Behavior Of Porous Media Research Articles

The Evaluation of a Technological Trend in Polymer Flooding for Heavy Oil Recovery

This work evaluated an emerging technological trend in polymer flooding for heavy oil recovery in the near future (i.e., the injection of polymer solution with higher viscosity [concentration] and larger slug size). The rheological properties and flow behavior in porous media of two typical enhanced oil recovery (EOR) polymers (a partially hydrolyzed polyacrylamide and a xanthan gum) and a novel hydrophobic polymer were first investigated to identify their potential functionality in displacing heavy oil. Tertiary oil recovery was then conducted by polymer flooding using a heavy oil of 1000 mPa·s. The results indicate that polymer flooding with higher viscosity and larger slug size can significantly improve oil recovery and produced water/oil ratio, which proves the technical and economic feasibility of this trend in oil fields. Xanthan gum exhibits an outstanding flow behavior and EOR performance in sandpack displacement tests compared to other polymers, making it a promising candidate for this trend.

Shale Reservoirs Multi-Fracture Fracturing Technique and Studies on Reservoirs Stresses

Theoretical studies have shown that the generation of the hydraulic fractures reduces or even reverses the stress anisotropy near the fractures and results in increasing the complexity of fractures. A finite element model was established in which the pore pressure elements were used to simulate the behavior of porous media and the pore pressure cohesive elements were adopted to catch the characters of hydraulic fractures. A special fracturing manner was adopted to create complicated fracture networks by reducing or even reversing the stress anisotropy between fractures. The geometries of hydraulic fractures, strains, stresses, pore pressure distributions and fluid pressures within the fractures are obtained. The results of the model are fit well with the corresponding theoretical data. The simulation results show that the stress anisotropy is reduced by the generation of the hydraulic fractures, multiple parallel transverse fractures of horizontal well even reverse the stress anisotropy in some place of the reservoir. The simulation results validate the feasibility of the theoretical studies and the expected complex network fractures could be created by adopting special fracturing manner.

Difference in pore contact angle and the contact angle measured on a flat surface and in an open space

Pore wetting is of importance to many industrial processes, such as microfluidics, petroleum engineering, CO2 storage and biophysical processes. Due to lack of measurement techniques, pore wetting has been estimated by using the contact angle measured on a flat surface. This may give misled the interpretation of multiphase flow behavior in porous media. In this study, the static contact angles of various liquids were investigated in single glass capillaries to indicate the difference between pore contact angle and the contact angle measured on flat surfaces. The liquids used are deionised water, 1-propanol, n-decane and crude oil. The glass capillaries used had a pore size range from 100 to 1000μm. The experiments were designed to consider the effects of glass pore size, surface tension and chemical structure of liquid on pore contact angle. The results indicate that the contact angle of liquids in a pore cannot be simply treated as 0° which is commonly applied in literature. The static contact angle in glass pores varies with pore size and the applied liquids. When the pore size of glass capillary decreases from 1000 to 300μm, the pore contact angles of DI water, 1-propanol, n-decane and crude oil increase from 20° to 30°, 19° to 39°, 20° to 26° and 15° to 20°, respectively. The static pore contact angle of a liquid in a glass capillary is different from the contact angle on a flat glass surface. This indicates that the previous application of a contact angle on a flat surface to a pore medium case might be inappropriate for some cases.

Mathematical Model of Foam Flowing Characteristics by Snap-Off Mechanisms at Steady State in Porous Media

Flow characteristics and regeneration processes of foams were influenced by lamella properties and pore-throat structure in porous media. In this article, porous media was simplified as a bunch of constricted capillary tubes according to grain size, pore-throat radius, and immobile water saturation in porous media. Based on an analysis of forces upon liquid lamella, a mathematical model of foam migration and regeneration at steady state was established according to the mass conservation law and the momentum conservation law in porous media. The model could be used to calculate some important parameters in porous media, such as pressure distribution, shearing stress, lamella morphology, liquid-layer thickness, regeneration bubble size, etc. A series of flow experiments were carried out to investigate the influence of liquid properties and pore-throat structure on flow characteristics and resistance behavior of foams in porous media. The experimental results showed that pressure distribution monotonously decreased along porous media. The theoretical results were in good agreement with the experimental results. Foam structure, that is, foam quality was an important factor upon foam resistance behavior in porous media. The strongest resistance ability of foams was achieved at foam quality of 85% in porous media.

Effect of residual oil saturation on hydrodynamic properties of porous media

To understand the effect of residual oil on hydraulic properties and solute dispersive behavior of porous media, miscible displacement column experiments were conducted using two petroleum products (diesel and engine oil) and a sandy soil. The effective water permeability, effective water-filled porosity, and dispersivity were investigated in two-fluid systems of water and oil as a function of residual oil saturation (ROS). At the end of each experiment, the distribution of ending ROS along the sand column was determined by the method of petroleum ether extraction-ultraviolet spectrophotometry. Darcy’s Law was used to determine permeability, while breakthrough curves (BTCs) of a tracer, Cl−, were used to calibrate effective porosity and dispersivity. The experimental results indicate that the maximum saturated zone residual saturation of diesel and engine oil in this study are 16.0% and 45.7%, respectively. Cl− is found to have no sorption on the solid matrix. Generated BTCs are sigmoid in shape with no evidence of tailing. The effective porosity of sand is inversely proportional to ROS. For the same level of ROS, the magnitude of reduction in effective porosity by diesel is close to that by engine oil. The relative permeability of sand to water saturation decreases with increasing amount of trapped oil, and the slope of the relative permeability–saturation curve for water is larger at higher water saturations, indicating that oil first occupies larger pores, which have the most contribution to the conductivity of the water. In addition, the reduction rate of relative permeability by diesel is greater than that by engine oil. The dispersivity increases with increasing ROS, suggesting that the blockage of pore spaces by immobile oil globules may enhance local velocity variations and increase the tortuosity of aqueous-phase flow paths.

Sodium Silicate Behavior in Porous Media Applied for In-Depth Profile Modifications

This paper addresses alkaline sodium silicate (Na-silicate) behavior in porous media. One of the advantages of the Na-silicate system is its water-like injectivity during the placement stage. Mixing Na-silicate with saline water results in metal silicate precipitation as well as immediate gelation. This work demonstrated that low salinity water (LSW, sea water diluted 25 times) could be used as a pre-flush in flooding operations. A water override phenomenon was observed during gel formation which is caused by gravity segregation. Dynamic adsorption tests in the sand-packed tubes showed inconsiderable adsorbed silicon density (about 8.5 × 10−10 kg/cm3 for a solution with 33 mg/L silicon content), which is less than the estimated mono-layer adsorption density of 1.4 × 10−8 kg/cm3. Na-silicate enhanced water sweep efficiency after application in a dual-permeability sand-pack system, without leak off into the oil-bearing low permeability (LP) zone. Field-scale numerical sensitivity studies in a layered reservoir demonstrated that higher permeability and viscosity contrasts and lower vertical/horizontal permeability ratio result in lower Na-silicate leakoff into the matrix. The length of the mixing zone between reservoir water and the injected Na-silicate solution, which is formed by low salinity pre-flush, acts as a buffer zone.

Investigation of Self-Similar Interface Evolution in Carbon Dioxide Sequestration in Saline Aquifers

In this work, we investigate numerically the injection of supercritical carbon dioxide into a deep saline reservoir from a single well. We analyze systematically the sharp-interface evolution in different flow regimes. The flow regimes can be parameterized by two dimensionless numbers, the gravity number, $$\Gamma $$ and the mobility ratio, $$\lambda $$ . Numerical simulations are performed using the volume of fluid method, and the results are compared with the solutions of the self-similarity equation established in previous works, which describes the evolution of the sharp interface. We show that these theoretical solutions are in very good agreement with the results from the numerical simulations presented over the different flow regimes, thereby showing that the theoretical and simulation models predict consistently the spreading and migration of the created $$\hbox {CO}_{2}$$ plume under complex flow behavior in porous media. Furthermore, we compare the numerical results with known analytic approximations in order to assess their applicability and accuracy over the investigated parametric space. The present study indicates that the self-similar solutions parameterized by the dimensionless numbers $$\lambda , \Gamma $$ are significant for examining effectively injection scenarios, as these numbers control the shape of the interface and migration of the $$\hbox {CO}_{2}$$ plume. This finding is essential in assessing the storage capacity of saline aquifers.

Mechanical Properties and Flow Behavior of Polymers for Enhanced Oil Recovery

The mechanical properties and flow behavior in porous media of three different polymer systems including a hydrophobically modified acrylamide-based copolymer (HMSPAM), a partially hydrolyzed polyacrylamide (HPAM), and a polysaccharide (xanthan gum) were evaluated to establish their functional differentiation as mobility control agents in enhanced oil recovery (EOR). The rheological properties of the polymers were described by the power-law model to investigate their non-Newtonian behavior. The first normal stress difference (N1) and Weissenberg number (We) were also used to compare their elastic properties. The experimental results showed that, at comparable shear viscosity, HMSPAM exhibited significant elasticity compared to HPAM and xanthan gum. Shear resistance tests indicated that all of the polymers experienced an extra stress when converging into a capillary tube due to the “entrance effect.” Xanthan gum was the most mechanically stable polymer. Moreover, HMSPAM showed the superior reformability which was quantified by the regained viscosity with relaxation time. This could be explained by the rapid re-association of the hydrophobic interactions. Sandpack flood tests indicated that HMSPAM rendered extremely high mobility control ability during polymer flooding suggesting its potential in EOR. However, this polymer also experienced significant retention within the porous media (potential injectivity and plugging problems), which may be attributed to the formation of bulky associative polymer networks. In this work, UV spectrometry was employed to monitor the concentration of the produced polymer solutions and quantify the polymer retention within porous media. This analytical approach offers great reliability and simplicity. It was concluded that the use of a particular polymer system depends on the oil reservoir conditions and the target EOR application.

Effect of particle hydrophobicity on CO2 foam generation and foam flow behavior in porous media

Studies of CO2 foam stabilized with silica nanoparticles at reservoir conditions were carried out for CO2 foam enhanced oil recovery (EOR) application. In the study described in this paper, three types of silica nanoparticles with varied wettability were employed to study the effects of particle hydrophobicity on CO2 foam generation at reservoir conditions. The results showed that nanoparticle surface hydrophobicity played an important role in CO2 foam generation. More CO2 foam was generated as the particle surface changed from strongly hydrophilic to somewhat hydrophobic. The bubble size of the CO2 foam decreased noticeably as the particle surface became more hydrophobic. Nanosilica particle-stabilized CO2 foam demonstrated a significant effect on the reduction of the CO2 mobility at a phase ratio between 2 and 11. The particle-stabilized CO2 foam also improved the apparent viscosity of the CO2 as the mixture flowed through a capillary tube.

Computation of Flow Through a Three-Dimensional Periodic Array of Porous Structures by a Parallel Immersed-Boundary Method

A parallel implementation of an immersed-boundary (IB) method is presented for low Reynolds number flow simulations in a representative elementary volume (REV) of porous media that are composed of a periodic array of regularly arranged structures. The material of the structure in the REV can be solid (impermeable) or microporous (permeable). Flows both outside and inside the microporous media are computed simultaneously by using an IB method to solve a combination of the Navier–Stokes equation (outside the microporous medium) and the Zwikker–Kosten equation (inside the microporous medium). The numerical simulation is firstly validated using flow through the REVs of impermeable structures, including square rods, circular rods, cubes, and spheres. The resultant pressure gradient over the REVs is compared with analytical solutions of the Ergun equation or Darcy–Forchheimer law. The good agreements demonstrate the validity of the numerical method to simulate the macroscopic flow behavior in porous media. In addition, with the assistance of a scientific parallel computational library, PETSc, good parallel performances are achieved. Finally, the IB method is extended to simulate species transport by coupling with the REV flow simulation. The species sorption behaviors in an REV with impermeable/solid and permeable/microporous materials are then studied.

Paradoxical drying of a fired-clay brick due to salt crystallization

We investigated how salt crystallization inside a porous building material influences the formation of a receding drying front. Nuclear Magnetic Resonance (NMR) is used to measure non-destructively both hydrogen and dissolved sodium ions during drying process. In this study, we focused on the influence of NaCl on the drying behavior of porous media. The results show that salt changes the drying behavior. At low relative humidities (RH~0%), the drying rate of a brick saturated with NaCl solution is much lower than the drying rate of water saturated brick. Moreover, the presence of salt suppresses the development of a receding front. In this case homogenous drying of the material continues till very low saturation values. This is due to salt crystallization near the surface of the brick that causes blockage of the pores. This blockage reduces evaporation rate at the surface and allows maintaining a continuous hydraulic connection between the surface of the porous medium and the liquid present inside the material till low saturation values. In the case of a salt solution saturated brick, increasing relative humidity to 55% and 70% leads to a paradoxical situation where the evaporation rate is greater for 55% and 70% RH than for 0% RH. The paradox is explained by the impact of evaporation rate on the efflorescence microstructure, leading to the formation of a blocking crust for sufficiently high evaporation rates and non-blocking efflorescence for sufficiently low evaporation rates. The fundamental difference between the two types of efflorescence is demonstrated from a simple imbibition experiment. Using a simple continuum scale model of drying, critical moisture content was determined and all the essential features of the experimental results are validated. It is shown that critical moisture content can be very low in the case of fired-clay brick due to the low threshold of the pore space, which is consistent with the relatively large pore size distribution of the fired-clay brick.

Influence of ionic strength and soil characteristics on the behavior of Cryptosporidium oocysts in saturated porous media

The physico-chemical behavior of Cryptosporidium oocysts was investigated during their transfer through an alluvial formation from Les Cayes (Haiti) via batch tests. Five approximately 3kg soil samples were collected and combined prior to batch tests from the alluvial formations. The experiments were carried out at soil pH by equilibrating different ranges of pure oocysts concentrations and soil samples with 3mM CaCl2 and 1mM NaBr as electrolyte. We used the Debye–Hückel equation describing ion activity in a solution for a given ionic strength. The equilibrium adsorption mechanism is used to enumerate the oocysts in the soil. The results suggest that the oocysts behavior in porous media depends on soil characteristics such as soil pH, the nature of the mineral and organic constituents of the soil and the ionic strength and activities in solution. These results show that a total transfer in batch containing NaBr solutions against a partial one in batch containing CaCl2 solutions depends on the oocysts media concentration. To confirm the oocysts number retained in soil, confocal microscopy was successfully used and the images demonstrate that the majority of oocysts were retained at the range of concentrations tested. The findings from this study demonstrated that the retention of C. Parvum in soils may be influenced by chemical conditions and soils characteristics, which are important for groundwater risk assessment.

Evaluation of hydraulic conductivity of reconstructed granular media generated using low-order probability functions

The hydraulic conductivity of three-dimensional artificial two-phase (fluid phase and solid phase) models with varying solid clustering sizes are evaluated to explore the effect of phase clustering, using low-order probability functions. The original random and heterogeneous microstructure models are made by placing randomly dispersed voxels with varying clustering sizes and the same porosity. The two-point correlation and lineal-path functions are applied to extract characteristics of phase clustering. The reconstructed models whose low-order probability functions are analogous to the original models are then made by a stochastic optimization process. This process allows one to generate equivalent reconstructed models to the original microstructure. The hydraulic conductivity values of both original and reconstructed models along three perpendicular directions are evaluated by solving Navier-Stoke’s equation and averaging local velocity values of fluids with the aid of finite element scheme. Results are analyzed to evaluate the applicability of reconstruction approach depending on the phase clustering. The fluid flow through porous media is further examined with the observation of flow resistance and percolation path. The effects of anisotropy of the fluid phase are also discussed to explore the applicability of stochastic optimization process. It is concluded that the low-order probabilistic functions provide an efficient tool to reconstruct three dimensional microstructures up to certain degree of clustering sizes and to simulate the flow behavior in porous media.

Simulation of Stress Changes of Shale Reservoirs during Hydraulic Fracturing to Create Fracture Networks

Theoretical studies have shown that the generation of hydraulic fractures reduces or even reverses the stress anisotropy between the fractures and results in increasing the complexity of fractures. A finite element model was established in which the pore pressure element was used to simulate the behavior of porous media and the pore pressure cohesive element was adopted to catch the characters of hydraulic fracture. A special fracturing manner was adopted to create complicated fracture networks by reducing or even reversing the stress anisotropy between fractures. The geometries of hydraulic fractures, strains, stresses, pore pressure distributions and fluid pressures within the fractures are obtained. The results of the model are fit well with the corresponding theoretical data. The simulation results show that the stress anisotropy is reduced resulting from the generation of the hydraulic fracture, multiple parallel transverse fractures of horizontal well further reduce or even reverse the stress anisotropy in some place of the reservoir. The simulation results validate the feasibility of the theoretical studies and the expected complex network fractures could be created by adopting the special fracturing manner.

Material Behavior of Porous Media

The drying of porous media is studied in this paper by means of the continuous approach and the control volume method. Both transport phenomena inside the porous medium and overall drying kinetics are analyzed. The model utilized in this study requires a lot of physical properties. All of them have been established experimentally. The capillary pressure, which depends on the moisture content, is obtained by a mercury intrusion curve.

Experimental measurement of compressibility coefficients of synthetic sandstone in hydrostatic conditions

For the characterization of the mechanical behavior of porous media in elastic conditions, the theory of poroelasticity is used. The number of poroelastic coefficients is greater in elastic conditions because of the complexity of porous media. The laboratory measurement of poroelastic coefficients needs a system that can control and measure the variables of poroelasticity. In this paper, experimental measurements of these coefficients are presented. Laboratory tests are performed using a system designed by the authors. Laboratory hydrostatic tests are performed on cylindrical samples in drained, pore pressure loading, undrained and dry conditions. Compressibilities (bulk and pore compressibility), effective stress and Skempton coefficients are measured by these tests. Samples are made of a composition (sand and cement) and are made by a compaction process synthetically. Calibration tests are performed for the setup to identify possible errors in the system and to correct the results of the main tests. This is done by performing similar compressibility tests at each stress level on a cylindrical steel sample (5.47 mm in diameter) with a longitudinal hole along it (hollow cylinder). A steel sample is used to assume an incompressible sample. The results of the tests are compared with the theory of poroelasticity and the obtained graphs and their errors are analyzed. This study shows that the results of the drained and pore pressure loading tests are compatible with poroelastic formulation, while the undrained results have errors because of extra fluid volume in the pore pressure system and calibration difficulties.

Microcapsule flow behaviour in porous media

This article investigates the possibility of using micro-capsules, with a gelling agent, hydroxypropyl cellulose, in the core, during enhanced oil recovery. The aim is to block off high permeability regions of a formation known as thief zones, thereby diverting the chase injection water into adjacent unswept low permeability regions. Temperature triggered micro-capsules were made by polymer precipitation through a solvent evaporation method, with poly(lactic-co-glycolic) acid as the polymer shell. Release studies with methylene blue demonstrated the temperature induced release from these micro-capsules. A customised tank was made to allow porous media flow and single permeability experiments were conducted. Even without the gelling agent, the micro-capsules gradually blocked the ballotini pore network. However, by varying the tank temperature, a drop in permeability was observed when the capsules released their core. Experiments with two permeability regions showed that the micro-capsules clogged up the high permeability layer more than the low permeability region.

Proper Index of Foam Statics Characteristics on Predicting Foam Dynamics Behavior in Porous Media

Proper foam statics index can give essential indications on foam dynamic behavior in porous media. In this paper, the statics characteristics are investigated through air-flow method for foam generated with Sodium Dodecyl Sulfate (SDS) surfactant. Parameters of foam height, foam half period time are recorded for various gas phases, surfactant concentrations and injecting gas flow rate, and foam morphology are also visually monitored. It is found the N2 generated foam has better characteristics on foam height, while poorer characteristics on foam half-time period compared to air and CO2 foam. Widely employed Foam Composite Index (FCI) is no longer suitable for predicting foam dynamic behavior, a Foam Index for predicting Dynamic Behavior in Porous Media (FIDBPM) is therefore defined to predict properly the foam transient propagation process in porous media.

A Fractal Model for Capillary Pressure of Porous Media

Capillary pressure is a basic parameter in the study of the behavior of porous media containing two or more immiscible fluid phases. In this study, the capillary pressure of porous media is predicted based on based on fractal property of pore in porous media. The formula of calculating the capillary pressure of porous media is given. The capillary pressure of porous media is expressed as a function of porosity, fractal dimension of pore and saturation. Based on the parametric effect analysis, we conclude that the capillary pressure of porous media is negatively correlated with the porosity and saturation. Besides, it is shown that the capillary pressure of unsaturated porous media decreases with the increase of saturation. No additional empirical constant is introduced. This model contains less empirical constants than the conventional correlations. The model predictions are compared with the existing experimental data and good agreement between the model predictions and experimental data is found. The validity of the present fractal model is thus verified.

Investigation of Low Frequency Elastic Wave Application for Fluid Flow Percolation Enhancement in Fractured Porous Media

In recent years, some numerical models have been proposed to investigate the effects of the elastic wave such as ultrasonic on fluid flow behavior in porous media. Nevertheless, none of these models are applicable to the fractured reservoirs, especially when the fluid is a Bingham plastic. In this work, the model proposed by P. P. Iassonov and I. A. Beresnev (2003) for flow under exposure of elastic wave in nonfractured porous media is considered and used for development of a new model of steady state flow of a Bingham plastic fluid in fractured reservoirs. The Kazemi's “block and fracture” model assuming negligible vertical permeability in blocks is considered for modeling. In addition, two-phase flow behavior under elastic wave in fractured system is investigated. The results showed that, at higher pressure gradients, vibration amplitude cannot highly influence the fluid percolation, in contrast at lower pressure gradients, the fluid flow through the fractured porous media can considerably be improved by increasing vibration amplitude. Also, it has been found that in two-phase flow systems, wave can increase the produced oil-water ratio in the fractured media. The results of this study can be applied to the fractured reservoir simulations and can be a path breaking to the future studies on the prediction of flow enhancement under elastic wave in the fractured reservoirs.