Efficient Demulsification Research Articles

PH-regulated superhydrophobic quartz sands for controllable oil-water separation

pH-regulated wettability transformation materials have gained increasing attention attributing to the capacity for sustainable oil-water separation. In this work, a smart quartz sand (OD-SiO2 @sand) with controllable wettability was designed as a filter media for efficient oil-water mixtures and water in oil emulsions separation. The OD-SiO2 @sand was synthesized by grafting nano-silica and modifying with two silane couplers, including N, N-Diethyl-3-(trimethoxysilyl)− 1-propanamine (DTP) and trimethoxy(octyl)silane (OTMS). OD-SiO2 @sand featured superhydrophobicity with a water contact angle (WCA) of 151.6°, which suggests selective separation capacity for oil and high permeation flux up to 4018 L.m−2∙h−1. Meanwhile, OD-SiO2 @sand exhibits superhydrophobicity and hydrophilicity in neutral and acidic solutions resulting from the reversible protonation of grafted DTP, which was revealed by 1H NMR and molecular dynamics simulations. OD-SiO2 @sand posed controllable oil-water separation performance, which remains superhydrophobicity with a WCA of 150.4° after 10 cycles of filtration processes upon pH regulation. Furthermore, OD-SiO2 @sand demonstrated efficient demulsification and separation capacity for various water in oil emulsions, achieving a purified oil size of less than 10 nm and a permeation flux up to 1850 L.m−2∙h−1. Thus, OD-SiO2 @sand shows promising applicability in the field of oil recovery and oil quality improvement.

Fish-gill inspired multifunctional nanofibrous membrane for efficient demulsification and pollutant sorption

Importance of multifunctional membranes for efficient purification of contaminated oily wastewater is globally realized due to depleting fresh water sources and environmental pollution. Electrospun superwettable membranes with heterostructures have attracted attention because of their versatile features, high surface area and multifunctionality. Herein, fish gill inspired superhydrophilic nanofibrous membranes of selective wettability were prepared using zeolitic imidazole framework (ZIF-8) decoration. A unique near-gel resin (nGR) emulsion electrospinning was employed to produce core-sheath structured nanofibrous membranes comprised of crosslinked polystyrene (PS) as the core and crosslinked polyvinyl alcohol (PVA) based sheath. An in-situ growth of ZIF-8 over the fibrous membrane's surface ensured retaining membrane's superhydrophilicity and underwater oleophobic behaviour and captured oil droplets to demulsify various oil/water emulsions during separation. ZIF-8 based biomimetic membrane achieved higher emulsion separation efficiency (98.9%) toward surfactant stabilized emulsions as compared to undecorated membrane. The membranes were also developed to attain multifunctionality via variation in ZIF-8 growth process. The membrane was evaluated for emulsion separation under various environmental conditions and its reusability up to 5 separation cycles. The controlled growth of ZIF-8 also facilitated heavy metal ion removal (85% at 100 ppb concentration) along with emulsion separation. The effect of growth loading on sorption capacity was evaluated in different oils and organic solvents. The membrane with high ZIF-8 growth showed excellent sorption capacity (4000%) toward toluene with consistent sorption up to 5 cycles of sorption-desorption. Overall, this study demonstrated a facile strategy to create multifunctional nanofibrous membrane through emulsion electrospinning, which can effectively be used in efficient emulsion separation, heavy metal ion removal and oil sorption.

Efficient Demulsification of Heavy Crude Oil Emulsions Using Bio‐Based Amphiphilic Esters

AbstractAbietic acid (AA) as a natural compound is used to synthesize two amphiphilic esters. AA was reacted with tetraethylene glycol (TG) or polyethylene glycol (PEG‐400) to obtain amphiphilic esters, AA‐TG, and AA‐PG, respectively. AA‐TG and AA‐PG were characterized using different techniques. In addition, the efficacy of these esters in demulsifying water‐in‐heavy crude oil emulsions was evaluated by means of several parameters. The demulsification efficacy (DE) of AA‐TG and AA‐PG reached 100 % in different cases. The results indicated that the DE was improved as the demulsifier concentration and temperature increased and the seawater ratio decreased. Furthermore, AA‐TG and AA‐PG achieved a higher DE and shorter demulsification time than the commercial demulsifier.

Probing the Demulsification Mechanism of Emulsion with SPAN Series Based on the Effect of Solid Phase Particles.

The solid particles in the produced fluids from the oil wells treated by compound flooding can greatly stabilize the strength of the interfacial film and enhance the stability of the emulsion, increasing the difficulty of processing these produced fluids on the ground. In this paper, the oil phase and the water phase were separated from the SPAN series emulsions by electrical dehydration technology and adding demulsifier agents. The changing trends of the current at both ends of the electrodes were recorded during the process. The efficient demulsification of the emulsion containing solid particles was studied from the perspective of oil-water separation mechanisms. Combined with the method of molecular dynamics simulation, the effect of the addition of a demulsifier on the free movement characteristics of crude oil molecules at the position of the liquid film of the emulsion were further analyzed. The results indicated that the presence of solid particles greatly increased the emulsifying ability of the emulsion and reduced its size. Under the synergistic effect of demulsifier and electric dehydration, the demulsification effect of the emulsion increased significantly, and the demulsification rate could reach more than 82%. The addition of demulsifiers changed the stable surface state of the solid particles. The free movement ability of the surrounding crude oil molecules was enhanced, which led to a decrease in the strength of the emulsion film so that the water droplets in the emulsions were more likely to coalesce and break. These results are of great significance for the efficient treatment of wastewater from oilfields, promoting the sustainability of environment-friendly oilfield development.

Demulsification Performance and Mechanism of Tertiary Amine Polymer-Grafted Magnetic Nanoparticles in Surfactant-Free Oil-in-Water Emulsion.

Numerous cationic magnetic nanoparticles (MNPs) have previously been developed for demulsifying oil-in-water (O/W) emulsion, and results showed that the cationic MNPs could effectively flocculate and remove the negatively charged oil droplets via charge attraction; however, to the best of our knowledge, there are no research reports regarding the synergetic influence of both the positive charge density and interfacial activity of MNPs on the demulsification performance. In this study, three tertiary amine polymer-grafted MNPs, namely, poly(2-dimethylaminoethyl acrylate)-grafted MNPs (M-PDMAEA), poly(2-dimethylamino)ethyl methacrylate)-grafted MNPs (M-PDMAEMA), and poly(2-diethylaminoethyl methacrylate)-grafted MNPs (M-PDEAEMA), were synthesized and evaluated for their demulsification performance. Results demonstrated that a high positive charge density and superior interfacial activity of MNPs could cause partial oil droplet re-dispersion when excessive MNPs were introduced, leading to a lower magnetic separation efficiency and narrower demulsification window. Herein, a demulsification window is defined as a range of nanoparticle dosages in which the MNPs can effectively demulsify the O/W emulsion under certain conditions. For highly positively charged MNPs, their good interfacial activity could aggravate the formation of a narrower demulsification window. When tertiary amine polymer-grafted MNPs carried a lower positive charge density or weak interfacial activity, that is, M-PDMAEA at pH 4.0, M-PDMAEMA at pH 5.0-9.0, and M-PDEAEMA at pH 9.0-10.0, wide demulsification windows were observed. Additionally, a recycling experiment suggested that MNPs could maintain high demulsification efficiency up to at least five cycles, indicating their satisfactory recyclability. The three tertiary amine polymer-grafted MNPs can be potentially used for efficient demulsification from surfactant-free O/W emulsion in various pH ranges.

Combination of coalescing spheres and electric fields generated by matrix electrodes to enhance W/O emulsion demulsification

The demulsification and dehydration of water-in-oil emulsions are crucial to waste oil resource treatment. However, the single current process and its devices can hardly meet the demand for efficient demulsification and dehydration in waste oil resource treatment. In this paper, we propose a treatment method that combines spherical coalescing particles with a matrix electrode structured electric field to enhance water-in-oil emulsions' demulsification and dehydration process and improve the dehydration efficiency. Static demulsification and dehydration experiments were conducted on water-in-oil emulsions, and the results showed that the combined treatment significantly improved the separation performance compared with electrical demulsification alone. The dehydration efficiency of the bidirectional pulsed electric field was 38% at a run duration of 4 min, while the combination treatment was 60%, an improvement of 22% under the experimental conditions. The creative content of this work can suggest new ideas for industrial applications.

Enhanced Coalescence of Fine Droplets by Medium Coalescence under an Electric Field

As more and more oilfields enter later stages of extraction, demulsification of water-in-oil (W/O) emulsions with high water content has become a challenging problem. To upgrade the current offshore oil treatment process, a compact and efficient demulsification treatment is highly desirable. In this paper, a novel enhanced treatment combining a direct current (DC) electric field and medium coalescence was proposed. Based on this idea, an electric-medium demulsifier was also designed for deep purification of W/O emulsions. The effects of operating conditions, emulsions characteristics and medium bed parameters on demulsification performance were investigated. The enhanced treatment showed better performance compared to electrostatic demulsification and medium coalescence alone, and was especially suitable for treating emulsions with strong emulsification. In short, at U = 3 kV, the demulsification efficiency increased by approximately 30% compared to that at U = 0 kV. This research provided a new approach for the treatment of W/O emulsions that has the advantages of wide operational flexibility, a tolerance for deteriorated characteristics and a rapid and thorough treatment process.

Construction of Gemini composite based on TiO2 pillared montmorillonite for efficient oil-water separation

Owing to the changeable components of oil–water system and the inflexible limitation of available materials during oil–water separation, the treatment of oily wastewater with wide pH, large discharge and high COD value remains a great challenge. In this study, a simple strategy was used to construct Gemini composite based on TiO2 pillared montmorillonite. The resultant montmorillonite-based Gemini composite (QATMt-x) exhibited high surface area (116.54 m2 g−1), surface potential (18.8 mV at pH2), good acid and alkali resistance, amphiphilic-multifunctional surface, and defective layered structure and, as a result, delivered high capability (ED ≥ 96 %) and long cyclic life for oil–water separation. More significantly, detailed mechanism studies reveal that the crucial reasons of oil–water separation on microemulsion and aqueous containing organic contaminant are demulsification through electron capture of the grafted chitosan, and adsorption by lipophilic saturated alkanes, titanium hydrates, (metal) hydroxyl and amine group, respectively. Hence, QATMt-x is particularly suitable for efficient demulsification in acidic media (pH 2) and for the adsorption of ecotoxic organic substances (e.g., perfluorooctanoic acid, methyl blue). In short, construction of Gemini surfactants based on low-cost inorganic carriers would offer new strategies in exploring amphipathic dual-functional layered structures for simultaneously efficient separation of multisystem oil–water scenarios.

Effect of liquid bridge evolution on the droplet non‐coalescence under a DC electric field

AbstractThe droplet non‐coalescence characteristics and mechanism under a DC electric field are investigated by comprehensively using high‐speed microscopic experiments, molecular dynamics simulations, and interface dynamics simulations. The researches show whether two droplets coalesce or not depends on the evolution of liquid bridge. The liquid bridge evolution is not only dominated by the electric force FE and the capillary force Fi, but also slowed down by the viscous force. The relative strength of FE and capillary force Fi relies on the electric capillary number Ca and the maximum liquid bridge radius R*max. The droplet non‐coalescence is more likely to happen as the Ca increases or the R*max decreases. Furthermore, the critical value Cac for droplet non‐coalescence reduces as the R*max decreases. The ion transportation causes uneven distribution of ions and thus strengthens the FE, resulting in the non‐coalescence. These results provide significant guidance for efficient demulsification of water‐in‐oil emulsion.

Influence of aggregate chemical composition on the demulsification rate of emulsified asphalt

Efficient demulsification is vital for the application of emulsified asphalt in road construction. In this paper, the effects of the main chemical components of the aggregates (CaCO3, MgO, Fe2O3, SiO2, Al2O3) on the demulsification process of emulsified asphalt were studied by experiment and simulation using a Gompertz model. The findings indicate that the surface energy, specific surface area, and pH of the chemical components of the aggregates are the most important factors influencing the demulsification speed of the emulsified asphalt. The choice of the aggregate’s main chemical components can accelerate demulsification speed, with the acceleration effect of Al2O3 on anionic (SDBS) emulsified asphalt and MgO on cationic (STAC) emulsified asphalt both reaching 60%. The fit between the Gompertz model and the experimental viscosity curve is greater than 0.93, which verifies the utility of using the Gompertz approach for studying emulsified asphalt-aggregate mortar viscosity changes. A demulsification evaluation function φ(t) of emulsified asphalt is proposed based on the parameters of the Gompertz model. When φ(t) is close to 1, the emulsified asphalt-aggregate mortar is fully demulsified, and setting φ(t)=1 allows the demulsification time of the emulsified asphalt-aggregate mortar to be calculated from the Gompertz model parameters.

Preparation of Carbon‐Based Nanodemulsifiers Derived from ZIF‐8 and their Demulsification Performance for Water‐in‐Oil Emulsions

AbstractIn this study, a carbon‐based nanodemulsifier (ZIF‐8@CNS) was prepared in order to lessen the harmful effects of crude oil emulsion on mechanical equipment and the environment and to provide a green and efficient demulsifier. A novel hydrophilic/lipophilic carbon‐based nanodemulsifier ZIF‐8@CNS was prepared by solvothermal method using ZIF‐8 and carbon nanospheres (CNS) as raw materials. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT‐IR) showed that ZIF‐8@CNS was successfully compounded. The interfacial activity experiment showed that the carbon nanospheres combined with ZIF‐8 had better hydrophilic and lipophilic balance and were more easily distributed at the oil‐water interface. The demulsification experiment of water‐in‐toluene emulsion with water content of 1 % was carried out. The results showed that when the dosage of ZIF‐8@CNS with 10 % carbon content was 300 mg/L, the residual water content in the emulsion oil phase was only 0.09 % within 15 min at room temperature. In addition, we propose a possible demulsification mechanism of the demulsifier. ZIF‐8@CNS is environmentally friendly and an effective oil‐water phase separation material with broad application prospects.

Dodecenylsuccinic anhydride-modified oxalate decarboxylase loaded with magnetic nano-Fe3O4@SiO2 for demulsification of oil-in-water emulsions

The inability to demulsify oil-in-water emulsions via green and efficient processes is a challenging problem in many industrial processes. As a novel biodemulsifier, protein demulsifiers display excellent dispersibility and stability, but their demulsification mechanisms are not clear, which severely restricts their large-scale production and application. In this study, the demulsification mechanism of the high-efficiency protein biodemulsifier oxalate decarboxylase (Bacm OxdC), which is secreted by the Bacillus mojavensis XH1 strain, for an oil-in-water emulsion was analyzed. The results showed that Bacm OxdC was spontaneously adsorbed at the oil-water interface and turned its hydrophobic amino acids outward to increase its hydrophobicity and break the emulsified system. Furthermore, it effectively reduced the oil-water interfacial tension and interfacial film strength, thereby reducing the oil-water interfacial energy and finally enabling demulsification. To further improve the demulsification efficiency and reusability, Fe3O4@SiO2@OxdC-DDSA was prepared. This method provided a magnetic response for Bacm OxdC and enabled efficient demulsification. The demulsification rate of Fe3O4@SiO2@OxdC-DDSA reached 98.1% at 24 h, which was 30.7% higher than that of the original Bacm OxdC. After three cycles, the demulsification rate still reached 89.3%, proving it has excellent recyclability. This work is the first study on the demulsification mechanism of protein biodemulsifiers and provides useful insights into the demulsification mechanism of biodemulsifiers for oil-in-water emulsions. In addition, a promising high-efficiency modification technique for protein biodemulsifiers was proposed, which provided information for the development of biodemulsifiers for oil-water separation.

Effect of Magnetic Graphene Oxide on Heavy Oil Demulsification

Chemical demulsification is the most efficient demulsification approach that can attain the desired separation efficiency and meet the environmental regulation standards whilst impose minimal economic burden on the petroleum industry. However, current demulsification methods using chemical demulsifiers suffer from significant secondary pollution, particularly after the demulsification process. Therefore, in this work, magnetic graphene oxide (MGO) was synthesized by a one-step co-precipitation method from graphene oxide (GO). The properties of MGO were then characterized by X-ray diffraction and Fourier transform infrared. MGO was successfully synthesized and used as the demulsifier for diluted heavy oil emulsions. Different MGO concentrations (40, 80, 120, 160, and 200 ppm) were used at different water cuts (20:80, 30:70, 40:60, 50:50, and 60:40 v/v%). Demulsification tests using the bottle test method indicated that MGO could separate the emulsions up to 99.98% efficiency due to the high surface area-to-volume ratio of nanoparticles and magnetic features, which enhanced the adsorptive capacity for separating water from the oil. The residual oil content in the separated water was then analyzed by an ultraviolet-visible spectrophotometer. The oil concentration in the separated water reduced to 398.8 mg/ml, corresponding to a demulsification efficiency of 99.98% observed at 40 ppm MGO concentration. The interfacial tension of the emulsions during demulsification was also analyzed, where the interfacial tension decreased with increasing MGO concentration.

Eco-friendly and efficient demulsification by chitosan biopolymer modified with titanium dioxide nanohybrid on carbonaceous substrates in (W/O) emulsions of crude oil

Eco-friendly and efficient demulsification by chitosan biopolymer modified with titanium dioxide nanohybrid on carbonaceous substrates in (W/O) emulsions of crude oil

PH and Magnetism Dual-Responsive Pickering Emulsion Stabilized by Dynamic Covalent Fe3O4 Nanoparticles.

Herein, we describe pH and magnetism dual-responsive liquid paraffin-in-water Pickering emulsion stabilized by dynamic covalent Fe3O4 (DC-Fe3O4) nanoparticles. On one hand, the Pickerinfigureg emulsions are sensitive to pH variations, and efficient demulsification can be achieved by regulating the pH between 10 and 2 within 30 min. The dynamic imine bond in DC-Fe3O4 can be reversibly formed and decomposed, resulting in a pH-controlled amphiphilicity. The Pickering emulsion can be reversibly switched between stable and unstable states by pH at least three times. On the other hand, the magnetic Fe3O4 core of DC-Fe3O4 allowed rapid separation of the oil droplets from Pickering emulsions under an external magnetic field within 40 s, which was a good extraction system for purifying the aqueous solution contaminated by rhodamine B. The dual responsiveness enables Pickering emulsions to have better control of their stability and to be applied more broadly.

Nano-modification of carboxylated polyether for enhanced room temperature demulsification of oil-water emulsions: Synthesis, performance and mechanisms

Oil-water emulsions separation is frequently required considering the production and environmental issues. Herein, a nano-modification strategy has been proposed for carboxylated poly(propylene oxide)-poly(ethylene oxide) block polyether (mANP) using epoxy-functionalized magnetic nanoparticles (Fe3O4@SiO2-GPTMS), achieving the construction of a highly efficient demulsifier (M-mANP). Bottle tests showed that M-mANP could separate over 98.5% of water from the asphaltene-stabilized water-in-oil (W/O) emulsion at mANP concentration of 150 ppm within 2 min at room temperature. The demulsification efficiency for crude oil-in-water emulsion was nearly 100%. According to interfacial tension and wettability tests, the nano-modification endows M-mANP with good amphiphilicity and high interfacial activity, which enables M-mANP to rapidly adsorb at the oil-water interface. Molecular dynamics simulation shows that abundant oxygen-containing groups (hydroxyl, ether bond, ester and carboxyl groups, Fe−O and Si−O bond) in M-mANP could strengthen the interaction with water, facilitating the replacement of asphaltene molecules at interfacial film. Observation of demulsification process by microscope reveals that the nano-size promotes M-mANP to bridge small dispersed droplets, enhancing the flocculation and coalescence of droplets. The nano-modified carboxylated polyether with outstanding demulsification ability shows a promising application for the treatment of different oil-water emulsions.

Functional graphene oxide coated diatomite for efficient and recyclable demulsification of crude oil-in-water emulsion

The separation of micro-sized oil droplets from crude oil-in-water (O/W) emulsion is urgently required by petroleum industry and the environmental protection. Herein, we demonstrate a magnetically recyclable diatomite-graphene oxide (M-DM-GO) composite relying on the superior adsorption performance of graphene oxide (GO) and cost-effectiveness of diatomite (DM). Combining the improved positive surface charge by chemical grafting polyethyleneimine (PEI) on the GO surface, the as-prepared M-DM-GO exhibited high demulsification efficiency (Ed) of 96.8% for crude O/W emulsion with pH 6.0 at optimal dosage of 350 mg/L. Importantly, M-DM-GO displayed favorable demulsification performances under broaden pH conditions, suggesting its wide application scopes. Meanwhile, due to the magnetic response capability, M-DM-GO ensured efficient demulsification performance with Ed> 90% after 5 cycles. The efficiency, recyclability and wide pH application conditions make the M-DM-GO have universal application prospects in the management of crude O/W emulsion.

Alginate-based poly ionic liquids for the efficient demulsification of water in heavy crude oil emulsions

This work deals with the synthesis, characterization, and application of alginate-based poly ionic liquids for efficient demulsification of water in oil emulsions. For the formation of renewable poly ionic liquid (PIL), sodium alginate (S.ALG) was converted to alginic acid (H.ALG), followed by an esterification process to produce corresponding polyester, (N.ALG). In the later stages, the formed N.ALG was subjected to a quaternization reaction using either 1-bromohexadecane or 1-bromononane in order to produce PILs (BH-ALG) and (BN-ALG), respectively. Then, the two formed PILs (BH-ALG and BN-ALG) were evaluated in terms of the chemical structure, surface and interfacial tensions, thermal stability, relative solubility number (RSN), and micelle size. While testing the efficiency of as-synthesized two PILs towards the demulsification of water in heavy crude oil (W/O) emulsions, both PILs were found to be efficient. Furthermore, an increase in efficiency was observed with the increase of PIL concentration and ratio of water in the emulsions. Among the two PILs, the BH-ALG displayed higher demulsification efficiency as against the BN-ALG, and this can be due to its higher hydrophobicity, and hence its ability to disperse in heavy crude oil as a continuous phase.

An Experimental Study on Efficient Demulsification for Produced Emulsion in Alkaline/Surfactant/Polymer Flooding

Abstract Tertiary oil recovery technologies, for example, alkaline/surfactant/polymer (ASP) flooding, can enhance oil recovery as an important oil displacement technology noteworthy in the present oilfields. However, it is the fact that the produced emulsion droplets have strong electronegativity, which will lead to the destabilization of electric field and affect the dehydration effect in the process of electric dehydration. This article innovatively proposed an efficient demulsification scheme, which uses polyaluminum chloride (PAC) as a chemical regulator to control electric field destabilization through the charge neutralization mechanism and then introduces demulsifier to promote oil–water separation. Furthermore, the dehydration temperature, power supply mode, and electric field parameters are optimized so as to achieve superior dehydration effect of ASP flooding produced liquid. The results indicate that PAC as a chemical regulator by exerting charge neutralization and electrostatic adsorption mechanism could reduce the electronegativity of the emulsified system, decrease the peak current of dehydration, shorten the duration of peak current of dehydration, improve the response performance of the electric field, and increase dehydration rate in the ASP flooding dehydration process. When the demulsifier dosage is 100–120 mg/l, using the composite separation process with the dehydration temperature of 45–50 °C for the thermochemical separation stage and 60 °C in the electrochemical dehydration stage and AC–DC composite electric field or pulse electric field can achieve better dehydration effect. The investigations in this study will provide support and basis for the efficient treatment of ASP flooding produced emulsion.

Efficient demulsification of cationic polyacrylate for oil-in-water emulsion: Synergistic effect of adsorption bridging and interfacial film breaking

The development of reverse demulsifier is an urgent need for the increasing amount of produced liquid in oilfield. Synthesis of reverse demulsifier containing multiple characteristics is an effective method. In view of this, this study reports a series of cationic polyacrylates as the reverse demulsifiers, which were prepared by using 3-chloro-1-propanol to modify the copolymer of acrylate and N-[3-(dimethylamino) propyl] methacryamide (DMAPMA). The properties and performance tests showed that the PMD1 prepared by using methyl acrylate (MA) as monomer (mass ratio of MA to DMAPMA was 2:1) has well water solubility, high interfacial activity, and the best demulsification efficiency. For treating the produced liquid from an offshore oilfield, demulsification efficiency of PMD1 was 94.7% with 50 mg/L dosage, which was much higher than that of the reagent in use (15.7%). Furthermore, the demulsification mechanism of PMD1 was studied by oil-water partition coefficient experiment, zeta potential measurement, optical tweezers method, elastic modulus measurement, and coalescence kinetics experiment. Prominent demulsification ability of PMD1 was attributed to the synergistic effect of adsorption bridging via cationic group and oil/water interfacial film breaking by acrylate group. The cationic polyacrylate combines the advantages of polyacrylate and polycation reverse demulsifiers, which display a great application prospect in the petroleum industry.