Flow Assurance Presentation - Rune Time 2

Scandpower Petroleum Technology

Flow Assurance and Multiphase flow part II Prof. Rune W. Time Depart Dep artmen mentt of Pet Petrol roleum eum Engi Enginee neerin ringg Univ Un iver ersi sity ty of St Stav avan ange gerr

Seminar Seminar at Aker Solutions, Solutions, Stavanger Stavanger – May 31st, 2011

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ut ine an time sc e u e

8.30 – 9.15

Flow regimes and impact on phase slippage, fluid concentratio concentrations ns and pressure drop in

9.25 – 10.15 Hydrates, wax and asphaltenes 10.25 10.2 5 -11.0 -11.00 0

Multipha Mult iphase se flow – infl influenc uence e from inte interfac rfaces, es,

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Seminar at Aker Solutions, Solutions, Stavanger Stavanger - May31st, 201 2011 1

ut ine an time sc e u e

8.30 – 9.15

Flow regimes and impact on phase slippage, fluid concentratio concentrations ns and pressure drop in

9.25 – 10.15 Hydrates, wax and asphaltenes 10.25 10.2 5 -11.0 -11.00 0

Multipha Mult iphase se flow – infl influenc uence e from inte interfac rfaces, es,

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PART II Hydrates, wax and asphaltenes + Scale, Emulsions and Erosion

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Flow assurance projects

– Norway

: a o s u p ase ec no ogy eve op en Programme 1993-97. Summary “Cost savings through Multiphase Solutions”. Products: • • • • • • •

Subsea multiphase meters and pumps Long-lasting multiphase chokes Mobile multi-test unit and total fluid management procedures ew n us ry s an ar mu p ase ow s mu a or Increased c-steel pipeline applicability (NORSOK) Leading edge hydrate mitigation procedures Heated pipeline concepts for hydrate and wax control

between Statoil, Saga and Hydro (SSH) launched in 1995 with objective to improve the methodology technical ability to transport and effectively separate them. Seminar at Aker Solutions, Stavanger - May31st, 2011

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Flow assurance and precipitation of solids • • • •

Hydrates: Ice substance ax: ara ne wax crysta c Asphaltenes: Aromatic solids In production oil systems very complex, heterogeneous and .

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Seminar at Aker Solutions, Stavanger - May31st, 2011

Wax, asphaltenes and more

…

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Mercaptans are the most odoriferous substances known to mankind and are the su s ances oun n un spray an e chemicals used to odorize natural gas, but in extremely low parts-per-billion concentrations. http://www.spentcaustic.com/tragedy.htm

http://tigger.uic.edu/~mansoori/HOD_html

also called thiols or organic sulfides


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Phase transitions

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Relevant phase transitions for flow assurance

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The long and transforming travel of oil from reservoir to tank

Hydrates

Asphaltenes

Wax

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HYDRATES (Hammerschmidt, 1934) • Gas hydrates are crystalline materials where water molecules form a framework containing cavities which are occupied by individual gases or gas mixtures (e.g. methane, ethane, propane, isobutane and inorganic . Ref: SSH Multiphase program: 235

Hy rate gas oa ing

Appearance


Burning ice

"Ice that burns" could provide enormous amounts of energy, but can it10 be made envi ronm ent all y friendl y? (Image: USGS)

versus ice:

Hydrate (clathrate) structures

http://www.pet.hw.ac.uk/research /hydrate/hydrates_what.cfm

”Cages” fit different molecules. How to know? - Experiments (inhibitors) Seminar at Aker Solutions, Stavanger - May31st, 2011

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Hydrate flow assurance issues Hydrates? Gulf of Mexico – ”Horizon” 2010 (Exam problem - Multiphase course)

Environmental issues

e r ng r g or zon exper ence a gas- c w e r ng for BP in the Gulf of Mexico on April 21 st 2010. The rig sank and oil leaked out from the well at a flow rate Q L = 10 L/s. Several methods have been proposed to prevent the oil from spreading on the sea surface. In one concept a large hood (funnel) as shown in the figure above will be positioned over the well head with a vertical pipeline system leading the oil up to the sea surface for collection.

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Hydrates and inhibitors Hydrates form when light hydrocarbons meet with water, typically at T < 15° - 25°C at elevated pressures. •

Conventional methods of hydrate control typically costs . Use of conventional inhibitors requires large storage tanks on systems for injection and possible regeneration.

“Thermodynamic” inhibitors (methanol or glycols) require concentrations around 30-70 % wt of water. •

•

New low concentration inhibitors (LCI), conc. < 0.5 %wt , T< 5 °C. 13


Low Concentration Inhibitors

(hydrate control)

LCIs work in two di erent anners: 1. The kinetic inhibitors impact on the kinetics, preventing or dela in h drate formation. 2. Hydrate modifiers allow hydrates to form, but as transportable particles. 14


Other hydrate mitigation techniques irect e ectrica Åsgard field

eating:

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Cold flow principle - Sintef

Stable dry hydrate slurry forms

Hydrate recycle loop Flow from wells

Hydrate recycle ’crash cools’ the incoming warm well stream

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Definition?

(J.B. Boussingault , 1837)

Asphaltenes are: - High molecular weight polycyclic organic compounds with nitrogen, oxygen and sulphur in their structure, in addition to carbon and hydrogen - Presence in petroleum fluids is defined as the fraction of petroleum fluid (or other carbonaceous sources such as coal), which is soluble in benzene and deposits, by addition of a low-boiling paraffin solvent. - Not crystallised upon deposition from petroleum fluids and as a result, its phase-transition from liquid to solid does not follow the same route as . - Not easily separated into individual purified components or fractions. Ultimate analysis not very significant, since resins are strongly adsorbed by asphaltenes - and not easily quantitatively separated from them. Ref: 09.IJOGCT.020203.MANSOORI

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Asphaltenes Benzene rings Cyclohexane rings

Four different asphaltene structures separated from different natural petroleum fluids.

Ref: 09.IJOGCT.020203.MANSOORI

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Asphaltenes - appearance Asphaltenes in North Sea crude oils North Sea crude oils generally contain 0.1-1.5 wt% asphaltenes (n-pentane insolubles). There are crude oils which contain more than 10 wt% asphaltenes.

Asphaltenes may precipitate in pores near the well bore

Asphaltenes in Ula separator

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Asphaltene risk in reservoirs

Ref: SSH

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Dried asphaltenes

http://baervan.nmt.edu/Petrophysics/group/intro-2-asphaltenes.pdf

Figure 1. Examples of the appearance (magnified about 15 times) of asphaltenes separated from Mars-P crude oil with an excess of (a) n pentane (n-C5) and (b) n-heptane (n-C7).

Some would argue that the n-C7 asphaltenes are the “real” asphaltenes, whereas the n-C5 material is a mixture of asphaltenes and resins. The “high end materials” in molecular weight, polarity and aromaticity — may separate into an asphaltene-rich phase in response to changes in pressure, composition, and/or temperature. Seminar at Aker Solutions, Stavanger - May31st, 2011

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When can asphaltenes cause problems? • , , Amount of asphaltene in oil less important than asphaltene stability.

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• Stability depends on asphaltene properties, and solvent properties of the oil. • Light oils with small amounts of asphaltenes more likely to cause problems than heavy oil with larger amounts of material in the asphaltene fraction. Heavier oil also contains intermediate components that are good asphaltene solvents whereas the light , , limited solubility. • Asphaltenes in heavier oils can also cause problems if they are destabilized by

. • Unstable asphaltenes can form separate phase that might plug the oil-bearing rock formation near a well . Can also aggregate at oil/water interfaces, stabilizing water-in-oil

• Can alter surface wetting properties or accumulate and plug well bores and flow lines. The first step toward predicting and avoiding any of these problems is knowing how to . 22


What is wax? Mainly long-chain alkanes with 20-50 carbon atoms, but also contain minor quantities of ranc e an cyc c y rocar ons. yp ca con en n or ea o s s - we g .

What is cloud point? Cloud point is the first temperature where wax starts to precipitate when an oil is cooled. It is often referred to as the wax appearance (or precipitation) temperature. Cloud point is typically 30-40°C, but may be as high as 50-55°C.

What is wax melting point? The melting point of wax deposits is normally about 20°C higher than the cloud point.

What is pour point and yield stress? Pour point is the temperature where sufficient amount of wax about 4 wei ht % is precipitated to make the oil take on a solid-like (gel) structure. The pour point of North Sea oils may be as high as 35°C and lower than -50°C. Below the pour point, the oil has a yield shear stress, i.e. the oil cannot flow unless it is subjected to a certain minimum shearin force shakin or pumpin . Fi ure 3 shows a t pical relationship between ield stress and restart pressure. 23


Wax plugs

Figure 1 Part of a wax plug retrieved from the pig trap at Statfjord B after pigging . 2006-Aberdeen-1-Tordal


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WATER-OIL EMULSIONS control Mixture versus

Pipeline oil-water flow Ref: L. Amundsen: PhD Thesis 2011, Helseth 2001

What are emulsions? When water and oil are mixed, one of the phases is dispersed as droplets into the other. In oil production, water is most often the dispersed phase. Depending on the supply of mixing energy, the dispersion may separate readily into pure water and pure oil, or it may stay as a stable emulsion. Emulsions are stabilised by components naturally present in the oil, such as asphaltenes, resins and organic acids. Solid particles like wax, scale and fines may also act as stabilising agents. 25 Seminar at Aker Solutions, Stavanger - May31st, 2011

a er-o emu s ons “ e ca e o n programme e ween a o , aga an y ro was launched in 1995 with the clear objective to improve the methodology for characterisation of dispersed multiphase systems and the technical ability to transport and effectively separate them ….”

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SCALE PRECIPITATION Figure 6.6 SrSO4 crystals precipitated from brine of SrSO4 supersaturatiori=5

Figure 7.4 Crystals precipitated from static brine BSS3 at 70°C, (Ba+Sr)/SO4=1, Sr/Ba=1000

Oilfield scale is mainly deposits of inorganic salts such as carbonates and sulphates of barium, strontium or . like sulphides, carbonates and hydrous oxides

Figure 7.58 Crystals grown from 50:50 mixed North sea water and South Brae under static condition, 'tree leaves' crystals

Ref: (Statoil,Saga,Hydro – Multiphase Technology Program) Ref: M. Yuan: PhD thesis, Heriot Watt, 1989

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Scale formation mechanisms Oilfield scale can form in one of two ways: Brine (e.g. formation water) may undergo change in conditions such as temperature or pressure. This generally gives rise to carbonate scales. wo ncompat e waters e.g. formation water rich in calcium, strontium and barium and sea wa er r c n su a e m x. s generally gives rise to sulphate scales.

The curves illustrate that calcite precipitation pressure drop gives precipitation DP1 , deposition gives a new pressure drop, DP2 , which in turn gives increasing deposition,DP3 .

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Scale mitigation Scale inhibitors are chemicals which stop or interfere with the nucleation, precipitation and adherence of mineral deposits.

What is a scale dissolver? Scale dissolvers are chemicals which dissolve scale by complexing with ions like barium strontium calcium and iron.

What is chelation or sequestration? Chelation or se uestration is the formation of soluble metal ion complexes in the presence of substances which normally would give a precipitate.

Other techniques ?

Electromagnetic Inhibition 29


http://www.ed2000.net/york/ yk_theo_disc.htm

EROSION Erosion mechanisms and materials

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Flow Assurance Presentation - Rune Time 2

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