Impacts of fluvial sedimentary heterogeneities on CO2 storage performance

Session H24B. Heterogeneity and Geologic Storage of CO2 IIThe heterogeneity of fluvial systems is a key parameter in sedimentology due to the associated impacts on flow performance. In a broader context, fluvial reservoirs are now targets for CO2 storage projects in several sedimentary basins (Paris Basin, North German Basin), thus calling for detailed characterization of reservoir behaviour and capacity. Fluvial reservoirs are a complex layout of highly heterogeneous sedimentary bodies with varying connectivity, depending on the sedimentary history of the system. Reservoir characterization must determine (a) the nature and dimension of the sedimentary bodies, and (b) the connectivity drivers and their evolution throughout the stratigraphic succession. Based on reservoir characterization, geological modelling must account for this information and can be used as a predictive tool for capacity estimation. Flow simulation, however, describes the reservoir behaviour with respect to CO2 injection. The present work focuses on fluvial reservoir performance and was carried out as part of a PhD (2008-2011) dedicated to the impact of sedimentary heterogeneity on CO2 storage performance. The work comprises three steps: ● Reservoir characterization based on detailed fieldwork (sedimentology and sequence stratigraphy) carried out in Central Arabia on the Minjur Sandstone. Twelve depositional environments and their associated heterogeneity are identified, and their layout is presented in a high-resolution sequence stratigraphy analysis. This step is summed up in a 3D geological model. ● Conceptual modelling based on this field data, using gOcad software and an in-house python code. The purpose was to study, for a given architecture, the impact of sedimentary heterogeneity on storage capacity estimations using two models: one with heterogeneity within the sedimentary fill (model A); the other without heterogeneity within the sedimentary fill (model B). A workflow was designed to estimate and compare the storage capacities for a series of some 50 scenarios. The results show that a strong compartmentalization, due to a shaly barrier, may decrease storage capacity by 11 to 25 percent. ● Flow-simulation of an 8-scenario sample extracted from the 50 possible scenarios. In contrast to the static modelling estimated capacities, the preliminary flow-simulation results indicate that capacity remains similar whichever model is applied (A or B). This is because the scale of the heterogeneity is similar to the extent of the CO2 plume, meaning that heterogeneity does not affect the amount of injected CO2 that can be stored in the sedimentary body. Nevertheless, connectivity strongly influences storage capacity, as determined by the 8 scenarios (model A) in which the total amount of CO2 injected ranges between 7 and 12 Mt over a 50-year period. Moreover, heterogeneity significantly increases pressure build-up, and may strongly disrupt the hydrodynamics in the aquifer

Impacts of fluvial reservoir heterogeneity on connectivity: Implications in estimating geological storage capacity for CO2

International audienceOur awareness of global warming and increasing greenhouse gas emissions emphasises the need to develop counteractive technologies. One promising tool in this respect would appear to be the geological storage of CO2, but there still remain uncertainties regarding the geological complexity of the subsurface. As in the oil and gas context, determining the scale of the heterogeneities that impact the reservoir storage capacity and fluid flow efficiency is crucial. In this paper, we propose to study the impact of two fluvial heterogeneity scales: (1) the architectural scale (megascopic scale) which consists in the connectivity between the main channel belts and (2) the scale of the channel belt (macroscopic scale) which considers the internal sedimentary fill, mainly composed of silty-sandy abandoned channel. To assert geological consistency, this study relies on a conceptual geological model discussed here and based on fieldwork in Saudi Arabia. This model incorporates sedimentary bodies ranging from fluvial braided to high- and low-wandering meandering type. Following the established concept, the largest reservoir bodies are found at the base and top of the system. A workflow is then proposed to statistically analyse the impact of the two considered heterogeneity scales onto CO2 storage characteristics. A code has been implemented to stochastically generate two series of 3D numerical models that account for the conceptual geological model. Each pair of models from the two series share the same architectural structure and only differ in their internal channel body infill. These two series of homologous 3D models support a statistical analysis of the impact of the heterogeneity representation on reservoir capacity. For a 25 km by 25 km by 60 m thick 3D model with a net to gross of 15%, the results show that estimated storage capacities can reach 5.7 Mt and 7.5 Mt respectively for the uppermost and the basal bodies. The presence of oxbow lakes, however, can lead to an estimated loss of capacity of about 11% (∼0.9 Mt) in the basal volumes and 20% (1.3 Mt) in the uppermost volumes

Managing clastic reservoir heterogeneity II: Geological modelling and reservoir characterisation of the Minjur Sandstone at the Khashm al Khalta type locality (Central Saudi Arabia)

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Managing clastic reservoir heterogeneity I: sedimentology and sequence stratigraphy of the Minjur Sandstone at the Khashm-al-Khalta type locality (Central Saudi Arabia)

International audienceThe Late Triassic (Norian–Rhaetian) Minjur Sandstone provides a remarkable case study for understanding and modelling the spatial distribution of sand bodies in a fluvial-deltaic system. As such it has been studied in connection with the geological storage of CO2 in complex heterogeneous formations. Detailed sedimentological mapping of the formation’s vertical and lateral variations in and around the type section at Khashm al Khalta (Khashm al Minjur), which is the area of interpreted maximum inlet/outlet activity, has provided a relatively detailed picture of the sequence stratigraphy. As originally described, shallow-marine flooding with the development of tidal mud flats and carbonate facies occurred near the middle of the formation, splitting it into a lower member dominated by subtidal, brackish and scattered fluvial environments, and an upper member marked by the appearance of meandering point bars capped upward by very proximal deposits forming thick (20 m) coarse-grained sandstone bars that can be followed over several kilometers. The general trend at formation scale is thus upward thickening and coarsening sedimentation related to an increasing clastic influx and the development of fluvial systems, with the fluvial upper member being dominated by amalgamated sand bars. The sequence stratigraphy indicates nine depositional sequences involving four depositional environments: sabkha, tidal, estuarine and fluvial-continental. The lower Minjur is a transgressive tract of four sequences of which Sequence 4 reflects maximum flooding and correlates with maximum flooding surface (MFS) Middle Norian Tr80. Sequence 5 corresponds to a meander system at the base of the upper Minjur, and is followed by sequences 6 to 9 reflecting an increasing clastic influx generating amalgamated coarse-grained bars. The upper Minjur thus represents a highstand systems tract

Onset of Iberian-European plate convergence: Late cretaceous flexural response of a hot lithosphere (Aquitaine Basin, France)

International audienceThe Aquitaine Basin is closely linked to the evolution of the Pyrenees, providing precious evidences of the early stages of the Pyrenean orogeny in the Late Cretaceous. Although the timing and geometry of the Early Cretaceous rifting stage is well constrained in the Pyrenees and surrounding north Pyrenean basins, the subsequent early inversion stage has resisted characterization. In this study, we used well log correlations and interpretation of seismic reflection profiles to determine the Late Cretaceous evolution of sedimentary record in the Aquitaine Basin, spanning the transition from the postrift stage to the beginning of convergence.We identified two main deformation stages during the Late Cretaceous with radicaly different basin's geometry between the western and eastern portion of the Aquitaine Basin. The Western Aquitaine Domain (Pau area) seems to remain under this thermal subsidence regime, inherited from the postrift stage initiated in the Turonian, with little to absent deformation stages. In contrast, the Eastern Aquitaine Domain records early inversion, as indicated by the occurrence of a well-defined Campanian flexural basin. In the central Aquitaine domain (Tarbes to Saint Gaudens area), Coniacian-Santonian period is marked by the sharply increasing distinction between a very low subsiding North Aquitaine Domain (condensed sedimentation), and a strongly subsiding South Aquitaine Domain. We interpret it as a consequence of lithospheric buckling resulting from far-field compressive strain between the Eurasia and Africa plates.During the Campanian, northward convergence of the Iberia plate led to the formation of a flexural basin with a narrower, steeper geometry than the subsequent Eocene basin that formed in nearly the same region during the Pyrenean orogeny. We attribute this difference to the development of the foreland over a not thermally reequilibrated lithosphere in Campanian time, roughly 10 Myr after rifting. This inheritance of a rifted state conferred a yet non-equilibrated lithosphere being thus of very low rigidity. and a susceptibility to . Sedimentary basins formed during both the Coniacian-Santonian and Campanian to early Maastrichtian were thus accommodated by short-wavelength flexural deformation of the lithosphere, and they were subject to a distinctive deformation pattern and an immediate response to the onset of compressive strain

A new approach for evaluating the impact of fluvial type heterogeneity in CO2 storage reservoir modeling

International audienceIn this sensitivity analysis on a 3D model of a heterogeneous fluvial reservoir, two scenario orders have been considered. The first one focuses on the first-order heterogeneity (i.e. a fluvial belt with a 100% sand content), and the other one on the second-order heterogeneity accounting for the internal sedimentary fill within the fluvial belt (oxbow lakes). CO2 injections were simulated using THOUGH2, and the dynamic simulations show large variations of reservoir performances. The first-order heterogeneity generates a large spectrum of storage capacities ranging from 30 to 50 Mt, to be related to the natural connectivity variability between fluvial belts induced by the avulsion process. Considering second-order heterogeneity reduces the storage capacities by 30%, highlighting the importance of representing such objects in complex heterogeneous systems. Moreover, it increases the dissolution process, increasing by the way the storage efficiency. The CO2 plume extension and geometry is also estimated to be strongly dependent on the level of heterogeneity. Finally, trapping into poorly connected fluvial point bars affects strongly the storage capacity of the mobile CO2 as well as the pressure field

UPPER CRETACEOUS PALEOGENE SEDIMENTARY RECORD OF THEPYRENEAN RETROFORELAND (AQUITAIN BASIN). DEFORMATIONSAND SEDIMENT DYNAMICS

International audienceThe southern foreland (proforeland) of the Pyrenean orogeny is one of the most well-known foreland inthe world, on the opposite its northern retroforeland (i.e the Aquitaine basin) which display a quite differenttectonic style is less documented apart from local petroleum studies. Strong efforts have been made in therecent years to improve the knowledge of the Pyrenean orogeny and Aquitaine basin. We present here asynthesis of the Aquitain basin evolution during Upper Cretaceous and Paleogene based on the integration ofmore than 1000 wells and 5000 km of seismic profiles. A harmonized and detailed litho-and sequencestratigraphy was build up for the entire period allowing to recompose large scale sections, thickness and faciesmap at the scale of 1 My, and sedimentary response to compressive deformation. The distribution, style andtiming of deformation of the retroforeland are precised thanks to refined stratigraphic constraints.Within Cenozoic, five major tecto-sedimentary cycles are identified:2 Paleocene cycles: A Danian-Selandian cycle (P1), and a Thanetian cycle (P2), both characterized bycarbonate plat-form growth and limited compressive deformations.3 Eocene cycles: An Ypresian-Lower Lutetian cycle (E1) composed of prograding deltas from east towest that redistribute material coming from the emerging mountain belt in eastern Pyrenees. This progradationtrend leads to relatively quick infilling of the available space and emersion of a large part of the basin.A Lutetian-Bartonian cycle (E2) composed of mixed carbonate siliciclastic deposits.A Priabonian cycle (E3) marked by a large scale emersion of the basin and deposition of fined-grainedcontinental sedimentation (Molasses d’Aquitaine).The timing of deformation is refined and confirms (1) the onset of compressive deformations duringupper Cretaceous, (2) the occurrence of a relatively quiet period during Paleocene (Danian-Lower Thanetian),and (3) a major period of basin deformation during Eocene. Within the basin, compressive deformations takeplace at both basin and local scale, the latter being mainly recorded as reactivation of inherited extensivefaulting dating from Albian and /or late Variscan extension.Within Eocene, two periods of deformation corresponding with the two successive tecto-sedimentarycycles (E1 and E2) are identified. Onset of compressive deformations is diachronous from east to west.Early Eocene deformations mainly take place in the eastern and central part of the basin, with reneweddeformations around Paleocene-Eocene boundary, coeval with the onset of terrigenous input from the growingmountain belt, and major pulse by Upper Ypresian. Late Lutetian-Early Bartonian deformations during cycleE2 are recorded throughout the basin and trigger major depocenter shifts.Together with the well known timing of the southern Pyrenean foreland deformations these data yieldsnumerous constraints about the Pyrenean orogenic prism evolution.Acknowledgments: These results were acquired during the Gaia project founded by TIGF, BRGM andAgence de l’Eau Adour/Garonne which aims to constrain the nature and dynamics of deep Upper cretaceousand Tertiary aquifers of the Aquitaine basin