Geologic Resources Notes: Oil

Geologic Resources

Types of Resources

  • Geological Resources, Energy Resources, Metals, and Nonmetallic Resources are all nonrenewable resources, with groundwater being an exception.

  • Resources are different from Reserves.

Sources of Energy

  • Energy from fossil fuels:

    • Oil, natural gas, and coal are derived from living organisms.

    • These materials have energy stored in H-C bonds, created by photosynthesis, which is solar energy from the past.

    • Oil, gas, and coal represent "fossilized sunshine."

Oil & Natural Gas

  • Petroleum includes crude oil and natural gas.

  • Occurrence of Oil & Gas:

    • Oil pool

    • Source rock: >2% organics

    • Reservoir rock

    • Trap: structural trap; stratigraphic trap

    • Deep enough burial: 7,500 to 11,000 ft

    • Oil field

Oil and Gas Genesis

  • Oil and gas are derived from plankton and marine algae.

  • Dead plankton and algae sink and accumulate offshore as fine mud.

  • Under anoxic conditions, the material is preserved.

  • Lithification forms a dark shale, a petroleum source rock.

Oil and Gas Genesis

  • The shale is buried and warms up.

    • Heating breaks organics down into waxy kerogen.

    • Kerogen-rich source rocks are called oil shales.

  • Heating decomposes kerogen into oil.

  • Oil and gas form within specific temperature ranges:

    • Oil and gas: 90°–160°C.

    • Gas only: 160°–250°C.

  • At temperatures >250°C, oil and gas decompose to form graphite and water.

Oil and Gas Genesis

  • The “oil window” (range of temperatures at which oil forms) is 90°–160°C.

  • Depth of the oil window depends on the geothermal gradient.

    • Typical geothermal gradient: 25°C/km, so the oil window is 3.5–6.5 km.

    • Some sedimentary basins have a lower gradient: 15°C/km, so the oil window is 5–11 km.

    • The natural gas window may be as deep as 9–15 km.

Hydrocarbon Systems

  • Creation of an oil or gas reserve requires four features:

    • A source rock, usually an organic-rich shale.

    • A migration pathway: fractures and/or bedding porosity.

    • A reservoir rock: permeable or can be fractured.

    • A trap.

    • These features must develop in a specific order.

Hydrocarbon Systems

  • Reservoir rocks and hydrocarbon migration:

    • Reservoir rocks store and transmit oil and gas.

      • Porosity: open space in the rock that stores fluid.

      • Permeability: ease of fluid movement through pore space.

        • Low permeability: small well yields.

        • High permeability: large well yields.

Hydrocarbon Systems

  • Reservoir rocks and hydrocarbon migration:

    • Oil and gas migrate upward from the source.

    • Migration is facilitated by porosity, fractures, permeability, pressure gradients, density, and buoyancy differences.

    • Reservoirs fluid is layered: gas overlies oil, overlies water.

    • Reservoirs can leak to form an oil seep at the surface.

Hydrocarbon Systems

  • Traps and seals:

    • Oil and gas reserves are found in traps.

    • Seal: a low-permeability rock that prevents upward migration.

    • Trap: reservoir and seal-rock system that contains and retains oil and gas.

Hydrocarbon Systems

  • Traps and seals:

    • Anticline trap: structural arch trap for oil or gas within a permeable bed such as a sandstone.

Hydrocarbon Systems

  • Traps and seals:

    • Salt-dome trap: salt buoyancy and plastic flow disrupt nearby rocks, forming traps.

How Salt Domes Trap Oil and Gas

  • Salt flows up as a weak mass; petroleum is trapped in the top of the dome.

  • Oil and gas are trapped on the sides of the impermeable dome.

  • Rocks above the salt dome are bowed up.

Hydrocarbon Systems

  • Traps and seals:

    • Fault trap: displacement juxtaposes rocks with varying permeability.

Hydrocarbon Systems

  • Traps and seals:

    • Stratigraphic trap: depositional features (such as sand “pinch-out” between shales) create traps.

Other Ways Petroleum Is Trapped

  • Normal faults, thrust faults, unconformities, and lenses can also trap oil.

Birth of the Oil Industry

  • Oil from seeps has been used for millennia.

  • The first oil well was drilled in Titusville, Pennsylvania, in 1859.

    • Wells allow fast removal of oil from the ground.

    • Oil was more available, and consumption boomed.

  • Within a decade, thousands of oil wells had been drilled.

Oil Exploration

  • Seismic reflection profiles layers and discontinuities.

    • Sound “bounces off” contrasts between layers.

    • Allows geologists to look for traps without drilling.

  • Seismic surveys are conducted on land and at sea and are a discipline of geophysics.

Oil Exploration

  • Diamond-coated rotary bit grinds rock.

  • Rapid circulation of high-density drilling mud:

    • Lifts cuttings to the ground surface.

    • Reduces the risk of blowouts.

    • Cools the drill bit.

Types of Oil Rigs

  • Include land rigs, jacket platforms, tension-leg platforms (TLP), truss SPARs, semi-submersibles, onshore platforms, jack-up rigs, internal turret-moored FPSOs, external turret-moored FPSOs, and dynamic positioned drilling ships/FPSOs.

Oil Production

  • When a reservoir is penetrated, the drilling ceases.

  • Steel casing is used to prevent the collapse of weaker rocks into the hole.

  • After the hole is cased, the well is tested and pumped.

Oil Production

  • Primary recovery:

    • Uses reservoir fluid pressure and pumping to extract oil.

    • Can only recover ~30% of the oil.

  • Secondary recovery:

    • Uses fluids (steam, CO2) to heat, “thin,” and push oil.

    • Hydraulic fracturing artificially increases permeability.

    • Can only recover ~20% of the oil.

Oil Production

  • Crude oil must be refined.

    • Crude oil is distilled into separate mixtures by weight.

    • Lighter molecules rise to the top of the distillation columns.

    • Heavier molecules remain at the bottom.

Oil and Gas

  • Industrial society depends on oil and natural gas.

  • Oil and gas (hydrocarbons) are complex organic molecules produced by once-living creatures.

  • May consist of only H and C.

  • Many hydrocarbon types occur as complex mixtures and are separated by refining.

Oil Reserves

  • Regions bordering the Persian Gulf contain the world’s largest reserves.

  • Oil reserves are distributed on all continents—some onshore and some offshore.

  • A barrel (bbl) of oil is 42 gallons or 159 liters.

Global Crude Oil Production (2023)

  • Crude Oil and Condensate Production in Thousands of Barrels per Day

  • The world produced 82,757 (Thousands of Barrels per Day)

  • Top producers:

    • United States: 12,927

    • Russia: 10,554

    • Saudi Arabia: 9,609

Arabian Peninsula Oil and Gas

  • The region around the Arabian Peninsula/Persian Gulf accounts for ¼ of the world’s oil production, 57% of oil reserves, and 45% of gas reserves.

Geologic Setting of Arabian Peninsula

  • The area includes the Arabian Plate, Arabian Shield, Zagros Fold Belt, and various fault types and basins.

Largest Oil Fields

  • 10 largest oil fields in the US (Cumulative Production + Est. Reserves):

    1. Prudhoe Bay, Alaska: 13+ billion barrels

    2. East Texas: 6.0 billion barrels

    3. Wilmington, California: 2.8 billion barrels

  • 10 largest oil fields in the World (Cumulative Production):

    1. Ghawar, Saudi Arabia: 75-83 billion barrels

    2. Burgan, Kuwait: 66-72 billion barrels

    3. Bolivar Coastal, Venezuela: 30-32 billion barrels

Petroleum Basins in the U.S.

  • Examples include the Williston Basin, Permian Basin, Gulf Coast Province, and Appalachian Basin.

Federal Off-shore Oil

  • Gulf of Mexico has a large number of oil fields with varying production levels, greater than all other regions combined.

World Oil Production and Consumption

  • Lists of countries with oil production in thousands of barrels daily, along with the change from 2008-2009.

  • World oil consumption from 1965-2009 is charted.

Oil Production and Distribution

  • Shows major world oil trade routes and energy flow in EJ (Exajoules).

California's Mystery Gasoline Surcharge

  • An unexplained price premium versus the U.S. in real Dec 2021 dollars per gallon is graphed from January 2000 to Dec 2021.

Peak Oil

  • Graph showing proved reserves, production, and ultimate oil availability over time.

Lower 48 Crude Oil Reserves & Production, 1945-2000

  • Graph showing crude oil reserves and annual production in billion barrels.

  • Peak Production was in 1970.

  • Peak Reserves was in 1959.

Oil Extinction

  • Oil extinction is likely to occur between 2050 to 2150.

  • Humanity faces many changes as oil runs out.

Mexico: Daily Production from One-Time Super-Giant "Cantarell" Oilfield

  • Production data is graphed from 1995-2009.

Cantarell Crude Oil Production

  • A map shows the location of the Cantarell oil field complex, along with a chart of barrels per day production from 2008-2010.

Oil Spills

  • Damage Control techniques:

    • Floating barriers and skimmers

    • Mop up with absorbent material (wood chips, peat moss, chicken feathers, …)

    • Burn it off

  • Spills from oil storage tanks, pipelines, and ships contaminate surface water and groundwater and may devastate large areas of coastline.

Oil Spills

  • About 10,000 spills each year in U.S. waters, amounting to 15 to 25 million gallons of oil annually.

  • Sources of spills:

    • Oil tankers

    • Drilling accidents

    • Careless disposal of used oil

    • Intentional destruction of pipelines

    • A few natural seeps do occur

Oil Wars