Increase Of Foam Quality Research Articles

Simultaneous injection of chemical agents and carbon dioxide to enhance the sweep efficiency from fractured tight core samples

Foams would play a substantial role in mobility control and are considered an efficient chemical agent to improve the oil recovery factor. Co-injection of foam and carbon dioxide (CO2) would be one of the optimum injectivity scenarios in fractured tight core samples. This paper aimed to experimentally investigate the surfactant alternating gas injection and CO2-foam injection and how to determine the optimum parameters like foam quality, flow rate, and the number of cycles. It is observed that 0.65 is the optimum foam quality for the fractured tight core samples, and by the increase of foam quality, the pressure drop has been decreased. By increasing foam quality, pressure drop increases up to a specific value (fg=0.65), and after this point, pressure drop has been decreased. Moreover, by the increase of injectivity cycles, pressure drop has increased subsequently. It is observed that five cycles are the optimum number of cycles, and after that, there is no pressure drop decrease in the system. Due to the surfactant property to control the mobility ratio, CO2 breakthrough has occurred at 1.2 PV. Its oil recovery factor at breakthrough is about 48%, and the total oil recovery factor is about 65%. CO2-foam were injected into the system, and due to the presence of a foaming agent in CO2, a CO2 breakthrough occurred at 1.8 PV. The total oil recovery factor is about 83% that indicated the efficiency of this scenario.

Modeling of Drilling Cuttings Transport by Foam in Horizontal Well Condition Using Computational Fluid Dynamics

Efficient cuttings transport is one of the most important parameters affecting the drilling rate of wells. Foam has a great potential to reduce drilling problems compared to conventional drilling fluids due to its unique properties such as low density and high viscosity. In this paper, cuttings transport with foam was studied using a computational fluid dynamics approach. In this study, the Eulerian multiphase model was used to describe cuttings-fluid mixture flow. Foam rheology was expressed by the non-Newtonian power-law model. Effects of foam quality and injection velocity, cuttings size, pipe eccentricity and rotational speed of drill pipes were studied. Modeling results were also compared with experimental data. Results showed that the increase of foam quality improved hole-cleaning operation mainly due to the enhanced foam viscosity. The increase in foam injection velocity led to a reduction in in-situ cuttings concentration. This was due to the foam capability to destruct stationary cuttings bed. It was found that pipe eccentricity resulted in the accumulation of cuttings in the annulus. But, an increase of the drill pipe rotational speed provided a better hole-cleaning, so that by increasing the rotational speed to 40 RPM, cuttings concentration decreased by 1.8 and 1.4 times in concentric and eccentric pipe, respectively.

Visual investigation of viscous cross-flow during foam injection in a matrix-fracture system

A micromodel setup has been implemented to visualize foam propagation into the matrix and recovery of the matrix’s fluid. For simplicity, the experiments have been conducted in the absence of oleic phase; however, the achievements of this study can significantly affect the knowledge of foam flow in fractured reservoirs for enhanced oil recovery processes. New qualitative descriptions have been presented in terms of viscous cross-flow using well designed experiments and discussions. The effect of viscous cross-flow on the recovery of the matrix’s fluid has been evidenced via a mechanistic study based on the comparison of the recovery variation versus the foam quality, injection rate, and injectant type. Meanwhile, generation and coalescence mechanisms have been investigated. The results of these experiments demonstrate that a convective viscous cross-flow orthogonal to the direction of the mainstream (flow direction in the fracture) has been generated during foam injection that can significantly recover the bypassed fluid. In addition, it has been shown that foam invasion within the matrix controls the amount of ultimate recovery factor and is proportional to the foam viscosity in the fracture. Furthermore, the amount of recovery of the bypassed fluid increases as the foam quality increases. However, increasing the total injection rate causes a decrease in fluid recovery due to shear thinning behavior of foam.

Experimental studies on CO2 foam performance in the tight cores

Enhanced oil recovery for tight reservoirs with extremely low permeability and porosity is becoming the new routine for reservoir engineering research. Foam flooding has already been proven as an effective approach to enhance the oil recovery in conventional reservoirs. However, limited research has been done on the phenomena and mechanism of foam performance in the tight porous media.In this study, a series of core flooding tests are performed to investigate the foam performance in the absence and presence of oil in tight core samples with different permeabilities from 0.1mD to 3.3 mD. The foam resistance factor, mobility reduction factor, and relative mobility of the displacing fluid are investigated by comparing the foam flooding processes with waterflooding and the co-injection processes of brine and gas. The effectiveness of applying foam flooding as a tertiary recovery method in the tight core samples is studied by comparing the production data, pressure drop data, and relative mobility of displacing fluid between foam flooding and waterflooding.Unlike conventional foam injection process, the increase of foam quality will not create more stable foam flow that gives significant higher foam resistance factor and much better mobility control as expected in the tight core samples. Also, the foam resistance factors even decrease with increasing injection rates at such a low permeability. These results suggest the foam with low foam quality and low injection rate may be the answer to tight reservoir EOR application.As for the oil production test, the experimental results support the effectiveness of foam flooding on reducing mobility compared with waterflooding and the co-injection of brine and gas. An additional 15–22% oil recovery factor is achieved by introducing foam flooding after waterflooding has done. Surprisingly, comparing with a long period of waterflooding without any oil production, the additional oil was successfully produced at a much lower pressure drop during the early stage of foam injection. Since extremely high pressure drop may not be a necessary constraint on foam flooding EOR process in tight reservoirs, it suggests the potential solution on questionable injectivity issue during foam flooding in the tight reservoirs by introducing an optimized discontinuous surfactant-alternating-gas gas process. Also, the relative mobility of displacing fluid is lowered by one order of magnitude compared with waterflooding in the presence of oil.

Stress and bubble pressure response of wet foam to continuous and oscillatory sinusoidal shear.

Wet foam, as a typical multiphase soft material, has complex spatial structure. Foam quality (i.e., gas fraction of a foam fluid), one of fundamental structure parameters of a foam system, generally has a significant influence on the mechanical response of the wet foam to the continuous and oscillatory shear. This study shows that the stress level of the wet foam, including the shear stress and the normal stress difference, rises with the foam quality. An exponential link between the yield stress of wet foam and the foam quality is demonstrated. In the oscillatory sinusoidal shear, a frequent fluctuation of the stress curve mainly occurs at the relatively higher strain rate, and the stress state in the foam is still maintained at the end of the oscillatory shear. Further, with the increase of foam quality, the loss modulus decreases when the foam does not yield, while the storage modulus as well as the loss modulus increases as the strain amplitude exceeds a certain value. Additionally, a nonlinear stress response of the wet foam is mainly attributed to the third harmonic component as the strain amplitude increases in the oscillatory shear. In the shear, the average level of bubble pressure in the foam increases with the foam quality, and it fluctuates with the strain owing to the elastic-plastic deformations of the films. Especially, in the oscillatory shear, the average bubble pressure fluctuates more frequently as the strain rate reaches a relatively higher value.

Effect of foam quality on flow behavior of liquid CO2-based foam fracturing fluid stabilized by hydrofluoroether

Hydrofluoroether C4F9OCH3, as a foaming agent in liquid CO2, is used to stabilize bubble in liquid CO2-based foam fracturing fluid which is waterless and no damage to oil-gas reservoir. However, characteristics of this environmental friendly CO2-based foam, such as the foam morphology and its flow behaviors in pipe, are insufficiently understood. Especially, foam quality, one of important characteristic parameters in a foam fluid, has significant effects on foam structure and flow behaviors of CO2-based foam. By means of the flow tests in pipes with different diameters, it was found that the CO2-based foam displayed wall slip phenomenon, and Oldroyd-Jastrzebski method was used to deal with this phenomenon. Effective viscosity of this CO2-based foam, as well as convective heat transfer coefficient initially increases and then decreases with the increase of foam quality. Due to dominant collision and friction among bubbles, their values reach the corresponding maximums when the foam quality is about 0.82. Meanwhile, the evolution of rheological parameters of CO2-based foam with the foam quality is shown as well, and the exponential relationship between yield stress and foam quality is illustrated. Additionally, as for the flow friction characteristics, it shows that fanning friction factor increases and drag reduction rate initially increases and then decreases as the foam quality is increased.

Rheological behavior of oil-based drilling foams

The application of foam in the petroleum field has been around since the late sixties. Foam has been successfully used in stimulation as well as drilling. It has desirable properties which make it very suitable for underbalanced drilling (UBD) and other oilfield applications such as cementing, well stimulation and fracturing. Aqueous foams have been in the industry for a long time. As a result, in the past, foam research was more focused on characterization of aqueous foams to optimize their hydraulic and hole cleaning performance (solids carrying capacity). Currently, modern foams such as polymer-based and oil-based foams are becoming more popular due to their superior performance. However, flow behavior of modern foams is complex and not well-understood.The principal objective of this study is to investigate flow behavior of oil-based foams. In order to achieve the study objective, experiments were performed using a recirculating flow loop that has three pipe viscometers. Tests were conducted at room temperature (25 ± 2 °C) and elevated pressure (0.67 MPa). Base liquid was prepared by mixing diesel (68%), mineral oil (30%) and surfactant (2%). Nitrogen was used as the gas phase. Foam quality (i.e. gas volume fraction) was varied from 34 to 68%. The effect of foam quality on bubble size was also investigated to provide further insight into the behavior of oil-based foams.Results showed non-Newtonian behavior of oil-based foams which becomes more prominent as foam quality increases. Moreover, like aqueous and polymeric foams, rheology of oil-based foams greatly depends on quality and base-liquid viscosity. Wall-slip effect was observed in the small diameter pipe (13.4 mm). The averaged bubble size of oil-based foams increased with foam quality.

Flow Behavior of Two-Dimensional Wet Foam: Effect of Foam Quality

The flow behaviors of two-dimensional (2D) wet monodisperse and polydisperse foams are investigated by the quasi-static simulation. We set the same inlet velocity on the cross section of the foam channel and then focus on the elastic–plastic deformation of the 2D wet foam according to the strain caused by the foam flow. The gas fraction in foam is referred to as foam quality and the effects of foam quality on the shear modulus, bubble dynamics, and stress–strain properties are obtained by the simulation. In the elastic domain, the shear modulus of monodisperse foam decreases exponentially with foam quality, but for the polydisperse foam, the shear modulus tends to increase. The shear banding of the polydisperse foam appears in the low strain and disappears gradually as the strain and foam quality increase. We adopt shear rate to represent the change rate of average bubbles displacements versus y-coordinates and find that the distribution of shear rate in the y-direction changes with iteration. Additionally, energy of the foam is stored and dissipated with the elastic–plastic deformation of the foam. The average shear stress generated by the foam structure and the initial increment of normal stress difference caused by the elastic deformation increase with the increase of foam quality.

Experimental Study on Frictional Resistance Characteristics of CO<sub>2</sub>-Emulsified Viscoelastic Surfactant Fracturing Fluid

Rheological properties and friction resistance properties of CO2-emulsified viscoelastic surfactant fracturing fluid were investigated on the large-scale test loop of foam fracturing fluid. When the velocity is below 2.8 m·s-1, the friction pressure drop gradient gradually decreases with the increase of foam quality, however, when the velocity is above 2.8 m·s-1, the friction pressure drop gradient of VES-CO2with higher foam quality is higher than lower foam quality. In addition, frictional pressure drop gradient of the pure CO2is higher than the VES-CO2fracturing fluid system when the velocity is more than 1.6 m·s-1. And frictional resistance coefficient decreases with the increase of foam quality and increases slightly with the increase of temperature. Experimental correlation between frictional resistance coefficient and Reynolds number is obtained and has high precision.

Study on the Rheology of Foam Fracturing Fluid with Mixture Model

Numerical simulation study on the rheology or foam fluid was carried through by treating inner phase as granular fluid with mixture model. The simulation results show that the gas phase is well distributed on cross-section. Besides, the higher the foam quality, the higher the velocity gradient near the wall. For turbulent properties, the turbulent kinetic energy and viscosity increase as the foam quality increases. With the same foam quality, the bigger the bubble diameter, the higher the turbulent viscosity and turbulent kinetic energy. What’s more, the foam quality 63% is a catastrophe point at which the rheology of foam fracturing fluid changes sharply. The change trend of turbulent viscosity along radial direction is different between the regions where the foam quality is below and over catastrophe point, and in the latter the change trend is flatter. From the simulation results it can be seen that the mixture model is more applicable and effective to the region where foam quality is over 63%.

Experimental study and application on profile control using high-temperature foam

Through single-core and dual-core experiments, blocking and profile control capability of high-temperature foam were investigated. Experiment results indicate that with the increase of foam quality, the resistance factor reduces, and the best foam quality is 0.50. The resistance factor increases with permeability, and decreases with temperature. Co-injection of surfactant solution and gas is better than SAG injection. During the hot water reverse injection period, resistance factor decreased to 75, and then basically remained stable. Irreducible oil in sandpack can reduce blocking capability to some extent. When the permeability ratio is less than 6, the profile control effect is good. As the increase of permeability ratio, profile control effect decreases. High-temperature foam still has some profile control capability in sandpacks with irreducible oil. Foam in porous media can withstand reverse flow of water under high-temperature conditions. In site application for steam profile control using high-temperature nitrogen foam, oil production improvement and water cut decrease are obvious. This technology is useful for improving oil production in cyclic steam stimulated wells.

Numerical simulation of transient cuttings transport with foam fluid in horizontal wellbore

With considering the interlayer mass transfer and fluid influx from the reservoir, a one-dimensional two-layer hydraulic model was established to describe the mechanism of transient cuttings transport with foam fluid in horizontal well section. The model was numerically calculated based on the modified SIMPLE algorithm, and the height of cuttings bed was predicted by the trial-and-error method. Sensitivity analysis was conducted on the affecting factors on the cuttings transport performance. Results show that cuttings deposition moves along the horizontal wellbore from the drilling bit, and finally achieves a steady state with dynamic balance. Dimensionless cuttings bed height decreases with the increase of foam quality or foam flow rate, but increases with the increase of drillpipe eccentricity, cuttings size or drilling rate. The influx of water and gas from the reservoir is helpful to improve the cuttings transport efficiency with foam. The proposed model offers theoretical guidelines for hydraulic parameter design and hole cleaning control in foamed horizontal drilling.

Pressure Loss at the Bit While Drilling with Foam

Foam is one of the most frequently used drilling fluids at underbalanced drilling operations. As foam flows, due to the pressure drop, a volumetric expansion is observed, which causes the foam quality to increase in the same direction with flow. Flow of foams through circular pipes and annular geometries are well studied. Interestingly, although one of the major sources of pressure drop is at the bit, there have been few studies of this subject for foams. Many drilling parameters including hole cleaning capacity, volumetric requirements of liquid and gas phase, and backpressure are out of control if the pressure drop at the bit is not accurately determined, even though pressure drops inside the pipes and wellbore are properly determined. This article introduces a more accurate model for estimating the pressure drop of foam flowing through the bit. The major difference between the proposed and the existing models is that the proposed model includes the effect of foam expansion and velocity change as a function of pressure. Pressure drop has been observed to increase significantly as the upstream pressure and foam average velocity increases when compared with the existing models. For the same flow conditions, pressure drop decreases as the foam quality increases, and as the upstream pressure increases, pressure drop also increases. The existing models cannot detect this event at all. In some cases, the pressure drop at the bit can be 10 times greater than the pressure drop predicted from existing models.

Drill Bit Pressure Drop During Foam Drilling Operations

Abstract Foam is one of the most frequently used drilling fluids for underbalanced drilling operations. This paper introduces a more accurate model than the existing models for estimating the pressure drop of foam flowing through the drill bit. The major difference between the proposed and existing models is that the proposed model includes the effect of foam expansion and velocity change as a function of pressure. It has been observed that pressure drop increases significantly as the upstream pressure and foam average velocity increases. For the same flow conditions, pressure drop decreases as the foam quality increases, and as the upstream pressure increases, pressure drop also increases. These events cannot be detected by existing models. In some cases, the pressure drop at the bit can be 10 times greater than the pressure drop predicted by existing models. Introduction Foam has been used as a drilling fluid in many drilling operations; especially in underbalanced drilling applications. In a number of cases, drilling with foam has shown to provide significant benefits, including increased productivity (by reducing formation damage), increased drilling rate, reduced operational difficulties associated with drilling in low pressure reservoirs (e.g. lost-circulation and differentially stuck pipe) and improved formation evaluation while drilling. Foams consist of a continuous liquid phase, forming a stable cellular structure that surrounds and entraps a gas phase. Special chemicals, called surfactants, are used to capture the gas phase; at least for a desired period of time. Foams are considered to be dry or wet, depending on the gas content. Wet foams have spherical bubbles with large amounts of liquid between the bubbles. Dry foam bubbles are polyhedral in shape, with definite contact between the bubbles. In between these two extremes, geometrical figures having both curved and flat faces can exist. Foams are thermodynamically unstable systems because they always contain more than a minimal amount of gas solution interface(1). This interface represents surface free energy, the amount of which can be estimated from knowledge of the surface tension and the interfacial area of the foam. Wherever a foam membrane breaks and the liquid coalesces, there is a decrease in surface free energy. Thus, the decomposition of foam into its constituent phase is a spontaneous process. Since the solution phase is always denser than the gaseous phase, there is a strong tendency for the liquid to separate or drain from the main body of foam unless it is circulated or agitated in some way. Foams can have extremely high viscosity. In all instances, their viscosity is greater than either the liquid or the gas that they contain(2). At the same time, their densities are much lower than the density of water. They are stable at high temperatures and pressures. So, by using foam as a drilling fluid, its high viscosity allows efficient cuttings transport and its low density allows underbalanced conditions to be established; thereby minimizing formation damage. Foams are also preferred when water influx is a problem because they can handle large amounts of water.