Oil and gas
uses/properties/intro
oil market
source rocks
transport
reservoir rocks
seal rocks
traps
exploration
production
environmental
uses
properties
plastics
fertilisers
energy production
API - American Petroleum Index
hydrocarbons and other organic compounds
index of how heavy a crude oil is
use examples
50s
30s-40s
below 15
average constituents of fuel
lightest chains
shortest hydrocarbons
most volatile
heaviest and longest chains
need cracking for commerical
heavy and dark
bitumin
mostly liquid
solid
gas-liquid
construction
coal
road surfaces
planes tend to use kerogen
measurement of oil is in barrels like whiskey barrels
Source rocks generate oil and gas
contain organic-rich materials
how are oil and gas generated?
types of kerogen
type 1
type 2
type 3
algae
phyto and zooplankton
terrestrial plants
once oil and gas are generated they start to migrate upwards towards surface
they can only migrate through porous rocks
e.g. organic rich mudstones
must contain at least 1% total organic carbon by weight
often sedimentary but not always
seal rocks stop migration of oil and gas out of reservoir rock
often halites, anhydrite
must be impermeable, no pores so fluids can't move
geophysics seismic magnetic airborne
must have anticline structure to trap oil and gas
global warming by burning fossil fuels produces CO2
diesel, fuel, hydrocarbons
cycloalkanes, alkanes, arenes
compounds with SON
refineries are designed for specific oil compositions
different oils different composition based on organic material derived from and changes over time
based on specific gravity index
hard to process, lots of waste
more energy to produce light chains
not energy efficient or cost effective
ideal for refinaries
clear
starts to evaporate at very low temperature
easier to extract and more commercial uses
disel in trains and ships - heavy oil
gasoline - petrol - lighter/shorter
bitumen for roads is longest
90 million barrels a day
renewables starting to replace additional oil we use every year
current oil price 85 dollars a barrel
companies can influence price
free market - oil sold and traded, price controlled by supply and demand
best 5-10% TOC to generate larger volume of oil
potential begins with first life
oil and gas production controlled by rate of organic productivity vs organic matter degradation
destruction
preservation
burial
production
mostly generated by algae and bacteria
lacking oxygen
generally close to land
shallow, warm water
close to rivers - bring nutrients
most organic matter eaten, oxidised on surface
enclosed basin no ocean currents to sweep away source rock
low oxygen preserve organic matter
algae die and fall to seabed
aerobic organisms can't survive
animals can't eat organic matter
can't carry out degradation
sediment deposition
not too much as this dilutes organic content
moving rock away from oxygen is better to reduce bacteria
oil shales
oil and gas
gas - coals
lipid rich
lipid rich
marine source rocks
humic
organic matter maturation
maturation
increases overburden pressure causing temperature to increase
temp determines organic matter products
must be buried deep enough for temp to be hot enough to generate oil
temp increases with depth due to heatflow from centre of earth
40-80 kerogen window- anerobic and abiotic breakdown of organic matter
oil window 100 to 150 degC breakdown C bonds and form short chains
gas window 150-200 depleting H
over 200 - overmature
lose H2O, CH4, Co2, O
peak oil C used to make hydrocarbons
can be generated for longer once C starts to run out
metagenesis
diagenesis
metagenesis
low O:C atomic ratio, high H:C atomic ratio
high O:C atomic ratio, low H:C atomic ratio
drives
pressure drives explusion of generated hydrocarbons
buoyancy, gravity, less dense than surrounding fluid
travel as microscopic bubbles of oil and gas
some reaches surface and evaporates
oil displaces water
bigger pores better, more space for oil to fill
levels of porosoity
secondary porosity controlled by diagenesis (compaction, dissolution, cementation)
primary porosity controlled by settling and energy at deposition
permeability
ability of oil to flow between pores
click to edit
sandstone/limestone
can't be too compacted or cemented
fractured granite/basalt
impossible to fracture - ductile
biggest reservoirs sealed by salt
most reservoirs sealed by mudstone
microporosity
structural or stratigraphic convex-up
gas less dense than oil so rises up
water below - everything in subsurface contains water
oil-water contact
gas-oil contact - contacts controlled by buoyancy - flat
drilling wells to provide view of the subsurface
routine borehole length > 8km
oil and gas fields
upstream, downstream, new energies
oil spills