wells per square kilometer or 259 wells per square mile). The goal of this study is to evaluate the evolution of subsurface meander-belt complexes through analysis of their overall stratigraphic architecture defined by the spatial distribution of sedimentary structures and stratigraphic surfaces of stacked point-bar sandstones, which severely affect the potential for producing the remaining oil in these mature oil fields. Five types of superposition structures, which reflect the shapes of the point-bar sand bodies in the superimposed regions between point bars, are identified by combining stacked and migrated seismic profiles, seismic forward models, and wire-line log profiles. The point bars belong to different stages of channel stories through the analysis of their superimposed structures and the vertical offset of the basal surfaces of point-bar sandstones. Five channel stories are recognized in the thin meander belt. They can be distinguished by the analyses of stratal slices, wire-line log profiles, and tracer data. These channel stories were found to exhibit unique morphometric characteristics: the thickness and width of the channel stories changed with the discharge of the paleoriver; the widths of the later channel stories became more stable through time and were not affected by the flow discharge during the deposition of the channel stories. The identified superimposed structures between subsequent point bars and morphometric parameters of channel stories are useful for the modeling of the target reservoir.

Seismic response to paleo-sand dunes in the Nugget Sandstone Formation, southwestern Wyoming

We have analyzed a 3D seismic survey acquired for a carbon sequestration project on top of the Moxa Arch in southwestern Wyoming. We observed a zone of discontinuous reflectors on vertical slices of seismic amplitude volume, whereas, the northwest–southeast lineations were observed on the time slices. We performed a seismic to well tie that suggested that the lineations occur within the Nugget Sandstone. The Nugget Sandstone is an eolian sandstone deposit of Early Jurassic age, deposited as a subtropical dune field, and equivalent to the Navajo Sandstone of southwestern Utah. Petrophysical analysis indicates that the Nugget Sandstone is dominated by clean sandstone (70%–80%), whereas evaporites, including halite and anhydrite, are present in certain zones. Previous outcrop studies on the Navajo Sandstone indicate the wind direction to be predominantly northeast–southwest. Seismic attributes, including coherence and curvature, displayed on stratal slices within the Nugget Sandstone interval indicate the presence of lineations in the northwest–southeast direction with irregular spacing. These lineations are approximately perpendicular to the inferred dominant wind direction. We computed the dominant wind direction from the average azimuth of the lineations as seen on the curvature attribute in the Nugget Sandstone interval. Geological feature: Eolian sand dunes with interdunal evaporites Seismic appearance: Parallel lineations with irregular spacing on seismic attribute horizon slices Alternative interpretations: Canyons at continental slopes; slope failures Features with a similar appearance: Marine bars; contourites Formation: The Nugget Sandstone — equivalent to the Navajo Sandstone Age: Early Jurassic Location: Moxa Arch, Wyoming Seismic data: Obtained by the University of Wyoming with U.S. DOE funding Contributors: Dhruv Agrawal, Brady Lujan, Sumit Verma, Shuvajit Bhattacharya, and Subhashis Mallick Analysis tools: Coherence and curvature attributes; seismic inversion; petrophysical inversion

Seismic geomorphology of shallow-water lacustrine deltas in the Paleocene Huanghua Depression, Bohai Bay Basin, eastern China

The most important sedimentary facies comprising shallow-water lacustrine deltas are distributary channels, and these form abundant ribbon-shaped sand bodies that are excellent petroleum reservoirs. However, distributary channel sandstones are notoriously difficult to correlate and characterize in the subsurface based on well data alone. Here, we show how seismic geomorphology can be used to map lacustrine deltaic sedimentary successions in the First Member of the Kongdian Formation within the Zilaitun Oilfield, Huanghua Depression (China). Using core and wireline logs, this study identified distributary channels as the dominant sedimentary facies. Together with mottled gray-green or maroon mudstones and locally shingled progradational seismic reflection architecture, this indicates that deltas were built in a weakly-oxidized shallow-water lacustrine environment. Next, core observations were linked to seismic data to produce a successive series of stratal slices and root mean square amplitude attribute (RMSAA) maps. The RMSAA maps allowed distributary channel, mouth bar, and beach bar facies to be identified and mapped across the study area. Two patterns of distributary channels emerged from the data: (1) a distributive pattern with a lower concentration of distributary channels; and, (2) an anastomosing deltaic pattern with a high concentration of bifurcated distributary channels. Based on the seismic geomorphological analysis we show that the succession records three phases of delta evolution - retrogradation, aggradation, and progradation - which combine to form 3rd-order sequences. From a petroleum reservoir point of view, the distributive pattern yields narrower, thicker, and less connected sand bodies than the anastomosing pattern. This is consistent with observations from modern shallow-water lacustrine delta systems, providing independent support for the interpretation and highlighting the effectiveness of using seismic geomorphology.

Reservoir architecture and evolution of meandering belt: A subsurface case in the Jiyang Depression, eastern China

The reservoir architecture of a meandering river deposition can indicate the heterogeneity of the subsurface reservoirs and deposition and evolution of the paleo-river. Although outcrop study has been useful in characterizing reservoir architecture, the study of the subsurface reservoir is still a challenge due to its complicated reservoir geometry and forming process. In this work, a mature oil field in Bohai Bay Basin, eastern China was investigated to understand the reservoir architecture and evolution of a Neogene meandering belt using drilling cores, well logging, 3D seismic data, and oil production data. In the study area, five types of litho-facies were observed indicating the specific hydrodynamic conditions. The results obtained two types of point bar combination models focused on (1) the point bars migration in the same direction at equal elevation and (2) erosion and superimposition of the multi-phase point bars. Abandoned channels in study area are classified into two types: Type Ⅰ is the “Early and long-term abandoned channel” and Type Ⅱ is the “Late and short-term abandoned channel”. Well log facies of Type Ⅰ presents a low sandstone/mudstone ratio while that of Type Ⅱ has a high sandstone/mudstone ratio. Both models exhibited the weakening of the seismic reflection amplitude and changes in the waveform. Based on the well log curves, stratal slicing, and seismic facies analysis, single point bars are interpreted more accurately. The meandering river in the study area, which was previously interpreted as a large single point bar, was comprehended as a meandering belt formed by a multi-phase point bar complex with three single point bars in the meander. Erosion and overlapping can be observed between the first and second phases of the point bars. In modern river deposition, similar meander reservoir architecture and its evolution can be observed. Additionally, reservoir engineering analysis showed that there are flow barriers between point bars of different phases. The reservoir architecture of a meandering belt was characterized and the depositional evolution of the paleo-river was reconstructed. The methods proposed is significant for qualitative interpretations of reservoirs such as morphology channel recognition, reservoir connectivity analysis, and lithology and interlayer prediction.

An alternative, seismic-assisted method of fluvial architectural-element analysis in the subsurface: Neogene, Shaleitian area, Bohai Bay Basin, China

We develop an alternative fluvial architectural-element analysis using limited core and wireline logs in sparse wells with the assistance of stacked and migrated 3D seismic data. To pursue high resolution, we implement a novel workflow that integrates seismic lithology, seismic geomorphology and core- and wireline-log-based sedimentology. Seismic lithology is performed using 90° phase wavelet and frequency fusion; lithofacies are classified by combining seismically derived lithology (shaliness) and core and wireline-log description of lithology, grain size, and sedimentary structures; seismic geomorphology is conducted on seismic stratal slices. A feasibility analysis concludes that macroform and large mesoform fluvial elements (4–50 m thick) can be revealed using 10–100 Hz bandwidth, 50 Hz dominant frequency, 3D seismic data. The workflow is applied to the study of the Neogene fluvial sediments in the Shaleitian area, Bohai Bay Basin, China. Nine fluvial architectural elements are recognized, including fluvial valley, floodplain, sand-filled and mud-filled channels, sand fan, lateral-accretion complex, sandbar, chute channel, incremental lateral accretion, and overbank. These elements were then assembled for various depositional styles in the meanderplain and braidplain. Interpretation of the fluvial architectural-element maps reveals (1) braidplains and meanderplains characterized by distinctive elements, (2) sand-filled and mud-filled channels that coexisted in the same system, (3) recurrent transitions between different channel types, and (4) thick braided fluvial sediments preserved in a large basin. This workflow provides new strategies to improve mineral exploration, development, and reservoir modeling in the Bohai Bay Basin as well as scantly drilled basins elsewhere.

Application of seismic sedimentology in lithostratigraphic trap exploration: A case study from Banqiao Sag, Bohai Bay Basin, China

A method of identifying lithostratigraphic traps based on seismic sedimentology is proposed. We first establish a 3D high-resolution (fifth-order) sequence stratigraphic framework by using the stratal slices. Then, the reservoir distribution and reservoir-seal assemblage are investigated within the high-resolution sequence framework. This method turns the interpretation of lithostratigraphic traps from traditional seismic facies-based approach to the dynamic analysis of high-resolution seismic geomorphic information. We divide the lower Sha-1 member in the Banqiao Sag, Bohai Bay Basin, East China, into fourth- and fifth-order sequences by applying our method. The fifth-order sequence corresponding to Sha1-2 shows that the fan delta-distal subaqueous fan depositional system can be observed at the bottom of Sha1-2. The bounding fault and paleogeomorphology control the deposition of sand, whereas the sand bodies in the fan delta and distal subaqueous fan are developed near the bounding fault and the open lake basin, respectively. We then predict the sand thickness based on the well logs and seismic amplitudes. Moreover, according to the structural features, at least four lithostratigraphic traps are identified. These traps form a good reservoir-seal assemblage with overlying mudstones deposited during the period of lacustrine level rising. The drilling results in Trap-3 suggest that, our method can be a method of choice for effectively identifying the lithostratigraphic traps, a significant measure for hydrocarbon exploration.

Combined inverse and forward numerical modelling for reconstruction of channel evolution and facies distributions in fluvial meander-belt deposits

The sedimentary record of meandering rivers contains a diverse and complex set of lithological heterogeneities, which impact natural resource management. Different methods exist to model such accumulated successions present in the subsurface by integrating knowledge of system evolutionary behaviour and geometries visible on seismic time or stratal slices. With reference to case-study examples, we review, discuss and employ two of these methods: (i) ChaRMigS generates possible scenarios for channel evolution and meander cut-offs by a reverse migration process; (ii) PB-SAND is a forward stratigraphic model which simulates fluvial point-bar geometry and facies distributions from known palaeo-channel geometries. We introduce a workflow to demonstrate how these two methods can be applied in combination to predict fluvial meander-belt facies distributions, using a subsurface dataset on a Pleistocene succession from the Gulf of Thailand where abandoned channels are visible on seismic time slices, but for which bar-accretion geometries and the exact timing of channel abandonment are unclear. Results show the value of a combined modelling approach to automate the stochastic generation of facies distributions constrained by seismic interpretations.

Integrated seismic and well-log analysis for the exploration of stratigraphic traps in the Carbonera Formation, Llanos foreland basin of Colombia

The Llanos foreland basin of Colombia is the country's most prolific oil producer, with the most known oil fields found in normal fault traps created during flexure of the foreland basin. The objective of the study is to evaluate the potential of stratigraphic traps in the Late Eocene-Early Miocene Carbonera Formation, a 400-1800 m-thick reservoir unit with numerous traps related to unfaulted, sand-prone fluvial deposits. We integrated 700 km2 of 3D seismic data with eight wells near the ~8600 bcd Cubiro field in the central area of the Llanos foreland. Interpretations of well logs and stratal slices through multi-attribute and iso-frequency amplitude cubes show that the Carbonera Formation contains tectonically-controlled, sinuous channel belts seen on seismic lines as strong, high-amplitude, concave reflections with variable width-to-depth ratio. Well logs through the Carbonera Formation record two regressive-transgressive cycles with greater preservation of non-reservoir, shaly transgressive deposits within the intermediate Carbonera members 5 and 3, and sandy, lowstand deposits in the lower and uppermost Carbonera members 7 and 1, respectively. Seismic and gamma-ray facies analyses allowed the distinction of prospective, sand-rich point bars, scrolls, and basal lag deposits from non-prospective, mud-rich abandoned channels. Stratal slices within the Carbonera Formation show changes from Late Eocene-Early Oligocene, northeast-flowing channel belts of a main axial fluvial system -proposed to be the proto-Meta River-, to a Late Oligocene southeast-flowing tributary channels interpreted as a result of eastward flexural migration, enhanced accommodation from loading of the Eastern Cordillera and a shift from an underfilled to overfilled foreland basin.

Pliocene hyperpycnal flow and its sedimentary pattern in D block of Rakhine Basin in Bay of Bengal

Abstract Based on core, logging, lab test and seismic data, sedimentary characteristics and pattern of marine hyperpycnal flow, the distribution rules of hyperpycnal flow reservoir, prediction method of favorable hyperpycnal flow reservoir zones, hydrocarbon accumulation model in hyperpycnal flow reservoir in D block of Bay of Bengal were investigated, and the favorable exploration zone and well sites were predicted. Pliocene in D block has typical hyperpycnal flow sediment, which is a set of fine-medium sandstone held between thick layers of marine mudstone and features a series of reverse grading unit and normal grading unit pairs. The hyperpycnal flow sediment appears as heavily jagged box shape, bell shape and tongue shape facies on log curves with linear gradient, and corresponds to multiple phases of deep channels on the seismic section and high sinuous channel on stratal slices. The sedimentary bodies formed by a single phase hyperpycnal flow which include five types of microfacies, namely, supply channel (valley), channel complex, branch channel, levee and sheet sand. The hyperpycnal flow sediments appear in multiple branches, multiple generations and stages in space, forming high-quality reservoirs in strips on the plane and superposition vertically, with fairly good physical properties. The channel complex sandstone, with large thickness, coarse particle size and good physical properties, is the most favorable exploration facies. Based on the guidance of the sedimentary model, distribution of the channel complex microfacies was delineated in detail by seismic reflection structure analysis, spectrum waveform characteristic analysis, slice and attribute fusion, and combined with the structural feature analysis, the favorable drilling zone was sorted out, effectively guiding the exploration deployment of the block.

Horizon slices of bandwidth-extended seismic data: optimizing thin bed interpretation from spectral decomposition

Fourth-order sequences in the northern central Miocene Gulf of Mexico are typically at or below seismic resolution and embedded in deformed strata with lateral thickness variations, making it difficult to image the corresponding paleo-depositional surfaces. Stratal or proportional slicing, involving proportionally slicing between two bounding reference horizons, can overcome these difficulties. However, if the target horizon can be readily interpreted, its horizon slice can provide the most accurate image. In this study, we first improved the resolution of the seismic data from the northern central Gulf of Mexico by bandwidth extension. Then, we autotracked a Miocene fourth-order sequence (M4) through the 50-Hz isofrequency volume obtained by the generalized spectral decomposition of the bandwidth-exteneded data. The horizon slice along M4 through the bandwidth-extended data provides a better image for incised-fluvial valleys and distributary channels compared with the stratal slice of the original data reported by earlier work. The corendered image of the variance and amplitude horizon slices further highlights the depositional features of M4. The horizon slice of M4 through the acoustic impedance volume, computed from inversion, shows that the incised-fluvial-valley fill is characterized by low impedance, suggesting good reservoir quality and that the distributary-channel fill is characterized by low to moderate impedance, suggesting fair to good reservoir quality. The definition of the horizon slice includes both the slice along the target horizon and those parallel to the reference horizon. We propose to call the slice along the target horizon a “horizon slice” and to use the term “horizon-parallel slices” for any slices parallel to an interpreted horizon.

Multiple fluvial styles in Late Miocene post-rift successions of the offshore Bohai Bay Basin (China): Evidence from a seismic geomorphological study

Abstract During the Late Miocene, river systems exhibiting different planform styles caused accumulation in the post-rift offshore Bohai Bay Basin in China; these changes in the fluvial style have profound implications for the evolution of the Bohai Sea shelf and the Late Miocene monsoon-controlled climate. Using three-dimensional (3D) seismic data and well and mud logging data, seismic- and well-based fluvial sequence stratigraphic analyses have been untaken. The lower Minghuazhen Member can be subdivided into four fourth-order sequences (SQm1 to SQm4), each of which contains low and high accommodation systems tracts. Five fluvial styles, including wide trunk incised valleys, narrow-medium incised tributary valleys, medium trunk channels, narrow-medium low-sinuosity channels, and narrow high-sinuosity channels, are recognized based on seismic expressions and well-log patterns. The seismic geomorphological study of selected stratal slices indicates the temporal change in the fluvial styles from low-to high-sinuosity channels between LAST and HAST. As shift in drainage direction from SSW to SEE occurs between SQm1 and SQm2, which may be attributed to the lateral migration of the Late Miocene paleo-Luan River and the paleo-Qinglong River that originated from Yanshan Mountain to the north. The development of wide incised braided trunk channels together with some narrow-medium incised tributary systems at the base of SQm3 and SQm4 can be interpreted as a response to climate-induced enhanced sediment supply. In addition, the paleoclimate reconstruction based on the palynological analysis reveals that the Late Miocene fluvial transition from a meandering river to a braided river occurring at SQm3 and SQm4 could be linked to multiple periods of short-lived intensification of the East Asian Summer Monsoon (EASM) during the late Late Miocene within an overall declining trend; this might have been conducive to triggering seasonal braided rivers under the higher monsoon rainfall.

Application of seismic attribute analysis in fluvial seismic geomorphology

Seismic attributes can be important predictors, either qualitative or quantitative, of reservoir geometries when they are correctly used in reservoir characterization studies. This paper discusses seismic attribute analyses and their usefulness in seismic geomorphology study of Moragot field of Pattani Basin, Gulf of Thailand. Early to Middle Miocene fluvial channel and overbank sands are the reservoirs in Pattani Basin. Due to their limited horizontal and vertical distribution, it is not always possible to predict the geometry and distribution of these sands based on the conventional seismic interpretation. This study utilized various seismic attributes, e.g., RMS amplitude analysis, spectral decomposition, semblance and dip-steered similarity, RGB blending to image the geometry and the spatial distribution of sand bodies in horizon and stratal slices at different stratigraphic intervals. Attribute analyses reveal, at shallow stratigraphic levels, RMS and semblance can successfully identify channel-shaped sand bodies and mud-filled channels associated with channel belts. On the other hand in deeper stratigraphic intervals, sand distribution can be imaged more effectively by using spectral decomposition and dip-steered similarity volumes. High-frequency spectral decomposition slices can image thin sands, and low-frequency slices can image thick sands quite effectively in deeper intervals. RGB blending of different frequency slices is particularly useful in delineating channel systems of various dimensions at deeper intervals. These images show the distribution of sands and mud-filled channels at various stratigraphic levels. The width of channel belts varies from 200 m to 3 km. These channel belts are N–S or NW–SE oriented. From the channel pattern and their dimensions, depositional environments can be predicted. Mud-filled channels identified in the horizon slices will act as a connectivity barrier between sand bodies at either side of the channel. They can also act as lateral and up-dip seal to form stratigraphic traps. The seismic attribute analyses clearly show the geometry and spatial distribution of sand bodies. Hence, this method for predicting sand body geometry might help in field development planning as well as in reducing exploration risk.

Regional Stratal Slice Imaging of the Northern Carnarvon Basin, Western Australia

Chevron has developed a method for merging, viewing, and interpreting multiple 3D seismic surveys in stratal slice domain. The products of this method are referred to as Regional Stratal Slice Volu...