Stratigraphic Model Research Articles

3-D tight sandstone gas outcrop simulation based on unmanned aerial vehicle oblique photography data— A case study from the Pingtouxiang outcrop in North Shanxi, China

Current methods of acquiring data from outcrops with tight gas rocks yield insufficient data. To resolve this, unmanned aerial vehicle (UAV) oblique photogrammetry was used to quantitatively assess the Pingtouxiang outcrop in the North Shanxi province, China. Rapid and flexible data acquisition, processing, and interpretation helped, develop a three-dimensional (3-D) geological model for a typical outcrop; here, the model of the delta deposit outcrop has 3-D coordinates that correspond to oblique image data, allowing for both the accurate location of field points and for measurements of the rock body. This provides the foundation for studying the stratigraphic architecture of the outcrop. Assessments of experimental sand plot contours and deposition patterns were carried out, in addition to the physical distribution of different sand bodies including superimposed distributary channels, superimposed distributary channels with sheet sand and bars or with continuous or isolated sheet sand. Different sand body types have varied scales and architecture patterns. Virtual well data, lithological calibration, and a geological model and database were used to establish 3-D stratigraphic and lithological models of a typical outcrop via sequential indicator simulation (SIS). Multi-point geostatistical simulations (MPS) were then used to establish a 3-D geological model of the sand bodies that is more in line with our current understanding of the geology of the outcrop area.

A cyclostratigraphic framework of the Upper Carboniferous Westoe and Cleaver formations in the southern North Sea Basin as a methodology for stratigraphic reservoir characterisation

Abstract Orbital driven climate control on sedimentation produces regional, stratigraphically repetitive characters and so cyclostratigraphic correlation can improve correlation and identify stratigraphic trends in borehole sections. This concept is commonly used to correlate marine and lacustrine strata. However, in the alluvial domain, its use is more challenging because internal, local dynamics controlling sedimentation may interfere with the expression of cyclic climate forcing. Intervals of low net-to-gross may be important for successful application in this domain as they tend to better document regional changes. This study applies climate-based stratigraphic correlation concepts to improve well correlations, characterise vertical sand distribution, and identify potential reservoir targets in a generally low net-to-gross interval. Coarsening upward sedimentary repetitions (cyclothems) are identified and correlated with high certainty in nineteen well sections in the upper Carboniferous Westoe and Cleaver formations of the Silverpit Basin. Local sedimentary dynamics provide variability in the character of the cyclothems and several types of cyclothem are classified. Correlation of sections using cyclothems recognised on wireline logs is done twice: once manually and once semi-automatically. The semi-automated correlation is based on calculation of deviation curves which depict stratigraphic changes that are less dependent on absolute wireline values and follow vertical trends more clearly. The correlations provide composite stratigraphies that are analysed using vertical proportions curves. Both approaches yield similar results in terms of stratigraphic trends. However, for detailed correlation of wells, the manual correlation is better at accounting for any local variability within the system. The same two zones of higher net-to-gross ratios are found using both correlation methods. These are linked to palaeoclimatic changes driven by long eccentricity and the proposed climate stratigraphic model has predictive value for identifying sandstone occurrence. The climate-based stratigraphic correlation improves the assessment reservoir distribution and properties on small (10–20 m thickness) and large (100–200 m thickness) stratigraphical scales.

Sedimentology, T-R sequence stratigraphy and geochemical characterization of sedimentary successions of the West and Central African Rift System, Koum Basin

The Koum Basin (KB) is among the numerous relatively unexplored sedimentary basins lining theWCARS(West and Central African Rift System), hence limiting the understanding of how sedimentation evolved along the full extent of the WCARS. The intensification of petroleum exploration within WCARS has further emphasized the need to study these greenfields. This study contributes in solving the above issue by establishing a sequence stratigraphic framework and expanding the sedimentological databank of the KB. Systematic fieldmapping and lithofacies analyses of theKB along three NNW-SSE traverse lines cross-cutting the basin exposed alternations of conglomerates, sandstones and shales, intercalated by siltstones and carbonate mudstones. Dinosaur, bivalve and plant fossils are common. X-Ray Fluorescence data of studied samples plot as non-marine, immature, low to moderately weathered shales and greywackes of intermediate to felsic igneous and quartzose sedimentary sources. Sedimentation occurred under oxic, through anoxic to dysoxic depositional conditions, in a semi-arid active continental margin. These deposits inferred to be fluvio-lacustrine, have been subjected to outcrop-based sequence stratigraphic analyses through section matching and correlation of its material-based sequence stratigraphic surfaces, following the Transgressive-Regressive sequence stratigraphic model. The deposits have been subdivided into five repetitive T-R sequence stratigraphic units, bounded by four first order unconformities (SB-1, SB-4, SB-5 and SB-6) and two correlative conformities (SB-2 and SB-3), representing deposition under repetitive base level rise and fall regimes. These results demonstrate that any potentialmarine incursion in the WCARS probably did not reach the Koum Basin.

Intelligent seismic stratigraphic modeling using temporal convolutional network

Deep learning (DL) has stimulated the intelligent processing and interpretation of seismic big data for oil and gas exploration in the past decade. In the applications to seismic stratigraphic modeling, most DL algorithms utilize a combination of ‘convolution + pooling’ to extract spatial features from seismic volume or images, which, however, may lead to a loss of the fine-grained information endowed in seismic time-series records inevitably. Here, we proposed a novel scheme for intelligent seismic stratigraphic interpretation based on temporal convolution network (TCN). The purpose of using TCN is to implement a trace-by-trace segmentation of lithologies by extracting spatio-temporal correlation of seismic record from a small amount of well log labels or manually interpreted geological profiles, thereby building a 3-D subsurface stratigraphic model. The proposed TCN model for seismic stratigraphic interpretation is trained, validated, and tested using the Netherlands F3 seismic dataset. The results suggest that, with a limited number of either manual interpretation profiles or well logs information, the proposed TCN algorithm can produce a highly accurate and laterally continuous 3-D stratigraphic model. Specifically, the mean pixel accuracy of prediction results of the above two schemes (compared to the real model) has achieved 98.23% and 96.09%, respectively. In addition, comparing TCN to the widely used encoder-decoder convolutional neural networks for seismic strata interpretation shows the outperformance of TCN scheme in terms of training time, model size, and prediction accuracy, while also revealing that the proposed TCN model can well identify thin strata in complex seismic data.

Relative sea‐level control on the building of two distinct shelf‐margin clinothems on the late‐Quaternary Pearl River margin: Insights from numerical stratigraphic forward modelling

AbstractAs one of the most important forcing factors, relative sea‐level changes exert a major influence on the building of shelf‐margin clinothems. However, it is still not well understood how these changes control the growth of shelf edges and the condition of sediments transporting into deep water, especially over the individual‐clinothem scale of several 100 ky. On the late‐Quaternary Pearl River margin, there are two distinct shelf‐margin clinothems: SQ3 and SQ4. They have different shelf‐edge trajectories (slight rising vs. steep rising) and different styles of deep‐water deposition (fan lobes consisting mainly of MTDs vs. fan lobes consisting mainly of turbidites). This work takes those SQ3 and SQ4 as study objects and runs a total of 136 experiments from the Dionisos stratigraphic forward model to investigate how relative sea‐level changes control the trajectories of shelf edges and the volumes of MTDs in deep water over the individual‐clinothem scale. Our quantitative results suggest that under the geological background of high sediment supply on the late‐Quaternary Pearl River margin, the duration of highstand systems tracts (HST) relative to lowstand systems tracts (LST) or forced regressive systems tracts (FST) has a significant influence on the building of individual shelf‐margin clinothems. If the relative duration of HST is either very short or very long, slight‐rising shelf‐edge trajectories and large‐volume MTDs would be formed, whereas if the relative duration of HST is comparable with LST or FST, steep‐rising shelf‐edge trajectories and limited MTDs would be formed. Through the constrains of the model set to the real geological condition of the SQ3 and SQ4 clinothems, it is found that SQ3 was caused by the quite long relative duration of HST, which made highstand deltaic systems advance over the pre‐existing shelf‐slope break, leading to significant accretion and instability of the shelf edge and thus, giving rise to the formation of slight‐rising shelf‐edge trajectories and fan lobes with high MTDs contents. SQ4, however, formed as a result of the comparable durations of HST, LST, and FST, which made highstand deltaic systems advance to but not beyond the previous shelf‐slope break allowing the subsequent FST to be directly perched on the clinoform slope. Such building processes did not drive pronounced accretion and instability of the shelf edge and thus, caused the formation of steep‐rising shelf‐edge trajectories and fan lobes with low MTDs contents.

Stratigraphic and palaeo-geomorphological evidence for the glacial-deglacial history of the last British-Irish Ice Sheet in the north-western Irish Sea

During its maximum extent around 25–23 ka BP, the British-Irish Ice Sheet extended to near the present-day shelf break with a large ice stream, the Irish Sea Ice Stream, occupied much of the present-day Celtic and Irish Seas. The different episodes of advance and retreat of the ice sheet have been extensively constrained onshore, with models based on feature characterisation and dating helping to understand the retreat pattern of the ice sheet. Offshore, glacial geomorphologies in the Irish Sea have been mostly recognised on the United Kingdom side but remains poorly constrained on the Irish side. In this paper, based on the analysis of an extensive seismic dataset, an update of the stratigraphic model of the northern Irish Sea, with new sub-units, is proposed with a mapping of newly discovered buried geomorphology. Characterisation of the geomorphology, including megascale glacial lineations, subglacial meltwater channels, moraines, and iceberg scours, has been used to extend the constraints on ice sheet retreat offshore. The transition from late glacial to marine setting has been constrained based on the mapping of marine sediment subunits and their terminations. This paper brings new constraints offshore, in a previously understudied area, and synthesises all the results into an updated conceptual model highlighting stratigraphic units succession and associated processes linked to geomorphology, within the context of a rapidly retreating ice stream.

Tracking depositional and geochemical variations in the Cambrian North China Platform: Insights from sedimentology, geochemistry, and C-O isotopic records

The Cambrian carbonate sequence in North China is of significant global and regional scientific importance due to its continuous and thick exposure and the data on the major environmental changes and biological events of the early Phanerozoic, which can be gleaned from it. While the well-exposed Cambrian outcrops have been utilized to unravel the processes governing these events, few studies have focused on the outcrops' spatio-temporal depositional patterns and geochemical variations. Therefore, our study address, these issues by integrating fieldwork with petrographic and geochemical analyses. In the North China Platform (NCP), the Cambrian carbonate sequence is predominantly composed of six third-order depositional sequences (~370–400 m thick) that can be divided into nine microfacies, representing three primary microfacies associations, namely tidal flat, lagoon, and shoal. In contrast to the standard carbonate sequence stratigraphy model and many other examples of Cambrian platforms, the deposition of oolitic grainstones in the NCP are overlain by the deep-water calcareous mudstone and shale during a period of slow fall of sea-levels. Such a particular style shows a similar trend to the Schlager model of a type III sequence boundary that formed between a highstand systems tract (HST) and a transgressive system tract (TST). Scanning electron microscope (SEM) observations show an abundance of microbial fossils, a nanosphere, and remnants of extracellular polymeric substances (EPS) inside the dark micrite of normal regressive deposits (oolitic grainstone), suggesting the significant role of microbial activity in the formation of ooids. The δ18O isotopic values range from −4.15 to −11.75‰ VPDB, portraying pervasive diagenetic alterations with a variable degree of diagenesis at different localities, and both marine- and burial-related diagenesis. In contrast, the δ13C VPDB values have a very narrow range, from −2 to +2‰ VPDB, suggesting little to no influence of meteoric diagenesis. At the same time, the slight depletion of δ13C isotope values may reflect the role of microbial processes during the genesis of ooids. This study highlights the importance of microbial activity and marine-related diagenetic overprints during the formation of carbonate facies in the Cambrian Period and provides evidence that carbon isotopic excursions observed during different major environmental and biological events in the NCP are related to primary signals and not altered by intensive meteoric diagenesis.

An exceptional sedimentary record of initial rifting on the East African Plateau in the Miocene: Lessons from depositional cyclicity and palaeoenvironmental proxies

AbstractKnowledge about the initial tectonic and depositional dynamics, as well as the influence of early rifting on climate and environmental evolution remains speculative to a large extent, because sediments are usually deeply buried. Within the East African Rift System, inversion tectonics uplifted a few of these successions to the surface hence presenting rare windows into the pre‐rift depositional history. One such example, an exceptional 700 m long and up to 60 m high fresh road cut provided the opportunity to study in detail initial rift successions of the southern Albertine Rift (Western Uganda). This focusses on the basal and poorly known Middle to Late Miocene in order to unravel the climatic, environmental, hydrological and tectonic evolution of the initial Albertine Rift. A large and robust multi‐proxy dataset was gathered comprising 169 m of stratigraphic thickness, which spans from 14.5 to 4.9 Ma according to a revised lithostratigraphic model. Fieldwork comprised logging of the sedimentary record, spectral gamma ray, magnetic susceptibility and 2D wall mapping with photomosaics. Additionally, the sections were sampled for bulk mineral and clay mineral analysis. The succession exposes a suite of lithofacies and architectural elements detailing the evolution of a fluvio‐lacustrine system. Five depositional environments were identified which show an overall back‐stepping trend from an alluvial plain to a delta plain and finally palustrine/shallow lacustrine conditions. Mesoscale base‐level cycles, preservation potential of architectural elements, and stacking pattern exhibit limited accommodation space. However, it increases over time. This overall trend indicates increasing tectonic subsidence, which can be explained by flexural downwarp within the pre‐rift phase and in the upper part grading into fault‐controlled crustal extension of the syn‐rift phase, which more and more disrupted a large‐scale river system. From the Middle Miocene up to the early Pliocene, this study revealed that palaeoclimate trends become marked by increasing and more fluctuating Th concentrations, loss of feldspar, intercalated lenses of hydroxosulphate minerals, and a shift from smectite‐dominated to kaolinite‐dominated clays. These signals are all interpreted as detrital except for the hydroxosulphates, and they mirror the increasing intensity of chemical weathering and stripping of soils in the catchment. A trend towards increasing humidity is supported by an increase in lacustrine sediment facies and a lake‐level rise. Nevertheless, intercalation of hydroxosulphate, ferricretes and pedogenised horizons prove ongoing seasonality and dry intervals. Finally, based on a revised stratigraphic model a sequence stratigraphic correlation of the outcrop's depositional cycles with basin‐scale cycles is presented. According to these cycles, transition from the pre‐rift to the syn‐rift stage is marked by an unconformity and a tectonic pulse in the latest Miocene. However, the response of fluvial supply, the depositional system as well as climate conditions are less punctuated and characterised by gradual trends and temporal delays. The long pre‐rift phase (ca 10 Myr) and the gradual transition to the syn‐rift phase is in accordance with the active rifting model, which is based on thermal thinning of the lithosphere by asthenospheric upwelling.

IMPACT ASSESSMENT AND INPUT PARAMETERS SELECTION FOR STRATIGRAPHIC FORWARD MODELLING (SFM)

In deep-water reservoirs, predicting geometry of sedimentary bodies and distribution of facies become inefficient due to data limitations. Stratigraphic forward modelling (SFM) appears as an alternate geological modelling method. High uncertainty is related to definition of input parameters and calibration of the SFM models. This study assesses responses and respective sensitivities of models from the Morro do Chaves Formation (Sergipe/Alagoas Basin) by carrying out SFM multi-realizations. These assessments allow the evaluation and reduction of uncertainties to define input parameters capable of generating models more suitable to the data observed.

STRATIGRAPHIC DEVELOPMENT OF THE DEVONIAN-CARBONIFEROUS COMPLEX OF THE SOUTHERN SIDE OF THE CASPIAN DEEP

This article presents a study of the stratigraphic development of the Devonian-carboniferous complex of the southern side of the Caspian basin, in which a comprehensive study of sedimentary formations of the subsalt complex and the creation of a stratigraphic model of the Late Paleozoic stage of evolution of the southern Caspian sedimentary basin was carried out based on a refined correlation scheme by Abilkhasimov (2015), with the inclusion of generalized data on the structures of Ansagan and Maksat. The basis for the development of a stratigraphic model in the Late Paleozoic of the Coastal zone of carbonate structures in the south of the Caspian sedimentary basin is the classical structural and formation analysis, which reflects the main features: stratigraphy, tectonics, lithological composition, sedimentation conditions, sediment thickness.

Disentangling tectonic and eustatic controls on forearc basin stratigraphy, Talara Basin, Peru

The controls on basin-fill stratigraphy such as sediment supply, climate, eustasy and tectonics are well understood in many basin types, but there are few examples documented from forearc basins. Traditional evolutionary models for forearc basins emphasise the importance of accretionary processes under a largely contractional tectonic regime. The Talara Basin of northwestern Peru preserves a lower Eocene stratigraphic record of dominantly extensional collapse tectonics punctuated by periods of uplift, driven by variability of the subduction process. The margin is dominated by subduction erosion and only minor accretion processes. In this geodynamic setting, we present for the first time a sedimentological and sequence stratigraphic model for the 350 m-thick fluvio-deltaic succession of the Pariñas Formation. Three depositional sequences are stacked into a highstand sequence set comprising proximal fluvial strata that correlate down dip into marginal marine and marine deposits. Syn-sedimentary normal faulting related to episodes of subduction erosion restricted much of the Pariñas to hanging-wall locations subject to minor-scale transgressions. The succession evolved from shelf-confined clinoforms to later basin margin scale clinoforms, related to long-term sea-level rise. The interaction of eustasy, sediment supply and episodes of subduction erosion are integrated into an evolutionary model that may have application in other non-accretionary forearc basins worldwide. Although the model shares characteristics with extensional models for rift basins, the episodic subduction-driven uplift events add another component of relative sea-level complexity.

Stratigraphic analysis of XES02: Implications for the sequence stratigraphic paradigm

ABSTRACT Sequence stratigraphy has the potential to provide a consistent method for integrating data, correlating strata, defining stratigraphic evolution, and generating quantifiable predictions. However, the consistent application requires a precise definition of concepts, stratigraphic units, bounding surfaces, and workflow. Currently no single generally accepted approach to sequence stratigraphic analysis exists, nor are there any robust tests of models and methods. Applying conventional sequence stratigraphic analysis to strata from an analog laboratory experiment (eXperimental EarthScape02, XES02) with known boundary conditions and chronology provides some initial robust testing of the models and methods. Despite stratigraphic architectures apparently consistent with those expected within the sequence stratigraphic paradigm, blind-test applications yield: 1) deducted erroneous base-level curves, 2) systems-tract classification mismatches, 3) disconnected systems-tracts type and actual base level, 4) time-transgressive basin-floor fans, and 5) missing systems tracts. Stratigraphic forward models using base-level curves derived from Wheeler diagrams cannot match the timing, redeposited-sediment volume, and depositional environments observed in the XES02 experiment. These mismatches result from common Wheeler diagram construction practice, producing poorly resolved base-level minima timing and base-level fall durations, hence inaccurate fall rates. Consequently, reconstructions of controlling factors based on stratal architectures remain uncertain, making predictions similarly uncertain. A reasonable path forward is to properly acknowledge these uncertainties while performing stratigraphic analysis and to address them through multiple scenario analysis and modeling.

Stratigraphic Modelling of the Lower/Middle Oxfordian (Upper Jurassic) Outer Ramp Deposits from the NE Paris Basin (France)

We investigate herein the lateral and vertical lithological heterogeneities of the Lower/Middle Oxfordian deposits (“Terrain à Chailles” and “Marnes des Eparges” formations) in the north-eastern Paris Basin. This new detailed stratigraphic framework documents the evolution at high resolution of an outer ramp based on regional correlations in order to constrain the evolution of petrological properties between the clayey “Argiles de la Woëvre” Formation and the more calcareous “Marnes et Calcaires à Coraux de Foug Formation. The “Argiles de la Woëvre” Formation is targeted for the deep storage of nuclear waste in north-eastern France. Nine wells are correlated over the “Zone of Interest for Further Research” (ZIRA), defined by the French agency for radioactive waste management (Andra), with a resolution of 0.5–1.0 m. The architecture and the age control of these formations have been refined, revealing that the “Terrain à Chailles” Formation is characterised by a regular slightly inclined sedimentation gently deeping in the SW direction and shows a lithological evolution from silty claystones to an increased occurrence of its calcareous content towards the top (Lower Oxfordian, uppermost mariae and cordatum ammonite zones). The above “Marnes des Eparges” Formation, characterised by claystone limestone alternations, is assigned to the Middle Oxfordian (plicatilis ammonite zone), deposited during a slightly enhanced subsidence phase in the SE part of the basin and documented and associated with onlaps geometries on the more proximal areas. However, this change in geometry does not affect petrological properties over ZIRA, as this is not accompanied by lithological changes. The environmental factors controlling petrological heterogeneities over ZIRA are also discussed. The stepwise increase in the carbonate content and the decrease in the detrital content towards the Lower to Middle Oxfordian deposits was likely triggered by a climate change towards drier conditions, modulated by sea level changes on a ramp morphology. A major condensation phase encompassing most of the Lower Oxfordian cordatum ammonite zone is also highlighted. The occurrence of a maximum regressive surface associated with gentle slope topography is a probable trigger for condensation. Changes in geometries are, however, associated with the activity of the Metz Fault, which potentially had an influence on the subsidence rates of the basin at that time.

Testing sea-level and carbonate production effects on stratal architecture of a distally steepened carbonate ramp (Upper Miocene, Menorca): A 3D forward modelling approach

Although distally steepened carbonate ramps have been studied by numerous researchers, the processes that control the development of these carbonate systems, including tectonics, differential carbonate production along the ramp profile, or antecedent physiography of the slopes, are an ongoing discussion. We use a stratigraphic forward model to test different hypotheses to unravel controls over distally steepened ramp development, referenced to the well-known Upper Miocene Menorca carbonate ramp (Spain). Sensitivity tests show that distally steepened ramps develop under complex interaction among accommodation, carbonate production and sediment transport parameters. Ramp slope initiation is favoured by still stands and falls of sea-level, in a setting with high-frequency sea-level fluctuations with amplitude between 20 m and 40 m. Low-frequency and higher amplitude sea-level fluctuations of about 115 m tend to form models with no significant slope development. The impact of antecedent slope on the geometry of ramps is determined by the paleoslope inclination, with flat to subhorizontal paleosurfaces resulting in ramps that mirror the antecedent slope. In contrast, steeper paleosurfaces tend to result in ramps with well-defined slopes. Our models, therefore, show that the ramp profile becomes more influenced by the depth constraints on the carbonate sediment producers than by the geometry of the underlying topography as the inclination of the paleosurface increases. The presented models also show that seagrass-dominated shallow carbonate production tends to result in steep slopes due to the low-transport characteristic imposed by seagrass trapping. This steepness can, however, be altered by the introduction of high transport sediment grains from deeper carbonate producers, which fill the slopes and more distal sections of the ramp profile.

Study on the influence of physical interlayers on the remaining oil production under different development modes

Abstract Using the complex stratigraphic structure model, we study the changes in remaining oil on the millimeter scale in different structural parts during the different water flooding development methods. According to the actual geological structure characteristics of the oil layer, We designed and produced the meter-level experimental model, which ensures the similarity between the model structure and actual oil layer structure. The recovery rate of the primary water flooding stage is 10.36%. The stage recovery rate addition of the change flow direction stage is 7.85%. The final recovery rate is 41.36%. The physical interlayer structure has an influence on the oil saturation change in the nearby layers. The oil saturation reduction value is highest in the left part of layer 3 in the primary water flooding stage, the reduction range is 24.81%. There are 2 parts and 1 part where the oil saturation decreases by more than 10.0% in the second boost flooding stage and the change flow direction stage, respectively.

Controls on large-scale architecture and facies distribution of an oolitic-microbial carbonate shelf margin, Nanpanjiang Basin, south China

Carbonate factory types and facies architecture of carbonate depositional systems result from complex interactions among several space- and time-dependent variables, including paleobathymetry, tectonic setting, water chemistry and oceanographic setting, clastic sediment influx, and accommodation. Whereas tropical factories that dominate modern settings have been documented and modelled extensively, microbial-oolitic systems, which are very common throughout the Paleozoic and Mesozoic, have received less attention.Continuous exposures along a platform-to-basin transect of an Early Triassic (Induan) microbial-oolitic carbonate ramp to shelf system in the Nanpanjiang Basin, South China, serves as a viable analogue to similar systems, including the Jurassic Smackover Formation of the Gulf of Mexico, and provide a natural laboratory to test these variables. Carbonate deposition following end-Permian regional drowning and retreat of the Yangtze Platform resulted in low-angle margin-slope systems during the Early Triassic. Lower Triassic carbonate systems display shifts in carbonate factory types, including skeletal, microbial, and abiotic factories, and lateral and vertical architectural variability.We applied stratigraphic forward modelling using DIONISOSFLOW, calibrated with detailed stratigraphic sections and facies mapping, to assess the impact of carbonate factory type, antecedent topography, and variations in accommodation on facies distribution and large-scale geometries of the carbonate shelf margin. Results from model simulations suggest that in the absence of skeletal carbonates in the Lower Triassic, the architecture of the carbonate margin is mainly controlled by rate of microbial growth along the slope.

Basin analysis palaeo‐landscape modelling: Testing the critical controls using experimental design constrained by a real 3D geological model, Gippsland Basin, Australia

AbstractThe main controlling variables for palaeo‐landscape evolution are investigated to assess their relative importance using the Gippsland Basin geological history. Palaeo‐landscape reconstruction is a complicated process controlled and affected by multiple variables, including tectonic, palaeo‐environment, sea‐level change, rainfall, sediment erosion, transportation, deposition, etc. The Basin and Landscape Dynamics software (Badlands) software was used with an efficient experimental design (ED) to guide the selected scenarios, process the results, and generate the multi‐variate equations that define and identify the important controlling variables. The ED was used to test and identify the main uncertainties and their possible ranges, based on actual field data, while at the same time ensuring that the full multi‐dimensional space for those variables was covered to enable the computation of multivariate equations from the minimum number of scenario runs. A full suite of 3D forward palaeo‐landscape models of the Gippsland Basin was built to reconstruct the basin history from its formation to the present (Early Cretaceous to Holocene, 137‐0 Ma). The models are compared to the corresponding full 3D realistic structural and stratigraphic model of the basin that has been built in Petrel (Schlumberger software). This constrains the sedimentary, stratigraphic, burial and thermal histories to the relative subsidence rates and basin‐fill for each geological sequence by using the model isopachs input to the Badlands modelling. The ED required only 22 scenarios to fit 12 identified variables and test for possible interactions with each other. The most significant variables are those that control sediment supply including non‐marine erodibility, rainfall, (Rainfall × Area) exponent m, Slope and critical slope while maximum % Marine Deposition and marine dispersal are also required to fill the marine accommodation space. Sea Level and subsidence only become significant when rapid enough to outpace sediment supply. The controlling factors change over time with basin development from rift to post‐rift phases and interactions are highly significant.

The supply-generated sequence: A unified sequence-stratigraphic model for closed lacustrine sedimentary basins with evidence from the Green River Formation, Uinta Basin, Utah, U.S.A.

Abstract Closed lakes and oceans are stratigraphically distinct systems. However, closed-lake stratigraphy is often interpreted using conventional sequence stratigraphic concepts which were generated for marine settings. As a consequence, lacustrine stratigraphy has long been vexing and applied on an ad-hoc basis. To remedy this, we present a novel, unified sequence stratigraphic model for hydrologically closed (endorheic) basins: the Supply-Generated Sequence (SGS) Model. This model was generated to interpret our outcrop-based correlation—the largest to date at ∼ 30 km—across the Sunnyside Interval member of the middle Green River Formation in Nine Mile Canyon near Price, Utah, USA. The SGS model is based on the fundamental sedimentological and hydrodynamic differences between closed lakes and marine settings wherein the relationship between water discharge and sediment discharge is highly correlated. The SGS model divides packages of genetic lacustrine strata by bounding correlative surfaces, conformable or unconformable, separating facies and surfaces associated with low clastic supply (e.g., carbonates, mudstones, or exposure surfaces) from facies characteristic of relatively higher amounts of clastic supply (subaerial channelized sandstones, subaqueous siltstones, and pedogenic mudstones). We use the SGS model to correlate regional sequences at a higher resolution than previous interpretations and find the greatest amount of clastic deposition occurs during periods of lake-level rise, indicating that the SGSs are characteristically transgressive. Additionally, this model removes the implicit and explicit base-level assumptions of previous sequence stratigraphic models while being agnostic to the source of increased sediment discharge and therefore generalizable to other closed lacustrine settings. We use the high-resolution supply-generated sequences (meters thick) to argue for a climatic origin of the cyclic Sunnyside interval deposits based on sequence durations (40–50 kyr), and aligning sequences with recognized early Eocene transitory hyperthermal event timing and their associated climatic shifts across the region, increasing riverine discharge of sediment and water.

A biotic perspective on the Oligo-Miocene evolution of the Maldives carbonate platform from forward stratigraphic modelling (Indian Ocean)

Forward stratigraphic modelling is a fast-developing modelling approach, used to test conceptual models, and predict stratigraphic architecture and depositional facies from basin to reservoir scales. Published subsurface applications demonstrate its added value by integrating multidisciplinary data as well as geological concepts into its constraints. When applied to carbonate depositional systems, composed of multiple sediment factories, the co-operating and interdependent production mechanisms remain poorly studied. By applying the technique to a well-studied section of the Maldives carbonate platform, a specific model design—adapted to the geological age and setting, and constrained by available data—sheds light on the interaction of its carbonate producers. The results yield a naturalistic depositional facies distribution and offer insight in the changing relationship between biotic communities during the platform evolution. After calibration, the reference model unequivocally links the formerly proposed genetic model to the seismostratigraphic architecture. Furthermore, the results show how environmental changes (seemingly of secondary impact compared to changes in physical accommodation in the stratigraphic record) can induce substantial fluctuations in carbonate production rates of biotic communities, affect the ecological accommodation, and thus impact the platform architecture. Therefore, it is crucial to treat carbonate production rates during periods of environmental change as variables with associated uncertainties in a forward stratigraphic model setup.

Stratigraphic Forward Modeling Assists Carbonate-Reservoir Characterization

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202775, “Application of Stratigraphic Forward Modeling to Carbonate-Reservoir Characterization: A New Paradigm From the Albion Research and Development Project,” by Jean Borgomano, Aix-Marseille University, and Gérard Massonnat and Cyprien Lanteaume, TotalEnergies, et al. The paper has not been peer reviewed. _ Improving carbonate-reservoir prediction, field development, and production forecasts, especially in zones lacking data, requires novel reservoir-modeling approaches, including process-based methods. Classical geostatistic modeling methods alone cannot match this challenge, particularly if subtle stratigraphic architectures or sedimentary and diagenetic geometries not directly identified as properties with well data control the reservoir heterogeneity. Stratigraphic forward-modeling approaches can provide pertinent information to carbonate-reservoir characterization. The complete paper describes a modeling package tested and calibrated with high-resolution stratigraphic outcrop models. It allows valid prediction of carbonate facies associations mimicking the spatial distribution mapped along the Urgonian platform transects. Background Classical carbonate-reservoir characterization protocols rely mainly on 3D geostatistical models based on well data, allowing the realization of 3D numerical grids of reservoir properties. These geostatistic property models are supported by deterministic geological interpretations such as stratigraphic well correlations that are commonly based on sequenced stratigraphic concepts and carbonate sedimentological interpretations. The stratigraphic framework obtained from these deterministic interpretations has a critical effect on further static and dynamic reservoir models because it constrains the spatial stationarity of the geostatistic property simulations or imposes discrete flow units or barriers. These deterministic carbonate sequence stratigraphic and associated sedimentological interpretations, however, introduce significant biases, uncertainties, and imprecisions in reservoir models and furthermore are not validated by process-based modeling approaches as one should expect from any scientific protocol. This lack of validation represents a fundamental scientific gap in classical reservoir-characterization work flows that is generally avoided in other scientific domains such as physics by iterations combining experimentation and process-based models to verify deterministic interpretations and hypothesis. The paradox is that this virtuous scientific method is applied at the ultimate stage of the reservoir flow modeling with the classical “flow history matching,” implying the following strong hypothesis (Fig. 1a): If the dynamic model obtained from the upscaled static model matches the dynamic history and the flow records of the studied field and carbonate reservoir, then the geological model, including the deterministic stratigraphic and sedimentary interpretations, is validated. Reservoir flow and dynamic behavior certainly are controlled by initial geological conditions, but those are not dependent on flow processes. According to fundamental scientific principles, geological interpretations and deterministic models must be validated by geological process-based models. To fill this scientific gap in the presented carbonate-reservoir characterization approach, the authors introduce process-based stratigraphical and sedimentological models that are calibrated on pertinent, well-studied outcrop analogs.