Stratigraphy and hydrocarbons ERTH 1010 & 1100

Deposition This simple example shows how the deposited strata is both spatial and temporal changing. With increasing time, deposits record these changes.

General rules Sediments are largely associated with water Supermarine - streams, rivers, lakes Marine - Shore, shelf, basin High energy - steep drainages and wave action - sands or coarser Low energy - ponded water: lakes, lagoons, basins, shallow drainages - silts and clays Relatively free from terrigenous (continental) clastic particles - good for life - carbonates

Energy changes Faster flow Slower flow Deposition changes with location in a stream As a stream makes a bend, water flow increases on the outside of the curve - erodes. Inside the curve, deposition.

Oxbow lakes Meandering rivers may change channels (during flooding). This may strand former channels.

Catskill delta

General relationships In the shoreline environment The source of clastic particles is dominated by the land (delivered by streamflow) Wave-sediment energies are typically greatest nearshore Organisms prefer less silty waters - are abundant in shelf waters.

Forces along shore Sedimentary environments are complex. Water energy is in the driver’s seat, but fluid dynamics is difficult to constrain. Courtenay, Vancouver Is., B.C.

Barrier Islands

Mustang Is., TX Adjacent to Corpus Christi, Mustang Island is a condo- haven, sport fishing port, and petroleum service port. Hurricane free for 25 years!

Barrier islands Barrier islands are nothing more than loose sand - transient on short time scales.

Deposits in section

Shallow seafloor Shallow water can be a boon to life - carbonate formation Corals are example of autotrophic - hetrotrophic symbiosis. Sunlight helps feed the organism.

Thatcher Park, NY South of Albany - one of the world’s best examples of the shallow sea environment. Helderberg group (largely carbonates).

Deltas and time Deltas form from low energy distribution of stream-borne sediments. With continued deposition, deltas extend outward into the basin.

Hydrocarbon formation Biogenic deposition Soft parts versus hard parts Soft parts made of carbohydrates, fats, proteins (C-O-H with P and N) Preservation requires low oxygen (reducing environments) remove O to get C-H The environments that produce materials that will become hydrocarbons are those that offend the average nose!

Small amounts Largely in clastic sediments and rocks Largely organic Yet greatly important in everyday life – oil is one of the biggest drivers of first world economies. Even if you don’t own a car – all of the clothes you wear and the food you eat was transported to you. Small amounts Largely in clastic sediments and rocks Largely organic Yet greatly important in everyday life – oil is one of the biggest drivers of first world economies. Even if you don’t own a car – all of the clothes you wear and the food you eat was transported to you. CH (Hydrocarbon)

Largely organic material - piles of dead plants and animals. Compressed and heated over time. Reducing (no extra O) conditions (chemical or biochemical). Largely organic material - piles of dead plants and animals. Compressed and heated over time. Reducing (no extra O) conditions (chemical or biochemical). Q: what type of rocks are being formed in the above diagram? The start…

Oil’s origins

Oil and origins Hydrocarbon takes time to “cook” But more importantly, it needs a way to accumulate - move from the source region into an area from which it can be economically extracted. Hydrocarbon takes time to “cook” But more importantly, it needs a way to accumulate - move from the source region into an area from which it can be economically extracted.

Organic material that may produce petroleum is called Kerogen. For a given temperature, kerogens made of buried algae yield more petroleum than leafy, woody, or peat materials Organic material that may produce petroleum is called Kerogen. For a given temperature, kerogens made of buried algae yield more petroleum than leafy, woody, or peat materials Q: which organic material yields the most petroleum? Kerogen Material

Cracking

The process of making hydrocarbon involves several steps – obviously not all organic matter becomes oil and gas. Specific conditions with respect to heating and low oxygen levels are required. The process of making hydrocarbon involves several steps – obviously not all organic matter becomes oil and gas. Specific conditions with respect to heating and low oxygen levels are required.

What is being made? C-H from C-H-O molecules. Methane (CH 4 ) to asphaltenes C n, n is 1 to 60, increasing n changes state. In CH 4, n is 1. What is being made? C-H from C-H-O molecules. Methane (CH 4 ) to asphaltenes C n, n is 1 to 60, increasing n changes state. In CH 4, n is 1. e.g. Straight-chain parafins n = 1-4 gas n = 5-16 liquid n > 16 solid e.g. Straight-chain parafins n = 1-4 gas n = 5-16 liquid n > 16 solid

Hydrocarbon general usage names Oil: predominantly liquid hydrocarbon Natural gas: predominantly gas hydrocarbon Coal: Hydrocarbon with substantial amounts of other material (e.g. oxygen-organics) Hydrocarbon general usage names Oil: predominantly liquid hydrocarbon Natural gas: predominantly gas hydrocarbon Coal: Hydrocarbon with substantial amounts of other material (e.g. oxygen-organics)

Paraffins (Arkanes)C n H 2n+2 Cycloparaffins (Cycloalkanes) C n H 2n Aromatics (Arenes) C n H 2n-6 Olefin (Alkenes) C n H 2n-2 Asphalitics (N, S, and O) Paraffins (Arkanes)C n H 2n+2 Cycloparaffins (Cycloalkanes) C n H 2n Aromatics (Arenes) C n H 2n-6 Olefin (Alkenes) C n H 2n-2 Asphalitics (N, S, and O) Q: which hydrocarbons burn more efficiently? Petroleum nomenclature

Oil is not very soluble in water (vice-versa) because of their different molecular structure. Water and oil are largely separate in nature – oil floats on water. Q: why does oil float on water?

Seismic surveying

Reflection Seismology Generating your own mini-earthquakes Collect the reflected signal with a series of small seismometers (geophones). Do the math to stack the data Do the math to spatially distribute the raypaths as a time function Do the math to convert travel time into depth Make a geologically reasonable interpretation of significant reflectors

Seismic Surveying Offshore exploration requires most work be done at the surface (on floating vehicles) The seismic waves travel through the water.

Seismic imaging

North Sea

Production drilling requires ability to crush and remove rock using a drill. The bit is supported by large segments of pipe, extended sequentially with increasing depth. A highly specialized fluid (mud) is used to float out rock fragments and lubricate stem and bit. Drilling

Drilling offshore

When oil is finally encountered it may be under some pressure - however, this pressure is released over time. Eventually, the oil must be pumped out of the rock pores. Additional treatments, such as “hydrofracking” and gas injection may help to maintain production levels.

From Hunt, 1979 Crude oil is a mixture of hydro carbons – some oxidize easier than others. Distillation separates hydrocarbons into groups – from light hydrocarbons in gasoline to heavy in motor oil Crude oil is a mixture of hydro carbons – some oxidize easier than others. Distillation separates hydrocarbons into groups – from light hydrocarbons in gasoline to heavy in motor oil Refining

Hydrocarbons We’ve previously seen viscosity increase in earth materials as a function of polymerization. Note a similar effect in these refined materials based on crude oil.

Recall that some petroleum generation uses gas to “chase out” sluggish oil. That gas is CO 2, typically removed from natural gas. We might be able to pump the CO 2 released at power plants into these former oil reservoirs for long term storage. BP Sequestration

Energy

Sources

Oil is not everywhere

There is more gas Natural gas is somewhat easier to find, particualrly in North America However, gas is difficult to transport. Gas wells generally have to be connected to a pipeline. Compressing gas into a liquid is expensive and energy intensive

ANWR

Where

How much

Hydrocarbons

Coal and content

Mining

Fossils

Coal in North America