Magnitude Of Permeability Research Articles

Quantitative estimation of permeability enhancement, production and depletion from microseismic data

It is a known fact that cost efficiency is the number one priority across the industry, perhaps even more so in today’s price environment. Operators are seeking technologies to improve profitability for unconventional field development. Getting a reliable estimate of production within days of completing an unconventional well is every operator’s dream. Armed with this knowledge operators would be able to evaluate the effectiveness of treatment and well spacing strategies without having to wait for months of actual production, allowing for them to arrive at an optimum development plan in a more timely fashion. In this article we demonstrate that microseismic monitoring, taken as an insitu, real time field observation of the completion of a well that integrates all the effects of rock properties, tectonic stresses and treatment parameters enables an estimate of well productivity within reasonable limits. In this method, microseismic data is used to describe a deterministic discrete fracture network model, differentiating between propped and un-propped fractures and further defining a fracture intensity in a given rock volume. This fracture intensity is translated into a measure of permeability enhancement, both magnitude and distribution, achieved through the process of hydraulic fracturing. Through reservoir simulation using this more complete model it is possible to estimate each well’s current and future productivity and the reservoir pressure depletion as a function of time. Current practices rely on unrealistic planar fracture models leading to to inaccurate predictions of unconventional wells’ production and drainage patterns. The approach presented here explicitly honours the microseismic measurements and provides a realistic representation of the induced fracture geometry and thus improved production and drainage estimates. These early production predictions are available within a few days after a well’s treatment, eliminating the typical 6-to-12-month waiting time for production results. The ability to create a model that is consistent with actual production, as shown in the case histories presented here, suggests that uncertainty is sufficiently constrained through the workflow outlined in this article.

Permeability and Flow Field Evolution Due to Dissolution of Calcite in a 3-D Porous Rock Under Geothermal Gradient and Through-Flow

Flow of undersaturated water in limestone aquifer can cause continuous permeability growth due to dissolution. We have simulated the evolution of permeability field of a 3-D porous limestone aquifer subjected to geothermal temperature gradient and vertical through-flow. The upward flow through porous limestone results in dissolution since calcite is a retrograde soluble mineral. In addition to permeability growth by promoting more dissolution, through-flow also inhibits Rayleigh Benard convection. To understand the temporal evolution of permeability and flow fields, we have performed several simulations with various combinations of initial permeability and through-flow magnitude. Since our computational domain is different in size and boundary conditions from past studies related to buoyant convection in porous medium, we have carried out simulations without reactive alteration to distinguish the hydrothermal systems as stable or unstable. The permeability growth is insignificant in the central part of the reservoir as the temperature gradient vanishes due to forced convection. Permeability growth is more near the edges, where temperature gradients are significant due to conductive heat transfer from the boundaries. For small magnitudes of through-flow, convection rolls are formed near the corners. However, the growth is very localized and rolls never form when magnitude of through-flow is large.

Development of a boundary magnetic charge method for computing magnetic fields in a system containing saturated magnetic materials

In previous research, we developed a three-dimensional (3D) boundary magnetic charge method (BMCM) for high-accuracy field calculations in a static magnetic field, even when there exist great differences between the magnitudes of permeability between neighboring magnetic materials. This method, however, cannot be applied to a system that contains saturated magnetic materials. In the present study, therefore, we have developed a novel method that addresses this issue. According to this new method, we divide the region containing the magnetic material into small-volume elements and divide the boundaries between neighboring small-volume elements into small-surface elements, assigning each element an appropriate initial value of permeability. The magnetic field inside and outside of the magnetic material is calculated using this permeability. The value of the permeability of each element is iteratively updated using μ–H data. The updated value of the permeability after the i-th iteration, μi, is compared with that of the previous value, μi−1. If the difference between the two values is within a preset range, the iteration process is judged to have converged and the value of μi is regarded as the final converged value of the permeability. The magnetic field at an arbitrary point in space and/or inside the body of the magnetic material is calculated from the converged permeability of each element. As a result, we have succeeded in developing a novel BMCM for the calculation of a static magnetic field with high accuracy in a system containing saturated magnetic materials.

Gas-Barrier Hybrid Coatings by the Assembly of Novel Poly(vinyl alcohol) and Reduced Graphene Oxide Layers through Cross-Linking with Zirconium Adducts.

Gas-barrier materials obtained by coating poly(ethylene terephthalate) (PET) substrates have already been studied in the recent literature. However, because of the benefits of using cheaper, biodegradable, and nonpolar polymers, multilayered hybrid coatings consisting of alternate layers of reduced graphene oxide (rGO) nanosheets and a novel high amorphous vinyl alcohol (HAVOH) with zirconium (Zr) adducts as binders were successfully fabricated through a layer-by-layer (LbL) assembly approach. Atomic force microscopy analysis showed that rGO nanoplatelets were uniformly dispersed over the HAVOH polymer substrate. Scanning and transmission electron microscopies revealed that multilayer (HAVOH/Zr/rGO)n hybrid coatings exhibited a brick-wall structure with HAVOH and rGO as buildings blocks. It has been shown that 40 layers of HAVOH/Zr/rGO ultrathin films deposited on PET substrates lead to a decrease of 1 order of magnitude of oxygen permeability with respect to the pristine PET substrate. This is attributed to the effect of zirconium polymeric adducts, which enhance the assembling efficiency of rGO and compact the layers, as confirmed by NMR characterization, resulting in a significant increment of the oxygen-transport pathways. Because of their high barrier properties and high flexibility, these films are promising candidates in a variety of applications such as packaging, selective gas films, and protection of flexible electronics.

Quantifying flow in variably wet microporous carbonates using object-based geological modeling and both lattice-Boltzmann and pore-network fluid flow simulations

ABSTRACT Micropores can constitute up to 100% of the total porosity within carbonate-hosted hydrocarbon reservoirs, usually existing within micritic fabrics. Here, three-dimensional computational representations of end-point micritic fabrics are produced using a flexible, object-based algorithm to further our understanding of the contribution that micropores make to flow. By methodically altering model parameters, we explore the state space of microporous carbonates, quantifying single and multiphase flow using lattice-Boltzmann and network models. In purely micritic fabrics, average pore radius (ranging from 0.26 to 0.44 μm) was found to have a positive correlation with single-phase permeability (1.7 to 2.7 md, respectively). Similarly, increasing average pore size resulted in decreasing residual oil saturation under both water-wet and 50% fractionally oil-wet states. Permeability was found to increase by an order of magnitude (from 0.6 to 7.5 md) within fabrics of varying total matrix porosity (from 18% to 35%) because of increasing pore size (0.37 to 0.56 μm, respectively), but minimal effect on multiphase flow was observed. Increased pore size due to micrite rounding notably increases permeability in comparison with original rhombic fabrics with the same porosity, but multiphase flow properties are unaffected. Finally, when moldic mesopores are added to a micritic matrix, they impact flow when directly connected. Otherwise, micropores control single-phase permeability magnitude. Importantly, recovery is dependent on both wetting scenario and pore-network homogeneity: under water-wet imbibition, increasing proportions of microporosity yield lower residual oil saturations. Together, these results quantify the importance of micropores in contributing to, or controlling, overall flow and sweep characteristics in such fabrics.

Permeability and porosity relationships of edifice-forming andesites: A combined field and laboratory study

Permeability of the edifice is one of the key parameters governing eruptive style, magnitude, and frequency of active stratovolcanoes. This study presents a suite of density and permeability field measurements from 572 samples of edifice-forming andesite from Volcán de Colima, Mexico. The breadth of the density distribution of the rocks collected (corresponding to porosity values from 2.5 to 73%), and the increasing bimodality towards the vent, are indicative of the explosive–effusive behaviour that characterises active composite volcanoes. Measured field permeabilities are in the range of 10−16 to 10−11m2, encompassing values significantly greater than those generally assumed for fluid transport in magma, and thus emphasising the importance of host-rock permeability in facilitating outgassing of volatiles and, in turn, governing eruption dynamics. For any given porosity we observe up to four orders of magnitude in permeability. This range of scatter was found to be unaffected for the most part by meso-scale textural differences, oxidation, or alteration. A complementary laboratory and microstructural study reveals that the andesites collected are microstructurally diverse and complex. For example, anomalously high surface areas are measured in samples with significant inter-microlite microporosity. However, these micropores do not serve to significantly increase porosity or pore connectivity, resulting in under-estimation of fluid pathway tortuosities using the Kozeny–Carman relation. Indeed, calculated tortuosity values highlight that the Kozeny–Carman relation poorly predicts connectivity and does not therefore capture the microstructural complexity of the studied volcanic rocks. A changepoint porosity value, where the permeability–porosity power-law exponent changes, is identified at around 14% porosity using a Bayesian Information Criterion analysis. Here we assume a change in the dominant microstructural element controlling fluid flow, i.e. from crack- to pore-dominated flowpath geometries. Microstructural analysis indicates that fluid flow in the low porosity andesites (<14%) of this study is governed by tortuous microcracks, while the more porous samples (>14%) display relatively large, interconnected pores. While the supposition that the power-law exponent changes at a distinct changepoint is a simplification, we find that it well describes permeability data from Volcán de Colima (from this study and those of previous authors). The exceptional heterogeneity of edifice-forming rocks is thought to have significant implications for lateral outgassing, eruption dynamics, as well as influencing regional edifice strength and stability.

Genetic unit averages of pseudo-normalized pore throat radius for improved permeability predictions (Niger Delta as case study)

Recent studies in permeability modeling demonstrate a relationship between measured permeability and normalized pore throat radius $$ \overline{{R_{\text{tot}} }} $$ that can be used as a predictor over six (6) orders of magnitude in permeability for the clastic reservoirs using Niger Delta dataset. The practical significance of this relationship indicates that the response variable (core permeability) is strictly valid within the confidence interval: 0.005 ≤ $$ \overline{{R_{\text{tot}} }} $$ (µm) ≤ 10. The proposed model was validated extensively exhibiting an excellent correlation coefficient and statistical significance as depicted by their p and t tests. A major input parameter for the proposed $$ \overline{{R_{\text{tot}} }} $$ permeability model is the pore throat radius at any given pressure step (R pi ). This is an intrinsic component of capillary pressures obtained from mercury injection capillary pressures (MICP) test. The proposed model is hampered due to unavailability of MICP dataset for all wells drilled to generate the R pi parameter. This paper seeks to develop genetic unit averages of pseudo-normalized pore throat radius as input parameter to the $$ \overline{{R_{\text{tot}} }} $$ proposed model for improved permeability modeling. We also present an upscaling from core plug scale to well log scale–pseudo normalized pore throat radius for application in uncored well intervals for various depositional environments within the study area. The statistical significance of the coefficient of the proposed model depicts the sample statistic to be too unlikely to have occurred by chance, with their p values strictly below the α level of 0.05. The proposed model validation indicates an excellent adjusted correlation coefficient and lower errors based on analysis of variance (ANOVA) using approximately 1000 routine core and well log dataset from the four distinct environments of deposition.

Permeability inhomogeneity accounting in terms of efficient development strategy

The main questions concerning flow and permeability anisotropy are: presence of anisotropy (is a reservoir anisotropic or not), orientation and degree of anisotropy. Answers were obtained through the analysis of grain fabric, spatial permeability spread and tracer injection data. The magnitude of permeability was determined to be within a range from 0.5 to 1 and with the azimuth of 48 from the North. Thereafter, the incorporation of new information about field K into the simulation model matched and the comparison of isotropic (the existing model) and anisotropic (the model upgraded with novel information) were performed. This process showed that the simple introduction of obtained anisotropy properties improved the history match, which was interpreted as the proof of anisotropy being present on both the macroscopic and microscopic scale. At the end, general recommendations for the optimal production practice in the anisotropic reservoir were proposed and the potential strategy for further development was suggested. This optimal strategy was created by changing several producing wells into injectors and it resulted in an overall oil production increase and individual well production increase amounting to as much as 20%.

Identification of small-scale low and high permeability layers using single well forced-gradient tracer tests: Fluorescent dye imaging and modelling at the laboratory-scale

Heterogeneity in aquifer permeability, which creates paths of varying mass flux and spatially complex contaminant plumes, can complicate the interpretation of contaminant fate and transport in groundwater. Identifying the location of high mass flux paths is critical for the reliable estimation of solute transport parameters and design of groundwater remediation schemes. Dipole flow tracer tests (DFTTs) and push-pull tests (PPTs) are single well forced-gradient tests which have been used at field-scale to estimate aquifer hydraulic and transport properties. In this study, the potential for PPTs and DFTTs to resolve the location of layered high- and low-permeability layers in granular porous media was investigated with a pseudo 2-D bench-scale aquifer model. Finite element fate and transport modelling was also undertaken to identify appropriate set-ups for in situ tests to determine the type, magnitude, location and extent of such layered permeability contrasts at the field-scale. The characteristics of flow patterns created during experiments were evaluated using fluorescent dye imaging and compared with the breakthrough behaviour of an inorganic conservative tracer. The experimental results show that tracer breakthrough during PPTs is not sensitive to minor permeability contrasts for conditions where there is no hydraulic gradient. In contrast, DFTTs are sensitive to the type and location of permeability contrasts in the host media and could potentially be used to establish the presence and location of high or low mass flux paths. Numerical modelling shows that the tracer peak breakthrough time and concentration in a DFTT is sensitive to the magnitude of the permeability contrast (defined as the permeability of the layer over the permeability of the bulk media) between values of 0.01–20. DFTTs are shown to be more sensitive to deducing variations in the contrast, location and size of aquifer layered permeability contrasts when a shorter central packer is used. However, larger packer sizes are more likely to be practical for field-scale applications, with fewer tests required to characterise a given aquifer section. The sensitivity of DFTTs to identify layered permeability contrasts was not affected by test flow rate.

Ferromagnetic resonance in ϵ-Co magnetic composites

We investigate the electromagnetic properties of assemblies of nanoscale ϵ-cobalt crystals with size range between 5 to 35 nm, embedded in a polystyrene matrix, at microwave (1–12 GHz) frequencies. We investigate the samples by transmission electron microscopy imaging, demonstrating that the particles aggregate and form chains and clusters. By using a broadband coaxial-line method, we extract the magnetic permeability in the frequency range from 1 to 12 GHz, and we study the shift of the ferromagnetic resonance (FMR) with respect to an externally applied magnetic field. We find that the zero-magnetic field ferromagnetic resonant peak shifts towards higher frequencies at finite magnetic fields, and the magnitude of complex permeability is reduced. At fields larger than 2.5 kOe the resonant frequency changes linearly with the applied magnetic field, demonstrating the transition to a state in which the nanoparticles become dynamically decoupled. In this regime, the particles inside clusters can be treated as non-interacting, and the peak position can be predicted from Kittelʼs FMR theory for non-interacting uniaxial spherical particles combined with the Landau–Lifshitz–Gilbert equation. In contrast, at low magnetic fields this magnetic order breaks down and the resonant frequency in zero magnetic field reaches a saturation value reflecting the interparticle interactions as resulting from aggregation. Our results show that the electromagnetic properties of these composite materials can be tuned by external magnetic fields and by changes in the aggregation structure.

Permeability tensor of three‐dimensional fractured porous rock and a comparison to trace map predictions

AbstractThe reduction from three‐ to two‐dimensional analysis of the permeability of a fractured rock mass introduces errors in both the magnitude and direction of principal permeabilities. This error is numerically quantified for porous rock by comparing the equivalent permeability of three‐dimensional fracture networks with the values computed on arbitrarily extracted planar trace maps. A method to compute the full permeability tensor of three‐dimensional discrete fracture and matrix models is described. The method is based on the element‐wise averaging of pressure and flux, obtained from a finite element solution to the Laplace problem, and is validated against analytical expressions for periodic anisotropic porous media. For isotropic networks of power law size‐distributed fractures with length‐correlated aperture, two‐dimensional cut planes are shown to underestimate the magnitude of permeability by up to 3 orders of magnitude near the percolation threshold, approaching an average factor of deviation of 3 with increasing fracture density. At low‐fracture densities, percolation may occur in three dimensions but not in any of the two‐dimensional cut planes. Anisotropy of the equivalent permeability tensor varies accordingly and is more pronounced in two‐dimensional extractions. These results confirm that two‐dimensional analysis cannot be directly used as an approximation of three‐dimensional equivalent permeability. However, an alternative expression of the excluded area relates trace map fracture density to an equivalent three‐dimensional fracture density, yielding comparable minimum and maximum permeability. This formulation can be used to approximate three‐dimensional flow properties in cases where only two‐dimensional analysis is available.

Computational analysis of cartilage implants based on an interpenetrated polymer network for tissue repairing

Interpenetrated polymer networks (IPNs), composed by two independent polymeric networks that spatially interpenetrate, are considered as valuable systems to control permeability and mechanical properties of hydrogels for biomedical applications. Specifically, poly(ethyl acrylate) (PEA)–poly(2-hydroxyethyl acrylate) (PHEA) IPNs have been explored as good hydrogels for mimicking articular cartilage. These lattices are proposed as matrix implants in cartilage damaged areas to avoid the discontinuity in flow uptake preventing its deterioration. The permeability of these implants is a key parameter that influences their success, by affecting oxygen and nutrient transport and removing cellular waste products to healthy cartilage. Experimental try-and-error approaches are mostly used to optimize the composition of such structures. However, computational simulation may offer a more exhaustive tool to test and screen out biomaterials mimicking cartilage, avoiding expensive and time-consuming experimental tests. An accurate and efficient prediction of material's permeability and internal directionality and magnitude of the fluid flow could be highly useful when optimizing biomaterials design processes. Here we present a 3D computational model based on Sussman–Bathe hyperelastic material behaviour. A fluid structure analysis is performed with ADINA software, considering these materials as two phases composites where the solid part is saturated by the fluid. The model is able to simulate the behaviour of three non-biodegradable hydrogel compositions, where percentages of PEA and PHEA are varied. Specifically, the aim of this study is (i) to verify the validity of the Sussman–Bathe material model to simulate the response of the PEA–PHEA biomaterials; (ii) to predict the fluid flux and the permeability of the proposed IPN hydrogels and (iii) to study the material domains where the passage of nutrients and cellular waste products is reduced leading to an inadequate flux distribution in healthy cartilage tissue. The obtained results show how the model predicts the permeability of the PEA–PHEA hydrogels and simulates the internal behaviour of the samples and shows the distribution and quantification of fluid flux.

Thermostat choice significantly influences water flow rates in molecular dynamics studies of carbon nanotubes

Extremely rapid water flow through carbon nanotubes has been observed in both experiment and simulation which has led to the suggestion that this material be used in a number of filtration applications. However, there is significant disparity in the magnitude of water permeability and the degree of flow enhancement compared with conventional porous materials in the literature. Here, we show that one of the causes of the disparity in simulation data is the variety of methods used to control temperature in molecular simulations. Not only can the choice of thermostat alter the flow rate and permeability by as much as five times, but it can determine whether the transport is observed to be frictionless or not. In addition to helping explain the disparate simulation results on transport in nanomaterials, this work provides some guidelines to help designing and interpreting molecular simulations of mass transport.

On self-potential data for estimating permeability in enhanced geothermal systems

We study the use of hypothetical self-potential (SP) data – more specifically streaming-potential data – for the inversion of subsurface permeability distributions, using the enhanced geothermal system at Soultz-sous-Forêts, France, and a synthetic geothermal hard-rock reservoir as examples. Simulations are carried out using the software SHEMAT-Suite. We perform this study based on results obtained via a massive Monte Carlo approach and additionally use the Ensemble Kalman Filter technique for the inversion. In a first step, we perform forward simulations and assume that SP data is measured along the production and injection wells. The SP monitoring data mainly depend on the near-field (150m) permeability around these wells. In this case, the SP signal is in good agreement with the distribution of the hydraulic head. In contrast, Darcy velocity and possible tracer pathways identified by tracer experiments cannot be identified uniquely based on SP data.Alternatively, stochastic inversion is done based on data recorded in deviated wells distributed around the production and injection wells. In this case, principal fluid pathways and permeability magnitudes are reproduced by stochastic inversion of the SP data. The results are comparable to results obtained by tracer experiments. Joint inversion of tracer and SP data yields the best results in terms of small estimation mismatch. Permeability and pathway geometry can be adequately estimated even for an incorrect coupling coefficient as long as it does not differ more than half an order of magnitude from the true value.

Numerical simulation on the influence of gob permeability on distribution of air leakage flow field

In the coal mine industry, permeability is a key factor to air leakage in gob, its value and distribution influence greatly the distribution of air leakage. CFD is applied to simulate the distribution of air leakage in gob at various permeability magnitudes. Gob refers to a porous medium made from loose coal and collapsed stratum mixture. It shows that the quantity of air leakage and distribution of air velocity, three zones of spontaneous combustion vary largely under condition of different magnitude of permeability. The permeability in gob is seen to gradually reduce. It shows the quantity of air leakage is small and air velocity in waste is low, and spontaneous combustion zone is close to the working face. The graph of relation between distance and air leakage rate shows that spontaneous combustion zone in gob will disappear on account of the lack air leakage rate. Therefore, by mean of technological measure such as gob grouting technique, it can reduce the permeability of gob, raise diffusion resistance of airflow, decrease air leakage from working area, and ease the danger of the spontaneous combustion.

Computational Model of Passive Diffusion Across the Retinal Pigment Epithelium

Retinal pigment epithelium (RPE) is an important part of the normal visual function. Located behind the retina, one of its main functions as a part of the blood-retinal barrier is to regulate the transport between the retina and systemic blood circulation. The barrier properties, and changes in them, have a role in certain retinal diseases, such as age-related macular degeneration. Previously, mostly pharmacokinetic compartmental models have been proposed. In this study, for the first time we introduce an accurate physical structure-based model of passive diffusion across the RPE.Our model relates the permeability coefficients of RPE structures to the physicochemical properties of materials forming the RPE. Model is based on a similar corneal diffusion model proposed by Edwards & Prausnitz (2001). Transcellular and paracellular diffusion components are described by separate permeability equations based on the material properties of each pathway and the basic interactions between each pathway and the characteristics of the diffusing molecule. The structure of our tight junction (TJ) model has not been utilized in other structure-based epithelial models of this type, and it takes into account both the pore pathway for small molecules and the leak pathway for large molecules.Our RPE model was able to predict correct magnitude for the permeabilities and its behavior corresponds to experimental results. Further, the permeability magnitude and behavior of the TJ model appear similar to the experimental data from intestine epithelial cell TJs. However, due to the inconsistent experimental data of RPE permeability, rigorous validation cannot be made.RPE barrier models would facilitate novel drug development against retinal diseases. Our model forms a good platform for the future development and refinements as it combines our knowledge of the RPE structure and diffusion.

Plotting and analysis of hodographs for studying the electrophysical parameters of objects using attachable eddy-current transducers

The results of experimental studies during the eddy-current testing of conducting (including ferromagnetic) objects are considered. A data correcting procedure was suggested; it allows one to decrease the requirements for the phase and frequency stability characteristics of the measuring circuit and to relate experimental results to a theoretic model. Initial and corrected hodographs for a number of materials with different electrophysical properties are reported. The magnetic permeability magnitudes of steel 30X13 were calculated for two electromagnetic-field exciting frequencies (15 kHz and 1 MHz).

ENaC-expressing neurons in the sensory circumventricular organs become c-Fos activated following systemic sodium changes

The sensory circumventricular organs (CVOs) are specialized collections of neurons and glia that lie in the midline of the third and fourth ventricles of the brain, lack a blood-brain barrier, and function as chemosensors, sampling both the cerebrospinal fluid and plasma. These structures, which include the organum vasculosum of the lamina terminalis (OVLT), subfornical organ (SFO), and area postrema (AP), are sensitive to changes in sodium concentration but the cellular mechanisms involved remain unknown. Epithelial sodium channel (ENaC)-expressing neurons of the CVOs may be involved in this process. Here we demonstrate with immunohistochemical and in situ hybridization methods that ENaC-expressing neurons are densely concentrated in the sensory CVOs. These neurons become c-Fos activated, a marker for neuronal activity, after various manipulations of peripheral levels of sodium including systemic injections with hypertonic saline, dietary sodium deprivation, and sodium repletion after prolonged sodium deprivation. The increases seen c-Fos activity in the CVOs were correlated with parallel increases in plasma sodium levels. Since ENaCs play a central role in sodium reabsorption in kidney and other epithelia, we present a hypothesis here suggesting that these channels may also serve a related function in the CVOs. ENaCs could be a significant factor in modulating CVO neuronal activity by controlling the magnitude of sodium permeability in neurons. Hence, some of the same circulating hormones controlling ENaC expression in kidney, such as angiotensin II and atrial natriuretic peptide, may coordinate ENaC expression in sensory CVO neurons and could potentially orchestrate sodium appetite, osmoregulation, and vasomotor sympathetic drive.

Geothermal convection in South Atlantic subsalt lacustrine carbonates: Developing diagenesis and reservoir quality predictive concepts with reactive transport models

Prolific hydrocarbon discoveries in the subsalt, commonly known as the “presalt,” section of Brazil and the conjugate African margin have created a business imperative to predict reservoir quality in lacustrine carbonates. Geothermal convection is a style of groundwater flow known to occur in rift settings, which is capable of diagenetic modification of reservoir quality. We simulated variable density groundwater flow coupled with chemical reactions to evaluate the potential for diagenesis driven by convection in subsalt carbonates. Rates of calcite diagenesis are critically controlled by temperature gradient and fluid flux following the principles of retrograde solubility. Simulations predict that convection could operate in rift carbonates prior to salt deposition, but with rates of dissolution in the reservoir interval only on the order of 0.01 vol. %/m.y., which is too low to significantly modify reservoir quality. The exception is around permeable fault zones and/or unconformities where flow is focused and dissolution rates are amplified to 1 to 10 vol. %/m.y. and could locally modify reservoir quality. After salt deposition, simulations also predict convection with a critical function for salt rugosity. The greatest potential for dissolution at rates of 0.1 to 1 vol. %/m.y. occurs where salt welds, overlying permeable carbonates thin to 500 m (1640 ft) or less. With tens of million years residence times feasible, convection under these conditions could locally result in reservoir sweet spots with porosity modification of 1% to 10% and potentially an order of magnitude or more in reservoir permeability. Integrating quantitative model–derived predictive diagenetic concepts with traditional subsurface data sets refines exploration to production scale risking of carbonate reservoir presence and quality.

The influence of load repetition in bone mechanotransduction using poroelastic finite-element models: the impact of permeability

Experimental evidence suggests that interstitial fluid flow is a stimulus for mechanoadaptation in bone. Bone adaptation is sensitive to the frequency of loading and rest insertion between load cycles. We investigated the effects of permeability, frequency and rest insertion on fluid flow in bone using finite-element models to understand how these parameters affect the mechanical stimulus. A simplified 3D poroelastic finite-element model of a beam in bending was developed, in order to simulate the behavior of interstitial fluid flow in the lacunar-canalicular system of mouse cortical bone. Two different load sets were considered: (1) a continuous haversine sinusoid, with frequency ranging from 1 to 30 Hz, and (2) a 10 Hz haversine with rest-insertion times ranging from 0 to 10 s. For both load sets, a range of intrinsic permeability from [Formula: see text] to [Formula: see text] was tested, and fluid flow was determined. Models with permeabilities down to [Formula: see text] follow a dose-response relationship between fluid flow and sinusoidal frequency. Smaller orders of magnitude of permeability proved to be relatively insensitive to frequency. Our results also suggest that there is a minimum time of rest between load cycles that is required to maximize fluid motion, which depends on the order of magnitude of the intrinsic permeability. We show that frequency and rest insertion may be optimized to deliver maximal mechanical stimulus as a function of permeability.