Flow control in hydrocarbon production lines has recently emerged as a key factor for successful oil development projects, especially in deep offshore contexts. The term “flow assurance” was coined by Petrobras (garantia de escoamento) in the early 1990s. Exploration and production techniques are used to identify hydrocarbon fields and extract their resources, but it is also necessary to transport them to a storage or processing facility as efficiently and cost-effectively as possible.
The context for deep offshore flow assurance
Companies have developed a variety of definitions for flow assurance (FA), which in basic terms involves maintaining a flow of effluents from oil wells. For us, it means conceptualizing and carrying out the operations, which include injections but not processes, needed to transfer effluents from the reservoir.
With deep-sea developments, FA faced new challenges resulting from unprecedented temperature and pressure conditions. Now more than ever, we must prioritize the economic value of these developments. This means inventing new, more streamlined architectures, but with more complex designs and facility operations.
FA covers the following scope:
- evaluating problems linked to the component fluids of production effluents
- designing circulation, export and injection lines, while taking into account hydraulic and thermal conditions to maximize efficiency, safety and security
- evaluating the behavior of these lines over time throughout the lifetime of the field
The FA approach is based on three main points: modelling flows and thermal transfers in production and export lines, addressing gas hydrate formation, and combating the development of wax crystals.
Flow assurance: overcoming formidable challenges
With regard to flow modelling, we know that future developments will be located in more challenging environments involving even greater transport distances, water depths and line diameters. This will require new architectures that take into account a form of effluent processing that is very limited or that takes place under conditions that include unusual pressure or temperature interactions, or even pulsating flows (slug fllow) over large distances.
Moreover, many uncertainties must still be studied and addressed by R&D, as the proposed plans have never been tested in deep offshore environments. The consequences of this lack of information are amplified by the challenging access conditions involved in the deployment of intervention methods.
This is the case for directing and validating flow models in lab experiments and studying flow interactions vs. fluid chemistry (e.g. for emulsions, viscous fluids or pulsating systems) and flow vs. structures.
In addition to flow modelling and the two major problems of gas hydrates and wax crystals, FA must also consider flow modelling for wells and conditions that lead to corrosion, erosion and sand deposits, as well as ways to predict and prevent deposits of asphaltenes, calcium naphthenates or various minerals (CaCO3, BaSO4, SrSO4, PbS, ZnS, etc.).
A rigorous methodology
To make up for a lack of data, we have created an exhaustive Corporate Reference System comprising Rules and Guides & Manuals relating to FA. These materials are crucial for several reasons: first because FA is a new discipline with no existing internationally recognized industrial standards; and second because these documents make it possible to incorporate operational feedback and R&D results regarding technology and modelling, which we can then adapt to operational requirements.
Current and future operations
In deep offshore projects, flow obstacles mainly arise from the chemistry of complex fluids. The goal of the FA approach is to anticipate and estimate risks for deposit formation, which is not an easy task.
For this reason, we do not yet know how to treat long multiphase lines for wax. As for hydrates, some solutions do currently exist, such as avoiding the hydrate zone or preserving production lines during shutdowns. Here at Total we are working on new solutions for our projects, such as the use of natural properties of some oils to delay hydrate formation or use low dosage hydrate inhibitor (LDHI) additives in order to operate in the hydrate zone without risk, whether temporarily or on a permanent basis. The use of LDHI in gas fields is unique to Total (South Pars in Iran in 2002 and Dolphin in Qatar in 2007).
Support for cutting-edge research
Total is an active player in various FA research projects, in collaboration with other companies. Our goals are to develop new modules and functionalities and to improve the precision, reliability and calculation time for these projects.
The projects pertain to FA for wells (vertical flows), transport and precipitation in the form of deposits (non-Newtonian fluids, hydrates in suspension, wax deposits), flow induced vibrations (FIV) especially in jumpers and spools, slug catching and optimizing calculation times.
Total also played a leading role in the development of the LedaFlow transient multiphase flow simulation software in partnership with ConocoPhillips and Sintef. The validation of and ongoing improvements to LedaFlow are now taking place via the LIFT forum (LedaFlow Improvements in Flow Technology), created through a joint industrial project (JIP) operated by Kongsberg and involving Total, Chevron, ConocoPhillips, ENI, Lundin and Woodside.
Technical Responses to New Challenges
Flow Assurance with Multiphase Pumps
Springs®, Cutting Edge Technology