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Introduction

There are various organic compounds that show lipophilic properties, especially at room temperatures; a notable example is “Wax” (Chi et al., 2018). They are hydrophobic but depict solubility in organic and nonpolar solvents. The number of chains or branches in a particular wax sample significantly affects its properties (Chi et al., 2017).  Petroleum wax is usually obtained from crude oil, as it is one of its constituents (Singh et al., 2017).

Wax formation depicts some unwanted phenomena, with precipitation, gelling and deposition being among them (Quan et al., 2020).

This experimental study aims at investigating the phenomenon of wax deposition, as this concept seriously affects various multinational oil companies in the oil industry both technically and economically (Adeyanju and Oyekunle, 2019). The deposition of waxes in oil pipelines constricts the pipelines, therefore restricting flow and reducing the flowrate of crude oil (Chi et al., 2019).  This blockage seriously affects production by tampering with various operating conditions especially causing pressure anomalies (Janamatti et al., 2019). It also translates to damage in formations at various spots near the wellbore, significantly causing irregularities in fluid composition and fluid flow due to the precipitation of the solid wax, and also significantly reducing the permeability of the membranes (Li et al., 2018).

The wax deposition does not usually occur in the wax’s solid state, but rather a mixture of phases where the wax crystals entraps the liquid – a gel (Wang et al., 2020). Hardening occurs with time; this is described as “aging” (Soedarmo et al., 2017).  The properties of waxy crude oil is significantly different to that of the wax-less crude oil in that the wax components precipitate out of the oil, this is responsible for properties like a significant increase in viscosity and the oil gelling (Sun et al., 2020). The main components of Wax are the significantly long chained alkanes and the heavy n-Paraffin molecules (Quan et al., 2019).

There is a production temperature at which the formation of the foremost wax crystals begin to occur, this is termed the Wax Appearance Temperature (WAT) (Xiao et al., 2018). This formation begins after cooling has taken place. At this point, the unusual occurrence of the wax precipitating out in its solid state could take place. This wax deposition on the pipeline walls occurs when the wax appearance temperature becomes higher than the temperature in the inside of the walls (El Gheriany et al., 2020).  The reduction in the temperature of the crude oil instigates the vaporization of lighter chained hydrocarbon molecules, this temperature reduction must occur below a certain point for this phenomenon to occur (Yang et al., 2020). The formation of highly insoluble crystals occurs as a result of the wax dissolution (Venkatesan et al., 2018). Asphaltenes and other components in their solid state act as nucleating agents in order to enable the wax deposition phenomenon. Hence, a deposit usually contains asphaltenes, salt and dirts among others (Piroozian et al., 2017).

Determination of the WAT and the amount of wax precipitated at a given temperature are critical for understanding the crude oil rheology and solids deposition (Agarwal et al., 2017). Various works have developed and tested a simulating wax deposition model in pipelines based on diverse literature (Kang et al., 2019). Results found in model pipelines indicate that deposition occurs due to radial mass diffusion driven by the concentration gradient induced by a temperature gradient (Li et al., 2021). They conclude that the Reynold numbers and the mass Peclet number profoundly influence the mass deposition rate (Li et al., 2021). They found a steep increase in the solid deposition with Reynolds number up to Re ≈ 100, where a more gradual increase is observed for higher Reynolds number. A further observation in their study was a decrease in the mass deposited when Re > 2000 (Li et al., 2020). They stated that the reason for this phenomenon from the fact that the shear forces will remove deposit on the wall and thereby decrease its thickness (Bell et al., 2021). When estimating the average molecular dilution coefficient, they found that there is an important connection between the mass Pellet number and the radial mass (Li et al., 2019). A substantial dependence of the deposited mass layer-thickness on the determined average diffusion coefficient was observed (Mansourpoor et al., 2019).

Problem Statement

A major challenge faced in the oil industry is wax deposition. It poses numerous concerns in both onshore and offshore operations, it also stands out as the major problem that affects the quality assurance of fluid flow in oil industries (Theyab and Yahya, 2018). The capital and operating costs involved in managing problems posed by the phenomenon of wax deposition are usually gargantuan (Alnaimat and Ziauddin, 2020).  These costs also extend to its prevention and various safety and environmental concerns arising from wax deposition (Gao et al., 2021). They amounts to major losses in billions of dollars globally (Theyab and Yahya, 2018).

Aim and Objectives

This study aims at investigating wax deposition in a test flow loop with the following objectives:

• Objective 1:  Studying the fundamentals of wax formation and the factors that influence and control wax deposition (Theyab and Yahya, 2018).
• Objective 2: Provision of essential information towards improving the understanding of wax deposition.
• Objective 3:  Experimental determination of the relationship between wax deposition rate and the inherent properties of certain crude oil samples (Makwashi, 2020).
• Objective 4: Evaluation of the implications of varying operating conditions (e.g. new fluid composition) on wax deposition rate (Aguiar et al., 2020).
• Objective 5:  Selection of the most effective wax inhibitor and the determination of its optimum dosage for specified crude oil samples (Oyekunle et al., 2017).

Research Questions

The identified research questions for this project are provided below:

• How would the experiment be  carried out?
• How would the evaluation be carried out?
• What decision would inform the selection of an appropriate wax inhibitor?
• How would the optimum dosage of the selected wax inhibitor be determined for various crude oil samples?

Deliverables

The deliverables of this project are a project report and obtained results.  Also, the report should contain a complete documentation of how the laboratory experiment was carried out, how the selection of wax inhibitor was arrived at, how various process variables were gotten, and how the optimum dosage of the selected wax inhibitor was determined.

Relevance

The study mainly focuses on studying wax deposition in a test flow loop, and determining the optimum dosage of the selected wax inhibitor for various crude samples.

Methodology

This project focuses on secondary research, laboratory experiments and process analysis, and they are discussed below:

Secondary research

The secondary research in this project will utilize a systematic approach (Johnson et al., 2016) to review the works of literature. The steps involved in the systematic review of the literature are provided below:

• Step 1: Identify the research questions that can be used for the project.
• Step 2: Identify the keywords that should be used to research the works of literature.
• Step 3: Extract the journals and books that are appropriate for this project.
• Step 4: Write the literature review chapter.

Laboratory experiments

The laboratory experiments would cover a large chunk of this project. They would be carried out in stages, and as such described below;

• Stage 1:  Sourcing for the required crude samples, and other required inputs
• Stage 2:  Developing an appropriate process route and test flow loop.
• Stage 3:  Carrying out the experiment.
• Stage 4:  Analyzing the process.
• Stage 5:  Selection of required wax inhibitor.
• Stage 6:  Determination of optimum dosage of wax inhibitor.
• Stage 7:  Varying process conditions.

Process Analysis

The totality of the process would be analyzed and this would also occur in stages;

• Stage 1:  Process Testing
• Stage 2:  Process Control
• Stage 3:  Process Optimization

Evaluation

The risk assessment conducted for this project is provided in the table below:

Table 1:  Risk assessment