Flow Assurance - a definition
Since the beginning of the 1990s the term "Flow Assurance" is used to designate the assurance of oil and gas transport in pipelines. It covers the fields from subterranean or subsea deposits over the drill hole up to the preparation and processing in refineries. These fields comprise versatile tasks and areas of special knowledge. The newer term "Flow Management" is used parallel with "Flow Assurance".
1. Crude oil consists of more than 1000 different components
Crude oil is a very complex mix of several thousand different hydrocarbons comprising variable amounts of heteroatoms like sulfur, oxygen, nitrogen as well as diverse metalorganic compounds. From soluted gases (hydrocarbons gaseous under standard conditions = atmospheric pressure and room temperature) to heavy substances like resins and asphaltenes it comprises many different fractions, which can be sorted and separated by their different physicochemical properties.
2. Composition differs from deposit to deposit
From deposit to deposit large differences in the composition of crude oil can be observed. The variety of conveyable oils spans from straw-coloured, low viscosity oils to deeply black, heavy oils.
3. Impurities in crude oil and petroleum gas
Crude oil and petroleum gas can not always be conveyed as pure oil or gas. Oil and gas can be mixed with water and oil can be mixed with gas enclosed in the deposit. This multi-phase mix can cause severe problems in transportation and processing.
You can differ between two- and three-phase mixes. Three-phase mixes are more common in oil production than two-phase mixes.
2-phase mixes: Crude oil and petroleum gas, crude oil and water or petroleum gas and water
- 3-phase mixes: Crude oil, petroleum gas and water
4. Changing ambient conditions during conveyance
Enclosed in the deposit with pressures of more than 1000 bar and temperatures of more than 100°C every oil is fluid and pourable. But on the way from the deposit to the surface the pressure and temperature decrease with every foot, which facilitates the formation of different precipitations. Already before reaching the drill hole first inhibitors (chemical agents inhibiting formation of precipitations) have to be added. Crude oil and petroleum gas adapt to the new ambient temperature at latest in the pipeline to the first processing station.
The situations described above provide the need for flow assurance each on its own and in their complex combination variations. The problems caused by described situations comprise a variety of precipitation forms like asphaltenes, wax, scale, gas hydrates and other particles in pipelines and processing plants. Furthermore, for example corrosion can occur or the optimal adjustment of pressure and temperature conditions during transport is difficult.
Precipitations decrease the flow rate by narrowing the pipeline diameter and can in worst case plug whole pipeline segments. This precipitations can only be removed with high efforts either physically (heating or shock pressure) or chemically (solvents). The costs and production downtime for these measures are very high.
To prevent or slow down the formation of precipitations inhibitors and additives have to be used to improve the flow properties.
As the different additives for improving flow properties and additives for influencing general properties interact, thereby changing their effects. Aside from the development of new additives these interactions are an area of research.
Manufacturers of chemicals and service providers in the area of flow assurance have to test their products under as realistic conditions as possible, with reliable and reproducable results. As a wide range of chemicals has to be tested under a variety of ambient conditions and with versatile methods, the measuring instruments have to be specially developed.