Gavin Meechan, Senior Consultant: Flow Assurance
“What does a flow assurance engineer do?”, it’s a question I’m often asked. The answer is not so straightforward and if you asked a group of different engineers the same question, it’s likely you would get a different answer from each person. I’ve heard many different definitions but I think the best one is:
“Flow assurance is a structured engineering process that develops strategies which guarantee and optimise production from the near wellbore to the point of processing by predicting, preventing and solving problems associated with the behaviour of the transported fluids”.
The role played by flow assurance engineers in a project not only includes providing predictions but also prevention strategies and remediation methods in case of the occurrence of solids deposition leading to a pipeline blockage or jeopardising production. Flow assurance engineers are also responsible for providing prediction and interpretation of fluid characteristics, flow hydraulics, thermal behaviours and the guidance of operation strategies and procedures. To do this successfully flow assurance engineers need to interface with multiple engineering disciplines involved in a project, including subsurface, pipeline and risers, subsea hardware, topsides process facilities, chemical vendors and fluid laboratories.
Flow assurance is an independent engineering discipline that sits between the subsurface and wells disciplines and the process and facilities disciplines. It has evolved more significance as the oil and gas industry has developed fields more and more remote from host processing facilities (>150km) and in ultra-deep water (>2000m). It is primarily about identifying and managing the production risks associated with long multiphase flowline and single-phase pipeline systems.
In addition to interfacing with multiple disciplines, flow assurance engineers are often involved across the entire engineering project life cycle from conceptual select studies through FEED and detailed engineering to commissioning and operations support.
Figure 1 – Flow Assurance Throughout the Project Life Cycle
Flow assurance issues typically start whenever flow from the reservoir is confined, this often happens in pipelines including wellbore tubing or in process plant facilities or subsea processing facilities such as valves, manifolds, separators and slug catchers.
The key to flow assurance is understanding the behaviour of the production fluids inside these confined spaces where changes to the properties of the fluid may adversely impact on the ability to maintain the required flowrate. For example, fluid phase changes (vapour, liquid or both) due to changing temperature and pressure may cause issues. Additionally, the presence of other components such as reservoir water, sand, corrosion product, wax or hydrate formation might also be problematic.
The exact objectives of flow assurance studies may change throughout the project life cycle; for example, during the design phase the focus might be on prediction and prevention of issues which impact production, whilst during the operation phase the focus is more likely to be on control and trouble shooting. However, overall, the key objective for flow assurance engineers will always be to make sure we understand in detail the behaviour of the production fluid so that the desired production flowrates can be achieved.
The best source of fluid physical property and behaviour data comes from PVT laboratory testing and reporting. A flow assurance engineer can benefit from the results of lab testing where production fluids undergo changes in pressure and temperature, are mixed together or separated. Pipeline or plant measured instrumentation data (pressure, temperature and flowrate data) and the experience of plant operations teams can also provide an excellent source of data in relation to fluid behaviour.
In flow assurance models the fluid behaviour is predicted by mathematical models. Once armed with good quality PVT lab data an important task for a flow assurance engineer is to select the right tool to predict the fluid behaviour observed in the lab or observed in the plant. There are many commercial software packages; it is important to use the correct tool for the job, for example the best tool for investigating hydrate formation might not be the best tool for predicting pressure surge due to valve closure. An understanding of the different software packages available is therefore also important to ensure useful and meaningful results are achieved.
The different scenarios investigated by the flow assurance engineering group at Crondall include both steady-state and transient work scopes. In terms of steady-state flow assurance analysis, the following activities are typical:
Thermo-hydraulic analysis to assess the capacity and capability of a production system to ensure that production profiles can be met without being hydraulically or velocity constrained.
Investigation of system insulation requirements to ensure the system operates at steady-state without entering the hydrate risk region or drop below the wax appearance temperature.
Generation of pipeline pressure, temperature, liquid hold-up, velocity and contents density profiles for input towards project mechanical design engineering work.
Input towards topsides or onshore facilities design and development of system operating philosophies.
Transient flow assurance analysis is also essential to assist in the development of a more in-depth understanding of a system’s operability. At Crondall Energy, the flow assurance engineering group perform transient studies in order to develop an understanding of the time-dependent issues associated with the operation of a system and the impact of these instabilities through simulation and analysis of the following typical operating scenarios:
Shutdown cool-down, including calculation of system no-touch times and settle-out pressures.
Depressurisation analysis covering time to depressurisation, topsides restriction orifice sizing, minimum fluid temperature calculations and assessment of potential liquid surge volumes received at the pipeline outlet.
System start-up simulations to calculate well warm up times, minimum fluid and pipe wall temperatures, liquid surge volumes and hydrate inhibitor injection requirements.
Rapid transient events such as liquid surge pressures in export systems or over-pressure protection (HIPPS) trips in upstream systems
Using the results and findings from both steady-state and transient analyses, the Crondall Energy flow assurance engineering group also regularly work closely with the client project teams to assist in the development of operating philosophies and operating procedures for a system. Typical examples include providing support in the development of hydrate and wax mitigation philosophies or supporting the generation of detailed operating procedures explaining the steps to be taken when performing transient operations such as depressurisation, start-up or shutdown.
The offshore oil industry, while facing a constant increase of the world energy demand and a decrease of the conventional oil reserves, is turning towards new technological oil reserves, especially deep offshore reserves or the development of small accumulations which necessitate lengthy tie-backs to existing infrastructure. As flow assurance issues become more and more critical and existing flow assurance design boundaries continue to be pushed, the role of the flow assurance engineer will continue to integral to the successful development and operation of offshore oil and gas fields.
If you would like to know more about our flow assurance capabilities and how Crondall Energy can support your requirements please contact myself, Gavin Meechan, or our flow assurance technical lead, Murray Anderson at email@example.com.