ydrocarbons
E H xam #1
Define:
Petroleum a t hick, dark brown or greenish liquid
o
Exists in the upper strata of some areas of the earths curst.
Consists of a compex mixture of various hydrocarbons, largely of
g the alkane series.
Biogenic Theory c rude oil and natural gas are products of
compression and heating of ancient vegetation over geological time
scales.
o
Oil and natural gas formed from the decayed remains of prehistoric
marine animals and terrestrial plants. Over many centuries,
organic matter, mixed with mud, is buried with thick sedimentary
layers
Catagenesis - Heat and pressure metamorphose the organic remains
i nto a waxy material called kerogen, and then into liquid and gaseous
hydrocarbons
Reservoirs porous rocks that contain hydrocarbons
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Hydrocarbons migrate through adjacent rock layers until they
becom t rapped in a reservoir
This creates an oil field and the liquid can be extracted by
d rilling and pumping
Oil Window depth at which oil can be found (150 m is generally
considered the oil window but the depths around the world are
t ypically 4-5 km.
Th ree Conditions for a reservoir a r ich source rock, a migration
conduit, and a t rap (seal)
Breakdown Reactions reactions that produce oil and natural gas,
kerogen breaks down to oil and natural gas by a large set of parallel
reactions, and oil eventually breaks down to natural gas by another set
of reactions
Abiogenic Theory l arge amounts of carbon exists naturally in the
p lanet, some in the form of hydrocabons. Hydrocarbons are less dense
t han aqueous pore f luids, and migrate upward through deep fracture
networks
Seven Sisters seven oil companies that were created by the division
of Rockefellers monopoly on oil. (B.P., Shell, Exxon, Mobil, Texaco,
Socal (Chevron ), and Gulf)
OPEC (The Organization of Petroleum Exporting Countries) a
permanent, in tergovernmental organization crated at the Baghdad
Conference of September 10-14, 1960. Consisted of I ran I raq Kuwait,
Saudi Arabia , and Venezuela.
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The founding five were joined by eight other memebers; Qatar,
I ndonesia, Libyan Arab Jamahiriya, UAE, Algeria, Nigeria,
Ecuador, Gabon, and Angola
P r ima ry Oil Recovery extraction of oil from a reservoir using the
reservoirs pressure to force oil to the surface.
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Only 20% of oil in a reservoir can be extracted by primary oil
recovery
Seconda ry Oil Recovery using various techniques, such as water
i njection, natural gas re-injection, to raise the reservoir pressure for oil
extraction
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Primary and Secondary oil recovery allow 25 35% of the
reservoirs oil to be recovered
Te rtia ry Oil Recovery reducing the oils viscosity to increase oil
p roduction
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used when prices are high; previously unprofitable wells are
b rought back into production
Thermally enhanced oil recovery a t ertiary oil recovery technique
i n which the oil is heated making it less viscous and easier to extract
Steam I njection - most common form of TEOR (thermally enhanced
oil recovery) waste heat from a power plant produces steam which is
t hen injected in to the reservoir
I n-situ Bu rning (form of TEOR) oil is byrned to heat the
surrounding oil or the use of detergents to decrease oil viscosity
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Te rtia ry recovery allows another 5 15% of oil to be
r ecovered
Creekology - oil was often found near creeks in r ivers. These creeks
and r ivers usually were located along the hinge of anticlines. The hinge
of the fold usually exhibts brit tle deformation, or loss of cohesion. This
causes the hinge to easily erode and create a valley for water to run
t hrough. Anticlines are perfect oil t raps.
Structural Geology spatial distribution of rock units with respect
t o their deformational histories
Sedimentology - study of modern sediments such as sand, silt, and
clay, and understanding the process that deposited them
Petrography a b ranch of petrology which focuses on detailed
descriptions of rocks
Organic Geochemistry s tudy of the impacts and chemical processes
t hat organisms and once living organisms have had on the Earth
Paleontology s tudy of prehistoric life including organisms evolution
and interactions with each other and their environments
Geophysical exploration surface methods to measure the physical
p roperties of the subsurface Earth, in order to detect the presence and
position of concentrations of ore minerals and hydrocarbons
Well Logging p ractice of making a detailed record of the geologic
formations penetrated by a borehole
Stratigraphy s tudy of rock layers and layering
Natu ral Gas a m ixture of hydrocarbons and varying quantities of
nonhydrocabons that exists either in the gaseous phase or in solution
w ith crude oil in natural underground reservoirs
D issolved Gas - gas in solution in crude oil contained in the reservoir
Associated Gas (gas cap gas) overlies and is in contact with crude
oil in the reservoir
Non-associated Gas gas in the reservoir that does not contain
sufficient quantities of crude oil
Gas H yd rates hydrates are ice-like substances found both off-shore
on continental margins in permafrost all over the globe and form when
gas, usually methane, is in contact with water under the r ight
t emperature and pressure conditions
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Gas hydrates represent one of the worlds largest untapped
reservoirs of energy and , according to some estimates, have the
potential to meet global energy needs for the next thousand years
H yd rate-gas Equilib rium separates lower temperature region
w here methane occurs as methane hydrate from higher temperature
region where methane occurs as pore-filling gas.
BSR (Bottom Simulating Reflection) above BSR, methane is
hydrate, below methane is free gas or pore filling gas
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Most concentrations are directly above BSR
C rude Oil a m ixture of hydrocarbons that exists in the liquid phase
i n natural underground reservoirs and remains liquid at atmospheric
p ressure after passing through surface separating facilities.
Heavy Oils oils that are denser then water
AP I oil density; where R60 is the ratio of the specific gravity of oil
over the specific gravity of water at 60F.
R60 r atio of the specific gravity of oil over the specific gravity of
water at 60F
Paraffins (CnH 2n +2) saturated hydrocarbons also called alkanes. At
normal temp and pressure, gaseous for n<5, liquid for n=5-15, and
v iscous liquids to waxes for n>15
Naphthenes (C n H 2n): cycloalkanes, are liquid at normal temp and
p ressure
Aromatics (benzene C 6H 6, toluene C 6H 5CH 3): molecular structure
based on a r ing of six carbon atoms
Heterocompounds: components of crude oil other than hydrogen and
carbon such as oxygen nitrogen sulfur and rare metal atoms (nickel
and vanadium).
Sufficient Reservoir P ressure (gas and some oil) perforation
t hrough the production zone
SP (spontaneous potential or self-potential) Log records the
electric potential between electrodes at the surface and in a borehole
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SP response depends mainly on the difference in salinity between
d rilling mud and the formation water, which relates to the
permeability of formationt
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Permeable sand vs. impermeable shale
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Reverse SP is at shallow depths and the salinity of the mud is
g reater than the salinity of the formation water
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In termediate depths suppressed SP occurs in which the mud
salinity is equal to the formation water salinity
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Normal SP occurs when the salinity of the formation water is
g reater than that of the mud
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Cannot be r un in cased holes, and is ineffective when R mf is
equal to R w
o
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E = Klog(Rmf /Rw)
K = 65 + 0.24TC
Resistivity Logs measures variations in formation resistivity; how
s trongly a material opposes the f low of electric current; salts have a
low resistivity or readily allow f low of electric current
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Normal Log used for normal muds
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Laterolog used for low resistivity salt muds; horizontal f low of
electric current into the formation
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I nduction Log used for high resistivi ty freshwater or oil based
m uds; induces a magnetic field and currents in the formation;
f luctuation of the currents according to the formation resistivity
Formation Resistivity Factor ( F=R O/R W)
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Formation resistivity increases with decreasing porosity
Archie Formula: F =RO/RW = a/m (m = cementation factor)
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For sands: F = 0.81/2
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For carbonates: F = 1/2
H umble Formula (soft formations) F = 0.62/2.15
Water Saturation - SWnFRW/Rt ;
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SW2=RO/Rt ; obtain water saturation of a reservoir from resistivity
logs of the rock in a suspected oil zone
Ratio Method: SW=(RXO/Rt )5/8 / (Rmf / RW)
Gamma-ray log and caliper: uses a scintillation counter to measure
t he natural radioactivity of formations
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important for identifying lithology
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can be ran through casing
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usually rand with a caliper log because hole diameter
e ffects reading
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Natural Gamma-ray spectrometry measures the presence of three
commonly occurring radioactive decay series (Th, U, and K)
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Mineral identification of clay minerals
Neutron Log bombards the format ion with neurons from a
r adioact ive source and then measures the induced gamma rays that
a re in proport ion to the hydrogen content of t he format ion
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Good gauge of porosity because hydrogen occurs in all format ion
f lu ids but not in the m inerals of rock mat rix
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Affected by porosity as well as hole size, lit hology, and hydrocarbons
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Higher apparent porosity from reading neut ron log in dirty
reservoir
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Lower apparent porosity reading from neut ron log in gas reservoir
Density Log measures formation density by emitting gamma
r adiation from the tool and recording the amount of gamma radiation
returning from the formation
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Density is a function of lithology
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Water = 1; sandstone = 2.65; limestone = 2.71; dolomite = 2.87; salt
= 2.04
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Porosity = Pma Plog / Pma Pf
Sonic Log (acoustic log) measures the t ravel time of p-waves from
one end to the other end of the sonde.
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P-waves are fastes in dolomite (7.01) compared to f luid (1.62)
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Used only in open uncased holes
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Less accurate than other porosity logs, but most affected by
L ithology
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Only means of measuring interval velocity, useful for seismic
i maging
Using three porosity logs can help dist inguish the effects from
l it hology, clay content, and presence of gas (use density and neut ron
logs in gas zones)
Nuclear Magnetic Resonance Logging (N MR) extremely effective
measurements of porosity and permeability
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Can differentiate movable from immovable water
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Polorization t ime is the t ime taken for the nuclei to be aligned with
BO
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Relaxation t ime is the time taken for the nuclei to return to normal
r andom orientation when the field Is removed
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Good measure of permeability
D ipmeter - a device to measure the direction of dip of rock beds
adjacent to the borehole
Magnetic Surveying force between two magnetic poles
Gravity Surveying measuring the difference in gravity between
l ithologies
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F ree air anomaly variation in G due to elevation of the
measuring station
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Bouger anomaly - variation in G due to the mass of rock between
t he survey station and a reference data; usually the sea level
(mountain ranges)
E = (0.3086 0.4191p)h
Salt domes have low gravity reading
Dikes have large magnetic reading
Reefs have a high gravity reading with respect to sed. Layers
Gravity and magnet ic surveys help to dist inguish basement st ructures
Sequence geological units or boundaries
Depositional Facies a d istinguishable rock body defined by i ts
u niqye physical att ributes such as li thology, fossils, bedding, and
deposition
Seismic Facies Analysis i nterpreting seismic reclectors between
sequence boundaries
Seismic att r ibute analysis t hin bed tuning and the wedge model
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Reflectivity
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Seismic
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I mpedance
Envelope
Vertical Seismic P rofile (VSP) measure the seismic response of
geophones at various depths in a wellbore to sources on the surface
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Walkaway VSP geophones placed at a fixed location inside
wellbore while the surface source moves
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Offset VSP f ixes the source to well horizontal distance
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Reverse VSP geophones placed at the surface and source is
detonated in the well bore
Uphole Surveys l and seismic studies using shallow drillings;
t raveltimes from a source near the top of the well to receivers along the
well are used to deduce a profile of interval velocit ies fo the near
surface format ions, the weathering thickness, and veriaitons of record
quality eith source/receiver depth.
4D Seismic encompasses a broad workflow from feasibility and
design, to acquisition and processing; continuously doing a survey
r ather than 3D in which surveys are completed at different times;
vector analysis of the image displacements between successive 3D
seismic image volumes
Steaming-factor map showing combination of isochron differences
and rms amplitude differences
Geological Map Plates composed of a number of overlaid layers,
shown in an exploded view
Notes
th
First oil wells were drilled in china in the 4 century or earlier
Depths of up to 243m were drilled using bits attached to bamboo poles
Tar roads were paved in Baghdad in the 8 century
Refining kerosene from coal brought in the modern history of
th
petroleum
Springs, Ontario is home to the first commercial oil well drilled in
North America
American petroleum industry began with Drakes discovery of oil in
1859 in Pennsylvania
90% of vehicular fuel needs are met by oil
40% of total energy consumption in the US
80% of accessible reserves are located in the Middle East
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62.5% from t he Arab 5 (Saudi Arabia, UAE, Iraq, Qatar, and
Kuwait
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USA = 3%
Pet roleum was a major factor in several m ilitary conflicts, including
W WII and the Persian Gulf War
Pet roleum explorat ion involves largely wit h geophysical methods such
as seism ic, gravity, and magnet ics, in conjunct ion wit h geologic and
well log analyses
Fi rst stage of ext ract ion of oil is to drill a well into a reservoir
(M ultilateral wells) Often many wells are drilled into the same
reservoir, to ensure that the extraction rate will be economically viable.
(Seconda ry wells) wells may be used to pump water, steam, acids, or
various gas mixtures into the reservoir to raise or maintain the
reservoir pressure, maintaining the economic extraction rate
P reconditions of a hydrocarbon reservoir:
1. Existence of organic r ich source rock to generate the hydrocarbons
2. Existence of sufficient heating of source rock to yield its
hydrocarbons
3. Existence of porous and permeable reservoir to contain the expelled
hydrocarbons
4. Existence of cap rock to seal the hydrocabons from escaping to the
earths surface
5. Source, reservoir, and seal must be arranged in such a way as to
t rap the hydrocarbons
I norganic
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Nit rogen, Inert Gases
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I ne r t Gases:
M ixed
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Helium, argon , k rypton, Radon
Carbon dioxide, hydrogen sulfide,
Mainly Organic
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Hydrogen, and hydrocarbons
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H yd rocarbons
D ry vs. Wet
Dry = Methane
Wet = Ethane, Propane, Butane
3
Dry gas: < 0.1 gal/1000ft condensates (liquid vapor)
Wet gas: > 0.3 gal/1000ft condensates
Gas with hydrogen sulfides is sour
Gas without hydrogen sulfides is considered sweet
Hydrocarbons are made from hydrogen and carbon and are the
3
s implest of organic compounds
Hydrocarbon gases = methane, ethane, propane, butane
H yd rocarbon Gases: C n H 2n + 2
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Methane: CH 4
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Et hane: C2H 6
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Propane: C3H 8
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Propene: C3H 6
Butane: C4H 10
Isobutane: C4H 10
o Pentane: C5H 12
o Hexane: C6H 14
Carbon Chain Length
o
5 9 carbons
Gasoline (C4-10)
o 12 carbons
Kerosine (C11-13), Diesel (C14-18)
o 20 carbons
Motor oil (C19-25)
o H undreds to thousands of carbons
H yd rogen I ndex Gases
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Plastics
Ethane, propane, isobutene, butane, isopentane, pentane, hexane
Non-hydrocarbons:
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Inert gases, nitrogen and hydrogen, carbon dioxide, hydrogen
sulfide
Inert Gases:
He: common m inor accessory in many natural gases of
considerable econom ic value
Ar: present in the earths atmosphere making it the most
common noble gas
Kr: occurs in t race amounts in the atmosphere, isolated by
f ract ionally dist illing liquefied air, used with other rare gases
i n lamps
Rn: radioact ive noble gas derived from decay of radium
Nit rogen and Hyd rogen
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N: frequent ly occurs naturally in earths crust
H: free hydrogen gas rarely occurs in the subsurface
Carbon Dioxide:
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Common in areas of extensive volcanic act ivity
Hydrogen Sulfide:
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Poisonous, terr ible smelling gas which is highly corrosive to steel,
causes operat ional problems in oil and gas fields
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Occurs as free gas and in solut ion with oil and brine
Gas H yd rates:
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Methane hydrate is the most common and is commonly found in the
deep ocean
Horizons (dashed lines) are distorted largely to variations in velocity of
sound through layers
Light oils of 0.83 or less specific gravity have an API gravity of greater
than 40
Heavy oils of 1 or greater specific gravity have an API gravity of less
than 10
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Oil density is inversely proportional to API
Chemical engineers interested in crude oil are concerned with the
quantities and physical properties of hydrocarbons in a crude
Geoscientists infer the source, maturation, history of crude oil
occurrence and are concerned with the molecular structures of oils
Rotary Drilling is the modern way, wellbore filled with drilling mud
Casing and casing program
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There are standards for bit and casing diameters
Diameters decrease the further depth you drill
Mudloggers record many drilling variables, including the rate of
penetration, mud temp, pore pressure, and shale density
Gas chromatographs monitor the presence of hydrocarbons
Offshore drilling is exponentially more expensive than onshore drilling
Offshore platforms are fabricated offshore
Estimated Ultimate Recovery depends on creation (by hydrofracs) of
large network of multi-azimuth vertical fractures.
Insufficient reservoir pressure is overcome by pumping
Info about the penetrated formations along a wellbore is inferred from
geophysical measurements (wireline logs)
High SP, High Resist ivity = permeable format ion full of oil, gas, or
f reshwater
High SP, low Resist ivity = permeable format ion saturated with salt
w ater
Low SP, High Resist ivity = t ight carbonate or sandstone
Low SP, Low Resist ivity = cont inuous shale
Rt > RXO = p roduction zone
RXO > Rt = water zone
Resistance = R L/A
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Resistivity decreases with increasing salinity and temp
Applying seismic stacking and seismic tomography allows a joint
analysis of local and global velocities as well as various artifacts
Visual remote sensing; an example is aerial photography