Stratal Slices Research Articles

Ancient Channel-Mouth Bifurcation Angles on Earth and Mars

Channel mouth bifurcation angles on modern river deltas are remarkably consistent with a theoretical prediction of 72°. However, the persistence of this angle through channel evolution and preservation into the stratigraphic record remains untested. Ancient channel mouth bifurcations were measured using stratal slices from 3D seismic volumes as well as outcropping delta deposits in Mars orbital imagery. We find that channel mouth bifurcations interpreted from terrestrial strata exhibit a mean angle of 71.9° ± 3.8° (95% confidence interval), consistent with modern deltas as well as theoretical and numerical predictions. Angles from martian strata preserved as inverted topography exhibit a mean angle of 80.1° ± 4.8°. A larger angle on Mars may be biased by measurements on eroding outcrops, or possibly the signature of altered sediment transport processes on Mars. Expanding channel network analysis into the stratigraphic archive for the first time provides a new mechanism interpreting paleohydraulics on Earth and Mars.

Seismic sedimentology analysis of meter-scale thin sand bodies in the Jurassic Qigu Formation, Yongjin area, Junggar Basin

Seismic sedimentology is an interdisciplinary field that integrates sedimentary geology and geophysics to accurately characterize the spatial and temporal distributions of sedimentary systems. This paper focuses on the Qigu Formation in the Yongjin area of the Junggar Basin, China. The objectives are to establish a high-resolution sequence stratigraphic framework and to clarify the types of sedimentary systems present. Various technical methods, including 90° phase adjustment, attribute clustering, red-green-blue attribute fusion, stratal slicing, and seismic phase-controlled waveform indication inversion, are employed to restore the vertical evolution history of the sedimentary system and quantitatively characterize the spatial-temporal distribution of the thin sand bodies in the Qigu Formation. The results revealed that the Qigu Formation is divided into a third-order sequence, consisting of a lowstand systems tract and a lacustrine transgressive systems tract. During the lowstand systems tract, a thick channel sand body developed in the delta front, exhibiting a non-muddy, intermittent normal grading structure. The lacustrine transgressive systems tract features thin, discontinuous channel sand bodies with mud layers, also forming an intermittent normal grading structure. Two distinct types of delta fronts are identified: the first, formed during the lowstand systems tract, is characterized by branching subaqueous distributary channels in a shallow-water environment. The second, associated with the lacustrine transgressive systems tract, displays a network-like distribution of subaqueous distributary channels in a relatively deeper-water environment.

Applying seismic sedimentology to characterize the architecture of a fan delta complex: Triassic Baikouquan formation, Mahu Sag, Junggar Basin, western China

Reservoir architecture is often heterogeneous and can affect the migration and accumulation of hydrocarbons. The Triassic Baikouquan Formation in the Mahu oilfield presents a unique opportunity to use seismic data for fan delta channel and lobe belt characterization in an area with a sparse well spacing of about 800–1200 m. The Baikouquan Formation comprises coarse-grained lacustrine fan delta units deposited by traction and debris flows. The occurrence, distribution, and morphology were investigated using petrography, frequency spectrum decomposition, stratal slices, seismic forward modeling, and wireline logs. Fan-shaped lobe complexes and distributary channel complexes (sixth-order architectural units) exhibiting relatively large lateral and vertical variation were identified from 45- and 60-Hz seismic profiles. Channel and fan-shaped lobe belts (fifth-order architectural units) were investigated by integrating provenances, architectural elements from individual wells, the ratio of conglomerate to formation, cross section analysis, and seismic stratal slices. Four channel belts and three fan-shaped lobe belts were recognized, occurring in six evolutionary stages. It was discovered that these channel and lobe belts had distinct geomorphological traits. Reservoir architecture and distribution was governed by paleogeomorphology, fluctuations in accommodation space, and sediment supply. The identified fifth-order architectural units are useful for reservoir modeling and contribute to remaining oil development. This study indicates the suitability of seismic sedimentology for characterizing reservoir architecture in areas with sparse well spacing.

Application of 9-component S-wave 3D seismic data to study sedimentary facies and reservoirs in a biogas-bearing area: A case study on the Pleistocene Qigequan Formation in Taidong area, Sanhu Depression, Qaidam Basin, NW China

To solve the problems in restoring sedimentary facies and predicting reservoirs in loose gas-bearing sediment, based on seismic sedimentologic analysis of the first 9-component S-wave 3D seismic dataset of China, a fourth-order isochronous stratigraphic framework was set up and then sedimentary facies and reservoirs in the Pleistocene Qigequan Formation in Taidong area of Qaidam Basin were studied by seismic geomorphology and seismic lithology. The study method and thought are as following. Firstly, techniques of phase rotation, frequency decomposition and fusion, and stratal slicing were applied to the 9-component S-wave seismic data to restore sedimentary facies of major marker beds based on sedimentary models reflected by satellite images. Then, techniques of seismic attribute extraction, principal component analysis, and random fitting were applied to calculate the reservoir thickness and physical parameters of a key sandbody, and the results are satisfactory and confirmed by blind testing wells. Study results reveal that the dominant sedimentary facies in the Qigequan Formation within the study area are delta front and shallow lake. The RGB fused slices indicate that there are two cycles with three sets of underwater distributary channel systems in one period. Among them, sandstones in the distributary channels of middle-low Qigequan Formation are thick and broad with superior physical properties, which are favorable reservoirs. The reservoir permeability is also affected by diagenesis. Distributary channel sandstone reservoirs extend further to the west of Sebei-1 gas field, which provides a basis to expand exploration to the western peripheral area.

An artificial intelligence workflow for horizon volume generation from 3D seismic data

Horizon-based subsurface stratigraphic model building is a tedious process, especially in geologically complex areas where seismic data are contaminated with noise and thus are of weak and discontinuous reflectors. Seismic interpreters usually use stratal (proportional) slices to approximately inspect 3D seismic data along seismic reflectors yet to be interpreted. We introduce an artificial intelligence workflow consisting of three deep learning steps to provide a conditioned seismic image that is easier to interpret, a stratigraphic model that outlines major formations, and moreover a relative geologic time volume that allows us to automatically extract an infinite number of horizons along any seismic reflectors within a seismic cube. Depending on the availability of interpreters, the proposed workflow can either run fully unsupervised without human inputs or using sparse horizon interpretation as constraints to further improve the quality of extracted horizons, providing flexibility in both efficiency and quality. Starting from only seismic images and a few key horizons interpreted on very sparse seismic lines, we demonstrate the workflow to generate a stack of complete horizons covering the entire seismic volume from offshore Australia.

Stratal surfaces honoring seismic structures and interpreted geologic time surfaces

Seismic horizons play a significant role in reservoir model construction and sedimentary facies interpretation, providing crucial low-frequency constraints for seismic inversion. In basin and regional interpretations, the assumption that seismic reflections represent a stratigraphic surface with constant geologic time is significant for guiding seismic interpretation. This assumption may fail when applied to local reservoir scales due to common geologic time transgressions of a particular event in regular wavelet frequency. There will be inconsistencies between seismic events and stratigraphic surfaces. To address this issue and obtain relatively accurate stratal interpretations, we develop a hybrid horizon extraction method honoring seismic structures and time-stratigraphic frameworks, in which seismic reflection structures provide local details and interpreted geologic time surfaces offer critical constraints. First, we develop concepts and a workflow using a realistic outcrop model. We develop a new geology-guided structure tensor by fitting a gradient vector of seismic images and geologic time surfaces. We also consider existing geologic conditions, such as unconformities, and fuse them into our method to calculate accurate slopes and generate reliable relative geologic time images at a fine scale, followed by making slices. Further, we extend our method to 3D seismic data volumes. Our experiments, conducted using simulated and field data, show the superiority and accuracy of our hybrid method compared with the slope-based and stratal slicing methods. These results highlight the potential for applying our method to fine-scale subsurface modeling.

A workflow for turbidite reservoir characterization—a case study of the Macedon member, Northern Carnarvon Basin, NW Australia

Deep-water turbidite systems on passive continental margins are of interest for oil and gas exploration. However, their complexity poses challenges for reservoir characterization. In this study, we proposed a reservoir characterization workflow for the Macedon member turbidite, employing a combination of 90° phase adjustment, geobody extraction, and genetic inversion, based on the abundant well logging and seismic data from the Enfield field, Northern Carnarvon Basin. Our workflow involved seismic sedimentology to determine the morphology of sand bodies and inversion to determine the net reservoir range, resulting in 3D geological attribute modeling. We applied a 90° phase adjustment correlated seismic events and well logging responses. By stratal slice interpretation and geological body extraction, it was revealed the turbidite reservoir distribution. Finally, we achieved net reservoir characterization of the Macedon member through genetic inversion porosity and geostatistical methods. The results showed that the Macedon turbidite reservoir can be divided into the top and base reservoirs. The top reservoir is sheet-like, and the base reservoir is channelized. The average porosity of the former was 24%, while the average porosity of the later is 20%. The top reservoir has better reservoir quality. Furthermore, we discussed sea level changes affect turbidite distribution and reservoir quality. During the Falling Stage Systems Tract (FSST), the long transportation distance led to relatively less sediment supply and a low sand/mud ratio, resulting in confined, channelized, poor quality turbidite reservoir. In contrast, during the Lowstand Systems Tract (LST), unconfined, amalgamated, good quality turbidite sheet reservoirs were formed. The improved workflow based on seismic sedimentology presented in this article proves effective in characterizing complex reservoirs and contributes to the simplified and efficient management of reservoirs.

Fluvial reservoir characterization through channel belt dimension and petrophysical analysis

The dimensions and connectivity of fluvial reservoirs vary greatly, making it challenging to characterize them using conventional approaches. In this study integrated channel belt dimension analysis from seismic geomorphology and empirical equations, well log facies, and petrophysical analysis were performed to characterize the fluvial reservoirs. The study interval consists of fluvial deposits and is divided into three reservoir zones, which are defined by four key regional markers (B, D, K, O). In these intervals, six (6) fluvial facies have been identified. Based on the log facies proportions and their stacking relationships, it is interpreted that the reservoirs in Zone 1 (B to D) were deposited in a proximal reach of a meandering system, Zone 2 (D to K) in a marginal marine setting, and Zone 3 (K) in a distal reach of a meandering system. The dimensions of fluvial channels and channel belts were determined using empirical equations. The results were compared with the observed dimensions of fluvial channels and channel belts from the seismic horizon and stratal slices of the same intervals. Zone 1 and 3 are characterized by broad meander belts (1000–4000 m) compared to zone 2 (600–1300m). Petrophysical analysis showed zone 1 and 3 have the better petrophysical properties compared to zone 2. Though zone 3 has the most well-developed sand bodies the best reservoir interval is zone 1 because of its higher porosity. Although channel belt dimensions have a significant influence on reservoir connectivity, they do not seem to have control on reservoir properties. The channel belt dimensions obtained from the empirical equations and interpreted from the seismic geomorphology analysis were found to be strikingly similar. Since three-dimensional seismic data is not available everywhere and seismic imaging quality decreases with depth, empirical equations can be used to analyze fluvial reservoir parameters and their connectivity at greater depths.

Getting the most out of a large data set: A case study for a large 3D seismic interpretation project in the Carnarvon Basin, NW Australia

A case study is presented for the seismic interpretation of a 3D seismic reprocessing project covering approximately 7200 km2 within a rift basin setting on the Northwest Shelf of Australia. The area includes two main petroleum plays: the Cretaceous Barrow Group Delta and the fluvio-deltaic Triassic Mungaroo Formation. Multiple 3D surveys of varying vintages were reprocessed to provide a unified continuous data set over the area. Seismic amplitude variation with offset inversions were conducted in time and depth domains to produce acoustic impedance and VP/VS volumes. The use of depth-domain inversion enabled more accurate inversion products to be developed with a large lateral and vertical zone of interest to assist in prospectivity assessments. Project time and cost constraints indicated a traditional seismic interpretation process would be ineffective and inefficient. The workflows applied included optimizations of the initial horizon interpretation to improve efficiency, machine learning (ML)-based automatic fault interpretation to save time, and bulk horizon interpretation for time savings and rapid stratal slicing. Utilizing ML and automated interpretation processes in conjunction with seismic inversion products enabled a full prospectivity assessment to be developed within six months. In addition to completing the work within the available time, the applied workflows allowed for significantly more time to be spent on prospectivity assessment rather than structural and stratigraphic interpretations.

Seismic interpretation of sandstone-type uranium deposits in the Songliao Basin, Northeast China

Nuclear energy is a clean energy source that can replace fossil energy on a large scale, and the nuclear energy industry has great advantages in terms of its technical maturity, economic potential, and sustainability. The stable supply of uranium ore, a type of energy mineral, is an important factor for the sustainable development of the nuclear energy industry; as a result, uranium ore has increasingly become the focus of current mineral exploration. We have used seismic attribute analysis, stratal slicing, and seismic inversion to characterize the Sifangtai Formation’s sandstone-type uranium deposit in area A of the central Songliao Basin. We conclude that seismic attribute analysis and the stratal slicing method can predict the continuous reservoir sand body in the study area, and seismic inversion can describe the spatial features of the reservoir sand body in detail. Further analysis of uranium-bearing drilling finds that uranium ore is located in the middle sand body of the lower segment of the Sifangtai Formation, in the middle of the study area, and that the predicted reservoir sand body meets the high-precision requirements for exploration. We use the combination of seismic interpretation and drilling analysis of uranium-bearing ore bodies to effectively predict the size and shape of uranium-bearing ore bodies, and this combined approach can provide guidance for uranium exploration. Furthermore, the results of this study also are significant for the prediction of sand bodies in uranium reservoirs.

Identification and Quantitative Characterization of Point Bars in Subsurface Meander-River Belt, Taking Chengdao Oilfield in Bohai Bay Basin as an Example

Reservoir architecture is an important basis for studying the sedimentary evolution of underground reservoirs and the distribution of remaining oil. Taking meander-river reservoir of Guantao Formation in Chengdao Oilfield as an example, characteristics of the evolution of subsurface meander-belt deposits were studied by seismic sedimentology. Seismic lithology is performed using -90° phase wavelet and frequency fusions; seismic geomorphology is conducted on seismic stratal slices. Six meandering belts were defined in the target layer, and the sediment at the bottom is characterized by the transformation from “braided” river to “meandering” river. The width of meander-river belt has no correlation with the maximum thickness of meander-river belt. But it has obvious negative correlation differences in the minimum thickness of meander–river belt. With the increase of width of the meander-river belt, the minimum thickness of the drilled meander-river belt decreases as a whole. The forward model based on the shape of point bar reveals the seismic architecture characteristics formed by the superposition of sand bodies at different positions of point bars. According to these characteristics, the point bars in the meandering zone can be explained. In the Ng33, Ng42, and Ng45 sub-layers of the study area, the corresponding meander-belt widths where the point bar (or point bar connecting body) cannot be effectively identified by well logging and seismic data, are, respectively, 800, 800, and 500 m. At the same time, when the width of the meander belt is greater than 1000 m, three or more than three point bars (or point bar connecting body) can be basically identified in the meander belt. The width of the point bar segments in the meander belt of the three main sub-layers is mostly 300–400 m, and the maximum width of the point bar segments is about 550 m, while the scale of point bars in Ng45 sub-layer meander belt is relatively small. The quantitative characteristics of point bar debris and the determined location of SBM and SIA sand bodies provide limited and valuable data support for the formation and simulation of underground meandering rivers, which are also useful for the model of the target reservoir.

Thin-interbedded reservoirs prediction based on seismic sedimentology

Interference of thin-interbedded layers in seismic reflections has great negative impact on thin-interbedded reservoirs prediction. To deal with this, two novel methods are proposed that can predict the thin-interbedded reservoirs distribution through strata slices by suppressing the interference of adjacent layer with the help of seismic sedimentology. The plane distribution of single sand bodies in thin-interbedded reservoirs can be clarified. (1) The minimum interference frequency slicing method, uses the amplitude-frequency attribute estimated by wavelet transform to find a constant seismic frequency with the minimum influence on the stratal slice of target layer, and then an optimal slice corresponding the constant frequency mentioned above can be obtained. (2) The superimposed slicing method can calculate multiple interference coefficients of reservoir and adjacent layers of target geological body, and obtain superimposed slice by weighted stacking the multiple stratal slices of neighboring layers and target layer. The two proposed methods were used to predict the distribution of the target oil layers of 6 m thick in three sets of thin-interbedded reservoirs of Triassic Kelamayi Formation in the Fengnan area of Junggar Basin, Northwestern China. A comparison with drilling data and conventional stratal slices shows that the two methods can predict the distribution of single sand bodies in thin-interbedded reservoirs more accurately.

Seismic diagenetic facies prediction of tight sandstone in the offshore sparse well area: An example from the Xihu Depression of the East China Sea Basin

The purpose of this study is to forecast the spatial distribution of diagenetic facies (DF) of tight sandstone in the offshore sparse wells area. Analytical test data, rock physics experiment data and prestack seismic data were used to study the spatial distribution of seismic diagenetic facies (SEISDF) of tight sandstone of the second (H4b) submember of the fourth (H4) member of the Huagang (E3h) Formation in the N gas-field, Xihu Depression, East China Sea Basin. Based on diagenesis and diagenetic minerals, core-based DF of the H4b sandstone were divided into chlorite-coated facies (CHF), calcite-cemented facies (CAF), dissolution facies (DIF), tightly compacted facies (TIF), and quartz-cemented facies (QUF). Various seismic elastic parameters were obtained by prestack elastic parameter inversion method, and sensitive seismic elastic parameters were selected according to the seismic identification principle of DF. In order to predict the spatial distribution of DF, four DF and sensitive seismic elastic parameters were integrated to establish a SEISDF prediction model based on supervised learning, and obtain a diagenetic facies comprehensive index (DFCI) that can distinguish four DF. Then, the 90° phase conversion technique of seismic lithology was used to realize the consistency of the DFCI between isochronous stratigraphic interfaces with core-based DF. The stratal slicing technique of seismic geomorphology was used to make stratal slices of the DFCI between isochronous stratigraphic interfaces. Representative stratal slices were singled out, and the spatial distribution of the SEISDF was interpreted. This study shows that the H4b1 sublayer primarily develops the TIF, while the H4b2 and H4b3 sublayers chiefly develop the QUF, CHF, and DIF. Compared with the H4b2 and H4b3 sublayers, the areas of the QUF and DIF in the H4b4, H4b5, and H4b6 sublayers slightly increase. The QUF are mainly distributed in the subaqueous distributary channel and a small number of sheet sand and channel bar depositional facies in the form of continuous sheets. The CHF are primarily developed in lenticular shape in the channel bar and a small amount of sheet sand and subaqueous distributary channel depositional facies. The most favorable DIF are chiefly developed in the subaqueous distributary channel, channel bar, and sheet sand depositional facies near the fault, which are distributed in strips. This study proposes a very valuable method for the SEISDF prediction of tight sandstone, which can provide a reference for the study of DF of similar strata in other sedimentary basins.

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.

Seismic-Geological Integrated Study on Sedimentary Evolution and Peat Accumulation Regularity of the Shanxi Formation in Xinjing Mining Area, Qinshui Basin

Accurate identification of the lithofacies and sedimentary facies of coal-bearing series is significant in the study of peat accumulation, coal thickness variation and coal-measured unconventional gas. This research integrated core, logging and 3D seismic data to conduct a comprehensive seismic–geological study on the sedimentary evolution characteristics and peat accumulation regularity of the Shanxi Formation in the Xinjing mining area of the Qinshui Basin. Firstly, the high-resolution sequence interface was identified, and the isochronous stratigraphic framework of the coal-bearing series was constructed. Then, the temporal and spatial evolution of sedimentary filling and sedimentary facies was dynamically analyzed using waveform clustering, phase rotation, stratal slice and frequency–division amplitude fusion methods. The results show that the Shanxi Formation in the study area can be divided into one third-order sequence and two fourth-order sequences. It developed a river-dominated deltaic system, mainly with delta plain deposits, and underwent a constructive–abandoned–constructive development stage. The locally distributed No. 6 coal seam was formed in a backswamp environment with distribution constrained by the distributary channels. The delta was abandoned at the later stage of the SS1 sequence, and the peat accumulation rate was balanced with the growth rate of the accommodation, forming a large-area distributed No. 3 thick coal seam. During the formation of the SS2 sequence, the No. 3 coal seam was locally thinned by epigenetic erosion of the river, and the thin coal belt caused by erosion is controlled by the location of the distributary channels and their extension direction. This study can provide a reference for the research on the distribution of thin sand bodies, sedimentary evolution and peat accumulation regularity in the coal-bearing series under the marine–continental transitional environment.

Some Improvements in Intensely Faulted Geological Setting Interpretation by a Multi-Scale Approach

Subsurface deformed zones and their characteristics have a substantial influence on the distribution of oil and gas reserves as well as on production. The use of seismic data for delineating structural compartments and for modelling fault blocks in a region subjected to intense, multiphase tectonic events can be a very difficult and non-unique task as multiple interpretive solutions are possible. Generally, authors describe and substantiate the modelling technology workflow based on complex multiscale averaging of horizontal seismic slices. In this paper our discussion is restricted to the specific case of intense multiphase and multidirectional deformations and routinely processed seismic data. Instead of fault systems that appear to follow trends matching regional tectonic styles, the elementary fault planes interpreted from seismic data sometimes look chaotic. To increase the reliability of seismic interpretation and derive reasonable geological models, modification of an effective fault modeling technique is introduced. It employs a multiscale, integrated geologic approach along with seismic effective modelling basics, i.e. comprising initial noise and data spectrum considerations, model simplification and adjustment to the interpretive setting. An effective fault model includes effective faults – linear approximations of unambiguous fault planes as well as groups of ‘scattered’ elementary planes. Effective faults are used to delineate different zones of comparable rock breaking deformation. These are characterized by an areal distribution of fault planes seen on stratal seismic slices. An approximation is made using specially processed seismic attribute stratal slices, which could be referred to as seismic multiscale fracturing images. The processing algorithms include smoothing, smart averaging, and coherent filtration. Piecewise, discontinuous values of raw seismic fracturing after smoothing provide an additional opportunity to delineate deformed zones and also to upgrade the geological model based on production data. The Chayandinskoye Field in East Siberia was chosen to demonstrate the effective fault modelling technique on an intensely faulted geological setting.

Seismic geomorphology applied to sediment dispersal patterns and an analysis of the stages of channel-lobe systems in the Yinggehai Basin, northern South China Sea

The lithostratigraphic plays in the Dongfang area of the Yinggehai Basin at the northern margin of the South China Sea consist of a Neogene multistage, thinly bedded, channel-lobe system. Integrating high-resolution 3D seismic, lithological and well log data shows that the channel-lobe system developed primarily in the lowstand system tract of the Huangliu Formation. We investigated the developmental stages of lobes based on the stacking relationships of seismic events, the degrees of channel downcutting in lobes, and the occurrences of sandstone facies observed in the stratal slices. The lobes finally identified 9 small-scale stages, which reveal a complete sedimentary cycle controlled by high-frequency sea-level fluctuations. Facies architectures such as main channels, channels and overbank deposits were identified by using seismic sedimentology and geomorphology. Seismic stratal slices display the different characteristics of the sediment dispersal patterns in the northern part (block DF-a) and the southern region (block DF-b). The northern part contains isolated lobes. The southern region mostly contains deeply incised channels and meander belts that are wider than those in the northern part. Three main sediment dispersal patterns have been recognized, namely, channel-lobe, channelized lobe and non-channelized lobe. Sea level fluctuation and topographic variations exert strong influences on spatial-temporal evolution of the sediment diffusion and are the key controlling factors for the patterns. The methodology used in this study characterizes the submarine fan development in an area with limited well control; this methodology is more accurate for reservoir-scale exploration and development compared to other uses.

Seismic sedimentology analysis of fluvial-deltaic systems in a complex strike-slip fault zone, Bohai Bay Basin, China: Implications for reservoir prediction

The Miocene fluvial-deltaic system in the Bohai Bay Basin exhibits difficulties in favourable reservoir prediction in a complex strike-slip fault zone in the Tanlu fault system. On the basis of 3D seismic data and 12 wells, we utilize two different RGB colour-blending methods from various datasets. The first method is derived from the 3D stacked, −90° phase seismic volume, and the second method is generated from the root mean square (RMS) volume attribute, which is extracted from −90° phase seismic data. Combined with the linear combination analysis of user control, we attempt to better quantify reservoir thickness and evolution of the fluvial-deltaic system in the Guantao Formation. The results show that stratal slices of the second RGB colour-blending method have a much greater ability to characterize sedimentary facies evolution and to analyse sand-thickness variations, which can effectively decrease the disadvantageous influence of multiple fault blocks on stratal slice views. In the vertical section, the linear combination analysis and the first RGB colour-blending method, however, have greater utility and resolution, which can be used to characterize the sand body by the width of seismic events or display the various sand thicknesses in different colours. The high-resolution anatomy of the fluvial-deltaic system in the Bohai Bay Basin not only explains current exploration effects but also effectively predicts thick sandstones with the most production potential in this complex region. This study may also have great significance for other complex areas or strata.

Discussion of seismic diagenetic facies of deep reservoir in the East China Sea Basin

Evaluation of seismic diagenetic facies is an effective interpretation procedure to characterize the spatial distribution of diagenetic facies in deep tight sandstones in offshore sparse well areas. Based on petrographic and seismic data, research on seismic diagenetic facies was used in the proposed workflow to predict the spatial distribution and distribution characteristics of seismic diagenetic facies for the third (H4c) sub-member of the fourth (H4) member of the E3h Formation in the Xihu Sag, East China Sea Basin, Eastern China. Herein, two discriminant functions between the core-derived diagenetic facies and the seismic elastic parameters of shear modulus, p-wave impedance, and porosity data volume were established using the supervised learning method, and seismic data X and seismic data Y containing diagenetic facies information were evaluated. Based on the linear function between seismic data X and seismic data Y, a new seismic data volume was calculated and a comprehensive index of diagenetic facies was proposed to describe the distribution of diagenetic facies. The comprehensive index of diagenetic facies can better identify the spatial distribution of diagenetic facies. The results of seismic diagenetic facies research mainly focused on (1) the spatial distribution of diagenetic facies and (2) the distribution characteristics of diagenetic facies. Based on core-derived diagenetic facies, typical stratal slices, and sedimentary microfacies, the spatial distribution of seismic diagenetic facies in the two sublayers of the H4c sandstone was accurately interpreted. The northern part of the H4c1 and H4c2 sublayers mainly developed quartz-cemented facies and a small amount of chlorite-coated quartz facies. The southern part and the surrounding areas of the H4c1 and H4c2 sublayers primarily developed tightly compacted facies. The area near four (F1, F2, F3, and F4) faults in the H4c1 sublayer mainly developed a small amount of dissolution facies, whereas the area near the F2 and F4 faults in the H4c2 sublayer primarily developed a small amount of dissolution facies. Furthermore, the distribution characteristics of seismic diagenetic facies were investigated from the perspective of sedimentary microfacies and diagenetic facies. The chlorite-coated facies is mainly distributed in the subaqueous distributary channel sedimentary microfacies. The dissolution facies is primarily distributed in the subaqueous distributary channel and sheet sand sedimentary microfacies near the faults. This study shows that the research of seismic diagenetic facies using petrographic data and seismic data can better predict the spatial distribution of diagenetic facies of deep tight sandstone.

Timelapse of the geomorphologic and stratigraphic evolution of a Late Cretaceous deep-sea fan, northern Santos basin, Brazil

Deep-sea fans are the terminal sinks of clastic sediment, nutrients and pollutants produced in continental landmasses. They are also major targets for oil and gas on continental margins. Several recent studies have applied seismic geomorphology to delineate deep-sea fans, however, most of them describe a relatively short period of the geologic time, disfavoring the observation of long-term geomorphologic changes and the resulting depositional architecture. We analyzed the geomorphologic evolution and architecture of the Maastrichtian, deeply buried, Maricá deep-sea fan in northern Santos Basin, offshore SE Brazil. Using three-dimensional seismic data and logs from three wells, we mapped five horizons (stratal slices), including fan base, fan top and three internal horizons. The examination of lobes and channel networks on each horizon resulted in a timelapse that capture major geomorphologic transformations of the deep-sea fan from inception to abandonment. The Maricá deep-sea fan is a sand-rich system deposited directly onto the irregular topography of the Maricá mass-transport deposit, and its geometry is also influenced by structural highs uplifted by active halokinesis. Six lobes were mapped, which present variable growing patterns and associated stratigraphic signatures indicative of aggradation, progradation, retrogradation, and lateral switching. Four types of channel morphology were identified (straight, sinuous, meandering, and braided-like). Channel length and sinuosity tend to increase with time in the whole fan and within individual lobes. Amplitude maps and well-log motifs suggest that sandy sediments occur mainly as channel-fill deposits and that different channel morphologies produce contrasting stratigraphic architectures and reservoir heterogeneities. Our results show that channel network and sand-body architecture evolve in a predictive fashion mostly controlled by fan aggradation. However, the interaction with the underlying topography causes morphologic changes at the lobe and depositional element scale that often deviate from the overall trend and affect sand distribution across the fan surface.