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1 Types of oil reservoirs -
Anticline Normal fault
Oil recovery stages -
Secondary Tertiary or Enhanced Oil Recover (EOR)
Primary recovery -
Uses the reservoirs natural energy as the drive
4 types of primary recovery
Gas dissolution or solution drive
Gas cap reservoir -
Gas cap pressurises oil reservoir and dr ives oil towards well
Gas Oil Ratio (GOR) remains constant then later rises
Water drive reservoir -
Water from aquifer pressurises oil reservoir
Water drives oil towards well perforations
Combination drive -
Gas cap pressurises oil reservoir
Gas and water drive oil towards well perforations
Gas dissolution or solution drive reservoir -
Gas dissolved in oil pressurises reservoir
Pressure falls quickly before reaching the bubble point and then slows
Secondary recovery -
Aided by surface injection of water or gas
2 types of secondary recovery
Water flooding Gas flooding
Water flooding -
Helps maintain reservoir pressure
Water injected around the periphery of field or the production well
Sweeps oil towards production well
1.2bbl of water injected per 1bbl of oil produced
Gas flooding -
Similar to water flooding
Gas compressors may be large power consumers
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.
This improves the sweep efficiency.
Other chemicals added such as surfactants or caustic soda
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.
The pressure and temperature is normally too high.
The well fluids consists of:
Drilling fluids and solids.
Crude oil composition -
Crude oil consists of a mixture of hundreds of different hydrocarbons.
Most compounds are from the paraffin or alkyl series, naphthenes and aromatics.
Crude also contains:
Dissolved gases – N2, CO2, H2S;
Sulphur compounds – mercaptans;
Organic nitrogen compounds;
Organic oxygen compounds.
Why use pseudo components -
Reduce number of components in simulation.
Many components have very similar properties.
Properties of some components may not be available.
Selecting pseudo components -
Divided into boiling point ranges. Normally divided into 5 or 7 ranges.
Average specific gravity also specified.
Other properties calculated from correlations:
Molecular weight Critical temperature
Crude oil yield and product specification -
Yields depend on the composition of the crude and the amount of refining.
Specifications vary widely dependent on destination. Oil specifications can be quite broad.
Gas specifications to domestic users are very tight.
Specifications are agreed between supplier and purchaser.
No universal product specification
Typical crude oil specification -
Water content below 0.1%
BS&W, Basic Sediment and Water less than 0.2%.
Salt content less than 10 ptb (pounds per thousand barrels.)
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).
Pentane and heavier 2.0% maximum.
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
is a broad term for liquids produced from a gas field.
Condensate is a clear or slightly coloured light, volatile liquid.
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.
Only suitable for shallow water.
Steel jacket (max depth 500m) -
The most common form of offshore structure.
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.
Can accommodate large loads. Located using dynamic positioning or anchors.
Tension leg platform (860 – 1400m) -
Vertically moored floating structure.
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.
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.