• Energy Research

Sketch-based interface and modelling is an approach to reservoir modelling that allows rapid and intuitive creation of 3D reservoir models to test and evaluate geological concepts and hypotheses and thus explore the impact of geological uncertainty on reservoir behaviour. A key advantage of such modelling is the quick creation and quantitative evaluation of reservoir model prototypes. Flow diagnostics capture key aspects of reservoir flow behaviour under simplified physical conditions that enable the rapid solution of the governing equations, and are essential for such quantitative evaluation. In this paper, we demonstrate a novel and highly efficient implementation of a flow diagnostics framework, illustrated with applications to geological storage of CO2. Our implementation permits ‘on-the-fly’ estimation of the key reservoir properties that control CO2 migration and storage during the active injection period when viscous forces dominate. The results substantially improve the efficiency of traditional reservoir modelling and simulation workflows by highlighting key reservoir uncertainties that need to be evaluated in subsequent full-physics reservoir simulations that account for the complex interplay of viscous, gravity, and capillary forces. The methods are implemented in the open-source Rapid Reservoir Modelling software, which includes a simple to use graphical user interface with no steep learning curve. We present proof-of-concept studies of the new flow diagnostics implementation to investigate the CO2 storage potential of sketched 3D models of shallow marine sandstone tongues and deep water slope channels.

We use a method combining experimental design, sketch-based reservoir modelling, and single-phase flow diagnostics to rapidly screen the impact of sedimentological heterogeneities that constitute baffles and barriers to CO2 migration in the Johansen and Cook formations at the Northern Lights CO2 storage site. The types and spatial organisation of sedimentological heterogeneities in the wave-dominated deltaic sandstones of the Johansen-Cook storage unit are constrained using core data from the 31/5-7 (Eos) well, previous interpretations of seismic data and regional well-log correlations, and outcrop and subsurface analogues. Delta planform geometry, clinoform dip, and facies-association interfingering extent along clinoforms control: (1) the distribution and connectivity of high-permeability medial and proximal delta-front sandstones, (2) effective horizontal and vertical permeability characteristics of the storage unit, and (3) pore volumes injected at breakthrough time (which approximates the efficiency of stratigraphic baffling). In addition, the lateral continuity of carbonate-cemented concretionary layers along transgressive surfaces impacts effective vertical permeability, and bioturbation intensity impacts effective horizontal and vertical permeability. The combined effects of these and other heterogeneities are also influential. Our results suggest that the baffling effect on CO2 migration and retention of sedimentological heterogeneity is an important precursor for later capillary, dissolution and mineral trapping.

AbstractAquifer thermal energy storage (ATES) has significant potential to provide largescale seasonal cooling and heating in the built environment, offering a low-carbon alternative to fossil fuels. To deliver safe and sustainable ATES deployments, accurate numerical modelling tools must be used to predict flow and heat transport in the targeted aquifers. This paper presents a simulation methodology for ATES based on surface-based geologic modelling (SBGM) and dynamic mesh optimisation (DMO). DMO has been previously applied in other fields of computational fluid dynamics to reduce the cost of numerical simulations. DMO allows the resolution of the mesh to vary during a simulation to satisfy a user-defined solution precision for selected fields, refining where the solution fields are complex and coarsening elsewhere. SBGM allows accurate representation of complex geological heterogeneity and efficient application of DMO. The paper reports the first systematic convergence study for ATES simulations, and demonstrates the application of these methods in two ATES scenarios: a homogeneous aquifer, and a realistic heterogeneous fluvial aquifer containing meandering, channelised sand bodies separated by mudstones. It is demonstrated that DMO reduces the required number of mesh elements by a factor of up to 22 and simulation time by a factor of up to 15, whilst maintaining the same accuracy as an equivalent fixed mesh. DMO offers significant potential to reduce the computational cost of ATES simulations in both homogeneous and heterogeneous aquifers.

Permeability variations due to sedimentological heterogeneity are important in controlling CO2 migration pathways, CO2 plume dynamics, and stratigraphic, capillary and dissolution trapping of CO2 in subsurface storage units and complexes. Thus, knowing these parameters is crucial to developing a CO2 injection strategy that maximizes storage and trapping efficiency. In this study we analyzed the sedimentological and permeability heterogeneity of the Bunter Sandstone Formation at the Endurance CO2 storage site, offshore UK, through integrated facies analysis, minipermeameter measurements, and thin section analysis. Detailed core logging and outcrop analysis were performed to identify facies and related heterogeneities. Twelve lithofacies have been identified in cores. By analyzing the stacking patterns of the facies, three facies associations and three architectural elements were identified in cores and outcrop analogues, respectively. Heterogeneities occur at all the scales ranging from mm-scale laminae to 10’s m-scale architectural elements. Permeability variations at outcrop and in core are closely related to sedimentological heterogeneities. Minipermeameter and core plug permeability data show up to three orders of magnitude variation across the facies. Cross-bedded (Sp, St, Sl, Spmc) and structureless (Sm) sandstones are the most permeable (4-5400 mD) facies, whereas pebbly conglomerates (Gmg) and laminated mudstones (Fl) are least permeable (0.18-89 mD) facies. Mottled and deformed sandstone (Smd) and crinkly laminated sandstone (Sc) have highly variable permeability (0.69-480 mD). Minipermeameter data reveal permeability varies by a factor of five at centimeter scale within planar cross-bedded (Sp), trough cross-bedded (St) and planar bedded sandstone (Sh) sandstone facies, while planar cross-bedded sandstone with mud clasts along foresets (Spmc) exhibit permeability variation up to a factor of four. Petrographic analysis of thin sections shows that these permeability variations are related to changes in grain size, clay content, and distribution of dolomite cements.