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1.
We investigated the mechanism of residual gas trapping at a microscopic level. We imaged trapped air bubbles in a Berea sandstone
chip after spontaneous imbibition at atmospheric pressure. The pore structure and trapped bubbles were observed by microfocused
X-ray computed tomography. Distributions of trapped bubbles in Berea and Tako sandstone were imaged in coreflooding at a capillary
number of 1.0 × 10 −6. Trapped bubbles are of two types, those occupying the center of the pore with a pore-scale size and others having a pore-network
scale size. In low-porosity media such as sandstone, connected bubbles contribute greatly to trapped gas saturation. Effects
of capillary number and injected water volume were investigated using a packed bed of glass beads 600μm in diameter, which
had high porosity (38%). The trapped N 2 bubbles are stable against the water flow rate corresponding to a capillary number of 1.0 × 10 −4. 相似文献
2.
Although, the effects of ultrasonic irradiation on multiphase flow through porous media have been studied in the past few
decades, the physics of the acoustic interaction between fluid and rock is not yet well understood. Various mechanisms may
be responsible for enhancing the flow of oil through porous media in the presence of an acoustic field. Capillary related
mechanisms are peristaltic transport due to mechanical deformation of the pore walls, reduction of capillary forces due to
the destruction of surface films generated across pore boundaries, coalescence of oil drops due to Bjerknes forces, oscillation
and excitation of capillary trapped oil drops, forces generated by cavitating bubbles, and sonocapillary effects. Insight
into the physical principles governing the mobilization of oil by ultrasonic waves is vital for developing and implementing
novel techniques of oil extraction. This paper aims at identifying and analyzing the influence of high-frequency, high-intensity
ultrasonic radiation on capillary imbibition. Laboratory experiments were performed using cylindrical Berea sandstone and
Indiana limestone samples with all sides (quasi-co-current imbibition), and only one side (counter-current imbibition) contacting
with the aqueous phase. The oil saturated cores were placed in an ultrasonic bath, and brought into contact with the aqueous
phase. The recovery rate due to capillary imbibition was monitored against time. Air–water, mineral oil–brine, mineral oil–surfactant
solution and mineral oil-polymer solution experiments were run each exploring a separate physical process governing acoustic
stimulation. Water–air imbibition tests isolate the effect of ultrasound on wettability, capillarity and density, while oil–brine
imbibition experiments help outline the ultrasonic effect on viscosity and interfacial interaction between oil, rock and aqueous
phase. We find that ultrasonic irradiation enhances capillary imbibition recovery of oil for various fluid pairs, and that
such process is dependent on the interfacial tension and density of the fluids. Although more evidence is needed, some runs
hint that wettability was not altered substantially under ultrasound. Preliminary analysis of the imbibition recoveries also
suggests that ultrasound enhances surfactant solubility and reduce surfactant adsorption onto the rock matrix. Additionally,
counter-current experiments involving kerosene and brine in epoxy coated Berea sandstone showed a dramatic decline in recovery.
Therefore, the effectiveness of any ultrasonic application may strongly depend on the nature of interaction type, i.e., co-
or counter-current flow. A modified form of an exponential model was employed to fit the recovery curves in an attempt to
quantify the factors causing the incremental recovery by ultrasonic waves for different fluid pairs and rock types. 相似文献
3.
Low Tension Polymer Flooding or Polymer Assisted Dilute Surfactant Flooding is generally deployed as a method to produce additional
oil trapped in oil reservoirs after waterflooding. Fundamental study of microscopic mechanisms and pore-level phenomena in
Polymer Assisted Dilute Surfactant Flooding needs more investigation. Of particular concern and interest is to probe into
and document the effect of pore morphology and structure on microscopic phenomena occurring at pore level. No previous works
on the effect of pore morphology in Polymer Assisted Dilute Surfactant Flooding has been reported in the literature. In this
study, one-quarter five-spot glass micromodels were deployed to examine the effect of porous media morphology and structure
on microscopic mechanisms as well as macroscopic behavior of Polymer Assisted Dilute Surfactant Flooding. Four types of pore
morphologies were employed to study this factor. Results show that the pore geometric properties in a porous medium will dictate
the degree of displacement front instability, capillary imbalance, viscous fingering, wetting characteristics and its distribution, and finally magnitude of ultimate oil recovery. We also found that the formation of flow scheme is dramatically influenced by the pre-designed injection scheme. 相似文献
4.
Transport in Porous Media - Countercurrent spontaneous imbibition (SI) is an important flow mechanism for oil recovery in fractured reservoirs during waterflooding. SI plays a key role in the... 相似文献
5.
Accurate models of multiphase flow in porous media and predictions of oil recovery require a thorough understanding of the
physics of fluid flow. Current simulators assume, generally, that local capillary equilibrium is reached instantaneously during
any flow mode. Consequently, capillary pressure and relative permeability curves are functions solely of water saturation.
In the case of imbibition, the assumption of instantaneous local capillary equilibrium allows the balance equations to be
cast in the form of a self-similar, diffusion-like problem. Li et al. [ J. Petrol. Sci. Eng. 39(3) (2003), 309–326] analyzed oil production data from spontaneous countercurrent imbibition experiments and inferred that
they observed the self-similar behavior expected from the mathematical equations. Others (Barenblatt et al. [ Soc. Petrol. Eng. J. 8(4) (2002), 409–416]; Silin and Patzek [ Transport in Porous Media 54 (2004), 297–322]) assert that local equilibirum is not reached in porous media during spontaneous imbibition and nonequilibirium
effects should be taken into account. Simulations and definitive experiments are conducted at core scale in this work to reveal
unequivocally nonequilbirium effects. Experimental in-situ saturation data obtained with a computerized tomography scanner
illustrate significant deviation from the numerical local-equilibrium based results. The data indicates: (i) capillary imbibition
is an inherently nonequilibrium process and (ii) the traditional, multi-phase, reservoir simulation equations may not well
represent the true physics of the process. 相似文献
6.
The ultimate driving force for counter-current spontaneous imbibition of a fluid into a porous material is the capillary pressure developed under dynamic conditions at the imbibition front. This is a difficult variable to measure. We report experiments using restricted counter-current spontaneous imbibition to find the maximum capillary pressure developed during imbibition of a light mineral oil (and brine) into initially air-filled sandstone core samples with one end-face open. The production of air from the core was prevented by covering its open face with a low permeability core segment set against the main test segment. The location of the imbibition front and the pressure resulting from compression of air ahead of the imbibition front were monitored. In some cases, in order to achieve stabilized gas pressures with the front still advancing through the core, the air in the core was compressed at the start of the imbibition test. The subsequently measured stabilized air pressures dropped only slightly as imbibition slowed. The measured pressures are directly related to the effective capillary pressures that drive spontaneous imbibition. After spontaneous imbibition ceased, the pressure was released by flow of air through the sealed end of the core and further spontaneous imbibition occurred in co-current mode. Comparison of the stabilized pressures with previously published oil/brine imbibition results showed close agreement after compensation for the difference in interfacial tension. 相似文献
7.
Capillary dominated flow or imbibition—whether spontaneous or forced—is an important physical phenomena in understanding the behavior of naturally fractured water-driven reservoirs (NFR’s). When the water flows through the fractures, it imbibes into the matrix and pushes the oil out of the pores due to the difference in the capillary pressure. In this paper, we focus on modeling and quantifying the oil recovered from NFR’s through the imbibition processes using a novel fully implicit mimetic finite difference (MFD) approach coupled with discrete fracture/discrete matrix (DFDM) technique. The investigation is carried out in the light of different wetting states of the porous media (i.e., varying capillary pressure curves) and a full tensor representation of the permeability. The produced results proved the MFD to be robust in preserving the physics of the problem, and accurately mapping the flow path in the investigated domains. The wetting state of the rock affects greatly the oil recovery factors along with the orientation of the fractures and the principal direction of the permeability tensor. We can conclude that our novel MFD method can handle the fluid flow problems in discrete-fractured reservoirs. Future works will be focused on the extension of MFD method to more complex multi-physics simulations. 相似文献
8.
A novel concept for modeling pore-scale phenomena included in several enhanced oil recovery (EOR) methods is presented. The
approach combines a quasi-static invasion percolation model with a single-phase dynamic transport model in order to integrate
mechanistic chemical oil mobilization methods. A framework is proposed that incorporates mobilization of capillary trapped
oil. We show how double displacement of reservoir fluids can contribute to mobilize oil that are capillary trapped after waterflooding.
In particular, we elaborate how the physics of colloidal dispersion gels (CDG) or linked polymer solutions (LPS) is implemented.
The linked polymer solutions consist of low concentration partially hydrolyzed polyacrylamide polymer crosslinked with aluminum
citrate. Laboratory core floods have shown demonstrated increased oil recovery by injection of linked polymer solution systems.
LPS consist of roughly spherical particles with sizes in the nanometer range (50–150 nm). The LPS process involve mechanisms
such as change in rheological properties effect, adsorption and entrapment processes that can lead to a microscopic diversion
and mobilization of waterflood trapped oil. The purpose is to model the physical processes occurring on pore scale during
injection of linked polymer solutions. A sensitivity study has also been performed on trapped oil saturation with respect
to wettability status to analyze the efficiency of LPS on different wettability conditions. The network modeling results suggest
that weakly wet reservoirs are more suitable candidates for performing linked polymer solution injection. 相似文献
9.
Counter-current spontaneous imbibition (COUCSI) in porous media is driven by capillary forces. Capillary action results in
a high capillary imbibition pressure at the imbibition front and a low capillary drainage pressure at the outlet face. It
is the difference between these two pressures that draws in the wetting phase and pushes out the non-wetting phase. A technique
for measuring the capillary pressure at an imbibition front under restricted flow conditions has been developed and applied
to Berea sandstone with a range of permeabilities. In the experiments, brine was the wetting phase and refined oil was the
non-wetting phase. One end face of a sandstone core was butted to a short section of a finer-pored rock. The composite core
surface was then sealed, apart from the end face of the low-permeability segment. A connection to a pressure transducer was
set in the opposite end face of the core. Initially, the main core segment was filled with oil. In most cases, the finer-pored
segment was filled with brine. Imbibition was started by immersing the core in brine. The purpose of the finer-pored segment
was to prevent the escape of non-wetting phase from the open face. For some tests there was an initial period of co-current
spontaneous imbibition (COCSI) created by allowing production of non-wetting phase through an outlet tapping in the sealed
end face. The outlet was then connected to the transducer and the imbibition changed to COUCSI. There followed an increase
in the monitored end pressure to a maximum as fluid redistributed within the core. For the tests in which the fine-pored segments
were pre-saturated with brine, even without an initial period of co-current imbibition, limited invasion of the main core
segment by brine resulted in an asymptotic rise of the end pressure to a maximum as the imbibition front dispersed. To confirm
that the dispersing front did not reach the dead end of the core, the distance of advance of the wetting liquid was detected
by a series of electrodes. The maximum value of the end pressure provides an estimate of the capillary pressure at an imbibition
front for COUCSI. The maximum capillary pressure generated by the invading fluids ranged from 6.6 kPa to 42 kPa for sandstone
with permeabilities between 1.050 (μm) 2 and 0.06 (μm) 2. 相似文献
10.
Residual oil saturation reduction and microbial plugging are two crucial factors in microbial-enhanced oil recovery (MEOR)
processes. In our previous study, the residual saturation was defined as a nonlinear function of the trapping number, and
an explicit relation between the residual oil saturation and the trapping number was incorporated into a fully coupled biological
(B) and hydrological (H) finite element model. In this study, the BH model is extended to consider the impact of rock heterogeneity
on microbial-enhanced oil recovery phenomena. Numerical simulations of core flooding experiments are performed to demonstrate
the influences of different parameters controlling the onset of oil mobilization. X-ray CT core scans are used to construct
numerical porosity-permeability distributions for input to the simulations. Results show clear fine-scale fingering processing,
and that trapping phenomena have significant effects on residual oil saturation and oil recovery in heterogeneous porous media.
Water contents and bacterial distributions for heterogeneous porous media are compared with those for homogenous porous media.
The evolution of the trapping number distribution is directly simulated and visualized. It is shown that the oil recovery
efficiency of EOR/MEOR will be lower in heterogeneous media than in homogeneous media, largely due to the difficulty in supplying
surfactant to unswept low-permeability zones. However, MEOR also provides efficient plugging along high-permeability zones
which acts to increase sweep efficiency in heterogeneous media. Thus, MEOR may potentially be more suited for highly heterogeneous
media than conventional EOR. 相似文献
11.
The prevailing current wisdom about how to properly formulate an algorithm to describe spontaneous and coupled spontaneous/induced capillary imbibition into and through the interstices of porous Darcian scale sediments implies, but perhaps incorrectly, that the early empirical relations of Buckley and Leverett (1942) can safely be employed. Here this persistently popular point of view is found to be inadequate since it overlooks taking into full account how common sense suggests that it is surface energy gradient driving forces which are the underlying cause for the occurrences of these processes. Specifically it will be noted that a satisfactory algorithm to model cases where spontaneous capillary imbibition occurs will not be one which ignores the fact that necessarily the local free surface energy is continuously diminished in magnitude until a minimum value together with a maximum entropy condition has been reached. Hence, the conclusion is drawn herein that the Buckley–Leverett formulations alone at best can only be used to describe what is called those induced capillary imbibition processes caused by the action of mechanical energy driving forces. 相似文献
12.
To investigate the influence of the organosilicon-acrylic on wetting properties of porous media, contact angle tests were
performed on two different sandstones. In addition, the effectiveness of the emulsion on wettability alteration of porous
media was validated by capillary rise and spontaneous imbibition tests. The results of wettability tests showed that the wettability
of two sandstones was altered from water-wet to gas-wet after treatment with the emulsion. The principle that the critical
radius of pore throats and wettability of porous media affect liquids flow was derived analytically and verified experimentally.
Coreflood results demonstrated that the latex resulted in increasing the water permeability through altering the rock wettability
to gas-wetting, then decreasing the friction drag between liquids and rocks surface. Thereby, the emulsion treatment could
increase the flowback rate of trapped liquids. Experimental results were in good agreement with the theoretical analysis.
In conclusion, all results indicated that the emulsion could alter the wettability from water-wet to intermediate gas-wet
and enhance water permeability in porous media. It was extrapolated that the emulsion had the tremendous potential to be applied
in field conditions, enhancing gas productivity through the cleanup of trapped water in the vicinity of the wellbore. 相似文献
13.
By utilizing fractal dimension as one of the parameters to characterize rocks, a mathematical model was derived to predict
the production rate by spontaneous imbibition. This fractal production model predicts a power law relationship between spontaneous
imbibition rate and time. Fractal dimension can be estimated from the fractal production model using the experimental data
of spontaneous imbibition in porous media. The experimental data of recovery in gas-water-rock and oil–water–rock systems
were used to test the fractal production model. The rocks (Berea sandstone, chalk, and The Geysers graywacke) in which the
spontaneous water imbibition experiments were conducted had different permeabilities ranging from 0.5 to over 1000 md. The
results demonstrate that the fractal production model can match the experimental data satisfactorily in the cases studied.
The fractal dimension data inferred from the model match were approximately equal to the values of fractal dimension measured
using a different technique (mercury-intrusion capillary pressure) in Berea sandstone. 相似文献
14.
Transport in Porous Media - During waterflooding, spontaneous imbibition is a fundamental recovery mechanism in fractured reservoirs. A large number of numerical and experimental studies have been... 相似文献
15.
The effect of fractures on oil recovery and in situ saturation development in fractured chalk has been determined at near
neutral wettability conditions. Fluid saturation development was monitored both in the matrix and in the fractures and the
mechanisms of fracture crossing were determined using high spatial resolution MRI. Capillary continuity across open oil-filled
fractures was verified by imaging the water bridges established within the fracture. Despite an alternate escape fracture
for the water, separate water bridges were shown to be stable for the entire duration of the experiments. The established
capillary contact resulted in oil recovery exceeding the spontaneous imbibition potential in the outlet-isolated cores by
ca. 10% PV. This is explained by viscous recovery provided by water bridges across open fractures. The size of the bridges
seemed to be controlled by the wettability of the rock and not by the differential pressure applied across the open fracture. 相似文献
16.
Capillary imbibition of a wetting fluid in a porous medium is studied. A method of constructing the exact solution of the corresponding problem is developed. An iteration procedure is developed for the case of countercurrent capillary imbibition. The salient features of the flow generated by capillary forces are revealed on the basis of numerical results. 相似文献
17.
In the oil industry, dynamic spontaneous imbibition plays an important role in several flow processes in porous media. A numerical
approach is developed to simulate dynamic spontaneous imbibition with variable inlet saturation and interfacial coupling.
The inclusion of interfacial coupling effects invalidates the assumption that the interfaces (fluid/fluid and fluid/solid)
act in the same way. The one-dimensional numerical simulation model is developed using a Lagrangian formulation discretized
in time and saturation. The solution of the partial differential equations utilizes an iteration process that includes two
material balance criteria to ensure the validity of the variable inlet saturation. Furthermore, an error analysis, the validation
of the model and a sensitivity study on the optimal number of time steps and saturation grid cells are undertaken. The numerical
simulation solution represents an accurate approach to investigate the effect of fluid and rock properties on dynamic spontaneous
imbibition. 相似文献
18.
Different functions describing matrix-fracture transfer were tested for counter-current capillary imbibition interaction.
The recovery curves obtained from capillary imbibition experiments were used to fit the transfer functions. The exponential
coefficients yielding the best fit to the experimental data were obtained and correlated to the effective parameters such
as viscosity, IFT, matrix length and diameter, matrix permeability and porosity, and wettability using multivariable regression
analysis. In order to obtain the recovery curves, experiments were conducted on Berea sandstone and Indiana limestone samples.
Cylindrical samples with different shape factors were obtained by cutting the plugs 1, 2.5, and 5 cm in diameter and 2.5,
5, and 10 cm in length. All sides were coated with epoxy except one end. More than fifty static imbibition experiments were
carried out on vertically and horizontally situated samples where the imbibition took place upward and lateral directions,
respectively. Brine–air, brine–kerosene, brine–mineral oil, and surfactant solution–mineral oil pairs were used as fluids.
For many matrix shape factors (especially longer and small diameter ones), dividing the recovery curve into three parts were
needed as the early, intermediate, and late times, which are typically distinguished by the time required for the imbibition
front to reach the closed boundary at the end of the core. Correlations among the exponential coefficients and rock/fluid
properties were developed. It was observed that different rock/fluid properties and transfer mechanisms (capillary imbibition
and gravity drainage) govern the process for each part. Hence, the analyses done in this study were useful not only for developing
explicit transfer functions but also identifying the physics of the counter-current imbibition recovery. 相似文献
20.
The cylindrical model is discussed and a new tube model is proposed to describe capillary imbibition kinetics in porous sedimentary rocks. The tube consists of a periodic succession of a single hollow spherical element of which the geometry is defined by the sphere radius and the sphere access radius. These two parameters are estimated experimentally for four rock types from their specific surface areas. Introducing those parameters in the model capillary imbibition kinetics, parameters are calculated and compared with the experimental ones. A direct relation between imbibition kinetics and specific surface area has been pointed out. 相似文献
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