Flow Assurance
Flow assurance is one of the most important areas of study of the Upstream process, which focuses on maintaining good flow conditions along the lifting and transportation of the produced fluids (oil, water, and gas). In the production system, a range of chemical and physical phenomena can occur because of the fluids’ composition and pressure/ temperature to which these fluids are subjected along the flowlines. On the propitious scenario, several phenomena can seriously impair or even block de flowlines.
The ALFA group has been developing fundamental and applied studies in Flow Assurance that englobe different subareas within the field of petroleum science, such as emulsions, wax, asphaltenes, inorganic scales, and crude oil foams. The studies are focused on mastering the phenomena, risks evaluation, methodologies, and techniques for mitigation/ remediation, as well as the effects of temperature and pressure on their efficiency. The studies are performed in laboratory scale, in static condition, as well as in pilot/ industrial scale, under flow-controlled conditions.
a. Wax
Crude oils with high content of paraffinic compounds, also known as wax fraction, are highly common, especially in light crude oils, as those usually found in Brazilian pre-salt reservoirs. The wax in this kind of crude can undergo a phase transition, thus forming tiny crystals, when subjected to the low temperatures at the seabed and other points of the production flowlines. The wax crystals can impact the production by forming gels during maintenance stops, making it hard to restart the production. Wax crystals can also accumulate on the production line walls and these deposits can grow and age, leading to a full blockage of the pipelines in worst case scenarios.
The ALFA group has studied the fundamentals of wax deposition for years, focusing on characterization of waxy crudes, a study on the relationship between the gelation and deposition phenomena, demonstrating that wax deposition is a phase transition rather than a molecular diffusion phenomenon, while also researching the chemical and physical properties of the crudes. ALFA also conducts studies regarding the efficiency of inhibitors (dispersants), Pour Point reducers, and other methods for mitigating wax deposition.
b. Emulsion
Emulsions are defined as liquid-liquid dispersions, which cause several problems for the oil production, such as the significant rise in the viscosity of the emulsified fluids. The increased viscosity severely impacts the efficiency of the crude lifting, as well as the lifetime of components of the lifting systems, such as ESPs. The ALFA group has been studying emulsions since 2007, focusing on emulsion stability, formulation, physical and chemical characterization, viscosity, and inversion point modeling. The last two research topics have been the focus of the emulsion studies because of their serious impacts on oil production. The knowledge of phase inversion boundaries in ESP’s is of high importance to understand instabilities usually observed in field production, information that can be strategically used to reduce damages to ESPs caused by the huge instabilities associated to the phase inversion. The knowledge of the main emulsion characteristics that define these parameters will be very important to develop novel prediction models or even improve the prediction ability of most models for viscosity and inversion point.
c. Foams
Foams are gas-liquid dispersions that can be produced by different processes. Along the crude oil lifting process, gas bubbles nucleate in the bulk of crudes when the pressure drops below the bubble point of the system, producing a layer of foam which, by density issues, accumulate at the upper part of three-phase separators.
In production, foams mostly impact the crude processing steps at surface unities, where they can cause separator overflow, instrumentation malfunction, fluid carriage through gas flow, contamination of the gas purification systems, etc.
The ALFA group has been studying the principles of the foam formation and collapsing processes, properties of liquid-gas interface, factors which contribute to foam stability, mechanisms of antifoamers and defoamers, focusing on the improvement of additive efficiency and on the development of new laboratory scale methodologies to test additives for foam control.
d. Scale
Inorganic deposits, usually called scales, are a type of deposit composed of low solubility inorganic compounds. There are several classes of salts and oxides that can precipitate and deposit along the production system, such as Carbonates (mostly CaCO3,) halite, iron oxide, sulphides and sulphates (mostly CaSO4, SrSO4, and BaSO4). The mechanisms behind scale formation (distinct for each type) are quite intricate and are still under investigation. Regardless of the type, the deposits can severely impair production by constricting or even blocking the lifting lines.
The occurrence of scales are usually caused by changes in fluid composition and/ or operational conditions (pressure, temperature, flow rate, etc). The focus of the ALFA group lies on the fundamentals of the deposition process, aiming to improve the predictability of thermokinetic models for static and dynamic systems.
e. Asphaltene
Asphaltenes are among the most important problems of production line blockages, mostly affecting light oils at specific pressure and temperature conditions. Asphaltene deposits are hard to deal with and may require expensive chemical and/ or mechanical techniques to clean the system. Thus, the most efficient way to deal with asphaltene deposition is by mitigating the complex process of precipitation and deposition with inhibitors.
The complex process of asphaltene precipitation and deposition has been studied for a long time but the development of reliable models still depends on the representativity of the small-scale experiments, such as PVT or solvent as precipitation inductors, for the real production systems. In this research line, the ALFA group focuses its studies on precipitation and deposition, a mechanism of inhibitors to mitigate the deposition process and the scale up of laboratory results.