PET—631 Origin of Oil and Gas

• Where does petroleum come from?Why is it normally found in huge pools under ground?Was it formed in a big pool where we find it, or did it gather there due to outside natural forces?

PET—631 Origin of Oil and Gas

• The oil pool is an end product to a 5-stage sequence of events:

• Raw materials,• Accumulation,• Transformation,• Migration and • Geologic time.• A better understanding of how accumulation and

transformation take place would help clarify the whole process.

• the elemental chemical analysis indicates 10-15% hydrogen and 82-87% carbon by weight.

• Any theory regarding the origin of petroleum must explain two sets of observations,

• one geological and the other chemical.

• Geological observations are that major accumulations:

• occur in sedimentary rocks occur in porous material totally encapsulated from other porous material.

• Traces Chemical observations are: • crude oil differs from recent

hydrocarbons formed in shallow environments, and

• crude has over 50% light hydrocarbons while light hydrocarbons are rare or absent in the recent variety.

PET—631 Origin of Oil and Gas

Inorganic Hypothesis:• There are two theories of origin: • Organic (bionic) or Inorganic (abionic).• Early theories postulated an inorganic origin when it

became apparent that there were widespread deposits of petroleum throughout the world.

• Dmitri Mendele'ev (1877), a Russian and the father of the periodic table of elements, reasoned that

• metallic carbides deep within Earth reacted with water at high temperatures to form acetylene (C2H2) which subsequently condensed to form heavier hydrocarbons.

• This reaction is readily reproduced in the laboratory.

Other hypotheses (Inorganic)• (Berthelot, 1860, Mendele'ev, 1902) were a

modification of the acetylene theory. • They theorized that the mantle contained iron

carbide which would react with percolating water to form methane:

• FeC2 + 2H2O = CH4 + FeO2• The problem was and still is the lack of

evidence for the existence of iron carbide in the mantle.

• These theories are referred to as the deep-seated terrestrial hypothesis.

Another inorganic hypothesis• Another inorganic hypothesis was suggested by

Sokoloff (1890) who proposed a cosmic origin.

• His theory was such as

• hydrocarbons precipitated as rain from original nebular matter from which the solar system was formed and then ejected from earth's interior onto surface rocks.

• This theory and others like it are referred to as the extraterrestrial hypothesis

Conclusion:• There are unquestioned instances of indigenous

magmatic oil. But the occurrences are rare and the volumes of accumulated oil (pools) are infinitesimally low.

• Other problematic issues:• Commercial accumulations are restricted to

sedimentary basins, petroleum seeps and accumulations are absent from igneous and metamorphic rocks, and gas chromatography can fingerprint the organic matter in shales that found in the adjacent pool.

• Thus current theory holds that most petroleum is formed by the thermal maturation of organic matter - An Organic Origin generated the vast reserves (pools) of oil and gas.

Organic Hypothesis:• There are a number of compelling reasons that support an

organic development hypothesis.• First and foremost, is the carbon-hydrogen-organic matter

connection. • Carbon and Hydrogen are the primary constituents of

organic material, both plant and animal.• Moreover, carbon, hydrogen, and hydrocarbons are

continually produced by the life processes of plants and animals.

• A major breakthrough occurred when it was discovered (Smith, 1952; Smith, 1954; Stevens, 1956; Hunt, 1957; Meinschein, 1959; Erdman, 1961; Kvenvolden, 1964; Silverman, 1965) that hydrocarbons and related compounds occur in many living organisms and are deposited in the sediments with little or no change.

Second observation• Second were observations dealing with the chemical

characteristics of petroleum reservoirs. • Nitrogen and porphyrins (chlorophyll derivatives in

plants, blood derivatives in animals) are found in all organic matter; they are also found in many petroleums.

• Presence of porphyrins also mean that anaerobic conditions must have developed early in the formation process because porphyrins are easily and rapidly oxidized and decompose under aerobic conditions.

• Additionally, low Oxygen content also implies a reducing environment.

• Thus there is a high probability that petroleum originates within an anaerobic and reducing environment.

Third observation• Third were observations dealing with the physical

characteristics.• Nearly all petroleum occurs in sediments that are

primarily of marine origin. • Petroleum contained in non-marine sediments

probably migrated into these areas from marine source materials located nearby.

• Furthermore, temperatures in the deeper petroleum reservoirs seldom exceed 300oF (141oC) . But temperatures never exceeded 392oF (200oC) where porphyrins are present because they are destroyed above this temperature.

• Therefore the origin of petroleum is most likely a low-temperature phenomenon.

Organic Hypothesis - Summary.

• The organic theory became the accepted theory about the turn of the century as the oil and gas industry began to fully develop and geologists were exploring for new deposits.

• Simply stated, the organic theory holds that the carbon and hydrogen necessary for the formation of oil and gas were derived from early marine life forms living on the Earth during the geologic past -- primarily marine plankton.

Coal Formation Coal deposits come from many epochs, but the best and most abundant are from the forests in the warm, swampy river deltas of the Carboniferous period, some 320 million years ago.

Formation of HydrocarbonAll fossil fuels, whether solid, liquid, or gas, are the result of organic material being covered by successive layers of sediment over the course of millions of years. Some deposits of coal can be found during the time of the dinosaurs. For example, thin carbon layers can be found during the late Cretaceous Period (65 million years ago) - the time of Tyrannosaurus Rex. But the main deposits of fossil fuels are from the Carboniferous Period.  Fossil fuels supply over 80% of the world’s energy needs.

Plankton and other forms of marine life

• Although plankton are microscopic, the ocean contains so many of them that over 95% of living matter in the ocean is plankton.

• The Sun's energy provides energy for all living things including plankton and other forms of marine life (Fig.1)

• As these early life forms died, their remains were captured by the processes of erosion and sedimentation (Fig 2).

Porphyrin

• . A porphyrin is a heterocyclic macrocycle derived from four pyrrole-like subunits interconnected via their α carbon atoms via methine bridges (=CH-).

• The macrocycle, therefore, is a highly conjugated system, and is consequently deeply coloured—the name porphyrin comes from a Greek word for purple.

• The macrocycle has 22 pi electrons.

• The parent porphyrin is porphine, and substituted porphines are called porphyrins.

• Many porphyrins occur in nature, such as in green leaves and red blood cells, and in bio-inspired synthetic catalysts and devices.

Structure of porphine, the simplest porphyrin

Space-filling model of porphyrin

Organic-rich mud and silt• Successive layers of organic-rich mud and silt covered

preceding layers of organic rich sediments and over time created layers on the sea floor rich in the fossil remains of previous life (Fig. 3).

• Thermal maturation processes (decay, heat, pressure) slowly converted the organic matter into oil and gas.

Thermal maturation processes• Add additional geologic time (millions of years) and the organic

rich sediments were converted into layers of rocks. • Add more geologic time and the layers were deformed,

buckled, broken, and uplifted; the liquid petroleum flowed upward through porous rock until it became trapped and could flow no further forming the oil and gas that we explore for at present (Fig. 4).

chemistry of the hydrocarbons• But the chemistry of the hydrocarbons found in

the end product (oil, gas) differ somewhat from those we find in living things.

• Thus changes, transformation, takes place between the deposition of the organic remains and the creation of the end product.

• The basic formula for the creation of petroleum (oil, gas) is:

• Petroleum End Product = ([Raw Material + Accumulation + Tranformation + Migration] + Geologic Time)

Marine Ecosystems

• Intertidal zone• Examples: • sandy beaches • rocks • estuaries • mangrove swamps • coral reefs • Some of these regions are quite productive.

Many of their inhabitants have adaptations that enable them to survive periodic exposure to the air and wave action.

• Neritic zone• This is the relatively shallow ocean that extends to the

edge of the continental shelf. Primary productivity here depends on planktonic algae growing as deep as the light can reach.

• Oceanic zone• Located over the ocean basins. Here, too, primary

productivity is pretty much limited to the depths that light can reach. The producers are planktonic algae that support secondary and higher consumers (e.g., fish) in the nekton.

• Despite its diversity of life, the net productivity of the open ocean is little better than that of a desert.

Marine Ecosystems

Photosynthesis. The process of merging hydrogen and carbon (from carbon dioxide and water) is accomplished through photosynthesis.

Organisms like diatoms, a one celled plant, can start the process of creating organic matter ("A" in the diagram).

As the carbon and hydrogen are trapped in the food chain for nourishment of other organisms, crude oil is not produced immediately.

However, as the death of these organisms and the burial of the organic matter in sediments is complete, crude oil will start to form (black layers in "B")

HOW OIL AND GAS ARE CREATED

• Crude is associated mainly with sedimentary rocks deposited in the marine environment.

• These deposits indicate that high productivity of organic carbon is important and contain many fossil microorganisms like diatoms and radiolarians.

Crude oil, tar, and natural gas Composition

• Element crude % weigh tar(asphalt) natural gas

• Carbon 82.2-87.1 80-85 65-80

• Hydrogen 11.7-14.7 8.5-11 1-25

• sulfur. 1-5.5 2-8 trace-.2

• nitrogen. 1-1.5 0-2 1-15

• oxygen. 1-4.5 - -

Fermentation• Today, we can create methane gas from decaying

organic matter through bacterial fermentation. Fermentation is a chemical transformation by bacteria that chemically alters different substances.

• It is likely that the environment for petroleum production is without oxygen, as sediment covers the organic matter.

• This is called a reducing environment. • It has been shown in the laboratory that reducing

bacteria tend to convert organic matter into a petroleum like substance.

• Reducing bacteria are very slow, and maybe that is why geologic time plays an important part.

Transformation of organic matter

• Heat combined with increased pressure aids the transformation of organic matter into petroleum products. But too much heat or too much pressure can prevent any oil from forming.

• Many geologists use petroleum formation to guide them on how much heat was in an area. For example, if oil is found, the temperature never exceeded 200E C or (392E F).

• As oil is being produced in source rocks like diatomite or limestone, the oil and gas will move into reservoir rocks that can trap the oil as shown in the diagram below

High productivity

Plate tectonics creates areas that are ideal for oil accumulation. High productivity, especially along continental coasts, is ideal.

Organic matter

• The Carbon Cycle • During the carbon cycle, autotrophs acquire CO2 from the atmosphere by diffusion through leaf

stomata, incorporating it into their biomass. Some of this becomes a carbon source for consumers and respiration returns CO2 to the atmosphere. Photosynthesis and cellular respiration form a link between the atmosphere and terrestrial environments (fig. 49.10). Carbon cycles in the environment very quickly. Plants have a high demand for CO2, yet CO2 is present in the atmosphere at a low concentration (0.03%). Carbon loss by photosynthesis is balanced by carbon release during respiration. Some carbon is diverted from cycling for longer periods of time, as when it accumulates in wood or other durable organic material. Decomposition eventually recycles this carbon to the atmosphere. However carbon can be diverted for millions of years, such as in the formation of coal and petroleum.

• The amount of atmospheric CO2 decreases in the Northern Hemisphere in summer due to increased photosynthetic activity. Amounts increase in the winter when respiration exceeds photosynthesis. Atmospheric CO2 is increased by combustion of fossil fuels by humans, disturbing the balance. The ocean may act as a buffer to absorb excess CO2. In aquatic environments photosynthesis and respiration are also important but carbon cycling is more complex due to interaction of CO2 with water and limestone. Dissolved CO2 reacts with water to form carbonic acid, which reacts with limestone to form bicarbonates and carbonate ions. As CO2 is used in photosynthesis, bicarbonates convert back to CO2; thus bicarbonates serve as a CO2 reservoir and some aquatic autotrophs can use dissolved bicarbonates directly as a carbon source.

• The ocean contains about 50 times the amount of carbon (in various inorganic forms) as is available in the atmosphere

Biogeochemical Cycles • As a part of biogeochemical

cycles, certain elements move through both living and non-living components of the Earth system. The living parts of the Earth system comprise the biosphere, while the non-living parts of the Earth include the hydrosphere, atmosphere, cryosphere, and geosphere. The same individual elements are recycled over and over in different parts of the Earth through biogeochemical cycles.

The carbon cycle, one of Earth's biogeochemical cycles

• The element carbon is a part of seawater, the atmosphere, rocks such as limestone and coal, soils, as well as all living things. On our dynamic planet, carbon is able to move from one of these realms to another as a part of the carbon cycle.

• Carbon moves from the atmosphere to plants.In the atmosphere, carbon is attached to oxygen in a gas called carbon dioxide (CO2). Through the process of photosynthesis, carbon dioxide is pulled from the air to produce food made from carbon for plant growth.

• Carbon moves from plants to animals.Through food chains, the carbon that is in plants moves to the animals that eat them. Animals that eat other animals get the carbon from their food too.

• Carbon moves from plants and animals to soils.When plants and animals die, their bodies, wood and leaves decays bringing the carbon into the ground. Some is buried and will become fossil fuels in millions and millions of years.

• Carbon moves from living things to the atmosphere.Each time you exhale, you are releasing carbon dioxide gas (CO2) into the atmosphere. Animals and plants need to get rid of carbon dioxide gas through a process called respiration.

• Carbon moves from fossil fuels to the atmosphere when fuels are burned.When humans burn fossil fuels to power factories, power plants, cars and trucks, most of the carbon quickly enters the atmosphere as carbon dioxide gas. Each year, five and a half billion tons of carbon is released by burning fossil fuels. Of this massive amount, 3.3 billion tons stays in the atmosphere. Most of the remainder becomes dissolved in seawater.

• Carbon moves from the atmosphere to the oceans. The oceans, and other bodies of water, absorb some carbon from the atmosphere. The carbon is dissolved into the water. Marine animals are able to use the carbon to build their skeletal material.

•

Microscopic marine life• Microscopic marine life, plankton, are considered to be the

primary source of all hydrocarbons. There are two types of plankton:

• Phytoplankton are the most important and comprise the bulk of the marine plankton. The most abundant volumetrically, are the Diatoms, siliceous unicellular plants. Diatoms contain minute droplets of oil that accumulate in their cellular structure late in the vegetative period.

• The other type of plankton is Zooplankton. Foraminifera and Radiolaria are the most widely represented fossils in young oil-bearing strata.

• Whatever the reason, the bulk of evidence favors planktonic aquatic organisms, zooplankton and phytoplankton, as the primary source material for the formation of oil and wet gas.

• Plankton (Phytoplankton, Zooplankton) create the oil by synthesizing fatty acids

The Carbon Cycle

• Carbon is an element. It is part of oceans, air, rocks, soil and all living things. Carbon doesn’t stay is one place. It is always on the move!

• Carbon moves from the atmosphere to plants.In the atmosphere, carbon is attached to oxygen in a gas called carbon dioxide (CO2). With the help of the Sun, through the process of photosynthesis, carbon dioxide is pulled from the air to make plant food from carbon.

• Carbon moves from plants to animals.Through food chains, the carbon that is in plants moves to the animals that eat them. Animals that eat other animals get the carbon from their food too.

Oil and Gas Generation and Yields: Compositional Kinetics

• IntroductionCompositional kinetic and yield analysis describes the rate at which organic matter decomposes into oil and gas as well as the yields of these compounds or compound-classes at various levels of conversion or maturity. It is needed to determine the yields and timing of generation of:

• dry gas (C1, methane) • wet gas (C2-C4) • light oil (C5-C14) • normal oil (C15+) • explain the first oil formed and expelled from source rocks • predict GOR and gas wetness at varying temperatures or

maturities

• Bulk kinetic modeling, i.e., decomposition of kerogen into hydrocarbons without description of products formed, has supplanted empirically-based TTI modeling as the latter does not take into account the variability in kerogen decomposition rates. However, while improving our estimates of the timing of hydrocarbon generation, bulk kinetic data does not provide any description of the products formed nor the timing of generation of the hydrocarbon moities listed above. Furthermore, bulk kinetics constrain all data to a single set of kinetic parameters, which limits its capability to predict early oil generation or the broad dry gas (methane) generation window.

• Compositional kinetic data, which measures the rate of kerogen decomposition into specific chemical moieties, provides detailed kinetic parameters and hydrocarbon yields for each of these fractions including dry and wet gas as well as light and normal oil.

• Further, these data show that the gas window varies among and within kerogen types, as do the condensate and oil windows. In addition these data explain the formation of early oil, i.e., the oil present in low to early oil window maturity source rocks.

• Development of a breakthrough in trapping capability by Humble Instruments has enabled the precise evaluation of C1 through C40+ hydrocarbons using the MACT10 instrument.

MACT10Multiple Automatic Cryogenic Trapping

• This instrument features Humble Instruments performance flow programmable pyrolysis injector the TEPI, multiple automatic cryogenic trapping, Agilent 6890 gas chromatograph with either flame ionization or mass spectrometer detectors; provides data for determining oil and gas compositional kinetics for detailed modeling hydrocarbon generation from petroleum source rocks.

MACT10Multiple Automatic Cryogenic Trapping

• This sophisticated instrument allows effluent from Pyrolysis (or other process effluents) to be trapped in up to 9 separate cryogenically cooled (-200 C) traps at specified times or temperatures. The complete analysis cycle consisting of trapping, desorbing, separation, detection and quantitation is programmable and automated under unattended computer control.

MACT10Multiple Automatic Cryogenic Trapping

• Diagrammatic sketch of the MACT10 system: The effluent from pyrolysis or other process effluents are trapped automatically in up to nine separate cryogenic traps at times or temperatures selected by the user. Subsequent separation, detection, and quantitation is completed automatically via software control.

MACT10Multiple Automatic Cryogenic Trapping

• MACT10 Plus System offers flexibility in sample introduction, processing, and detection techniques. These techniques include open or closed system - isothermal or nonisothermal pyrolysis, qualitative or quantitative analysis, flame ionization, mass spectrometer, or compound-class specific detectors.

Sample Introduction Options

• Sample Introduction Options• Humble Instruments TEPI featuring uniform temperature profile, in-

sample temperature measurement and recording, and flow or pressure programming is featured on the MACT10 Plus System. The Humble TEPI is constructed of either stainless steel or quartz and can be operated in isothermal and nonisothermal modes with 1° C precision. Nonisothermal pyrolysis can be completed with programming rates up to 60° C/minute to final temperatures of 750° C.

• The TEPI can be utilized for thermal extraction gas chromatography which is useful for solvent free evaluation of volatile components such as hydrocarbons, pollutants, contaminates, and other unknown compounds in solid, semi-solid or liquid samples.

MACT10 interfaced to the Agilent GCD system

MACT10 interfaced to the Agilent 6890 gas chromatograph with FID and MSD 5973 detectors

coupled to the HISI pyrolysis inlet.

The MACT10 operating software makes complicated sequencing completely automatic and trouble free.

Thermal Extraction – Pyrolysis Inlet (TEPI)

• Thermal Extraction – Pyrolysis Inlet (TEPI) interfaced to a gas chromatograph with FID, MSD, or other detectors plus data system, provide an integrated solution to a wide range of analytical needs. We offer the SR Analyzer-TEPI as a standalone instrument for use with any GC system or integrated workstations (recommended) for utilization of fast, high resolution GC analysis of volatile or pyrolyzed products allowing results in minutes instead of hours.

SR Analyzer-TEPI/Thermal Extraction Advantages

• SR Analyzer-TEPI/Thermal Extraction Advantages• Preservation of volatiles (more accurate analyses) • No solvents required (environmentally-sound) • No sample preparation (low cost operation) • Fast, high resolution GC compatible (quick results) • Easy to maintain and operate (high productivity)

Background

• Kerogen, the organic matter that forms oil and gas under increasing thermal stress, has two reactive components (Cooles et al., 1985). There is oil and gas prone organic matter as well as an inert carbon residue (Figure 1). While most bulk kinetic and basin modeling programs only account for gas formation from oil cracking, there is also significant gas formed directly from kerogen depending on kerogen composition.

Figure 1. Diagrammatic illustration of kerogen composition, which leads to oil

and gas formation directly from kerogen cracking and gas from oil cracking.

HISI Analytic Technologies

• HISI Analytic Technologies' MACT10 was developed for assessment of the oil and the gas portions of kerogen (see Appendix for analytical details). MACT10 data is used to evaluate in chemical detail the products formed from kerogen in terms of both oil and gas formation. Of course, oil cracking must also be accounted for in assessing total gas yields.

Compositional yields of resolved hydrocarbons from MACT10 experimental data.

• The resulting data can be used to assess the yield of various compound classes (Figure 2).

• These yield data for this lacustrine (Type I) sample are not very surprising demonstrating that a high yield of oil is expected. However, for other samples the yield results have sometimes been quite surprising. For example, the Type II kerogen shown in Figure 3 yields over 53% gas!

Figure 3.

• Figure 3. A Type II kerogen, which is about 20-30% converted, has a very high gas yield. This explains overpressuring in this formation and inherent "sealing" of the source rock inhibiting expulsion. Without oil expulsion, oil cracking will proceed.