Stratigraphic Forward Modelling Research Articles

Effective application of geological process modeling for unravelling carbonate build-up complexity: A case study from the EX-Carbonate build-up in central Luconia Province, Malaysia

In the dynamic field of carbonate reservoir Exploration, the need for specialized models is vital, assisting as a key tool to facilitate interdisciplinary collaboration and enhance strategies for predicting reservoir behavior. This study examines the use of geological process (GPM), a standard tool to simulate forward stratigraphic modelling, particularly focusing on the Central Luconia Province in the South China Sea. Central Luconia Province stands out for its extensive carbonate build-ups and is recognized as a prolific hydrocarbon reservoir. Forward Stratigraphic Modelling (FSM) leads to a paradigmatic change in geological modeling. Unlike geostatistical models controlled by geometrical parameters, FSM relies on mathematical representations of the physical rules determining erosion, transport, and sedimentation in carbonate growth. This tool, supported by various researchers, has proven its ability in quantitative sedimentary system analysis across diverse temporal and spatial scales. This study located in EX Field showcases the ability of stratigraphic forward modeling in replicating sedimentary complexities and resulting stratigraphic architecture of the EX isolated carbonate platform. The methodology links parameters from existing literature with multiscale data. Additionally, carbonate production laws, contingent on water depth, play a pivotal role in the meticulous modeling process. This work illustrates the efficacy of geological process modelling as a transformative approach for unraveling the complexities of carbonate systems, particularly in regions with prolific hydrocarbon reservoirs like Central Luconia. The incorporation of literature-derived parameters and multiscale data serves as evidence of the model's ability to offer nuanced understandings of the dynamic evolution of carbonate platforms, thereby advancing our understanding of reservoir prediction and future management strategies.

Forward numerical modelling of pleistocene marine strata, North-West of Morocco

Numerical stratigraphic forward modelling is useful to understand and reconstruct the relative sea-level and sediment supply history responsible for particular strata. This analysis uses BARSIM, a simple 2D forward stratigraphic process-response model that simulates wave and storm processes, applied with an inverse modelling optimisation method to better understand the history of Pleistocene strata in the Achakkar basin of the Tangier region, Morocco. Observations of grain size and bed thickness in four outcrop vertical sections are matched with BARSIM model output to estimate the lowest-error best-fit relative sea level and sediment supply histories that may have controlled deposition of the observed strata assuming deposition over a 10 ky period, consistent with available dating from outcrop sections. The best-fit relative sea level history drops from 4.88 to −2.82 m with two lower-amplitude highstands in between, most likely representing interglacial eustatic and tectonic event. The best-fit sediment supply is variable through time and different for each vertical section, with greatest variation from 11.7 to 2.11 m2y-1 over the 10 ky interval in the north-east vertical section. The spatial and temporal variation of sediment supply in the four vertical sections represents typically dynamic depositional conditions in shallow marine nearshore areas. On the other hand, it can indicate high stratigraphic incompleteness caused by periods of non-deposition or erosion with temporal variations in sediment supply. The optimum way for the simple model to reproduce short intervals of high sedimentation rate separated by longer periods of hiatus and deposition followed by erosion results in a discontinuous stratigraphic record.

Unravelling controls on multi‐source‐to‐sink systems: A stratigraphic forward model of the early–middle Cenozoic of the SW Barents Sea

AbstractSource‐to‐sink dynamics are subjected to complex interactions between erosion, sediment transfer and deposition, particularly in an evolving tectonic and climatic setting. Here we use stratigraphic forward modelling (SFM) to predict the basin‐fill architecture of a multi‐source‐to‐sink system based on a state‐of‐the‐art numerical approach. The modelling processes consider key source‐to‐sink parameters such as water discharge, sediment load and grain size to simulate various sedimentary processes and transport mechanisms reflecting the dynamic interplay between erosion in the catchment area, subsidence, deposition and filling of the basin. The Cenozoic succession along the SW Barents Shelf margin provides a key area to examine controls on source‐to‐sink systems along a transform margin that developed during the opening of the North Atlantic when Greenland and Eurasian plates were separated (ca. 55 Ma onwards). Moreover, the gradual cooling which culminated in major glaciations in the northern hemisphere during the Quaternary (ca. 2.7 Ma), has affected the spatio‐temporal evolution of the sediment routing along the western Barents Shelf margin. This study aims to characterize the relative importance of different source areas within the source‐to‐sink framework through SFM. In the early Eocene, the SW Barents Shelf experienced a relatively equal sediment delivery from three principal source areas: (i) Greenland to the north, (ii) the Stappen High to the east, representing a local source terrain, and (iii) a major southern source (Fennoscandia). In the middle Eocene, our best‐fit modelling scenario suggests that the northern and the local eastern sources dominated over the southern source, collectively supplying large amounts of sand into the basin as evidenced by the submarine fans in Sørvestsnaget Basin. In the Oligocene (ca. 33 Ma) and Miocene (ca. 23 Ma), significant amounts of sediments were sourced from the east due to shelf‐wide uplift. Finally, this study highlights the dynamic nature and controls of sediment transfer in multi‐source‐to‐sink systems and demonstrates the potential of SFM to unravel tectonic and climatic signals in the stratigraphic record.

The triassic formations of Kuwait: From geological concepts to numerical forward stratigraphic modelling applications

The Triassic exploration campaign onshore Kuwait initiated during the 1980s was mainly based on the evaluation of regional 2D seismic data. To date, few scattered wells have penetrated this succession reaching the Minjur, Jilh and Sudair mixed clastic and carbonate formations. The latter reservoirs are expected to hold potential gas and condensates that are yet to be proven. This communication aims at deciphering the spatial and temporal evolution of sedimentary architectures and associated Triassic depositional environments and facies along Kuwait. An integrated G&G assessment utilizing multi-disciplinary and multi-scale dataset allowed to identify the major petroleum system elements and develop sequential conceptual depositional models. The proposed models are then tested using numerical process-based forward stratigraphic applications. The seismic interpretation points to dominantly south to north oriented progradations centered on the Dibdibah low with thicknesses reaching around 1300 ft in the Sudair. In addition, progradations oriented from East to West highlight the location of the basin margins around the Kuwait Arch and its northern extension. These prograding tendencies are also identified in the overlying Jilh Formation. Onlapping reflectors point to transgressional systems related to flooding events that are expected to deposit marine fine-grained carbonatesand thus act as potential seals. Minjur Formation on the other hand, shows thick siliciclastic deposits along the southern sector of the Kuwait Arch. These fluvio-deltaic deposits are 150 feet thick and thin towards the west. Stratigraphic modelling allowed to test and constrain the paleobathymetric evolution of the system. The latter ranges between 0 and 20 m (inner ramp) and 20–40 m (Middle ramp) and reaches up to 80 m in the deeper sectors of the basin. The resultant facies at 3rd- 4th stratigraphic order highlights the evolution of lithologies and facies with regards to the various system tracts leading to a better understanding of the timing and spatial extent of mixed carbonate systems, evaporites and siliciclastics. Future works will focus on a higher resolution mapping of geobodies and prospects using integrated shared earth approaches including seismic multi-attribute assessment and 3D inversion and characterization driven by novel artificial intelligence workflows.

Sea-level oscillations within the last interglacial: Insights from coral reef stratigraphic forward modelling

Understanding past sea-level variations is essential to constrain future patterns of sea-level rise in response to warmer climate conditions. Due to good preservation and the possibility to use various geochemical methods to date fossil sea-level index points, the Last Interglacial (Marine Isotope Stage, MIS, 5e, 130–116 ka) is often regarded as one of the best climate analogs for a future warmer climate. MIS 5e coastal stratigraphic sequences, such as fossil coral reefs, are characterized by abrupt shifts in their geological facies, steps within the reef topography or backstepped morphologies, which have been often interpreted as proxies for abrupt sea-level fluctuations within the interglacial. However, the observational evidence and magnitude of such abrupt changes are controversial. Here, we run nearly 50 thousand simulations of a 2D kinematic reef model that can reproduce coral reef growth and demise through time. Our aim is to investigate the parameters of space, the sea-level scenarios, and the processes which multiple-stepped MIS 5e fossil reefs form. As inputs to the model, we use both published and synthetic sea-level histories (17 sea-level curves, with different sea-level oscillation patterns), and a wide range of reef growth and marine erosion rates, and bedrock foundation slopes. Our results show that the only sea-level history that could explain the generation of an emerged MIS 5e backstepped reef is a first sea-level peak followed by an abrupt rise in sea level and a second short-term peak. Any other multiple-stepped stratigraphy can be explained by the interplay between reef growth, marine erosion, and bedrock slope.

Sensitivity of modelled passive margin stratigraphy to variations in sea level, sediment supply and subsidence

AbstractWe produced a 10 Myr synthetic stratigraphic section using a forward stratigraphic model that generates marine deltaic stratigraphy over geological timescales. We recursively fit the model using a Bayesian inversion algorithm to test: (1) if it could be accurately reconstructed; (2) if the parameters used to create it could be recovered; and (3) the sensitivity of the model output to given model parameters and the attendant physical processes. The original synthetic stratigraphic section was produced with cyclical sea‐level variations of 40 and 30 m with 2.4 and 10 Myr periods respectively. Sediment was also supplied cyclically, in 2.4 and 10 Myr cycles with amplitudes of 30 and 80 tons/100 kyr, respectively, varying from a mean of 232 tons/100 kyr. Parameter values were sampled to fit the model using a Markov chain Monte Carlo algorithm, resulting in a ±5 m (1σ) variation between the experimental output and the original. Sea level varied by ±7 m (1σ) within the posterior distribution of parameters. As a result, both the 10 Myr and 2.4 Myr sea‐level cycles could be extracted from the original output. The variation in sediment supply was approximately ±38 tons/100 kyr (1σ) and, as a result, only the larger long‐term supply variations could be accurately recovered in refitting the model. The variation in thermal, flexural and total subsidence across those parameter sets is less than ±10 m (1σ). The original section experienced 150 m of total subsidence at the depocentre. Our results demonstrate the distinct and interpretable imprint of sea level and subsidence on continental margin stratigraphy can be quantified. Moreover, we conclude that sea‐level change produces a defined effect on the geometries of stratigraphic architecture, and that techniques applied for the purpose of delineating sea‐level variation from continental margin strata have a well‐founded conceptual basis.

Investigating the controls on architecture and facies distribution of a carbonate ramp to shelf system: Insights from stratigraphic forward modeling of the Jurassic Smackover Formation, Gulf of Mexico

To develop a better understanding of the controls on the stratigraphic architecture of carbonate systems, it is necessary to quantify the impact of the physical and chemical variables responsible. The growth, distribution, and nature of carbonate factories are dependent on various space and time-dependent variables, such as paleotopography, accommodation, sediment supply, energy and slope of the system, and water chemistry.The Upper Jurassic Smackover Formation is a heterogeneous hydrocarbon source rock and reservoir in the semi-restricted Conecuh Embayment of southwestern Alabama. It consists of a lower transgressive unit composed of microbialite and mudstone/wackestone, and an upper regressive mixed carbonate-siliciclastic unit composed of oolitic packstone-grainstone, microbialite, bioturbated to laminated carbonate mudstone, and shale. The physiographic setting of the Conecuh Embayment, along with the variability in the carbonate factory types, eustatic sea level fluctuations, and sea-water circulation presents an exceptional site for evaluating the controls on carbonate platform/shelf margin to slope architecture.Stratigraphic forward modeling using DionisosFlow, calibrated with a geologic cross-section built from well log and core data, was carried out to test the impact of antecedent topography, accommodation, and carbonate factory type on the facies distribution and architecture of the carbonate shelf. Results of our study indicate that geometries in the transgressive Smackover shelf are controlled by accommodation and rate of carbonate production, while limited accommodation controlled the stratigraphic architecture of the regressive system.

Placing constraints on the nature of short‐term eustatic curves

AbstractThe isolation of the eustatic signal from the sedimentary record is a challenging task, and accordingly, there is no consensus on the magnitude and pace (rate) of eustatic events in the geological record. Here we critically assess various published short‐term Cretaceous eustatic curves using insights from forward stratigraphic modelling. We generate a range of simulations with varying eustatic rates and sediment supply against a background of constant subsidence. From these, we generate statistics on the accommodation change associated with the various systems tracts for different sediment supply. We quantify the minimum rate needed to generate transgressive systems tracts (TST). Using this threshold and average subsidence rates for passive margins and intracratonic basins, we document some key challenges with a range of Cretaceous eustatic curves. While it is possible to complexify, this approach through the inclusion of other parameters, our results provide a framework for evaluating eustatic (or relative sea level) curves in terms of the implied rate of change of accommodation. Given these caveats, we also show that many estimates of the magnitude of short‐term transgressions are of insufficient rate to generate observable TST. Further, our work places an upper limit on the time frame over which aquifer and thermo‐eustasy can have observable impacts on the rock record, providing support for the action of glacio‐eustasy during the Cretaceous.

Refining patterns of melt with forward stratigraphic models of stable Pleistocene coastlines

Abstract. The warmest peak of the Last Interglacial (ca. 128–116 ka) is considered a process analogue and is often studied to better understand the effects of a future warmer climate on the Earth's system. In particular, significant efforts have been made to better constrain ice sheet contributions to the peak Last Interglacial sea level through field observation of paleo relative sea level indicators. Along tropical coastal margins, these observations are predominantly based on fossil shallow coral reef sequences, which also provide the possibility of gathering reliable U-series chronological constraints. However, the preservation of many Pleistocene reef sequences is often limited to a series of discrete relative sea level positions within the interglacial, where corals suitable for dating were preserved. This, in turn, limits our ability to understand the continuous evolution of paleo relative sea level through an entire interglacial, also affecting the possibility of unraveling the existence and pattern of sub-stadial sea level oscillations. While the interpretation of lithostratigraphic and geomorphologic properties is often used to overcome this hurdle, geological interpretation may present issues related to subjectivity when dealing with missing facies or incomplete sequences. In this study, we try to step back from a conventional approach, generating a spectrum of synthetic Quaternary subtropical fringing reefs for a site in southwestern Madagascar (Indian Ocean). We use the Dionisos forward stratigraphic model (from Beicip-Franlab) to build a fossil reef at this location. In each model run, we use distinct Greenland and Antarctica ice sheet melt scenarios produced by a coupled ANICE–SELEN glacial isostatic adjustment model. The resulting synthetic reef sequences are then used test these melt scenarios against the stratigraphic record. We propose that this sort of stratigraphic modeling may provide further quantitative control when interpreting Last Interglacial reef sequences.

Multiple sediment source infill in a low-accommodation basin: implications for the late Paleozoic sediment routing system in the southeastern Ordos Basin

AbstractLate Paleozoic strata in the southeastern Ordos Basin comprise targeted reservoirs for tight gas exploration. As a typical intracratonic basin, the Ordos Basin is characterized by low-accommodation space and a complex sediment infilling process, which attracts much attention. During the early Permian, the southeast area was fed by sediments from multiple sediment sources, which makes it difficult to identify the pinch-out of the sand bodies and reconstruct the sediment routing system. In this study, we reconstruct the paleo-topography of the late Paleozoic setting using high-resolution 2D and 3D seismic data. Thus, we identify two types of topography: the eastern block is presented as a semiclosed depression, and the western block is observed as a flat platform. Based on detrital zircon U–Pb data and heavy mineral assemblages, we reconstruct the provenance area and show that early Permian sediments originate from the northern margin of the Ordos Basin and from the northern Qinling orogenic belt in the south. By integrating the trace element contents, carbon and oxygen isotope data and sedimentary structure from core samples, we can observe the paleoenvironment and the corresponding facies associations in these blocks. The eastern block was infilled by a prograding delta; the western block was infilled by a tide-dominated delta or a wavy-dominated delta. By using stratigraphic forward modelling, we find that most sediments in the semiclosed setting are progradational and intensely interacted. In contrast, the sediments in the western block present an open setting, infilled and gently interacted. The fine-grained deposits were not easily preserved due to tidal or wave reworking processes in the shallow-water marine setting, and they were transported into deep-water areas. Furthermore, to explore the dominant factors in a pattern of fluvial–deltaic sand bodies formed in the low-accommodation basin, we rebuild the sediment routing system parameters and plot them on a bubble chart. According to the fitness between the depositional volume and the above parameters, we determine the key factors in the routing systems that formed. The results show that the sediment supply has a high relevance to the depositional volume in a semiclosed setting, such as the eastern block, while the terrain height may drive sedimentation in an open marine setting, such as the western block. We demonstrate that two different infill patterns and different sand-body stacking patterns with multiple sediment sources in a low-accommodation basin may serve as a model for similar settings.

Quantifying the sensitivity of distributive fluvial systems to changes in sediment supply and lake level using stratigraphic forward modelling

ABSTRACTStratigraphic forward modelling has been used to quantify the sensitivity of sandbody connectivity in a distributive fluvial system to changes in sediment supply and lake level. Recent stratigraphic forward modelling using SedsimX from StrataMod Pty Limited of the Oligocene to Miocene Huesca distributive fluvial system in northern Spain was used as a base‐case for this sensitivity analysis. Based on literature research and initial modelling, a sediment supply sensitivity range of 0.22 to 21.85 km3/kyr and lake‐level sensitivity range of −1000 to 1000 mm/kyr were used. Results show that the stratigraphic architecture of the modelled distributive fluvial system is more sensitive to changes in sediment supply than to changes in lake level. While an increase in the rate of sediment supply results in an increase in preserved average grain size, aggradation rates and sandbody connectivity at the same distance from the apex, the average grain size, aggradation rate and sandbody connectivity all decrease with increasing distance from fan apex. The main difference in the stratigraphic architecture can be found in the proximal zones. Only oversupplied models, with much higher sediment supply than the base‐case, deposited fully amalgamated channelized deposits with laterally continuous, tabular beds with occasional scoured surfaces. Models with base‐case sediment supply contain channelized sandy deposits within a fine‐grained floodplain environment. Models with sediment supply much lower than the base‐case had no deposition in the proximal zone. Lake‐level rise leads to reduced distal erosion of sediments, concentration of silts close to the lake shore, and higher aggradation rates and thicker sandbodies in the proximal zone. The sensitivity analysis highlights that the parameters governing the formation of distributive fluvial systems have different weightings but are ultimately all interconnected and interdependent. This quantitative framework can be used as a predictive tool for subsurface exploration in distributive fluvial systems.

Fluvial-style migration controls autogenic aggradation in submarine channels: Joshua Channel, eastern Gulf of Mexico

Abstract There has been debate over the processes acting on deep-water channels, with comparisons made to the evolution of meandering fluvial systems. We characterized a three-dimensional seismic-reflection dataset of the Joshua deep-water channel–levee system located in the eastern Gulf of Mexico and interpreted 13 horizons showing its kinematic evolution over a 25 km reach. Over this reach, we documented channel migration through systematic bend expansion and downstream translation, which was sustained through channel aggradation as sinuosity increased from 1.25 to 2.3 at abandonment. An abrupt decrease in sinuosity was associated with a neck cutoff, which changed the subsequent migration direction of the channel in that locality. These processes are analogous to the evolution of meandering fluvial systems. We show that increasing channel sinuosity correlates to a reduction in channel slope and hypothesize that this promoted increasingly depositional turbidity currents that led to channel aggradation. Using a simple forward stratigraphic model in which vertical movements of the channel are governed by a stream power law, we show how aggradation can be driven autogenically. Trends in sinuosity, aggradation and slope are in broad agreement between the Joshua Channel and the model. This highlights the potential importance of intrinsic channel processes as a control on system evolution.

Realistic permeability distributions in faults and sediments: The key to predicting fluid flow in sedimentary basins

AbstractThe permeability of faults and their sedimentary host rocks is a critical input for models of fluid flow in sedimentary basins. Permeability of sedimentary rocks can vary by orders of magnitude over short distances due to variations in sedimentary facies, as well as being strongly anisotropic. Structural features also affect permeability, with faults acting as fluid conduits or barriers depending on the nature of the sedimentary host rock. Constraining these variations in permeability is challenging where outcrops are lacking and drillhole data are sparse. This study describes a workflow using stratigraphic forward modelling to estimate the permeability distribution (both magnitude and anisotropy) in sedimentary rocks and associated faults, which is then used in fluid flow simulations. Permeability is represented as a tensor in the global coordinate system, enabling the use of an unstructured mesh that is independent of stratigraphic layering. The workflow is demonstrated in a sub‐basin of the Proterozoic McArthur Basin of northern Australia. A range of fault permeability scenarios are explored, where fault permeability is a function of host rock properties. The simulation results demonstrate the importance of capturing the direction of permeability anisotropy in dipping strata, as well as highlighting the effect of different fault permeability scenarios. The workflow is particularly well‐suited to scenarios where there are sufficient boreholes to constrain a stratigraphic forward model, but insufficient to determine the permeability distribution by interpolation. Potential applications include mineral and hydrocarbon exploration, groundwater studies, contaminant dispersal modelling, and CO2 sequestration.

Predictable time preservation on passive continental margins revealed from forward stratigraphic models

AbstractAlthough the majority of the world's sedimentary basins are located along passive continental margins, the link between their stratigraphy and time architecture has not been fully investigated in three dimensions. Here, using a 3D numerical forward stratigraphic model, we report a previously unidentified trend: an increase in temporal completeness from the shelf to the upper slope and a reduction towards the basin floor. Sedimentation rates from our results are consistent with those measured from a global dataset; our results are also consistent with a chronostratigraphically well‐constrained subsurface example: the Eocene of the Santos Basin, offshore Brazil. Because our results reproduce both globally and locally observed time‐preservation trends, we suggest the use of such models to inform time architecture in the context of surface and subsurface accumulations. Applying these concepts will not only provide a spatiotemporal framework for passive‐margin settings but will provide a more complete understanding of the inherently incomplete geological record.

Extrinsic controls on turbidity fan lobes spatial distribution and potential reservoir presence prediction in half-graben lacustrine basin during early syn-rift: Insights from stratigraphic forward modelling

Turbidite strata are common along faulted margins of half-graben lacustrine basins, but complex lobe evolution may cause significant variability and uncertainty in the spatial distribution of turbidite sand bodies. This study integrates core samples, seismic and well log data from the Dongying Depression lacustrine basin in East China, and uses these data as inputs to a reduced-complexity stratigraphic forward model of turbidite fan lobe evolution. Data-unconstrained sensitivity analysis is used to investigate sensitivity of fan-lobe spatial distribution to fault-related subsidence rate, basin-margin slope, sediment input volume, and sediment input volume oscillation period. A data-constrained multiple-scenario approach then varied parameters within defined uncertainty ranges to generate a series of best-fit models to predict optimal reservoir presence locations. Results indicate that syn-rift segmentation of the Shengbei fault leads to spatial and temporal variation of fault-related subsidence in the hanging wall basin. External controls exert systematic impact on the spatial distribution of both smaller-scale flow beds and larger-scale fans on basin floor. Higher rates of fault-related subsidence and smaller sediment input volume produce more laterally confined fan lobe distribution. Higher basin-margin slope gradient produces more laterally clustered turbidites, but does not change fan lobe location, indicating break of slope is a more significant control on fan location. Multiple scenario reservoir presence probability maps suggest that bypass-dominated middle and inner fan areas, and smaller lengths of retrogradation-dominated feeder channels are most promising reservoir locations.

An automatic workflow for risk analysis on spatial output properties using kriging‐based surrogate models—Application to stratigraphic forward modelling

AbstractStratigraphic numerical forward process‐based models represent the formation and evolution of sedimentary basins through time. Their main deliverable is a 3D digital grid which can help to better understand the sedimentary basin infill. These models depend on several input parameters that need to be characterized for the studied basin. However, available data such as well logs and seismic data may not provide enough information to identify a unique possible value for these parameters. It is then crucial to take the uncertainty induced by this non‐uniqueness into account in the decision‐making process. As a single numerical stratigraphic forward simulation can be very time consuming, solutions are needed to limit the computational cost required to estimate such uncertainties. In particular, machine learning techniques can be used to build meta‐models that mimic the simulator and provide fast estimations of its outputs for any values of the input parameters. The key step for the efficiency of such an approach stands in the choice of the set of simulations (or training set) used to build the meta‐models: it should be informative enough to obtain accurate predictions for the output properties of interest, but also of reasonable size to limit simulation time. Then, meta‐models can be used to investigate a large number of models and make uncertainty quantification easier. Here, we focus on the prediction of spatial outputs of interest approximated from the joint use of several kriging‐based meta‐models combined to reduced basis decomposition. Sequential approaches have been proposed in the literature to identify training sets iteratively for a kriging‐based meta‐model, building upon the specific structure of such surrogates. We propose here to extend these approaches to the context of spatial output predictors. The results obtained on two synthetic test cases, representing a carbonate platform and a clastic environment, highlight the potential of the proposed approach for risk analysis to iteratively build training sets with a satisfactory efficiency in terms of simulation time and prediction accuracy.

Submarine channel stacking patterns controlled by the autogenic 3D kinematics of meander bends

Abstract Channel kinematics play a pivotal but underappreciated role in determining submarine meandering channel stacking patterns. A stratigraphic forward model is here applied to turbidite systems to generate synthetic stratigraphic architectures and to compare channel trajectories recorded on cross-sections with the kinematics of meander bends. Various channel stacking patterns, which may be classified into four types, are obtained from a single set of constant parameters. This variety of stacking patterns observed from one 2D section to another is thus autogenic. It is the consequence of the 3D migration of meander bends. It reflects the number of consecutive bends that have intercepted the cross-section, which depends on the channel downstream migration rate. These 3D effects alone are sufficient to explain variations in the apparent migration rate and the reversal of migration direction. As a result, sigmoidal geometries can be preserved in aggrading systems without a significant change in channel geometry or varying aggradation and migration rates. Finally, despite these 3D effects, stratigraphic mobility numbers still provide good constraints on bend kinematics. These results should apply to meandering rivers and other meandering systems.

Sedimentary process of channel-feeding fan delta in the south of Albert Rift, Uganda: Insight from sensitivity analysis of forward stratigraphic modeling

Channel-feeding fan deltas without any conglomerates have recently been discovered on the steep slope in the Albert basin at the northern end of the west branch of the East African Rift. However, the new deposition system's mechanics and patterns are unknown. To reveal the sedimentary process of the distinctive fan delta, we integrate forward stratigraphic modeling (FSM) technology with interpretations of the core, well logs, and 3D seismic data. Firstly, a reference FSM model is constructed to describe the evolution of the fan delta, taking into account initial bathymetry, source supply, lake level, and fluvial discharge as independent variables. Then, the Orthogonal Experimental Design (OED) is employed based on the uncertainty analysis of each independent factor to generate FSM multi-realizations for formation thickness and Net-to-Gross. Sensitivity analysis of Multi-FSM realizations reveal that source supply is the most influential variable affecting formation thickness and texture. Combined with the tectonic evolution of Albert Basin, the formation dip during the deposition period is much smaller than present. Multiple incised channels were formed in the provenance area, which became the primary source system of the fan delta, facilitating the sediments' transportation over a certain distance to produce well-developed cross-bedding sandstone. The channel-feeding fan delta has a narrower plain and wider front, and the principal sand body is high-quality distributary channel. The discovery of the channel-feeding fan delta without any gravel formed on the steep slope of the rift basin enriches the theory of deposition in rift basins. In addition, the application of FSM technology helps to improve the quantification of sedimentary processes.

ClinoformNet-1.0: stratigraphic forward modeling and deep learning for seismic clinoform delineation

Abstract. Deep learning has been widely used for various kinds of data-mining tasks but not much for seismic stratigraphic interpretation due to the lack of labeled training datasets. We present a workflow to automatically generate numerous synthetic training datasets and take the seismic clinoform delineation as an example to demonstrate the effectiveness of using the synthetic datasets for training. In this workflow, we first perform stochastic stratigraphic forward modeling to generate numerous stratigraphic models of clinoform layers and corresponding porosity properties by randomly but properly choosing initial topographies, sea level curves, and thermal subsidence curves. We then convert the simulated stratigraphic models into impedance models by using the velocity–porosity relationship. We further simulate synthetic seismic data by convolving reflectivity models (converted from impedance models) with Ricker wavelets (with various peak frequencies) and adding real noise extracted from field seismic data. In this way, we automatically generate a total of 3000 diverse synthetic seismic datasets and the corresponding stratigraphic labels such as relative geologic time models and facies of clinoforms, which are all made publicly available. We use these synthetic datasets to train a modified encoder–decoder deep neural network for clinoform delineation in seismic data. Within the network, we apply a preconditioning process of structure-oriented smoothing to the feature maps of the decoder neural layers, which is helpful to avoid generating holes or outliers in the final output of clinoform delineation. Multiple 2D and 3D synthetic and field examples demonstrate that the network, trained with only synthetic datasets, works well to delineate clinoforms in seismic data with high accuracy and efficiency. Our workflow can be easily extended for other seismic stratigraphic interpretation tasks such as sequence boundary identification, synchronous horizon extraction, and shoreline trajectory identification.

A new objective function designed for the calibration of stratigraphic forward models

This paper presents a novel and quantitative method of comparing facies successions of distinct sizes and resolutions, adapted for the automated calibration of stratigraphic forward models (SFM). The method, which corresponds to the calculation of an objective function, consists of correlating time-sampled SFM results with space-sampled well logs using a strategy inspired by methods of automated well log correlation. The method was designed to be generic and to accept multi-variate definition of facies, so that it can be applied in a variety of geological contexts (e.g., mixed carbonate-clastic environments). The method demonstrated properties suitable for automated calibration, such as a smooth and almost convex relationship with individual simulation parameters. The method was applied to a case-study using gradient-based, meta-heuristic, Bayesian, and random optimization strategies in an 8-dimensional uncertain space. The results show that calibrated models can be found, but there are still non-uniqueness issues due to compensation effects between uncertain parameters. Therefore, a calibration strategy capable of identifying these multiple solutions is necessary to propagate geological uncertainties in petroleum system assessments and field production predictions.