Designing of a washing composition model to conduct the hot flushing wells producing paraffin crude oil
Introduction
Wax deposition is one of the most common problems in oil production and transportation in the Ural-Volga fields (Ilyushin et al., 2021; Rogachev and Aleksandrov, 2021). Wax deposition is a mixture of a wide range of nonpolar high-molecular-weight alkanes that can crystallize from crude oils or solutions primarily due to temperature decrease. The main problems prevailing in Perm Krai include wax deposition, high-viscosity emulsions, active corrosion of equipment, scale build-up, large amounts of solids, etc. (Fig. 1).
At present, the problem of wax deposition becomes increasingly challenging in the context of reserves depletion and increase in the number oil fields transitioning into the mature state of assets (Jalalnezhad and Kamali, 2016; Khaibullina et al., 2020). This transition results in the change in performance data of formation fluids production: water production increase, bottom-hole and reservoir pressure decline and production composition change (Wang et al., 2019). Such performance trends contribute to premature organic deposition (Rogachev et al., 2021) and often result in shifting the wax deposition onset point from the tubing to the pore space of the productive formation.
The process of wax deposition in the formation fluid flow is accompanied by its accumulation on the cold surfaces - on the tubing inner or outer walls (Bai et al., 2019; Vyatkin et al., 2021). Organic deposition on the tubing's inner surfaces reduces the hydraulic radius and, consequently, increases pressure in the well or oil gathering system. This poses a high accident risk (Zheng et al., 2021; Gawas et al., 2015). Organic depositions may also accumulate in the power parts of oil-field equipment (Bell et al., 2021). This reduces its service life and results in its failure (Lei et al., 2016; Quan et al., 2016). Since wax deposition induces severe consequences, removal of wax deposits are a priority in subsoil users' operations (Ali et al., 2022; Ilyushin et al., 2022a).
Wax deposition can be controlled in two ways: by deposition prevention and removal (Akramov and Yarkeeva, 2017; Lyapina et al., 2017). The above methods can be classified by active factor (Ilyushin et al., 2022b; Struchkov and Rogachev, 2017) with application of the corresponding technology (Table 1) (Ilyushin et al., 2022c; Wang et al., 2017; Sousa et al., 2019).
Physical methods of preventing the formation of deposits can reduce the ability of solid deposits to deposit (adhesion) on the surface of equipment.At the same time, the chemical composition of the extracted products remains unchanged, which is a positive side. The disadvantage is the high price of equipment, the complexity of selecting oil treatment conditions and low technological efficiency.
Chemical removal of wax deposits is one of the most promising and environmentally safe methods to remove paraffin deposits in wells and pipelines (El-Dalatony et al., 2019; Thota and Onyeanuna, 2016). This method shows high process efficiency, easy use of chemical agents and their prolonged effect. Based on (Ilyushin et al., 2022d; Martyushev, 2020; Towle et al., 2011; White et al., 2018) it can be concluded that all removers and solvents of wax deposits, discussed in the Russian and foreign literature, can be classified into hydrocarbon organic solvents and aqueous solution. The main drawback in the use of organic solvents is their high cost and fire risk (Akhsanov et al., 1994; Ketova et al., 2020). Therefore, aqueous compositions with surfactants have come into common practice. Surfactants is substance such as a detergent that, when added to a liquid, reduces its surface tension, thereby increasing its spreading and wetting properties. Their cost being much lower, a relatively high wash temperature shall be maintained along with the use of much larger volumes of the working agent at low dosages of active solids to gain sufficient process efficiency.
The most well-proven technological operations for the purpose of thermal removal of organic deposits into producing wells can be divided in three groups: washing with hot water, hot oil or steam (Jiang et al., 2020; Yuan, 2016; Ilushin et al., 2022). The disadvantages of these methods are: the lack of control of the composition, properties of the coolant and the inability to remove organic deposits placed on a high depth (He and Gao, 2013).
The aqueous compositions under review fall into a group of detergent solutions, since their primary action consists in dispersion and washout of deposits. When using detergent compositions, the main stages (Fig. 2) are dispersing, washout, wetting the metal surface and deposits, as well as their stabilisation, i.e. preventing their re-deposition on the cleaned surface. The compositions under review are used at high temperatures to reduce their viscosity and improve penetration into deposits through cracks and pores. This can be also contributed by adding surfactants to the solution, which decreases the surface tension at the boundary of the detergent and wax deposits (Fig. 2, Stage 1). When the detergent penetrates into the deposits, their dispersion (Stage 2) and washout by partial dissolution, melting of organic deposits and breaking of adhesive contact with the metal surface (Stage 3) take place. Re-deposition of wax deposition on the cleaned surface is prevented by a protective film created on the surface and by keeping the removed depositions in suspension (Stage 4). The protective film is created by surfactants in the detergent composition, while a structure-forming agent is added to the detergent to keep the wax particles in suspension (Ibragimov et al., 1986).
The operational task consists in the reasonable choice of an optimal formulation for detergents and hydrocarbon solvents in industrial conditions; moreover, agent delivery, well treatment and removal of washed out deposits into the gathering and transportation system shall be considered in terms of cost efficiency. The set task is solved through the development of effective models of a detergent using available chemicals and its application technology that allows reducing costs for it use and re-use with a minimum impact on the oil gathering and processing system. This work aims to develop an efficient and cost-effective basic detergent model and a technology of its application in the wells producing paraffinic oil.
Section snippets
Investigated oil temple
Well ‘M’ of oilfield ‘N’ has been selected as a target for the hot detergent choice. Physical and chemical properties of the target's formation fluid are given in Table 2.
Determination of the necessary components of the detergent
The analysis of scientific research papers (Krivoshchekov et al., 2021; Pacheco-Sanchez and Mansoori, 1997; Levitina, 2008; Kudasheva et al., 2010) has determined the optimal list of components for the development detergent solution given in Table 3.
Determination of the optimal composition and conditions of application of the detergent
To determine the optimal ratio of components in the detergent solution under
Results determination of the optimal concentration of the active ingredient's
Laboratory test to define the active ingredient's optimal concentration is the initial stage of determining the best detergent formulation (Fig. 4). The results of assessment of variation in the organic deposits removal efficiency against the active ingredient concentration are shown in Table 4. The study was carried out under test temperature 45 °C, WAT is 26 °C.
Table 4 shows that with an increase in concentration above 2.5%, the wax deposition removal efficiency does not increase, and it
Conclusions
During the development of washing composition model to conduct the hot flushing wells producing paraffin crude waxy oil authors received achievements as following:
- 1.
The highest efficiency of the detergent solution has been observed with 2.5% active ingredients composition. It is established that exceeding 2.5% concentration does not lead to increasing of deposits removal efficiency.
- 2.
The efficiency of using hot water is significantly lower - by a factor of 1.95–2.13 than that of the detergent
Credit author statement
Aleksandr Lekomtsev: Conceptualization, Data curation, Writing- Reviewing and Editing. Anton Kozlov: Software, Writing – original draft, Investigation. Wanli Kang: Methodology, Software, Validation. Aleksey Dengaev: Software, Validation, Visualization.
Funding
This research was carried out with the financial support of the Ministry of Science and Higher Education of the Russian Federation in the framework of the program of activities of the Perm Scientific and Educational Center “Rational Subsoil Use”.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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