Role of surfactants, polymer, nanoparticles, and its combination in inhibition of wax deposition and precipitation: A review

Wax deposition is one of the most critical issues of crude oil production, transportation, and processing. Waxes, which are the heavy components in crude oil like paraffin, are dissolved in the underground oil reservoir, at a higher temperature (~60 °C) which keeps them in a liquid phase [1,2]. As oil is extracted, temperature change occurs and wax deposition starts to form which causes the waxes to start to crystalize and get deposited on surfaces [2]. When the mass content of wax crystals exceeds 1–2%, a 3-D network of wax gels forms containing entrapped oil inside the network [3,4]. The continuous accumulation of these sticky and gummy-like gels increases oil viscosity and increases the pressure drop [1,5]. When the gel yield stress is high enough to exceed the pipeline pressure gradient, oil starts losing its fluidity, causing pipeline blockage that can result in equipment failure. The low-temperature environment enforces the wax deposition process, especially in cold countries or at subsea facilities, where the temperature is less than the wax crystallization point (wax apparent point, WAT) [1,2,6]. The accumulated wax-crystal layers cause pipeline blockage and facility equipment failure, leading to production loss and higher maintenance costs [6].

Process design takes into consideration the mitigation of the wax deposition in equipment and the transporting pipelines, such as heat tracing and thermal insulation [5]. Predictive models can also be used for design considerations and wax deposition remediation schedules [7]. Wax deposits are usually periodically removed by mechanical pigging and chemical remediation [5,8]. These techniques add more production and operational costs [2,7]. Wax deposition control has gained a lot of interest in the past decades [5,[9], [10], [11]], specifically chemical wax control management [5].

Chemical wax control is summarized in three main categories, namely: crystal modifiers, dispersants, and solvents [[12], [13], [14]]. Crystal modifiers (or pour point depressants, PPDs) are mostly linear or comb-shaped copolymers, e.g., maleic anhydride copolymers (MAC) and polyethene-butene polymers (PEB). The crystal modifiers act by interacting with the growing wax crystals and altering their surface characteristics [5,12,15,16]. This alters the crystal domain types and inhibits continuous wax crystal growth [15]. Dispersants or surfactants, such as alkyl sulfonates, have the same basic role as the PPD modifiers. Dispersants prevent wax agglomerations by surfactants adsorbing (coating) the wax crystals or the equipment's interior surfaces. The adsorbed dispersants repel wax crystals and molecules from agglomeration or bonding on the surface, forming a fluidizable slurry or emulsion-like fluid rather than becoming adhered to the walls [14,17]. Chemical solvents (e.g., xylene, toluene, hexane CCl4, and CS4) are commonly used in the field by dissolving or melting away the deposits [14,18]. These treatments have several drawbacks, such as the lack of general applicability, where the inhibitor is efficient with specific types of crude and not with others [19]. Also, the continuous increase in chemical cost, energy consumption, and environmental concerns that are combined with chemical treatments have increased challenges in wax research and development efforts [11].

The tremendous development in nanotechnology has attracted several studies to involve nanoparticle technology in wax inhibition [10,11]. In fact, nanoparticles (NPs) are the foundation of the development of nanotechnologies, and several reviews describing their preparation and applications are available in the open literature [20]. In addition to their small size (e.g., below 100 nm, at least in one dimension), nanoparticles have a large specific surface area per unit volume holding specific atomic sites that enhance their adsorption and catalytic properties. Nanoparticles portray novel and unique properties not found in their bulk counterparts. Various nanoparticles have been modified and used as wax inhibitors, such as silica [21], clay [22], and carbon nanostructures [23,24]. Further, Nanoparticles have been successfully employed in the oil industry for enhanced oil recovery applications [25], lubricants improvement [26], asphaltene adsorption, and heavy oil upgrading [27]. Thus, the development of new inhibitors by proposing nanoparticle technology, in the form of hybrid-nanoparticles is highly desirable in this field [10,11,28]. Using nano-inhibitors with small dosages and high efficiency can lower operating costs and increase production rates by mitigating or inhibiting the formation of deposited or gelatinous wax layers. Therefore, understanding the mechanisms of interactions between these nanoparticles and oil waxes during crystallization is crucial for the development of effective inhibitors.

In this review paper, the recent research on wax deposition inhibition has been analyzed and summarized. The inhibition mechanisms of various types of inhibitors were identified based on the inhibitor type and category. The techniques of synthesizing and modification of novel wax inhibitors are discussed. The key performance parameters and characterization techniques of the available literature are presented. Also, bibliometric analysis methodology has been conducted based on the available Scopus database reported from 2000 to 2022. Analysis of the recently published articles provides details on the global research trends in the field of wax deposition. The outcome of this review is to discuss the latest progress, challenges, and future directions of wax deposition during oil and gas production.

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