Wettability Of Matrix Research Articles

Dynamic Interactions between Matrix and Fracture during Miscible Gravity Drainage in Naturally Fractured Reservoirs

Miscible gas or solvent injection has received increasing attention in recent years as an efficient method for improving oil recovery from naturally fractured reservoirs. Because of the large permeability difference between fracture and matrix, the success of this method depends to a large extent on the degree of enhancement of the mass-exchange rate between the solvent flowing through the fracture and the oil residing in the matrix. In this study, a series of experiments were conducted to investigate the mass-transfer rate between the fracture and the matrix when a solvent is injected through the fracture system. The effects of injection rate, fracture aperture, water saturation, matrix wettability, and fluid properties on the recovery behavior were examined. The interaction between the matrix and fracture was visualized for solvent injection by means of computed tomography (CT) scanning, which can be used to validate theories of enhanced transfer in fractured media. The results obtained with a simulatio...

Analytical Estimation of Water-Oil Relative Permeabilities through Fractures

Modeling multiphase flow through fractures is a key issue for understanding flow mechanism and performance prediction of fractured petroleum reservoirs, geothermal reservoirs, underground aquifers and carbon-dioxide sequestration. One of the most challenging subjects in modeling of fractured petroleum reservoirs is quantifying fluids competition for flow in fracture network (relative permeability curves). Unfortunately, there is no standard technique for experimental measurement of relative permeabilities through fractures and the existing methods are very expensive, time consuming and erroneous. Although, several formulations were presented to calculate fracture relative permeability curves in the form of linear and power functions of flowing fluids saturation, it is still unclear what form of relative permeability curves must be used for proper modeling of flow through fractures and consequently accurate reservoir simulation. Basically, the classic linear relative permeability (X-type) curves are used in almost all of reservoir simulators. In this work, basic fluid flow equations are combined to develop a new simple analytical model for water-oil two phase flow in a single fracture. The model gives rise to simple analytic formulations for fracture relative permeabilities. The model explicitly proves that water-oil relative permeabilities in fracture network are functions of fluids saturation, viscosity ratio, fluids density, inclination of fracture plane from horizon, pressure gradient along fracture and rock matrix wettability, however they were considered to be only functions of saturations in the classic X-type and power (Corey [35] and Honarpour et al. [28, 29]) models. Eventually, validity of the proposed formulations is checked against literature experimental data. The proposed fracture relative permeability functions have several advantages over the existing ones. Firstly, they are explicit functions of the parameters which are known for each of simulation computational cells or easy to measure in laboratory. It is also the first model that takes gravity effects and wettability of fracture walls into consideration and individually developed for water and oil-wet systems. Furthermore, the newly developed formulations are simple, efficient and accurate. Thus, they are recommended for implementation in dual and multiple continuum commercial reservoir simulators.

Pore-Scale Investigation of Phase Distribution and Residual-Oil Development During Secondary and Tertiary Solvent Injection

Summary Flow of three phases, of which one is miscible with another, in porous media may commonly be encountered during enhanced-oil-recovery (EOR) applications in oil reservoirs. Typical examples include solvent (miscible-gas) injection alternated with water and coinjection or alternate injection of steam (or hot water) and solvent in heavy-oil/bitumen reservoirs. Oil, water, and solvent flow together under immiscible (water/oil and water/solvent) and miscible (oil/solvent) conditions at the same time, and the distribution of phases and removal of residual oil in those types of processes depend on many parameters. This paper reports microscale experimental investigations on this complex flow process and provides an extensive parametric analysis on the microscopic displacement efficiency of oil recovery using miscible solvent. For this purpose, micromodels created by use of a replica of sandstones were used. Waterflood residual-oil displacement requires contact of the injected solvent with the blocked oil. The efficiency of this process depends on several parameters, including matrix wettability, oil viscosity, initial water saturation, and reservoir heterogeneity. On the other hand, the sequence of injection of solvent and water is considered as another parameter by which oil recovery can be affected significantly. The results of the micromodel-visualization experiments showed that injection of solvent before the introduction of any water to the reservoir can increase the recovery factor significantly. Existence of the water phase in the reservoir creates capillary barriers that prevent oil/solvent contact. The matrix wettability and oil viscosity were observed to be critically important to the amount of oil recovery.

Structure Property Correlation of Al Based MMC Reinforced with Cu Coated Rice Husk Ash SiO2 Particles

Metal coated reinforcements in metal matrix composites are advancing in the field of engineering to produce high quality composites by liquid metallurgy route due to improvement of wettability between reinforcement and matrix. In the present study, a comparative analysis of mechanical properties was carried out on Al based composite (with varying wt% of Mg) reinforced with uncoated and Cu coated RHA (rice husk ash) SiO2 particles. Tensile testing results of the composites indicate that UTS and YS of the composites reinforced with Cu coated SiO2 particles was significantly higher than uncoated particles. The Cu coated SiO2 particles act as a protrusion over the matrix carrying the major portion of the applied tensile load and thus composites are protected from failure. When Mg reaches 1.5 wt%, wettability of matrix with reinforcement is maximum, leading to the formation of hard compounds such as CuO, CuAlO2 and Al2CuMg at interface. This enhances interfacial bonding strength as well as load transfer from matrix to reinforcement, which leads to higher tensile strength along with ductility.

Multiscale Simulation of WAG Flooding in Naturally Fractured Reservoirs

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 164837, ’Multiscale Simulation of WAG Flooding in Naturally Fractured Reservoirs,’ by Mohamed Ahmed Elfeel, Adnan Al-Dhahli, Sebastian Geiger, SPE, and Marinus I.J. van Dijke, Heriot-Watt University, prepared for the 2013 EAGE Annual Conference and Exhibition/SPE Europec, London, 10-13 June. The paper has not been peer reviewed. Naturally fractured reservoirs (NFRs) contain a significant amount of remaining petroleum reserves and are now being considered for water-alternating-gas (WAG) flooding as secondary or tertiary recovery. The authors face the challenge of reservoir simulation of WAG by building models at various scales, starting with pore scale and expanding to an intermediate scale and then to reservoir scale. They show how pore-network modeling and fine-grid modeling where the fractures and matrix are represented explicitly can be used to increase the accuracy of numerical simulations at field scale. Introduction A significant portion of the world’s remaining petroleum resources is located in NFRs, including supergiant fields in the Middle East. A detailed understanding of the recovery processes involved in extracting hydrocarbons from NFRs by use of enhanced-oil-recovery techniques is key to increasing ultimate recovery for such reservoirs. Waterflooding has been used with various degrees of success in NFRs. For unfavorable (i.e., mixed- to oil-wet) matrix wettability, however, waterflooding can be ineffective. Gas/oil gravity drainage (GOGD) provides an important drive mechanism that can be effective irrespective of the rock wettability. In NFRs, fractures increase the exposure of the injected gas to oil in reservoir rock, which renders GOGD more effective than it is in unfractured reservoirs. Consequently, gas injection has been applied in many NFRs. However, because the gas mobility is very high compared with that of water and oil, so is the risk of bypassed oil and gravity override, which can lead to very early gas breakthrough. This is particularly true for NFRs. WAG flooding combines the merits of the two injection fluids on macroscopic and microscopic scales while stabilizing the injection front, delaying breakthroughs, and, therefore, leading to increased oil recovery compared with continuous water or gas injection. Reservoir simulation of WAG injection is very challenging because a representative three-phase saturation model is required to predict relative permeability and capillary pressure as water and gas saturations increase and decrease alternately. Three-phase relative permeability and capillary pressure data are extremely difficult to measure experimentally. Even if experimental evaluation becomes feasible, an infinite number of saturation paths can occur in the reservoir. This necessitates the use of empirical, or interpolation, models to predict three-phase relative permeability and capillary pressure from two-phase experiments. In NFRs, capillary pressure and relative permeability functions have a major effect on fluid exchange between matrix blocks and fractures. Predicting the effects of the interplay of viscous, capillary, and gravity forces is challenging because fluid flow is viscous-dominated in the fractures while transfer between fractures and matrix blocks is dominated by capillary and gravity forces. Because most of the oil is contained inside the matrix, capillary and gravity forces can be more important in NFRs than in conventional reservoirs.

Experimental Investigation of Matrix Wettability Effects on Water Imbibition in Fractured Artificial Porous Media

Spontaneous water imbibition into the matrix blocks is known as the main mechanism for increased oil recovery from naturally fractured oil reservoirs. The rate of oil recovery and its ultimate value is mostly affected by wettability of the rocks and their pore structure. Oil viscosity also greatly influences the rate of oil recovery.A novel experimental model was utilized to study the imbibition mechanism under different wettability conditions. Matrix blocks made from different grain types and size distributions of glass beads were saturated with two different types of synthetic oil, to mimic the oil-saturated matrixes. The wetting characteristic of the models used in this study were altered by a standard chemical treatment process. Wettability, grain type and size distribution, as well as oleic phase properties, were changed to find the effect of these parameters on oil recovery efficiency.The results revealed that presence of a small fraction of oil-wet grains drastically affects oil recovery by capillary imbibition. A criterion was obtained to describe the effects of wetting property of the matrix blocks on oil recovery efficiency by capillary imbibition. The effect of gravity force, resulting from the density difference between oil in the matrix block and the water in the fracture, was also analyzed using inverse Bond number (NB−1). Application of this dimensionless number was found to be limited by the height of the porous medium. The results also confirm that oil production rate during imbibitions is greatly influenced by oil viscosity.

Effects of the imbibitional flow of steam on oil recovery from carbonate reservoirs

Carbonate reservoirs contain over 90% of oil within an extremely tight matrix and are usually oil-wet, which makes them unfavorable for oil production. During water injection, water does not imbibe into the matrix, but flows preferentially through the fractures, resulting in very low oil recoveries. It is proposed that steam or hot water is injected, inducing a wettability change and rendering the matrix water-wet. Then, water can move into the matrix by capillary imbibition. From this perspective, it is crucial to analyze the contributions of conductive and convective heat transfer during steam injection.The mechanism of wettability changes is accounted for when steam is injected into carbonate reservoirs. The effect of strong capillary pressure in a tight matrix on the oil recovery is also examined. The purpose of this study is to evaluate the rate of conduction and convection and to determine optimum conditions that maximize heat transfer and wettability alteration in the tight matrix. An analytical solution and numerical results were compared for heat conduction within the matrix during steam injection. Investigations were also performed to determine the optimum injection time, steam injection pressure and steam quality required to make the carbonate matrix water-wet and maximize oil recovery. The results from this study show that convectional flow might be the most important heat-transfer mechanism to shorten the matrix wettability converting time. Based on analysis of the thermal process, an optimum steam injection strategy can be designed for a given matrix permeability and fracture spacing.

EXPERIMENTAL INVESTIGATION OF WETTABILITY EFFECT AND DRAINAGE RATE ON TERTIARY OIL RECOVERY FROM FRACTURED MEDIA

Vertical displacement of oil by gas is one of the most efficient methods for oil recovery from naturally fractured reservoirs. Unlike the homogeneous media, the ultimate oil recovery by gravity drainage in fractured media is more dependent on the production rate. Hence finding the optimum production rate for more oil recovery with respect to the properties of media seems to be essential. In this work, unconsolidated packed models of cylindrical geometry surrounded by fractures were utilized to perform a series of flow visualization experiments during which the contribution of different parameters such as the extent of matrix wettability and the withdrawal rate were studied. In addition, mutual effects of wettability and production rate on tertiary oil recovery efficiency through controlled and free fall gravity drainage processes were also investigated. Experimental results obtained from tertiary gravity drainage experiments demonstrated that just before gas breakthrough, lower withdrawal rates facilitate the tertiary oil recovery under the film flow mechanism, which leads to a higher ultimate recovery factor. However, after gas breakthrough, monitoring oil recovery by gravity drainage showed that higher production rates recovered more oil. Furthermore, under tertiary recovery processes in low-production cases, oil-wet systems achieved higher recovery factors, while at high withdrawal rates, more oil was recovered for 50% oil-wet media.

Water mixing during spontaneous imbibition at different boundary and wettability conditions

The displacement of connate water by spontaneously imbibing water was determined for chalk core plugs at different wettability conditions. The development and distribution of both aqueous phases were determined by nuclear tracer imaging (NTI) to obtain 1D fluid saturation profiles. Two boundary geometries were applied to investigate the displacement and water mixing during strictly counter-current imbibition (One-End-Open: OEO) and during both co- and counter-current imbibition (Two-Ends-Open: TEO). The connate water was displaced from the open end face exposed to the invading water phase for both boundary geometries and all wettabilities, but the rate and displacement efficiency were highly influenced by the matrix wettability. The average connate water saturation did not change during spontaneous imbibition, but its distribution in the core plug changed as the invading water phase saturation increased in all tests. A connate water bank formed at strongly water-wet conditions for both boundary conditions. In both cases the connate water accumulation constituted the entire fraction of water saturation at these positions, with little or no mixing between the connate and invading water phase during the displacement. At the end of the test the connate water accumulated in the middle of the core at TEO imbibition and at the closed end face during OEO. At weakly water-wet conditions the connate water banking was reduced and the mixing of waters was increased. The invading water displacement of the connate water was also reduced, and the aqueous phases mixed by diffusion when redistribution of fluids stopped.

Wettability Impacts on Oil Displacement in Large Fractured Carbonate Blocks

Two-dimensional imaging of water and oil saturations during waterfloods in fractured carbonate rock models was obtained using nuclear tracer imaging and magnetic resonance imaging. Large outcrop chalk and limestone blocks were aged in crude oil to obtain wetting conditions from strongly water-wet to weakly oil-wet. The change in the oil recovery mechanism as the wettability shifted was investigated with and without the presence of fractures. Visualization of local, in situ fluid saturations during waterfloods improved the interpretation of the displacement process and oil recovery mechanisms. Experimental results demonstrate how fractures determine the displacement pattern differently depending on the matrix wettability conditions during waterfloods. At strongly water-wet conditions, the fractures had a minor impact on the ultimate recovery but significantly changed the progression of the water front compared to the unfractured case. At less water-wet or oil-wet conditions, capillary imbibition of water from the fracture to the matrix was reduced and fractures had a major impact on the ultimate recovery and water breakthrough time.

Clarifications on Oil/Heavy Oil Recovery Under Ultrasonic Radiation Through Core and 2D Visualization Experiments

Abstract Our previous research on the effects of ultrasonic waves on oil recovery conducted at the University of Alberta had shown that capillarity and interfacial tension (IFT) might be responsible for the observed improvements in incremental oil recovery. Although the results seem encouraging, questions about the mechanism and effective parameters causing additional recovery still remain. To analyze the influence of parameters other than IFT and capillary forces, we conducted capillary imbibition experiments on cylindrical Berea sandstone core samples under ultrasonic radiation, and the results are presented in this paper. Through this experimental scheme, we focused on:the effect of initial water saturation for rocks with different wettability;oil viscosity; andmatrix wettability. The cores were placed into imbibition cells where they were contacted with an aqueous phase. Every experiment was conducted with and without ultrasonic radiation for comparison. Different intensities of ultrasonic waves were tested as well. To investigate the acoustic interaction between rock and fluid, we performed certain visualization experiments. We used 2D glass bead models to clarify the effects of ultrasonic waves on the oil displacement process for different oil viscosities and matrix wettability through comparative analysis. The qualitative and quantitative observations and analyses presented are expected to provide additional understanding regarding investigations in the use of in situ recovery of oil/heavy oil, as well as surface extraction. Introduction Acoustic energy was considered as one of the unconventional EOR methods to replace or to be applied with conventional ones. Studies have been conducted to understand the effects of acoustic energy on oil recovery over the last four decades. Duhon and Campbell(1) performed waterflood tests of cores with ultrasonic energy and showed that the ultrasonic energy improved the oil recovery and displacement efficiency in the cores. Beresnev and Johnson(2) performed a critical analysis of the work done in this area up to the early 1990s and provided a comprehensive review of the seismic and ultrasonic stimulation studies. They concluded that the elastic wave and seismic excitations of porous media affect permeability and production rates in most cases Kuznetsov et al.(3) reviewed seismic techniques for enhanced oil recovery and observed an increase in oil/water relative permeabilities and also oil recovery after elastic vibration. They concluded that this increase is due to fines removal by vibration. Roberts et al.(4) applied mechanical stresses to rock samples which were placed inside a core holder and observed changes in permeability and an increase in wettability in the non-wetting phase. There also exists field-scale applications of sound waves of different characteristics. Spanos et al.(5) observed improvements in waterflooding and injectivity when pressure pulses were applied by a hydraulically-operated tool. Westermark et al.(6) applied a complex system of vibration tools in the field and observed an improvement in permeability at certain intensities and up to a 20% increase in the oil production rate. Zhu et al.(7) documented the results of the application of a special downhole vibration tool in several oil fields in China, pointing out that sand content, water content, viscosity and density of oil decreased after treatment.

Primary and Secondary Oil Recovery From Different-Wettability Rocks by Countercurrent Diffusion and Spontaneous Imbibition

Summary This study investigates optimum matrix-oil-recovery strategies in naturally fractured reservoirs (NFRs) for different wettabilities and rock types. We compare the recovery efficiencies of two cases: (a) primary countercurrent spontaneous imbibition followed by the diffusion of a miscible phase (secondary recovery) and (b) primary diffusion of miscible fluid without preflush of matrix by spontaneous imbibition. For these recovery strategies, the effects of the matrix shape factor, matrix wettability, and type of miscible displacing phase on the rate of recovery and development of residual-oil saturation were clarified experimentally. Cylindrical Berea-sandstone and Indiana-limestone 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. The external surface except one end was coated with epoxy. Static imbibition experiments were conducted on vertically situated samples in which the fractures were at the bottom and matrix/fracture interaction took place in an upward direction. Mineral oil and crude oil were used as oleic phases. Brine was selected as aqueous phase for the primary spontaneous-imbibition recovery. For primary- and secondary-miscible-displacement experiments, n-heptane was used as solvent. Wettability of water-wet Berea-sandstone samples was altered by aging to observe its effects on the dynamics of spontaneous countercurrent imbibition and diffusion. Parametric analyses were performed for the appraisal of the secondary-and tertiary-recovery potential of NFRs by immiscible-and miscible-fluid injections. The optimal recovery strategies (recovery rate, recovery time, and ultimate recovery) for different rock properties were identified and classified. In water-wet cases, starting the recovery with capillary imbibition followed by diffusion was found to be the optimal way (i.e., both effective and efficient). For limestone or aged-sandstone samples, starting the recovery by diffusion yielded a faster recovery rate and higher ultimate recovery.

Efficiency of diffusion controlled miscible displacement in fractured porous media

Experiments were performed to study the diffusion process between matrix and fracture while there is flow in fracture. 2-inch diameter and 6-inch length Berea sandstone and Indiana limestone samples were cut cylindrically. An artificial fracture spanning between injection and production ends was created and the sample was coated with heat-shrinkable teflon tube. A miscible solvent (heptane) was injected from one end of the core saturated with oil at a constant rate. The effects of (a) oil type (mineral oil and kerosene), (b) injection rates, (c) orientation of the core, (d) matrix wettability, (e) core type (a sandstone and a limestone), and (f) amount of water in matrix on the oil recovery performance were examined. The process efficiency in terms of the time required for the recovery as well as the amount of solvent injected was also investigated. It is expected that the experimental results will be useful in deriving the matrix–fracture transfer function by diffusion that is controlled by the flow rate, matrix and fluid properties.

Influence of wettability and surface activity on release behavior of hydrophilic substances from lipid matrices

The aim of this study was to investigate the role of matrix and drug properties on controlled release from triglyceride matrices. Mini-cylinders of 2 mm diameter, 2.2 mm height and 7 mg weight were produced by compression of lipid powder obtained by using a polyethylene glycol (PEG) co-lyophilization method for the model substances lysozyme and FITC-dextran (M w 4000 Da). Lysozyme was released with decreasing velocity from glyceryl trilaurate, -myristate, -palmitate and -stearate for more than 14 months. Release correlated well with triglyceride lipophilicity defined by the chain length of the fatty acids. Contact angle measurements and the analysis of buffer penetration visualized by confocal microscopy emphasized the role of matrix wettability as a prerequisite for release. A comparison with FITC-dextran revealed that the protein itself enhances matrix wettability and hence its release due to its surface active properties. FITC-dextran remained trapped within the matrix only to be released at lower compression force or after the addition of surfactant. Protein added externally to the release buffer at 0.1% (w/v) was not efficient in lowering the contact angle and increasing the release rate of FITC-dextran. Tween®20 and 81 could be used in different concentrations (0.1, 0.01 and 0.001% (w/v)) to alter lysozyme and FITC-dextran release profiles: resulting release rates showed a close dependence on the contact angle of the respective release medium and triglyceride matrix material. However, both Tweens® seem to act not only by reducing the release medium contact angle but also by moderately affecting interparticulate adhesion of the matrix material.

Effects of SiC particulates on the fatigue behaviour of an Al-alloy matrix composite

In this study, the fatigue behaviour of aluminium matrix–silicon carbide (SiC) particulate reinforced composite specimens was investigated in comparison to the matrix aluminium alloy containing 12 wt% Si. Three different weight percentages of SiC particulates: 5, 10, and 15 in the size range of 40–60 μm were injected into the melt. Mg was also added to improve the wettability of Al-alloy matrix over SiC particulates resulting in better interfacial bonding. Test specimens were machined from squeeze casting billets. Hardness, bending and fatigue tests indicated that reinforcing the Al-alloy matrix with SiC particulates improved the hardness, flexural strength and fatigue resistance with increasing content of SiC particulates. Stress levels yielding less than 10 7 cycles to fracture were applied. Cracks initiated at the debonded particulate–matrix interface and/or by the cracking of the coarse particulates. SiC particulates improved fatigue resistance mainly by acting as barriers to cracks and/or deflecting the growth plane of cracks resulting in decreased crack propagation rates.

Gas and oil production from waterflood residual oil: effects of wettability and oil spreading characteristics

In the depressurisation of reservoirs already produced to waterflooded residual oil, solution gas is released when the reservoir pressure drops to below the bubble point. This gas becomes mobilised when the critical gas saturation has been reached. Additionally, the oil itself can become mobile from its residual state and can also be produced under suitable physical conditions. The critical gas saturation, the rate of saturation change, and the gas saturation remaining at the end of the depressurisation process (unrecoverable gas) are important parameters in determining the overall economic performance when depressurising a reservoir. In this, and previous work, we are demonstrating that these quantities depend additionally upon other factors which affect the fluid distribution and the rate of gas generation, particularly the surface and interfacial properties. For instance, earlier visual experiments in glass micromodels suggested that wettability and oil spreading coefficient could substantially influence both the value of the critical gas saturation and the growth pattern for the developing gas bubbles, and thus the gas flow. In order to confirm these observations and to provide quantitative data, further experiments in large sintered packs, with different matrix wettability and with oils having different spreading coefficients (e.g. oil spreading onto a gas–water interface), have been carried out and are reported here. These new experiments show that the magnitude of the critical gas saturation for a water-wet system is about the same irrespective of whether the oil is spreading or non-spreading, but it is much higher than for the oil-wet case. In addition, oil is also produced but the rate of production is dependent upon the rock wettability and the oil characteristics. We find that in a water-wet medium, for spreading oils, the physical form of the oil becomes transformed from being immobile ganglia into mobile oil films, which can then be transported by the gas. For non-spreading oils, oil has to be pushed out by the gas as discontinuous ganglia so less is oil produced. In contrast, in an oil-wet system, the oil phase already exists as a continuous film on the surface of the solid so that the generation of gas effectively expands the oil phase, enabling the oil to be produced in larger quantities even at lower gas saturations. These new experiments give further evidence that rock wettability has an important influence on the performance of gas production from residual oil. Additionally, significant amounts of oil may be recovered after waterflooding from the residual condition, which could have a beneficial impact on the economics of the depressurisation.

Dimensionless groups for three-phase gravity drainage flow in porous media

The downward displacement of oil by gas (either through gas cap expansion or by gas injection) at the crest of the reservoir is an attractive method of oil recovery. The drainage of oil under gravity forces is a potentially efficient method as it can reduce the remaining oil saturation to below that obtained after waterflooding. This paper describes a series of experiments of gas invasion under gravity-dominated conditions with special attention to the effects of wettability and water saturation on three-phase flow. The experiments were performed in bead-pack models by spontaneous gas invasion at both low and high water saturations with a spreading oil. Different oil recovery rates were observed depending on the wettability of the beads and initial water saturation. At irreducible water saturation, the process appeared to be less efficient for the oil-wet conditions, while similar oil recoveries are observed for both oil-wet and water-wet media at residual oil saturation. Different recovery rates occur with different fluid morphology, which depend on the matrix wettability and the balance between gravity, viscous and capillary forces. The results have been analysed using dimensionless groups. The Bond ( N B) and capillary numbers ( N C) were modified to include the 3-phase effects of gas, oil and water. However, for these cases the Bond and capillary numbers alone were insufficient to fully describe the dynamics of oil recovery by gravity drainage. Therefore, a new dimensionless group combining the effects of gravity and viscous forces to capillary forces was defined as: N= N B+ A( μ d/ μ g) N C, where A is a scaling factor (in all our experiments A=−17225) and ( μ d/ μ g) is the viscosity ratio between the displaced and displacing phase. A linear relationship was found between this new group and the total recovery for all the scenarios tested. The slope was approximately 40 for three cases, i.e., water-wet case at irreducible water saturation, and water-wet and oil-wet cases at residual oil saturation. The oil-wet case at irreducible water saturation has a larger slope, probably due to the blocking effect of water. These experimental results may be used as a benchmark to test theoretical models of three-phase flow under gravity dominated conditions. The new dimensionless group should improve the understanding of the pore scale mechanisms so that these processes can be included in the development of network models and in the processes of upscaling laboratory results.

Measurement and modeling of hydraulic characteristics of unsaturated porous media with mixed wettability

The spatial distribution of the solid grain's wettability strongly influences the phase-interconnection, phase-flow and solute transport in unsaturated porous media. Non-uniform wetting conditions can arise in soils and aquifers from natural or anthropogenic impacts. In this study, a water–air system in porous media consisting of several types of granular materials is considered. A conceptual model for pressure-wise estimation of water saturation and relative unsaturated hydraulic conductivity of such materials is proposed. The model uses the boundary water retention curves and corresponding wetting angles of the pure components of the mixture as the input parameters. The approach is based on simplified statistical and geometrical assumptions for describing the mixed porous material and its capillary behavior. In the experimental part of this study, three materials with different wetting angles (quartz sand, silanized quartz and teflon grains) were used both as pure and as homogeneously mixed packings to conduct experiments with a water–air system in short columns under well-controlled laboratory conditions. The hydraulic characteristics were determined for packings with various mixing ratios. The non-uniform matrix wettability was found to strongly influence the water retention behavior of the packings, whereas its impact on the water-saturation-dependent hydraulic conductivity was weak. The measured data are compared to model predictions. The results show that the model is capable of providing good qualitative estimates of both the boundary water retention curves and the curves of the relative hydraulic conductivity for all investigated materials.

Functional Imaging with Chemically Amplified Resists and Organic Molecules

Chemically amplified resists were tested for preparing universal templates to bind various organic species in micron-scale patterns (functional images). UV exposure and heating of a poly(di-tert-butyl fumarate-co-styrene):onium salt resist produced alternating areas of nonpolar ester and polar acid/anhydride polymers. Various compounds that were fluorescent dyes or amines could then be placed selectively either into or onto exposed or nonexposed areas, according to the nature of solvents and binding species. The ease and extent of immobilization were found to depend on (i) resist composition, (ii) matrix wettability and permeability by a solvent, and (iii) covalent, ionic, dipole−dipole, or other sorbate−matrix binding interactions.

Effects of pore structure and wettability on the electrical resistivity of partially saturated rocks—A network study

A network model of porous media is used to assess the effects of pore structure and matrix wettability on the resistivity of partially saturated rocks. Our focus is the magnitude of the saturation exponent n from Archie's law and the hysteresis in resistivity between drainage and imbibition cycles. Wettability is found to have the dominant effect on resistivity. The network model is used to investigate the role of a wetting film in water‐wet systems, and the behavior of oil‐wet systems. In the presence of a thin wetting film in water‐wet systems, the observed variation in n with saturation is reduced significantly resulting in lower n values and reduced hysteresis. This is attributed to the electrical continuity provided by the film at low‐water saturation between otherwise physically isolated portions of water. Oil‐wet systems, when compared with the water‐wet systems, are found to have higher n values. In addition, the oil‐wet systems exhibit a different form of hysteresis and more pronounced hysteresis. These differences in the resistivity response are attributed to differences in the pore scale distribution of water. The effects of pore structure are assessed by varying pore size distribution and standard deviation of the pore size distribution and considering networks with pore size correlation. The most significant parameter is found to be the pore size correlation. When the sizes of the neighboring pores of the network are correlated positively, the magnitude of n and hysteresis are reduced substantially in both the water‐wet and oil‐wet systems. This is attributed to higher pore accessibility in the correlated networks. The results of the present study emphasize the importance of conducting laboratory measurements on core samples with reservoir fluids and wettability that is representative of the reservoir. Hysteresis in resistivity can be present, particularly in oil‐wet systems, and should be considered in the interpretation of resistivity data.