Influence of intensity and frequency of ultrasonic waves on capillary interaction and oil recovery from different rock types

Recent advances of ultrasound applications in the oil and gas industry

In the last two decades, ultrasound (US) technologies research has increasingly earned attention for applications in the oil and gas industry. Numerous laboratory and field research have proven ultrasonics as an efficient, sustainable and cost-effective technology for improving well productivity. This paper pursues the elaboration of a comprehensive review of the most recent research related to ultrasonic technologies for applications in the oil and gas industry. Statistical analysis of different functional categories and classification of the research publications were performed. Considering the research reviewed, there is a huge gap between numerical and field studies in comparison with the numerous laboratory studies, deeming it necessary to increase efforts on developing mathematical and numerical models and field-testing cases of the ultrasonic effect. A comprehensive review of the ultrasonic waves' mechanisms of action for enhanced oil recovery (EOR) and emulsification/demulsification was conducted. Despite the lack of consensus regarding the mechanisms, cavitation and thermal effects on wellbore fluid and formation rock have been widely accepted as two of the most influencing mechanisms. A compilation of the state-of-the-art research of numerical, laboratory and field studies in the last two decades was assembled. Most authors agreed that ultrasonics is a highly efficient method for EOR and emulsion treatment if the optimal conditions are identified and achieved. The development of screening criteria for the application of ultrasonic waves was recommended, as this technique and the same parameters should not be utilized for all reservoir types. Treatment with ultrasound waves has shown improvement of oil recovery efficiency rates of over 90% and viscosity reduction values over 80%. The most efficient results were observed when in combination with another conventional EOR method, where ultrasound boosts recovery efficiency. Potential new applications related to rock mechanics and additional research topics were also recommended.

In-depth analysis of ultrasonic-induced geological pore re-structures

Understanding and manipulating geological pore structures is of paramount importance for geo-energy productions and underground energy storages in porous media. Nevertheless, research emphases for long time have been focused on understanding the pore configurations, while few work conducted to modify and restructure the porous media. This study deploys ultrasonic treatments on typical geological in-situ core samples, with follow-up processes of high-pressure mercury injections and nitrogen adsorptions and interpretations from nuclear magnetic resonance and x-ray diffraction. The core permeability and porosity are found to increase by 8.3 mD, from 4.1 to 12.4 mD, and by 0.95%, from 14.03% to 14.98%, respectively. Meanwhile, the number and size of the micro- and mesopore are increased with progressing of ultrasonic treatment, while those of the macropore decrease, which finally increase the permeability and porosity. The increase of micro- and mesopore number, from x-ray diffraction results, is attributed to the migration and precipitation of clay minerals caused through ultrasonic wave. The relocation of clay minerals also helps to improve the pore-throat connectivity and modify the micro-scale heterogeneity. Basically, this study reveals the characterizations of geological pore reconfigurations post-ultrasonic treatments and interprets the associated mechanisms, which provides guidance to manipulate the geological pores and be of benefit for further porous media use in science and engineering.

Oily Wastewater Treatment: Overview of Conventional and Modern Methods, Challenges, and Future Opportunities

Industrial developments in the oil and gas, petrochemical, pharmaceutical and food sector have contributed to the large production of oily wastewater worldwide. Oily wastewater pollution affects drinking water and groundwater resources, endangers aquatic life and human health, causes atmospheric pollution, and affects crop production. Several traditional and conventional methods were widely reported, and the advantages and limitations were discussed. However, with the technology innovation, new trends of coupling between techniques, use of new materials, optimization of the cleaning process, and multiphysical approach present new paths for improvement. Despite these trends of improvement and the encouraging laboratory results of modern and green methods, many challenges remain to be raised, particularly the commercialization and the global aspect of these solutions and the reliability to reduce the system’s maintenance and operational cost. In this review, the well-known oily wastewater cleaning methods and approaches are being highlighted, and the obstacles faced in the practical use of these technologies are discussed. A critical review on the technologies and future direction as the road to commercialization is also presented to persevere water resources for the benefit of mankind and all living things.

Impact of ultrasonic treatment process on pour point of vegetable oils based liquid insulation

This study presents an application of ultrasonic technology in the high voltage liquid insulation domain towards the reduction of pour point of vegetable oil samples for the utilization of vegetable oils as liquid insulation in cold climate areas on power transformers. Pour point reduction has been achieved by processing the vegetable oil samples by using ultrasonic treatment process with 100 W and 30 kHz ultrasonic waves for various exposure times of 15, 30, 45 and 60 min. Edible vegetable oils such as sunflower oil, palm oil, sesame oil and non edible vegetable oils such as honge oil, neem oil and punna oil are considered as two categories of vegetable oils for this experimental investigation. Ultrasonic treatment process results in the reduction of pour point of vegetable oils to meet out the standard value of pour point for liquid insulation as per IEEE Standard C57.147, 2018. A significant reduction in pour point temperature of vegetable oil samples have been obtained with an increased exposure time. The obtained variations in pour point after exposure with ultrasonic waves may be due to the possible changes in crystallization kinetics of fatty acids components of vegetable oil samples due to energy input of ultrasonic waves. The experimental results have given a way towards the positive encouragement and development with ultrasonic treatment for achieving low pour point vegetable oils as liquid insulation in power transformers for applications on cold climatic areas.

Recent applications of ultrasonic waves in improved oil recovery: A review of techniques and results

Ultrasound technique is an inexpensive and ecofriendly technology commonly used in oil and gas industry to improve oil recovery and its applications have been successfully tested in both laboratory and field scales. In this technique, high-power ultrasonic waves are utilized downhole to improve oil recovery and reduce formation damage in near wellbore region that causes a reduction in hydrocarbon production rate due to the penetration of mud, scale deposition, etc. In most of the cases, barriers for the oil flow to the wellbore are effectively removed by using the ultrasound technique and the effect of improved oil recovery may last up to several months. The aim of this paper is to provide an overview of recent laboratory, field and mathematical studies to serve as reference for future extensive examination of ultrasound assisted improved oil recovery. As an added value to this field of study, research gaps and opportunities based on the review of recent works were identified and factors that needs to be considered to improve the outcome of future studies were recommended.

Study on frequency optimization and mechanism of ultrasonic waves assisting water flooding in low-permeability reservoirs

Water flooding is one of widely used technique to improve oil recovery from conventional reservoirs, but its performance in low-permeability reservoirs is barely satisfactory. Besides adding chemical agents, ultrasonic wave is an effective and environmental-friendly strategy to assist in water flooding for enhanced oil recovery (EOR) in unconventional reservoirs. The acoustic frequency plays a dominating role in the EOR performance of ultrasonic wave and is usually optimized through a series of time-consuming laboratory experiments. Hence, this study proposes an unsupervised learning method to group low-permeability cores in terms of permeability, porosity and wettability. This grouping algorithm succeeds to classify the 100 natural cores adopted in this study into five categories and the water flooding experiment certificates the accuracy and reliability of the clustering results. It is proved that ultrasonic waves can further improve the oil recovery yielded by water-flooding, especially in the oil-wet and weakly water-wet low-permeability cores. Furthermore, we investigated the EOR mechanism of ultrasonic waves in the low-permeability reservoir via scanning electron microscope observation, infrared characterization, interfacial tension and oil viscosity measurement. Although ultrasonic waves cannot ameliorate the components of light oil as dramatically as those of heavy oil, such compound changes still contribute to the oil viscosity and oil-water interfacial tension reductions. More importantly, ultrasonic waves may modify the micromorphology of low-permeability cores and improve the pore connectivity.

Experimental investigation of ultrasonic treatment effectiveness on pore structure

During the whole life of oil production, enhancing the efficiency and optimizing the production of wells always have been discussed. Formation damage is one of the most frequent reasons for oil wells productivity reduction. This phenomenon can be caused by different factors such as fine migration, drilling mud invasion, asphaltene precipitation, capillary blockage reservoir fluids, and inorganic precipitation. Acidizing and hydraulic fracturing are two conventional well treatment methods usually applied to overcome the formation damage. However, due to destructive side effects of these methods, new methods such as Ultrasonic technology have helped to overwhelm these challenges. The usefulness of this method has been previously proven experimentally and operationally, but the effect of this technology on the pore structure has not been completely explored yet. In this paper, the effect of the ultrasonic wave on the pore structure during well stimulation is investigated. For this purpose, five samples of carbonate and sandstone with different rock textures were investigated to determine the effect of ultrasonic waves on flow behavior and microscopic pore structure through absolute permeability test, scanning electron microscope (SEM) images and petrography. The results showed that ultrasonic waves may affect pore structure through; initiation of micro-fracture and/or detachment of rock particle. The micro-fracture initiation is expected to increase the permeability while the detached particle may reduce or increase permeability through the clogging or opening the pore throat. For example, it was observed that ultrasonic waves significantly increase the permeability of Oolitic carbonate samples, while the controversial changes were observed in sandstone samples.

The ultrasound thermal cracking for the tar-sand bitumen

The influence of ultrasonic irradiation on the tar-sand bitumen in the process of thermal cracking with an inert atmosphere was investigated thoroughly. The product distribution and coke characteristic produced by the conventional thermal cracking (CTC) and ultrasound thermal cracking (UTC) were invested at the following condition: ultrasound frequency 20 kHz, ultrasonic power 2000 W, reaction time 2 h, reaction temperature from 400 to 440 °C. The result of the liquid products distribution indicated that UTC can significantly increase gasoline yield and diesel yield, and dramatically reduce VGO (Vacuum Gas Oil) yield and residuum (greater than 500 °C) yield. The analysis of gas products showed that there were no significant differences for the gas distribution between the two reactions (methods), indicating that reaction of UTC still conformed to a radical chain mechanism, but the ratio of olefin/paraffin was greatly reduced in the process of UTC, which was attributed to the hydrogen transfer reaction promoted by ultrasound. The result of the analysis by SEM, FT-IR, Raman, XRD and Zeta potential demonstrated that there was a significant difference for the morphology of cokes produced by the two methods. Mesocarbon microbeads (MCMB) was discovered in the process of UTC, which should be due to that the polymerization of the free macro-radicals produced from PAHs (Polycyclic Aromatic Hydrocarbons) promoted by ultrasonic cavitation. In addition, it can be inferred that the viscosity of the second liquid phase was reduced by ultrasonic mechanical function through the breakage of the stack of asphaltene molecules cross-linked by van der Waals force. According to the mesophase theory, the ultrasound irradiation promoted the formation of the second liquid phase, extended its existence time and reduced its viscosity, resulting in the formation of MCMB controlled by the surface tension during the process of UTC.

Experimental investigation on the effect of ultrasonic waves on reducing asphaltene deposition and improving oil recovery under temperature control

A well-known complication in the oil reservoir during oil production is asphaltene deposition in and around the production wellbore. Deposition of asphaltene around the production wellbore may cause a significant pressure drop and in turn loss of efficiency in the production process. Various mechanical and chemical methods have been employed in order to reduce asphaltene formation or to eliminate the precipitate. A novel technique which presented a great potential for prevention or elimination of asphaltene is spreading out the high energy ultrasound wave within the oil reservoir. In this study, in a glass micro-model, asphaltene precipitation was first simulated in a transparent porous medium and its removal by application of high energy ultrasound wave was then investigated. To simulate asphaltene precipitation, the micro-model was first saturated with oil and then a normal-pentane was injected. This was followed by flooding the porous media with brine while propagating ultrasound waves (30 kHz and 100 W) to eliminate asphaltene precipitation. The experiment setup was equipped with a temperature controller. The results indicate a significant reduction in asphaltene precipitation in the oil reservoir may be achieved by application of ultrasound energy. Asphaltene particle deposition has been solved reversibly in the oil layer of porous medium and with the oil layering mechanism, the rate of oil production has been increased. In some spots, water/oil emulsion has been formed because of the ultrasonic vibration on the wall. Both the crude and synthetic oils were examined.

Effect of ultrasound radiation duration on emulsification and demulsification of paraffin oil and surfactant solution/brine using Hele-shaw models

Ultrasound technique is one of the unconventional enhanced oil recovery methods which has been of interest for more than six decades. However, the majority of the oil recovery mechanisms under ultrasound reported in the previous studies are theoretical. Emulsification is one of the mechanisms happening at the interface of oil and water in porous media under ultrasound. Oppositely, ultrasound is one of the techniques using in oil industry for demulsification of oil/water emulsion. Therefore, the conditions in which emulsification becomes dominant over demulsification under ultrasound should be more investigated. Duration of ultrasound radiation could be one of the factors affecting emulsification and demulsification processes. In this study a technique was developed to investigate the effect of long and short period of ultrasound radiation on emulsification and demulsification of paraffin oil and surfactant solution in porous media. For this purpose, the 2D glass Hele-shaw models were placed inside the ultrasonic bath under long and short period of radiation of ultrasound. A microscope was used above the model for microscopic studies on the interface of oil and water. Diffusion of phases and formation of emulsion were observed in both long and short period of application of ultrasound at the beginning of ultrasound radiation. However, by passing time, demulsification and coalescence of brine droplets inside emulsion was initiated in long period of ultrasound application. Therefore, it was concluded that emulsification could be one of the significant oil recovery mechanisms happening in porous media under short period of application of ultrasound.

An extended model for ultrasonic-based enhanced oil recovery with experimental validation

This paper suggests a new ultrasonic-based enhanced oil recovery (EOR) model for application in oil field reservoirs. The model is modular and consists of an acoustic module and a heat transfer module, where the heat distribution is updated when the temperature rise exceeds 1 °C. The model also considers the main EOR parameters which includes both the geophysical (i.e., porosity, permeability, temperature rise, and fluid viscosity) and acoustical (e.g., acoustic penetration and pressure distribution in various fluids and mediums) properties of the wells. Extended experiments were performed using powerful ultrasonic waves which were applied for different kind of oils & oil saturated core samples. The corresponding results showed a good matching with those obtained from simulations, validating the suggested model to some extent. Hence, a good recovery rate of around 88.2% of original oil in place (OOIP) was obtained after 30 min of continuous generation of ultrasonic waves. This leads to consider the ultrasonic-based EOR as another tangible solution for EOR. This claim is supported further by considering several injection wells where the simulation results indicate that with four (4) injection wells; the recovery rate may increase up-to 96.7% of OOIP. This leads to claim the high potential of ultrasonic-based EOR as compared to the conventional methods. Following this study, the paper also proposes a large scale ultrasonic-based EOR hardware system for installation in oil fields.

Effective ultrasound electrochemical degradation of methylene blue wastewater using a nanocoated electrode

A novel sonoelectrochemical catalytic oxidation-driven process using a nanocoated electrode to treat methylene blue (MB) wastewater was developed. The nano-scale (nanocoated) electrode generated more hydroxyl radicals than non-nano-scale (non-nanocoated) electrodes did. However, hydroxyl radicals were easily adsorbed by the nanomaterial and thus were not able to enter the solution. Supersonic waves were found to enhance the mass-transfer effect on the nanocoated electrode surface, resulting in rapid diffusion of the generated hydroxyl radicals into the solution. In solution, the hydroxyl radicals then reacted with organic pollutants in the presence of ultrasonic waves. The effect of the nanocoated electrode on the MB wastewater treatment process was enhanced by ultrasound when compared to the non-nanocoated electrode used under the same conditions. The synergy of the nanocoated electrode and ultrasonic waves towards MB degradation was then studied. The optimum operating conditions resulted in a 92% removal efficiency for TOC and consisted of a current of 600 mA, an ultrasound frequency of 45 kHz, and a supersonic power of 250 W. The mechanism of ultrasound enhancement of the nanocoated electrode activity with respect to MB treatment is discussed. The reaction intermediates of the sonoelectrochemical catalytic oxidation process were monitored, and degradation pathways were proposed. The sonoelectrochemical catalytic oxidation-driven process using nanocoated electrodes was found to be a very efficient method for the treatment of non-biodegradable wastewater.

A technique for evaluating the oil/heavy-oil viscosity changes under ultrasound in a simulated porous medium

Theoretically, Ultrasound method is an economical and environmentally friendly or "green" technology, which has been of interest for more than six decades for the purpose of enhancement of oil/heavy-oil production. However, in spite of many studies, questions about the effective mechanisms causing increase in oil recovery still existed. In addition, the majority of the mechanisms mentioned in the previous studies are theoretical or speculative. One of the changes that could be recognized in the fluid properties is viscosity reduction due to radiation of ultrasound waves. In this study, a technique was developed to investigate directly the effect of ultrasonic waves (different frequencies of 25, 40, 68 kHz and powers of 100, 250, 500 W) on viscosity changes of three types of oil (Paraffin oil, Synthetic oil, and Kerosene) and a Brine sample. The viscosity calculations in the smooth capillary tube were based on the mathematical models developed from the Poiseuille's equation. The experiments were carried out for uncontrolled and controlled temperature conditions. It was observed that the viscosity of all the liquids was decreased under ultrasound in all the experiments. This reduction was more significant for uncontrolled temperature condition cases. However, the reduction in viscosity under ultrasound was higher for lighter liquids compare to heavier ones. Pressure difference was diminished by decreasing in the fluid viscosity in all the cases which increases fluid flow ability, which in turn aids to higher oil recovery in enhanced oil recovery (EOR) operations. Higher ultrasound power showed higher liquid viscosity reduction in all the cases. Higher ultrasound frequency revealed higher and lower viscosity reduction for uncontrolled and controlled temperature condition experiments, respectively. In other words, the reduction in viscosity was inversely proportional to increasing the frequency in temperature controlled experiments. It was concluded that cavitation, heat generation, and viscosity reduction are three of the promising mechanisms causing increase in oil recovery under ultrasound.

Depinning and creeplike motion of wetting fronts in weakly vibrated granular media

We study the effect of weak vibrations on the imbibition of water in granular media. In our experiments, we have observed that as soon as the vibration is applied, an initially pinned wetting front advances in the direction of imbibition. We found that the front motion is governed by the avalanches of localized intermittent advances directed at 45° to the imbibition direction. When the rescaled gravitational acceleration of vertical vibrations is in the range of 0.81≤G≤0.95, we observed an almost steady motion of wetting front with a constant velocity v(cr)(G)∝exp(-1/G) during more than 20 min, whereas at lower accelerations (0.5≤G≤0.8) the front velocity decreases in time as v∝t(-δ). We suggest that the steady motion of an imbibition front in a weakly vibrated granular medium can be treated as a creep motion associated with nonthermal temporal fluctuations of packing density in a weakly vibrated granular medium.

Visual analysis of immiscible displacement processes in porous media under ultrasound effect

The effect of sonic waves, in particular, ultrasonic radiation, on immiscible displacement in porous media and enhanced oil recovery has been of interest for more than five decades. Attempts were made to investigate the effect through core scale experimental or theoretical models. Visual experiments are useful to scrutinize the reason for improved oil recovery under acoustic waves of different frequency but are not abundant in literature. In this paper, we report observations and analyses as to the effects of ultrasonic energy on immiscible displacement and interaction of the fluid matrix visually in porous media through two-dimensional (2D) sand pack experiments. 2D glass bead models with different wettabilities were saturated with different viscosity oils and water was injected into the models. The experiments were conducted with and without ultrasound. Dynamic water injection experiments were preferred as they had both viscous and capillary forces in effect. The displacement patterns were evaluated both in terms of their shape, size, and the interface characteristics quantitatively and qualitatively to account for the effects of ultrasonic waves on the displacement and the reason for increased oil production under this type of sonic wave. More compact clusters were observed when ultrasonic energy was present in water-wet systems. In the oil-wet cases, more oil was produced after breakthrough when ultrasound was applied and no compact clusters were formed in contrast to the water-wet cases.

Resonant acoustical pumping of a compressible viscous fluid through a planar duct or a circular tube

Pumping of a compressible viscous fluid through a planar duct or a circular tube due to running waves on the surface of the duct or tube is studied on the basis of the Navier-Stokes equations. The flux is calculated to second order in the amplitude of the exciting surface waves. It is shown that the flux exhibits a resonance as a function of frequency, leading to a high pumping velocity near resonance.