Pore Fluid Flow Research Articles

Synkinematic evolution of stylolite porosity

Stylolites form by the transportation and precipitation of dissolved materials in pore fluids due to concentration gradients that develop in rocks under stress. This is a coupled chemical-hydraulic-mechanical (CHM) process, resulting from the interplay between chemical dissolution, pore fluid flow and stress during stylolite growth. Although the CHM feedbacks that develop around stylolite seams lead to porosity compartmentalization, the dynamic processes controlling porosity evolution during stylolite growth remain unknown. Here, thrust-induced stylolites in micritic limestones of the Eilean Dubh Formation that crop out in the footwall of the Caledonian Ullapool/Moine Thrust in NW Scotland are used to investigate the dynamic processes controlling stylolite growth. Stylolite microstructures observed in detail, using a backscatter electron image mosaic (102,600 × 18,239 pixels; 0.17μm/pixels), both reveal stylolite seams (core zones) surrounded by zones of increased-porosity (damage zones) and suggest a four stage self-organization process for stylolite growth and evolution. In the first stage, stress concentration in the micritic matrix led to the partial dissolution of the matrix, forming new pores adjacent to pyrites grains. In the second stage, the new pores facilitated local dissolution, which in turn promoted their growth, establishing a positive feedback loop between texture and solubility that enlarged the local porous zone by self-organization. In the third stage, the porous zones facilitated the influx of externally derived fluids and differentiated into core zones, with syn-kinematic precipitation of secondary pyrites and clay minerals, and damage zones, with ongoing dissolution. In the fourth stage, the porous zones propagated perpendicular to the shortening direction and became interlinked, forming mature stylolites with a core zone in the centre surrounded on both sides by damage zones with high porosities. The fluid flux along the stylolites during their formation was likely controlled by episodic movements along the Ullapool Thrust.

Transient thermal management characteristics of a porous fin with radially outwards fluid flow

Thermal management and energy storage problems often utilize extended surfaces, also known as fins for enhanced heat transfer. While thermal conduction is usually the dominant mode of heat transfer in a solid fin, the use of porous fins that include advective thermal transport due to porous fluid flow has also been investigated. In particular, the steady state thermal performance of a porous fin with pressure-driven radially outwards flow has been studied. While such results are helpful for studying problems that are inherently steady state in nature, such results do not readily apply to problems where heat removal or energy storage occurs only over a short period of time. This work presents transient thermal analysis of a porous fin with radial porous fluid flow driven by a pressure gradient. It is shown that the transient temperature field in the fin is governed by a transient convection-diffusion-reaction (CDR) equation, the solution for which is derived in the form of Bessel functions. Based on this solution, the evolution of fin performance with time is examined. Comparison of heat removed by the porous fin with a baseline case without any fin is carried out. The time taken to reach steady state is calculated. Key non-dimensional parameters appearing in this problem are identified and their impact on fin performance over time is investigated. Since fin porosity improves advective thermal transport but suppresses diffusive transport at different rates at different times, therefore, it is shown that for a given operating time, there may exist an optimal porosity that maximizes the rate of heat removal. It is shown that the operating time period of the fin plays a key role in determining whether fin porosity strongly impacts heat removal rate or not. Consequently, it is shown that it is important to consider transient effects in determining whether the use of a porous fin is beneficial at all, and, if so, what is the optimal fin porosity to use. This work contributes towards porous fin theory, and offers practical design guidelines for improving and optimizing the transient performance of porous fins.

Percolation characteristics of pore fluid during hydrate depressurization dissociation from multi-phase multi-field coupling analysis

The recovery of gas from hydrate-bearing reservoirs is essentially controlled by pore fluid flow. Four numerical models with different multi-phase multi-field were established in this work based on the thermo-hydro-chemical model, considering ice phase, fluidized sand phase, depositing sand phase, and ice, fluidized sand and depositing sand phases, respectively. These above models were used to simulate the dissociation of hydrate-bearing cores by depressurization and to investigate the effects of freezing and melting behavior, sand production behavior, and their combined behavior on pore fluid migration. By comparing the simulations with and without the ice phase, it can be found that the permeability decreases sharply due to ice generation resulting in a decrease of 89.16% in pore-water velocity and of 99.95% in pore-gas velocity. This indicates an inhibition of pore fluid migration by freezing behavior. Meanwhile, it can be found that the ice melting behavior can temporarily promote pore-water migration but has no obvious promotion for pore-gas migration. It is difficult for the pore fluid to percolate in the regions prone to ice generation during hydrate dissociation. In addition, the permeability at 300 min with sand detachment is 16% higher than that without sand detachment. But at the same time, the pore water velocity is 28.44% smaller since sand detachment behavior does not directly power pore fluid migration. By comparing the simulations with and without the combined behavior, it can be concluded that the freezing behavior and the sand production behavior can jointly weaken the pore fluid mobility. Significantly, the former has a stronger negative effect on the pore fluid mobility than the latter during the depressurization dissociation of the hydrate-bearing sediment.

Eclogitisation of dry and impermeable granulite by fluid flow with reaction-induced porosity: Insights from hydro-chemical modelling

Eclogitisation is a major metamorphic process of continental subduction zones, where transformation of dry lower crustal rocks into eclogites seems to correlate with seismogenic events. Eclogitisation can occur at high pressure during hydration of granulite, but the physical processes controlling the hydration of dry, impermeable granulite remain poorly understood. Here, we present a new fully coupled hydro-chemical model of a non-deforming porous rock which undergoes metamorphic reactions in response to fluid pressure variations. Conservation equations for total and solid mass are solved, and fluid and solid densities are calculated with look-up tables computed from models relying on equilibrium thermodynamics. Our model shows that a fluid pressure pulse generates a pressure gradient that causes densification when the pressure required for eclogitisation is reached. The reaction generates porosity and subsequent porous fluid flow into the initially non-porous impermeable granulite. This process lasts as long as the pressure pulse is maintained, but high pressure within eclogite can persist for a longer time. The hydration front propagates tens of centimetres into the granulite in the order of weeks to months. We show that propagation of a hydration-reaction front is effectively a diffusive process, with diffusivity in the order of 10−9▪ for eclogitisation as in Holsnøy, Norway. Reactive hydration of impermeable granulite is possible because its solid density is smaller than that of eclogite. We discuss the application of our model for eclogitisation and also for other reactions for which hydration of impermeable rock is possible.

Simulating dual solutions of coupled pore-fluid flow and chemical dissolution problems in fluid-saturated heterogeneous porous media

PurposeThe objective of this paper is to establish a solution strategy for obtaining dual solutions, namely trivial (conventional) and nontrivial (unconventional) solutions, of coupled pore-fluid flow and chemical dissolution problems in heterogeneous porous media.Design/methodology/approachThrough applying a perturbation to the pore-fluid velocity, original governing partial differential equations of a coupled pore-fluid flow and chemical dissolution problem in heterogeneous porous media are transformed into perturbed ones, which are then solved by using the semi-analytical finite element method. Through switching off and on the applied perturbation terms in the resulting perturbed governing partial differential equations, both the trivial and nontrivial solutions can be obtained for the original governing partial differential equations of the coupled pore-fluid flow and chemical dissolution problem in fluid-saturated heterogeneous porous media.FindingsWhen a coupled pore-fluid flow and chemical dissolution system is in a stable state, the trivial and nontrivial solutions of the system are identical. However, if a coupled pore-fluid flow and chemical dissolution system is in an unstable state, then the trivial and nontrivial solutions of the system are totally different. This recognition can be equally used to judge whether a coupled pore-fluid flow and chemical dissolution system involving heterogeneous porous media is in a stable state or in an unstable state. The proposed solution strategy can produce dual solutions for simulating coupled pore-fluid flow and chemical dissolution problems in fluid-saturated heterogeneous porous media.Originality/valueA solution strategy is proposed to obtain the nontrivial solution, which is often overlooked in the computational simulation of coupled pore-fluid flow and chemical dissolution problems in fluid-saturated heterogeneous porous media. The proposed solution strategy provides a useful way for understanding the underlying dynamic mechanisms of the chemical damage effect associated with the stability of structures that are built on soil foundations.

Computational simulation of the ore-forming processes associated with the Sanshandao-Haiyu gold belt, Jiaodong Peninsula, eastern China: implications for the duration of ore formation

The Sanshandao-Haiyu gold belt, Jiaodong Peninsula, Eastern China accounts for more than 1,400 t gold resources, which is always recognized as a coupled result of structural deformation, pore-fluid flow, and hydrothermal alteration-mineralization processes. However, the ore-forming processes associated with this gold belt has not been fully understood by the coupled perspective. In this paper, we use computational modeling to study the spatial distribution of dilation (positive volumetric strain) and the mineralization rate, which can predict the mineralization patterns from a chemical perspective, so as to solve the fully coupled problem during ore-forming processes. The model was loaded on the FLAC3D platform to test four scenarios: 1) Syn-compression in the NW-SE direction; 2) syn-compression in the WNW-ESE direction; 3) syn-compression in the NNW-SSE direction, and 4) syn-extension in the NW-SE direction. The simulation results show that only the syn-compressional scenario can produce wide dilation zones with a distribution pattern similar to the known orebodies. The higher dilation zones with the volumetric strain (>0.1%) and the highest pore-fluid flux are closely associated with the fault geometry, particularly for the gentle segments near the steep-flat transition areas. Besides, the dilation zones also occur with very high absolute values of pore-fluid pressure gradient and temperature gradient, indicating significantly perturbed physical-chemical conditions. The receiver operating characteristic (ROC) curves of the mineralization rate show that the area under the curve (AUC = 0.862) of the NW-SE syn-compression model is the highest among these four scenarios, indicating a major paleo compression stress direction of NW-SE during ore-forming period. Furthermore, based on the mineralization rate, we estimated that the mineralization duration of the Sanshandao-Haiyu gold belt would be less than 100,000 years. These simulation results can not only enhance our understanding of the ore-forming processes in the Sanshandao-Haiyu gold belt and Jiaodong Peninsula but also demonstrate that these can be used directly or indirectly for deep mineral exploration.

Mantle wedge olivine modifies slab-derived fluids: Implications for fluid transport from slab to arc magma source

Abstract Boron is an effective tracer of fluid processes in subduction zones. High B and δ11B in arc magmas require efficient B transfer from the slab to magma source regions. The Higashi-akaishi metaperidotite body in the Sanbagawa high-pressure belt, Japan, is composed of locally serpentinized mantle wedge peridotites exhumed in a subduction channel. Cores of coarse-grained primary mantle olivine have 1–4 µg/g B, enriched compared to typical mantle olivine, and δ11B of −10‰ to −1‰, consistent with incorporation of fluids from dehydrating slab at ~90–120 km depth. Rims of primary mantle olivine as well as olivine neoblasts have even higher B (5–20 µg/g) and higher δ11B (−8‰ to +2‰) due to incorporating slab fluids at depths of ~70–100 km. Antigorite, formed below 650 °C, shows comparable δ11B and B contents as olivine rims. The data show that olivine is capable of scavenging significant amounts of B from fluids by diffusion and recrystallization at sub-arc pressures and temperatures. Considering the large amount of olivine in the mantle wedge, transport of slab-derived material to magma sources requires processes with minimal interaction with mantle peridotite, such as intensely channelized fluid flow or ascent of mélange diapirs, and limited porous fluid flow.

Three-dimensional characterisation of pore networks and fluid flow in segregated heaps in the presence of crushed ore and agglomerates

Due to the differences in ore feeds and stacking procedures, segregated pore networks are commonly observed in industrial heap leaching operations, which strongly affect the pore-scale fluid flow and the resulting metal leaching efficiency. Three segregated models, namely, the agglomeration model or AM with intra-particle pores, the crushed ore model or COM with inter-particle pores and the mixed segregated model or MSM with both intra- and inter-particle pores, are defined in this work. The segregated pore network in the MSM consists of agglomerates and crushed particles. The models were obtained by performing micro-computed tomography scanning experiments in packed beds followed by image processing algorithms. Several fluid flow-related parameters were quantified to understand the effects of segregated pore networks on fluid flow in heap leaching. The isolated and connected pores co-exist in porous ore heaps, and the latter determines heap hydrodynamics. The number of connected pores in the AM is higher than in the COM. However, the connected pores with too small pore throats are very slow in fluid transfer by capillarity, resulting in stagnant regions in ore beds. A smaller tortuosity value was also observed in the COM, resulting in fast-flowing preferential fluid flow paths. These are unfavourable to yield uniform fluid flow distributions in industrial heaps. The results of this work suggest the prerequisites for improving fluid flow distribution in heaps, including well-organised heap construction procedures, controlling the particle size distribution and large-scale studies coupled with non-invasive imaging and flow simulations.

A numerical exploration of hyporheic zone solute transport behavior estimated from electrical resistivity inversions

An increasing number of studies have combined saline tracer injections with time-lapse electrical resistivity (ER) surveys to explore solute exchange within the hyporheic zone. The reliability and resolution of ER surveys of the hyporheic zone are rarely discussed. Here, we use a numerical modeling approach to assess how ER imaging resolves changes in saline tracer concentration within the hyporheic zone given different synthetic scenarios. We create a 3-D synthetic stream and surrounding hyporheic zone with an ER electrode transect and solve the coupled equations for porous fluid flow and solute transport. Then, we solve for the 3-D conduction of current between electrodes to create synthetic time-lapse ER surveys and invert the simulated resistances to obtain 2-D bulk electrical conductivity (σb) images perpendicular to the stream, which we compare with the known synthetic σb fields. The σb fields in the inversion generally capture the shape of the simulated σb fields, but with smoothing and artifacts as a function of the inversion process. Consequently, the calculated cross-sectional area of tracer plume is inaccurate. At inversion pixels beneath the stream, the accuracy of the inverted σb breakthrough curves when compared to the synthetic “truth” varies with stream size, pixel depth, and to a lesser extent injection time. The tails of these pixel breakthrough curves beneath the stream are consistently underestimated compared to the synthetic “truth,” i.e., σb in the inversions appear to return to background faster by one to six hours. The time series of average apparent bulk electrical conductivity requires no inversion and captures lingering saline tracer better than bulk EC breakthrough curves at individual pixels in the inversions.

Microscopic occurrence and movability mechanism of pore water in deep shale gas reservoirs: A typical case study of the Wufeng-Longmaxi Formation, Luzhou block, Sichuan Basin

Water in pore system (i.e., pore water) is of great significance for shale gas exploration and exploitation. However, the microscopic occurrence and movability mechanism of pore water is still unclear. In this study, the pore water of deep shale gas reservoirs of the Wufeng-Longmaxi Formation in the Luzhou block was quantitatively evaluated by a new theoretical approach. The microscopic distribution and movability of pore water were investigated by combining NMR technology and theoretical models, and then the influencing factors were discussed. The results show that the signal amplitude of dry shale originates from clay minerals and organic matter. For clay minerals, illite has the greatest influence on the signal amplitude, followed by illite-smectite mixed layer and chlorite. Pore water mainly exists in an adsorbed phase, with an average adsorbed ratio of 69.26%, and an average adsorption thickness (H) of 0.5392 nm. Adsorbed and free water coexist in pores of 3–100 nm, and have equivalent content and saturation in pores of 10 nm and 6–7 nm, respectively. The specific surface area and pore volume control the occurrence of adsorbed and free water respectively. With the increase in average pore size, the water-holding capacity of pore system weakens. Adsorbed water mainly occurs in pores related to organic matter and quartz, while free water tends to occur in clay minerals pores. The adsorption affinity of spherical pores is the strongest, followed by cylindrical and slit pores. The effective pore size threshold available for fluid flow in spherical, cylindrical, and slit pores is 6H, 4H, and 2H respectively. With increasing centrifugal pressure difference, the water saturation decreases, the adsorbed ratio and mobility increase. Shale with higher pore volume has stronger mobile potential and mobility. Clay minerals are essential for pore water movability, while organic matter and brittle minerals inhibit pore water movability. This study offers a novel approach for quantitatively characterize the occurrence and transport of pore water and potentially has wide application prospects.

A spectral element time domain (SETD) method based on poroelastic linear slip conditions for 3D wave propagation in fractured porous media

In this study, we present a spectral element time domain (SETD) method for the simulation of wave propagation in fractured porous media. To avoid volumetric meshing of the extremely thin-layer fractures, we incorporate the fractures into spectral element model by treating them as geometrical interfaces, where the interaction between solid deformation and pore fluid flow is described by the poroelastic linear-slip conditions across the fractures. For different kinds of fractures (i.e. permeable, open, and impermeable), the explicit time schemes are presented for solving the stress tensor and fluid pressure over the fracture surfaces, which are subsequently implemented into the SETD framework to involve both elastic scattering and wave-induced fluid flow (WIFF) effects. Through various numerical examples, the proposed algorithm is shown to be able to accurately and effectively simulate and characterize the wave propagation in 3D porous media containing discrete and intersecting fractures with different permeabilities.

Control on carbonate reservoir properties along a shallowing-upward sequence: The middle oxfordian jura inner platform predictive model

The study of the Bonnevaux section from the Middle Oxfordian Jura inner platform (France) highlights that a shallowing-upward sequence showing a large variability of original microfacies linked to various depositional environments (open sea to lagoon) can be exclusively composed of microporous limestones. A spatial evolution of reservoir qualities and transport properties of these microporous limestones is recognized at the platform scale: a correlated increase in total porosity (from 2.8 to 21.3%) and permeability (from 0.0001 to 16 mD) and a decrease in trapped porosity (from 100 to ∼50%) is observed from the upper offshore to the back-shoal lagoon environments. The increase in permeability observed at the platform scale is correlated with an evolution of the unimodal distribution of pore access radii and an increase in threshold radius (from 0.033 to 0.570 μm). It results from a diachronism in the control of meteoric pore-fluid flows by the microporosity (vs macroporosity) during the burial diagenesis. A later control of meteoric pore-fluid flows by the microporosity related to differences in cementation (1) reduces the fluid-rock interactions in the micrite areas and consequently promotes open fabrics with larger pore access radii and (2) allows to preserve larger pore access radii in the intercrystalline pore network of cements. In the case of reservoir qualities, this later control (1) promotes a higher total porosity in the micrite areas in relation with more open fabrics and (2) allows to preserve larger pore access inducing a lower trapped porosity. The macroporosity can played a key role when the blocky cementation of the pore space is partial. This study also reveals that a submarine lithification can prevent the petrophysical impact of a pore-fluid meteoric input during the burial diagenesis.

Reservoir characteristics and pore fluid evaluation of Shan 23 Submember transitional shale, eastern Ordos Basin, China: Insights from NMR experiments

The Lower Permian Shanxi Formation in the Eastern Ordos Basin is a set of transitional shale, and it is also a key target for shale gas exploration in China. Three sets of organic-rich transitional shale intervals (Lower shale, Middle shale and Upper shale) developed in Shan 23 Submember of Shanxi Formation. Based on TOC test, X-diffraction, porosity, in-situ gas content experiment and NMR experiments with gradient centrifugation and drying temperature, the reservoir characteristics and pore fluid distribution of the three sets of organic-rich transitional shale are studied. The results show that: 1) The Middle and Lower shales have higher TOC content, brittleness index and gas content, reflecting better reservoir quality, while the Upper shales have lower gas content and fracturing ability. The total gas content of shale in the Middle and Lower shales is high, and the lost gas and desorbed gas account for 80% of the total gas content. 2) The Middle shale has the highest movable water content (32.58%), while the Lower shale has the highest capillary bound water content (57.52%). In general, the capillary bound water content of marine-continental transitional shale in the Shan 23 Submember of the study area is high, ranging from 39.96% to 57.52%. 3) Based on pore fluid flow capacity, shale pores are divided into movable pores, bound pores and immovable pores. The Middle shale and the Lower shale have high movable pores, with the porosity ratio up to 27%, and the lower limit of exploitable pore size is 10 nm. The movable pore content of upper shale is 25%, and the lower limit of pore size is 12.6 nm. It is suggested that the Lower and Middle shales have more development potential under the associated development technology.

UNRAVELING THE COMPLEX DYNAMICS OF FLUID FLOW IN POROUS MEDIA: EFFECTS OF VISCOSITY, POROSITY, AND INERTIA ON THE MOTION OF FLUIDS

This study investigates novel solitary wave solutions of the Gilson–Pickering ([Formula: see text]) equation, which is a model that describes the motion of a fluid in a porous medium. An analytical scheme is applied to construct these solutions, utilizing the extended Khater method in conjunction with the homogenous balance technique. The derived expressions for the solitary wave solutions are exact and are presented in terms of hyperbolic functions. The [Formula: see text] equation is valuable for a wide range of applications, including oil and gas reservoir engineering, groundwater flow, and flow in biological tissues. Additionally, this model is employed to describe the behavior of waves in various physical systems such as fluids and plasmas. Specifically, it models the propagation of dispersive waves in a media that exhibits both dispersion and dissipation. To ensure the accuracy of the constructed solutions, a numerical scheme is employed. The properties of the solitary wave solutions are analyzed, and their physical implications are explored. The results of this investigation reveal a rich variety of solitary wave solutions that exhibit interesting behaviors, including oscillatory and non-oscillatory behavior, which are elucidated through various types of distinct graphs. Consequently, this study provides significant insights into the behavior of fluid flow in porous media and its applications in various fields, including oil and gas reservoir engineering and groundwater flow modeling. The analytical and numerical methods employed in this investigation demonstrate their potential for studying nonlinear evolution equations and their applications in the physical sciences.

PREFACE: COMPUTATIONAL HEAT AND FLUID FLOW IN POROUS MEDIA (PART 1)

This is the Preface of the Special Issue dedicated to the 8th Asian Symposium on Computational Heat Transfer and Fluid Flow (ASCHT 2021).

Hydrodynamic Hysteresis and Solute Transport in Agglomerated Heaps under Irrigation, Stacking, and Bioleaching Controlling

Hydrodynamic hysteresis exists widely in agglomerated heaps with well-developed intra-pores, and it directly affects solute transports and bioleaching reaction. In this paper, the dynamic liquid retention behavior under different heap porosity and irrigation condition is quantified via a novel real-time, in-situ liquid retention characterizing system (RILRCS), and the potential effects of initial liquid retention on solute transport and leaching reaction are carefully discussed. The results show that the immobile liquid is dominant in agglomerated heaps. The ratio of immobile and mobile liquid (η) dynamically changes due to mineral dissolution and new flow path appearances. The η normally increases and mobile liquid occupies a higher proportion due to acidic leaching reactions, especially at a smaller Rg (10.32 mm) and a larger u (0.10 mm/s). The dynamic liquid retention is more sensitive to the diameter of packed feeds (Rg) and superficial flow rate (u) instead of leaching reactions. This might be because the damage of leaching reaction on minerals pores/voids is limited and cannot extensively change the potential pore channels or fluid flow paths. Based on pulse tracing and conductivity tests, we reveal that the solute resides longer under a slower u and smaller packed Rg condition, which corresponds well with desirable copper leaching efficiency. Specifically, the liquid hysteresis behavior is more obvious at a lower u (0.01 mm/s) and smaller Rg (10.32 mm). This paper gives a good reference to ascertain the liquid retention and hydrodynamic hysteresis and promote mineral leaching performance.

Gas Migration Episodes Observed During Peridotite Alteration in the Samail Ophiolite, Oman.

Serpentinization and carbonation of mantle rocks (peridotite alteration) are fundamentally important processes for a spectrum of geoscience topics, including arc volcanism, earthquake processes, chemosynthetic biological communities, and carbon sequestration. Data from a hydrophone array deployed in the Multi-Borehole Observatory (MBO) of the Oman Drilling Project demonstrates that free gas generated by peridotite alteration and/or microbial activity migrates through the formation in discrete bursts of activity. We detected several, minutes-long, swarms of gas discharge into Hole BA1B of the MBO over the course of a 9month observation interval. The episodic nature of the migration events indicates that free gas accumulates in the permeable flow network, is pressurized, and discharges rapidly into the borehole when a critical pressure, likely associated with a capillary barrier at a flow constriction, is reached. Our observations reveal a dynamic mode of fluid migration during serpentinization, and highlight the important role that free gas can play in modulating pore pressure, fluid flow, and alteration kinetics during peridotite weathering.

Imbibition Characteristic of Fractured Tight Sandstone Reservoir

“Fracture network stimulation + imbibition replacement” is a new attempt to effectively develop tight sandstone reservoirs, and the fractures provide conditions for fluid imbibition replacement. On the basis of nuclear magnetic resonance and pseudo-color processing technology, combined with the imbibition experiments, this paper studies the imbibition process of fractured tight sandstone reservoirs, clarifies the effect of each level of pore-throat on imbibition, and realizes the visualization of the imbibition process. The results show that, in fractured tight sandstone reservoirs, the fluid displacement occurs in fractures first, followed by pore-throat. Most of the imbibition recovery is contributed by the macropore, the contribution of the mesopore to imbibition recovery is very weak, and the contributions of the micropore and the pinhole are even less. In the process of imbibition, capillary force and gravitational force are key parameters controlling fluid flow in pores and fractures. The replacement of fluid normally takes place in the early stage of imbibition, especially on the first day of imbibition, then the imbibition rate gradually decreases and finally tends to be stable.

Investigating porosity structure effects on hydrothermal mineralization patterns within permeable horizontal layers of fluid-saturated rocks: Semi-analytical approach through generic models

The porosity structures of a permeable rock can have remarkable effects on pore-fluid flow within the rock. According to the modern mineralization theory, the mineralization pattern in a hydrothermal ore-forming system is strongly dependent on the pore-fluid flow velocity, so that different porosity structures of a permeable rock can affect significantly hydrothermal mineralization patterns within the permeable layers consisting of fluid-saturated porous rocks. This paper presents a semi-analytical approach, in which pore-fluid velocity is directly used as fundamental primary variables in the governing equations of the problem and the property matrices of finite elements are analytically evaluated in a purely mathematical manner, to ensure the high accuracy of the obtained pore-fluid velocity, which is involved in controlling mineralization patterns in hydrothermal ore-forming systems. After the proposed semi-analytical approach is verified through comparing the numerical solution with the analytical solution for a benchmark problem, it has been used to investigate how different porosity structures can affect the hydrothermal mineralization patterns within permeable horizontal layers consisting of fluid-saturated porous rocks through using a generic model, which can be viewed as the representation of a generalized and simplified geological model. Main outcomes of this study have demonstrated that: (1) the proposed semi-analytical approach can produce highly-accurate numerical solutions for solving coupled pore-fluid flow and heat transfer problems in fluid-saturated porous rocks with different porosity structures; (2) the different porosity structure within a permeable horizontal layer consisting of fluid-saturated porous rocks can have a significant effect on the hydrothermal mineralization pattern of the permeable horizontal layer; (3) layered pore-fluid vertical velocity focusing may take place within a permeable horizontal layer involving a heterogeneous porosity structure.

Deviation from Darcy Law in Porous Media Due to Reverse Osmosis: Pore-Scale Approach

Shale and tight hydrocarbons are vital to global energy dynamics. The fluid flow in sub-micron pores of tight oil reservoirs varies from bulk fluid flow. The Darcy law is widely accepted to model creeping flow in petroleum reservoirs. However, traditional reservoir modeling approaches fail to account for the sub-micron mechanisms that govern fluid flow. The accuracy of tight oil reservoir simulators has been improved by incorporating the influence of sub-micron effects. However, there are still factors that affect sub-micron fluid mobility that need investigation. The influence of a chemical potential gradient on fluid flow in sub-micron pores was modeled by solving Darcy and the transport and diluted species equations. The findings indicate that when a chemical potential gradient acts in the opposite direction of a hydraulic pressure gradient (reverse osmosis), there exists a limiting pressure threshold below which a non-linear flow pattern deviating from the Darcy equation is observed. Furthermore, the simulation based on tight reservoir pore parameters shows that when the effect of a chemical potential gradient is added, the resultant flux is 8–49% less. Hence, including the effect of the chemical potential gradient will improve the accuracy of sub-micron pressure dynamics and flow velocity.