Geology Basins Flashcards
UofG Basins elective 2023
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What controls sediment supply?
and Basin Types
Tectonics (need to fill a hole!) and Climate
- Rift - Stretch therefore rapid subsidence, then decrease profile
- Passive Margin - Continued extension, creates oceanic crust (constructional and starved passive margins)
- Strike - Slip - Flower Structures
- Foreland - Loading causes subsidence eg. south falkland basin
What creates the waves for seismic?
- Hammer and dynamite (onshore)
- Airgun (offshore)
Seismic Receivers
- Hydrophones (offshore)
- Geophones (onshore)
Seismic Recorders
Seismograph
What does seismic data present?
The measured changes in density through changes in velocity of seismic waves
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What does seismic allow us to do?
- Identify potential targets
- Understand geological history of region
- Identify potential hazards
- Quantify potential resources
Seismic Strat.
How would you identify Onlap/Offlap
Dip less than surface they terminate on
Seismic Strat
How would you identify Down lap
Dip greater than surface they terminate on
Seismic Strat
How would you identify Toplap
Dip greater than surface at which they terminate. Mirror of downlap
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Play requirements
- Source
- Migration pathway
- Reservoir
- Seal
- Trap
Play Concept
Source
Sed. rock - sufficient organic mats
1st Carbs and proteins, then lipids and ligins
Oil and gas from aqueous - mainly gas from terrestrial
- Sed. decreases therefore increase concentration organic matter
- Anoxic environment therefore lack of circulation
Main source rock depositional environments
lacustrine eg. green river formation, Utah
Delta eg. Missionary bay Mangroves
Deep Marine eg. Black sea
What are the key types of well data?
Core, Mud logging, and wireline
Play Concepts
What is Primary Migration
- Flow out of source
- Low permeability: fracture in source promote expulsion
- Kerogen to petroleum = increase vol. therefore promiotes micro-fracturs and increase pA
What does Gamma ray show?
Quantities of K, Th, and U within rocks
Low values usually sandstone, high values usually shale
Help to understand depositional environment
Play Concepts
What is Secondary Migration
- Flow from sources
- HCs more buoyant that water and decrease solubility
therefore drives migration
What does Neutron Data show?
Indicates porosity by No. hydrogen atoms
Hydrogen present in water and HCs
Count rate is low in high porosity rocks, and high in low porosity rocks
(where less H, neutrons bounce back therefore high return, where more H, neutrons scatter, therefore less return)
Play Concepts
Reservoir requirments?
Porous and permeable
Play Concepts
What can the reservoir be affected by?
Cementation/Compaction
How heterogenous are units? (How dif.?)
Play Concept
Other Reservoir info?
Dissolution of limestone can create reservoir
Darcy units used to measure perm.
- 1 Darcy = very good res. Nichols 2009
Play Concepts
What are the best reservoirs?
- Well sorted sandy desserts
- Shallow seas
- Oolittic Grainstones
- Boundstones
(Less important)
- Rivers
- Deltas
- Submarine fans
Presence of mud and cementation decreases porosity
What does Density data show?
Gamma rays emitted
Collide with electrons
Scatter
Returning rays counted
High bulk density = lots of electrons = scattering = low return rate
Play Concepts
What makes a seal effective?
- Low porosity and permeability
- Capillary pressure greater than buoyancy pressure
- Regionally extensive
- Ductile (bends not fracture)
Play Concepts
What are the best seals?
- Fine grained sediments (shales) greater gamma
- Evaporates (can move) very low gamma
Play concepts
Structural Traps
- Anticlinal (no fractures?)
- Salt dome (future movement?)
- Fault trap (Clay smearing? Cataclasis?)
Play Concept
What is a trap?
Conc. of HCs
Play Concept
Stratigraphic traps
- Pinchout
- Unconformity
- Reef
What can be done with Neutron Density Data
-Both used together for accurate evaluation of porosity
-Where they track together = Sst
-Where they are separate = different lithologies or gas
-Where there is gas - density log values are high and neutron log values are low
-Use with Gamma rays for better understanding
3 key types of explorations
-buy into existing field
-explore other parts of an identified producing region
-explore new region
Pros and cons of buying into existing field
Pros:
-high success rate
-good infrastructure
Cons:
-high buy in costs
-low potential returns
Pros and cons of exploring others parts of identified region
Pros:
-good understanding of existing system
-lots of potentially cheaper data
Cons:
-more difficult targets
-lower potential returns
Pros and cons of exploring new region
Pros:
-potentially high returns
Cons:
-high risk
-limited existing data therefore expensive
How can gravity help search for HCs
-Stage 1 of investigations
-Variations in r alters observed g
-Underlying densities change observed g
-Therefore can identify anomalies
-Can make assumptions about subsurface when comparing to observed measurements
-Oil can produce a gravity low
-Cost effective way of getting regional data
-Used IF substantial density contrasts are expected
What has an influence on heat flow
-crustal thinning
-mantle upwelling
-water circulation
-sills and dykes
-salt
-the rocks themselves
-can effect oil window
Features:
-Rootlets upper tidal flats
-Flaser/lenticular bedding
-Ripple cross lamination
-Heterolithic Strat.
-Bi-directional herringbone
Tidal Estuary - Coastal
Features:
-Mouth bar deposits - well sorted
-Delta plain = fine grained sand, interbedded with silt
-Beach = wave ripples and medium sand
-Delta front = mudstone interbedded with sand and bioturbation
Wave dominated delta - Delta
Features:
-Bi-directional features, herringbone
-Mud drapes during slack water
Tidal Dominated Coast - Coastal
Features:
-Inner shelf grain/packstone
-Outer shelf pack/whackstone
-Slope redeposited limestone
-Shelf edge grainstone shoals
-Slump deposits
-Deep water carbonate
Non-rimmed Carbonate shelf - Shallow Marine Carbonate
Features:
Boundstone at top
-Forereef slope rudstone and redeposited limestone
-Slump deposits
-Pelagic and Carbonate mudstone turbidites further out
Carbonate Rimmed Shelf - Shallow Marine Carbonate
Features:
-Grain Stones shoals in top
-Ooids
-Bioclastic Material
-Mid-ramp redeposited material
-Outer-ramp mud/wackstone
Carbonate Ramp - Shallow Marine
Feautures:
-Delta Plain = Fine grained sand and silt with current ripples
-Delta channels = medium sand with current ripples
-Moth bar = massive medium sand
-Delta front = bioturbation, slumping structures, fossils
River Dominated Delta - Delta
Features:
-Beach = medium sand
-Estuary mouth = cross bedding, fossils and current ripples
-Central lagoon = bioturbation and limestone
-Bay head delta = cross strat and bioturbation
Wave dominated Estuary - Coastal
Features:
-Shoreface = cross strat. and bedded sands
-Reworked sands before tidal currents and storms
-Offshore transition zone = hummocky cross-strat., interbedded with bioturbated mud
-Offshore = bioturbation, mudstone
Tidal Influenced Shelf succession - Shallow Marine
Features:
-Cross-strat.
-Mud drapes
-Bi-directional features, herringbone
Tidal Dominated Delta - Delta
Features:
-Shoreface = wave ripples and swale
-Offshore transition = thin sheets mud and sst, hummocky cross-strat
-Offshore = bioturbation
Storm Dominated Shelf - Shallow Marine
Features:
-Grading up into finer grained deposit
-Matrix or clast support where cobbles and boulders embedded in fine sediment
Debris Flow - Deep Marine
Features:
-Rootlets, muds and sands
-Channel fill succession of TxB sands
-Fining upwards
-Lateral accretion surfaces
-Scoured channel base
-Finer grain sizes than a Braider River
Meandering River - Fluvial
Features:
-Mix of sand, gravel, and mud
-Inner fan = thick conglomerate and sst turbidites
-Thin levee deposits
-Mid fan = coarsening up succession of sandy turbidites
-Distal fan = fine grained turbidites
Submarine Fans - Deep Marine
Features:
-Rootlets
-Fine sand and muds
-Trough cross bedding in channels, fining up
-Coarsest sediments lower flat laminated
-Scoured channel base
Braided River - Fluvial
Features:
-Depositional couplets (alternating fine and course material)
-Antidunes upstream
-Clast imbrication
-Poorly sorted silt and clay
Alluvial Sheetflood deposit - Alluvial
Features:
-Disc structures
-Laminated and cross-bedded sand
-Pebbly and water escape structures
-Reverse grading at bottom of sequence
Lowe Sequence Turbidite Flow - Deep marine
Features:
-Matrix supported
-Crude clast imbrication of bigger clasts
-Poorly sorted
Debris Flow - Alluvial
Features:
-Muds and wave rippled sands
-Deeper laminated dark shales
-Thin turbiditic sands
Lacustrine Deposit - Lacustrine
Features:
-Cross laminated sands and ripples
-Parallel laminated sands
-Massive sands and granules rapidly deposited under upper flow regime
-Scoured erosional base
Bouma Sequence Turbidite Flow - Deep Marine
What is the control on marine sedimentation?
Base level (sea level)
What is progradation (normal)
S>A
Level, seaward
What is progradation (forced regression)
S>A where sea level lower
Down, seaward
What is retrogradation
A>S where sea level rises
Up, Landward
What is aggradation
A=S where sea level rises
Up, static
What is Sequence Stratigraphy
“study of stratal stacking patterns and changes thereof in a time framework” (Catuneanu et al. 2009)
What is a Sequence Boundary (SB)
-The surface in which the first signs of erosion occur due to sea level fall
-From aggradation to progradation (forced)
Highstand System Tract (HST)
-Sea level rising
-Steep curve steadying out
Therefore aggradation (where steep), then progradation (where levels out)
Falling Stage System Tract (FSST)
-Fluvial systems incise and transport sediment basinwards
-Downward shift in facies (foreshore lies on offshore transition with SB between)
Lowstand System Tract (LST)
-Relative sea level at min
-Sea level begins to rise (limited) - therefore Accom.
-Progradational to Aggradational
-Onlapping, clinoforms that thicken updip
Transgressive Surface (TS)
-A>S (where Supply is constant)
-Sedimentation migrates landward
-TS marks sea level rise
Transgressive System Tract (TST)
-Sea level rise increases
-A>S (supply is constant)
-Retrogradational
-Onlap, clinoforms thicken landward
Maximum Flooding Surface (MFS)
-Hiatus in deposition occurs
-Surface above which is MFS
-The most landward region of the marine realm
Allogenic
Basin wide
World Wide
Autogenic
within system
Two types of Geothermal systems
-High temp >180C
-Low temp <100C
Two Shallow Geothermal Energy Soruces
-Heat pumps - Open loop and closed loops. Open is heat exchange with groundwater. Closed is heat exchange from installed boreholes. Local Scale Heating
-Mine water systems - Old mines, storage and pathways for water, heated water extracted, boreholes used. e.g. Heerleen, Netherlands. Midland Valley, Scotland (Glasgow. Adams et al. 2009)
Geothermal Energy facts
-Volcanic activity
-Water pumped to hot granites
-Requires permeability (fractures)
-Can be natural fractures or fracking
Three components to Geothermal Energy
Heat, Water, Permiability
Geothermal Potential UK
-26C/Km gradient
-3000m depth would be 88C
-Post carboniferous sed basins best
Eden Project - hot granite under Cornwall
Where is hydrogen found
Water, HCs (most effective), organic matter
What is hydrogen used for
burned as combustible fuel, or fuel cells
Hydrogen Storage
-reservoir
-cap (ductile and high capillary pA)
-Trap structure
-Salt caverns can be used
-seal needs to be better quality than for HCs as higher buoyancy pA/>leak ability
Where is CO2 critical at?
31C and 7.38MPa
What is needed for CCS
Reservoir, Seal, Trap
What infrastructure is in place after HCs
Rigs, Wells, Pipelines
UK CCS example
Teeside, South Wales, Grangemouth, Acorn Project in North Sea
Requirements for Nuclear Waste Storage
Space, no migration, stable groundwater, no protected areas, wont be affected by future climates
Three types of Nuclear Storage Rock Types
-Salt as impermeable
-Low strength - low permeability clays and mudstone
-High strength - low permeability granites/slates
Other nuclear storage requirements
Depth of 200-1000m
Thickness of 10s of metres
Several kms wide
