Publications
153 results found
Lyu Z, Lei Q, Yang L, et al., 2021, A novel approach to optimising well trajectory in heterogeneous reservoirs based on the fast-marching method, Journal of Natural Gas Science and Engineering, Vol: 88, Pages: 1-12, ISSN: 1875-5100
To achieve efficient recovery of subsurface energy resources, a suitable trajectory needs to be identified for the production well. In this study, a new approach is presented for automated identification of optimum well trajectories in heterogeneous oil/gas reservoirs. The optimisation procedures are as follows. First, a productivity potential map is generated based on the site characterisation data of a reservoir (when available). Second, based on the fast-marching method, well paths are generated from a number of entrance positions to a number of exit points at opposite sides of the reservoir. The well trajectory is also locally constrained by a prescribed maximum curvature to ensure that the well trajectory is drillable. Finally, the optimum well trajectory is selected from all the candidate paths based on the calculation of a benefit-to-cost ratio. If required, a straight directional well path, may also be derived through a linear approximation to the optimised non-linear trajectory by least squares analysis. Model performance has been demonstrated in both 2D and 3D. In the 2D example, the benefit-to-cost ratio of the optimised well is much higher than that of a straight well; in the 3D example, laterals of various curvatures are generated. The applicability of the method is tested by exploring different reservoir heterogeneities and curvature constraints. This approach can be applied to determine the entrance/exit positions and the well path for subsurface energy system development, which is useful for field applications.
Jacquemyn C, Pataki MEH, Hampson GJ, et al., 2021, Sketch-based interface and modelling of stratigraphy and structure in three dimensions, Journal of the Geological Society, Vol: 178, Pages: 1-17, ISSN: 0016-7649
Geological modelling is widely used to predict resource potential in subsurface reservoirs. However, modelling is often slow, requires use of mathematical methods that are unfamiliar to many geoscientists, and is implemented in expert software. We demonstrate here an alternative approach using sketch-based interface and modelling, which allows rapid creation of complex three-dimensional (3D) models from 2D sketches. Sketches, either on vertical cross-sections or in map-view, are converted to 3D surfaces that outline geological interpretations. We propose a suite of geological operators that handle interactions between the surfaces to form a geologically realistic 3D model. These operators deliver the flexibility to sketch a geological model in any order and provide an intuitive framework for geoscientists to rapidly create 3D models. Two case studies are presented, demonstrating scenarios in which different approaches to model sketching are used depending on the geological setting and available data. These case studies show the strengths of sketching with geological operators. Sketched 3D models can be queried visually or quantitatively to provide insights into heterogeneity distribution, facies connectivity or dynamic model behaviour; this information cannot be obtained by sketching in 2D or on paper.
Alarouj M, Ijioma A, Graham MT, et al., 2021, Numerical modelling of self-potential in subsurface reservoirs, Computers & Geosciences, Vol: 146, Pages: 1-19, ISSN: 0098-3004
We report a new, open-source, MATLAB-based 3D code for numerically simulating the self-potential (SP) in subsurface reservoirs. The code works as a post-processor, using outputs from existing reservoir flow and transport simulators at a selected timestep to calculate the SP throughout the reservoir model. The material properties required to calculate the SP are user defined and may be constant or vary in each cell. The code solves the equations governing flow and transport of electrical charge and global charge conservation using a control-volume-finite-difference scheme. Electrical currents associated with the SP may spread beyond the reservoir model domain, and the code allows for the domain to be extended vertically and laterally to account for this. Here, we present the governing equations and the numerical method used and demonstrate application of the code using an example in which we predict the SP signals associated with oil production from a subsurface reservoir supported by water injection.
Costa Sousa M, Silva J, Silva C, et al., 2020, Smart modelling of geologic stratigraphy concepts using sketches, Smart Tools and Applications in computer Graphics (STAG) 2020, Publisher: The Eurographics Association, Pages: 89-100
Several applications of Earth Science require geologically valid interpretation and visualization of complex physical structures in data-poor subsurface environments. Hand-drawn sketches and illustrations are standard practices used by domain experts for conceptualizing their observations and interpretations. These conceptual geo-sketches provide rich visual references for exploring uncertainties and helping users formulate ideas, suggest possible solutions, and make critical decisions affecting the various stages in geoscience studies and modelling workflows. In this paper, we present a sketch-based interfaces and modelling (SBIM) approach for the rapid conceptual construction of stratigraphic surfaces, which are common to most geologic modelling scales, studies, and workflows. Our SBIM approach mirrors the way domain users produce geo-sketches and uses them to construct 3D geologic models, enforcing algorithmic rules to ensure geologically-sound stratigraphic relationships are generated, and supporting different scales of geology being observed and interpreted. Results are presented for two case studies demonstrating the flexibility and broad applicability of our rule-based SBIM approach for conceptual stratigraphy.
Yekta A, Salinas P, Hajirezaie S, et al., 2020, Reactive transport modeling in heterogeneous porous media with dynamic mesh optimization, Computational Geosciences: modeling, simulation and data analysis, Vol: 25, Pages: 357-372, ISSN: 1420-0597
This paper presents a numerical simulator for solving compositional multiphase flow and reactive transport. The simulator was developed by effectively linking IC-FERST (Imperial College Finite Element Reservoir SimulaTor) with PHREEQCRM. IC-FERST is a next-generation three-dimensional reservoir simulator based on the double control volume finite element method and dynamic unstructured mesh optimization and is developed by the Imperial College London. PHREEQCRM is a state-of-the-art geochemical reaction package and is developed by the United States Geological Survey. We present a step-by-step framework on how the coupling is performed. The coupled code is called IC-FERST-REACT and is capable of simulating complex hydrogeological, biological, chemical, and mechanical processes occurring including processes occur during CO2 geological sequestration, CO2 enhanced oil recovery, and geothermal systems among others. In this paper, we present our preliminary work as well as examples related to CO2 geological sequestration. We performed the model coupling through developing an efficient application programming interface (API). IC-FERST-REACT inherits high-order methods and unstructured meshes with dynamic mesh optimization from IC-FERST. This reduces the computational cost by placing the mesh resolution where and when necessary and it can better capture flow instabilities if they occur. This can have a strong impact on reactive transport simulations which usually suffer from computational cost. From PHREEQCRM the code inherits the ability to efficiently model geochemical reactions. Benchmark examples are used to show the capability of IC-FERST-REACT in solving multiphase flow and reactive transport.
Kostorz WJ, Muggeridge AH, Jackson MD, 2020, An efficient and robust method for parameterized nonintrusive reduced-order modeling, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Vol: 121, Pages: 4674-4688, ISSN: 0029-5981
- Author Web Link
- Cite
- Citations: 5
Li S, Jackson MD, Agenet N, 2020, Role of the calcite-water interface in wettability alteration during low salinity waterflooding, FUEL, Vol: 276, ISSN: 0016-2361
- Author Web Link
- Cite
- Citations: 14
Osman H, Graham GH, Moncorge A, et al., 2020, Is cell-to-cell scale variability necessary in reservoir models?, Mathematical Geosciences, Vol: 53, Pages: 271-296, ISSN: 1573-8868
Reservoir models typically contain hundreds-of-thousands to millions of grid cells in which petrophysical properties such as porosity and permeability vary on a cell-to-cell basis. However, although the petrophysical properties of rocks do vary on a point-to-point basis, this variability is not equivalent to the cell-to-cell variations in models. We investigate the impact of removing cell-to-cell variability on predictions of fluid flow in reservoir models. We remove cell-to-cell variability from models containing hundreds of thousands of unique porosity and permeability values to yield models containing just a few tens of unique porosity and permeability values grouped into a few internally homogeneous domains. The flow behavior of the original model is used as a reference. We find that the impact of cell-to-cell variability on predicted flow is small. Cell-to-cell variability is not necessary to capture flow in reservoir models; rather, it is the spatially correlated variability in petrophysical properties that is important. Reservoir modelling effort should focus on capturing correlated geologic domains in the most realistic and computationally efficient manner.
Lei Q, Jackson MD, Muggeridge AH, et al., 2020, Modelling the reservoir-to-tubing pressure drop imposed by multiple autonomous inflow control devices installed in a single completion joint in a horizontal well, Journal of Petroleum Science and Engineering, Vol: 189, Pages: 1-16, ISSN: 0920-4105
Autonomous inflow control devices (AICDs) are used to introduce an additional pressure drop between the reservoir and the tubing of a production well that depends on the fluid phase flowing into the device: a larger pressure drop is introduced when unwanted phases such as water or gas enter the AICD. The additional pressure drop is typically represented in reservoir simulation models using empirical relationships fitted to experimental data for a single AICD. This approach may not be correct if each completion joint is equipped with multiple AICDs as the flow at different AICDs may be different. We use high-resolution numerical modelling to determine the total additional pressure drop introduced by two AICDs installed in a single completion joint in a horizontal well. The model captures the multiphase flow of oil and water through the inner annulus into each AICD. We explore a number of relevant oil-water inflow scenarios with different flow rates and water cuts. Our results show that if only one AICD is installed, the additional pressure drop is consistent with the experimentalzly-derived empirical formulation. However, if two AICDs are present, there is a significant discrepancy between the additional pressure drop predicted by the simulator and the empirical relationship. This discrepancy occurs because each AICD has a different total and individual phase flow rate, and the final steady-state flow results from a self-organising mechanism emerging from the system. We report the discrepancy as a water cut-dependent correction to the empirical equation, which can be used in reservoir simulation models to better capture the pressure drop across a single completion containing two AICDs. Our findings highlight the importance of understanding how AICDs modify flow into production wells, and have important consequences for improving the representation of advanced wells in reservoir simulation models.
Kampitsis AE, Adam A, Salinas P, et al., 2020, Dynamic adaptive mesh optimisation for immiscible viscous fingering, COMPUTATIONAL GEOSCIENCES, Vol: 24, Pages: 1221-1237, ISSN: 1420-0597
- Author Web Link
- Cite
- Citations: 11
Zhang Z, Geiger S, Rood M, et al., 2020, Fast flow computation methods on unstructured tetrahedral meshes for rapid reservoir modelling, Computational Geosciences, Vol: 24, Pages: 641-661, ISSN: 1420-0597
Subsurface reservoir models have a high degree of uncertainty regarding reservoir geometry and structure. A range of conceptual models should therefore be generated to explore how fluids-in-place, reservoir dynamics, and development decisions are affected by such uncertainty. The rapid reservoir modelling (RRM) workflow has been developed to prototype reservoir models across scales and test their dynamic behaviour. RRM complements existing workflows in that conceptual models can be prototyped, explored, compared, and ranked rapidly prior to detailed reservoir modelling. Reservoir geology is sketched in 2D with geological operators and translated in real-time into geologically correct 3D models. Flow diagnostics provide quantitative information for these reservoir model prototypes about their static and dynamic behaviours. A tracing algorithm is reviewed and implemented to compute time-of-flight and tracer concentrations efficiently on unstructured grids. Numerical well testing (NWT) is adopted in RRM to further interrogate the reservoir model. A new edge-based fast marching method is developed and implemented to solve the diffusive time-of-flight for approximating pressure transients efficiently on unstructured tetrahedral meshes. We demonstrate that an implementation of the workflow consisting of integrated sketch-based interface modelling, unstructured mesh generation, flow diagnostics, and numerical well testing is possible.
Collini H, Li S, Jackson MD, et al., 2020, Zeta potential in intact carbonates at reservoir conditions and its impact on oil recovery during controlled salinity waterflooding, Fuel, Vol: 266, Pages: 1-16, ISSN: 0016-2361
It is well known that oil recovery from carbonate reservoirs can be increased by modifying the injected brine composition in a process ‘controlled salinity water-flooding’ (CSW). However, the mineral- to pore- scale processes responsible for improved oil recovery (IOR) during CSW remain ambiguous and there is no method to predict the optimum CSW composition for a given crude-oil-brine rock system. Here we report the first integrated experimental measurements of zeta potential and IOR during CSW obtained at reservoir conditions. The zeta potential is a measure of the electrical potential at mineral-brine and oil-brine interfaces and controls the electrostatic forces acting between these interfaces.We find that the measured zeta potential in clean samples saturated with formation brine is typically positive and becomes more negative with brine dilution irrespective of temperature. After aging and wettability alteration, the zeta potential changes and we suggest a more positive zeta potential indicates a positive zeta potential at the oil-brine interface and vice-versa. Injecting low salinity brine yields IOR when the oil-brine zeta potential is identified to be negative, but no response when it is identified to be positive, consistent with the hypothesis that IOR during CSW is caused by an increase in the repulsive electrostatic force acting between mineral-brine and oil-brine interfaces. We suggest that the optimum brine composition for IOR during CSW should be chosen to yield the largest change in zeta potential at the mineral-brine interface with opposing polarity to the oil-brine interface and can be determined using the experimental method reported here.
Salinas P, Pain C, Osman H, et al., 2020, Vanishing artifficial diffusion as a mechanism to accelerate convergence for multiphase porous media flow, Computer Methods in Applied Mechanics and Engineering, Vol: 359, Pages: 1-15, ISSN: 0045-7825
Numerical solution of the equations governing multiphase porous media flow is challenging. A common approach to improve the performance of iterative non-linear solvers for these problems is to introduce artificial diffusion. Here, we present a mass conservative artificial diffusion that accelerates the non-linear solver but vanishes when the solution is converged. The vanishing artificial diffusion term is saturation dependent and is larger in regions of the solution domain where there are steep saturation gradients. The non-linear solver converges more slowly in these regions because of the highly non-linear nature of the solution. The new method provides accurate results while significantly reducing the number of iterations required by the non-linear solver. It is particularly valuable in reducing the computational cost of highly challenging numerical simulations, such as those where physical capillary pressure effects are dominant. Moreover, the method allows converged solutions to be obtained for Courant numbers that are at least two orders of magnitude larger than would otherwise be possible.
Onyenanu G, Hampson G, Fitch P, et al., 2019, Characterisation of effective permeability in heterolithic, distal lower shoreface sandstone reservoirs: Rannoch Formation, Brent Group, UK North Sea, Petroleum Geoscience, Vol: 25, Pages: 519-531, ISSN: 1354-0793
The reservoir properties of distal lower-shoreface and distal wave-dominated delta-front deposits, which consist of sandstone beds with locally scoured bases and mudstone interbeds, are poorly understood. The lower Rannoch Formation (Middle Jurassic Brent Group) forms an interval of such heterolithic sandstones in many North Sea reservoirs, and is used to illustrate a workflow for rapid estimation of reservoir properties and their sensitivity to key parameters. Mudstone-interbed thickness distributions in cored reservoir successions are compared to the thickness distribution of sandstone scour-fills in an outcrop analogue(s) in order to identify mudstones with the potential to form laterally extensive barriers to vertical flow. Effective kv/kh at the scale of several typical reservoir-model grid cells (200 × 100 × 20 m) is estimated in intervals bounded by these mudstone barriers via a simple analytical technique that is calibrated to previously documented reservoir-modelling experiments, using values of sandstone proportion measured in cored reservoir successions. Using data from the G2 parasequence (Grassy Member, Blackhawk Formation, east-central Utah, USA) outcrop analogue, mudstones bounding 3–8 m-thick, upwards-coarsening successions in the lower Rannoch Formation may define separate stratigraphic compartments in which grid-cell-scale effective kv/kh is estimated to be 0.0001–0.001 using a streamline-based analytical method.
MacAllister DJ, Graham MT, Vinogradov J, et al., 2019, Characterising the self-potential response to concentration gradients in heterogeneous sub-surface environments, Journal of Geophysical Research. Solid Earth, Vol: 124, Pages: 7918-7933, ISSN: 2169-9356
Self‐potential (SP) measurements can be used to characterise and monitor, in real‐time, fluid movement and behaviour in the sub‐surface. The electrochemical exclusion‐diffusion (EED) potential, one component of SP, arises when concentration gradients exist in porous media. Such concentration gradients are of concern in coastal and contaminated aquifers, and oil and gas reservoirs. It is essential that estimates of EED potential are made prior to conducting SP investigations in complex environments with heterogeneous geology and salinity contrasts, such as the UK Chalk coastal aquifer. Here, we report repeatable laboratory estimates of the EED potential of chalk and marls using natural groundwater (GW), seawater (SW), deionised (DI) water and 5 M NaCl. In all cases the EED potential of chalk was positive (using a GW/SW concentration gradient the EED potential was c.14 to 22 mV), with an increased deviation from the diffusion limit at the higher salinity contrast. Despite the relatively small pore size of chalk (c.1 μm), it is dominated by the diffusion potential and has a low exclusion‐efficiency, even at large salinity contrasts. Marl samples have a higher exclusion‐efficiency which is of sufficient magnitude to reverse the polarity of the EED potential (using a GW/SW concentration gradient the EED potential was c.‐7 to ‐12 mV) with respect to the chalk samples. Despite the complexity of the natural samples used, the method produced repeatable results. We also show that first order estimates of the exclusion‐efficiency can be made using SP logs, supporting the parameterisation of the model reported in Graham et al. (2018), and that derived values for marls are consistent with the laboratory experiments, while values derived for hardgrounds based on field data indicate a similarly high exclusion‐efficiency. While this method shows promise in the absence of laboratory measurements, more rigorous estimates should be made where possible and can be conducted following
Osman H, Salinas P, Pain C, et al., 2019, An Enriched Control Volume Finite Element Method for Multi-Phase Flow in Porous Media on Challenging Meshes, EAGE annual
Osman H, Salinas P, Pain C, et al., 2019, An enriched control volume finite element method for multi-phase flow in porous media on challenging meshes
© 81st EAGE Conference and Exhibition 2019. All rights reserved. We introduce a new, efficient control volume finite element method that improves the modelling of multi-phase flow in heterogeneous porous media. The method uses discontinuous piecewise linear functions enriched with bubble functions for velocity and discontinuous piecewise linear functions for pressure evaluated on control volumes (CVs). LBB stability is maintained with a very efficient velocity:pressure degrees of freedom ratio of 1.25 on tetrahedral meshes. Classical CVFE methods on the other hand may reach a ratio of 5. The method does not require CVs to span element boundaries and as a result is able to accurately preserve saturation discontinuities across material boundaries. Finally, the use of control volume representation for pressure yields significant improvements in stability of the method on challenging meshes.
Onyenanu G, Hampson GJ, Fitch P, et al., 2019, Effects of erosional scours on reservoir properties of heterolithic, distal lower shoreface sandstones, Petroleum Geoscience, Vol: 25, Pages: 235-248, ISSN: 1354-0793
Distal intervals of interbedded sandstones and mudstones in shallow-marine, wave-dominated shoreface and deltaic reservoirs may contain significant hydrocarbon resources, but their reservoir properties are difficult to predict. Relatively small-scale (200 × 100 × 20 m) three-dimensional object-based reservoir models, conditioned to outcrop analogue data, have been used to investigate the controls on the proportion of sandstone, the proportion of sandstone beds that are connected by sandstone-filled erosional scours and the effective vertical-to-horizontal permeability ratio (kv/kh) of such intervals. The proportion of sandstone is controlled by sandstone-bed and mudstone-interbed thickness, and by parameters that describe the geometry, dimensions and lateral-stacking density of sandstone-filled scours. Sandstone-bed connectivity is controlled by the interplay between the thickness of mudstone interbeds and sandstone-filled erosional scours. Effective kv/kh is controlled by the proportion of sandstone, which represents the effects of variable distributions and dimensions of mudstones produced by scour erosion, provided that scour thickness is greater than mudstone-interbed thickness. These modelling results provide a means of estimating the effective kv/kh at the scale of typical reservoir-model grid cells using values of mudstone-interbed thickness and the proportion of sandstone that can potentially be provided by core data.
Edmonds M, Cashman KV, Holness M, et al., 2019, Architecture and dynamics of magma reservoirs, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 377, ISSN: 1364-503X
Sparks RSJ, Annen C, Blundy JD, et al., 2019, Formation and dynamics of magma reservoirs, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 377, ISSN: 1364-503X
Jacquemyn C, Jackson MD, Hampson GJ, 2019, Surface-based geological reservoir modelling using grid-free NURBS curves and surfaces, Mathematical Geosciences, Vol: 51, Pages: 1-28, ISSN: 1874-8953
Building geometrically realistic representations of geological heterogeneity in reservoir models is a challenging task that is limited by the inflexibility of pre-defined pillar or cornerpoint grids. Surface-based modelling workflow uses grid-free surfaces that allows efficient creation of geological models without the limitations of pre-defined grids. Surface-based reservoir modelling uses a boundary representation approach in which all heterogeneity of interest (structural, stratigraphic, sedimentological, diagenetic) is modelled by its bounding surfaces, independent of any grid. Volumes bounded by these surfaces are internally homogeneous and thus no additional facies or petrophysical modelling is performed within these geological domains and no grid or mesh discretization is needed during modelling. Any heterogeneity to be modelled within such volumes is incorporated by adding surfaces. Surfaces and curves are modelled using a parametric NURBS (non-uniform rational B-splines) description. These surfaces are efficient to generate and manipulate, and allow fast creation of multiple realizations of geometrically realistic reservoir models. Multiple levels of surface hierarchy are introduced to allow modelling of all features of interest at the required level of detail; surfaces at one hierarchical level are constructed so as to truncate or conform to surfaces of a higher hierarchical level. This procedure requires joining, terminating and stacking of surfaces to ensure that models contain “watertight” surface-bounded volumes. NURBS curves are used to represent well trajectories accurately, including multi-laterals or side-tracks. Once all surfaces and wells have been generated, they are combined into a reservoir model that takes into account geological relationships between surfaces and preserves realistic geometries.
Abdul Hamid SA, Adam A, Jackson MD, et al., 2019, Impact of truncation error and numerical scheme on the simulation of the early time growth of viscous fingering, International Journal for Numerical Methods in Fluids, Vol: 89, Pages: 1-15, ISSN: 0271-2091
The truncation error associated with different numerical schemes (first order finite volume, second order finite difference, control volume finite element) and meshes (fixed Cartesian, fixed structured triangular, fixed unstructured triangular and dynamically adapting unstructured triangular) is quantified in terms of apparent longitudinal and transverse diffusivity in tracer displacements and in terms of the early time growth rate of immiscible viscous fingers. The change in apparent numerical longitudinal diffusivity with element size agrees well with the predictions of Taylor series analysis of truncation error but the apparent, numerical transverse diffusivity is much lower than the longitudinal diffusivity in all cases. Truncation error reduces the growth rate of immiscible viscous fingers for wavenumbers greater than 1 in all cases but does not affect the growth rate of higher wavenumber fingers as much as would be seen if capillary pressure were present. The dynamically adapting mesh in the control volume finite element model gave similar levels of truncation error to much more computationally intensive fine resolution fixed meshes, confirming that these approaches have the potential to significantly reduce the computational effort required to model viscous fingering.
Jackson MD, Blundy J, Sparks RSJ, 2018, Chemical differentiation, cold storage and remobilization of magma in the Earth's crust, Nature, Vol: 564, Pages: 405-409+, ISSN: 0028-0836
The formation, storage and chemical differentiation of magma in the Earth’s crust is of fundamental importance in igneous geology and volcanology. Recent data are challenging the high-melt-fraction ‘magma chamber’ paradigm that has underpinned models of crustal magmatism for over a century, suggesting instead that magma is normally stored in low-melt-fraction ‘mush reservoirs’1,2,3,4,5,6,7,8,9. A mush reservoir comprises a porous and permeable framework of closely packed crystals with melt present in the pore space1,10. However, many common features of crustal magmatism have not yet been explained by either the ‘chamber’ or ‘mush reservoir’ concepts1,11. Here we show that reactive melt flow is a critical, but hitherto neglected, process in crustal mush reservoirs, caused by buoyant melt percolating upwards through, and reacting with, the crystals10. Reactive melt flow in mush reservoirs produces the low-crystallinity, chemically differentiated (silicic) magmas that ascend to form shallower intrusions or erupt to the surface11,12,13. These magmas can host much older crystals, stored at low and even sub-solidus temperatures, consistent with crystal chemistry data6,7,8,9. Changes in local bulk composition caused by reactive melt flow, rather than large increases in temperature, produce the rapid increase in melt fraction that remobilizes these cool- or cold-stored crystals. Reactive flow can also produce bimodality in magma compositions sourced from mid- to lower-crustal reservoirs14,15. Trace-element profiles generated by reactive flow are similar to those observed in a well studied reservoir now exposed at the surface16. We propose that magma storage and differentiation primarily occurs by reactive melt flow in long-lived mush reservoirs, rather than by the commonly invoked process of fractional crystallization in magma chambers[14].
Li S, Collini H, Jackson MD, 2018, Anomalous Zeta Potential Trends in Natural Sandstones, GEOPHYSICAL RESEARCH LETTERS, Vol: 45, Pages: 11068-11073, ISSN: 0094-8276
Lei Q, Xie Z, Pavlidis D, et al., 2018, The shape and motion of gas bubbles in a liquid flowing through a thin annulus, Journal of Fluid Mechanics, Vol: 285, Pages: 1017-1039, ISSN: 0022-1120
We study the shape and motion of gas bubbles in a liquid flowing through a horizontal or slightly inclined thin annulus. Experimental data show that in the horizontal annulus, bubbles develop a unique ‘tadpole-like’ shape with a semi-circular cap and a highly stretched tail. As the annulus is inclined, the bubble tail tends to vanish, resulting in a significant decrease of bubble length. To model the bubble evolution, the thin annulus is conceptualised as a ‘Hele-Shaw’ cell in a curvilinear space. The three-dimensional flow within the cell is represented by a gap-averaged, two-dimensional model, which achieved a close match to the experimental data. The numerical model is further used to investigate the effects of gap thickness and pipe diameter on the bubble behaviour. The mechanism for the semi-circular cap formation is interpreted based on an analogous irrotational flow field around a circular cylinder, based on which a theoretical solution to the bubble velocity is derived. The bubble motion and cap geometry is mainly controlled by the gravitational component perpendicular to the flow direction. The bubble elongation in the horizontal annulus is caused by the buoyancy that moves the bubble to the top of the annulus. However, as the annulus is inclined, the gravitational component parallel to the flow direction becomes important, causing bubble separation at the tail and reduction in bubble length.
Salinas P, Pavlidis D, Xie Z, et al., 2018, A robust mesh optimisation method for multiphase porous media flows, Computational Geosciences, Vol: 22, Pages: 1389-1401, ISSN: 1420-0597
Flows of multiple fluid phases are common in many subsurface reservoirs. Numerical simulation of these flows can bechallenging and computationally expensive. Dynamic adaptive mesh optimisation and related approaches, such as adaptivegrid refinement can increase solution accuracy at reduced computational cost. However, in models or parts of the modeldomain, where the local Courant number is large, the solution may propagate beyond the region in which the mesh isrefined, resulting in reduced solution accuracy, which can never be recovered. A methodology is presented here to modifythe mesh within the non-linear solver. The method allows efficient application of dynamic mesh adaptivity techniques evenwith high Courant numbers. These high Courant numbers may not be desired but a consequence of the heterogeneity of thedomain. Therefore, the method presented can be considered as a more robust and accurate version of the standard dynamicmesh adaptivity techniques.
Vinogradov J, Jackson MD, Chamerois M, 2018, Zeta potential in sandpacks: Effect of temperature, electrolyte pH, ionic strength and divalent cations, Colloids and Surfaces A: Physicochemical and Engineering Aspects, Vol: 553, Pages: 259-271, ISSN: 0927-7757
Rocks in many subsurface settings are at elevated temperature and are saturated with brines of high ionic strength (high salinity) containing divalent ions. Yet most laboratory measurements of zeta potential in earth materials are obtained at room temperature using simple monovalent electrolytes at low ionic strength. Consequently, the zeta potential at conditions relevant to many subsurface settings is not known. We report experimental measurements of the temperature dependence of the zeta potential in well characterised, natural quartz sandpacks over the temperature range 23–120 °C saturated with electrolytes containing divalent ions at a range of concentrations relevant to natural systems. We find that the key control on zeta potential in these unbuffered experiments is pH, which varies in response to temperature and electrolyte composition. The zeta potential is negative irrespective of sample or electrolyte, but its magnitude is strongly correlated to pH, which varies both with temperature and the concentration of divalent ions. The pH decreases with increasing temperature at low ionic strength, but is independent of temperature at high ionic strength. The pH is also typically lower in the presence of divalent ions, irrespective of the total ionic strength. The zeta potential increases in magnitude with increasing pH. Different relationships between zeta potential, temperature and concentration of divalent ions could be obtained in buffered experiments where the pH is fixed at a given value.
Malcolm G, Jackson M, MacAllister DJ, et al., 2018, Self-potential as a predictor of seawater intrusion in coastal groundwater boreholes, Water Resources Research, Vol: 54, Pages: 6055-6071, ISSN: 0043-1397
Monitoring of self‐potentials (SP) in the Chalk of England has shown that a consistent electrical potential gradient exists within a coastal groundwater borehole previously affected by seawater intrusion (SI) and that this gradient is absent in boreholes further inland. Furthermore, a small but characteristic reduction in this gradient was observed several days prior to SI occurring. We present results from a combined hydrodynamic and electrodynamic model, which matches the observed phenomena for the first time and sheds light on the source mechanisms for the spatial and temporal distribution of SP. The model predictions are highly sensitive to the relative contribution of electrochemical exclusion and diffusion potentials, the ‘exclusion efficiency’, in different rock strata. Geoelectric heterogeneity, largely due to marls and hardgrounds with a relatively high exclusion efficiency, was the key factor in controlling the magnitude of the modelled SP gradient ahead of the saline front and its evolution prior to breakthrough. The model results suggest that, where sufficient geoelectric heterogeneity exists, borehole SP may be used as an early warning mechanism for SI.
Onyenanu GI, Jacquemyn CEMM, Graham GH, et al., 2018, Geometry, distribution and fill of erosional scours in a heterolithic, distal lower shoreface sandstone reservoir analogue: Grassy Member, Blackhawk Formation, Book Cliffs, Utah, USA, Sedimentology, Vol: 65, Pages: 1731-1760, ISSN: 0037-0746
Many shoreface sandstone reservoirs host significant hydrocarbon volumes within distal intervals of interbedded sandstones and mudstones. Hydrocarbon production from these reservoir intervals depends on the abundance and proportion of sandstone beds that are connected by erosional scours, and on the lateral extent and continuity of interbedded mudstones. Cliff‐face exposures of the Campanian ‘G2’ parasequence, Grassy Member, Blackhawk Formation in the Book Cliffs of east‐central Utah, USA, allow detailed characterization of 128 erosional scours within such interbedded sandstones and mudstones in a volume of 148 m length, 94 m width and 15 m height. The erosional scours have depths of up to 1·1 m, apparent widths of up to 15·1 m and steep sides (up to 35°) that strike approximately perpendicular (N099 ± 36°) to the local north–south palaeoshoreline trend. The scours have limited lateral continuity along strike and down dip, and a relatively narrow range of apparent aspect ratio (apparent width/depth), implying that their three‐dimensional geometry is similar to non‐channelized pot casts. There is no systematic variation in scour dimensions, but ‘scour density’ is greater in amalgamated (conjoined) sandstone beds over 0·5 m thick, and increases upward within vertical successions of upward‐thickening conjoined sandstone beds. There is no apparent organization of the overall lateral distribution of scours, although localized clustering implies that some scours were re‐occupied during multiple erosional events. Scour occurrence is also associated with locally increased amplitude and laminaset thickness of hummocky cross‐stratification in sandstone beds. The geometry, distribution and infill character of the scours imply that they were formed by storm‐generated currents coincident with riverine sediment influx (‘storm floods’). The erosional scours increase the vertical and lateral connectivity
Deveugle PEK, Jackson MD, Hampson GJ, 2018, A comparative study of reservoir modeling techniques and their impact on predicted performance of fluvial-dominated deltaic reservoirs: reply, AAPG Bulletin, Vol: 102, Pages: 1664-1667, ISSN: 0149-1423
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.