Geoenergy - oil and gas Flashcards
Value chain?
- Acquire – the acreage
- Explore – find petroleum (Frontier (Arctic) to Mature (North Sea))
- Appraise – determine size and complexity
- Develop – drill wells and build facility
- Produce – get the petroleum out
- Abandon – turn it over to gas storage?
Cost of the value chain?
- Acreage acquisition – shoot seismic + bid for right to drill
- Exploration – shoot seismic and drill wells
- Appraisal – More detailed, higher wavelength seismic and drill more wells
- Development – Lots of wells
- Production – even more wells + seismic
- Field redevelopment??
- Near field exploration??
- Abandonment – remove facility – North Sea decommission est £50-60 billion
Value chain cycle time?
• Clair Field o 30 years • Ardmore Field o 21+ months • Small field, close to existing field = close infrastructure
Forming petroleum accumulation?
- Source: Where the oil forms
- Reservoir – rock from which we can produce the oil
- Seal – What stops the oil leaking to the surface
- Trap – shape of the oil container in the Earth (inverted)
Source?
• Preservation of organic matter (plant remains) o Anoxic conditions • Peat bogs • Black sea • Lake Tanganyika o Typical environments: • Silled basins • Shallow seas • Coastal upwelling • Stratified lakes
Reservoir?
- Permeable or very fractured
- Sand
- High porosity
Seal?
• Fine grained, low permeability • Mudstones (shale’s), salt o Desert and temperate lakes o Rivers and deltas o Shallow and deep seas o Salt and mudstone • Salt will anneal itself to stop fracture = best
Traps?
- Domes (anticlines)
- Fault blocks
- Salt diapirs
Migrations and timing?
- If petroleum migrates from the source rock before a trap is formed or a seal is deposited then no petroleum accumulation will form
- The oil and gas will leak to surface and be biodegraded
Porosity and permeability?
Porosity: affects storage of petroleum
Permeability: affects the flow of petroleum
Fracking: increasing permeability of rock
Net to gross?
Net: The porous part of the reservoir
Gross: The whole reservoir package
So it is a ratio of how much of the rock is a permeable reservoir compared to the whole non-flowing reservoir
Water saturation?
- Oil and gas never fully saturate the pore space in a reservoir
- Clean gas sands about Sw 5%
- Clean oil sands may have Sw 10%
- Dirty (shaley) oil sands may have Sw 50%
Because of this leave about 65% of oil in ground
Formation volume factors
Oil
• Shrinks when brought to surface because gas is exolved about 1 to 2
Gas
• Expands when brought to surface because of pressure drop – may be measured in 100s and hence usually expressed as a GAS EXPANSION FACTOR
Tools for exploration:
• Satellite images – salt domes = traps
• Gravity and magnetics
• Seismic – look for rift basin (tilted fault blocks) + salt diapirism + Post-rift subsidence
• Wireline logs – tools run into the well on wireline or as part of the drilling
o Measures rock properties, fluid properties, void properties (porosity, permeability), pressure, temperature, fluid flow
• Core and cuttings – look for porosity and oil stains
• Fluid samples – oil and gas = high resistivity
• Outcrop data
• Petroleum seepage
• Gamma log – sandstones and limestones tend to have low natural radioactivity and mudstones tend to have relatively high natural radioactivity – shale = more radioactive – sand = less
Petroleum play
Requires:
• Mature source rock
• Reservoir
• Regional seal
Plays are reservoir, seal combinations
Fairway is when both are present so an accumulation could occur
