Two-dimensional Glass Micromodel Research Articles

Effects of reservoir rock pore geometries and ultrasonic parameters on the removal of asphaltene deposition under ultrasonic waves

Asphaltene deposition around the wellbore is a major cause of formation damage, especially in heavy oil reservoirs Ultrasonic stimulation, rather than chemical injection, is thought to be a more cost-effective and environmentally friendly means of removing asphaltene deposition. However, it seems to be unclear how crucial features like reservoir pore geometries and ultrasonic parameters affect this ultrasound treatment.In this work, five two-dimensional glass micromodels with different pore geometries were designed to assess the impact of pore geometries on the ultrasonic removal of asphaltene deposition. Experiments were undertaken in an ultrasound bath at a set frequency (20 kHz) and adjustable powers (100–1000 W). Direct image analysis before, during and after sonication was used to assess the impact of pore geometry and a change in ultrasonic parameter on the removal of asphaltene deposition. The effectiveness of ultrasound treatment at various sonication periods were found to be reliant on the pore geometries of the individual micromodels. For micromodels with throat sizes 300 µm and pore shapes as circle, square and triangle, an increase in ultrasonic power from 400 to 1000 W resulted in an increase in the percentage of removed asphaltene deposition after 2 h from 12.6 to 14.7, 11.5 to 14.63, and 5.8 to 7.1 percent, respectively.

Experimental study of the influence of oil-wet calcite cements on oil migration and implications for clastic reservoirs

The influence of oil-wet calcite cements on oil migration in clastic reservoirs is of significant interest in the field of petroleum exploration. However, the microscopic migration of oil in microscopic pore spaces with oil-wet calcite cements has not been directly observed. Microscopic observations of oil migration were conducted in a glass micromodel at normal temperature and pressure to investigate the influence mechanism of oil-wet calcite cements on oil migration in pore spaces. The calcites were precipitated as cements prior to the oil migration. A two-dimensional glass micromodel with two interconnected spaces with the same pore throat structures was used in the experimental study. A new method to create firmly adhering calcites was used to precipitate equal amounts of calcites in the two interconnected spaces. The oil migration was recorded in real-time under a microscope throughout the experiment. The experimental results show that oil migration occurs faster in spaces with than without oil-wet calcites. During the oil migration in the pore-throat spaces, the oil migrates towards the surfaces of the oil-wet calcites when the oil is in contact with the calcites. The presence of oil-wet calcites significantly reduces the oil breakthrough pressure. The electrostatic attraction between the carboxylic groups and calcites and the intermolecular forces between the carboxylic groups and organic molecules in the oil cause the oil migration towards the surfaces of the oil-wet calcites. The experimental results indicate that oil preferentially migrates into clastic reservoirs that possess appropriate amounts of oil-wet calcite cements precipitated prior to oil emplacement.

Simultaneous measurement of water permeability and methane hydrate pore habit using a two-dimensional glass micromodel

In this study, we developed an in situ chamber to measure water permeability as a function of the methane hydrate (MH) habit in pore space using a two-dimensional glass micromodel by adding a methane-dissolved water source unit to prevent MH dissociation. This unit enabled us to adjust the amount of methane dissolved in the water by controlling the pressure and temperature. We simultaneously observed MH crystallization behavior and measured the water permeability of the porous media. The growth rate of MH and the pore habit formation changed with subcooling, ΔT. As ΔT increased, the shape of the pattern transformed from a hexagonal plate to a dendrite and hexagonal plate, and finally, to a dendrite. The glass pillar played a role in inhibiting the growth of dendritic patterns. The plugging process of the porous media following MH formation was also observed. We compared our results with various water permeability models of MH sediments and found that the nonempirical relative permeability (NRP) models showed relatively good agreement. This was likely because the NRP models enhanced the effect of the gas phase. However, a gap remains between the NRP model predictions and our experimental results. On the other hand, there was no possibility of agreement other than the NRP models because the gas phase was not included in the equation.

Pore Scale Visualization of Low Salinity Water Flooding as an Enhanced Oil Recovery Method

The controlling mechanisms behind low salinity water flooding (LSWF) as an Enhanced Oil Recovery (EOR) method are not well understood. So far, a limited number of researchers have tried to provide visual and direct evidence of the underlying mechanisms behind the LS effect. In this paper, to investigate the dynamics of displacement throughout LSWF, clean and clay-coated two-dimensional glass micromodels were used, with the wettability status set at both water-wet and oil-wet conditions. Hence, pore-scale displacement mechanisms in the presence and absence of clay, as well as in the drainage and imbibition-dominated two-phase flow, were studied. In water-wet systems, in the absence and presence of clays, LSW hindered “snap-off” perhaps due to the development of a viscoelastic water–oil interface. The wettability alteration toward more water wetness was observed for oil-wet systems. The observations are discussed in terms of the expansion of the Electrical Double Layer (EDL). Fines migration played an insig...

An experimental study of the performance of low-molecular weight polymer for enhanced heavy oil recovery in a heterogeneous media

The goal of enhanced oil recovery is to improve sweep efficiency in the reservoir by the injection of artificial materials in order to reduce the trapped oil saturation. In this study, the application of an anionic polyacrylamide polymer was investigated for heavy oil recovery based on the results of rheological measurements and oil recovery experiments. The properties of the polymer solution were interpreted by the use of well-known rheological models and oil recovery experiments were performed using a heterogeneous two-dimensional glass micromodel saturated with heavy oil of 270 cP. To provide a better understanding of the microscopic efficiency of the process, analysis of continuously provided pictures during the experiments by the use of image processing technique was performed. Rheological results combined with microscopic observations revealed that the non-Newtonian behavior of the solution enhances the sweep efficiency of the both pore throats and pore bodies. Macroscopic observations showed the ultimate oil recovery of 56% and dramatic improvement in breakthrough time during polymer flood in comparison to water flood. In addition, the microscopic pictures disclosed that the pulling effect and stripping mechanisms are responsible mechanisms for the high microscopic sweep efficiency during polymer flooding.

Experimental studying of pore morphology and wettability effects on microscopic and macroscopic displacement efficiency of polymer flooding

Pore morphology and wettability of a porous medium have dominating effects on microscopic displacement efficiency, and consequently on the ultimate oil recovery. To provide a better understanding of the effects of these parameters on microscopic displacement mechanisms and macroscopic performance of a polymer flood process, a comprehensive experimental study was conducted using five two-dimensional glass micromodels. A combination of three wettability conditions and five different pore structures was used in this study. The selected scenarios include four homogeneous synthetic pore networks at water-, mixed- and oil-wet conditions. A random network that represents the pore space in Berea sandstone was also used for further investigation. Image processing technique was applied to analyze and compare displacement mechanisms and displacement process efficiency in each experiment. Microscopic mechanisms, such as oil and polymer solution trapping, configuration of wetting and non-wetting phases, flow of continuous and discontinuous strings of polymer solution, polymer solution snap-off, distorted flow of polymer solution, emulsion formation, and microscopic pore-to-pore sweep of oil phase were observed and monitored in conducted experiments. Experimental results showed that water- and mixed-wet media generally have comparable and higher recoveries in contrast with oil-wet media. Moreover, the results confirmed a significant dependency on the pore structure and wettability of the media on both displacement mechanisms as well as oil recoveries. This experimental study illustrates the successful application of glass micromodel techniques for studying enhanced oil recovery (EOR) processes in a five-spot pattern, and also provides a useful reference for understanding the displacement mechanisms involved in a polymer flood process at different pore morphologies and wettabilities of porous media.

Study of Microscopic and Macroscopic Displacement Behaviors of Polymer Solution in Water-Wet and Oil-Wet Media

Performance of a polymer flood process requires the knowledge of rheological behavior of the polymer solution and reservoir properties such as rock wettability. To provide a better understanding of effects of polymer chemistry and wettability on the performance of a polymer flood process, a comprehensive experimental study was conducted using a two-dimensional glass micromodel. A series of water and polymer flood processes were carried out at different polymer molecular weights, degrees of polymer hydrolysis, and polymer concentrations in both water-wet and oil-wet systems. Image processing technique was applied to analyze and compare microscopic and macroscopic displacement behaviors of polymer solution in each experiment. From micro-scale observations, the configuration of connate water film, polymer solution trapping, flow of continuous and discontinuous strings of polymer solution, piston-type displacement of oil, snap-off of polymer solution, distorted flow of polymer solution, emulsion formation, and microscopic pore-to-pore sweep of oil phase were observed and analyzed in the strongly oil-wet and water-wet media. Rheological experiments showed that a higher polymer molecular weight, degree of hydrolysis, and concentration result in a higher apparent viscosity for polymer solution and lower oil–polymer viscosity ratio. It is also shown that these parameters have different impacts on the oil recovery in different wettabilities. Moreover, a water-wet medium generally had higher recovery in contrast with an oil-wet medium. This experimental study illustrates the successful application of glass micromodel techniques for studying enhanced oil recovery (EOR) processes in five-spot pattern and provides a useful reference for understanding the displacement behaviors in a typical polymer flood process.

Vibration-induced mobilization of trapped oil ganglia in porous media: Experimental validation of a capillary-physics mechanism

The development of methods for mobilizing residual organic liquids trapped in porous media is becoming increasingly important as world demand for oil increases and because of the need to remediate aquifers degraded by slow-dissolving organic contaminants. Low-frequency elastic wave stimulation is one such technique, but until recently the lack of a mechanistic understanding of the effects of vibration on mobilization of oil ganglia has prevented the method from being applied predictably in the field. Recently, a simple capillary-physics mechanism has been developed to explain vibration-induced mobilization of a trapped non-wetting organic phase in porous media. Specific predictions that follow from this hypothesized mechanism are that vibrations will be most effective in mobilizing trapped oil when the acceleration amplitude is within an optimal range of values (that depend on the magnitudes of the capillary forces trapping the ganglia and the imposed static pressure gradients) and for sufficiently low vibration frequencies. In this paper we describe two-dimensional glass micromodel experiments that support these predictions.

Scaling theory of drying in porous media

Concepts of immiscible displacements in porous media driven by mass transfer are utilized to model drying of porous media. Visualization experiments of drying in two-dimensional glass micromodels are conducted to identify pore-scale mechanisms. Then, a pore network approach is used to analyze the advancing drying front. It is shown that in a porous medium, capillarity induces a flow that effectively limits the extent of the front, which would otherwise be of the percolation type, to a finite width. In conjuction with the predictions of a macroscale stable front, obtained from a linear stability analysis, the process is shown to be equivalent to invasion percolation in a stabilizing gradient. A power-law scaling relation of the front width with a diffusion-based capillary number is also obtained. This capillary number reflects the fact that drying is controlled by diffusion in contrast to external drainage. The scaling exponent predicted is compatible with the experimental results of Shaw [Phys Rev. Lett. 59, 1671 (1987)]. A framework for a continuum description of the upstream drying regimes is also developed.

Visual Investigation of Retrograde Phenomena and Gas Condensate Flow in Porous Media

The mechanism of retrograde condensation and the flow of gas-condensate in horizontal porous media under simulated reservoir conditions were visually studied. Two-dimensional glass micromodels with homogeneous pore structures, as well as heterogeneous patterns, reproduced from real rock micrographs were employed in this study. Depletion tests were carried out using synthetic multicomponent hydrocarbon gas mixtures and also a North Sea gas condensate. The multiphase flow behaviour of the tested systems, as observed and recorded on video, is presented here along with the measured data. In water-wet pores, condensate was observed to be formed as a continuous thin film on connate water, which was the preferred site for condensation. Pressure reduction below the system cricondenbar resulted in the growth of the condensate almost exclusively on water rings at pore throats and dead end pores. The condensate was observed to flow through thin films even at low saturations, with little contribution to the condensate recovery. The rate of pressure depletion influenced the gas flow shear and was found to strongly affect the condensate propagation. Local instabilities could promote significant condensate movement in pore sections which would only be retarded further downstream by capillary effects diminishing the condensate recovery. Relative permeability-saturation relation-ships for gas-condensate flow should not be expected to take the same form as the oil-gas relative permeability for solution gas or external gas drive.

A Method of Making Two-dimensional Glass Micromodels of Pore Systems

Abstract Two-dimensional micro models of pore systems can be made in glass by use of a photo-imaging technique followed by chemical etching of the glass. The method is a modification of one used for making printed circuits in the electronics industry. Pore systems with many thousands of Individual elements of specified geometry and arrangement can be fabricated. Such models are useful for observing the effects of pore and fluid variables on the trapping and subsequent mobilization of residual phases during secondary and tertiary recovery processes. Introduction This paper describes a method for making transparent, two-dimensional micro models of pore systems in glass. The displacement of one fluid by another in a porous medium, say water displacing oil in a reservoir rock, is affected by the geometry and surface properties of the pores in the medium, the properties of the fluids and their interactions with each other and the solid surfaces, as well as on the forces acting on the system. The complex interactions among moving multiphase fluids and porous media can be observed conveniently in transparent, two-dimensional micro models and this can provide a better understanding of the processes. The advantage of two-dimensional models over other idealized porous media, such as packs of glass beads, is that the geometry and topology of the system can be specified precisely. A disadvantage is that three-dimensional networks have topologic properties not shared by two-dimensional networks. For example, bicontinua cannot exist in two dimensions(1). Attempts have been made in the past to mechanically scribe a pattern on wax-coated glass and to etch this pattern with hydrofluoric acid(2). However, such a process relies on the manual dexterity of the model maker and does not lend itself to making complex or repetitive patterns. Others have used mono-layer packs of glass beads successfully(3.4), but such systems do not allow precise control of pore geometry nor wide variability of pore geometry within a single system. Bonnet and Lenormand(5) and Mahers et al.(6) (1981) produced micro models in nylon film using a photo-etching procedure similar to one commonly used for making printing plates. The advantage over previous methods is that large and complex models composed of many thousands of pores of specified geometry and arrangements can be photo-reduced to give pores of sizes approaching those commonly found in reservoir rocks. The technique described in this paper uses photo imaging followed by chemical etching in glass and has the limitation that pores less than about 20 μm in radius are difficult to etch with precision. However, in the case of pores bounded by glass, the roughness and wettability are more easily controlled than in models with surfaces of nylon or resin. The method is similar to one used for making printed circuits in the electronics industry, but modification-is necessary because the available photo resists cannot withstand exposure to hydrofluoric acid and the resultant etch in the glass is shallow and commonly imperfect. Davis and Jones(10) used similar techniques with photo-sensitive resists and acid water.