EARTH 221 Flashcards
(27 cards)
What is the difference in properties between aliphatic compounds and naphthene and aromatic compounds
Aliphatics burn cleaner, but only make up 25% of crude oil
Naphthene and aromatics don’t burn as cleanly, create weird by-products but are sometimes used in industry. Often toxic/polluting and difficult to break down
What conditions are required for the formation of petroleum?
Source rock abundant in organic carbon (black shale)
Source rock buried to depth where higher temperature converts organic matter to petroleum
Reservoir rock with high porosity and permeability
Structural/stratigraphic trap to seal petroleum in reservoir
What happens during the diagenesis stage of petroleum formation?
Mostly changes organic matter t waxy kerogen with increasing temperature and pressure
What happens during the catagenesis stage of hydrocarbon formation?
Thermal “cracking” of kerogen to smaller, lighter molecules to produce crude oil and natural gas
What happens during the metamorphism stage of hydrocarbon formation?
Complete breakdown of crude oil to methane and graphite due to high temperature and pressure
What are oil sands?
Formed as conventional oil, but oil migrates through sediments, some of which comes up near the surface, forming a deposit of loose or partially consolidated sand containing oil
What is the difference between a mineral deposit and an ore deposit?
Mineral deposit is a natural accumulation of a metallic/non-metallic mineral/minerals, ore deposit is a mineral deposit with a high enough concentration of minerals that extraction is economically viable
Why does ice have a lower density than water?
Water is clumps of H2O molecules, ice has a lower density as it is a crystal lattice, and the molecules are held further apart than they would be in liquid water (water expands when it freezes)
Why is water considered a “universal solvent”?
Partial negative and positive charges in H2O are so strong that they can attract an ion and destroy an ionic bond (dissolution)
What is the difference between dissolved and suspended compounds (in water)?
Difference in size (cutoff not universally agreed, depends on pore size filter used)
What are the types of chemical weathering?
Dissolution (dissolve mineral into its ions with water)
Acid dissolution (dissociation of acid molecule releasing H+)
Oxidation-reduction (electron transfer)
Hydrolysis (water splitting; imporant for silicate minerals)
What is the principle of electroneutrality?
Dissolved constituents in water must always sum to a net charge of zero
How is the TDS (total dissolved solids) calculated?
Sum of all dissolved species in mg/L
How can TDS be measured?
Electrical conductivity (higher conductivity = greater TDS)
How is a Piper diagram constructed?
Express cations as % of total cations
Express anions as % of total anions
Plot each on bottom ternary plots
Project upward onto Piper quadrangle
Use hydrological facies to determine nature of water origin
What are the four Piper diagram hydrological facies?
Top: Calcium sulfate waters
Left: Calcium bicarbonate waters
Right: Sodium chloride waters
Bottom: Sodium bicarbonate waters
What hydrogeological environment are calcium sulfate waters indicative of?
Gypsum dissolution or sulfide oxidation
What hydrogeological environment are calcium bicarbonate waters indicative of?
Carbonate dissolution or silicate weathering
What hydrogeological environment are sodium bicarbonate waters indicative of?
Silicate weathering (usually low TDS)
What hydrogeological environment are sodium chloride waters indicative of?
Halite dissolution or influence of sea/road salt
What are the major weaknesses of piper diagrams?
Only take 7 major ions into account
Must ignore any other ions so sum is 100%
So best for uncontaminated water
Does’t work for anoxic or low-oxygen environments
Not all groundwaters follow the chemical evolution sequence
How is water hardness removed/reduced?
Boiling water
Use of water softeners (replace 2+ ions with soluble 1+ Na)
Water filters with activated carbon
What are the two main DOM (dissolved organic matter) classifications?
Labile - easy to break down and high energy yield for bacteria
Refractory - not easy to break down
What is the trend in DOM with depth of water?
DOM produced at surface by algae is more labile than DOM in deep lakes/oceans
