Mobile Fluid Research Articles

Experimental investigation on T2 cutoffs of tight sandstones: Comparisons between outcrop and reservoir cores

T2 cutoff is a key representative parameter of rock pore structure, which can reflect the degree of mobile fluid as a function of variable water saturation controlled by the extent of centrifuging. However, few studies of T2 cutoff have been done on tight sandstones. In this study, residual fluid of samples after a series of centrifuges were scanned by NMR to determine T2 cutoffs (the relaxation time separating mobile from immobile water) and the extent of mobile fluid as a function of variable water saturation controlled by the extent of centrifuging. Results indicate that all reservoir cores exhibit bimodal NMR T2 distributions, while outcrop cores mainly show unimodal NMR T2 distributions. Tight sandstones showlittle or no mobile fluid controlled by pore throats with radii ≥1 μm, including outcrops and reservoir samples. In conclusion, T2 cutoffs of cores with bimodal NMR T2 distributions and the ones with unimodal NMR T2 distributions were obtained,respectively,at 418 psi and 208 psi, while the former cores exhibit larger T2 cutoffs than the later ones. The critical mobile pore radius for outcrop samples exhibiting a unimodal spectral NMR T2 distribution is 100 nm, whereas the critical pore radius of 50 nm is identified for reservoir samples which display a bimodal T2 distribution. T2gm (The geometric means of T2 fluid distribution at 100% saturation) may propagate error when applying the Schlumberger Doll Research (SDR) model to tight sandstones, whereas T2wa (the weighted average NMR T2 values for the mobile fluid distribution) shows promise as a parameter to predict pore connectivity.

Modeling ore generation in a magmatic context

Magmatic ore deposit models are constructed from a set of measurables (e.g., ore grade, fluid composition, structure) from which important parameters (temperature, pressure, chemistry) can be estimated and possible genetic processes can be constrained. Such models include direct, inverse or iterative problems. Direct problems separately consider an Eulerian and a Lagrangian formulation. In the first case, an analytical approach describes the bulk system from an external frame, whereas the Lagrangian approach provides a description from a discrete element attached to the system. Conversely, inverse problems mostly rely on a system of equations or differential equations. Their solution requires a matrix inversion, using statistical criteria to bracket errors. Subsequently, an iterative approach is adopted, commencing with an initial bulk model that is successively refined to fit the observations. The direct problem always results in a unique solution, though the formulation is highly overdetermined. Such unique solution highly depends on the input parameters, and multiple solutions vary with the initial imposed conditions. Conversely, the inverse problem is underdetermined by construction. Accordingly, it provides a set of solutions, generally identified and separated by statistical tests, as exemplified by the least squares approximation. Both methods intrinsically ignore feedback loops. Iterative methods are weak in quantifying the results. Based on the insights gained from this review, we developed a new integrative model for porphyry deposits that relies on the magmatic segregation of metals through a fluid sparging process. A formulation under the direct problem basically considers the enrichment factor for groups of metals (e.g., Cu, Mo, Au). A Lagrangian approach using a lattice Boltzmann model examines metal diffusion from the melt toward an immiscible phase, commonly a salty aqueous fluid. Metals first diffuse in the melt, the motion of which slows down when the mush development reduces the porosity, thus tapping the mobile fluid phase. Gas bubbles turn to tubes. They offer more mobility and allow the progression of the fluid phase, leading to metal advection, followed by metal precipitation. The quantitative results are poorly constrained owing to the large uncertainties on the input parameters but the metal enrichment factor fits observations from crustal abundance to ore grade levels. Nevertheless, the results aid in designing an inverse approach linking metal enrichment to metal partitioning, diffusion and viscous melt motion. From this approach, a simple diagram can be deduced using a logarithmic scale to smooth the parametric uncertainties. The diagram serves to illustrate the link between the above parameters and metal enrichment, also explaining differences in ore grade for different metals-magma pairs.

Characterization of two-phase displacement mechanisms in porous media by capillary and viscous forces estimation using the lattice Boltzmann simulations

This paper proposes a method for characterization of the two-phase displacement mechanisms (viscous fingering, capillary fingering, stable front, and crossover) in porous media. The approach is based on separate estimation of the capillary and viscous forces and subsequent calculation of the ratio between them (designated as W). The value W determines the dominance of capillary force and is essentially the inverse capillary number. The advantage of this approach consists in taking into account the scale of the samples and predicting the flow mechanisms using parameters measured in laboratory conditions. The balance between viscous and capillary forces is controlled by surface tension and fluid viscosities. For flow simulation, the lattice Boltzmann equations and the color-gradient model are applied. The values of W equal to 0.5 and 2, which define the boundary of the crossover zone and separate it from the flow mechanisms, were determined and the proposed method was successfully validated on three two-dimensional samples of porous media with different permeability coefficients. It revealed a directly proportional effect of permeability on W. As a result, the surface tensions, which determine the boundaries of viscous fingering, capillary fingering, stable front, are shifted towards smaller values with increasing permeability. Also, the effect of the permeability and displacement mechanisms on the displacement efficiency before, after and at quasi-steady regime was investigated. The tendency to efficiency decrease with increasing surface tension and decrease in viscosity ratio was revealed for quasi-steady regime. The absence of the mobile wetting fluid after breakthrough is detected for crossover and capillary fingers. No-displacement regime after breakthrough and, consequently, effectiveness drop to minimal values in quasi-steady regime occurs at lower surface tensions with increasing permeability.

THE BRACHISTOCHRONIC MOVEMENT OF A MATERIAL POINT IN THE HORIZONTAL VECTOR FIELD OF A MOBILE FLUID

Background. Since the brachistochronic motion of a material point in a flat vector field of a mobile fluid was not previously considered, the formulated variational problem of searching for extremal trajectories in such a formulation is new and relevant.Objective. The aim of the study is to obtain the algebraic equations of extremal trajectories of motion, along which the material point moves from a given starting point to a given finish point in the shortest possible time.Methods. The solution of the problem was carried out using classical methods of the calculus of variations (to obtain a differential equation for the motion of a material point), as well as using Taylor series (for approximate integration of the resulting differential equation). For a given variant of the boundary conditions, approximate algebraic equations of extremals of the motion of a material point were established in the form of segments of power series. A comparative analysis of the time of movement was carried out both along extreme trajectories and along an alternative shortest path – along a straight line, which connects two given points of start and finish.Results. It is shown that the considered variational problem has two different solutions, which differ only in sign. At the same time, only one solution provides the minimum time for the movement of a material point between the given start and finish points. Studies have also found that the extremal trajectory of the brachistochronic movement of a point is not straight and has an oscillatory character.Conclusions. The proposed approach allows plotting in advance such a logistical route of a material point (motorboat) in a flat vector field of a mobile fluid between the given start and finish points, which ensures the minimum travel time between them. In this case, the extremal trajectory will not necessarily be the shortest line that connects the start and finish points.

Analytical modeling nanoparticles‐fines reactive transport in porous media saturated with mobile immiscible fluids

AbstractThis work develops a new analytical solution for the reactive flow of aqueous nanofluid into porous media originally saturated with a mobile aqueous suspension containing fine particles and a mobile oleic‐phase. The enhancement of nanoparticles on fines attachment onto rock grains is modeled through the increase of the maximum retention capacity of rock grains. Implementing the splitting technique and stream‐function converts the original 3 × 3 system of partial‐differential equations into 2 × 2 sub‐system of nanoparticles‐fines reactive transport, and a lifting equation where only phase saturation appears. Then, method of characteristics is applied to achieve the analytical solution, the validity of which is tested by numerical simulation. The historical profiles of suspended/adsorbed nanoparticles, suspended/attached fines, and phase saturation along 1‐D porous medium are reproduced. The impact of injected nanoparticles concentration and carrier fluid saturation on fines attachment is investigated. This work provides a simple‐yet‐rigorous approach to evaluate nanofluid injection to control fines migration in multiphase flow.

Independent Pressure and Flow Rate Control Enabled by Hydraulic Free Piston Engine

Fluid power consumes a significant portion of energy annually with relatively low efficiency, especially for mobile applications. This is mainly due to the current architecture where an internal combustion engine (ICE) driven hydraulic pump is used to supply fluid to various driving and working circuits. This architecture as well as the response time limitation of the ICE and the hydraulic pump cause significant fluid throttling loss and low-efficiency engine operation at part load conditions. As a novel alternative, the hydraulic free piston engine (HFPE) eliminates the mechanical crankshaft and integrates the ICE and the hydraulic pump into one unit. Due to its ultimate freedom on the piston motion and reduced inertia, the HFPE has the potential to produce variable fluid power in an efficient manner with fast response time. In this paper, such potential is investigated. The working principle of a prototype HFPE is described and a comprehensive HFPE model is developed. A novel control method, namely the independent pressure and flow rate control (IPFC), is proposed to regulate the HFPE's output flow rate at any given load pressure and realize throttleless fluid control. The effectiveness of the method is demonstrated through simulations, which show the capability of the control method in providing different output flow rates at variable load pressures within tens of milliseconds. Additionally, a detailed analysis of the HFPE efficiency, in terms of thermal efficiency of the engine and mechanical efficiency of the pump, has been conducted under different working conditions. The results show that with the IPFC, the HFPE is an efficient and flexible mobile fluid power source.

Formation of highly nonlinear dust-acoustic solitary waves due to high-temperature electrons and ions

The nonlinear propagation of dust-acoustic solitary waves (DASWs) in an unmagnetized dusty plasma consisting of two distinct temperature ions, two distinct temperature electrons and mobile dust fluid has been investigated by employing reductive perturbation method. It has been assumed that the two distinct temperature ions follow the Maxwell–Boltzmann distribution and nonthermal (Cairn’s) distribution separately while the two distinct temperature electrons follow the nonextensive (Tsallis) distribution and superthermal (Kappa) distribution separately. The system has been treated by deriving and solving a set of three highly nonlinear equations such as K-dV, modified K-dV and Gardner equations. It has been noted that the basic properties of the DASWs are significantly modified by the presence of the nonthermal ions, nonextensive electrons and superthermal electrons. The possible applications of this investigation in astrophysical, space and laboratory plasma systems have also been briefly addressed.

Novel Observations of Salinity Transport in Low-Salinity Waterflooding

Summary Low-salinity waterflooding (LSWF) is a promising process that could lead to increased oil recovery. To date, the greatest attention has been paid to the complex oil/water/rock chemical reactions that might explain the mechanisms of LSWF, and it is generally accepted that these result in behavior equivalent to changing oil and water mobility. This behavior is modeled using an effective salinity range and weighting function to gradually switch from high- to low-salinity relative permeability curves. There has been limited attention on physical transport of fluids during LSWF, particularly at large scale. We focus on how the salinity profile interacts with water fronts through the effective salinity range and dispersion to alter the transport behavior and change the flow velocities, particularly for the salinity profile. We examined a numerical simulation of LSWF at the reservoir scale. Various representations of the effective salinity range and weighting function were also examined. The dispersion of salinity was compared with a theoretical form of numerical dispersion based on input parameters. We also compared salinity movement with the analytical solution of the conventional dispersion/advection equation. From simulations we observed that salinity is dispersed as analytically predicted, although the advection velocity might be changed. In advection-dominated flow, the salinity profile moves at the speed of the injected water. However, as dispersion increases, the mixing zone falls under the influence of the faster-moving formation water and, thus, speeds up. To predict the salinity profile theoretically, we have modified the advection term of the analytical solution as a function of the formation- and injected-water velocities, Péclet number, and effective salinity range. This important result enables prediction of the salinity transport by this newly derived modification of the analytical solution for 1D flow. We can understand the correction to the flow behavior and quantify it from the model input parameters. At the reservoir scale, we typically simulate flow on coarse grids, which introduces numerical dispersion or must include physical dispersion from underlying heterogeneity. Corrections to the equations can contribute to improving the precision of the coarse-scale models, and, more generally, the suggested form of the correction can also be used to calculate the movement of any solute that transports across an interface between two mobile fluids. We can also better understand the relative behaviors of passive tracers and those that are adsorbed.

A New Type of Noble Metal Mineralization in Fluidolites of the Poperechny Deposit, Lesser Khingan, Russia

The fluid-explosive breccias of the Poperechny iron–manganese deposit, Lesser Khingan, Russia, contain high concentrations of platinum group elements (PGE), gold, and silver. Noble metals are represented by isoferroplatinum crystals, Os–Ir alloys, PGE sulfoarsenides, and gold grains with a size of tenths of a millimeter and micron-sized segregations of native silver. The mineral composition of the PGE of the Poperechny deposit is consistent with that of the ore and placer objects of the Ural–Alaskan type and corresponds to the isoferroplatinum–osmium magmatic assemblage. The euhedral morphology of the isoferroplatinum and PGE sulfoarsenides indicates that they were formed in a stable environment at the crust–mantle boundary owing to partial melting of slab rocks. The appearance of PGE minerals in the magmatic–hydrothermal system under subsurface conditions is related to a highly mobile gas-saturated fluid flux capable of transferring deep mineral phases. The high content of PGE (up to 11.3 g/t), gold (up to 2.58 g/t), and silver (up to 256 g/t) in the fluidolites of the Poperechny deposit makes it possible to revise the criteria for searching for the bedrocks and placer sources of noble metals in the Lesser Khingan.

Effect of q-nonextensive hot electrons on bifurcations of nonlinear and supernonlinear ion-acoustic periodic waves

Nonlinear and supernonlinear ion-acoustic periodic waves are investigated in a three-component unmagnetized plasma which consists of mobile fluid cold ions, Maxwellian cold electrons and q-nonextensive hot electrons employing phase plane analysis. Using the traveling wave transformation, the plasma system is reduced to a planar autonomous dynamical system. Utilizing phase plane analysis of planar dynamical systems, all possible phase portraits including nonlinear homoclinic orbit, nonlinear periodic orbit, supernonlinear homoclinic orbit and supernonlinear periodic orbit are presented depending on physical parameters q,α,σ and V. Using numerical simulations, nonlinear and supernonlinear ion-acoustic periodic waves are shown for different conditions. It is found that the nonextensive parameter q plays a crucial role in the bifurcations of nonlinear and supernonlinear ion-acoustic periodic waves. Our study may be applicable to understand the nonlinear and supernonlinear periodic features in auroral plasma.

Probably Benign Breast Nodular Lesions (BI-RADS 3): Correlation between Ultrasound Features and Histologic Findings

The purpose of this retrospective study was to determine the validity of the BI-RADS system in ultrasound findings assigned to BI-RADS 3 category, using cytologic and histologic results as a benchmark. Our study population consisted of 122 ultrasound nodular lesions in 122 women who underwent fine-needle aspiration cytology and biopsy for probably benign lesions (Breast Imaging Reporting and Data System [BI-RADS] category 3). Contrary to what was previously reported in the literature (risk of malignancy of BI-RADS 3 <2%), malignancy was the outcome in seven of 122 cases (5.7%). Our study also found that the presence of a cellular component with a mobile fluid–fluid level in a cystic lesion and small (<3 mm) anechoic components in solid lesions is not always an indication of benignity. Our experience seems to indicate the need to consider the presence of non-homogeneous echoes in the corpuscular cyst and solid nodular lesions with cystic components as suspicious, especially in lesions with large dimensions. Therefore it would be necessary to conduct further studies to establish a dimensional criterion in the assessment of the malignant nature of the mentioned lesions. The management of probably benign nodular lesions should not only be guided by BI-RADS classification; it is also necessary to include clinical and anamnestic data and apply a multidisciplinary approach to select cases that require histologic verification instead of the usual follow-up.

Effects of axial magnetic field and nonextensivity on small amplitude dust acoustic solitary waves in dusty plasma

The nonlinear propagation of small amplitude dust‐acoustic (DA) solitary waves in magnetized dusty plasma consisting of negatively charged mobile dust fluid, and Boltzmann‐distributed electrons and ions with two distinct temperatures following a q‐nonextensive distribution are investigated. In this article, a number of nonlinear equations, namely, the Korteweg–de‐Vries (K‐dV) equations, have been derived by employing the reductive perturbation technique that is valid for a small but finite amplitude limit. The effects of nonextensivity of ions with two distinct temperatures and dust concentration on the amplitude and width of DA solitary waves are investigated theoretically. It is observed that both the nonextensive and low‐temperatures ions significantly modify the basic properties and polarities of DA solitary waves. It is shown that both positive and negative potential DA solitons occur in this case. The implications of these results to some astrophysical environments and space plasmas (e.g., stellar polytropes, peculiar velocity distributions of galaxies, and collisionless thermal plasma), and laboratory dusty plasma systems are briefly mentioned.

Occurrence characteristics and controls over mobile fluids in a tight sandstone reservoir

Using nuclear magnetic resonance (NMR) technology, this paper proposes a new pore structure parameter called ‘effective mobile fluid saturation’, which can account for two factors that influence mobile fluids in pores: the stiction of hydrophilic particulates on the surfaces of pores and the constraints of tiny throats. The new parameter quantifies the effective content of the mobile fluids and compensates for the deficiencies using conventional parameters like ‘mobile fluid saturation’. Pore-throat connectivity is crucial for effective mobile fluid saturation, which reaches its highest point when the sorting coefficient is in the range of 1.5–2.0. Recognition of the pore-throat configuration is crucial in assessing the effectiveness of mobile fluids in tight sandstone reservoirs. Factors that influence the effectiveness of mobile fluids in three types of pore structures are discussed from a diagenetic perspective, including the development of microfractures and secondary pores, recrystallisation, clay mineral precipitation, and other micropore structure characteristics.

Stabilization of miscible viscous fingering by a step growth polymerization reaction

Fingering is a hydrodynamic instability that occurs when a more mobile fluid displaces a fluid of lower mobility. When the primary source of the mobility difference is viscosity, the instability is termed viscous fingering. Viscous fingering is often, though not always, undesirable in industrial processes, particularly secondary petroleum recovery. Linear stability analysis by Hejazi et al. has indicated that the production of a non-monotonic viscosity profile can stabilize the interface. Herein, we use step-growth polymerization at the interface between two miscible monomers as a model system. In particular, a dithiol monomer displaced a diacrylate that reacted to form a linear polymer that behaves as a Newtonian fluid. Viscous fingering was imaged in a horizontal Hele-Shaw cell via Schlieren, which is sensitive to changes in index of refraction, and therefore polymer conversion. By varying reaction rate via initiator concentration along with flow rate via a syringe pump, we were able to demonstrate increasing stabilization of the flow with increasing Damkohler number.

Manipulation of viscous fingering in a radially tapered cell geometry

When a more mobile fluid displaces another immiscible one in a porous medium, viscous fingering propagates with a partial sweep, which hinders oil recovery and soil remedy. We experimentally investigate the feasibility of tuning such fingering propagation in a nonuniform narrow passage with a radial injection, which is widely used in various applications. We show that a radially converging cell can suppress the common viscous fingering observed in a uniform passage, and a full sweep of the displaced fluid is then achieved. The injection flow rate Q can be further exploited to manipulate the viscous fingering instability. For a fixed gap gradient α, our experimental results show a full sweep at a small Q but partial displacement with fingering at a sufficient Q. Finally, by varying α, we identify and characterize the variation of the critical threshold between stable and unstable displacements. Our experimental results reveal good agreement with theoretical predictions by a linear stability analysis.

Coalescence Dynamics of Mobile and Immobile Fluid Interfaces.

Coalescence dynamics between deformable bubbles and droplets can be dramatically affected by the mobility of the interfaces with fully tangentially mobile bubble-liquid or droplet-liquid interfaces expected to accelerate the coalescence by orders of magnitude. However, there is a lack of systematic experimental investigations that quantify this effect. By using high speed camera imaging we examine the free rise and coalescence of small air-bubbles (100 to 1300 μm in diameter) with a liquid interface. A perfluorocarbon liquid, PP11, is used as a model liquid to investigate coalescence dynamics between fully mobile and immobile deformable interfaces. The mobility of the bubble surface was determined by measuring the terminal rise velocity of small bubbles rising at Reynolds numbers, Re, less than 0.1 and the mobility of free PP11 surface by measuring the deceleration kinetics of the small bubble toward the interface. Induction or film drainage times of a bubble at the mobile PP11-air surface were found to be more than 2 orders of magnitude shorter compared to the case of bubble and an immobile PP11-water interface. A theoretical model is used to illustrate the effect of hydrodynamics and interfacial mobility on the induction time or film drainage time. The results of this study are expected to stimulate the development of a comprehensive theoretical model for coalescence dynamics between two fully or partially mobile fluid interfaces.

Computational study of the role of fluid content and flow on the lumbar disc response in cyclic compression: Replication of in vitro and in vivo conditions

The intervertebral disc viscoelastic response is governed primarily by its fluid content and flow. Invivo measurements demonstrate that the disc volume, fluid content, height and nucleus pressure completely recover during resting even after diurnal loading with twice longer duration (16 vs. 8 h). In view of much longer periods required for the recovery of disc height and pressure in vitro, concerns have been raised on the fluid inflow through the endplates that might be hampered by clogged blood vessels post mortem. This in silico study aimed to identify fluid-flow dependent response of discs and conditions essential to replicate in vitro and in vivo observations.An osmo-poroelastic finite element model of the human lumbar L4-L5 disc-bone unit was used. Simulating earlier in vitro experiments on bovine discs, the loading protocol started with 8 h preload at 0.06 MPa followed by 30 high/low compression loading cycles each lasting 7.5min at 0.5/0.06 MPa, respectively. Three different endplate configurations were investigated: free in- and outflow, no inflow and closed endplates with no flow. Additionally, the preload magnitude was increased from 0.06 MPa to 0.28 MPa and 0.50 MPa, or the initial nucleus hydration was reduced from 83% to 50%.For 0.06 MPa preload, the model with no inflow best matched in vitro trends. The model with free inflow increased segment height and nucleus pressure while the model with no fluid inflow resulted in a relatively small recovery in segment height and a rather constant nucleus pressure during unloading periods.Results highlight an excessive mobile fluid content as well as a restricted fluid inflow through endplates as likely causes of the discrepancies between in vivo and in vitro studies. To replicate in vivo conditions in vitro and in silico, disc hydration level should be controlled by adequate selection of preload magnitude/period and/or mobile fluid porosity.

Duplex Tear Film Evaporation Analysis

Tear film thinning, hyperosmolarity, and breakup can cause irritation and damage to the human eye, and these form an area of active investigation for dry eye syndrome research. Recent research demonstrates that deficiencies in the lipid layer may cause locally increased evaporation, inducing conditions for breakup. In this paper, we explore the conditions for tear film breakup by considering a model for tear film dynamics with two mobile fluid layers, the aqueous and lipid layers. In addition, we include the effects of osmosis, evaporation as modified by the lipid, and the polar portion of the lipid layer. We solve the system numerically for reasonable parameter values and initial conditions and analyze how shifts in these cause changes to the system's dynamics.

Capillary fluid dynamics within unconventional rocks investigated by scanning electron microscopy

ABSTRACT Fresh cores from tight-rock samples of subsurface hydrocarbon reservoirs retain mobile fluids. These fluids have complex chemical compositions and a large spectrum of molecules with different diameters and polarities. When investigated using high-resolution field-emission scanning electron microscopy (SEM), the imposed vacuum over hours of time causes pore fluids trapped in the rock sample to flow and interact with the mineral matrix. This paper reports the capillary fluid dynamics effect observed on freshly milled cross sections of tight chalk at high resolution. Multiphase fluid dynamic simulations confirm the aggregation of heavier fluid molecules on the geometrical irregularities of the pore space. As a consequence of this pitfall, the differentiation of solid organic matter versus variably viscous hydrocarbons from SEM data is subject to a fundamental revision.

Advantageous Reservoir Characterization Technology in Extra Low Permeability Oil Reservoirs

This paper took extra low permeability reservoirs in Dagang Liujianfang Oilfield as an example and analyzed different types of microscopic pore structures by SEM, casting thin sections fluorescence microscope, and so on. With adoption of rate-controlled mercury penetration, NMR, and some other advanced techniques, based on evaluation parameters, namely, throat radius, volume percentage of mobile fluid, start-up pressure gradient, and clay content, the classification and assessment method of extra low permeability reservoirs was improved and the parameter boundaries of the advantageous reservoirs were established. The physical properties of reservoirs with different depth are different. Clay mineral variation range is 7.0%, and throat radius variation range is 1.81 μm, and start pressure gradient range is 0.23 MPa/m, and movable fluid percentage change range is 17.4%. The class IV reservoirs account for 9.56%, class II reservoirs account for 12.16%, and class III reservoirs account for 78.29%. According to the comparison of different development methods, class II reservoir is most suitable for waterflooding development, and class IV reservoir is most suitable for gas injection development. Taking into account the gas injection in the upper section of the reservoir, the next section of water injection development will achieve the best results.