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Electrostatics
1 Types of oil reservoirs -
Anticline Normal fault
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Stratigraphic
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Thrust fault
Oil recovery stages -
Primary
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Secondary Tertiary or Enhanced Oil Recover (EOR)
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Infill
Primary recovery -
Uses the reservoirs natural energy as the drive
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4 types of primary recovery
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Gas cap
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Water drive
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Combination drive
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Gas dissolution or solution drive
Gas cap reservoir -
Gas cap pressurises oil reservoir and dr ives oil towards well
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Gas Oil Ratio (GOR) remains constant then later rises
Water drive reservoir -
Water from aquifer pressurises oil reservoir
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Water drives oil towards well perforations
Combination drive -
Gas cap pressurises oil reservoir
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Gas and water drive oil towards well perforations
Gas dissolution or solution drive reservoir -
Gas dissolved in oil pressurises reservoir
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Pressure falls quickly before reaching the bubble point and then slows
Secondary recovery -
Aided by surface injection of water or gas
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2 types of secondary recovery
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Water flooding Gas flooding
Water flooding -
Helps maintain reservoir pressure
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Water injected around the periphery of field or the production well
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Sweeps oil towards production well
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1.2bbl of water injected per 1bbl of oil produced
Gas flooding -
Similar to water flooding
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Gas compressors may be large power consumers
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Gas may strip out light ends which may impact equity allocation
Tertiary recovery or Enhanced Oil Recovery (EOR) -
Uses thermal, chemical or miscible gas process
Thermal EOR Steam injection -
Steam injected to heat oil and drive it to production well
In situ combustion -
Air injected and ignited to drive hot oil to production well
Microwave heating -
Microwave source lowered into well to heat surrounding well
Hot water injection -
Similar to water flooding but oil viscosity is also lowered
Chemical EOR -
Polymer flood uses long chain polymers to increase water viscosity.
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This improves the sweep efficiency.
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Other chemicals added such as surfactants or caustic soda
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In deep wells were the CO2 remains a supercritical liquid. CO2is miscible with oil, and lowers viscosity and surface tension.
Well fluids -
Oil coming directly from the well cannot be marketed without processing.
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The pressure and temperature is normally too high.
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The well fluids consists of:
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Oil
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Associated gas
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Produced water
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Drilling fluids and solids.
Crude oil composition -
Crude oil consists of a mixture of hundreds of different hydrocarbons.
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Most compounds are from the paraffin or alkyl series, naphthenes and aromatics.
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Crude also contains:
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Dissolved gases – N2, CO2, H2S;
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Sulphur compounds – mercaptans;
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Organic nitrogen compounds;
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Organic oxygen compounds.
Why use pseudo components -
Reduce number of components in simulation.
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Many components have very similar properties.
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Properties of some components may not be available.
Selecting pseudo components -
Divided into boiling point ranges. Normally divided into 5 or 7 ranges.
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Average specific gravity also specified.
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Other properties calculated from correlations:
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Molecular weight Critical temperature
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Critical pressure
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Acentric factor
Crude oil yield and product specification -
Yields depend on the composition of the crude and the amount of refining.
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Specifications vary widely dependent on destination. Oil specifications can be quite broad.
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Gas specifications to domestic users are very tight.
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Specifications are agreed between supplier and purchaser.
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No universal product specification
Typical crude oil specification -
Water content below 0.1%
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BS&W, Basic Sediment and Water less than 0.2%.
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Salt content less than 10 ptb (pounds per thousand barrels.)
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Reid vapour pressure less than 10 psia at 100 °F
Typical LPG specification -
Vapour pressure 208 psig at 100°F (14.3 barg at 37.8 °C). 95% evaporation at 36 °F (2.2 °C).
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Pentane and heavier 2.0% maximum.
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Total sulphur 140 ppm.
Natural gas liquids (NGL) -
A broad term for liquids condensed during separation and compression of the gas phase. Typical components are propane, butane, pentane and some hexane
Condensate -
is a broad term for liquids produced from a gas field.
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Condensate is a clear or slightly coloured light, volatile liquid.
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Composition ranges from butane to about oc tane.
Offshore structures Artificial Island (depth 0-10m) -
Can either be built up from dredged material or be purpose built.
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Only suitable for shallow water.
Steel jacket (max depth 500m) -
The most common form of offshore structure.
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Platform is piled to the seabed for stability
Compliant tower (depth 365 – 660m) -
Similar to a fixed platform, but can sustain significant lateral deflection.
Semi-submersible (depth 640 – 2400m) -
Large floating structures used for drilling or production.
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Can accommodate large loads. Located using dynamic positioning or anchors.
Tension leg platform (860 – 1400m) -
Vertically moored floating structure.
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Virtually all vertical movement is eliminated
Spars (1000 – 2400m) -
Vertical cylinder moored to sea bed
Floating Production Storage and Offloading (13 – 1800m) -
ship shape vessel anchored over field. Subsea wells tied back to FPSO through flexible risers.
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Facilities include processing, accommodation, storage and tanker loading.
Jack-up (max depth 120m) -
Normally used for temporary drilling rig to drill over subsea template or unmanned platform.