flow assurance presentation - rune time 2

Flow Assurance and Multiphase flowScandpower Petroleum Technology

ppart II

Prof. Rune W. Time

Department of Petroleum EngineeringUniversity of Stavanger

Seminar at Aker Solutions, Stavanger – May 31st, 2011 1

O li d i h d lOutline and time schedule

8.30 – 9.15 Flow regimes and impact on phase slippage, fluid concentrations and pressure drop in pipelinespipelines

9.25 – 10.15 Hydrates, wax and asphaltenes

10.25 -11.00 Multiphase flow – influence from interfaces, compression effects and waves compression effects and waves

Seminar at Aker Solutions, Stavanger - May31st, 20112

PART II

Hydrates, wax and asphaltenes

+Scale, Emulsions and Erosion


Flow assurance projects – Norway

1993 1997: St t ils Multiph s T chn l D l pm nt 1993-1997: Statoils Multiphase Technology Development 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 proceduresN indust st nd d multiph s fl simul t • New industry standard multiphase flow simulator

• Increased c-steel pipeline applicability (NORSOK)• Leading edge hydrate mitigation procedures • Heated pipeline concepts for hydrate and wax control

1995: A dedicated joint R&D programme1995: A dedicated joint R&D programmebetween Statoil, Saga and Hydro (SSH) launched in 1995 with objective to improve the methodology for characterisation of dispersed multiphase systems and for characterisation of dispersed multiphase systems and technical ability to transport and effectively separate them.


Flow assurance and precipitation of solids

• Hydrates: Ice substanceW : P ffi t lli• Wax: Paraffine wax crystallic

• Asphaltenes: Aromatic solids • Scale: Wall deposited heavy soluble mineral depositsScale: Wall deposited heavy soluble mineral deposits

In production oil systems very complex, heterogeneous and some times even difficult to discrimate at first sightsome times even difficult to discrimate at first sight.


Wax, asphaltenes and more ….

Mercaptans are the most odoriferoussubstances known to mankind and are the

b t f d i Sk k d thsubstances found in Skunk spray and thechemicals used to odorize natural gas, but

in extremely low parts-per-billionconcentrations.

http://www.spentcaustic.com/tragedy.htm


http://tigger.uic.edu/~mansoori/HOD_html also called thiols or organic sulfides6

Phase transitions

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Relevant phase transitions for flow assurance


The long and transforming travel of oilfrom reservoir to tank

Hydrates

Asphaltenes

Wax


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 inorganicmolecules such as CO2 and H2S)

Ref: SSH Multiphase program: 235

molecules such as CO2 and H2S).

H d l diAppearance

Hydrate gas loadingBurning ice


"Ice that burns" couldprovide enormous amountsof energy, but can it be madeenvironmentally friendly?(Image: USGS)

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versus ice:

Hydrate (clathrate) structures

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

”Cages” fit different molecules. How to know?Chemical modelling (molecular dynamics)- Chemical modelling (molecular dynamics)

- Experiments (inhibitors)


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Hydrate flow assurance issues

Hydrates?

Gulf of Mexico – ”Horizon” 2010(Exam problem - Multiphase course)

Environmentalissues

Th d illi i “H i ” i d ki k hil d illiThe drilling rig “Horizon” experienced a gas-kick while drilling for BP in the Gulf of Mexico on April 21st 2010. The rig sank and oil leaked out from the well at a flow rate QL = 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


g pwith 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 NOK 300 million for a field.NOK 300 million for a field.

Use of conventional inhibitors requires large storage tanks on the platforms and costlythe platforms and costly 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 different manners:LCIs work in two different manners

1. The kinetic inhibitors impact on the kinetics, preventing or delaying hydrate formation. y g y

2. Hydrate modifiers allow hydrates to form, but as transportable particles.


Other hydrate mitigation techniques

D l l h Direct electrical heating: Åsgard field


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Cold flow principle - Sintef

Stable dry hydrateslurry forms

Flow from

Hydraterecycle loop

wells

Hydrate recycle ’crashcools’ the incoming

warm well stream


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ASPHALTENESASPHALTENES(J.B. Boussingault , 1837)Definition?

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 paraffin waxparaffin wax.

- 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


h lAsphaltenes

Benzene rings

Cyclohexane rings

Four different asphaltenestructures separated from different natural

petroleum fluids.

Ref: 09.IJOGCT.020203.MANSOORI


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 in Ula separatorAsphaltenes may precipitate in pores

near the well bore


h l k Asphaltene risk in reservoirs


Ref: SSH

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Dried asphaltenes

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

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

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.


When can asphaltenes cause problems?

Asphaltenes can cause problems in oil production transportation and processing• Asphaltenes can cause problems in oil production, transportation, and processing. Amount of asphaltene in oil less important than asphaltene stability.

• 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 oil consist largely of paraffinic materials in which by definition asphaltenes have veryoil consist largely of paraffinic materials in which, by definition, asphaltenes have very limited solubility.

• Asphaltenes in heavier oils can also cause problems if they are destabilized by mixing with another crude oil during transportation or by other steps in oil processingmixing with another crude oil during transportation or by other steps in oil processing.

• 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 emulsions or at oil/solid interfacesemulsions or at oil/solid interfaces

• 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 evaluate asphaltene stabilityevaluate asphaltene stability.


WAXWAX

DefinitionsDefinitionsWhat is wax?Mainly long-chain alkanes with 20-50 carbon atoms, but also contain minor quantities of b h d d li h d b T i l t t i N th S il i 1 15 i ht%branched and cyclic hydrocarbons. Typical content in North Sea oils is 1-15 weight%.

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 weight %) is p p ( g )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 shearing force (shaking or pumping). Figure 3 shows a typical relationship between yield


g ( g p p g) g yp p ystress and restart pressure.

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Wax plugs

Figure 1 Part of a wax plug retrieved from the pig trap at Statfjord B after pigging the pipeline from Snorre B to Statfjord B (Sept 2001)

2006-Aberdeen-1-Tordal

the pipeline from Snorre B to Statfjord B (Sept. 2001)


WATER-OIL EMULSIONS control

Mixtureversus emulsionemulsion

Pipeline oil-water flowRef: 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 p p p p gsupply 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 y yasphaltenes, resins and organic acids. Solid particles like wax, scale and fines may also act as stabilising agents.


W t il l iWater-oil emulsions“ A d di t d j i t R&D b t St t il S d H d (SSH) “ A dedicated joint R&D programme between Statoil, Saga and Hydro (SSH) 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 ….”


SCALE PRECIPITATION

Figure 6.6 SrSO4 crystals precipitated from brine ofSrSO4 supersaturatiori=5

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

What is oilfield scale?

Figure 7.58 Crystals grown from 50:50 mixed North sea water and South Brae under

What is oilfield scale?Oilfield scale is mainly deposits of inorganic salts such as carbonates and sulphates of barium, strontium or calcium. Scale may also be salts of iron static condition, 'tree leaves'

crystals

calcium. Scale may also be salts of ironlike sulphides, carbonates and hydrous oxides


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.

T i ibl ( Two incompatible waters (e.g. formation water rich in calcium, strontium and barium and sea

t i h i s lph t ) mix ThisThe curves illustrate that calcite precipitation occurs by a positive feedback mechanism;water rich in sulphate) mix.This

generally gives rise to sulphatescales.

occurs by a positive feedback mechanism; pressure drop gives precipitation DP1 , deposition gives a new pressure drop, DP2 , which in turn gives increasing deposition,DP3 .


Scale mitigationWhat is a scale inhibitor?What is a scale inhibitor?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 complexingwith ions like barium, strontium, calcium and iron.w th ons l ke bar um, stront um, calc um and ron.

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

ElectromagneticInhibitionOther techniques ?

http://www.ed2000.net/york/yk_theo_disc.htmSeminar at Aker Solutions, Stavanger - May31st, 2011

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EROSION

Erosion mechanisms and materials


Erosion test of “IPC” downholeinstrumentation system

Project with Aker Maritime Well Services 1998

Inflow, chokeM lti h

Project with Aker Maritime Well Services, 1998

Multiphasemeteringdevice

Erosion test Flow regime dependence!

FlowFlow

direction


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flow assurance presentation - rune time 2

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