ALBERT

Description: The structure of the Eocene Ainsa basin is dominated by kilometre-scale thrusts and folds that have trends at c . 70° to that of the main Pyrenean structures. Late uplift and erosion provide excellent exposure of this fold-and-thrust system and its growth strata. Field observations integrated with 2D seismic and well data support the 3D reconstructions presented in this paper. Structural reconstructions of pre- and syn-growth geometries contribute substantial improvements to the understanding of the structure of the area and provide a unique insight into the timing of Pyrenean structures. This study demonstrates that oblique features in the Ainsa basin can be grouped into two main systems: the La Fueba thrust system, an oblique-lateral ramp to one of the main Pyrenean thrusts, and the kilometre-scale folds of the Sobrabe system, a set of anticlines that grew as part of a relaying system of folds. In this study we propose a chronology of deformation based on the geometry of the basin fill, which has been used to frame the general tectonosedimentary evolution of the Ainsa basin. The relative timing of structures indicates that the La Fueba structures predate the Sobrarbe structures, which originated as orogen-parallel structures, and obliquity developed during the growth of these structures through clockwise vertical-axis rotation.

Description: Understanding and predicting reservoir presence and characteristics at regional to basin scales is important for evaluating risk and uncertainty in hydrocarbon exploration. Simulating reservoir distribution within a basin by a stratigraphic forward model enables the integration of available prior information with fundamental geologic processes embedded in the numerical model. Stratigraphic forward model predictions can be significantly improved by calibrating the models to independent constraints, such as thicknesses from seismic or well data. A three-dimensional basin-scale stratigraphic forward-modeling tool is coupled with an inversion algorithm. The inversion algorithm is a modification of the neighborhood algorithm (a type of genetic algorithm), which is designed to sample complex multimodal objective functions and is parallelized on computer clusters to accelerate convergence. The process generates a set of representative geological models that are consistent with prior ranges for uncertain parameters, calibration constraints, and associated tolerance thresholds. The workflow is first demonstrated on two data sets: a synthetic example based on a clastic passive margin and a real hydrocarbon exploration example for slope and basin-floor stratigraphic traps in the Neocomian (Lower Cretaceous) of the West Siberian Basin. The analysis of calibrated models provides constraints on stratigraphic controls, and allows prediction of locations with higher potential to develop stratigraphic traps. These locations are related to complex interactions between paleobathymetry, subsidence, eustatic fluctuations, characteristics of sediment-input sources, and sediment-transport parameters. Results show the potential of stratigraphic forward modeling combined with inverse methods as an additional tool to support conventional play-based exploration and reservoir-presence prediction.

Description: 〈span〉〈div〉Abstract〈/div〉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.〈/span〉

Description: The external and internal geometry of four turbidite systems outcropping around the Buil syncline (Ainsa basin, Spanish Pyrenees) has been reconstructed with reservoir-scale resolution in three dimensions (3-D). The irregular geometry of the syncline and the resolution required for the reconstruction cannot be resolved with cross sections. Therefore, reconstruction has been carried out with a new methodology that applies a 3-D dip-domain geometrical model and 3-D restoration techniques to achieve reservoir-scale resolution in kilometric-scale reconstructions. This methodology is aimed at resolving 3-D geometries in folded areas and regions with variable thickness stratigraphy. The 3-D reconstruction of the Buil syncline reveals the synsedimentary growth of an intrabasinal anticline and the foreland lithospheric flexure associated with tectonic loading north of the Ainsa basin. Oscar Fernández received his degree in geology in 1999 from the Universitat de Barcelona. Since then, he has been carrying out research as a structural geologist in the Geodynamics and Basin Analysis Group (Universitat de Barcelona). His research is focused on 3-D structural reconstruction methodologies.Josep Anton Muñoz is professor of structural geology at the Universitat de Barcelona. He received his Ph.D. in 1985 from the Universitat de Barcelona and worked for the Servei Geològic de Catalunya from 1985 to 1990, when he joined the Universitat de Barcelona. His research interests include the structure of thrust and fold belts, tectonosedimentary relationships, and tectonics of collisional orogens. He is currently focusing on the construction of 3-D structural models. Pau Arbués received his degree in geology in 1987 from the Universitat Autònoma de Barcelona. He has worked as an independent consultant for 11 years, contracting research for the Servei Geològic de Catalunya and various oil companies. For the last 5 years, he has been working as a researcher in sedimentology for the Geodynamics and Basin Analysis Group (Universitat de Barcelona). Oriol Falivene received his degree in geology in 2002 from the Universitat de Barcelona. He works as a researcher in reservoir modeling and sedimentology for the Geodynamics and Basin Analysis Group (Universitat de Barcelona). His areas of interest include turbidite and alluvial fan reservoir analogs. A professor of stratigraphy at the Universitat de Barcelona, M. Marzo's research interests focus on the application of clastic sedimentology, sequence stratigraphy, reservoir modeling, and basin analysis to the exploration and production of hydrocarbons. He has been involved in several research projects funded by oil companies in southern Europe, North Sea, South America, and northern Africa.

Description: Understanding and predicting reservoir presence and characteristics at regional to basin scales is important for evaluating risk and uncertainty in hydrocarbon exploration. Simulating reservoir distribution within a basin by a stratigraphic forward model enables the integration of available prior information with fundamental geologic processes embedded in the numerical model. Stratigraphic forward model predictions can be significantly improved by calibrating the models to independent constraints, such as thicknesses from seismic or well data. A three-dimensional basin-scale stratigraphic forward-modeling tool is coupled with an inversion algorithm. The inversion algorithm is a modification of the neighborhood algorithm (a type of genetic algorithm), which is designed to sample complex multimodal objective functions and is parallelized on computer clusters to accelerate convergence. The process generates a set of representative geological models that are consistent with prior ranges for uncertain parameters, calibration constraints, and associated tolerance thresholds. The workflow is first demonstrated on two data sets: a synthetic example based on a clastic passive margin and a real hydrocarbon exploration example for slope and basin-floor stratigraphic traps in the Neocomian (Lower Cretaceous) of the West Siberian Basin. The analysis of calibrated models provides constraints on stratigraphic controls, and allows prediction of locations with higher potential to develop stratigraphic traps. These locations are related to complex interactions between paleobathymetry, subsidence, eustatic fluctuations, characteristics of sediment-input sources, and sediment-transport parameters. Results show the potential of stratigraphic forward modeling combined with inverse methods as an additional tool to support conventional play-based exploration and reservoir-presence prediction.

Description: This study uses one-dimensional convolution seismic models to better understand which features of slope turbidite systems can (or cannot) be observed on real seismic data, aiming to improve subsurface seismic interpretation. Synthetic seismic sections and cubes were built from reservoir-scale three-dimensional facies models of the outcropping Ainsa turbidite system. This turbidite system developed in a foredeep and wedge-top depositional setting within a slope system. The turbidite system consists of laterally and vertically stacked sandstone- and debrite-dominated channel fills, grading into heterolithic and mudstone units, with intercalations of slump-deformed mudstone-rich units. Typical petrophysical values for subsurface Cenozoic sediments were assumed for the seismic models, which are presented at 25-, 50-, and 75-Hz resolution. Seismic models enabled the comparison between architectural and facies distributions observed in the outcrops and the geological models to their possible seismic expression in the subsurface. Comparisons show how seismic expression degrades when seismic resolution decreases. By using models at different geological scales, the effects of each heterogeneity scale are identified. Precise delineation of the internal architecture and facies distribution within channel complexes is beyond the reach of all seismic frequencies. The position of channel complex tops and margins is uncertain because of their gradual character. Differentiating between sandstone- and debrite-filled channels is not straightforward, and bed-scale heterogeneities within the sandstone-dominated channels are barely distinguishable in the seismic data. The net-to-gross predictive capability of root-mean-square amplitude extractions varies depending on the seismic frequency and unit thickness. Oriol Falivene received his Ph.D. in reservoir-scale facies modeling of outcrop analogs from the Geomodels Institute-Group of Geodynamics and Basin Analysis (University of Barcelona) in January 2007. He worked for a year and a half for BP in London on reservoir modeling and sedimentology-stratigraphy. He is currently working for Shell International Exploration and Production, doing research in stratigraphic forward modeling and its application to hydrocarbon exploration. Pau Arbués received his degree in geology in 1987 from the Universitat Autonoma de Barcelona. He has worked as an independent consultant for 11 years, contracting research for the Servei Geologic de Catalunya and various oil companies. For the last 11 years, he has been working as a researcher in sedimentology for the Geomodels-Geodynamics and Basin Analysis Group (Universitat de Barcelona). Juanjo Ledo is professor of geophysics at the Universitat de Barcelona since 2003. He received his Ph.D. in 1996 from the Universitat de Barcelona, and after that, he did a PostDoc at the Geological Survey of Canada in Ottawa (1997–2002). In 2002, he obtained a Ramón y Cajal award from the Spanish Government to return to the Universitat de Barcelona. His research interest includes the geophysical characterization of reservoirs at different scales, joint interpretation of geophysical (mainly EM) and geological data of near-surface geological structures as well as investigation of the crust and upper mantle. Beatriz Benjumea received a Ph.D. (1999) in geophysics from the University of Granada (Spain). Her postdoctoral experience included near-surface seismics research at the Geological Survey of Canada. She currently works at the Institut Geologic de Catalunya (Spain) and collaborates as an assistant teacher in the master course of geophysics of the University of Barcelona (Spain). Her research interests include application of shallow seismic reflection and refraction methods to determine and characterize near-surface structures and its integration with other geophysical and geological data. Josep Anton Muñoz is a professor of structural geology at the Universitat de Barcelona. He received his Ph.D. in 1985 from the Universitat de Barcelona and worked for the Servei Geologic de Catalunya from 1985 to 1990, when he joined the Universitat de Barcelona. His research interests include the structure of thrust and fold belts, tectonosedimentary relationships, tectonics of collisional orogens, and construction of three-dimensional structural models. He is currently the director of the Geomodels Research Institute. Oscar Fernández obtained his Ph.D. in earth sciences from the Universitat de Barcelona in 2004. Since then, he has consulted worldwide on structural geology for Midland Valley Exploration and has been part of the FracPerm development team for Roxar. He is currently part of the Geoscience and Subsurface Description team in the Exploration and Production Technology group in BP. Sara Martínez-Loriente did her final undergraduate report dealing with the generation of synthetic seismic profiles within the Group of Geodynamics and Basin Analysis (University of Barcelona) in 2006. She is currently undertaking her Ph.D. in the Marine Technology Unit of the CSIC. She spent the last three years learning the acquisition, processing, and interpretation of multichannel seismic profiles, as well as refraction and wide-angle reflection seismic data.