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[Sand and sediment transfer to deep water in Icehouse continental margins is quantified departing from an original model of the Brazos fluvio‐deltaic system (USA). Short‐term variability due to local process is superimposed to long‐term trends and masks the base level signal. However, for entire base level cycle sand transferred to deep water is mainly controlled by the proportion of time in which the delta remains docked at the shelf‐edge. , Abstract Sequence stratigraphy for clastic continental margins predicts the development of sand‐rich turbidite deposits during specific times in relation to base‐level cycles. It is now widely understood that deltas can extend to the shelf‐edge forced by high sediment flux and/or base level, providing a direct connection to transfer sediment and sand to the slope and basin floor even during high base level periods. Herein, we build a stratigraphic forward model for the last 120 kyr of the fluvio‐deltaic to deep‐water Brazos system (USA) where sediment partitioning along an Icehouse continental margin can be evaluated. The reduced‐complexity stratigraphic forward model employs geologically constrained input parameters and mass balance. The modelled architecture is consistent with the location of depositional units previously mapped in the shelf. Sand bypasses the shelf and upper slope between 35 to 15 kyr before present and only about 20%–30% of all the sediment and sand supplied to the system is transferred to deep water. Several scenarios based on the initial Brazos model investigate the relationships between base level and deep‐water sand ratio (DWSR). DWSR is defined as the relative amount of sand transferred to the deep‐water portions of the system subdivided by the total sand input to the model. Linear correlations between DWSR and base level change rates or base level are very poor. Short‐term variability due to local processes (for example avulsions) is superimposed to the long‐term trends and mask the base level signal. DWSR for an entire base‐level cycle is mainly controlled by the proportion of time the delta stays docked at the shelf‐edge. Stratigraphic forward models are useful to complement field observations and quantify how different processes control stratigraphy, which is important for making predictions in areas with limited information.]

Carbonate platforms grow through the precipitation, transport, and final deposition of carbonate sediment out of seawater. Quantifying the relative contributions of initial production versus subsequent transport in determining the growth rates and geometries of platforms remains a significant challenge. In this study, stratigraphic forward modeling is used to quantify the roles of sediment production, transport, and deposition during each growth stage of a Permian-Triassic carbonate platform with a complex growth history. Parameter optimization and sensitivity analysis show that, within the range of reasonable values, the morphology of the platform is most sensitive to sediment transport, moderately sensitive to maximum carbonate production rate, and least sensitive to the productivity-depth curve. The ramp-to-high relief, steep-sloped platform transition during Early Triassic time can be explained by any factor that limits sediment transport from shallow water areas of high production to the slope and basin. Reefs may play a role in limiting sediment transport on many platforms but other processes, such as early marine cementation or carbonate production along the slope, may be equally capable of yielding this shift in platform geometry. In this particular case, early lithification of ooid and skeletal shoals on the platform margin, perhaps facilitated by unusually high carbonate saturation state of seawater, may have inhibited sediment transport into the basin prior to the development of a reef on the platform margin. Later, Anisian progradation of the platform margin can be explained by the development of a slope factory rather than requiring increased sediment transport from the platform top. The development of an escarpment margin in the Ladinian is mainly influenced by accommodation in the slope profile created by antecedent Anisian topography. A general implication from the model results is that the growth of steep-sloped carbonate platforms lacking slope factories may often be limited by transport of sediment from the platform top to accommodation on the slope rather than by the intrinsic production capacity of the platform top factory.

A novel reduced-complexity approach to 3D forward modeling of siliciclastic stratigraphy is presented for the simulation of erosion, transport, and sedimentation in continental, transitional, and marine depositional domains. The numerical model is based on defining centerlines that connect sediment input points to the shoreline. For each centerline, erosional and depositional surfaces bound depositional domains, and sand and mud proportions are assigned to each domain. The position of each depositional surface follows a set of geologic rules and ensures mass balance with sediment input. The numerical model is tested by simulating the basin-fill architecture of the XES02 laboratory experiment run at the University of Minnesota, which generates stratigraphy mimicking a passive-margin basin fill. Automatic calibration is used to test multiple combinations of uncertain model input parameters to find those that produce scenarios consistent with the experimental stratigraphy. Calibrated models accurately reproduce shoreline and mass-balance centroid migration, marine sediment proportions, and shoreline trajectories measured in the XES02 experiment. The models also provide reasonable approximations of sand distribution. Of interest, falling shoreline trajectories in the experiment and the calibrated models develop coeval to topset aggradation or topset incision depending on rate of base-level fall. The results reported herein validate the numerical approach for simulating sand distribution in an experimental basin, representing a first step towards the application of the numerical model in fluvio-deltaic settings. For field applications, analogue data can be used to independently constrain the geometry of surfaces bounding depositional domains and their composition. The simplicity of the numerical model then enables multiple realizations by quickly varying uncertain boundary conditions, allowing probabilistic predictions in settings with limited data constraints.

Forecasting coal resources and reserves is critical for coal mine development. Thickness maps are commonly used for assessing coal resources and reserves; however they are limited for capturing coal splitting effects in thick and heterogeneous coal zones. As an alternative, three-dimensional geostatistical methods are used to populate facies distribution within a densely drilled heterogeneous coal zone in the As Pontes Basin (NW Spain). Coal distribution in this zone is mainly characterized by coal-dominated areas in the central parts of the basin interfingering with terrigenous-dominated alluvial fan zones at the margins. The three-dimensional models obtained are applied to forecast coal resources and reserves. Predictions using subsets of the entire dataset are also generated to understand the performance of methods under limited data constraints. Three-dimensional facies interpolation methods tend to overestimate coal resources and reserves due to interpolation smoothing. Facies simulation methods yield similar resource predictions than conventional thickness map approximations. Reserves predicted by facies simulation methods are mainly influenced by: a) the specific coal proportion threshold used to determine if a block can be recovered or not, and b) the capability of the modelling strategy to reproduce areal trends in coal proportions and splitting between coal-dominated and terrigenous-dominated areas of the basin. Reserves predictions differ between the simulation methods, even with dense conditioning datasets. Simulation methods can be ranked according to the correlation of their outputs with predictions from the directly interpolated coal proportion maps: a) with low-density datasets sequential indicator simulation with trends yields the best correlation, b) with high-density datasets sequential indicator simulation with post-processing yields the best correlation, because the areal trends are provided implicitly by the dense conditioning data.

Sedimentary facies is a key control on petrophysical properties within subsurface reservoirs and facies modelling is a critical aspect of reservoir modelling. Several modelling methods exist and selecting the best approach for a specific case is challenging and time-consuming. Outcrop analogues provide detailed information on architecture, geometry and facies connectivity that is not directly available in the subsurface. By modelling outcrop data it is possible to test and compare different modelling strategies systematically in a case where the geology is well constrained. The Eocene aged, Sant Llorenc del Munt fan-delta complex (NE Spain) is a well exposed, transgressive–regressive fan-delta. Outcrop data were used to test a variety of modelling strategies in which the density of conditioning wells, stratigraphic subdivision, modelling algorithm and trends were all varied. The results of these modelling exercises were compared against themselves and against a close-to-deterministically built Base Case reconstruction using a series of static measures including the distribution of fan-delta front reservoir facies, directional connectivity and reservoir-to-well connectivity. The results highlight the following: (a) the impact of the conditioning well density on improving the stratigraphic architecture reproduction in the different modelling approaches; (b) that surface-based modelling subdivisions including the maximum flooding surface to separate independent grids for modelling the transgressive and regressive sequence sets can be detrimental when compared to using only the top and base of the composite sequence unless additional constraints are included; (c) that an algorithm combining a linear trend and a Gaussian field is the most suitable algorithm for reproducing this type of architecture, but requires defining a 3D trend; and (d) the need for using trends to reproduce the architecture when well data are sparse. These results provide guidelines for modelling analogue fan-delta reservoirs in the subsurface.

The Eocene Sant Llorenc del Munt fan-delta complex developed in the Ebro foreland basin. The stratigraphy of this succession, about 1000 m thick, has been described as made up of several transgressive–regressive composite sequences, each composed of a stack of fundamental sequences, in turn made up of a transgressive systems tract and an overlying regressive systems tract. Systems tracts are composed of several facies belts: proximal alluvial fan, distal alluvial fan, fan-delta front, carbonate platform, and fan-delta slope and prodelta. A 3D facies model of a 130 m thick stratigraphic succession was built using outcrop data from one of the composite sequences. The modelling followed a hierarchical approach. A deterministic method was used to reconstruct the surfaces bounding fundamental sequences and their constituent systems tracts. Data input was outcrop traces digitized on photorealistic terrain models. The stacking trend and interfingering of adjacent facies belts within each systems tract was added by means of a geostatistical algorithm and was conditioned to measured stratigraphic logs. The analysis of the resultant 3D facies distributions allows revising the architectural interpretation of the studied interval, leading to the conclusion that the observed arrangements are accommodation, not supply-driven. Furthermore, the 3D models were flow simulated in two injector-producer scenarios: up-depositional and down-depositional dip waterflooding. Flow simulation results show that the depositional architecture of the studied succession controls potential recovery efficiencies, in that a considerable proportion of moveable oil is trapped at the dead-ends in depositional pinch-outs of the main potential reservoir (fan-delta front deposits). Also that up-dip waterflooding predicts better recovery efficiencies than down-dip. The dataset, methods, and results herein make the Sant Llorenc del Munt complex a ready-for-application analogue for marine-transitional reservoirs.

Coal exploration and mining in extensively drilled and sampled coal zones can benefit from 3D statistical facies interpolation. Starting from closely spaced core descriptions, and using interpolation methods, a 3D optimum and robust facies distribution model was obtained for a thick, heterogeneous coal zone deposited in the non-marine As Pontes basin (Oligocene-Early Miocene, NW Spain). Several grid layering styles, interpolation methods (truncated inverse squared distance weighting, truncated kriging, truncated kriging with an areal trend, indicator inverse squared distance weighting, indicator kriging, and indicator kriging with an areal trend) and searching conditions were compared. Facies interpolation strategies were evaluated using visual comparison and cross validation. Moreover, robustness of the resultant facies distribution with respect to variations in interpolation method input parameters was verified by taking into account several scenarios of uncertainty. The resultant 3D facies reconstruction improves the understanding of the distribution and geometry of the coal facies. Furthermore, since some coal quality properties (e.g. calorific value or sulphur percentage) display a good statistical correspondence with facies, predicting the distribution of these properties using the reconstructed facies distribution as a template proved to be a powerful approach, yielding more accurate and realistic reconstructions of these properties in the coal zone.

The Eocene aged, Sant Llorenc del Munt fan-delta complex is a well exposed, transgressive–regressive fan-delta, which crops out in NE Spain. Outcrop data were used to test a variety of modelling strategies in which well conditioning, stratigraphic subdivision, modelling algorithm and trends were all varied. The results of these modelling exercises were compared against themselves and against a close-to-deterministically built Base Case reconstruction using a series of static measures including the distribution of fan-delta front reservoir facies, directional connectivity and reservoir-to-well connectivity. The results highlight how well conditioning improves the reproduction of the stratigraphic architecture in the different modelling approaches. That stratigraphic subdivisions including the maximum flooding surface to separate independent grids for modelling the transgressive and regressive sequence sets can actually be detrimental unless additional constrains are included. That an algorithm combining a linear trend and a Gaussian field is the most suitable algorithm for reproducing this type of architecture, but requires defining a three-dimensional trend. And finally, the need for using trends to properly reproduce the architecture when well data are sparse. These results provide guidelines for modelling analogue fan-delta reservoirs in the subsurface.