Heterogeneous Porous Systems Research Articles

Evidence for active generation and seepage of sub-salt natural gas/condensate blend in the east offshore Nile Delta, Egypt: integrated geochemical, petrophysical and seismic attribute approaches

Offshore Nile Delta in Egypt represents an enormous hydrocarbon province with recent projected gas and condensate discoveries of more than 50 trillion cubic feet “TCF”. Most of these occur in the post-salt hydrocarbon plays where biogenic gases are dominant. This study integrates organic geochemistry, seismic geomorphology and petrophysics in order to decipher the origin, and accumulation conditions of the wet gas/condensate blend in the Upper Miocene sub-salt Wakar Formation sandstones in Port Fouad Marine “PFM” Field, offshore Nile Delta. Hydrocarbon pay zones are scattered thin (< 10 m) sandstones deposited in as turbiditic channel/levee complex facies. Spatial distribution of vertical gas chimneys (∼ 2 km wide) rooting-down to the Messinian Rosetta salt is associated with the lateral pinching-out of the turbiditic sandstones. Organically-rich (total organic carbon “TOC” > 1 w.t.%, hydrogen index “HI” > 200 mgHC/gTOC) and mature (Tmax > 430 °C, vitrinite reflectance “VR” > 0.6 %Ro), source rocks are restricted to Upper Miocene Wakar and Oligo-Miocene Tineh formations. The latter contains more mature organofacies (up to 1.2 %Ro) and type II/III kerogen, thereby demonstrating a good capability to generate wet gases. The studied gas is wet and has thermogenic origin with signs of secondary microbial alteration, whereas the condensate contains a mixture of marine and terrestrial input. Molecular biomarkers of the condensate, isotopic and molecular composition of the gas reveals a generation of condensate prior to gas expulsion from the source. The Wakar sandstones have a heterogeneous pore system where three reservoir rock types (RRTI, RRTII and RRTIII). RRTI rocks present the bulk composition of the Wakar pay zones. Spatial distribution of RRTI facies likely control the accumulation of the sub-salt hydrocarbons. Our results provide a new evidence on an active petroleum system in the sub-salt Paleogene successions in the offshore Nile Delta where concomitant generation of gas/condensate blend has been outlined.

Application of space renormalisation technique for spatiotemporal analysis of effective thermal conductivity in multiphase porous materials

Effective thermal conductivity (k¯) is a critical parameter influencing heat transfer in multiphase porous materials. This study introduces a computational approach using the space renormalisation technique to derive k¯ from segmented X-ray micro-CT images of porous media. By accounting for pore-scale heterogeneity, this approach enables detailed spatiotemporal analysis of k¯ in different porous structures. The application of this technique is demonstrated through the prediction and spatiotemporal analysis of k¯ in three different porous rock samples experiencing multiphase fluid flow: (i) steady-state two-phase flow in Estaillades carbonate, (ii) sequential flooding in Bentheimer sandstone, and (iii) immiscible three-phase flow in Ketton limestone. Results show distinct directional variations in k¯ according to phase saturations and redistributions, highlighting the sensitivity of the approach to the microstructural characteristics of porous media. The space renormalisation technique efficiently predicts k¯ with significantly reduced computational costs compared to traditional finite difference methods, making it suitable for real-time applications. The findings provide deeper insights into the dynamic heat transfer mechanisms in heterogeneous porous systems, with implications for various porous media applications such as enhanced oil recovery, geothermal energy extraction, and the design of heat exchangers in engineering systems.

Experimental and computational aspects of molecular frustrated Lewis pairs for CO2 hydrogenation: en route for heterogeneous systems?

Catalysis plays a crucial role in advancing sustainability. The unique reactivity of frustrated Lewis pairs (FLPs) is driving an ever-growing interest in the transition metal-free transformation of small molecules like CO2 into valuable products. In this area, there is a recent growing incentive to heterogenize molecular FLPs into porous solids, merging the benefits of homogeneous and heterogeneous catalysis - high activity, selectivity, and recyclability. Despite the progress, challenges remain in preventing deactivation, poisoning, and simplifying catalyst-product separation. This review explores the expanding field of FLPs in catalysis, covering existing molecular FLPs for CO2 hydrogenation and recent efforts to design heterogeneous porous systems from both experimental and theoretical perspectives. Section 2 discusses experimental examples of CO2 hydrogenation by molecular FLPs, starting with stoichiometric reactions and advancing to catalytic ones. It then examines attempts to immobilize FLPs in porous matrices, including siliceous solids, metal-organic frameworks (MOFs), covalent organic frameworks, and disordered polymers, highlighting current limitations and challenges. Section 3 then reviews computational studies on the mechanistic details of CO2 hydrogenation, focusing on H2 splitting and hydride/proton transfer steps, summarizing efforts to establish structure-activity relationships. It also covers the computational aspects on grafting FLPs inside MOFs. Finally, Section 4 summarizes the main design principles established so far, while addressing the complexities of translating computational approaches into the experimental realm, particularly in heterogeneous systems. This section underscores the need to strengthen the dialogue between theoretical and experimental approaches in this field.

Lattice Boltzmann simulation of dissolution patterns in porous media: Single porosity versus dual porosity media

Understanding the influence of porous media structure, particularly dual porosity, on solvent transport and pore geometry evolution during chemical reactions is a complex and critical area of study. This research leverages the lattice Boltzmann method to investigate how the presence of aggregates in a medium affects solvent transport and pore space development, focusing on distinct dissolution regimes: face and wormhole dissolution. The study addresses the challenge of managing variable pore sizes in dual porosity media by developing specialized GPU algorithms, which efficiently handle fine grids and complex pore spaces. The findings reveal that dual porosity significantly enhances dissolution rates in both the face and wormhole dissolution regimes. Intriguingly, while the pattern of face dissolution remains largely unchanged, dual porosity markedly alters the pattern of wormhole dissolution. In dual-porosity media, the wormholes tend to be narrower and more elongated compared to the wider wormholes observed in single-porosity media. This variation is attributed to the reaction area dynamics, where the reduced reactive surface area along the main wormhole path in dual-porosity media results in less solvent engagement in the reaction processes. Moreover, the research provides insights into the microscale interactions in porous media, emphasizing how variations in microscale porosity can have substantial impacts on the overall dissolution dynamics. The study results are not only significant for understanding the fundamental aspects of chemical dissolution in porous media but also have practical implications in fields such as geo-energy and groundwater remediation. These findings help optimizing reaction processes in complex and heterogeneous porous systems, highlighting the need for detailed consideration of microstructural characteristics in modeling and industrial applications.

Universal Relationship between Mass Flux and Properties of Layered Heterogeneity on the Contaminant-Flushing Process

To remove contaminants from a layered heterogeneous porous system where the flow direction is parallel to the horizontal layering, the flushing front may advance faster in one layer than the other, resulting in a significant vertical concentration gradient across the layer interface. This gradient leads to mass exchange between the layers due to the vertical dispersive transport. Such a mass exchange phenomenon can greatly alter the mass (and heat if the temperature is a concern) distribution in a multi-layer porous media system but has never been investigated before in a quantitative manner. In this study, high-resolution finite-element numerical models have been employed to investigate how transport properties affect contaminant transport during flushing, using a two-layer system as an example. The results showed that the porosity and retardation factor play similar roles in affecting mass flux across the interface. Increasing the porosity (or retardation factor) of one layer with a faster flushing velocity would decrease the total mass flux across the interface of the layers, while increasing the porosity (or retardation factor) of the layer with a slower flushing velocity played an adverse influence. Furthermore, increasing the transverse dispersivity of any layer increased the mass flux across the interface of the two layers. However, changes in the transverse dispersivity did not affect the spatial range (or gap along the flow direction) in which significant vertical mass flux occurs. This study has important implications for managing contaminant remediation in layered aquifers.

Mechanistic insights into contaminant transport dynamics in the saturated porous system in the presence of low permeability region using numerical simulations and temporal moment analysis.

The influence of low permeability porous media (LPPM) on contaminant transport dynamics in saturated porous systems was investigated using numerical simulations and temporal moments of contaminant concentrations. Two-dimensional flow and contaminant transport simulations were conducted, considering various parameters such as longitudinal dispersivity (ranging from 15 to 60m), the ratio of transverse to longitudinal dispersivity (ranging from 0.05 to 0.2), retardation factor (ranging from 1 to 4), and hydraulic gradient (ranging from 0.005 to 0.02) for both homogeneous and heterogeneous porous systems. The findings revealed significant differences in the transport behavior of conservative and highly reactive contaminants between the porous systems without and with the LPPM region. The center of mass of contaminant plume and peak concentration zone were observed inside the LPPM region for the heterogeneous porous system, especially during the source off-loading period. Furthermore, asymmetric distributions of the zeroth temporal moment (ZTM), mean residence time (MRT), and variance of the breakthrough curve (BTC) were observed along the longitudinal distance within the LPPM region for heterogeneous porous system, highlighting the impact of heterogeneity on contaminant plume evolution dynamics. The moment analysis results provided insights into the influence of LPPM region on time-averaged contaminant transport dynamics in adjacent porous systems. These findings can help risk managers understand the complex fate and transport dynamics in heterogeneous porous systems. Future studies could explore the modelling of multispecies contaminants in heterogeneous saturated porous systems subjected to fluctuating water table.

Porosity distribution in the Devonian Antrim Shale: Controlling factors and implications for gas sorption

Unconventional reservoirs, such as oil and gas shales, are characterized by diverse and heterogeneous pore systems, and their detailed knowledge is critical for understanding fluid storage and transport mechanisms. The Devonian Antrim Shale in the Michigan Basin is an unconventional, primarily biogenic gas accumulation with a technical recoverable resource of 19.9 Tcf. While its general formation properties are known, the details of porosity distribution and pore morphology are lacking. This study provides a comprehensive description of the total porosity, pore size distribution, pore morphology and mineral associations for various members of the Antrim Shale sampled at three locations across the basin, and then investigates the factors controlling porosity distribution and the implications for gas sorption. Results indicate that the black-shale members, the Lachine and Norwood, are characterized by a lower porosity (0.1–2%) compared to the organic-lean members, the Paxton and Upper Antrim (2–7% porosity). Total porosity tends to decrease with the increase in organic content in the Antrim Shale as organic matter, in particular solid bitumen, occludes available pore space between mineral grains in the organic-rich black shale members. Organic matter displays little to no porosity of its own at the SEM resolution, but gas adsorption measurements indicate the presence of micropores (<2 nm), whose amount correlates positively to the total organic content. The Norwood member (TOC values up to 25%) is characterized by the largest share of micropores (up to 37% of the total porosity volume), while the organic-lean Paxton Member (TOC < 6%) has the least amount of microporosity (1–6%). Only the Lachine Member and select Upper Member samples showed larger organic matter pores, visible in the SEM images (∼50–100 nm). Mesopores (2–50 nm) are the dominant pore size group in the Antrim Shale, forming 45% to 76% of the pore space, and most of the pores are interparticle and intraparticle pores in and around clays, quartz, feldspar and pyrite grains. No single mineral component influences the total porosity distribution, but clay content exhibits a weak positive correlation to the meso-macro porosity. As microporosity is known to contribute the most to gas adsorption capacity of unconventional reservoirs, TOC appears to be most important factor controlling both CH4 and CO2 storage potential of the Antrim Shale. The Norwood Member, characterized by the highest TOC and microporosity volume as well as surface area of the micropores, is predicted to have the highest gas adsorption capacity but direct sorption measurements will be needed to confirm that. This study highlights some important differences with previous observations about porosity relationship to organic and mineral components of shale reservoirs, and expands the understanding of shale pore systems in the low-maturity range of organic-rich shales.

Effective toluene removal from aqueous solutions using fast pyrolysis-derived activated carbon from agricultural and forest residues: Isotherms and kinetics study

In this study, the production and characterization of activated carbons (ACs) from agricultural and forest residue using physical activation are discussed. Biomass-based biochars produced during fast pyrolysis process is introduced as alternative precursors to produce AC and the integrated process for the co-production of porous adsorbent materials from biochar via the fast pyrolysis process is suggested. Moderate surface areas and good adsorption capacities were obtained from switchgrass (SWG) and pine tops (PT) based AC. The surface areas were 959 and 714 m2/g for SWG- and PT-based AC, respectively. The adsorption capacities using toluene as pollutant for two model systems of 180 and 300 ppm were measured and ranged between 441-711 and 432–716 mg/g for SWG-based and PT-based AC, respectively. The nitrogen adsorptive behavior, Lagergren pseudo-second-order kinetic (PSOK) model and kinetics isotherms studies describe a heterogeneous porous system, including a mesoporous fraction with the existence of a multilayer adsorption performance. The presence of micropores and mesopores in SWG- and PT-based AC suggests potential commercial applications for using pyrolytic biochars for AC production.

Prediction of lithology in lacustrine carbonates using well logs: The Cretaceous Barra Velha Formation in Santos Basin, offshore Brazil

Abundant hydrocarbons have been produced from the pre‐salt lacustrine carbonates of the Cretaceous Barra Velha Formation in the Santos Basin of offshore Brazil. The highly heterogeneous lithology and pore systems make it difficult to predict the reservoir quality via petrophysical well logs. Core description, computed tomography (CT) scanning, thin sections and wireline well logs are utilized to characterize the lithology, pore spaces are reservoir quality of the Cretaceous Barra Velha Formation pre‐salt lacustrine carbonates in the Santos Basin. The results show that the lithology mainly includes shrubstone, grainstone, laminated micrite and massive micrite. The pore systems are dominated by secondary pores, such as intergranular pores, dissolution pores and intercrystalline pores as well as modified primary pores. Geological well logs (conventional well logs, electrical and sonic image logs and nuclear magnetic resonance [NMR] logs) are integrated to build the predictable models of the carbonate reservoirs. The shrubstone, which is dominated by intergranular pores, has the highest reservoir quality, which can be derived from NMR logs. Grainstone contains both primary intergranular pores and abundant secondary dissolution pores. The laminated and massive micrite contain only micropores and therefore have the lowest reservoir quality. Lastly, conventional well logs integrated with electrical and sonic image logs are utilized to predict the distribution of lithology and reservoir quality in single wells, and the results are testified by the NMR log data. The shrubstone and grainstone are future exploration targets of the Cretaceous Barra Velha Formation in the Santos Basin. The results are hoped to give insights into the petrophysical behaviours of various lithologies, and provide theoretical and technical guidance for reservoir evaluation and prediction.

Effects of Periodic Pore Ordering on Photocatalytic Hydrogen Generation with Mesoporous Semiconductor Oxides

Crystalline and 3D continuous mesoporous quaternary CsTaWO6 semiconductors are prepared with different degrees of long‐range periodic order and local order, respectively, to investigate the influence of periodic pore order on the photocatalytic performance in hydrogen evolution of mesoporous photocatalysts. The degree of long‐range order of the mesopores is changed by modifying the ratio between metal precursors and soft polymer template poly(isoprene‐b‐styrene‐b‐ethylene oxide) (PI‐b‐PS‐b‐PEO; ISO) in the sol–gel synthesis. Long‐range periodic order is found to have no appreciable advantage compared with an only locally ordered continuous pore system. On the contrary, nonperiodically ordered mesopores result in higher activity toward photocatalytic hydrogen evolution, even with slightly smaller pore diameter and lower cumulative pore volume. Most importantly, it is shown that pore connectivity and heterogeneous pore systems in mesoporous photocatalysts play a major role for hydrogen evolution when other parameters are confirmed to be not rate limiting.

Insights into in-situ catalytic degradation of plastic wastes over zeolite-based catalyst from perspective of three-dimensional pore structure evolution

Insightfully understanding the process of volatiles from plastic depolymerization entering from the exterior into internal structure of catalyst favors to rationalize the catalyst design in scale-up principles. Herein, catalytic degradation of plastic wastes with fluid catalytic cracking catalyst (FCC) was investigated in-depth. The yield and composition of liquid and gas products over various FCCs were studied quantitatively. The structural evolution of catalyst on overall scope, including the topology of heterogeneous pore systems and spatial distribution of zeolite was probed by X-ray nano-CT. The results showed that FCC enhanced the transformation of C16-C30 chains to C9-centered monocyclic aromatics. The nano-CT analysis of FCCs illustrated remarkable loss of exterior porosity after reaction, particularly at the depth of ∼16.5μ m from the outmost layer. While the interior pores were marginally affected, indicating large hydrocarbons incapable of engaging with active sites to full advantage, which preferably occupied large-size pores (>385 nm) of external surface.

Two-phase flow in heterogeneous porous media: A multiscale digital model approach

Pore-scale fluid flow simulation on digital rocks from X-ray CT experiments can predict the physical properties and analyze the distribution characteristics of the fluids, which is critical for many problems in environmental remediation and geo-materials. It is straightforward to numerically simulate the multiphase flow on the digital rocks from CT scanning if they are homogeneous. However, it is of great difficulty to obtain large and high-resolution digital models of heterogeneous samples containing multiscale features only by CT scanning since the CT machines strike a balance between the field of view and resolution. In addition, the current methods of multiphase flow modeling face challenges in dealing with large samples and heavy computations. To address such issues, a unified and integrative modeling approach for constructing multiscale digital images and simulating multiphase flow in complex and heterogeneous pore systems was presented. Firstly, we developed a hybrid modeling method for producing multiscale digital models to represent the heterogeneous pore systems on which two-phase flow simulations are computed. The results show that the constructed models built by the hybrid method contain more tiny pores than the ones from regular CT imaging and exhibit better connectivity and permeability. The pore/throat size distributions, porosity, and permeability of the digital models produced by the hybrid method are closer to the experimental data than the ones from the single-scale models. Moreover, the non-uniform meshes for complex pore systems and parallel computing on a supercomputing cluster are combined to improve the computational efficiency of the two-phase flow simulation. The distribution characteristics of fluids in pore systems at the end of two-phase flow were also analyzed, which improves our understanding of two-phase flow.

Application of the dynamic mean field theory to fluid transport in slit pores.

We explore the applicability of the lattice model and dynamic mean field theory as a computationally efficient tool to study transport across heterogeneous porous media, such as mixed matrix membranes. As a starting point and to establish some basic definitions of properties analogous to those in the off-lattice systems, we consider transport across simple models of porous materials represented by a slit pore in a chemical potential gradient. Using this simple model, we investigate the distribution of density and flux under steady state conditions, define the permeability across the system, and explore how this property depends on the length of the pore and the solid-fluid interactions. Among other effects, we observe that the flux in the system goes through a maximum as the solid-fluid interaction is varied from weak to strong. This effect is dominated by the behavior of the fluid near the walls and is also confirmed by off-lattice molecular dynamics simulations. We further extend this study to explore transport across heterogeneous slit pore channels composed of two solids with different values of solid-fluid interaction strengths. We demonstrate that the lattice models and dynamic mean field theory provide a useful framework to pose questions on the accuracy and applicability of the classical theories of transport across heterogeneous porous systems.

A new method to improve the NMR log interpretation in drilling mud-invaded zones: A case study from the Brazilian Pre-salt

The Santos Basin hosts several giant carbonate oilfields in the Pre-salt province and is one of the most important hydrocarbon discoveries in the past years. These carbonate reservoirs present exceptional reservoir quality with a challenging depositional and diagenetic history that produced complex and heterogeneous pore systems. As one of the most effective tools for in-situ porosity and permeability evaluation, the nuclear magnetic resonance (NMR) well log plays an essential role in the Pre-salt petrophysical evaluation and its signal interpretation must be performed carefully. This work proposes a new approach to detect and improve the interpretation of zones with unreal NMR logging tool readings in areas heavily affected by drilling mud invasion in caverns/vugs, which causes a T2 distribution shift towards lower relaxation times. This work analyses well log data from 28 wells in the Sapinhoá Field, supported by special core analyses (SCAL) and routine core analyses (RCAL), as well as plugs, sidewall cores and thin sections data. The proposed approach generates synthetic NMR Free Fluid and T2 distributions with minimum error and replaces the faulty data, consisting in five main steps, (1) computing new curves to be used as inputs; (2) detecting the zones affected by the invasion; (3) water saturation calculation by the saturation height modeling method; (4) calculating a synthetic NMR free fluid curve based on a relationship between a NMR-derived water saturation and the saturation height model; and (5) using the Random Forests algorithm to estimate a synthetic T2 distribution. The proposed method has a minimized error and resulted an increase of up to 10% thickness in the pay zone and a reduction of up to 9% in water saturation average, which may represent enormous amounts of oil depending on the reservoir area. This study provides a new method, which can be used in the improvement of petrophysical interpretations in highly heterogeneous carbonate reservoirs and thus reducing the exploratory and development risks. • Drilling mud invades vug pores and results in misleading NMR readings; • A new methodology is proposed to create a synthetic NMR free fluid and T2 distribution with minimum error; • An increase of 10% in pay thickness and a reduction of 9% in average water saturation was achieved in the Pre-salt reservoirs; • The methodology is proper for the petrophysical evaluation of highly heterogeneous carbonate reservoirs

Non-local diffusion models for fractured porous media with pressure tests applications

In this work, different Generalized Double Porosity Models for anomalous fluid flow in fractured porous media are presented, and transient production decline applications discussed. The effects of subdiffusive and superdiffusive flows in fracture networks coupled to subdiffusive transport inside the matrix are explored, and some insights into how to identify these types of flow in geological formations like aquifers and oil fields, through transient production decline analysis are given. Additionally, we discuss different interpretations of the models parameters that allow, under the same analysis, to estimate the length scales of the system main heterogeneities. Moreover, we show that superdiffusive flow regimes could be a consequence of highly heterogeneous porous systems described by scale-free permeability distributions. Finally, we show that the use of non-local models of the type herein discussed, admit a novel way to construct effective single porosity models for the long time description of double porosity systems.

Convergence - Divergence of the Finite Volume Method for the Fluid and Heat Flow in Heterogeneous Porous Rocks

Fluid velocity has an important impact in the Finite Volume numerical method (FVM) used to model fluid and energy flows in heterogeneous porous media. This formulation is based on the energy flow conservation equations under local thermal non-equilibrium conditions (LTNE). The heat transfer from the solid matrix to the moving non-isothermal fluid inside the pores is simulated for several velocities and global different heat transfer coefficients. During the numerical simulation of coupled heat/mass flow in a heterogeneous porous system it is necessary to average highly variable physical parameters at the boundaries between different domains represented geometrically in the computational mesh of the FVM. This can be effectively achieved using appropriate average techniques at the contact interfaces of each domain. The averaging process should correctly represent the behaviour of the fluid velocity crossing different areas of the reservoir. Many numerical divergence problems arise from the fluid velocity value and the interfacial interactions at the boundaries of different continua. The averages have a decisive influence on the numeric results of the simulation. A very stable, convergent averaging scheme for the FVM is presented herein and compared to new analytical diffusion-convection models. Especial attention is paid to the dynamic process of cold water (50°C) injected into a geothermal reservoir at higher temperature (350°C). The fluid temperature profile is calculated when the fluid migrates at constant speed through a permeable corridor from a fluid injection point to an extraction zone. The physical reason for the divergence of a numerical model, and the exploration of the range of validity of the LTNE hypothesis during the injection of cold water into a hot reservoir are both explained.

Influence of the wettability on the residual fluid saturation for homogeneous and heterogeneous porous systems

The influence of wettability on the residual fluid saturation is analyzed for homogeneous and heterogeneous porous systems. Several simulations under different wettability, flow rate, and heterogeneity conditions were carried out using a two-component lattice-Boltzmann method. The fluid flow driving force and initial conditions were imposed using a specific methodology that allows a clear distinction between the results obtained for immiscible displacement when the porous medium is initially saturated with one fluid (called primary) and when two fluids are filling the porous spaces (called secondary). The results show that the primary sweeping process is more effective when the displaced fluid is non-wetting. We observe that the heterogeneity has an important role for the whole process since it disturbs the fluid interfaces inducing the flow in the longitudinal and transversal directions, improving considerably the effectiveness of the primary displacement when compared with ideally homogeneous cases. We noted that for oil contact angles, θo, higher than a critical value, no residual oil is found. In all homogeneous cases, the critical value is 120°. The residual fluid increases proportionally to the capillary number for primary displacements, but it also depends on the system heterogeneity and wetting conditions. For secondary displacements in heterogeneous systems, the highest residual oil saturation is found for completely oil-wet conditions, with values ranging from 29% to 41% and tending to zero for all cases when θo &amp;gt; 120°. The initial water–oil distribution is found to be a determining factor in the amount of trapped oil after the waterflooding process.

Trait-specific dispersal of bacteria in heterogeneous porous environments: from pore to porous medium scale.

The dispersal of organisms controls the structure and dynamics of populations and communities, and can regulate ecosystem functioning. Predicting dispersal patterns across scales is important to understand microbial life in heterogeneous porous environments such as soils and sediments. We developed a multi-scale approach, combining experiments with microfluidic devices and time-lapse microscopy to track individual bacterial trajectories and measure the overall breakthrough curves and bacterial deposition profiles: we, then, linked the two scales with a novel stochastic model. We show that motile cells of Pseudomonas putida disperse more efficiently than non-motile mutants through a designed heterogeneous porous system. Motile cells can evade flow-imposed trajectories, enabling them to explore larger pore areas than non-motile cells. While transported cells exhibited a rotation in response to hydrodynamic shear, motile cells were less susceptible to the torque, maintaining their body oriented towards the flow direction and thus changing the population velocity distribution with a significant impact on the overall transport properties. We also found, in a separate set of experiments, that if the suspension flows through a porous system already colonized by a biofilm, P. putida cells are channelled into preferential flow paths and the cell attachment rate is increased. These two effects were more pronounced for non-motile than for motile cells. Our findings suggest that motility coupled with heterogeneous flows can be beneficial to motile bacteria in confined environments as it enables them to actively explore the space for resources or evade regions with unfavourable conditions. Our study also underlines the benefit of a multi-scale approach to the study of bacterial dispersal in porous systems.

Pore typing using nuclear magnetic resonance, an example with samples from cretaceous pre-salt lacustrine carbonates in the Santos Basin, Brazil

The Brazilian sub-salt play carbonate reservoirs present highly complex and heterogeneous pore systems, making it difficult to define their petrophysical properties, which is essential for the reservoir characterization. Nuclear magnetic resonance (NMR) has emerged as an effective tool in the petrophysical characterization of carbonates, both on the core and log scales. This work uses plug samples from the Barra Velha Formation in the Santos Basin, SE Brazil, which is characterized by unconventional lacustrine carbonate deposits dominated by shrub-like forms and spherulitic allochems. The porosity types were defined based on NMR laboratory analysis associated with petrographic descriptions and high-resolution X-ray computed tomography. From the NMR results it is possible to define irreducible water saturation and calculate porosity and permeability for each sample. The results obtained through the resonance technique showed high correlation with the porosity and permeability values obtained by gas injection. Additionally, the interpretation of the data enabled the division of samples into porous and tight categories and the definition of groups with characteristics of tight, good and excellent reservoirs. The interpreted data contributes to a better understanding of the petrophysical properties of these complex and heterogeneous samples.

PORE SYSTEM QUANTIFICATION AND CHARACTERIZATION IN VOLCANIC ROCKS: A CASE STUDY FROM THE LOWER CRETACEOUS SERRA GERAL GROUP, PARANÁ BASIN, SOUTHERN BRAZIL

Studies of pore systems in volcanic rocks are of increasing importance due to these rocks' potential as reservoirs for hydrocarbons. For this paper, samples of basaltic pahoehoe, rubbly pahoehoe and acidic lava from the Lower Cretaceous Serra Geral Group (Paraná Basin, southern Brazil) were analysed in order to quantify and characterize the constituent pore systems. The Serra Geral Group volcanics were erupted as part of the Paraná‐Etendeka Igneous Province in the Early Cretaceous (Valanginian – Hauterivian). Analyses included experimental measurements by permo‐porosimeter integrated with X‐ray microtomography (μ‐CT) image analysis of vertical and horizontal sample plugs. In addition petrographic analyses were carried out to characterize pore types in thin section. The experimental porosity values ranged from 0.11 to 13.08% and most permeability values were generally lower than 0.0004 mD. Values varied as much within flow zones as they did between them.Porosity and permeability values were not sufficient for the Serra Geral Group volcanics to be considered as a potential reservoir analogue. However the wide range in values was attributed to the processes which controlled the origin and development of the pore system. Primary pores observed included intracrystalline sieve, vesicular and interflow laminar types; secondary porosity, such as spongy, interclast and intra‐matrix pore types, was related to dissolution and the precipitation of secondary minerals. The porosity values obtained by μ‐CT (between &lt;0.01 and 3.37%) were lower than those experimentally measured by permo‐porosimeter. This was attributed to the presence of multi‐scale pores in the volcanic rocks sampled, and also to limitations with image resolution. Even so, the use of μ‐CT allowed the visualization of porosity variations and was useful in characterizing the pore system.The results presented in this paper demonstrate that the volcanic rocks in the Serra Geral Group have a heterogeneous pore system, similar to that in carbonate rocks.